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WO2023245840A1 - 隔离膜、其制备方法及其相关的二次电池和用电装置 - Google Patents

隔离膜、其制备方法及其相关的二次电池和用电装置 Download PDF

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Publication number
WO2023245840A1
WO2023245840A1 PCT/CN2022/112589 CN2022112589W WO2023245840A1 WO 2023245840 A1 WO2023245840 A1 WO 2023245840A1 CN 2022112589 W CN2022112589 W CN 2022112589W WO 2023245840 A1 WO2023245840 A1 WO 2023245840A1
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WIPO (PCT)
Prior art keywords
optionally
coating
isolation film
filler
nanocellulose
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PCT/CN2022/112589
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English (en)
French (fr)
Inventor
马艳云
杨建瑞
徐�明
魏满想
Original Assignee
宁德时代新能源科技股份有限公司
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Priority to CN202280019557.2A priority Critical patent/CN116982209A/zh
Publication of WO2023245840A1 publication Critical patent/WO2023245840A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/426—Fluorocarbon polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/429—Natural polymers
    • H01M50/4295—Natural cotton, cellulose or wood
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/494—Tensile strength
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/10—Batteries in stationary systems, e.g. emergency power source in plant
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present application belongs to the field of battery technology, and specifically relates to an isolation film, its preparation method and related secondary batteries and electrical devices.
  • secondary batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.
  • energy storage power systems such as hydraulic, thermal, wind and solar power stations
  • electric tools electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.
  • thermal safety issues have received more and more attention.
  • the current methods used to improve the thermal safety performance of secondary batteries are often not conducive to balancing the energy density of secondary batteries. Therefore, how to make secondary batteries take into account high energy density, high thermal safety performance and long service life is a key challenge in secondary battery design.
  • the purpose of this application is to provide an isolation film, its preparation method and related secondary batteries and electrical devices.
  • the isolation film has the characteristics of excellent heat resistance, low moisture content and good electrolyte infiltration characteristics, thereby making Secondary batteries using this separator can combine high energy density, high thermal safety performance and long service life.
  • a first aspect of the present application provides an isolation membrane, including a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating includes nanocellulose and fillers, and the isolation membrane
  • the moisture content is Appm
  • the thickness of the coating is H ⁇ m
  • the isolation film satisfies 250 ⁇ A/H ⁇ 1500.
  • the isolation film can combine high heat resistance, low moisture content and good electrolyte wetting characteristics.
  • 500 ⁇ A/H ⁇ 1500 optionally, 600 ⁇ A/H ⁇ 1000.
  • This helps the coating to have a more stable spatial network structure and a more appropriate content of hydroxyl functional groups, so that the isolation film can have high heat resistance, low moisture content and good electrolyte wetting characteristics, and the secondary battery can have high heat resistance. Safety performance, long cycle life and long storage life.
  • 400 ⁇ A ⁇ 1000, optionally, 500 ⁇ A ⁇ 800 This helps the coating to have a more stable spatial network structure and a more appropriate content of hydroxyl functional groups, so that the isolation film can better combine high heat resistance, low moisture content and good electrolyte wetting characteristics, and can further Improve the cycle life and storage life of secondary batteries.
  • 0 ⁇ H ⁇ 1.5 optionally, 0.2 ⁇ H ⁇ 0.8. This helps to increase the energy density of secondary batteries.
  • the nanocellulose includes at least one of cellulose nanofibers, cellulose nanowhiskers and bacterial nanocellulose, optionally cellulose nanowhiskers.
  • Cellulose nanowhiskers can have a higher degree of crystallinity, which can reduce their hydrophilicity, thereby facilitating the discharge of water during the drying process, so that the isolation film of the present application can have a lower moisture content.
  • the nanocellulose includes at least one of unmodified nanocellulose and modified nanocellulose, optionally modified nanocellulose.
  • the modified nanocellulose includes a modifying group
  • the modifying group includes an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group and a phosphate group. at least one of, optionally including at least one of a sulfonic acid group, a boric acid group and a phosphoric acid group.
  • the modified nanocellulose includes a hydroxyl group and a modifying group, and the molar ratio of the modifying group to the hydroxyl group is 1:4 to 4:1, optionally 2:3 to 7:3.
  • the molar ratio of the modified group to the hydroxyl group is within an appropriate range, the heat resistance and ion transport characteristics of the isolation membrane can be further improved, and the isolation membrane can have a lower moisture content.
  • the aspect ratio of the nanocellulose is 5 to 80, optionally 10 to 40.
  • the heat resistance and ion transport characteristics of the isolation membrane can be further improved.
  • the average diameter of the nanocellulose is 10 nm to 40 nm, optionally 10 nm to 35 nm.
  • the heat resistance, ion transport characteristics and voltage breakdown resistance characteristics of the isolation membrane can be further improved.
  • the average length of the nanocellulose is 100 nm to 600 nm, optionally 200 nm to 500 nm.
  • the heat resistance and ion transport characteristics of the isolation membrane can be further improved.
  • the weight average molecular weight of the nanocellulose is 10,000 to 60,000, optionally 30,000 to 50,000.
  • the equilibrium degree of polymerization of the nanocellulose is 150DP to 300DP, optionally 200DP to 250DP.
  • the weight average molecular weight and/or degree of polymerization of nanocellulose is within a suitable range, not only can the nanocellulose be prevented from clogging the pore structure of the isolation membrane, but the viscosity of the coating slurry can also be kept within a suitable range, thereby coating When the slurry has better fluidity and wettability, it is more conducive to improving the quality of the coating.
  • the content of the nanocellulose in the coating is 6 to 35 wt%, optionally 10 to 30 wt%, based on the total weight of the coating.
  • the content of the filler in the coating is ⁇ 60wt%, optionally 65wt% to 90wt%, based on the total weight of the coating.
  • the content of nanocellulose and/or filler is within a suitable range, it can ensure that the coating slurry has a suitable viscosity, which is more conducive to coating, and is also beneficial to the isolation film having a lower moisture content and good electrolyte infiltration. properties; in addition, it is also conducive to the formation of a stable spatial network structure between fillers and nanocellulose.
  • the filler includes at least one selected from inorganic particles and organic particles.
  • the decomposition temperature of the filler is above 200°C.
  • the filler includes a first filler, and the first filler is a secondary particle morphology formed by agglomeration of primary particles.
  • the nanocellulose can also be overlapped in the gaps between the primary particles of the filler that constitute the secondary particle morphology, so that the nanocellulose and the first filler overlap to form an integrated effect, whereby the coating It can have a more stable spatial network structure, and the isolation membrane can have appropriate porosity and stable pore structure, and the isolation membrane can also take into account low moisture content and good electrolyte wetting characteristics.
  • the content of the first filler is 50wt% to 100wt%, optionally 90wt% to 99wt%, based on the total weight of the filler.
  • the average particle size Dv50 of the first filler is ⁇ 200nm, and can be selected from 50nm to 200nm.
  • the BET specific surface area of the first filler is ⁇ 20m 2 /g, optionally 25m 2 /g to 50m 2 /g.
  • the average particle size Dv50 and the BET specific surface area When at least one of the content of the first filler, the average particle size Dv50 and the BET specific surface area is within the above range, it can overlap with the nanocellulose to form an integrated effect, so that the coating can have a more stable spatial network structure. , and at the same time, the isolation film can have better heat resistance and electrolyte wetting properties.
  • the first filler includes inorganic particles with secondary particle morphology
  • the crystal forms of the inorganic particles with secondary particle morphology include ⁇ crystal form, ⁇ crystal form, and ⁇ crystal form. and at least two of the eta crystal forms, optionally including at least two of the alpha crystal forms, theta crystal forms and the gamma crystal forms.
  • the first filler includes inorganic particles with secondary particle morphology
  • the crystal form of the inorganic particles with secondary particle morphology includes the ⁇ crystal form
  • the content of the ⁇ crystal form is ⁇ 50wt%, optionally 60wt% to 85wt%, based on the total weight of the inorganic particles of the secondary particle morphology.
  • Selecting first fillers of different crystal forms helps to improve at least one of the heat resistance and electrolyte wetting characteristics of the isolation film.
  • the filler further includes a second filler, and the second filler is in the form of primary particles. This can better play the supporting role of the second filler, improve the heat resistance of the isolation film, and also help the coating have more pore structure and less moisture content when the amount is smaller.
  • the content of the second filler is ⁇ 50wt%, optionally 1wt% to 10wt%, based on the total weight of the filler.
  • the average particle size Dv50 of the second filler is 100 nm to 800 nm, optionally 200 nm to 400 nm.
  • the BET specific surface area of the second filler is ⁇ 10m 2 /g, optionally 4m 2 /g to 9m 2 /g.
  • the supporting role of the second filler can be better exerted, which is beneficial to the discharge of water during the drying process and makes the coating Maintaining appropriate porosity and stable pore structure during long-term charge and discharge processes can further improve the ion transport characteristics of the isolation membrane and the wetting characteristics of the electrolyte.
  • the second filler includes inorganic particles with a primary particle morphology
  • the crystal form of the inorganic particles with a primary particle morphology includes at least one of an ⁇ crystal form and a ⁇ crystal form.
  • the alpha crystalline form is included. This can further improve the heat resistance of the isolation film.
  • the second filler includes inorganic particles with primary particle morphology
  • the crystal form of the inorganic particles with primary particle morphology includes ⁇ crystal form
  • the content of ⁇ crystal form is ⁇ 90wt% , optionally 95wt% to 100wt%, based on the total weight of the inorganic particles of the primary particle morphology.
  • the coating further includes a non-granular binder, optionally, the non-granular binder includes an aqueous solution binder. This facilitates the preparation and application of coating slurries.
  • the non-granular binder is present in the coating in an amount of ⁇ 1 wt%, based on the total weight of the coating. This application can enable the isolation film to maintain high adhesion and good ion transmission characteristics while reducing the amount of binder.
  • the thickness of the porous substrate is ⁇ 6 ⁇ m, optionally 3 ⁇ m to 5 ⁇ m. This helps further improve the energy density of secondary batteries.
  • the porous substrate has a porosity of 32% to 48%, optionally 34% to 39%.
  • the porosity of the porous substrate is conducive to further improving the ion transmission characteristics of the isolation membrane on the premise of ensuring high heat resistance of the isolation membrane; at the same time, it can also ensure that the secondary battery has a high discharge rate and reduce the The battery self-discharges.
  • the areal density of the coating is 0.6g/m 2 to 1.5g/m 2 , optionally 0.8g/m 2 to 1.1g/m 2 . This helps to form a coating with better heat resistance.
  • the isolation film further includes an adhesive layer, the adhesive layer is disposed on at least a portion of the surface of the coating, the adhesive layer includes a granular adhesive, which can
  • the granular binder includes at least one of acrylic monomer homopolymers or copolymers, acrylic monomer homopolymers or copolymers, and fluorine-containing olefin monomer homopolymers or copolymers. kind.
  • the adhesive layer can not only prevent the coating from peeling off and improve the safety performance of the secondary battery, but also improve the interface between the isolation film and the electrode and improve the cycle performance of the secondary battery.
  • the longitudinal thermal shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 5%, optionally 0.5% to 4%.
  • the transverse thermal shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 5%, and can optionally be 0.5% to 4%.
  • the perforation strength of the isolation film is ⁇ 350gf, optionally 370gf to 450gf.
  • the longitudinal tensile strength of the isolation film is ⁇ 2000kg/cm 2 , optionally 2500kg/cm 2 to 4500kg/cm 2 .
  • the transverse tensile strength of the isolation film is ⁇ 2000kg/cm 2 , optionally 2500kg/cm 2 to 4500kg/cm 2 .
  • the air permeability of the isolation film is ⁇ 300s/100mL, and can be selected from 100s/100mL to 200s/100mL.
  • the porosity of the isolation membrane is 30% to 45%, optionally 32% to 36%.
  • the wetted length of the isolation film is ⁇ 30mm, optionally from 30mm to 80mm.
  • the wetting speed of the isolation film is ⁇ 3 mm/s, and may be selected from 3 mm/s to 10 mm/s.
  • the performance of the isolation film meets one or more of the above conditions, it is beneficial to improve at least one of the energy density, thermal safety performance, capacity development characteristics and service life of the secondary battery.
  • the second aspect of this application provides a method for preparing the isolation membrane of the first aspect of this application, including the following steps: S1, providing a porous substrate; S2, preparing a coating slurry: adding nanocellulose and filler in a solvent in a predetermined ratio Mix in medium to prepare the coating slurry; S3, coating: apply the coating slurry on at least one surface of the porous substrate to form a coating and dry it to obtain an isolation film, wherein, The isolation membrane includes a porous substrate and a coating disposed on at least one surface of the porous substrate. The coating includes nanocellulose and fillers. The moisture content of the isolation membrane is App ppm. The coating The thickness of the layer is H ⁇ m, and the isolation film satisfies 250 ⁇ A/H ⁇ 1500.
  • the preparation method of the isolation film of the present application obtains the coating through one-time coating, which greatly simplifies the production process of the isolation film.
  • the coating uses a coater, and the coater includes a gravure roller.
  • the number of lines of the gravure roller is 100LPI to 300LPI, optionally 125LPI to 190LPI.
  • the coating speed is 30m/min to 120m/min, optionally 60m/min to 90m/min.
  • the coating line speed ratio is 0.8 to 2.5, optionally 0.8 to 1.5.
  • the drying temperature is 40°C to 70°C, optionally 50°C to 60°C.
  • the drying time ranges from 10 seconds to 120 seconds, optionally from 20 seconds to 80 seconds.
  • the method further includes the following steps: S4, secondary coating: apply a slurry containing a granular binder on at least a portion of the surface of the coating, and after drying Form an adhesive layer.
  • a third aspect of the present application provides a secondary battery, including the separator film of the first aspect of the present application or a separator film prepared by the method of the second aspect of the present application.
  • a fourth aspect of the present application provides an electrical device, including the secondary battery of the third aspect of the present application.
  • the isolation film provided by this application has the characteristics of excellent heat resistance, low moisture content and good electrolyte wetting characteristics, so that the secondary battery using the isolation film can take into account high energy density, high thermal safety performance and long service life.
  • the electrical device of the present application includes the secondary battery provided by the present application, and therefore has at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of an embodiment of the secondary battery of the present application.
  • FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1 .
  • FIG. 3 is a schematic diagram of an embodiment of the battery module of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of a power consumption device including the secondary battery of the present application as a power source.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • a secondary battery includes an electrode assembly and an electrolyte.
  • the electrode assembly includes a positive electrode piece, a negative electrode piece, and an isolation film.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece to prevent short circuit between the positive electrode and the negative electrode. function, and at the same time, active ions can pass freely to form a loop.
  • Thinning the separator film is an effective measure to increase the energy density of secondary batteries.
  • the isolation film used in commercial secondary batteries is usually a polyolefin porous film, such as a polyethylene porous film, a polypropylene porous film or a polypropylene/polyethylene/polypropylene three-layer composite film, with a melting point between 130°C and 160°C. Therefore, when its thickness is reduced, the heat resistance of the isolation film becomes worse and it will shrink severely when heated, thereby increasing the risk of short circuit between the positive and negative electrodes.
  • the current measures are mainly to coat a heat-resistant inorganic ceramic layer on the polyolefin porous membrane, which can increase the mechanical strength of the isolation membrane, reduce the shrinkage of the isolation membrane when heated, and reduce the positive electrode and risk of negative short circuit.
  • the particle size of commercially available inorganic ceramic particles is larger, which will increase the overall thickness of the isolation film, resulting in the inability to balance the energy density of secondary batteries, especially in the field of power batteries, which is not conducive to improving the cruising range; in addition, due to the The particle size of inorganic ceramic particles is larger, so the number of layers accumulated on the polyolefin porous membrane is smaller (usually ⁇ 5 layers), which results in limited improvement in the heat resistance of the isolation membrane.
  • Nanonization of inorganic ceramic particles can reduce the thickness of the coating and alleviate the adverse impact on the energy density of secondary batteries.
  • the coating formed by nanonization of inorganic ceramic particles has low porosity and is easy to block the micropores of the polyolefin porous film, thus leading to isolation.
  • the overall porosity of the membrane is reduced, the ionic resistance is increased, and it is not conducive to active ion transmission.
  • due to the high specific surface area of nanoscale inorganic ceramic particles and the contact between particles is point contact, a large amount of binder is required to ensure the adhesion between particles, but the amount of binder is large. Blocking problems are prone to occur, which is detrimental to the rate performance of the secondary battery. For example, dendrites are easily formed on the surface of the negative electrode, which is also detrimental to the capacity and energy density of the secondary battery.
  • inorganic ceramic particles have the characteristic of easily adsorbing water.
  • their specific surface area increases significantly, which leads to a significant increase in the moisture content of the isolation film.
  • the moisture in the isolation film will gradually be released and enter the electrolyte.
  • the most widely used electrolyte system in commercial application is a mixed carbonate solution of lithium hexafluorophosphate. Lithium hexafluorophosphate has poor thermal stability in high temperature environments. It will decompose at higher temperatures to form PF 5.
  • PF 5 is not suitable for trace amounts of phosphate in the electrolyte.
  • the barrier film also needs to have a low moisture content.
  • the isolation film With the application and promotion of secondary batteries, people have higher and higher requirements for the service life of secondary batteries.
  • the gradual drying out and failure of the isolation film is an important reason for the decline of secondary battery capacity. This is because after the isolation film dries up, the internal resistance of the battery increases, resulting in incomplete charging and discharging, which in turn causes the secondary battery capacity to decay rapidly and greatly reduces the service life of the secondary battery. Therefore, the isolation membrane also needs to have good electrolyte wetting properties.
  • the inventor of the present application surprisingly discovered during the research process that by arranging a coating containing nanocellulose and fillers on the surface of the porous substrate of the isolation membrane, and reasonably controlling the ratio of the moisture content of the isolation membrane to the thickness of the coating, the isolation membrane can achieve both High heat resistance, low moisture content and good electrolyte wetting characteristics enable secondary batteries to combine high energy density, high thermal safety performance and long service life.
  • the first aspect of the embodiment of the present application provides a separation membrane, including a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating includes nanocellulose and fillers.
  • the moisture content of the isolation film is App ppm
  • the thickness of the coating is H ⁇ m
  • the isolation film satisfies 250 ⁇ A/H ⁇ 1500.
  • the isolation film can combine high heat resistance, low moisture content and good electrolyte wetting characteristics.
  • the nanocellulose structure is rich in hydroxyl groups, making it highly hydrophilic. Therefore, when used alone, it can easily lead to a higher moisture content in the isolation film, which in turn affects the electrochemical performance of the secondary battery.
  • the coating of the present application includes both nanocellulose and filler.
  • the nanocellulose can be built with the filler to form a stable spatial network structure, which is conducive to the discharge of moisture during the drying process, thereby enabling the isolation film of the present application to have a lower moisture content.
  • the inventor of this application has discovered through extensive research that when controlling the moisture content Appm of the isolation film containing nanocellulose and fillers and the thickness H ⁇ m of the coating to satisfy A/H between 250 and 1500, the coating can have good Due to the spatial network structure and appropriate content of hydroxyl functional groups, the isolation film can have both low moisture content and good electrolyte wetting characteristics, and then the secondary battery using it can have good electrochemical performance. In particular, it has Long cycle life and long storage life.
  • the coating of the present application includes both nanocellulose and fillers, and the nanocellulose and fillers can be overlapped together to give the coating a stable spatial network structure. Therefore, the coating also has high heat resistance and can reduce isolation.
  • the degree of shrinkage of the film when heated reduces the risk of short circuit of the positive and negative electrodes, making the secondary battery have high thermal safety performance; at the same time, because the coating of the present application has high heat resistance, a thinner porous substrate can be selected, and then the secondary battery can Secondary batteries are also capable of combining high energy density.
