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CN114068870A - Positive plate and lithium ion battery comprising same - Google Patents

Positive plate and lithium ion battery comprising same Download PDF

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Publication number
CN114068870A
CN114068870A CN202111521912.XA CN202111521912A CN114068870A CN 114068870 A CN114068870 A CN 114068870A CN 202111521912 A CN202111521912 A CN 202111521912A CN 114068870 A CN114068870 A CN 114068870A
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Prior art keywords
coating
binder
positive
positive electrode
lithium
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CN114068870B (en
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张健
彭冲
李俊义
徐延铭
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
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  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

The invention provides a positive plate and a lithium ion battery comprising the same, wherein the positive plate comprises a positive current collector and a positive coating, and the positive coating comprises a first coating and a second coating; the first coating is coated on the surface of the positive current collector, and the second coating is coated on the surface of the first coating; the first coating layer includes an inorganic filler, a first conductive agent, and a first binder; the second coating layer includes a positive electrode active material, a second conductive agent, and a second binder; when in useX1/(Y1×SY1+Z1×SZ1)>X2/(Y2×SY2+Z2×SZ2) (ii) a The lithium ion battery has good safety performance, and the probability of battery fire and failure is greatly reduced when mechanical abuse (acupuncture and heavy impact) occurs. Meanwhile, the cycle performance of the lithium ion battery is not affected, and the effect of the cycle performance of the lithium ion battery is equivalent to that of the cycle performance of the conventional lithium ion battery, namely the safety performance of the lithium ion battery is obviously improved on the premise of keeping the cycle performance of the lithium ion battery.

Description

Positive plate and lithium ion battery comprising same
The present application claims priority of a prior application entitled "a positive electrode sheet and a lithium ion battery comprising the positive electrode sheet" filed from the intellectual property office of china with patent application number 202011468005.9 on 12/14/2020, the entire content of which is incorporated herein by reference.
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a positive plate and a lithium ion battery comprising the same.
Background
The lithium ion battery has the advantages of high platform voltage, high energy density, no memory effect, long service life and the like, and is widely applied to the fields of smart phones, notebook computers, Bluetooth, wearable equipment and the like. However, in some extreme cases, for example, when the lithium ion battery is subjected to mechanical damage (needle prick, heavy impact, etc.), an internal short circuit may occur, and the lithium ion battery with the internal short circuit may emit a large amount of heat in a short time, resulting in a fire and a failure of the battery, which has a great potential safety hazard.
Research shows that when the lithium ion battery is subjected to internal short circuit, various short circuit modes exist, wherein the short circuit between the positive current collector foil and the negative electrode plate is the most dangerous mode.
Disclosure of Invention
The invention provides a positive plate and a lithium ion battery comprising the same, wherein the use of the positive plate can solve the problems of fire failure and the like of the lithium ion battery under the condition of mechanical abuse, the safety performance of the lithium ion battery is improved, meanwhile, the cycle performance of the lithium ion battery is not influenced, and the cycle performance of the lithium ion battery is equivalent to the cycle performance effect of the conventional lithium ion battery, namely, the safety performance of the lithium ion battery is obviously improved on the premise of keeping the cycle performance of the lithium ion battery.
The invention is realized by the following technical scheme:
a positive plate comprises a positive current collector and a positive coating, wherein the positive coating comprises a first coating and a second coating, the first coating is coated on the surface of the positive current collector, and the second coating is coated on the surface of the first coating; the first coating layer includes an inorganic filler, a first conductive agent, and a first binder, and the second coating layer includes a positive electrode active material, a second conductive agent, and a second binder;
wherein, X1/(Y1×SY1+Z1×SZ1)>X2/(Y2×SY2+Z2×SZ2)；
Wherein, X1Is the content of the first binder, Y1Is the content of inorganic filler, Z1Is the content of the first conductive agent; sY1The specific surface area of the inorganic filler; sZ1Is the specific surface area of the first conductive agent; x2Is the content of the second binder, Y2Is the content of the positive electrode active material, Z2Is the content of the second conductive agent; sY2Is the specific surface area of the positive electrode active material; sZ2Is the specific surface area of the second conductive agent.
