CN113745646A - Lithium ion battery of silicon cathode system - Google Patents
Lithium ion battery of silicon cathode system Download PDFInfo
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- CN113745646A CN113745646A CN202111052441.2A CN202111052441A CN113745646A CN 113745646 A CN113745646 A CN 113745646A CN 202111052441 A CN202111052441 A CN 202111052441A CN 113745646 A CN113745646 A CN 113745646A
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 70
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 70
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 21
- 239000010703 silicon Substances 0.000 title claims abstract description 21
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 15
- 239000002210 silicon-based material Substances 0.000 claims abstract description 49
- 239000003575 carbonaceous material Substances 0.000 claims abstract description 45
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 25
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 18
- 239000007773 negative electrode material Substances 0.000 claims abstract description 12
- 239000011230 binding agent Substances 0.000 claims description 20
- 239000006258 conductive agent Substances 0.000 claims description 19
- 229920002125 Sokalan® Polymers 0.000 claims description 10
- 239000002270 dispersing agent Substances 0.000 claims description 9
- 239000007774 positive electrode material Substances 0.000 claims description 9
- 229920002401 polyacrylamide Polymers 0.000 claims description 2
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 2
- 229920003048 styrene butadiene rubber Polymers 0.000 claims description 2
- 239000002245 particle Substances 0.000 description 12
- 239000006229 carbon black Substances 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 9
- 239000004584 polyacrylic acid Substances 0.000 description 9
- 229910002804 graphite Inorganic materials 0.000 description 7
- 239000010439 graphite Substances 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- 239000011149 active material Substances 0.000 description 6
- 239000002002 slurry Substances 0.000 description 6
- 238000000576 coating method Methods 0.000 description 5
- 230000014759 maintenance of location Effects 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 4
- 230000001351 cycling effect Effects 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 239000007788 liquid Substances 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 239000013543 active substance Substances 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 239000011889 copper foil Substances 0.000 description 2
- 125000004122 cyclic group Chemical group 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 238000004806 packaging method and process Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 description 1
- OBNDGIHQAIXEAO-UHFFFAOYSA-N [O].[Si] Chemical compound [O].[Si] OBNDGIHQAIXEAO-UHFFFAOYSA-N 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
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- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910021382 natural graphite Inorganic materials 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 102200023921 rs1010930015 Human genes 0.000 description 1
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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
- 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
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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
- H01M4/134—Electrodes based on metals, Si or alloys
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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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
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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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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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
- H01M4/36—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
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- 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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Abstract
The invention provides a lithium ion battery of a silicon negative electrode system, which comprises a positive plate and a negative plate, wherein the negative plate comprises a negative current collector and a negative active layer arranged on at least one functional surface of the negative current collector, a negative active material in the negative active layer comprises a carbon material and a silicon material, and D50 of the carbon materialCarbon (C)D50 of said silicon materialSiliconMass m of the carbon material1Mass m of the silicon material2SaidThe thickness H of the negative active layer satisfies the relation 1; the ratio of the surface capacity of the negative plate to the surface capacity of the positive plate is 1.00-1.15. The lithium ion battery provided by the invention has better energy density and cycle performance.
Description
Technical Field
The invention relates to a lithium ion battery of a silicon cathode system, and relates to the technical field of secondary batteries.
Background
With the arrival of the 5G era, the status of the lithium ion battery is more and more important, and with the continuous development of the related technology of the lithium ion battery, the energy density and the quick charging capability of the lithium ion battery are both closer and closer to the limits, which requires a new breakthrough in the technology and a deep innovation for the existing chemical system.
The conventional lithium ion battery comprises a positive plate, a negative plate and electrolyte, wherein the positive plate comprises a positive current collector and a positive active layer, the negative plate comprises a negative current collector and a negative active layer, the positive active layer and the negative active layer both comprise active materials, and the working principle of the lithium ion battery is mainly completed by the insertion and extraction of lithium ions between the positive active material and the negative active material.
However, silicon materials have a serious problem of swelling during cycling, which affects the cycling performance of lithium ion batteries. Therefore, attention is paid to how to achieve both the energy density and the cycle performance of lithium ion batteries.