  • A/H can be a range of 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1250, 1500 or any above value.
  • the moisture content of the isolation film can be measured by a moisture meter.
  • the test method can be the Karl Fischer moisture meter.
  • the test instrument can be the Metrohm 831 Karl Fischer moisture meter.
  • the moisture content Appm of the separator film satisfies A ⁇ 1000, so that less water is dissolved from the separator film and released into the electrolyte during the charging and discharging process of the secondary battery, which in turn contributes to the secondary battery charging and discharging process.
  • the secondary battery has good electrochemical properties, and in particular, the secondary battery can have high capacity development characteristics and low volume expansion rate.
  • the inventor of this application unexpectedly discovered during the research process that the lower the moisture content of the isolation membrane, the better.
  • the moisture content of the isolation membrane is too low, for example, less than 400 ppm, the gap between the isolation membrane and the electrolyte will be reduced.
  • the interface characteristics become worse, such as the liquid absorption capacity of the isolation film is reduced and the wetting characteristics of the electrolyte become worse.
  • the isolation film will quickly dry up and fail, resulting in rapid internal resistance of the secondary battery. increase, the capacity decreases rapidly, and the service life is greatly shortened.
  • the moisture content Appm of the isolation film satisfies 400 ⁇ A ⁇ 1000.
  • A can be a range of 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000 or any number above.
  • This helps the coating to have a more stable spatial network structure and a more appropriate content of hydroxyl functional groups, so that the isolation film can better combine high heat resistance, low moisture content and good electrolyte wetting characteristics, and can further Improve the cycle life and storage life of secondary batteries.
  • the thickness H ⁇ m of the coating satisfies 0 ⁇ H ⁇ 1.5.
  • H can be a range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or any of the above values.
  • the areal density of the coating is 0.6g/m 2 to 1.5g/m 2 , optionally 0.8g/m 2 to 1.1g/m 2 . This helps to form a coating with better heat resistance.
  • the thickness of the porous substrate may be ⁇ 6 ⁇ m, optionally 3 ⁇ m to 5 ⁇ m.
  • the coating of the present application can significantly improve the heat resistance of the isolation film, thereby enabling the use of thinner porous substrates, which helps to further increase the energy density of secondary batteries.
  • the porous substrate may have a porosity of 32% to 48%, optionally 34% to 39%.
  • the porosity of the porous substrate is conducive to further improving the ion transmission characteristics of the isolation membrane on the premise of ensuring high heat resistance of the isolation membrane; at the same time, it can also ensure that the secondary battery has a high discharge rate and reduce the The battery self-discharges.
  • the porous substrate can include a porous polyolefin-based resin film (such as polyolefin-based resin film). At least one of ethylene, polypropylene, polyvinylidene fluoride), at least one of porous glass fiber and porous non-woven fabric.
  • the porous substrate may be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer may be the same or different.
  • Nanocellulose refers to the general name of cellulose with any dimension in the nanoscale (for example, within 100 nm), which has the characteristics of both cellulose and nanoparticles. Nanocellulose can be a polymer nanomaterial extracted from wood, cotton, etc. in nature through one or more means of chemistry, physics, biology, etc. It has wide sources, low cost, biodegradability, and high modulus.
  • Nanocellulose also has good high temperature resistance and has small volume change after heating, which can improve the heat resistance of the isolation film. At the same time, compared with traditional inorganic ceramic particles, nanocellulose has a smaller density, so It can also reduce the weight of the secondary battery and increase the weight energy density of the secondary battery. In addition, nanocellulose also helps to make the coating have tiny and uniform nanopores to prevent current leakage, thus enabling the isolation membrane to have both high ion transport characteristics and good voltage breakdown resistance.
  • the nanocellulose may include cellulose nanofibrils (CNF, also known as nanofibrillar cellulose or microfibrillated cellulose), cellulose nanowhiskers (Cellulose nanocrystals, CNC, At least one of cellulose nanocrystals, nanocrystalline cellulose) and bacterial nanocellulose (Bacterial nanocellulose, BNC, also known as bacterial cellulose or microbial cellulose) can be selected as cellulose nanowhiskers.
  • Cellulose nanowhiskers can have a higher degree of crystallinity, which can reduce their hydrophilicity, thereby facilitating the discharge of water during the drying process, so that the isolation film of the present application can have a lower moisture content.
  • cellulose nanowhiskers can easily overlap with fillers, giving the coating a more stable spatial network structure, which can further improve the performance of the isolation film.
  • the nanocellulose may include at least one of unmodified nanocellulose (also known as hydroxyl nanocellulose) and modified nanocellulose, optionally modified nanocellulose.
  • the modified nanocellulose includes modifying groups.
  • the modifying group may include at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boronic acid group, and a phosphate group, optionally including a sulfonic acid group, a boronic acid group, and a phosphate group. At least one of the phosphate groups.
  • nanocellulose has the above-mentioned specific modified groups, on the one hand, it can effectively improve the heat resistance of the isolation film and improve the thermal safety performance of the secondary battery. On the other hand, it is also beneficial to isolation. On the premise of having good electrolyte wetting characteristics, the membrane also has a low moisture content, which can further improve the electrochemical performance of the secondary battery.
  • nanocellulose When nanocellulose has the above-mentioned specific modified groups, nanocellulose can also be built with fillers to form a more stable spatial network structure, which can further improve the ion transport characteristics and voltage breakdown resistance of the isolation membrane, thereby also It is beneficial to match high-voltage cathode active materials and further improve the energy density of secondary batteries.
  • the presence of modified groups can also reduce the proportion of hydroxyl groups, thereby ensuring that the coating slurry has a suitable viscosity, which is more conducive to coating, thus improving the production efficiency of the isolation film and the uniformity of the coating.
  • the modified nanocellulose includes a hydroxyl group and a modifying group
  • the molar ratio of the modifying group to the hydroxyl group may be 1:4 to 4:1, optionally 2: 3 to 7:3.
  • the molar ratio of the modified group to the hydroxyl group is within an appropriate range, the heat resistance and ion transport characteristics of the isolation membrane can be further improved, and the isolation membrane can have a lower moisture content.
  • the molar ratio of the modified group to the hydroxyl group is too small, the further improvement effect of the modified group on the heat resistance and ion transmission characteristics of the isolation membrane may not be obvious; when the modified group When the molar ratio of groups to hydroxyl groups is too large, the electrolyte wetting characteristics of the isolation membrane may be affected. For example, the ion transport characteristics of the isolation membrane may become worse, which may affect the cycle life and storage life of the secondary battery, and may also cause isolation. The heat resistance of the film decreases, which may also affect the thermal safety performance of the secondary battery.
  • the types of modified groups in nanocellulose can be determined using infrared spectroscopy.
  • the infrared spectrum of the material can be tested to determine the characteristic peaks it contains, thereby determining the type of modifying group.
  • the materials can be analyzed by infrared spectroscopy using instruments and methods known in the art, such as using an infrared spectrometer (such as the IS10 Fourier transform infrared spectrometer of the American Nicolet Company), in accordance with GB/T 6040- The 2019 General Principles of Infrared Spectroscopy Analysis Methods were tested.
  • the aspect ratio of the nanocellulose may be from 5 to 80, optionally from 10 to 40.
  • the heat resistance and ion transport characteristics of the isolation membrane can be further improved. And it can effectively avoid the following situations: when the aspect ratio of nanocellulose is too small, the overlapping effect with the filler is poor, the heat resistance of the coating may become worse, and during the drying process of the coating, some nanofibers Due to the lack of support from the filler, the cellulose is prone to collapse, which in turn is prone to pore clogging, which in turn hinders the transmission of active ions and water discharge, affecting the cycle performance and capacity of the secondary battery; when the aspect ratio of nanocellulose When it is too large, the nanopores of the coating formed by overlapping it with the filler will be smaller, which may also lead to poor ion transmission properties of the isolation membrane.
  • the average diameter of the nanocellulose may be 10 nm to 40 nm, optionally 10 nm to 35 nm.
  • the heat resistance, ion transport characteristics and voltage breakdown resistance characteristics of the isolation membrane can be further improved. And it can effectively avoid the following situation: when the average diameter of nanocellulose is too large, the nanopores of the coating formed by overlapping it with the filler may be larger, which may lead to the deterioration of the voltage breakdown resistance characteristics of the isolation film, and at the same time, its The overlapping effect with fillers is poor, and the heat resistance of the coating may become worse.
  • part of the nanocellulose is prone to collapse due to the lack of support from the fillers, and is prone to pore blocking problems. This will also hinder active ion transmission and water discharge, affecting the cycle performance and capacity of the secondary battery.
  • the average length of the nanocellulose may range from 100 nm to 600 nm, optionally from 200 nm to 500 nm.
  • the heat resistance and ion transport characteristics of the isolation membrane can be further improved.
  • the coating slurry has high viscosity and poor flow, which may affect the coating of the coating slurry and thus affect the quality of the coating obtained, such as affecting the heat resistance and ion transmission characteristics of the isolation membrane.
  • the average length and average diameter of nanocellulose can be determined by the following method: cut out a 3.6mm ⁇ 3.6mm sample from any area of the isolation film, and use a scanning electron microscope (such as ZEISS Sigma 300) to measure the coating in the sample According to the microstructure of the microstructure, select the high vacuum mode, the operating voltage is 3kV, the magnification is 30,000 times, and obtain the SEM image; according to the obtained SEM image, select multiple (for example, more than 5) test areas to perform length statistics.
  • a scanning electron microscope such as ZEISS Sigma 300
  • each test area is 0.5 ⁇ m ⁇ 0.5 ⁇ m, and then the average length obtained in each test area is taken as the average length of nanocellulose; according to the obtained SEM image, use Nano Measurer particle size distribution statistical software to select multiple ( For example, more than 5) test areas are used to count the diameters.
  • the size of each test area is 0.5 ⁇ m ⁇ 0.5 ⁇ m, and then the average value of the diameters obtained in each test area is taken as the average diameter of nanocellulose.
  • the weight average molecular weight of the nanocellulose may range from 10,000 to 60,000, optionally from 30,000 to 50,000.
  • the equilibrium degree of polymerization of the nanocellulose may be 150 DP to 300 DP, optionally 200 DP to 250 DP.
  • the weight average molecular weight and/or degree of polymerization of nanocellulose is within a suitable range, not only can the nanocellulose be prevented from clogging the pore structure of the isolation membrane, but the viscosity of the coating slurry can also be kept within a suitable range, thereby coating
  • the slurry has better fluidity and wettability, it is more conducive to improving the quality of the coating. For example, it can further improve the heat resistance and ion transmission characteristics of the isolation film.
  • the shape of the nanocellulose may include at least one of the following: tubular (eg, hollow tubular), fiber, and rod.
  • tubular eg, hollow tubular
  • fiber e.g., glass fiber
  • rod e.g., rod
  • the content of the nanocellulose in the coating may be 6 to 35 wt%, optionally 10 to 30 wt%, based on the total weight of the coating.
  • the content of nanocellulose is within a suitable range, it can ensure that the coating slurry has a suitable viscosity, which is more conducive to coating, and also helps the isolation film to have a lower moisture content and good electrolyte wetting characteristics; in addition, It is also conducive to the formation of a stable spatial network structure between nanocellulose and fillers, which can further improve the performance of the isolation membrane, such as reducing the moisture content of the isolation membrane, improving the heat resistance, ion conduction capacity, and resistance to external force extrusion of the isolation membrane. voltage capability and withstand voltage breakdown capability, etc.
  • the content of the filler in the coating may be ⁇ 60 wt%, optionally 65 to 90 wt%, based on the total weight of the coating.
  • the filler content is within a suitable range, it can ensure that the coating slurry has a suitable viscosity, which is more conducive to coating, and also helps the isolation film to have a lower moisture content and good electrolyte wetting characteristics; in addition, there are It is conducive to forming a stable spatial network structure with nanocellulose, thereby further improving the performance of the isolation film, such as reducing the moisture content of the isolation film, and improving the heat resistance, tensile strength, puncture resistance and external extrusion resistance of the isolation film. wait.
  • the volume of the entire battery will increase.
  • the negative active material is embedded
  • the volume increase after active ions is higher.
  • the isolation film also needs to have good resistance to external extrusion.
  • the presence of fillers helps the coating have a stable spatial network structure, which can improve the ion transmission characteristics and heat resistance of the isolation membrane; in addition, it can also improve the tensile strength, puncture resistance and external extrusion resistance of the isolation membrane. .
  • the filler may include at least one of inorganic particles and organic particles.
  • the decomposition temperature of the filler is above 200°C, so that the filler can have good thermal stability and is not easily decomposed, which can further improve the heat resistance of the isolation film.
  • Inorganic particles have high thermal stability and are not easily decomposed, and usually have hydroxyl groups on their surfaces, which make them easy to build with nanocellulose to form a stable spatial network structure.
  • the inorganic particles include at least one of inorganic particles with a dielectric constant of more than 5, inorganic particles with ion conductivity but not storing ions, and inorganic particles capable of electrochemical reactions. .
  • the inorganic particles with a dielectric constant of more than 5 include boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, Cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, Magnesium aluminum silicate, magnesium lithium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O 3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O 3 (abbreviated as PLZT, 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1), Pb(Mg 3 Nb
  • each inorganic particle may be modified by chemical modification and/or physical modification.
  • the chemical modification methods include coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer graft modification, etc.
  • the physical modification method can be mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc.
  • the agglomeration of inorganic particles can be reduced through modification treatment, so that they can be built with nanocellulose to form a more stable and uniform spatial network structure; in addition, by selecting coupling agents, surface active materials or polymer modifications with specific functional groups
  • the chemical inorganic particles also help to improve the coating's wettability to the electrolyte and improve the coating's adhesion.
  • the inorganic particles that have ion conductivity but do not store ions include Li 3 PO 4 , lithium titanium phosphate Li x1 Ti y1 (PO 4 ) 3 , lithium aluminum titanium phosphate Li x2 A ly2 Ti z1 (PO 4 ) 3.
  • the inorganic particles capable of electrochemical reactions include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials and lithium-titanium compounds.
  • Organic particles have good thermal stability and are not easily decomposed, which can improve the heat resistance of the isolation film; at the same time, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overcharging, abuse, thermal abuse, etc., the organic particles The particles can also melt and be sucked into the micropores of the porous substrate due to capillary action to close the cells and break the circuit, which is beneficial to ensuring the high safety performance of the secondary battery.
  • the organic particles include, but are not limited to, polyethylene particles, polypropylene particles, polystyrene particles, cellulose, cellulose modifiers (such as carboxymethyl cellulose), melamine resin particles, phenolic resin Particles, polyester particles (such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin particles, polyimide particles, polyamide imide Amine particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyether ether ketone particles, polyaryl ether ketone particles, copolymers of butyl acrylate and ethyl methacrylate (such as acrylic acid At least one of the cross-linked polymers of butyl ester and ethyl methacrylate).
  • the glass transition temperature of the organic particles may be above 130°C. Therefore, when the internal temperature of the secondary battery reaches 130°C, the organic particles will not change from the glassy state to the viscous fluid state, thus ensuring that the isolation film does not shrink violently.
  • the organic particles include, but are not limited to, melamine formaldehyde resin particles, phenolic resin particles, polyester particles, silicone resin particles, polyimide particles, polyamide-imide particles, polyaramid particles, At least one of polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyether ether ketone particles, and polyaryl ether ketone particles.
  • the filler includes a first filler, which is a secondary particle morphology formed by agglomeration of primary particles.
  • the filler with secondary particle morphology has a larger specific surface area and has better affinity with nanocellulose.
  • nanocellulose can also overlap the gaps between the primary particles that constitute the filler with secondary particle morphology.
  • the nanocellulose and the first filler are overlapped to form an integrated effect, so that the coating can have a more stable spatial network structure, and the isolation film can have an appropriate void ratio and a stable pore structure, and the isolation film can also have a more stable spatial network structure. It combines low moisture content with good electrolyte wetting properties.
  • the content of the first filler is 50 to 100 wt%, optionally 90 to 99 wt%, based on the total weight of the filler.
  • the content of the first filler is within an appropriate range, it is conducive to forming an integrated effect by overlapping with nanocellulose, so that the coating can have a more stable spatial network structure, which can further improve the heat resistance and tensile strength of the isolation film. Tensile strength, puncture resistance and external extrusion resistance.
  • the average particle size Dv50 of the first filler is ⁇ 200 nm, optionally ranging from 50 nm to 200 nm. This can make the first filler have a higher specific surface area, thereby increasing the affinity between the first filler and nanocellulose, and conducive to the overlapping of the first filler and nanocellulose to form an integrated effect, whereby the coating It can have a more stable spatial network structure, and the isolation film can have better heat resistance and electrolyte wetting properties.
  • the BET specific surface area of the first filler is ⁇ 20m 2 /g, optionally 25m 2 /g to 50m 2 /g. Therefore, the first filler has better affinity with nanocellulose, which is conducive to the integration effect of overlapping with nanocellulose. Therefore, the coating can have a more stable spatial network structure, and the isolation film can have better Heat resistance and electrolyte wetting properties.
  • the first filler includes inorganic particles with secondary particle morphology
  • the crystal forms of the inorganic particles with secondary particle morphology include ⁇ crystal form, ⁇ crystal form, ⁇ crystal form and eta crystal form. At least two of the forms optionally include at least two of ⁇ crystal form, ⁇ crystal form and ⁇ crystal form.
  • the inorganic particles in the secondary particle morphology of the ⁇ crystal form have diffraction peaks at 2 ⁇ of 57.48° ⁇ 0.2° and 43.34° ⁇ 0.2° in an X-ray diffraction spectrum measured by using an X-ray diffractometer.
  • the content of the ⁇ crystalline form is ⁇ 1.2wt%, optionally 1.2wt% to 10wt%, more optionally 1.2wt% to 5wt%, based on the secondary particle morphology of the inorganic particles. Total weight.
  • Inorganic particles with a secondary particle morphology of the ⁇ crystal form have diffraction peaks at 36.68° ⁇ 0.2° and 31.21° ⁇ 0.2° in 2 ⁇ in an X-ray diffraction spectrum measured by using an X-ray diffractometer.
  • the content of the ⁇ crystalline form is ⁇ 50wt%, optionally 60wt% to 85wt%, more optionally 60wt% to 82.5wt%, based on the total weight of the inorganic particles with secondary particle morphology count.
  • Inorganic particles with a secondary particle morphology of the ⁇ crystal form have diffraction peaks at 66.95° ⁇ 0.2° and 45.91° ⁇ 0.2° in 2 ⁇ in an X-ray diffraction spectrum measured by using an X-ray diffractometer.
  • the content of the ⁇ crystalline form is ⁇ 10wt%, optionally 15wt% to 60wt%, more optionally 15wt% to 35wt%, based on the total weight of the inorganic particles with secondary particle morphology. .
  • the inorganic particles of the secondary particle morphology of the eta crystal form have diffraction peaks at 31.89° ⁇ 0.2° and 19.37° ⁇ 0.2° in 2 ⁇ in an X-ray diffraction spectrum measured by using an X-ray diffractometer.
  • the content of the eta crystal form is ⁇ 5wt%, optionally ⁇ 2wt%, and more optionally ⁇ 1wt%, based on the total weight of the inorganic particles of the secondary particle morphology.
  • Inorganic particles with a secondary particle morphology in the ⁇ crystal form have the advantages of high hardness, good heat resistance, low dielectric constant, high safety and high true density; inorganic particles with a secondary particle morphology in the ⁇ crystal form have moderate The specific surface area and hardness can better simultaneously improve the heat resistance and ion transmission characteristics of the isolation film; inorganic particles with secondary particle morphology of ⁇ crystal form and eta crystal form have the advantage of large specific surface area. Therefore, selecting first fillers of different crystal forms helps to improve at least one of the heat resistance and electrolyte wetting characteristics of the isolation film.