According to the invention, X1/(Y1×SY1+Z1×SZ1)>1.5X2/(Y2×SY2+Z2×SZ2)。
Preferably, X1/(Y1×SY1+Z1×SZ1)>4X2/(Y2×SY2+Z2×SZ2)。
According to the invention, X1/(Y1×SY1+Z1×SZ1) 0.004-0.15 g/m2Preferably 0.01 to 0.1g/m2. E.g. 0.004g/m2、0.005g/m2、0.006g/m2、0.008g/m2、0.01g/m2、0.02g/m2、0.03g/m2、0.04g/m2、0.05g/m2、0.06g/m2、0.07g/m2、0.08g/m2、0.09g/m2、0.1g/m2、0.11g/m2、0.12g/m2、0.13g/m2、0.14g/m2Or 0.15g/m2。
According to the invention, X2/(Y2×SY2+Z2×SZ2) 0.002 to 0.003g/m2。
The research finds that X is satisfied1/(Y1×SY1+Z1×SZ1)>X2/(Y2×SY2+Z2×SZ2) The first coating layer of (a) may be preferably bonded to the positive electrode current collector, wherein X1/(Y1×SY1+Z1×SZ1) And X2/(Y2×SY2+Z2×SZ2) Each represents the amount of binder per unit mass of the surface of the bound substance (such as the inorganic filler and the first conductive agent, or such as the positive electrode active material and the second conductive agent); and the binding properties are related to the amount of binder and the specific surface area of the bound particles. The larger the amount of the binder, the smaller the specific surface area, the more the binder per specific surface area, and the better the bonding effect. The first coating and the positive current collector are not easy to separate due to good adhesion. The adhesive force between the first coating and the positive current collector can realize that the surface of the positive current collector can be well protected by the first coating and is not easy to expose under the condition of mechanical abuse (acupuncture and heavy impact), so that the positive current collector is not easy to exposeThe contact probability of the positive current collector and the negative plate is reduced, so that the short circuit probability of the positive current collector and the negative plate is reduced, and the safety of the battery is improved.
According to the invention, X1+Y1+Z1＝1；X2+Y2+Z21 is ═ 1; wherein, X1、Y1、Z1、X2、Y2、Z2Is as defined above.
The invention also provides a lithium ion battery which comprises the positive plate.
The invention has the beneficial effects that:
the invention provides a positive plate and a lithium ion battery comprising the same, wherein the positive plate comprises a positive current collector and a positive coating, and the positive coating comprises a first coating and a second coating; the first coating is coated on the surface of the positive current collector, and the second coating is coated on the surface of the first coating; the first coating layer includes an inorganic filler, a first conductive agent, and a first binder; the second coating layer includes a positive electrode active material, a second conductive agent, and a second binder; when X is present1/(Y1×SY1+Z1×SZ1)>X2/(Y2×SY2+Z2×SZ2) (ii) a Wherein, X1Is the content of the first binder, Y1Is the content of inorganic filler, Z1Is the content of the first conductive agent; sY1The specific surface area of the inorganic filler; sZ1Is the specific surface area of the first conductive agent; x2Is the content of the second binder, Y2Is the content of the positive electrode active material, Z2Is the content of the second conductive agent; sY2Is the specific surface area of the positive electrode active material; sZ2Is the specific surface area of the second conductive agent. The lithium ion battery has good safety performance, and the probability of battery fire and failure is greatly reduced when mechanical abuse (acupuncture and heavy impact) occurs. Meanwhile, the cycle performance of the lithium ion battery is not affected, and the effect of the cycle performance of the lithium ion battery is equivalent to that of the cycle performance of the conventional lithium ion battery, namely the safety performance of the lithium ion battery is obviously improved on the premise of keeping the cycle performance of the lithium ion battery.