Disclosure of Invention
The invention provides a lithium ion battery of a silicon negative electrode system, which not only relieves the volume expansion of a silicon material, but also gives consideration to the gram capacity of a positive plate and the structural stability of a positive active material by controlling the particle size, the mass ratio and the thickness relation of a negative active material layer of the carbon material and the silicon material and the CB value so as to solve the problem that the energy density and the cycle performance of the lithium ion battery cannot be taken into consideration.
The invention provides a lithium ion battery of a silicon negative electrode system, which comprises a positive plate and a negative plate, wherein the negative plate comprises a negative current collector and a negative active layer arranged on at least one functional surface of the negative current collector;
wherein the negative active material in the negative active layer comprises a carbon material and a silicon material, D50 of the carbon materialCarbon (C)D50 of said silicon materialSiliconMass m of the carbon material1Mass m of the silicon material2The thickness H of the negative active layer satisfies the relation 1:
D50carbon (C)、D50SiliconAnd the units of H are the same, m1And m2The units are the same;
the ratio of the surface capacity of the negative plate to the surface capacity of the positive plate is 1.00-1.15.
The invention provides a lithium ion battery, which comprises a positive plate and a negative plate, wherein the positive plate comprises a positive current collector and a positive active layer arranged on at least one functional surface of the positive current collector, the negative plate comprises a negative current collector and a negative active layer arranged on at least one functional surface of the negative current collector, the functional surfaces of the current collectors are two opposite surfaces with larger area, specifically the upper surface and the lower surface of the current collector, for bearing the active layers, and the active layers are arranged on the upper surface and/or the lower surface of the current collector; when the pole piece is a negative pole piece, the negative pole active layer comprises a negative pole active material, the negative pole active material comprises a carbon material and a silicon material, and the invention limits the relationship between the particle size and the mass ratio of the carbon material and the silicon material and the thickness of the negative pole active layer and the ratio of the surface capacity of the negative pole piece and the positive pole pieceFor convenience of description, the present invention defines a numerical value calculated according to a formula shown in formula 1 for the particle size, mass ratio, and thickness of the negative active layer of the carbon material and the silicon material as an M value, which may reflect a ratio of the number of particles of the silicon material in the negative active layer to the number of particles of the carbon material, specifically, D50Carbon (C)And D50SiliconThe carbon material and the silicon material respectively refer to corresponding particle size values when the cumulative distribution in the carbon material and the silicon material reaches 50%, the units of the two are the same, for example, the particle size values can be mum, and the particle sizes can be measured by a laser particle sizer; the mass ratio of the carbon material to the silicon material means a ratio of the mass of the carbon material to the mass of the silicon material in the negative electrode active layer, and the units of the two are the same, such as grams; the thickness H of the negative electrode active layer means the thickness of the negative electrode active layer on one functional surface of the negative electrode current collector, and the unit thereof is the same as that of D50; the CB value is the surface capacity of the negative electrode sheet/the surface capacity of the positive electrode sheet, and the surface capacity is the capacity per unit area, which is equal to the capacity exerted by the lithium ion battery divided by the area of the active material, and the inventor finds that the CB value and the gram capacity are in a linear relationship, and a graph of the relationship between the CB value and the gram capacity is shown in fig. 1, wherein the linear equation is that y is 137.98x +28.355, and R is20.9604, namely, as the CB value is continuously increased, the gram capacity of the positive electrode is continuously increased, which is helpful for improving the energy density of the lithium ion battery, but excessive increase of CB causes thickening of the negative electrode sheet, increase of the amount of delithiation of the positive electrode, and easy collapse of the structure of the positive electrode active material, which causes deterioration of the cycle performance, therefore, on the basis of ensuring the particle number of the silicon material, finding the optimal CB value is an effective means for taking into account both the energy density and the cycle performance of the lithium ion battery, namely, when the CB value is 1.00-1.15, the relation between the gram capacity of the positive electrode and the structural stability of the positive electrode active material can be effectively taken into account, so that the lithium ion battery has better cycle performance and energy density. In the actual preparation process of the lithium ion battery, after the active materials in the positive plate and the negative plate are determined, the CB value is mainly related to the surface density of the positive plate and the negative plate, and a person skilled in the art can determine the surface density of the positive plate and the negative plate according to the CB value. The invention controls the grain diameters of the carbon material and the silicon materialThe relation between the mass ratio and the thickness of the negative active layer and the CB value are 1.00-1.15, so that the volume expansion of the silicon material is relieved, the gram capacity of the positive plate and the structural stability of the positive active material are considered, and the lithium ion battery has better energy density and cycle performance.