  • the first filler includes inorganic particles with secondary particle morphology
  • the crystal form of the inorganic particles with secondary particle morphology includes the ⁇ crystal form
  • the content of the ⁇ crystal form is ⁇ 50wt%, It can be 60wt% to 85wt%, more optionally 60wt% to 82.5wt%, based on the total weight of the inorganic particles with secondary particle morphology.
  • the first filler includes inorganic particles with secondary particle morphology
  • the crystal forms of the inorganic particles with secondary particle morphology include ⁇ crystal form, ⁇ crystal form, ⁇ crystal form and eta crystal form.
  • the content of ⁇ crystal form is 1.2wt% to 5wt%
  • the content of ⁇ crystal form is 60wt% to 82.5wt%
  • the content of ⁇ crystal form is 15wt% to 35wt%
  • the content of eta crystal form is ⁇ 1wt%
  • the X-ray diffraction spectrum of inorganic particles with secondary particle morphology can be tested according to the following method: after drying the inorganic particles with secondary particle morphology, grind them in a mortar (such as agate mortar) for 30 minutes, and then use Test with a ray diffractometer (such as Miniflex600-C) to obtain the X-ray diffraction spectrum.
  • a mortar such as agate mortar
  • a ray diffractometer such as Miniflex600-C
  • the first filler includes inorganic particles with secondary particle morphology.
  • the inorganic particles with secondary particle morphology can be prepared as follows: oxidizing the precursor solution of the inorganic particles through high-pressure sputtering. Reaction, then heating at 600°C to 900°C (for example, 1 hour to 3 hours) to form small particles, and then drying and shaping at 150°C to 250°C (for example, 30 minutes to 60 minutes) to obtain secondary particle morphology of inorganic particles.
  • the filler further includes a second filler, and the second filler is in the form of primary particles.
  • the filler with a primary particle shape has a larger particle size and higher strength, which can better play its supporting role in the coating, reduce the amount of binder, and improve the heat resistance of the isolation film; and it also helps When the amount is small, the isolation membrane has more pore structure and less moisture content, which can further improve the ion transmission characteristics of the isolation membrane and the wetting characteristics of the electrolyte.
  • the content of the second filler is ⁇ 50 wt%, optionally 1 to 10 wt%, based on the total weight of the filler. This can better play the supporting role of the second filler, facilitate water discharge during the drying process, and enable the coating to maintain appropriate porosity and stable pore structure during long-term charge and discharge processes, which can further improve the performance of the isolation film. Ion transport properties and electrolyte wetting properties.
  • the second filler has an average particle size Dv50 of 100 nm to 800 nm, optionally 200 nm to 400 nm. This can better play the supporting role of the second filler, facilitate water discharge during the drying process, and enable the coating to maintain appropriate porosity and stable pore structure during long-term charge and discharge processes, which can further improve the performance of the isolation film. Ion transport properties and electrolyte wetting properties.
  • the BET specific surface area of the second filler is ⁇ 10 m 2 /g, optionally 4 m 2 /g to 9 m 2 /g. This can better play the supporting role of the second filler, facilitate water discharge during the drying process, and enable the coating to maintain appropriate porosity and stable pore structure during long-term charge and discharge processes, which can further improve the performance of the isolation film. Ion transport properties and electrolyte wetting properties.
  • the second filler includes inorganic particles with primary particle morphology
  • the crystal forms of the inorganic particles with primary particle morphology include at least one of ⁇ crystal form and ⁇ crystal form, optionally including ⁇ crystal form.
  • Inorganic particles in the form of primary particles in the alpha crystalline form have the advantages of high hardness, good heat resistance, low dielectric constant, high safety and high true density, which can further improve the heat resistance of the isolation film.
  • the second filler includes inorganic particles with primary particle morphology
  • the crystal form of the inorganic particles with primary particle morphology includes ⁇ crystal form
  • the content of ⁇ crystal form is ⁇ 90wt%, optionally It is 95wt% to 100wt%, based on the total weight of the inorganic particles of the primary particle morphology.
  • the coating may also include a non-granular binder.
  • a non-granular binder There is no particular limitation on the type of non-granular binder in this application, and any well-known material with good adhesiveness can be selected.
  • the non-granular binder includes an aqueous solution binder, which has the advantages of good thermodynamic stability and environmental protection, thereby facilitating the preparation and coating of the coating slurry.
  • the aqueous solution-type binder includes aqueous solution-type acrylic resin (for example, acrylic acid, methacrylic acid, sodium acrylate monomer homopolymer or copolymer with other comonomers), polyvinyl alcohol (PVA), isobutylene -At least one of maleic anhydride copolymer and polyacrylamide.
  • aqueous solution-type acrylic resin for example, acrylic acid, methacrylic acid, sodium acrylate monomer homopolymer or copolymer with other comonomers
  • PVA polyvinyl alcohol
  • isobutylene -At least one of maleic anhydride copolymer and polyacrylamide isobutylene -At least one of maleic anhydride copolymer and polyacrylamide.
  • the content of the non-granular binder in the coating is ⁇ 1 wt%, based on the total weight of the coating.
  • the nanocellulose and fillers in the coating of the present application can build up a stable spatial network structure, thereby enabling the isolation film to maintain high adhesion and good ion transmission characteristics while reducing the amount of binder.
  • the isolation film may further include an adhesive layer disposed on at least a portion of the surface of the coating, the adhesive layer including a granular adhesive.
  • the adhesive layer can not only prevent the coating from peeling off and improve the safety performance of the secondary battery, but also improve the interface between the isolation film and the electrode and improve the cycle performance of the secondary battery.
  • the granular binder includes at least one of acrylic monomer homopolymers or copolymers, acrylic monomer homopolymers or copolymers, and fluorine-containing olefin monomer homopolymers or copolymers.
  • the comonomers include, but are not limited to, at least one of acrylate monomers, acrylic monomers, olefin monomers, halogen-containing olefin monomers, fluoroether monomers, and the like.
  • the particulate binder includes a vinylidene fluoride-based polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and/or a copolymer of vinylidene fluoride monomer and comonomer.
  • VDF vinylidene fluoride monomer
  • the comonomer may be at least one of olefin monomers, fluorine-containing olefin monomers, chlorine-containing olefin monomers, acrylate monomers, acrylic acid monomers, and fluoroether monomers.
  • the comonomer may include trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroethylene (Alkyl vinyl) ether (such as perfluoro (methyl vinyl) ether PMVE, perfluoro (ethyl vinyl) ether PEVE, perfluoro (propyl vinyl) ether PPVE), perfluoro (1,3- At least one of perfluoro(2,2-dimethyl-1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).
  • VF3 trifluoroethylene
  • CTFE chlorotrifluoroethylene
  • TFE tetrafluoroethylene
  • HFP hexafluoropropylene
  • Alkyl vinyl) ether such as perfluoro (methyl vinyl) ether PMVE
  • the longitudinal (MD) thermal shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 5%, optionally 0.5% to 4%.
  • the transverse direction (TD) thermal shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 5%, optionally 0.5% to 4%.
  • the isolation film of the present application has low thermal shrinkage in both the transverse and longitudinal directions, thereby further improving the safety performance of the secondary battery.
  • the perforation strength of the isolation film is ⁇ 350gf, optionally 370gf to 450gf.
  • the isolation film of the present application has high perforation strength, which can further improve the safety performance of secondary batteries.
  • the longitudinal tensile strength of the isolation film is ⁇ 2000kg/cm 2 , optionally 2500kg/cm 2 to 4500kg/cm 2 .
  • the transverse tensile strength of the isolation film is ⁇ 2000kg/cm 2 , optionally 2500kg/cm 2 to 4500kg/cm 2 .
  • the isolation film of the present application has high tensile strength in both the transverse and longitudinal directions. Therefore, when the secondary battery expands, the isolation film is less likely to be damaged, thereby further improving the safety performance of the secondary battery.
  • the air permeability of the isolation film is ⁇ 300s/100mL, optionally between 100s/100mL and 200s/100mL.
  • the isolation membrane of the present application has good air permeability, thereby improving ion transmission characteristics.
  • the isolation membrane has a porosity of 30% to 45%, optionally 32% to 36%. This can improve the ion transport characteristics of the isolation membrane and reduce battery self-discharge.
  • the wetted length of the isolation film is ⁇ 30mm, optionally 30mm to 80mm.
  • the wetting speed of the isolation film is ⁇ 3 mm/s, optionally 3 mm/s to 10 mm/s.
  • the isolation membrane of the present application has good electrolyte wetting characteristics, thereby improving ion transmission characteristics and secondary battery capacity.
  • the average particle size Dv50 of the material is a meaning known in the art, and can be measured using instruments and methods known in the art. For example, you can refer to the GB/T 19077-2016 particle size distribution laser diffraction method and use a laser particle size analyzer (such as Master Size 3000) for testing.
  • a laser particle size analyzer such as Master Size 3000
  • the specific surface area of a material has a well-known meaning in the art, and can be measured using instruments and methods known in the art.
  • the nitrogen adsorption specific surface area analysis test can be performed by the Tri-Star 3020 specific surface area pore size analysis tester of the American Micromeritics Company.
  • thermal shrinkage rate, perforation strength, tensile strength and air permeability of the isolation film all have meanings known in the art, and can be measured using methods known in the art. For example, you can refer to the standard GB/T 36363-2018 for testing.
  • the wetting length and wetting speed of the isolation film have well-known meanings in the art, and can be measured using methods known in the art.
  • An exemplary test method is as follows: Cut the isolation film into a sample with a width of 5mm and a length of 100mm, fix both ends of the sample and place it horizontally; drop 0.5mg of electrolyte in the center of the sample for the specified time (1min in this application) Finally, take pictures and measure the length of electrolyte diffusion, thereby obtaining the wetting length and wetting speed of the isolation film.
  • multiple (for example, 5 to 10) samples can be taken for testing, and the test results are obtained by calculating the average value.
  • the electrolyte can be prepared as follows: mix ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) at a mass ratio of 30:50:20 to obtain an organic solvent, and mix the fully dried LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol/L.
  • the coating parameters of the above-mentioned isolation membrane are the coating parameters of one side of the porous substrate.
  • the second aspect of the embodiment of the present application provides a method for preparing the isolation membrane of the first aspect of the embodiment of the present application, including the following steps: S1, providing a porous substrate; S2, preparing a coating slurry: nanocellulose and filler according to Mix a predetermined proportion in a solvent to prepare the coating slurry; S3, coating: apply the coating slurry on at least one surface of the porous substrate to form a coating and dry it to obtain isolation.
  • the isolation membrane includes a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating includes nanocellulose and fillers, and the moisture content of the isolation membrane is Appm , the thickness of the coating is H ⁇ m, and the isolation film satisfies 250 ⁇ A/H ⁇ 1500.
  • the solvent in S2, may be water, such as deionized water.
  • the coating slurry may also include other components, for example, it may also include dispersants, wetting agents, binders, etc.
  • the solid content of the coating slurry in S2, can be controlled between 28% and 45%, for example, between 30% and 38%.
  • the solid content of the coating slurry when the solid content of the coating slurry is within the above range, it can effectively reduce the film surface problems of the coating and reduce the probability of uneven coating, thereby further improving the energy density and safety performance of the secondary battery.
  • the above-mentioned nanocellulose can be obtained as follows: S21, provide cellulose powder with a whiteness of ⁇ 80%; S22, mix and react the obtained cellulose powder with the modified solution, and then wash to remove the cellulose powder. Mix to obtain cellulose nanowhiskers; S23, adjust the pH of the obtained cellulose nanowhiskers to neutral (for example, pH 6.5 to 7.5), and grind and cut to obtain nanocellulose.
  • the above-mentioned cellulose powder with a whiteness of ⁇ 80% can be purchased from the market, or chemical methods (such as acid hydrolysis method, alkali treatment method, Tempo catalytic oxidation method) or biological methods (such as enzyme treatment method) can be used. ), mechanical methods (such as ultrafine grinding, ultrasonic crushing, high-pressure homogenization), etc.
  • the fiber raw materials used to prepare the above-mentioned cellulose powder with a whiteness of ⁇ 80% may include plant fibers, such as cotton fiber (such as cotton fiber, kapok fiber), hemp fiber (such as sisal fiber, ramie fiber, jute fiber, flax fiber, Hemp fiber, abaca fiber, etc.), at least one of brown fiber, wood fiber, bamboo fiber, and grass fiber.
  • plant fibers such as cotton fiber (such as cotton fiber, kapok fiber), hemp fiber (such as sisal fiber, ramie fiber, jute fiber, flax fiber, Hemp fiber, abaca fiber, etc.), at least one of brown fiber, wood fiber, bamboo fiber, and grass fiber.
  • the above-mentioned cellulose powder with a whiteness of ⁇ 80% can also be prepared in the following manner: after the fiber raw material is opened and deslaged, it is treated with an alkali solution (such as a NaOH aqueous solution, the concentration of which can be 4wt% to 20wt %, optionally 5wt% to 15wt%) cooking, and then sequentially undergo water washing to remove impurities (for example, the number of water washings is 3 to 6 times), bleaching (for example, sodium hypochlorite and/or hydrogen peroxide can be used), pickling to remove impurities, and water washing to remove impurities. impurities, water displacing, and airflow drying to obtain cellulose powder.
  • an alkali solution such as a NaOH aqueous solution, the concentration of which can be 4wt% to 20wt %, optionally 5wt% to 15wt
  • water washing for example, the number of water washings is 3 to 6 times
  • bleaching for example, sodium hypoch
  • the modification solution may be an acid solution (such as sulfuric acid aqueous solution, boric acid aqueous solution, phosphoric acid aqueous solution, acetic acid aqueous solution) or an alkali solution (such as urea organic solvent solution).
  • the modified solution is an acid solution.
  • the concentration of the acid solution may be 5 to 80 wt%.
  • a sulfuric acid aqueous solution is selected as the modification solution
  • the concentration of the acid solution can be 40 wt% to 80 wt%, whereby nanocellulose with a sulfonic acid group can be obtained.
  • a boric acid aqueous solution is selected as the modification solution
  • the concentration of the acid solution can be 5 to 10 wt%, whereby nanocellulose with boric acid groups can be obtained.
  • a phosphoric acid aqueous solution is selected as the modification solution
  • the concentration of the acid solution can be 45wt% to 75wt%, whereby nanocellulose with phosphate groups can be obtained.
  • an acetic acid aqueous solution is selected as the modification solution
  • the concentration of the acid solution can be 40 wt% to 80 wt%, whereby nanocellulose with carboxylic acid groups can be obtained.
  • the urea organic solvent solution is a urea xylene solution, whereby nanocellulose with amine groups can be obtained.
  • the mass ratio of the cellulose powder to the modified solution may be 1:2.5 to 1:50, optionally 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution can be 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution can be 1:20 to 1:50.
  • the modified solution is a phosphoric acid aqueous solution
  • the mass ratio of the cellulose powder to the acid solution can be 1:5 to 1:30.
  • an acetic acid aqueous solution is selected as the modification solution
  • the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30.
  • a urea organic solvent solution is selected as the modification solution, the mass ratio of the cellulose powder to the urea organic solvent solution may be 1:4 to 1:40.
  • the reaction when the modified solution is an acid solution, the reaction can be performed at a temperature no higher than 80°C, optionally at a temperature of 30°C to 60°C,
  • the reaction time between the cellulose powder and the modified solution can be 0.5 to 4 hours, optionally 1 hour to 3 hours.
  • the reaction when the modified solution is an alkaline solution, the reaction can be carried out under conditions of 100°C to 145°C, and the reaction time of the cellulose powder and the modified solution Can be 1h to 5h.
  • a grinder may be used for grinding, and a high-pressure homogenizer may be used for cutting.
  • Nanocellulose with different average diameters and/or different average lengths can be obtained by adjusting the grinding parameters of the grinder (such as the number of grinding times, grinding time, etc.) and the cutting parameters of the high-pressure homogenizer.
  • the coating uses a coater.
  • This application has no special restrictions on the model of the coating machine.
  • a commercially available coating machine can be used.
  • the coater includes a gravure roller for transferring the coating slurry to the porous substrate.
  • the number of lines of the gravure roller is 100LPI to 300LPI, more optionally, it is 125LPI to 190LPI.
  • the coating method may adopt transfer coating, spin spray coating, dip coating, etc.
  • the coating speed can be controlled between 30m/min and 120m/min, such as between 60m/min and 90m/min.
  • the coating speed is within the above range, film surface problems of the coating and the probability of uneven coating can be effectively reduced, thereby further improving the energy density and safety performance of the secondary battery.
  • the linear speed ratio of the coating in S3, can be 0.8 to 2.5, for example, it can be 0.8 to 1.5, 1.0 to 1.5.
  • the drying temperature may be 40°C to 70°C, for example, it may be 50°C to 60°C.
  • the drying time may be from 10 seconds to 120 seconds, for example, from 20 seconds to 80 seconds, or from 20 seconds to 40 seconds.
  • the performance of the isolation film of the present application can be further improved.
  • Those skilled in the art can selectively regulate one or more of the above process parameters according to actual production conditions.
  • the method further includes the following steps: S4, secondary coating: apply a slurry containing a granular binder on at least part of the surface of the coating, and form a bond after drying layer.
  • the preparation method of the isolation film of the present application obtains the coating through one-time coating, which greatly simplifies the production process of the isolation film.
  • each raw material used in the preparation method of the isolation film of the present application can be obtained commercially.
  • a third aspect of the embodiment of the present application provides a secondary battery.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery includes an electrode assembly and an electrolyte.
  • the electrode assembly includes a positive electrode piece, a negative electrode piece, and a separator.
  • the isolation film is disposed between the positive electrode piece and the negative electrode piece, It mainly plays the role of preventing short circuit between the positive and negative electrodes, and at the same time allows active ions to pass through.
  • the secondary battery may be a lithium-ion battery, a sodium-ion battery, etc.
  • the secondary battery may be a lithium-ion secondary battery.
  • the secondary battery of the third aspect of the embodiment of the present application includes the isolation film of the first aspect of the embodiment of the application or a separation film prepared by the method of the second aspect of the embodiment of the application, the isolation film is spaced between the positive electrode plate and the between the negative electrode pieces.
  • at least the side of the isolation film close to the negative electrode piece has the coating of the first aspect of the embodiment of the present application. Therefore, the secondary battery of the present application can take into account high energy density, high thermal safety performance and long service life.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the positive electrode current collector has two surfaces opposite in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive active material may include, but is not limited to, at least one of lithium-containing transition metal oxides, lithium-containing phosphates and their respective modified compounds.
  • the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt At least one of manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds.
  • lithium-containing phosphate may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium iron manganese phosphate, lithium iron manganese phosphate and carbon. at least one of the composite materials and their respective modifying compounds.
  • the cathode active material for the lithium-ion battery may include a lithium transition metal oxide with the general formula Li a Ni b Co c M d O e Af and its at least one of the modified compounds. 0.8 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 1 ⁇ e ⁇ 2, 0 ⁇ f ⁇ 1, M is selected from Mn, Al, Zr, Zn, Cu, Cr , at least one of Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.
  • a lithium transition metal oxide with the general formula Li a Ni b Co c M d O e Af and its at least one of the modified compounds. 0.8 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 1 ⁇ e ⁇ 2, 0 ⁇ f ⁇ 1, M is selected from Mn, Al, Zr, Zn, Cu, Cr , at least one of Mg, Fe, V, Ti and B, and A is
  • cathode active materials for lithium ion batteries may include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333), LiNi 0.5 Co 0.2 At least one of Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , and LiMnPO 4 kind.
  • the positive active material may include but is not limited to sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.) , at least one of Prussian blue materials.
  • cathode active materials for sodium ion batteries may include NaFeO 2 , NaCoO 2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1/2 Ti 1/2 O 2 , NaNi 1/2 Mn 1/2 O 2 , Na 2/3 Fe 1/3 Mn 2/3 O 2 , NaNi 1/3 Co 1/3 Mn 1/3 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Prussian blue materials, the general formula is X p M' q (PO 4 ) r O x Y 3-x at least one of the materials.