Drawings
Figure 1 example 1 SEM remained on the surface of the pole piece after the peel test.
Figure 2 SEM of the pole pieces before peel-off test example 1.
Detailed Description
As described above, the present invention provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode coating, wherein the positive electrode coating includes a first coating and a second coating, the first coating is coated on the surface of the positive electrode current collector, and the second coating is coated on the surface of the first coating; the first coating layer includes an inorganic filler, a first conductive agent, and a first binder, and the second coating layer includes a positive electrode active material, a second conductive agent, and a second binder;
wherein, X1/(Y1×SY1+Z1×SZ1)>X2/(Y2×SY2+Z2×SZ2)；
Wherein, X1Is the content of the first binder, Y1Is the content of inorganic filler, Z1Is the content of the first conductive agent; sY1The specific surface area of the inorganic filler; sZ1Is the specific surface area of the first conductive agent; x2Is the content of the second binder, Y2Is the content of the positive electrode active material, Z2Is the content of the second conductive agent; sY2Is the specific surface area of the positive electrode active material; sZ2Is the specific surface area of the second conductive agent.
According to the invention, the median particle diameter D of the inorganic filler50Less than the median particle diameter D of the positive electrode active material50。
According to the invention, the content of the first binder in the first coating layer is greater than the content of the second binder in the second coating layer.
According to the present invention, the positive electrode current collector is bonded to a part of the first binder, and a part of the positive electrode active material is bonded to another part of the first binder.
In the present invention, the median particle diameter D of the inorganic filler50Smaller than the positive electrode active materialMedian particle diameter D50And the positive electrode active material in the second coating layer is embedded into the first coating layer (see the SEM image shown in fig. 2 of the present application in particular), so that a part of the first binder in the first coating layer is in contact with the positive electrode current collector, and another part of the first binder is in contact with the positive electrode active material, that is, a structure is formed in which the positive electrode current collector is bonded to a part of the first binder, and a part of the positive electrode active material is bonded to another part of the first binder.
According to the invention, only the second coating on the surface of the positive current collector and/or partial particles of the first coating can be stripped from the surface of the positive current collector after the stripping test.
For example, only the particles of the second coating layer on the surface of the pole piece subjected to the stripping test are stripped from the positive pole piece, only the particles of the positive active material of the second coating layer can be detected on the surface of the stripped pole piece, and the particles of the first coating layer are not detected; or,
and after the stripping test, part of particles of the coating on the surface of the pole piece are stripped from the positive pole piece, and the inorganic filler particles of the first coating and the positive active material particles of the second coating can be detected on the surface of the stripped pole piece, but do not leak out of the positive current collector.
More specifically, when the inorganic filler is lithium iron phosphate and the positive electrode active material is lithium cobaltate, the Co and O elements are detected in EDS on the surface of the positive electrode coating remaining on the positive electrode current collector after the positive electrode coating of the positive electrode sheet is peeled off. This result indicates at least that the adhesion between the first coating layer and the positive electrode current collector is greater than the adhesion between the first coating layer and the second coating layer, and/or the adhesion between the first coating layer and the positive electrode current collector is greater than the adhesion between the positive electrode active material particles of the second coating layer.
According to the invention, the median particle diameter D of the inorganic filler500.05-8 μm; the specific surface area is 0.6-12 m2(ii) in terms of/g. The use of small particle size inorganic fillers can make the first coating thinner and denser.
According to the invention, the median particle diameter D of the positive electrode active material50Is 10-20 μm; the specific surface area is 0.1 to 0.3m2(ii) in terms of/g. Selection of this particle size range provides a higher compacted density, increasing the capacity density.
According to the present invention, the inorganic filler forming the first coating layer and the positive electrode active material of the second coating layer are the same or different, the first conductive agent and the second conductive agent and the content thereof are the same or different, and the first binder and the second binder and the content thereof are the same or different.