In order to further alleviate the problem of poor cycle performance of the lithium ion battery caused by volume expansion of the silicon material, the silicon material can be concentrated on one side of the negative electrode active layer close to the negative electrode current collector, and the active material on one side far away from the negative electrode current collector is mainly a carbon material, that is, the negative electrode active layer comprises a first negative electrode active layer and a second negative electrode active layer, the first negative electrode active layer and the second negative electrode active layer are sequentially stacked on at least one functional surface of the negative electrode current collector, the negative electrode active material in the second negative electrode active layer is a carbon material, and in the cycle process of the lithium ion battery, the carbon material arranged on the surface of the negative electrode plate can provide a buffer passage for the silicon material inside, so that the volume expansion of the silicon material can be alleviated, and the cycle performance of the lithium ion battery can be further improved.
When the negative electrode active layer comprises double layers, in a formula shown in formula 1, when D50 of carbon materials in the first negative electrode active layer and the second negative electrode active layer are the same, D50 is directly substituted into formula 1 for calculation, when D50 of the carbon materials in the first negative electrode active layer and the second negative electrode active layer are different, D50 mean value (the calculation formula is D50A A% + D50B B%, A% and B% are proportions of two different carbon materials in the negative electrode active layer) is substituted into formula 1 for calculation, the thickness H of the negative electrode active layer is the total thickness of the first negative electrode active layer and the second negative electrode active layer on one functional surface of the negative electrode current collector, and the mass m of the carbon materials is m1The total mass of the carbon material in the first negative electrode active layer and the second negative electrode active layer, the mass m of the silicon material2Is the total mass of the silicon material in the first negative electrode active layer and the second negative electrode active layer.
The lithium ion battery can be prepared by combining with the conventional technical means by a person skilled in the art, for example, firstly mixing a carbon material and a silicon material according to a certain mass ratio to obtain a negative active material, and matching with a conductive agent, a binder and a dispersing agent to obtain a negative active layer slurry, and then coating the negative active layer slurry on at least one functional surface of a negative current collector to obtain a negative plate; when the negative active layer comprises a second negative active layer, the difference lies in that first negative active layer slurry and second negative active layer slurry need to be prepared respectively, and coating is carried out according to the structure to obtain a negative plate, and in order to simplify the coating process, double-cavity die heads can be matched for carrying out double-layer coating; the preparation method comprises the steps of mixing a positive active material, a conductive agent and a binder according to a certain mass ratio to obtain positive active slurry, coating the positive active slurry on at least one functional surface of a positive current collector to obtain a positive plate, matching the positive plate and a negative plate with a diaphragm to obtain a battery core, and then carrying out processes of liquid injection, packaging, formation, sorting and the like to prepare the lithium ion battery.
In a specific embodiment, the carbon material and the silicon material used in the present invention are conventional materials in the art, for example, the carbon material is one or two of natural graphite and artificial graphite, and the silicon material is one or more of silicon, silicon oxygen and silicon carbon, according to formula 1, the calculated M value is affected by D50 of the carbon material and the silicon material, the ratio of the mass of the silicon material and the carbon material, and the total thickness of the negative electrode active layer, which can be adjusted by those skilled in the art according to actual needs, specifically, D50 of the carbon material is 10-18 μ M; the silicon material has a D50 of 4-10 μm.
When the anode active layer includes the second anode active layer, D50 of the carbon material in the second anode active layer may be the same as or different from D50 of the carbon material in the first anode active layer, for example, D50 of the carbon material in the second anode active layer may also be 10 to 18 μm.
The mass ratio of the carbon material to the silicon material is (99.5:0.5) - (0.5: 99.5).