  • M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn
  • Y is a halogen anion, which can be at least one of F, Cl and Br.
  • the modified compounds of each of the above-mentioned positive electrode active materials may be doping modifications and/or surface coating modifications of the positive electrode active materials.
  • the positive electrode film layer optionally further includes a positive electrode conductive agent.
  • a positive electrode conductive agent includes superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, and graphene. and at least one of carbon nanofibers.
  • the mass percentage of the cathode conductive agent is ⁇ 5%.
  • the positive electrode film layer optionally further includes a positive electrode binder.
  • the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene At least one of ethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the mass percentage of the cathode binder is ⁇ 5% based on the total mass of the cathode film layer.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and At least one of polyethylene (PE).
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying, and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative active material may be a negative active material known in the art for secondary batteries.
  • the negative active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.
  • the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitride composite and silicon alloy material.
  • the tin-based material may include at least one of elemental tin, tin oxide and tin alloy materials.
  • the negative electrode film layer optionally further includes a negative electrode conductive agent.
  • a negative electrode conductive agent may include superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite at least one of ene and carbon nanofibers.
  • the mass percentage of the negative electrode conductive agent is ⁇ 5%.
  • the negative electrode film layer optionally further includes a negative electrode binder.
  • the negative electrode binder may include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, At least one of polyacrylic acid (PAA), polymethacrylic acid (PMAA), polyacrylic acid sodium (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS). kind.
  • the mass percentage of the negative electrode binder is ⁇ 5%.
  • the negative electrode film layer optionally includes other additives.
  • other auxiliaries may include thickeners, such as sodium carboxymethylcellulose (CMC), PTC thermistor materials, and the like.
  • CMC sodium carboxymethylcellulose
  • PTC thermistor materials such as sodium carboxymethylcellulose (CMC)
  • the mass percentage of the other additives is ⁇ 2%.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and At least one of polyethylene (PE).
  • the negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying, and cold pressing.
  • the negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.
  • the negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer.
  • the negative electrode sheet described in the present application further includes a conductive undercoat layer (for example, made of Conductive agent and adhesive).
  • the negative electrode sheet described in this application further includes a protective layer covering the surface of the negative electrode film layer.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.
  • the electrolyte salt may include but is not limited to lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), hexafluoroborate Lithium fluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonimide (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB) ), at least one of lithium difluoroborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTF
  • the electrolyte salt may include but is not limited to sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium hexafluoromethanesulfonate (NaAsF 6 ), sodium bisfluorosulfonimide (NaFSI), sodium bistrifluoromethanesulfonimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), difluoroxalic acid boric acid At least one of sodium (NaDFOB), sodium dioxaloborate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorodioxalophosphate (NaDFOP) and sodium tetrafluorooxalophosphate (NaTFOP).
  • NaPF 6 sodium hexafluorophosphate
  • NaBF 4 sodium tetra
  • the solvent may include, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), At least one of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sul
  • additives are optionally included in the electrolyte.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, and additives that improve the battery’s performance. Additives for low temperature power performance, etc.
  • the positive electrode piece, the isolation film and the negative electrode piece can be made into an electrode assembly through a winding process and/or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).
  • This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. As shown in FIG. 1 , a square-structured secondary battery 5 is shown as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 is used to cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process and/or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and can be adjusted according to needs.
  • the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte may be assembled to form a secondary battery.
  • the positive electrode sheet, isolation film, and negative electrode sheet can be formed into an electrode assembly through a winding process and/or a lamination process.
  • the electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, static
  • the secondary battery is obtained through processes such as placement, formation, and shaping.
  • the secondary batteries according to the present application can be assembled into a battery module.
  • the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a schematic diagram of the battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 is used to cover the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • a fourth aspect of the embodiments of the present application provides an electrical device, which includes at least one of a secondary battery, a battery module or a battery pack of the present application.
  • the secondary battery, battery module or battery pack may be used as a power source for the electrical device or as an energy storage unit for the electrical device.
  • the electrical device may be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric Golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the power-consuming device can select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • FIG. 6 is a schematic diagram of an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • battery packs or battery modules can be used.
  • the power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc.
  • the electrical device is usually required to be light and thin, and secondary batteries can be used as power sources.
  • Nanocellulose C2 to C10 were prepared in a similar manner to nanocellulose C1, and the differences are detailed in Table 1.
  • the high-pressure homogenizer equipment performs nanoscale cutting to obtain nanocellulose with an amine-modified group with an average length of 425 nm and an average diameter of 25 nm, and the molar ratio of amine groups to hydroxyl groups is 4:3.
  • the molar ratio of the modified group to the hydroxyl group can be measured by the following method: According to the phthalic anhydride method in GB/T 12008.3-2009, the hydroxyl value of the raw cellulose and modified nanocellulose (per gram The number of milligrams of potassium hydroxide equivalent to the hydroxyl content in the sample), the numerical unit obtained is mg KOH/g, which is converted into mmol/g as the hydroxyl content. Subtract the hydroxyl content of the modified nanocellulose from the hydroxyl content of the raw cellulose to obtain the content of the modified group (that is, the content of the modified hydroxyl group). From this, the mole of the modified group and the hydroxyl group can be calculated. Compare.
  • coating slurry combine the nanocellulose C1 prepared above, filler alumina (secondary particle morphology, average particle size Dv50 is 140nm, BET specific surface area is 30m 2 /g), binder aqueous solution polymer Acrylic acid was mixed evenly with an appropriate amount of solvent deionized water according to the mass ratio of 20:79.1:0.9 to obtain a coating slurry with a solid content of 35wt%.
  • filler alumina secondary particle morphology, average particle size Dv50 is 140nm, BET specific surface area is 30m 2 /g
  • binder aqueous solution polymer Acrylic acid was mixed evenly with an appropriate amount of solvent deionized water according to the mass ratio of 20:79.1:0.9 to obtain a coating slurry with a solid content of 35wt%.
  • the surface density of the coating located on one side of the PE porous substrate is 1.1g/m 2 and the thickness is 0.8 ⁇ m.
  • the coating machine includes a gravure roller. The number of lines of the gravure roller is 175LPI, the coating speed is 90m/min, the coating line speed ratio is 1.2, the drying temperature is 55 ⁇ 5°C, and the drying time is 50 seconds.
  • Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70 to obtain an organic solvent.
  • Fully dried LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol/L.
  • the positive electrode sheet, isolation film, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in the outer packaging, dried and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, Get a secondary battery.
  • the secondary battery was prepared using a method similar to that in Example 1, except that the amounts of nanocellulose C1 and filler added during the preparation of the separator were different.
  • the specific parameters are shown in Table 2.
  • the secondary battery was prepared using a method similar to Example 1, except that the type of nanocellulose used in the preparation of the separator was different.
  • the specific parameters are shown in Table 1 and Table 2.
  • the secondary battery was prepared using a method similar to that in Example 1, except that the filler alumina used in the preparation of the separator had a different specific surface area.
  • the specific parameters are shown in Table 2.