According to the invention, the first coating comprises the following components in percentage by mass: 40-93 wt% of inorganic filler, 2-15 wt% of first conductive agent and 5-58 wt% of first binder.
Preferably, the first coating comprises the following components in percentage by mass: 60-91 wt% of inorganic filler, 3-10 wt% of first conductive agent and 8-30 wt% of first binder. When the content of the first binder is within the range, the first binder can have a good binding effect with a positive current collector, the energy density can be reduced and the performance of a battery cell can be deteriorated due to the fact that the content of the first binder is too high, and the range and the median particle diameter D are selected50Inorganic fillers in the range of 0.05 to 8 μm combine to form a strongly adherent and dense base coat.
Illustratively, the inorganic filler comprises 40 wt%, 45 wt%, 48 wt%, 50 wt%, 55 wt%, 58 wt%, 60 wt%, 62 wt%, 65 wt%, 68 wt%, 70 wt%, 72 wt%, 75 wt%, 78 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, 90 wt%, 92 wt%, 93 wt% of the components of the first coating layer by mass;
illustratively, the first conductive agent accounts for 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt% of each component in the first coating layer by mass;
illustratively, the first binder is present in the first coating in an amount of 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 33 wt%, 35 wt%, 38 wt%, 40 wt%, 45 wt%, 48 wt%, 50 wt%, 55 wt%, 58 wt% based on the weight of each component.
According to the invention, the second coating comprises the following components in percentage by mass: 93-99 wt% of positive electrode active material, 0.5-5 wt% of second conductive agent and 0.5-2 wt% of second binder. The second binder is selected in this content range to provide better bonding while maintaining a higher energy density.
Preferably, the second coating comprises the following components in percentage by mass: 95-98 wt% of positive electrode active material, 1-3 wt% of second conductive agent and 1-2 wt% of second binder.
Illustratively, the mass percentage of the positive electrode active substance in each component of the second coating is 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%;
illustratively, the second conductive agent accounts for 0.5 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt% of each component in the second coating layer;
illustratively, the second binder accounts for 0.5 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt% of each component in the second coating layer.
According to the invention, the first conductive agent and the second conductive agent are the same or different and are independently selected from at least one of conductive carbon black, carbon nanotubes and graphene.
According to the invention, the first binder and the second binder are the same or different and are independently selected from at least one of polyvinylidene fluoride and modified polyvinylidene fluoride.
Wherein, the polyvinylidene fluoride and the modified polyvinylidene fluoride are both products sold in the market.
According to the present invention, the crystallinity of the first binder is < 40%, because a low crystallinity is advantageous for having a good bonding effect.
According to the present invention, the crystallinity of the second binder is < 40%, because a low crystallinity is advantageous for having a good bonding effect.
According to the invention, the modified polyvinylidene fluoride is acrylate modified polyvinylidene fluoride. The acrylate group contains carboxyl, and the acrylate group can form a chemical bond with a positive current collector (such as aluminum foil) to realize strong bonding with the positive current collector.
According to the invention, the molecular weight of the polyvinylidene fluoride or modified polyvinylidene fluoride is 100-150 ten thousand, such as 110 ten thousand and 130 ten thousand. The selection of the binder with larger molecular weight can enhance the binding performance, reduce the content of the binder and enhance the energy density.
According to the invention, the inorganic filler is selected from lithium-containing transition metal oxides, in particular from one or more of Lithium Cobaltate (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), Lithium Manganese Phosphate (LMP), Lithium Vanadium Phosphate (LVP), Lithium Manganate (LMO), lithium rich manganese base;
or, the inorganic filler is selected from ceramic materials, and is specifically selected from one or more of alumina, boehmite, magnesium oxide and magnesium hydroxide;
or, the inorganic filler is selected from a mixture of at least one of lithium-containing transition metal oxides and at least one of ceramic materials.
In the present invention, the inorganic filler functions as a skeleton support.