The total thickness H of the negative electrode active layers is 40 to 160 μm, and it should be noted that, here, the total thickness of the negative electrode active layers, when the negative electrode active layers include a first negative electrode active layer and a second negative electrode active layer, the thickness H of the negative electrode active layer is the total thickness of the first negative electrode active layer and the second negative electrode active layer.
In addition, because the conductivity of the silicon material is poor, when the negative active material in the negative active layer comprises the silicon material, the conductivity of the active layer should be properly improved, and because the conductivity of the carbon tube in the conventional conductive agent in the field is far greater than that of the conventional carbon black conductive agent, the first negative active layer comprising the silicon material further comprises the carbon tube, and the mass of the carbon tube is 0.001% -10% of the total mass of the first negative active layer.
It is understood that as the content of the silicon material in the first negative active layer increases, the content of the carbon tubes also increases, but the dispersion property of the carbon tubes is not good, the lithium ion battery has a risk of gassing, and in order to balance the conductivity of the silicon material and the safety of the lithium ion battery, the carbon tubes and carbon black may be mixed as a conductive agent, and specifically, the first negative active layer includes carbon black.
When the negative electrode active layer includes the second negative electrode active layer, the present invention does not limit the kind of the conductive agent in the second negative electrode active layer, and those skilled in the art may set it according to actual needs, for example, the conductive agent may include only carbon black.
The negative active layer further comprises a binder selected from one or more of PAA, SBR, polyacrylamide and polyacrylonitrile.
As a result of the research of the inventors, the binder PAA (polyacrylic acid) helps to alleviate the volume expansion of the silicon material, and thus, when the silicon material is included in the negative electrode active layer, PAA may be preferable as the binder, i.e., the first negative electrode active layer includes the binder PAA.
When the negative electrode active layer includes the second negative electrode active layer, the present invention does not limit the kind of the binder in the second negative electrode active layer, and those skilled in the art may set the binder to be SBR according to actual needs.
In summary, the first negative active layer includes, by mass, 95% to 97.5% of a negative active material, 0.5% to 2.5% of a conductive agent, 1.2% to 2.5% of a binder, and 0.5% to 1.5% of a dispersant;
when the negative electrode active layer comprises a second negative electrode active layer, the second negative electrode active layer comprises 95-98% of carbon material, 0-2% of conductive agent, 1-2% of binder and 1-2% of dispersing agent by mass percentage.
The surface capacity of the positive plate and the negative plate can be designed by those skilled in the art according to the CB value, and generally, the positive active layer comprises, by mass, 91.0% to 99.8% of a positive active material, 0.05% to 3.0% of a conductive agent, and 0.05% to 3.0% of a binder.
In summary, by setting a proper formula of the silicon negative electrode system lithium ion battery, the relationship between the particle size and the mass ratio of the carbon material and the silicon material in the negative electrode sheet and the thickness of the negative electrode active layer satisfies the requirement shown in formula 1, and the CB value is 1.00-1.15, so that the requirements of the energy density and the cycle performance of the lithium ion battery can be satisfied at the same time.
The implementation of the invention has at least the following advantages:
1. according to the invention, by controlling the relationship between the particle size and the mass ratio of the carbon material and the silicon material and the thickness of the negative active layer and controlling the CB value to be 1.00-1.15, the volume expansion of the silicon material is relieved, and the gram capacity of the positive plate and the structural stability of the positive active material are considered, so that the lithium ion battery has better energy density and cycle performance.