  • the morphology of the filler alumina secondary particles used in Example 18 has an average particle size Dv50 of 350 nm and a BET specific surface area of 15 m 2 /g.
  • the morphology of the filler alumina secondary particles used in Example 19 has an average particle size Dv50 of 175 nm and a BET specific surface area of 20 m 2 /g.
  • the morphology of the filler alumina secondary particles used in Example 20 has an average particle size Dv50 of 113 nm and a BET specific surface area of 35 m 2 /g.
  • the morphology of the filler alumina secondary particles used in Example 21 has an average particle size Dv50 of 85 nm and a BET specific surface area of 40 m 2 /g.
  • the secondary battery was prepared using a method similar to Example 1, except that the areal density of the coating in the preparation of the separator was different.
  • the specific parameters are shown in Table 2.
  • the secondary battery was prepared using a method similar to Example 1, except that the filler used alumina with secondary particle morphology (average particle size Dv50 is 140 nm, BET specific surface area is 30 m 2 /g) and primary particle morphology.
  • a mixture of alumina average particle size Dv50 is 600nm, BET specific surface area is 7m 2 /g), the specific addition amount is shown in Table 2.
  • the secondary battery was prepared using a method similar to Example 1, except that the types of nanocellulose used in the preparation of the separator were different and the fillers used were alumina with primary particle morphology (average particle size Dv50 was 1000 nm, The BET specific surface area is 5m 2 /g), and the specific parameters are shown in Table 1 and Table 2.
  • test instrument can be the Swiss Metrohm 831 Karl Fischer moisture analyzer.
  • Sample preparation Use a punch machine to punch the isolation film prepared above into samples with a width of 50mm and a length of 100mm. Take 5 parallel samples and place them on A4 paper and fix them. Then place the A4 paper containing the samples on a layer with a thickness of 1mm to 5mm corrugated paper.
  • Sample test Set the temperature of the blast oven to 150°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, put the A4 paper placed on the corrugated paper into the blast oven and start timing until the set time is reached (this application After 1h), measure the length and width of the isolation film, and the values are marked a and b respectively.
  • the testing instrument can be Xionggu KRK Wangyan air permeability tester.
  • Examples 1-28 provide coatings containing nanocellulose and fillers on both surfaces of the porous substrate of the isolation membrane, and control the ratio of the moisture content of the isolation membrane to the thickness of the coating to satisfy 250 ⁇ A/ H ⁇ 1500, which can make the thinned isolation film have low moisture content while also having high heat resistance and high air permeability, thus enabling the secondary battery to have both high thermal safety performance and long service life, and the hot box of the secondary battery
  • the failure temperature is above 150°C
  • the capacity retention rate of the secondary battery after 500 cycles at 25°C is above 88%
  • the capacity retention rate of the secondary battery after being stored at 60°C for 30 days is above 84%.

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Abstract

本申请提供一种隔离膜、其制备方法及其相关的二次电池和用电装置，所述隔离膜包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，其中，所述涂层包括纳米纤维素和填料，所述隔离膜的水分含量为A ppm，所述涂层的厚度为Hμm，并且所述隔离膜满足250≤A/H≤1500。本申请提供的隔离膜具有耐热性优良、水分含量低以及对电解液浸润特性良好等特点，从而使得使用该隔离膜的二次电池可兼顾高能量密度、高热安全性能和长使用寿命。

Description

隔离膜、其制备方法及其相关的二次电池和用电装置
相关申请的交叉引用
本申请要求享有于2022年06月24日提交的名称为“一种隔离膜、其制备方法及其相关的二次电池和用电装置”的专利申请PCT/CN2022/101261的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于电池技术领域，具体涉及一种隔离膜、其制备方法及其相关的二次电池和用电装置。
背景技术
近年来，二次电池被广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。随着二次电池的应用及推广，其使用寿命和安全问题，特别是热安全问题受到越来越多的关注。然而，目前用于提高二次电池热安全性能的方式往往不利于平衡二次电池的能量密度。因此，如何使二次电池兼顾高能量密度、高热安全性能和长使用寿命是二次电池设计的关键挑战所在。
发明内容
本申请的目的在于提供一种隔离膜、其制备方法及其相关的二次电池和用电装置，该隔离膜具有耐热性优良、水分含量低以及对电解液浸润特性良好等特点，从而使得使用该隔离膜的二次电池可兼顾高能量密度、高热安全性能和长使用寿命。
本申请第一方面提供一种隔离膜，包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，其中，所述涂层包括纳米纤维素和填料，所述隔离膜的水分含量为A ppm，所述涂层的厚度为Hμm，并且所述隔离膜满足250≤A/H≤1500。
本申请的发明人经大量研究意外发现，通过在隔离膜的多孔基材的至少一个表面设置包含纳米纤维素和填料的涂层并使隔离膜水分含量与涂层厚度的比值控制在上述特定范围内，能够使隔离膜兼顾高耐热性、低水分含量和良好的电解液浸润特性。
在本申请的任意实施方式中，500≤A/H≤1500，可选地，600≤A/H≤1000。由此有助于涂层具有更稳定的空间网络结构和更合适含量的羟基官能团，从而能够使隔离膜兼顾高耐热性、低水分含量和良好的电解液浸润特性，使二次电池兼顾高热安全性能、长循环寿命和长存储寿命。
在本申请的任意实施方式中，400≤A≤1000，可选地，500≤A≤800。由此有助于涂层具有更稳定的空间网络结构和更合适含量的羟基官能团，从而能够使隔离膜更好地兼 顾高耐热性、低水分含量和良好的电解液浸润特性，并能够进一步提升二次电池的循环寿命和存储寿命。
在本申请的任意实施方式中，0＜H≤1.5，可选地，0.2≤H≤0.8。由此有助于提升二次电池的能量密度。
在本申请的任意实施方式中，所述纳米纤维素包括纤维素纳米纤维、纤维素纳米晶须和细菌纳米纤维素中的至少一种，可选为纤维素纳米晶须。纤维素纳米晶须可具有较高的结晶度，由此可降低其亲水性，进而有利于干燥过程中水分排出，从而能使本申请的隔离膜具有较低的水分含量。
在本申请的任意实施方式中，所述纳米纤维素包括未改性纳米纤维素和改性纳米纤维素中的至少一种，可选为改性纳米纤维素。
在本申请的任意实施方式中，所述改性纳米纤维素包括改性基团，且所述改性基团包括胺基、羧酸基、醛基、磺酸基、硼酸基和磷酸基中的至少一种，可选地包括磺酸基、硼酸基和磷酸基中的至少一种。当纳米纤维素具有上述特定的改性基团时，一方面能够有效提高隔离膜的耐热性，提升二次电池的热安全性能，另一方面还有利于隔离膜在具有良好电解液浸润特性的前提下还具有较低的水分含量，从而能够进一步提升二次电池的电化学性能。
在本申请的任意实施方式中，所述改性纳米纤维素包括羟基和改性基团，且所述改性基团与所述羟基的摩尔比为1:4至4:1，可选为2:3至7:3。当改性基团与羟基的摩尔比在合适的范围内时，能够进一步提升隔离膜的耐热性和离子传输特性，并有助于使隔离膜具有较低的水分含量。
在本申请的任意实施方式中，所述纳米纤维素的长径比为5至80，可选为10至40。当纳米纤维素的长径比在合适的范围内时，能够进一步提高隔离膜的耐热性和离子传输特性。
在本申请的任意实施方式中，所述纳米纤维素的平均直径为10nm至40nm，可选为10nm至35nm。当纳米纤维素的平均直径在合适的范围内时，能够进一步提高隔离膜的耐热性、离子传输特性和耐电压击穿特性。
在本申请的任意实施方式中，所述纳米纤维素的平均长度为100nm至600nm，可选为200nm至500nm。当纳米纤维素的平均长度在合适的范围内时，能够进一步提高隔离膜的耐热性和离子传输特性。
在本申请的任意实施方式中，所述纳米纤维素的重均分子量为10000至60000，可选为30000至50000。
在本申请的任意实施方式中，所述纳米纤维素的平衡聚合度为150DP至300DP，可选为200DP至250DP。
当纳米纤维素的重均分子量和/或聚合度在合适的范围内时，不仅可以避免纳米纤维素堵塞隔离膜的孔道结构，而且可以使得涂层浆料的粘度在合适范围，由此涂布时浆料流动性和浸润性更优，进而更加有利于提升涂层的质量。
在本申请的任意实施方式中，所述涂层中的所述纳米纤维素的含量为6wt％至35wt％，可选为10wt％至30wt％，基于所述涂层的总重量计。
在本申请的任意实施方式中，所述涂层中的所述填料的含量为≥60wt％，可选为65wt％至90wt％，基于所述涂层的总重量计。
纳米纤维素和/或填料的含量在合适的范围内时，能够保证涂层浆料具有合适的粘度，更有利于涂布，还有利于隔离膜具有较低的水分含量和良好的电解液浸润特性；此外，还有利于填料与纳米纤维素搭建形成稳定的空间网络结构。
在本申请的任意实施方式中，所述填料包括选自无机颗粒和有机颗粒中的至少一种。
在本申请的任意实施方式中，所述填料的分解温度在200℃以上。
在本申请的任意实施方式中，所述填料包括第一填料，所述第一填料为由一次颗粒团聚形成的二次颗粒形貌。此时，纳米纤维素还可以搭接在构成所述二次颗粒形貌的填料的一次颗粒之间的空隙中，使于纳米纤维素和第一填料搭接形成一体化效果，由此涂层可以具有更稳定的空间网络结构，进而隔离膜可具有合适的空隙率和稳定的孔道结构，并且隔离膜还可兼顾低水分含量和良好的电解液浸润特性。
在本申请的任意实施方式中，所述第一填料的含量为50wt％至100wt％，可选为90wt％至99wt％，基于所述填料的总重量计。
在本申请的任意实施方式中，所述第一填料的平均粒径Dv50为≤200nm，可选为50nm至200nm。
在本申请的任意实施方式中，所述第一填料的BET比表面积为≥20m 2/g，可选为25m 2/g至50m 2/g。
当第一填料的含量、平均粒径Dv50和BET比表面积中的至少一者在上述范围内时，能与纳米纤维素搭接形成一体化效果，由此涂层可以具有更稳定的空间网络结构，同时隔离膜可以具有更好的耐热性和对电解液的浸润特性。
在本申请的任意实施方式中，所述第一填料包括二次颗粒形貌的无机颗粒，且所述二次颗粒形貌的无机颗粒的晶型包括α晶型、θ晶型、γ晶型和η晶型中的至少两种，可选地包括α晶型、θ晶型和γ晶型中的至少两种。
在本申请的任意实施方式中，所述第一填料包括二次颗粒形貌的无机颗粒，所述二次颗粒形貌的无机颗粒的晶型包括θ晶型，且θ晶型的含量为≥50wt％，可选为60wt％至85wt％，基于所述二次颗粒形貌的无机颗粒的总重量计。
通过选择不同晶型的第一填料有助于提升隔离膜的耐热性和电解液浸润特性中的至少一者。
在本申请的任意实施方式中，所述填料还包括第二填料，所述第二填料为一次颗粒形貌。由此能够更好地发挥第二填料的支撑作用，提升隔离膜的耐热性，并且还有助于在用量较少时使涂层具有更多的孔道结构和更少的水分含量。
在本申请的任意实施方式中，所述第二填料的含量为≤50wt％，可选为1wt％至10wt％，基于所述填料的总重量计。
在本申请的任意实施方式中，所述第二填料的平均粒径Dv50为100nm至800nm，可选为200nm至400nm。
在本申请的任意实施方式中，所述第二填料的BET比表面积为≤10m 2/g，可选为4m 2/g至9m 2/g。
当第二填料的含量、平均粒径Dv50和BET比表面积中的至少一者在上述范围内时，能够更好地发挥第二填料的支撑作用，有利于干燥过程中水分排出，并使涂层在长期充放电过程中保持合适的空隙率和稳定的孔道结构，进而能够进一步提升隔离膜的离子传输特性以及对电解液的浸润特性。
在本申请的任意实施方式中，所述第二填料包括一次颗粒形貌的无机颗粒，所述一次颗粒形貌的无机颗粒的晶型包括α晶型和γ晶型中的至少一种，可选地包括α晶型。由此能够进一步改善隔离膜的耐热性。
在本申请的任意实施方式中，所述第二填料包括一次颗粒形貌的无机颗粒，所述一次颗粒形貌的无机颗粒的晶型包括α晶型，且α晶型的含量为≥90wt％，可选为95wt％至100wt％，基于所述一次颗粒形貌的无机颗粒的总重量计。
在本申请的任意实施方式中，所述涂层还包括非颗粒状的粘结剂，可选地，所述非颗粒状的粘结剂包括水溶液型粘结剂。由此有利于涂层浆料的制备和涂布。
在本申请的任意实施方式中，所述涂层中的所述非颗粒状的粘结剂的含量为＜1wt％，基于所述涂层的总重量计。本申请能够在减少粘结剂用量的前提下使隔离膜还能保持高粘结性和良好的离子传输特性。
在本申请的任意实施方式中，所述多孔基材的厚度为≤6μm，可选为3μm至5μm。由此有助于进一步提升二次电池的能量密度。
在本申请的任意实施方式中，所述多孔基材的孔隙率为32％至48％，可选为34％至39％。多孔基材的孔隙率在合适的范围内时，有利于在确保隔离膜高耐热性的前提下，进一步提高隔离膜的离子传输特性；同时还可以保证二次电池具有高放电倍率，并降低电池自放电。
在本申请的任意实施方式中，所述涂层的面密度为0.6g/m 2至1.5g/m 2，可选为0.8g/m 2至1.1g/m 2。由此有助于形成耐热性更好的涂层。
在本申请的任意实施方式中，所述隔离膜还包括粘接层，所述粘接层设置在所述涂层的至少一部分表面上，所述粘接层包括颗粒状的粘结剂，可选地，所述颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物、含氟烯烃单体均聚物或共聚物中的至少一种。粘接层不仅能够防止涂层脱落，提高二次电池的安全性能，而且能够改善隔离膜与电极的界面，提升二次电池的循环性能。
在本申请的任意实施方式中，所述隔离膜在150℃、1h下的纵向热收缩率为≤5％，可选为0.5％至4％。
在本申请的任意实施方式中，所述隔离膜在150℃、1h下的横向热收缩率为≤5％，可选为0.5％至4％。
在本申请的任意实施方式中，所述隔离膜的穿孔强度为≥350gf，可选为370gf至450gf。
在本申请的任意实施方式中，所述隔离膜的纵向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2。
在本申请的任意实施方式中，所述隔离膜的横向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2。
在本申请的任意实施方式中，所述隔离膜的透气度为≤300s/100mL，可选为100s/100mL至200s/100mL。
在本申请的任意实施方式中，所述隔离膜的孔隙率为30％至45％，可选为32％至36％。
在本申请的任意实施方式中，所述隔离膜的润湿长度为≥30mm，可选为30mm至80mm。
在本申请的任意实施方式中，所述隔离膜的润湿速度为≥3mm/s，可选为3mm/s至10mm/s。
当隔离膜的性能满足上述条件中的一个或几个时，有利于提升二次电池的能量密度、热安全性能、容量发挥特性和使用寿命中的至少一者。
本申请第二方面提供一种制备本申请第一方面的隔离膜的方法，包括以下步骤：S1，提供多孔基材；S2，配制涂层浆料：将纳米纤维素和填料按照预定比例在溶剂中混合，配制成所述涂层浆料；S3，涂布：将所述涂层浆料涂布于所述多孔基材的至少一个表面上，形成涂层并干燥，获得隔离膜，其中，所述隔离膜包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，所述涂层包括纳米纤维素和填料，所述隔离膜的水分含量为A ppm，所述涂层的厚度为Hμm，并且所述隔离膜满足250≤A/H≤1500。本申请的隔离膜的制备方法通过一次涂布制得涂层，大大简化了隔离膜的生产工艺流程。
在本申请的任意实施方式中，所述涂布采用涂布机，所述涂布机包括凹版辊，所述凹版辊的线数为100LPI至300LPI，可选为125LPI至190LPI。
在本申请的任意实施方式中，所述涂布速度为30m/min至120m/min，可选为60m/min至90m/min。
在本申请的任意实施方式中，所述涂布的线速比为0.8至2.5，可选为0.8至1.5。
在本申请的任意实施方式中，所述干燥温度为40℃至70℃，可选为50℃至60℃。
在本申请的任意实施方式中，所述干燥时间为10秒至120秒，可选为20秒至80秒。
将上述各工艺参数控制在所给范围内，可以进一步改善本申请的隔离膜的性能。
在本申请的任意实施方式中，所述方法还包括以下步骤：S4，二次涂布：将包含颗粒状的粘结剂的浆料涂布在所述涂层的至少一部分表面上，干燥后形成粘接层。
本申请第三方面提供一种二次电池，包括本申请第一方面的隔离膜或通过本申请第二方面的方法制备的隔离膜。
本申请第四方面提供一种用电装置，包括本申请第三方面的二次电池。
本申请提供的隔离膜具有耐热性优良、水分含量低以及对电解液浸润特性良好等特点，从而使得使用该隔离膜的二次电池可兼顾高能量密度、高热安全性能和长使用寿命。本申请的用电装置包括本申请提供的二次电池，因而至少具有与二次电池相同的优势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的二次电池的一实施方式的示意图。
图2是图1的二次电池的实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4所示的电池包的实施方式的分解示意图。
图6是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
在附图中，附图未必按照实际的比例绘制。附图标记说明如下：1电池包，2上箱体，3下箱体，4电池模块，5二次电池，51壳体，52电极组件，53盖板。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的隔离膜、其制备方法及其相关的二次电池和用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A 为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
在本申请中，术语“多个”、“多种”是指两个或两种以上。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。
除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测试方法进行测定，例如，可以按照本申请的实施例中给出的测试方法进行测定。
通常情况下，二次电池包括电极组件和电解液，电极组件包括正极极片、负极极片和隔离膜，隔离膜设置在正极极片和负极极片之间，主要起到防止正极和负极短路的作用，同时可以使活性离子自由通过形成回路。随着二次电池的应用及推广，人们对二次电池能量密度的要求也越来越高。隔离膜减薄是提升二次电池能量密度的一个有效措施。目前商业化二次电池采用的隔离膜通常为聚烯烃多孔膜，例如聚乙烯多孔膜、聚丙烯多孔膜或聚丙烯/聚乙烯/聚丙烯三层复合膜，其熔点在130℃至160℃之间，由此，当其厚度减薄后，隔离膜的耐热性变差，受热时会严重收缩，从而增加了正极和负极短路风险。