According to the present invention, the positive active material is selected from one or more of Lithium Cobaltate (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), Lithium Manganese Phosphate (LMP), Lithium Vanadium Phosphate (LVP), Lithium Manganate (LMO), and lithium-rich manganese base.
According to the invention, the positive current collector is selected from aluminium foil.
According to the invention, the thickness of the positive current collector is 8-15 μm.
According to the invention, the thickness of the first coating (thickness after rolling) is 2-10 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm; the thickness of the second coating layer (thickness after rolling) is 30-80 μm, such as 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm or 80 μm.
The invention also provides a preparation method of the positive plate, which comprises the following steps:
1) respectively preparing slurry for forming a first coating and slurry for forming a second coating;
2) and coating the slurry for forming the first coating and the slurry for forming the second coating on the two side surfaces of the positive current collector to prepare the positive plate.
According to the invention, in step 2), the coating is a double coating, a gravure coating, an extrusion coating, a transfer coating.
Exemplarily, the step 2) specifically includes the following steps:
and coating the slurry for forming the first coating on the surface of the positive current collector to form the first coating, and coating the slurry for forming the second coating on the surface of the first coating to form the second coating, so as to obtain the positive plate.
The invention also provides a lithium ion battery which comprises the positive plate.
According to the present invention, the lithium ion battery further comprises a negative electrode sheet.
According to the invention, the negative plate comprises a negative active material, and the negative active material is selected from one or more of artificial graphite, natural graphite, mesocarbon microbeads, lithium titanate, silicon-carbon negative electrode and silicon-oxygen negative electrode.
The invention also provides a preparation method of the lithium ion battery, which comprises the following steps:
a) preparing a positive plate and a negative plate;
b) and rolling, slitting, flaking, winding (or laminating), packaging, injecting, forming, grading, OCV and other procedures are carried out on the positive plate and the negative plate to prepare the lithium ion battery.
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
The modified PVDF used in the examples described below was an acrylate modified PVDF, commercially available under the trade designation Solef 5130. The molecular weight of the acrylate modified PVDF is 110 ten thousand, and the crystallinity is 30-32%.
PVDF used in the examples described below is commercially available as PVDF manufactured by Arkema corporation under the designation HSV-900. The molecular weight of the PVDF is 100 ten thousand, and the crystallinity is 25%.
In the description of the present invention, it should be noted that the terms "first", "second", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
The adhesion test used in the following examples was as follows:
dissecting after the lithium ion battery is completely discharged (0.5C is discharged to 3.0V), taking out the positive plate, placing the positive plate in an environment with the temperature of 25 +/-3 ℃ and the dew point of-30 ℃ for 2h, cutting the positive plate into positive plate small pieces with the length of 240mm and the width of 30mm, cutting the adhesive tapes into adhesive tape small pieces according to the specification of the length of 200mm and the width of 24mm by using an NITTO No.5000NS adhesive tape, adhering one surface of each adhesive tape small piece on a steel plate (260mm 50mm), adhering the positive plate small pieces on the other surface of each adhesive tape small piece to ensure that the positive plate small pieces completely cover the adhesive tape small pieces, rolling for 3 times in a reciprocating manner by using a hand-held roller (the diameter of 95mm, the width of 45mm and the weight of 2kg), adhering the positive plate small pieces and the adhesive tape small pieces together, then testing (180-degree stripping) by using a tensile machine (a KJ-1065 series of Dongguan family), automatically recording the tensile value which changes along with the stripping displacement by a testing device, and drawing a curve of the tensile value changing along with the peeling displacement, wherein the abscissa is the peeling displacement, the ordinate is the tensile value, and the tensile value when the curve is level and the peeling displacement is more than 5mm is taken as the adhesive force.
The test method for the safety test used in the following examples is as follows:
(1) and (3) needle punching test:
the cell was fully charged and the center of the cell was punctured perpendicular to the plane of the cell at 130mm/s using a 3mm steel needle.