2. According to the invention, the double-layer negative electrode active layer is arranged, so that the carbon material arranged on the surface of the negative electrode plate can provide a buffer channel for the silicon material below in the circulation process of the lithium ion battery, the volume expansion of the silicon material is favorably relieved, and the circulation performance of the lithium ion battery is further improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a graph of CB value versus gram capacity according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The lithium ion battery provided by the embodiment comprises a positive plate and a negative plate, wherein:
the positive plate comprises a positive current collector aluminum foil and positive active layers arranged on two functional surfaces of the positive current collector aluminum foil, the positive active layers comprise 97.6 parts by mass of lithium cobaltate, 1.3 parts by mass of a conductive agent (a carbon tube comprising carbon black, the mass ratio of the carbon black to the carbon tube is 4:1) and 1.1 parts by mass of a binder PVDF, and the surface density of the positive plate is 20.91mg/cm2。
The negative plate comprises a negative current collector copper foil, and a first negative active layer and a second negative active layer which are sequentially stacked on two functional surfaces of the negative current collector copper foil,
the first negative electrode active layer includes 97.0 parts by mass of a negative electrode active layer material, 1.3 parts by mass of a dispersant CMC-Na, 1.2 parts by mass of a binder PAA, and 0.5 parts by mass of a conductive agent, wherein the negative electrode active material includes graphite and silicon, and a mass ratio of the graphite to the silicon is 9:1, graphite has a D10 of 6.0 μm, a D50 of 15.0 μm and a D90 of 27.0 μm; silicon has a D10 of 3.5 μm, a D50 of 6.0 μm, and a D90 of 10.0 μm; the conductive agent comprises carbon black and a carbon tube, and the mass ratio of the carbon black to the carbon tube is 9: 1;
the second negative electrode active layer includes 97.5 parts by mass of graphite, 1.0 part by mass of dispersant CMC-Na, 1.0 part by mass of binder PAA, and 0.5 part by mass of conductive agent carbon black.
First negative electrode activityThe thickness of the layer is 30 μm, the thickness of the second negative electrode active layer is 30 μm, and the total areal density of the negative electrode sheet is 9.48mg/cm2。
The lithium ion battery provided by the present example has an M value of 2.47 and a CB value of 1.08.
The preparation method of the lithium ion battery provided by the invention comprises the following steps: preparing a positive plate and a negative plate according to the parameters, welding a tab, and then winding the tab and a diaphragm to obtain a battery cell, wherein the diaphragm is an Asahi chemical conversion 5+2+2 oil system diaphragm; and then packaging, injecting liquid, forming, performing secondary sealing to ensure that the coefficient of the residual liquid amount is more than 1.2, and finally sorting to finish the manufacture of the soft-package polymer lithium ion battery.
Example 2
The lithium ion battery provided by the embodiment can be referred to the embodiment 1, and is characterized in that the total areal density of the negative electrode sheet is 9.39mg/cm2The CB value is 1.07.
Example 3
The lithium ion battery provided by the embodiment can be referred to the embodiment 1, and is characterized in that the total areal density of the negative electrode sheet is 9.30mg/cm2The CB value is 1.06.
Example 4
The lithium ion battery provided by the embodiment can be referred to the embodiment 1, and is characterized in that the total areal density of the negative electrode sheet is 9.21mg/cm2The CB value is 1.05.
Example 5
The lithium ion battery provided by the embodiment can be referred to the embodiment 1, and is characterized in that the total areal density of the negative electrode sheet is 9.13mg/cm2The CB value is 1.04.
Example 6
The lithium ion battery provided in this example can be referred to example 1, except that the total areal density of the negative electrode sheet is 9.04mg/cm2The CB value is 1.03.
Example 7
The lithium ion battery provided by the embodiment can be referred to the embodiment 1, and is characterized in that the total areal density of the negative electrode sheet is 8.95mg/cm2The CB value is 1.02.
Example 8
The lithium ion battery provided by the embodiment can be referred toReferring to example 1, the difference is that the total areal density of the negative electrode sheet is 8.86mg/cm2The CB value is 1.01.
Example 9
The lithium ion battery provided by the embodiment can be referred to embodiment 1, and is characterized in that the total areal density of the negative electrode sheet is 8.78mg/cm2The CB value is 1.00.
Example 10
The lithium ion battery provided by the present embodiment can refer to embodiment 1, and the difference is that:
the negative plate comprises a negative current collector and a negative active layer arranged on the surface of the negative current collector, wherein the negative active layer comprises 97.0 parts by mass of a negative active substance, 1.3 parts by mass of a dispersant CMC-Na, 1.2 parts by mass of a binder PAA and 0.5 part by mass of a conductive agent, the negative active substance comprises graphite and silicon, the mass ratio of the graphite to the silicon is 95:5, and the total areal density of the negative plate is 9.39mg/cm2。
The silicon-doped negative plate provided by the embodiment has an M value of 2.48 and a CB value of 1.07 through calculation.