为了解决上述问题，目前采用的措施主要是在聚烯烃多孔膜上涂布一层耐热性的无机陶瓷层，其能增加隔离膜的机械强度、减少隔离膜在受热时的收缩程度，降低正极和负极短路风险。但是，市售无机陶瓷颗粒的粒径较大，由此会增加隔离膜整体厚度，导致无法平衡二次电池的能量密度，特别是在动力电池领域，不利于续航里程提升；此外，由于市售无机陶瓷颗粒的粒径较大，由此其在聚烯烃多孔膜上的堆积层数较少(通常为≤5层)，进而导致其对隔离膜耐热性的改善效果有限。无机陶瓷颗粒纳米化可以降低涂层厚度，缓解对二次电池能量密度的不利影响，但是纳米化无机陶瓷颗粒形成的涂层孔隙率低且容易堵塞聚烯烃多孔膜的微孔，由此导致隔离膜整体的孔隙率降低、离子阻抗增加且不利于活性离子传输。同时，由于纳米化无机陶瓷颗粒的比表面积较高，且颗粒之间的接触形式为点接触，由此需要使用大量粘结剂以保证颗粒之间的粘结性，但是粘结剂用量较大时易出现堵孔问题，从而对二次电池的倍率性能不利，例如负极表面容易形成枝晶，进而还对二次电池的容量发挥和能量密度不利。
此外，无机陶瓷颗粒具有易吸附水的特性，特别地，无机陶瓷颗粒纳米化后，其比表面积大幅增加，由此导致隔离膜的水分含量明显增加。二次电池在长期充放电过程中，隔离膜中的水分会逐渐释放出来并进入电解液中。目前商业化应用最广的电解液体系为六氟磷酸锂的混合碳酸酯溶液，六氟磷酸锂在高温环境下的热稳定性较差，其在较高温度下会分解生成PF 5，PF 5对于电解液中微量的水分具有较高的敏感性，遇水会产生HF，由此会增加电解液的酸度，进而容易腐蚀正极活性材料和正极集流体、造成正极活性材料中过渡金属离子溶出，从而影响二次电池的电化学性能。因此，隔离膜还需要具有低水分含量。
随着二次电池的应用及推广，人们对二次电池使用寿命的要求也越来越高。二次电池在长期充放电过程中，隔离膜逐渐干涸失效是导致二次电池容量衰退的一个重要原因。这是由于隔离膜干涸后，电池内阻增加，导致充放电不能完全进行，进而导致二次电池容量衰减较快，大大降低了二次电池的使用寿命。因此，隔离膜还需要具有良好的电解液浸润特性。
但是，现有技术的隔离膜往往很难兼顾高耐热性、低水分含量和良好的电解液浸润 特性。
本申请的发明人在研究过程中惊奇发现，通过在隔离膜多孔基材表面设置包含纳米纤维素和填料的涂层，并合理控制隔离膜水分含量与涂层厚度的比值，能够使隔离膜兼顾高耐热性、低水分含量和良好的电解液浸润特性，进而能够使二次电池兼顾高能量密度、高热安全性能和长使用寿命。
隔离膜
具体地，本申请实施方式第一方面提供了一种隔离膜，包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，其中，所述涂层包括纳米纤维素和填料，所述隔离膜的水分含量为A ppm，所述涂层的厚度为Hμm，并且所述隔离膜满足250≤A/H≤1500。
本申请的发明人经大量研究意外发现，通过在隔离膜的多孔基材的至少一个表面设置包含纳米纤维素和填料的涂层并使隔离膜水分含量与涂层厚度的比值控制在上述特定范围内，能够使隔离膜兼顾高耐热性、低水分含量和良好的电解液浸润特性。
纳米纤维素结构富含羟基，使其具有较强的亲水性，因此其单独使用时容易导致隔离膜的水分含量较高，进而影响了二次电池的电化学性能。本申请的涂层同时包括纳米纤维素和填料，纳米纤维素能够与填料搭建形成稳定的空间网络结构，有利于干燥过程中水分排出，从而能使本申请的隔离膜具有较低的水分含量。
本申请的发明人经过大量研究发现，当控制包含纳米纤维素和填料的隔离膜的水分含量A ppm与涂层的厚度Hμm满足A/H在250至1500之间时，涂层能具有良好的空间网络结构和合适含量的羟基官能团，由此隔离膜既能具有低水分含量，又能具有良好的电解液浸润特性，进而采用其的二次电池能具有良好的电化学性能，特别地，具有长循环寿命和长存储寿命。此外，本申请的涂层同时包括纳米纤维素和填料，并且纳米纤维素和填料能够搭接在一起使涂层具有稳定的空间网络结构，由此涂层还具有高耐热性，能够降低隔离膜受热时的收缩程度，降低正极和负极短路风险，使二次电池具有高热安全性能；同时，由于本申请的涂层具有高耐热性，由此可以选用更薄的多孔基材，进而二次电池还能够兼顾高能量密度。
所述隔离膜的水分含量A ppm与所述涂层的厚度Hμm满足250≤A/H≤1500。例如，A/H可以为300，400，500，600，700，800，900，1000，1100，1200，1250，1500或以上任何数值所组成的范围。可选地，300≤A/H≤1500，500≤A/H≤1500，500≤A/H≤1250，500≤A/H≤1100，500≤A/H≤1000，600≤A/H≤1250，600≤A/H≤1100或600≤A/H≤1000。由此有助于涂层具有更稳定的空间网络结构和更合适含量的羟基官能团，从而能够使隔离膜兼顾高耐热性、低水分含量和良好的电解液浸润特性，使二次电池兼顾高热安全性能、长循环寿命和长存储寿命。
隔离膜的水分含量可以通过水分测定仪进行测定，测试方法可以采用卡尔费休水分测定法，测试仪器可以采用瑞士万通831型卡尔费休水分测定仪。
在一些实施例中，所述隔离膜的水分含量A ppm满足A≤1000，由此在二次电池充放电过程中从隔离膜溶出并释放到电解液中的水分较少，进而有助于二次电池具有良好的电化学性能，特别地，二次电池可具有高容量发挥特性和低体积膨胀率。
另外，本申请的发明人在研究过程中还意外发现，隔离膜的水分含量并不是越低越好，当隔离膜的水分含量过低，例如低于400ppm时，隔离膜与电解液之间的界面特性变 差，例如隔离膜的吸液量降低、对电解液的浸润特性变差，由此二次电池在长期充放电过程中，隔离膜会快速干涸失效，进而导致二次电池内阻迅速增加、容量迅速衰减、使用寿命大幅缩短。
在一些实施例中，所述隔离膜的水分含量A ppm满足400≤A≤1000。例如，A可以为400，450，500，550，600，650，700，750，800，850，900，950，1000或以上任何数值所组成的范围。可选地，400≤A≤900，400≤A≤800，400≤A≤700，400≤A≤600，500≤A≤900，500≤A≤800或500≤A≤700。由此有助于涂层具有更稳定的空间网络结构和更合适含量的羟基官能团，从而能够使隔离膜更好地兼顾高耐热性、低水分含量和良好的电解液浸润特性，并能够进一步提升二次电池的循环寿命和存储寿命。
在一些实施例中，所述涂层的厚度Hμm满足0＜H≤1.5。例如，H可以为0.1，0.2，0.3，0.4，0.5，0.6，0.7，0.8，0.9，1.0，1.1，1.2，1.3，1.4，1.5或以上任何数值所组成的范围。可选地，0＜H≤1.4，0＜H≤1.3，0＜H≤1.2，0＜H≤1.1，0＜H≤1.0，0＜H≤0.9，0＜H≤0.8，0.1≤H≤0.8，0.2≤H≤0.8，0.3≤H≤0.8，0.4≤H≤0.8或0.5≤H≤0.8。由此有助于提升二次电池的能量密度。
在一些实施例中，所述涂层的面密度为0.6g/m 2至1.5g/m 2，可选为0.8g/m 2至1.1g/m 2。由此有助于形成耐热性更好的涂层。
在一些实施例中，所述多孔基材的厚度可为≤6μm，可选为3μm至5μm。本申请的涂层能使隔离膜的耐热性得到显著提升，由此可以选用更薄的多孔基材，从而有助于进一步提升二次电池的能量密度。
在一些实施例中，所述多孔基材的孔隙率可为32％至48％，可选为34％至39％。多孔基材的孔隙率在合适的范围内时，有利于在确保隔离膜高耐热性的前提下，进一步提高隔离膜的离子传输特性；同时还可以保证二次电池具有高放电倍率，并降低电池自放电。
本申请对多孔基材的材质没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的基材，例如，所述多孔基材可包括多孔聚烯烃基树脂膜(例如聚乙烯、聚丙烯、聚偏氟乙烯中的至少一种)、多孔玻璃纤维和多孔无纺布中的至少一种。所述多孔基材可以是单层薄膜，也可以是多层复合薄膜。所述多孔基材为多层复合薄膜时，各层的材料可以相同，也可以不同。
二次电池能量密度提升的另一个方向是提高电压，例如采用高电压正极活性材料，但是，提高电压会对隔离膜的稳定性产生显著的影响，由此需要隔离膜满足具有良好的耐电压击穿特性。本申请的隔离膜涂层包括纳米纤维素，纳米纤维素是指任一维尺寸在纳米级(例如100nm以内)的纤维素的总称，其既具有纤维素的特性，又具有纳米颗粒的特性。纳米纤维素可以是通过化学、物理、生物等中的一种或多种手段从自然界中的木材、棉花等提取出的高分子纳米材料，具有来源广泛、成本低、生物可降解、模量高、比表面积高等优势，因此其是传统石化资源的优良替代品，可以有效地缓解环境污染和石化资源紧张等问题。纳米纤维素还具有良好的耐高温特性，且受热后体积变化较小，由此能够提高隔离膜的耐热性；同时，与传统无机陶瓷颗粒相比，纳米纤维素的密度较小，由此还能够降低二次电池的重量，提高二次电池的重量能量密度。此外，纳米纤维素还有助于使涂层具有微小且均匀的纳米孔，防止电流泄露，由此能够使隔离膜兼顾高 离子传输特性和良好的耐电压击穿特性。
在一些实施例中，所述纳米纤维素可包括纤维素纳米纤维(Cellulose nanofibrils，CNF，又称为纳米纤丝纤维素或微纤化纤维素)、纤维素纳米晶须(Cellulose nanocrystals，CNC，又称为纤维素纳米晶、纳米晶体纤维素)和细菌纳米纤维素(Bacterial nanocellulose，BNC，又称为细菌纤维素或微生物纤维素)中的至少一种，可选为纤维素纳米晶须。纤维素纳米晶须可具有较高的结晶度，由此可降低其亲水性，进而有利于干燥过程中水分排出，从而能使本申请的隔离膜具有较低的水分含量。此外，纤维素纳米晶须还容易与填料搭接在一起，使涂层具有更稳定的空间网络结构，从而还能够进一步提升隔离膜的性能。
在一些实施例中，所述纳米纤维素可包括未改性纳米纤维素(又称羟基纳米纤维素)和改性纳米纤维素中的至少一种，可选为改性纳米纤维素。
所述改性纳米纤维素包括改性基团。在一些实施例中，所述改性基团可包括胺基、羧酸基、醛基、磺酸基、硼酸基和磷酸基中的至少一种，可选地包括磺酸基、硼酸基和磷酸基中的至少一种。
发明人在进一步研究中发现，当纳米纤维素具有上述特定的改性基团时，一方面能够有效提高隔离膜的耐热性，提升二次电池的热安全性能，另一方面还有利于隔离膜在具有良好电解液浸润特性的前提下还具有较低的水分含量，从而能够进一步提升二次电池的电化学性能。
当纳米纤维素具有上述特定的改性基团时，纳米纤维素还能与填料搭建形成更稳定的空间网络结构，从而能够进一步提升隔离膜的离子传输特性和耐电压击穿特性，由此还有利于匹配高电压正极活性材料，并进一步提升二次电池的能量密度。
此外，改性基团的存在还能降低羟基的比例，由此能够保证涂层浆料具有合适的粘度，更有利于涂布，从而还能提高隔离膜的生产效率和涂层的均一性。
在一些实施例中，所述改性纳米纤维素包括羟基和改性基团，且所述改性基团与所述羟基的摩尔比可为1:4至4:1，可选为2:3至7:3。当改性基团与羟基的摩尔比在合适的范围内时，能够进一步提升隔离膜的耐热性和离子传输特性，并有助于使隔离膜具有较低的水分含量。并且能够有效避免以下情况：当改性基团与羟基的摩尔比过小时，改性基团所起到的对隔离膜耐热性和离子传输特性的进一步改善效果可能不明显；当改性基团与羟基的摩尔比过大时，隔离膜的电解液浸润特性可能受到影响，例如隔离膜的离子传输特性可能变差，进而可能影响二次电池的循环寿命和存储寿命，同时还可能导致隔离膜的耐热性下降，进而还可能影响二次电池的热安全性能。
纳米纤维素中改性基团的种类可以采用红外光谱法进行测定。例如，可以测试材料的红外光谱，确定其包含的特征峰，从而确定改性基团的种类。具体地，可以用本领域公知的仪器及方法对材料进行红外光谱分析，例如采用红外光谱仪(如美国尼高力(nicolet)公司的IS10型傅里叶变换红外光谱仪)，依据GB/T 6040-2019红外光谱分析方法通则进行测试。
在一些实施例中，所述纳米纤维素的长径比可为5至80，可选为10至40。当纳米纤维素的长径比在合适的范围内时，能够进一步提高隔离膜的耐热性和离子传输特性。并且能够有效避免以下情况：当纳米纤维素的长径比过小时，其与填料的搭接效果较差， 涂层的耐热性可能变差，并且在涂层烘干过程中，部分纳米纤维素由于缺少填料的支撑作用还容易坍塌，进而还容易产生堵孔问题，由此还会阻碍活性离子传输和水分排出，影响二次电池的循环性能和容量发挥；当纳米纤维素的长径比过大时，其与填料搭接形成的涂层的纳米孔较小，由此也可能导致隔离膜的离子传输特性变差。
在一些实施例中，所述纳米纤维素的平均直径可为10nm至40nm，可选为10nm至35nm。当纳米纤维素的平均直径在合适的范围内时，能够进一步提高隔离膜的耐热性、离子传输特性和耐电压击穿特性。并且能够有效避免以下情况：当纳米纤维素的平均直径过大时，其与填料搭接形成的涂层的纳米孔较大，由此可能导致隔离膜的耐电压击穿特性变差，同时其与填料的搭接效果较差，涂层的耐热性可能变差，并且在涂层烘干过程中，部分纳米纤维素由于缺少填料的支撑作用还容易坍塌，进而还容易产生堵孔问题，由此还会阻碍活性离子传输和水分排出，影响二次电池的循环性能和容量发挥。
在一些实施例中，所述纳米纤维素的平均长度可为100nm至600nm，可选为200nm至500nm。当纳米纤维素的平均长度在合适的范围内时，能够进一步提高隔离膜的耐热性和离子传输特性。并且能够有效避免以下情况：当纳米纤维素的平均长度过短时，其与填料的搭接效果较差，涂层的耐热性可能变差，并且在涂层烘干过程中，部分纳米纤维素由于缺少填料的支撑作用还容易坍塌，进而还容易产生堵孔问题，由此还会阻碍活性离子传输和水分排出，影响二次电池的循环性能和容量发挥；当纳米纤维素的平均长度过长时，涂层浆料粘度大、流动差，由此可能会影响涂层浆料的涂布进而影响所获得的涂层质量，例如影响隔离膜的耐热性和离子传输特性。
纳米纤维素的平均长度和平均直径可以通过以下方法进行测定：从隔离膜中任选一区域裁切出3.6mm×3.6mm的样品，利用扫描电子显微镜(例如ZEISS Sigma 300)测绘样品中涂层的微观形貌结构，选择高真空模式，工作电压为3kV，放大倍数为3万倍，获得SEM图；根据获得的SEM图，选取多个(例如5个以上)测试区域进行长度的统计，每个测试区域的尺寸为0.5μm×0.5μm，之后取各个测试区域得到的长度的平均值作为纳米纤维素的平均长度；根据获得的SEM图，利用Nano Measurer粒径分布统计软件，选取多个(例如5个以上)测试区域进行直径的统计，每个测试区域的尺寸为0.5μm×0.5μm，之后取各个测试区域得到的直径的平均值作为纳米纤维素的平均直径。
在一些实施例中，所述纳米纤维素的重均分子量可为10000至60000，可选为30000至50000。
在一些实施例中，所述纳米纤维素的平衡聚合度可为150DP至300DP，可选为200DP至250DP。
当纳米纤维素的重均分子量和/或聚合度在合适的范围内时，不仅可以避免纳米纤维素堵塞隔离膜的孔道结构，而且可以使得涂层浆料的粘度在合适范围，由此涂布时浆料流动性和浸润性更优，进而更加有利于提升涂层的质量，例如，能够进一步提高隔离膜的耐热性和离子传输特性。
在一些实施例中，所述纳米纤维素的形状可包括以下中的至少一种：管状(例如中空管状)、纤维状和杆状。合适形状的纳米纤维素更有利于其与填料搭建形成稳定的空间网络结构，由此能够进一步提升隔离膜的离子传输特性和耐外力挤压能力。
在一些实施例中，所述涂层中的所述纳米纤维素的含量可为6wt％至35wt％，可选为10wt％至30wt％，基于所述涂层的总重量计。纳米纤维素的含量在合适的范围内时，能够保证涂层浆料具有合适的粘度，更有利于涂布，还有利于隔离膜具有较低的水分含量和良好的电解液浸润特性；此外，还有利于纳米纤维素与填料搭建形成稳定的空间网络结构，由此能够进一步提升隔离膜的性能，例如降低隔离膜的水分含量，提升隔离膜的耐热性、离子导通能力、耐外力挤压能力和耐电压击穿能力等。
在一些实施例中，所述涂层中的所述填料的含量可为≥60wt％，可选为65wt％至90wt％，基于所述涂层的总重量计。填料的含量在合适的范围内时，能够保证涂层浆料具有合适的粘度，更有利于涂布，还有利于隔离膜具有较低的水分含量和良好的电解液浸润特性；此外，还有利于与纳米纤维素搭建形成稳定的空间网络结构，从而进一步提升隔离膜的性能，例如降低隔离膜的水分含量，提升隔离膜的耐热性、拉伸强度、耐穿刺能力和耐外力挤压能力等。
二次电池在长期充放电过程中，由于正极活性材料和负极活性材料微观结构变化的不可逆，导致整个电池的体积会有所增大，特别地，当二次电池快速充电时，负极活性材料嵌入活性离子后的体积增大程度更高。电池膨胀后会对隔离膜产生挤压和/或拉伸作用，容易导致隔离膜破损，由此会增加正极和负极短路风险。因此，隔离膜还需要具有良好的耐外力挤压能力。填料的存在有助于涂层具有稳定的空间网络结构，由此能够提升隔离膜离子传输特性和耐热性；此外，还能够提升隔离膜的拉伸强度、耐穿刺能力和耐外力挤压能力。
在一些实施例中，所述填料可包括无机颗粒和有机颗粒中的至少一种。
在一些实施例中，可选地，所述填料的分解温度在200℃以上，由此填料可具有热稳定性好且不易分解的特性，进而可以进一步提升隔离膜的耐热性。
无机颗粒具有热稳定性高且不易分解的特性，且其表面通常具有羟基，由此容易与纳米纤维素搭建形成稳定的空间网络结构。在一些实施例中，可选地，所述无机颗粒包括具有5以上介电常数的无机颗粒、具有离子传导性但不储存离子的无机颗粒和能够发生电化学反应的无机颗粒中的至少一种。
可选地，所述具有5以上介电常数的无机颗粒包括勃姆石、氧化铝、氧化锌、氧化硅、氧化钛、氧化锆、氧化钡、氧化钙、氧化镁、氧化镍、氧化锡、氧化铈、氧化钇、氧化铪、氢氧化铝、氢氧化镁、碳化硅、碳化硼、氮化铝、氮化硅、氮化硼、氟化镁、氟化钙、氟化钡、硫酸钡、硅酸镁铝、硅酸镁锂、硅酸镁钠、膨润土、水辉石、钛酸锆、钛酸钡、Pb(Zr,Ti)O 3(简写为PZT)、Pb 1-mLa mZr 1-nTi nO 3(简写为PLZT，0＜m＜1，0＜n＜1)、Pb(Mg 3Nb 2/3)O 3-PbTiO 3(简写为PMN-PT)、及其各自的改性无机颗粒中的至少一种。可选地，各无机颗粒的改性方式可为化学改性和/或物理改性。所述化学改性方式包括偶联剂改性(例如采用硅烷偶联剂、钛酸酯偶联剂等)、表面活性剂改性、聚合物接枝改性等。所述物理改性方式可为机械力分散、超声分散、高能处理等。通过改性处理能够减少无机颗粒的团聚，由此使其与纳米纤维素搭建形成更稳定和更均一的空间网络结构；此外，通过选择具有特定官能团的偶联剂、表面活性材料或聚合物改性无机颗粒，还有助于提升涂层对电解液的浸润特性和提升涂层的粘结性。
可选地，所述具有离子传导性但不储存离子的无机颗粒包括Li 3PO 4、磷酸钛锂Li x1Ti y1(PO 4) 3、磷酸钛铝锂Li x2Al y2Ti z1(PO 4) 3、(LiAlTiP) x3O y3型玻璃、钛酸镧锂Li x4La y4TiO 3、硫代磷酸锗锂Li x5Ge y5P z2S w、氮化锂Li x6N y6、SiS 2型玻璃Li x7Si y7S z3和P 2S 5型玻璃Li x8P y8S z4中的至少一种，0＜x1＜2，0＜y1＜3，0＜x2＜2，0＜y2＜1，0＜z1＜3，0＜x3＜4，0＜y3＜13，0＜x4＜2，0＜y4＜3，0＜x5＜4，0＜y5＜1，0＜z2＜1，0＜w＜5，0＜x6＜4，0＜y6＜2，0＜x7＜3，0＜y7＜2，0＜z3＜4，0＜x8＜3，0＜y8＜3，0＜z4＜7。由此能够进一步提升隔离膜的离子传输特性。
可选地，所述能够发生电化学反应的无机颗粒包括含锂过渡金属氧化物、含锂磷酸盐、碳基材料、硅基材料、锡基材料和锂钛化合物中的至少一种。
有机颗粒具有热稳定性好且不易分解的特性，由此可以提升隔离膜的耐热性；同时，当二次电池因为过充滥用、热滥用等使其内部温度达到有机颗粒的熔点时，有机颗粒还可以融化，并因毛细作用而被吸入多孔基材的微孔中起到闭孔和断路的作用，从而有利于保证二次电池具有高安全性能。
在一些实施例中，所述有机颗粒包括但不限于聚乙烯颗粒、聚丙烯颗粒、聚苯乙烯颗粒、纤维素、纤维素改性剂(例如羧基甲基纤维素)、三聚氰胺树脂颗粒、酚醛树脂颗粒、聚酯颗粒(例如聚对苯二甲酸乙二酯、聚萘二甲酸乙二酯、聚对苯二甲酸丁二酯)、有机硅树酯颗粒、聚酰亚胺颗粒、聚酰胺酰亚胺颗粒、聚芳酰胺颗粒、聚苯硫醚颗粒、聚砜颗粒、聚醚砜颗粒、聚醚醚酮颗粒、聚芳醚酮颗粒、丙烯酸丁酯与甲基丙烯酸乙酯的共聚物(例如丙烯酸丁酯与甲基丙烯酸乙酯的交联聚合物)中的至少一种。
在一些实施例中，可选地，所述有机颗粒的玻璃化转变温度可以在130℃以上。由此当二次电池内部温度达到130℃时，有机颗粒不会由玻璃态转变为粘流态，由此能够确保隔离膜不剧烈收缩。更可选地，所述有机颗粒包括但不限于三聚氰胺甲醛树脂颗粒、酚醛树脂颗粒、聚酯颗粒、有机硅树酯颗粒、聚酰亚胺颗粒、聚酰胺酰亚胺颗粒、聚芳酰胺颗粒、聚苯硫醚颗粒、聚砜颗粒、聚醚砜颗粒、聚醚醚酮颗粒、聚芳醚酮颗粒中的至少一种。
在一些实施例中，所述填料包括第一填料，所述第一填料为由一次颗粒团聚形成的二次颗粒形貌。二次颗粒形貌的填料的比表面积较大，与纳米纤维素的亲和性更好，同时纳米纤维素还可以搭接在构成所述二次颗粒形貌的填料的一次颗粒之间的空隙中，使于纳米纤维素和第一填料搭接形成一体化效果，由此涂层可以具有更稳定的空间网络结构，进而隔离膜可具有合适的空隙率和稳定的孔道结构，并且隔离膜还可兼顾低水分含量和良好的电解液浸润特性。
在一些实施例中，所述第一填料的含量为50wt％至100wt％，可选为90wt％至99wt％，基于所述填料的总重量计。第一填料的含量在合适的范围内时，有利于与纳米纤维素搭接形成一体化效果，由此涂层可以具有更稳定的空间网络结构，从而能够进一步提升隔离膜的耐热性、拉伸强度、耐穿刺能力和耐外力挤压能力。
在一些实施例中，所述第一填料的平均粒径Dv50为≤200nm，可选为50nm至200nm。由此能使第一填料具有较高的比表面积，从而能够增加第一填料与纳米纤维素的亲和性，并有利于第一填料与纳米纤维素搭接形成一体化效果，由此涂层可以具有更稳定的空间网络结构，隔离膜可以具有更好的耐热性和对电解液的浸润特性。
在一些实施例中，所述第一填料的BET比表面积为≥20m 2/g，可选为25m 2/g至50m 2/g。由此第一填料与纳米纤维素的亲和性更好，有利于与纳米纤维素搭接形成一体化效果，由此涂层可以具有更稳定的空间网络结构，同时隔离膜可以具有更好的耐热性和对电解液的浸润特性。
在一些实施例中，所述第一填料包括二次颗粒形貌的无机颗粒，且所述二次颗粒形貌的无机颗粒的晶型包括α晶型、θ晶型、γ晶型和η晶型中的至少两种，可选地包括α晶型、θ晶型和γ晶型中的至少两种。
α晶型的二次颗粒形貌的无机颗粒在通过使用X射线衍射仪测定的X射线衍射谱图中，在2θ为57.48°±0.2°和43.34°±0.2°处具有衍射峰。在一些实施例中，α晶型的含量为≥1.2wt％，可选为1.2wt％至10wt％，更可选为1.2wt％至5wt％，基于所述二次颗粒形貌的无机颗粒的总重量计。
θ晶型的二次颗粒形貌的无机颗粒在通过使用X射线衍射仪测定的X射线衍射谱图中，在2θ为36.68°±0.2°和31.21°±0.2°处具有衍射峰。在一些实施例中，θ晶型的含量为≥50wt％，可选为60wt％至85wt％，更可选为60wt％至82.5wt％，基于所述二次颗粒形貌的无机颗粒的总重量计。
γ晶型的二次颗粒形貌的无机颗粒在通过使用X射线衍射仪测定的X射线衍射谱图中，在2θ为66.95°±0.2°和45.91°±0.2°处具有衍射峰。在一些实施例中，γ晶型的含量为≥10wt％，可选为15wt％至60wt％，更可选为15wt％至35wt％，基于所述二次颗粒形貌的无机颗粒的总重量计。
η晶型的二次颗粒形貌的无机颗粒在通过使用X射线衍射仪测定的X射线衍射谱图中，在2θ为31.89°±0.2°和19.37°±0.2°处具有衍射峰。在一些实施例中，η晶型的含量为≤5wt％，可选为≤2wt％，更可选为≤1wt％，基于所述二次颗粒形貌的无机颗粒的总重量计。
α晶型的二次颗粒形貌的无机颗粒具有硬度高、耐热性好、介电常数低、安全性高和真密度大的优势；θ晶型的二次颗粒形貌的无机颗粒具有适中的比表面积和硬度，由此能够更好地同时改善隔离膜的耐热性和离子传输特性；γ晶型和η晶型的二次颗粒形貌的无机颗粒具有比表面积大的优势。因此，通过选择不同晶型的第一填料有助于提升隔离膜的耐热性和电解液浸润特性中的至少一者。