(2) And (3) testing the impact of the weight:
the cell was fully charged, the cell was placed in a plane, a steel column 15.8 + -0.2 mm in diameter was placed in the center of the cell with the longitudinal axis of the column parallel to the plane, allowing a weight of 9.1 + -0.1 kg to fall freely from a height of 610 + -25 mm onto the column above the center of the cell.
Example 1
The first step is as follows: preparing first coating slurry, mixing 80 wt% of lithium iron phosphate (LFP), 15 wt% of modified PVDF and 5 wt% of carbon black, adding NMP, and stirring to prepare the slurry.
The second step is that: and preparing second coating slurry, mixing 97 wt% of lithium cobaltate, 1 wt% of conductive carbon black, 0.8 wt% of carbon nano tube and 1.2 wt% of PVDF, adding NMP, and stirring to prepare the slurry.
The third step: preparing negative electrode slurry, mixing 96 wt% of artificial graphite, 1 wt% of conductive carbon black, 1.5 wt% of SBR and 1.5 wt% of CMC, adding deionized water, and stirring to prepare the slurry.
The fourth step: and (3) preparing the positive pole piece, coating the first coating slurry obtained in the first step on the surface of a positive current collector by using an extrusion coating process to form a first coating with the thickness of 5 microns, and coating the second coating slurry obtained in the second step on the surface of the first coating to form a second coating with the thickness of 40 microns to obtain the binding power positive pole piece.
The fifth step: and (4) preparing a negative pole piece, namely coating the negative pole slurry obtained in the step three on a negative pole current collector to obtain the negative pole piece.
And a sixth step: and rolling, slitting, sheet making, winding (or laminating), packaging, injecting, forming, grading, OCV (open circuit control) and other processes are carried out on the positive and negative pole pieces to prepare the lithium ion battery.
The prepared lithium ion battery is subjected to a bonding force test, and the section of the stripped pole piece is shown in figure 1. The left side is a stripped surface, the right side is a complete surface, only partial particles of the second coating layer are stripped from the stripped surface of the pole piece, and the first coating layer is well preserved (the thickness of the first coating layer is less than 10 mu m), which shows that the bonding effect of the first coating layer is better than that of the second coating layer.
Examples 2 to 9
The other steps are the same as example 1, and only differ in the selection and content of each material in the first step, and/or the selection and content of each material in the second step are specifically shown in table 1.
Comparative example 1
The other steps are the same as example 1, and only differ in the selection and content of each material in the first step, and/or the selection and content of each material in the second step are specifically shown in table 1.
As can be seen from the above examples and comparative examples,
when X is present1/(Y1×SY1+Z1×SZ1)>X2/(Y2×SY2+Z2×SZ2) When the lithium ion battery is used, the problems that the lithium ion battery is in fire failure and the like under the condition of mechanical abuse can be solved, the safety performance of the lithium ion battery is improved, meanwhile, the cycle performance of the lithium ion battery is not affected, the effect of the cycle performance of the lithium ion battery is equivalent to that of the existing lithium ion battery, and the safety performance of the lithium ion battery is obviously improved on the premise of keeping the cycle performance of the lithium ion battery.
In particular, when X1/(Y1×SY1+Z1×SZ1)>4X2/(Y2×SY2+Z2×SZ2) During the process, the safety performance of the lithium ion battery can be further improved by using the positive plate, the binding force between the first coating and the positive current collector is greater than 30N/m, namely, under the condition that the lithium ion battery is subjected to mechanical abuse, the first coating can well protect the positive current collector, and the problems of fire failure and the like caused by contact with a negative electrode are avoided.