在一些实施例中，所述第一填料包括二次颗粒形貌的无机颗粒，所述二次颗粒形貌的无机颗粒的晶型包括θ晶型，且θ晶型的含量为≥50wt％，可选为60wt％至85wt％，更可选为60wt％至82.5wt％，基于所述二次颗粒形貌的无机颗粒的总重量计
在一些实施例中，所述第一填料包括二次颗粒形貌的无机颗粒，所述二次颗粒形貌的无机颗粒的晶型包括α晶型、θ晶型、γ晶型和η晶型，并且α晶型的含量为1.2wt％至5wt％，θ晶型的含量为60wt％至82.5wt％，γ晶型的含量为15wt％至35wt％，η晶型的含量为≤1wt％，均基于所述二次颗粒形貌的无机颗粒的总重量计。
二次颗粒形貌的无机颗粒的X射线衍射谱图可以按照如下方法测试得到：将二次颗粒形貌的无机颗粒烘干后，在研钵(如玛瑙研钵)中研磨30min，之后使用X射线衍射仪(如Miniflex600-C)进行测试，得到X射线衍射谱图。测试时可采用Cu靶材，Ni滤波片，管压40KV，管流15mA，连续扫描范围5°-80°。
在一些实施例中，所述第一填料包括二次颗粒形貌的无机颗粒，二次颗粒形貌的无机颗粒可以按照如下方法制备：将无机颗粒的前驱体溶液通过高压溅射的方式进行氧化反应，之后在600℃至900℃下进行加热(例如1小时至3小时)形成小颗粒，然后再在150℃至250℃下进行干燥定型(例如30分钟至60分钟)获得二次颗粒形貌的无机颗粒。
在一些实施例中，所述填料还包括第二填料，所述第二填料为一次颗粒形貌。一次颗粒形貌的填料的粒径较大、强度较高，由此能够更好地发挥其在涂层中的支撑作用，降低粘结剂用量，提升隔离膜的耐热性；并且还有助于在用量较少时使隔离膜具有更多的孔道结构和更少的水分含量，进而能够进一步提升隔离膜的离子传输特性以及对电解液的浸润特性。
在一些实施例中，所述第二填料的含量为≤50wt％，可选为1wt％至10wt％，基于所述填料的总重量计。由此能够更好地发挥第二填料的支撑作用，有利于干燥过程中水分排出，并使涂层在长期充放电过程中保持合适的空隙率和稳定的孔道结构，进而能够进一步提升隔离膜的离子传输特性以及对电解液的浸润特性。
在一些实施例中，所述第二填料的平均粒径Dv50为100nm至800nm，可选为200nm至400nm。由此能够更好地发挥第二填料的支撑作用，有利于干燥过程中水分排出，并使涂层在长期充放电过程中保持合适的空隙率和稳定的孔道结构，进而能够进一步提升隔离膜的离子传输特性以及对电解液的浸润特性。
在一些实施例中，所述第二填料的BET比表面积为≤10m 2/g，可选为4m 2/g至9m 2/g。由此能够更好地发挥第二填料的支撑作用，有利于干燥过程中水分排出，并使涂层在长期充放电过程中保持合适的空隙率和稳定的孔道结构，进而能够进一步提升隔离膜的离子传输特性以及对电解液的浸润特性。
在一些实施例中，所述第二填料包括一次颗粒形貌的无机颗粒，所述一次颗粒形貌的无机颗粒的晶型包括α晶型和γ晶型中的至少一种，可选地包括α晶型。α晶型的一次颗粒形貌的无机颗粒具有硬度高、耐热性好、介电常数低、安全性高和真密度大的优势，由此能够进一步改善隔离膜的耐热性。
在一些实施例中，所述第二填料包括一次颗粒形貌的无机颗粒，所述一次颗粒形貌的无机颗粒的晶型包括α晶型，且α晶型的含量为≥90wt％，可选为95wt％至100wt％，基于所述一次颗粒形貌的无机颗粒的总重量计。
在一些实施例中，所述涂层还可包括非颗粒状的粘结剂。本申请对非颗粒状的粘结剂的种类没有特别的限制，可以选用任意公知的具有良好粘结性的材料。可选地，所述非颗粒状的粘结剂包括水溶液型粘结剂，其具有热力学稳定性好且环保的优势，由此有利于涂层浆料的制备和涂布。作为示例，所述水溶液型粘结剂包括水溶液型丙烯酸类树脂(例如，丙烯酸、甲基丙烯酸、丙烯酸钠单体均聚物或与其他共聚单体共聚物)、聚乙烯醇(PVA)、异丁烯-马来酸酐共聚物、聚丙烯酰胺中的至少一种。
可选地，所述涂层中的所述非颗粒状的粘结剂的含量为＜1wt％，基于所述涂层的总重量计。本申请的涂层中的纳米纤维素与填料能够搭建形成稳定的空间网络结构，由此能够在减少粘结剂用量的前提下使隔离膜还能保持高粘结性和良好的离子传输特性。
在一些实施例中，所述隔离膜还可包括粘接层，所述粘接层设置在所述涂层的至少一部分表面上，所述粘接层包括颗粒状的粘结剂。粘接层不仅能够防止涂层脱落，提高二次电池的安全性能，而且能够改善隔离膜与电极的界面，提升二次电池的循环性能。
可选地，所述颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物、含氟烯烃单体均聚物或共聚物中的至少一种。所述共聚单体包括但不限于丙烯酸酯类单体、丙烯酸类单体、烯烃单体、含卤素烯烃单体、氟醚类单体等中的至少一种。
可选地，所述颗粒状的粘结剂包括偏二氟乙烯基聚合物，例如偏二氟乙烯单体(VDF)的均聚物和/或偏二氟乙烯单体与共聚单体的共聚物。所述共聚单体可为烯烃单体、含氟烯烃单体、含氯烯烃单体、丙烯酸酯类单体、丙烯酸类单体、氟醚类单体中的至少一种。可选地，所述共聚单体可包括三氟乙烯(VF3)、三氟氯乙烯(CTFE)、1,2-二氟乙烯、四氟乙烯(TFE)、六氟丙烯(HFP)、全氟(烷基乙烯基)醚(例如全氟(甲基乙烯基)醚PMVE、全氟(乙基乙烯基)醚PEVE、全氟(丙基乙烯基)醚PPVE)、全氟(1,3-间二氧杂环戊烯)和全氟(2,2-二甲基-1,3-间二氧杂环戊烯)(PDD)中的至少一种。
在一些实施例中，隔离膜在150℃、1h下的纵向(MD)热收缩率为≤5％，可选为0.5％至4％。
在一些实施例中，隔离膜在150℃、1h下的横向(TD)热收缩率为≤5％，可选为0.5％至4％。
本申请的隔离膜横向和纵向两个方向均具有低热收缩率，由此能够进一步提升二次电池的安全性能。
在一些实施例中，隔离膜的穿孔强度为≥350gf，可选为370gf至450gf。本申请的隔离膜具有高穿孔强度，由此能够进一步提升二次电池的安全性能。
在一些实施例中，隔离膜的纵向拉伸强度≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2。
在一些实施例中，隔离膜的横向拉伸强度≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2。
本申请的隔离膜在横向和纵向两个方向均具有高拉伸强度，由此在二次电池膨胀时，隔离膜出现破损的概率较小，从而能够进一步提升二次电池的安全性能。
在一些实施例中，所述隔离膜的透气度为≤300s/100mL，可选为100s/100mL至200s/100mL。本申请的隔离膜具有良好的透气度，由此能够提升离子传输特性。
在一些实施例中，所述隔离膜的孔隙率为30％至45％，可选为32％至36％。由此能够提升隔离膜的离子传输特性并降低电池自放电。
在一些实施例中，隔离膜的润湿长度为≥30mm，可选为30mm至80mm。
在一些实施例中，隔离膜的润湿速度为≥3mm/s，可选为3mm/s至10mm/s。
本申请的隔离膜具有良好的电解液浸润特性，由此能够提升离子传输特性和二次电池容量发挥。
在本申请中，材料的平均粒径Dv50为本领域公知的含义，可采用本领域已知的仪器及方法进行测定。例如可以参照GB/T 19077-2016粒度分布激光衍射法，采用激光粒度分析仪(例如Master Size 3000)进行测试。
在本申请中，材料的比表面积为本领域公知的含义，可采用本领域已知的仪器及方法进行测定。例如可以参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(BrunauerEmmett Teller)法计算得出。可选地，氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
在本申请中，隔离膜的热收缩率、穿孔强度、拉伸强度和透气度均具有本领域公知的含义，可以采用本领域已知的方法进行测量。例如，均可参照标准GB/T 36363-2018进行测试。
在本申请中，隔离膜的润湿长度、润湿速度均具有本领域公知的含义，可以采用本领域已知的方法进行测量。示例性测试方法如下：将隔离膜裁切成宽度为5mm、长度为100mm的样品，将样品两端固定后水平放置；取0.5mg电解液滴在样品中央，达到规定时间(本申请为1min)后，拍照并测量电解液扩散的长度，由此得到隔离膜的润湿长度和润湿速度。为了保证测试结果的准确性，可取多个(例如5至10个)样品进行测试，并且测试结果通过计算平均值得到。电解液可以按照如下方法配制：将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)按照质量比30:50:20进行混合得到有机溶剂，将充分干燥的LiPF 6溶解于上述有机溶剂中配制成浓度为1mol/L的电解液。
需要说明的是，上述隔离膜的涂层参数(例如面密度、厚度等)均为多孔基材单侧的涂层参数。
当涂层设置在多孔基材的两侧时，其中任意一侧的涂层参数满足本申请，即认为落入本申请的保护范围内。
制备方法
本申请实施方式第二方面提供一种制备本申请实施方式第一方面的隔离膜的方法，包括以下步骤：S1，提供多孔基材；S2，配制涂层浆料：将纳米纤维素和填料按照预定比例在溶剂中混合，配制成所述涂层浆料；S3，涂布：将所述涂层浆料涂布于所述多孔基材的至少一个表面上，形成涂层并干燥，获得隔离膜，其中，所述隔离膜包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，所述涂层包括纳米纤维素和填料，所述隔离膜的水分含量为A ppm，所述涂层的厚度为Hμm，并且所述隔离膜满足250≤A/H≤1500。
在一些实施例中，在S2中，所述溶剂可以为水，例如去离子水。
在一些实施例中，在S2中，所述涂层浆料还可以包括其他组分，例如，还可以包括分散剂、润湿剂、粘结剂等。
在一些实施例中，在S2中，所述涂层浆料的固含量可以控制在28％至45％之间，例如，可以在30％至38％之间。当涂层浆料的固含量在上述范围内时，可以有效减少涂层的膜面问题以及降低涂布不均匀出现的概率，从而进一步改善二次电池的能量密度和安全性能。
在一些实施例中，上述纳米纤维素可以按照如下方法获得：S21，提供白度≥80％的纤维素粉末；S22，将所获得的纤维素粉末与改性溶液混合并反应后，经过洗涤除杂，获得纤维素纳米晶须；S23，将获得的纤维素纳米晶须的pH调节至中性(例如pH为6.5至7.5)，并经研磨、切割获得纳米纤维素。
可选地，在S21中，上述白度≥80％的纤维素粉末可以通过市购获得，或者采用化学法(例如酸解法、碱处理法、Tempo催化氧化法)、生物法(例如酶处理法)、机械法(例如超细研磨、超声破碎、高压均质)等获得。用于制备上述白度≥80％的纤维素粉末的纤维原料可以包括植物纤维，例如棉纤维(例如棉花纤维、木棉纤维)、麻纤维(例如剑麻纤维、苎麻纤维、黄麻纤维、亚麻纤维、大麻纤维、蕉麻纤维等)、棕纤维、木纤维、竹纤维、草纤维中的至少一种。
在一些实施例中，上述白度≥80％的纤维素粉末也可通过以下方式制备获得：将纤维原料经过开松除渣后，用碱液(例如NaOH水溶液，其浓度可为4wt％至20wt％，可选为5wt％至15wt％)蒸煮，然后再顺序经过水洗除杂(例如水洗次数为3次至6次)、漂白(例如可用次氯酸钠和/或双氧水)、酸洗除杂、水洗除杂、驱水、气流干燥，获得纤维素粉末。
在一些实施例中，在S22中，所述改性溶液可为酸溶液(例如硫酸水溶液、硼酸水溶液、磷酸水溶液、醋酸水溶液)或碱溶液(例如尿素有机溶剂溶液)。可选地，所述改性溶液为酸溶液。
可选地，所述酸溶液的浓度可为5wt％至80wt％。当改性溶液选用硫酸水溶液时，所述酸溶液的浓度可为40wt％至80wt％，由此可以获得具有磺酸基的纳米纤维素。当改性溶液选用硼酸水溶液时，所述酸溶液的浓度可为5wt％至10wt％，由此可以获得具有硼酸基的纳米纤维素。当改性溶液选用磷酸水溶液时，所述酸溶液的浓度可为45wt％至75wt％，由此可以获得具有磷酸基的纳米纤维素。当改性溶液选用醋酸水溶液时，所述酸溶液的浓度可为40wt％至80wt％，由此可以获得具有羧酸基的纳米纤维素。
可选地，所述尿素有机溶剂溶液为尿素二甲苯溶液，由此可以获得具有胺基的纳米纤维素。
在一些实施例中，在S22中，可选地，所述纤维素粉末与所述改性溶液的质量比可为1:2.5至1:50，可选为1:5至1:30。
当改性溶液选用硫酸水溶液时，所述纤维素粉末与所述酸溶液的质量比可为1:5至1:30。当改性溶液选用硼酸水溶液时，所述纤维素粉末与所述酸溶液的质量比可为1:20至1:50。当改性溶液选用磷酸水溶液时，所述纤维素粉末与所述酸溶液的质量比可为1:5至1:30。当改性溶液选用醋酸水溶液时，所述纤维素粉末与所述酸溶液的质量比可为1:5至1:30。当改性溶液选用尿素有机溶剂溶液时，所述纤维素粉末与所述尿素有机溶剂溶液的质量比可为1:4至1:40。
在一些实施例中，在S22中，当所述改性溶液为酸溶液时，所述反应可在不高于80℃的条件下进行，可选为在30℃至60℃的条件下进行，所述纤维素粉末与所述改性溶液的反应时间可为0.5h至4h，可选为1h至3h。
在一些实施例中，在S22中，当所述改性溶液为碱溶液时，所述反应可在100℃至145℃的条件下进行，所述纤维素粉末与所述改性溶液的反应时间可为1h至5h。
在一些实施例中，在S23中，研磨可以采用研磨机，切割可以采用高压均质机。通过调节研磨机的研磨参数(例如研磨次数、研磨时间等)以及高压均质机的切割参数能够获得具有不同平均直径和/或不同平均长度的纳米纤维素。
在一些实施例中，在S3中，所述涂布采用涂布机。本申请对涂布机的型号没有特殊限制，例如可以采用市购涂布机。可选地，所述涂布机包括凹版辊，所述凹版辊用于将涂层浆料转移到多孔基材上。可选地，所述凹版辊的线数为100LPI至300LPI，更可选为125LPI至190LPI。
在一些实施例中，在S3中，所述涂布方式可以采用转移涂布、旋转喷涂、浸涂等。
在一些实施例中，在S3中，所述涂布速度可以控制在30m/min至120m/min之间，例如在60m/min至90m/min之间。当涂布速度在上述范围内时，可以有效减少涂层的膜面问题以及降低涂布不均匀出现的概率，从而进一步改善二次电池的能量密度和安全性能。
在一些实施例中，在S3中，所述涂布的线速比可以为0.8至2.5，例如可以为0.8至1.5，1.0至1.5。
在一些实施例中，在S3中，所述干燥温度可以为40℃至70℃，例如可以为50℃至60℃。
在一些实施例中，在S3中，所述干燥时间可以为10秒至120秒，例如可以为20秒至80秒，20秒至40秒。
将上述各工艺参数控制在所给范围内，可以进一步改善本申请的隔离膜的性能。本领域的技术人员可以根据实际生产情况，选择性地调控上述一个或多个工艺参数。
在一些实施例中，所述方法还包括以下步骤：S4，二次涂布：将包含颗粒状的粘结剂的浆料涂布在所述涂层的至少一部分表面上，干燥后形成粘接层。
本申请的隔离膜的制备方法通过一次涂布制得涂层，大大简化了隔离膜的生产工艺流程。
本申请的隔离膜的制备方法中使用的一些原料及其含量等参数可以参考本申请实施方式第一方面的隔离膜，此处不再赘述。如果没有特别的说明，在本申请的隔离膜的制备方法中所使用的各原料均可以通过市购获得。
二次电池
本申请实施方式第三方面提供一种二次电池。
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。通常情况下，二次电池包括电极组件和电解液，所述电极组件包括正极极片、负极极片和隔离膜，所述隔离膜设置在所述正极极片和所述负极极片之间，主要起到防止正极和负极短路的作用，同时可以使活性离子通过。
本申请对二次电池种类没有特别的限制，例如，所述二次电池可以为锂离子电池、钠离子电池等，特别地，所述二次电池可以为锂离子二次电池。
本申请实施方式第三方面的二次电池包括本申请实施方式第一方面的隔离膜或采用本申请实施方式第二方面的方法制备的隔离膜，所述隔离膜间隔于所述正极极片和所述负极极片之间。可选地，至少所述隔离膜靠近所述负极极片的一侧具有本申请实施方式第一方面的涂层。由此，本申请的二次电池能兼顾高能量密度、高热安全性能和长使用寿命。
[正极极片]
在一些实施例中，所述正极极片包括正极集流体以及设置在所述正极集流体至少一 个表面且包括正极活性材料的正极膜层。例如，所述正极集流体具有在自身厚度方向相对的两个表面，所述正极膜层设置在所述正极集流体的两个相对表面中的任意一者或两者上。
当本申请的二次电池为锂离子电池时，所述正极活性材料可包括但不限于含锂过渡金属氧化物、含锂磷酸盐及其各自的改性化合物中的至少一种。所述锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其各自的改性化合物中的至少一种。所述含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其各自的改性化合物中的至少一种。
在一些实施例中，为了进一步提高二次电池的能量密度，用于锂离子电池的正极活性材料可以包括通式为Li aNi bCo cM dO eA f的锂过渡金属氧化物及其改性化合物中的至少一种。0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti和B中的至少一种，A选自N、F、S和Cl中的至少一种。
作为示例，用于锂离子电池的正极活性材料可包括LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2(NCM333)、LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)、LiNi 0.6Co 0.2Mn 0.2O 2(NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、LiNi 0.85Co 0.15Al 0.05O 2、LiFePO 4、LiMnPO 4中的至少一种。
当本申请的二次电池为钠离子电池时，所述正极活性材料可包括但不限于含钠过渡金属氧化物、聚阴离子材料(如磷酸盐、氟磷酸盐、焦磷酸盐、硫酸盐等)、普鲁士蓝类材料中的至少一种。
作为示例，用于钠离子电池的正极活性材料可包括NaFeO 2、NaCoO 2、NaCrO 2、NaMnO 2、NaNiO 2、NaNi 1/2Ti 1/2O 2、NaNi 1/2Mn 1/2O 2、Na 2/3Fe 1/3Mn 2/3O 2、NaNi 1/3Co 1/3Mn 1/3O 2、NaFePO 4、NaMnPO 4、NaCoPO 4、普鲁士蓝类材料、通式为X pM’ q(PO 4) rO xY 3-x的材料中的至少一种。在通式X pM’ q(PO 4) rO xY 3-x中，0＜p≤4，0＜q≤2，1≤r≤3，0≤x≤2，X选自H +、Li +、Na +、K +和NH 4 +中的至少一种，M’为过渡金属阳离子，可选为V、Ti、Mn、Fe、Co、Ni、Cu和Zn中的至少一种，Y为卤素阴离子，可选为F、Cl和Br中的至少一种。
在本申请中，上述各正极活性材料的改性化合物可以是对所述正极活性材料进行掺杂改性和/或表面包覆改性。
在一些实施例中，所述正极膜层还可选地包括正极导电剂。本申请对所述正极导电剂的种类没有特别的限制，作为示例，所述正极导电剂包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的至少一种。在一些实施例中，基于所述正极膜层的总质量，所述正极导电剂的质量百分含量为≤5％。
在一些实施例中，所述正极膜层还可选地包括正极粘结剂。本申请对所述正极粘结剂的种类没有特别的限制，作为示例，所述正极粘结剂可包括聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物和含氟丙烯酸酯类树脂中的至少一种。在一些 实施例中，基于所述正极膜层的总质量，所述正极粘结剂的质量百分含量为≤5％。
在一些实施例中，所述正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铝箔。所述复合集流体可包括高分子材料基层以及形成于所述高分子材料基层至少一个表面上的金属材料层。作为示例，所述金属材料可包括铝、铝合金、镍、镍合金、钛、钛合金、银和银合金中的至少一种。作为示例，所述高分子材料基层可包括聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的至少一种。
所述正极膜层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。所述正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
[负极极片]
在一些实施例中，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面且包括负极活性材料的负极膜层。例如，所述负极集流体具有在自身厚度方向相对的两个表面，所述负极膜层设置在所述负极集流体的两个相对表面中的任意一者或两者上。
所述负极活性材料可采用本领域公知的用于二次电池的负极活性材料。作为示例，所述负极活性材料可包括但不限于天然石墨、人造石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂中的至少一种。所述硅基材料可包括单质硅、硅氧化物、硅碳复合物、硅氮复合物和硅合金材料中的至少一种。所述锡基材料可包括单质锡、锡氧化物和锡合金材料中的至少一种。
在一些实施例中，所述负极膜层还可选地包括负极导电剂。本申请对所述负极导电剂的种类没有特别的限制，作为示例，所述负极导电剂可包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的至少一种。在一些实施例中，基于所述负极膜层的总质量，所述负极导电剂的质量百分含量为≤5％。
在一些实施例中，所述负极膜层还可选地包括负极粘结剂。本申请对所述负极粘结剂的种类没有特别的限制，作为示例，所述负极粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸类树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)和羧甲基壳聚糖(CMCS)中的至少一种。在一些实施例中，基于所述负极膜层的总质量，所述负极粘结剂的质量百分含量为≤5％。
在一些实施例中，所述负极膜层还可选地包括其他助剂。作为示例，其他助剂可包括增稠剂，例如，羧甲基纤维素钠(CMC)、PTC热敏电阻材料等。在一些实施例中，基于所述负极膜层的总质量，所述其他助剂的质量百分含量为≤2％。
在一些实施例中，所述负极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铜箔。所述复合集流体可包括高分子材料基层以及形成于所述高分子材料基层至少一个表面上的金属材料层。作为示例，所述金属材料可包括铜、铜合金、镍、镍合金、钛、钛合金、银和银合金中的至少一种。作为示例，所述高分子材料基层可包括聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的至少一种。
所述负极膜层通常是将负极浆料涂布在负极集流体上，经干燥、冷压而成的。所述负极浆料通常是将负极活性材料、可选的导电剂、可选地粘结剂、其他可选的助剂分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，但不限于此。
所述负极极片并不排除除了所述负极膜层之外的其他附加功能层。例如在某些实施例中，本申请所述的负极极片还包括夹在所述负极集流体和所述负极膜层之间、设置在所述负极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施例中，本申请所述的负极极片还包括覆盖在所述负极膜层表面的保护层。
[电解液]
在二次电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出，电解液在正极极片和负极极片之间起到传导活性离子的作用。本申请对电解液的种类没有特别的限制，可根据实际需求进行选择。
所述电解液包括电解质盐和溶剂。所述电解质盐和所述溶剂的种类不受具体的限制，可根据实际需求进行选择。
当本申请的二次电池为锂离子电池时，作为示例，所述电解质盐可包括但不限于六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)和四氟草酸磷酸锂(LiTFOP)中的至少一种。
当本申请的二次电池为钠离子电池时，作为示例，所述电解质盐可包括但不限于六氟磷酸钠(NaPF 6)、四氟硼酸钠(NaBF 4)、高氯酸钠(NaClO 4)、六氟砷酸钠(NaAsF 6)、双氟磺酰亚胺钠(NaFSI)、双三氟甲磺酰亚胺钠(NaTFSI)、三氟甲磺酸钠(NaTFS)、二氟草酸硼酸钠(NaDFOB)、二草酸硼酸钠(NaBOB)、二氟磷酸钠(NaPO 2F 2)、二氟二草酸磷酸钠(NaDFOP)和四氟草酸磷酸钠(NaTFOP)中的至少一种。
作为示例，所述溶剂可包括但不限于碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸乙烯酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)和二乙砜(ESE)中的至少一种。
在一些实施例中，所述电解液中还可选地包括添加剂。例如，所述添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温功率性能的添加剂等。
在一些实施例中，所述正极极片、所述隔离膜和所述负极极片可通过卷绕工艺和/或叠片工艺制成电极组件。
在一些实施例中，所述二次电池可包括外包装。该外包装可用于封装上述电极组件及电解液。
在一些实施例中，所述二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。所述二次电池的外包装也可以是软包，例如袋式软包。所述软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)和聚丁二酸丁二醇酯(PBS)中的至少一种。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图1是作为一个示例的方形结构的二次电池5。
在一些实施例中，如图2所示，外包装可包括壳体51和盖板53。壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53用于盖设所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺和/或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，可根据需求来调节。
本申请的二次电池的制备方法是公知的。在一些实施例中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺和/或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
在本申请的一些实施例中，根据本申请的二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图3是作为一个示例的电池模块4的示意图。如图3所示，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图4和图5是作为一个示例的电池包1的示意图。如图4和图5所示，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2用于盖设下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
用电装置
本申请实施方式第四方面提供一种用电装置，所述用电装置包括本申请的二次电池、电池模块或电池包中的至少一种。所述二次电池、电池模块或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述用电装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置的示意图。该用电装置为纯电动车、混合动力电动车、 或插电式混合动力电动车等。为了满足该用电装置对高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
纳米纤维素C1的制备
纤维素粉末制备
将棉花短绒通过开棉机开松除渣后，使用5wt％的NaOH水溶液在150℃蒸煮2h，然后再顺序经过水洗除杂(水洗次数为3次)、次氯酸钠漂白、稀盐酸洗涤除杂、水洗除杂(水洗次数为1次)、驱水、气流干燥后，获得白度为≥85％的棉花纤维素粉末。
纤维素的酯化
将所获得的棉花纤维素粉末1kg与60wt％的硫酸水溶液30kg混合，在60℃下反应1.5h，反应结束后，再顺序经过水洗除杂(水洗次数为3次)、过滤、除酸除杂，获得具有磺酸基改性基团的纤维素纳米晶须。
纤维素的中和
用10wt％的NaOH水溶液先将具有磺酸基改性基团的纤维素纳米晶须的pH调至中性，然后用研磨机高速处理2.5h将其分散，研磨次数为2次，再使用高压均质机设备进行纳米级切割，得到平均长度为425nm、平均直径为25nm的具有磺酸基改性基团的纳米纤维素C1，并且磺酸基与羟基的摩尔比为5:3。
纳米纤维素C2至C10的制备
纳米纤维素C2至C10按照与纳米纤维素C1类似的方法制备，不同之处详见表1。
纳米纤维素C11的制备
纤维素粉末制备
将棉花短绒通过开棉机开松除渣后，使用5wt％的NaOH水溶液在150℃蒸煮2h，然后再顺序经过水洗除杂(水洗次数为3次)、次氯酸钠漂白、稀盐酸洗涤除杂、水洗除杂(水洗次数为1次)、驱水、气流干燥后，获得白度为≥85％的棉花纤维素粉末。在10℃条件下，将获得的棉花纤维素粉末与20wt％的NaOH水溶液混合，搅拌2h、过滤、水洗2次后，获得碱纤维素粉末。
纤维素的酯化
将所获得的碱纤维素粉末50g与尿素200g置于带油水分离器的三口反应器中，待尿素溶解后，再加入5g二甲苯，搅拌下升温至137℃，反应4h后终止，然后经过水洗(水洗次数为3次)、过滤、干燥，获得纤维素氨基甲酸酯。
纤维素的中和
将所获得的纤维素氨基甲酸酯溶解在5wt％的NaOH水溶液中，得到均匀的纤维素氨 基甲酸酯溶液，然后用研磨机高速处理2.5h将其分散，研磨次数为2次，再使用高压均质机设备进行纳米级切割，得到平均长度为425nm、平均直径为25nm的具有胺基改性基团的纳米纤维素，并且胺基与与羟基的摩尔比为4:3。
改性基团与羟基的摩尔比可以通过以下方法测得：依据GB/T 12008.3-2009中的邻苯二甲酸酐法分别测试得到原料纤维素和改性纳米纤维素的羟值(与每克试样中羟基含量相当的氢氧化钾毫克数)，得到的数值单位为mg KOH/g，将其转化为mmol/g，作为羟基含量。以原料纤维素的羟基含量减去改性纳米纤维素的羟基含量，即可得改性基团的含量(即被改性的羟基的含量)，由此计算得到改性基团与羟基的摩尔比。
纳米纤维素C12至C14的制备
采用未改性纳米纤维素，产品型号为CNWS-50，购自中科雷鸣(北京)科技有限公司，可以使用研磨机和/或高压均质机进一步处理，以获得具有不同平均直径和/或不同平均长度的纳米纤维素。具体详见表1。
表1
Figure PCTCN2022112589-appb-000001
实施例1
(1)隔离膜的制备
S1，提供PE多孔基材：厚度为4.8μm，孔隙率为39％。
S2，配制涂层浆料：将上述制备的纳米纤维素C1、填料氧化铝(二次颗粒形貌，平均粒径Dv50为140nm，BET比表面积为30m 2/g)、粘结剂水溶液型聚丙烯酸按照质量比20:79.1:0.9在适量的溶剂去离子水中混合均匀，得到固含量为35wt％的涂层浆料。
S3，涂布：将所配制的涂层浆料用涂布机涂布在PE多孔基材的两个表面上，通过干燥、分切工序，得到隔离膜。位于PE多孔基材单侧的涂层的面密度为1.1g/m 2、厚度为0.8μm。涂布机包括凹版辊，凹版辊的线数为175LPI，涂布速度为90m/min，涂布线速比为1.2，干燥温度为55±5℃，干燥时间为50秒。
(2)正极极片的制备
将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、导电剂炭黑(Super P)、粘结剂聚偏二氟乙烯(PVDF)按照质量比96.2:2.7:1.1在适量的溶剂N-甲基吡咯烷酮(NMP)中混合均匀，得到正极浆料；将正极浆料涂布于正极集流体铝箔上，通过烘干、冷压、分条、裁切等工序，得到正极极片。正极极片的面密度为0.207mg/mm 2，压实密度为3.5g/cm 3。
(3)负极极片的制备
将负极活性材料人造石墨、导电剂炭黑(Super P)、粘结剂丁苯橡胶(SBR)和羧甲基纤维素钠(CMC)按照质量比96.4:0.7:1.8:1.1在适量的溶剂去离子水中混合均匀，得到负极浆料；将负极浆料涂布于负极集流体铜箔上，通过烘干、冷压、分条、裁切工序，得到负极极片。负极极片的面密度为0.126mg/mm 2，压实密度为1.7g/cm 3。
(4)电解液的制备
将碳酸乙烯酯(EC)和碳酸甲乙酯(EMC)按照质量比30:70进行混合得到有机溶剂，将充分干燥的LiPF 6溶解于上述有机溶剂中配制成浓度为1mol/L的电解液。
(5)二次电池的制备
将正极极片、隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件；将电极组件置于外包装中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
实施例2-6
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中纳米纤维素C1和填料的加入量不同，具体参数详见表2。
实施例7-17
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中采用的纳米纤维素种类不同，具体参数详见表1和表2。
实施例18-21
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中采用的填料氧化铝的比表面积不同，具体参数详见表2。
实施例18采用的填料氧化铝二次颗粒形貌，平均粒径Dv50为350nm，BET比表面积为15m 2/g。实施例19采用的填料氧化铝二次颗粒形貌，平均粒径Dv50为175nm，BET比表面积为20m 2/g。实施例20采用的填料氧化铝二次颗粒形貌，平均粒径Dv50为113nm，BET比表面积为35m 2/g。实施例21采用的填料氧化铝二次颗粒形貌，平均粒径Dv50为85nm，BET比表面积为40m 2/g。
实施例22-26
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中涂层的面密度不同，具体参数详见表2。
实施例27-28
二次电池采用与实施例1类似的方法制备，不同之处在于填料采用二次颗粒形貌的氧化铝(平均粒径Dv50为140nm，BET比表面积为30m 2/g)和一次颗粒形貌的氧化铝(平均粒径Dv50为600nm，BET比表面积为7m 2/g)的混合物，具体加入量详见表2。
对比例1-4
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中采用的纳米纤维素种类不同以及采用的填料均为一次颗粒形貌的氧化铝(平均粒径Dv50为1000nm，BET比表面积为5m 2/g)，具体参数详见表1和表2。
表2
Figure PCTCN2022112589-appb-000002
测试部分
(1)隔离膜的水分含量测试
将空皿置于干燥箱中在45℃加热8h后，再置于干燥器内冷却1h。称取0.08g至0.1g隔离膜样品置于冷却后的空皿中，之后将空皿置于水分测定仪中在170℃加热10min，测试隔离膜的水分含量。测试方法。采用卡尔费休水分测定法，测试仪器可以采用瑞士万通831型卡尔费休水分测定仪。
(2)隔离膜的热收缩率测试
样品制备：将上述制备的隔离膜用冲压机冲切成宽度为50mm、长度为100mm的样品，取5个平行样品放置在A4纸上并固定，再将装有样品的A4纸放置在厚度为1mm至5mm的瓦楞纸上。
样品测试：将鼓风式烘箱温度设置为150℃，待温度达到设定温度并稳定30min后，将放置在瓦楞纸上面的A4纸放入鼓风式烘箱，开始计时，到达设定时间(本申请为1h)后，测量隔离膜的长度和宽度，数值分别标记为a和b。
热收缩率计算：纵向(MD)热收缩率＝[(100-a)/100]×100％，横向(TD)热收缩率＝[(50-b)/50]×100％，取5个平行样品的平均值作为测试结果。
(3)隔离膜的透气度测试
在25℃下，测定100mL空气通过隔离膜所需要的时间，取5个平行样品的平均值作为测试结果。测试仪器可以采用熊谷KRK王研式透气度测试仪。
(4)二次电池的循环性能测试
在25℃下，将二次电池以1C恒流充电至4.2V，继续恒压充电至电流为≤0.05C，此时二次电池为满充状态，记录此时的充电容量，即为第1圈充电容量；将二次电池静置5min后，以1C恒流放电至2.8V，此为一个循环充放电过程，记录此时的放电容量，即为第1圈放电容量。将二次电池按照上述方法进行循环充放电测试，记录每圈循环后的放电容量。二次电池25℃循环500圈后的容量保持率(％)＝500圈循环后的放电容量/第1圈放电容量×100％。
(5)二次电池的高温存储性能测试
在25℃下，将二次电池以1C恒流充电至4.2V，继续恒压充电至电流为≤0.05C，将二次电池静置5min后，以1C恒流放电至2.8V，记录此时的放电容量，即为存储前的容量。在25℃下，将二次电池以1C恒流充电到4.2V，继续恒压充电至电流为≤0.05C，此时二次电池为满充状态，然后将二次电池放入60℃的恒温箱，存储30天后取出，之后将二次电池以1C恒流放电至2.8V，记录此时的放电容量，即为存储后的容量。二次电池60℃存储30天后的容量保持率(％)＝存储后的容量/存储前的容量×100％。
(6)二次电池的热箱测试
在25℃下，将二次电池以1C恒流充电至4.2V，继续恒压充电至电流为≤0.05C，静置5min；然后在DHG-9070A DHG系列高温烘箱中带夹具测试各二次电池，以5℃/min的速率从室温升至80±2℃，保持30min；之后再以5℃/min升温速度升温，每升温5℃，保温30min，直至二次电池失效。升温过程中监控二次电池表面温度变化，当温度开始急剧上升时对应的烘箱温度即为二次电池的热箱失效温度。二次电池的热箱失效温度越高，表明二次电池的热安全性能越好。
表3
Figure PCTCN2022112589-appb-000003
由表3可见，实施例1-28通过在隔离膜的多孔基材的两个表面设置包含纳米纤维素和填料的涂层，并控制隔离膜水分含量与涂层厚度的比值满足250≤A/H≤1500，可以使减薄的隔离膜在具有低水分含量的同时还具有高耐热性和高透气度，进而能够使二次电池兼顾高热安全性能和长使用寿命，二次电池的热箱失效温度在150℃以上，二次电池25℃循环500圈后的容量保持率在88％以上，二次电池60℃存储30天后的容量保持率在84％以上。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领 域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (18)

  1. 一种隔离膜，包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，其中，所述涂层包括纳米纤维素和填料，所述隔离膜的水分含量为A ppm，所述涂层的厚度为Hμm，并且所述隔离膜满足250≤A/H≤1500。
  2. 根据权利要求1所述的隔离膜，其中，
    500≤A/H≤1500，可选地，600≤A/H≤1000；和/或，
    400≤A≤1000，可选地，500≤A≤800；和/或，
    0＜H≤1.5，可选地，0.2≤H≤0.8。
  3. 根据权利要求1或2所述的隔离膜，其中，所述纳米纤维素包括纤维素纳米纤维、纤维素纳米晶须和细菌纳米纤维素中的至少一种，可选为纤维素纳米晶须。
  4. 根据权利要求1-3中任一项所述的隔离膜，其中，所述纳米纤维素包括未改性纳米纤维素和改性纳米纤维素中的至少一种，可选为改性纳米纤维素，
    可选地，所述改性纳米纤维素包括改性基团，且所述改性基团包括胺基、羧酸基、醛基、磺酸基、硼酸基和磷酸基中的至少一种，进一步可选地包括磺酸基、硼酸基和磷酸基中的至少一种；和/或，
    可选地，所述改性纳米纤维素包括羟基和改性基团，且所述改性基团与所述羟基的摩尔比为1:4至4:1，进一步可选为2:3至7:3。
  5. 根据权利要求1-4中任一项所述的隔离膜，其中，所述纳米纤维素满足如下条件(1)至(5)中的至少一者：
    (1)所述纳米纤维素的长径比为5至80，可选为10至40；
    (2)所述纳米纤维素的平均直径为10nm至40nm，可选为10nm至35nm；
    (3)所述纳米纤维素的平均长度为100nm至600nm，可选为200nm至500nm；
    (4)所述纳米纤维素的重均分子量为10000至60000，可选为30000至50000；
    (5)所述纳米纤维素的平衡聚合度为150DP至300DP，可选为200DP至250DP。
  6. 根据权利要求1-5中任一项所述的隔离膜，其中，
    所述涂层中的所述纳米纤维素的含量为6wt％至35wt％，可选为10wt％至30wt％，基于所述涂层的总重量计；和/或，
    所述涂层中的所述填料的含量为≥60wt％，可选为65wt％至90wt％，基于所述涂层的总重量计。
  7. 根据权利要求1-6中任一项所述的隔离膜，其中，
    所述填料包括选自无机颗粒和有机颗粒中的至少一种；和/或，
    所述填料的分解温度在200℃以上。
  8. 根据权利要求1-7中任一项所述的隔离膜，其中，所述填料包括第一填料，所述第一填料为由一次颗粒团聚形成的二次颗粒形貌；
    可选地，所述第一填料满足如下条件(1)至(5)中的至少一者：
    (1)所述第一填料的含量为50wt％至100wt％，可选为90wt％至99wt％，基于所述填料的总重量计；
    (2)所述第一填料的平均粒径Dv50为≤200nm，可选为50nm至200nm；
    (3)所述第一填料的BET比表面积为≥20m 2/g，可选为25m 2/g至50m 2/g；
    (4)所述第一填料包括二次颗粒形貌的无机颗粒，且所述二次颗粒形貌的无机颗粒的晶型包括α晶型、θ晶型、γ晶型和η晶型中的至少两种，可选地包括α晶型、θ晶型和γ晶型中的至少两种；
    (5)所述第一填料包括二次颗粒形貌的无机颗粒，所述二次颗粒形貌的无机颗粒的晶型包括θ晶型，且θ晶型的含量为≥50wt％，可选为60wt％至85wt％，基于所述二次颗粒形貌的无机颗粒的总重量计。
  9. 根据权利要求8所述的隔离膜，其中，所述填料还包括第二填料，所述第二填料为一次颗粒形貌；
    可选地，所述第二填料满足如下条件(1)至(5)中的至少一者：
    (1)所述第二填料的含量为≤50wt％，可选为1wt％至10wt％，基于所述填料的总重量计；
    (2)所述第二填料的平均粒径Dv50为100nm至800nm，可选为200nm至400nm；
    (3)所述第二填料的BET比表面积为≤10m 2/g，可选为4m 2/g至9m 2/g；
    (4)所述第二填料包括一次颗粒形貌的无机颗粒，所述一次颗粒形貌的无机颗粒的晶型包括α晶型和γ晶型中的至少一种，可选地包括α晶型；
    (5)所述第二填料包括一次颗粒形貌的无机颗粒，所述一次颗粒形貌的无机颗粒的晶型包括α晶型，且α晶型的含量为≥90wt％，可选为95wt％至100wt％，基于所述一次颗粒形貌的无机颗粒的总重量计。
  10. 根据权利要求1-9中任一项所述的隔离膜，其中，所述涂层还包括非颗粒状的粘结剂，
    可选地，所述非颗粒状的粘结剂包括水溶液型粘结剂；
    可选地，所述涂层中的所述非颗粒状的粘结剂的含量为＜1wt％，基于所述涂层的总重量计。
  11. 根据权利要求1-10中任一项所述的隔离膜，其中，
    所述多孔基材的厚度为≤6μm，可选为3μm至5μm；和/或，
    所述多孔基材的孔隙率为32％至48％，可选为34％至39％；和/或，
    所述涂层的面密度为0.6g/m 2至1.5g/m 2，可选为0.8g/m 2至1.1g/m 2。
  12. 根据权利要求1-11中任一项所述的隔离膜，其中，所述隔离膜还包括粘接层，所述粘接层设置在所述涂层的至少一部分表面上，所述粘接层包括颗粒状的粘结剂，可选地，所述颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物、含氟烯烃单体均聚物或共聚物中的至少一种。
  13. 根据权利要求1-12中任一项所述的隔离膜，其中，所述隔离膜满足如下条件(1)至(9)中的至少一者：
    (1)所述隔离膜在150℃、1h下的纵向热收缩率为≤5％，可选为0.5％至4％；
    (2)所述隔离膜在150℃、1h的横向热收缩率为≤5％，可选为0.5％至4％；
    (3)所述隔离膜的穿孔强度为≥350gf，可选为370gf至450gf；
    (4)所述隔离膜的纵向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2；
    (5)所述隔离膜的横向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2；
    (6)所述隔离膜的透气度为≤300s/100mL，可选为100s/100mL至200s/100mL；
    (7)所述隔离膜的孔隙率为30％至45％，可选为32％至36％；
    (8)所述隔离膜的润湿长度为≥30mm，可选为30mm至80mm；
    (9)所述隔离膜的润湿速度为≥3mm/s，可选为3mm/s至10mm/s。
  14. 一种制备权利要求1-13中任一项所述的隔离膜的方法，包括以下步骤：S1，提供多孔基材；S2，配制涂层浆料：将纳米纤维素和填料按照预定比例在溶剂中混合，配制成所述涂层浆料；S3，涂布：将所述涂层浆料涂布于所述多孔基材的至少一个表面上，形成涂层并干燥，获得隔离膜，
    其中，所述隔离膜包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，所述涂层包括纳米纤维素和填料，所述隔离膜的水分含量为A ppm，所述涂层的厚度为Hμm，并且所述隔离膜满足250≤A/H≤1500。
  15. 根据权利要求14所述的方法，其中，所述涂布步骤满足如下条件(1)至(5)中的至少一者：
    (1)所述涂布采用涂布机，所述涂布机包括凹版辊，所述凹版辊的线数为100LPI至300LPI，可选为125LPI至190LPI；
    (2)所述涂布速度为30m/min至120m/min，可选为60m/min至90m/min；
    (3)所述涂布的线速比为0.8至2.5，可选为0.8至1.5；
    (4)所述干燥温度为40℃至70℃，可选为50℃至60℃；
    (5)所述干燥时间为10秒至120秒，可选为20秒至80秒。
  16. 根据权利要求14或15所述的方法，还包括以下步骤：S4，二次涂布：将包含颗粒状的粘结剂的浆料涂布在所述涂层的至少一部分表面上，干燥后形成粘接层。
  17. 一种二次电池，包括权利要求1-13中任一项所述的隔离膜或通过权利要求14-16中任一项所述的方法制备的隔离膜。
  18. 一种用电装置，包括权利要求17所述的二次电池。
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