TABLE 1 Pole piece peel force magnitude and safety test results for each example and comparative example
Figure BDA0003407819660000111
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The positive plate comprises a positive current collector and a positive coating, wherein the positive coating comprises a first coating and a second coating, the first coating is coated on the surface of the positive current collector, and the second coating is coated on the surface of the first coating; the first coating layer includes an inorganic filler, a first conductive agent, and a first binder, and the second coating layer includes a positive electrode active material, a second conductive agent, and a second binder;
wherein, X1/(Y1×SY1+Z1×SZ1)>X2/(Y2×SY2+Z2×SZ2)；
Wherein, X1Is the content of the first binder, Y1Is the content of inorganic filler, Z1Is the content of the first conductive agent; sY1The specific surface area of the inorganic filler; sZ1Is the specific surface area of the first conductive agent; x2Is the content of the second binder, Y2Is the content of the positive electrode active material, Z2Is the content of the second conductive agent; sY2Is the specific surface area of the positive electrode active material; sZ2Is the specific surface area of the second conductive agent.
2. The positive electrode sheet according to claim 1,
X1/(Y1×SY1+Z1×SZ1)>1.5X2/(Y2×SY2+Z2×SZ2)；
preferably, X1/(Y1×SY1+Z1×SZ1)>4X2/(Y2×SY2+Z2×SZ2)。
3. According to claimThe positive electrode sheet according to claim 1 or 2, wherein X1/(Y1×SY1+Z1×SZ1) 0.004-0.15 g/m2(ii) a And/or, X2/(Y2×SY2+Z2×SZ2) 0.002 to 0.003g/m2。
4. The positive electrode sheet according to any one of claims 1 to 3, wherein the inorganic filler has a median particle diameter D50Less than the median particle diameter D of the positive electrode active material50。
5. The positive electrode sheet according to any one of claims 1 to 4, wherein the content of the first binder in the first coating layer is greater than the content of the second binder in the second coating layer; and/or the presence of a gas in the gas,
the positive electrode current collector is bonded to a part of the first binder, and a part of the positive electrode active material is bonded to another part of the first binder.
6. The positive plate according to any one of claims 1 to 5, wherein the first coating layer comprises the following components in percentage by mass: 40-93 wt% of inorganic filler, 2-15 wt% of first conductive agent and 5-58 wt% of first binder.
7. The positive plate according to any one of claims 1 to 6, wherein the second coating layer comprises the following components in percentage by mass: 93-99 wt% of positive electrode active material, 0.5-5 wt% of second conductive agent and 0.5-2 wt% of second binder.
8. The positive electrode sheet according to any one of claims 1 to 7, wherein the first binder and the second binder are the same or different and are independently selected from at least one of polyvinylidene fluoride and modified polyvinylidene fluoride; and/or the presence of a gas in the gas,
the crystallinity of the first binder is < 40%; and/or the presence of a gas in the gas,
the modified polyvinylidene fluoride is acrylate modified polyvinylidene fluoride; and/or the presence of a gas in the gas,
the molecular weight of the polyvinylidene fluoride or the modified polyvinylidene fluoride is 100-150 ten thousand.
9. The positive electrode sheet according to any one of claims 1 to 8, wherein the inorganic filler is selected from lithium-containing transition metal oxides, in particular from one or more of Lithium Cobaltate (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), Lithium Manganese Phosphate (LMP), Lithium Vanadium Phosphate (LVP), Lithium Manganate (LMO), lithium rich manganese base; or,
the inorganic filler is selected from ceramic materials, and is specifically selected from one or more of alumina, boehmite, magnesium oxide and magnesium hydroxide; or,
the inorganic filler is selected from a mixture of at least one of lithium-containing transition metal oxides and at least one of ceramic materials; and/or the presence of a gas in the gas,
the positive active substance is selected from one or more of Lithium Cobaltate (LCO), a nickel-cobalt-manganese ternary material (NCM), a nickel-cobalt-aluminum ternary material (NCA), a nickel-cobalt-manganese-aluminum quaternary material (NCMA), lithium iron phosphate (LFP), Lithium Manganese Phosphate (LMP), Lithium Vanadium Phosphate (LVP) and Lithium Manganate (LMO).
10. A lithium ion battery comprising the positive electrode sheet according to any one of claims 1 to 9.
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