Example 11
The lithium ion battery provided in this example can be referred to example 10, except that the total areal density of the negative electrode sheet is 10.09mg/cm2The CB value is 1.15.
Comparative example 1
The lithium ion battery provided by the present comparative example can be referred to example 1, except that:
the negative plate comprises a negative current collector and a negative active layer arranged on the surface of the negative current collector, wherein the negative active layer comprises 97.5 parts by mass of graphite, 1.0 part by mass of dispersant CMC-Na, 1.0 part by mass of binder PAA and 0.5 part by mass of conductive agent carbon black, and the CB value is 1.07.
Comparative example 2
The lithium ion battery provided by the present comparative example was referenced to example 10, except that the total areal density of the negative electrode sheet was 10.18mg/cm2The CB value is 1.16.
The energy density, the capacity retention rate and the cycle expansion rate of the lithium ion batteries provided in the above examples 1 to 11 and comparative examples 1 to 2 were measured, and the test methods and the test results were as follows:
1. the energy density test method comprises the following steps: measuring the lithium ion battery by adopting a charge-discharge system of 0.2C charge, 0.5C discharge and 0.025C cut-off at 25 ℃; the plateau voltage of the lithium ion battery is the plateau voltage under 0.2C-rate discharge. The Energy Density (ED) of the lithium ion battery is calculated according to the following formula:
ED capacity platform voltage/(cell length cell width cell thickness).
2. Method for testing the retention rate of the circulation capacity and the expansion rate at 25 ℃: the lithium ion batteries of examples and comparative examples were cycled at 25 ℃ for 700T on a cycling regime of 2C charge, 0.5C discharge, 0.025C cut-off; capacity retention rate ═ discharge capacity (per revolution)/initial capacity; cyclic expansion ratio (thickness after cycle-initial thickness)/initial thickness.
3. Method for testing the retention rate of the circulation capacity and the expansion rate at 45 ℃: the lithium ion batteries of examples and comparative examples were cycled 500T at 45 ℃ in a cycling regime of 1C charged, 0.5C discharged, 0.025C cut-off; capacity retention rate ═ discharge capacity (per revolution)/initial capacity; cyclic expansion ratio (thickness after cycle-initial thickness)/initial thickness.
Table 1 test results of lithium ion batteries provided in examples 1 to 11 and comparative examples 1 to 2
According to comparative example 2 and examples 1 to 11, it is known that the cycle performance of the lithium ion battery is drastically deteriorated when the CB value is greater than 1.15, and thus, the CB value should be maintained in the range of 1.00 to 1.15; meanwhile, according to the data provided in examples 1 to 9 and examples 10 to 11, it is known that the double-layered negative active layer contributes to further improvement of the energy density and cycle performance of the lithium ion battery.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. The lithium ion battery of a silicon negative electrode system is characterized by comprising a positive plate and a negative plate, wherein the negative plate comprises a negative current collector and a negative active layer arranged on at least one functional surface of the negative current collector;
wherein the negative active material in the negative active layer comprises a carbon material and a silicon material, D50 of the carbon materialCarbon (C)D50 of said silicon materialSiliconMass m of the carbon material1Mass m of the silicon material2The thickness H of the negative active layer satisfies the relation 1:
D50carbon (C)、D50SiliconAnd the units of H are the same, m1And m2The units are the same;
the ratio of the surface capacity of the negative plate to the surface capacity of the positive plate is 1.00-1.15.
2. The lithium ion battery of claim 1, wherein the negative electrode active layer comprises a first negative electrode active layer and a second negative electrode active layer, the first negative electrode active layer and the second negative electrode active layer are sequentially stacked and arranged on at least one functional surface of the negative electrode current collector, and a negative electrode active material in the second negative electrode active layer is a carbon material.
3. The lithium ion battery according to claim 1 or 2, wherein in the negative electrode active layer, D50 of the carbon material is 10 to 18 μm.
4. The lithium ion battery according to claim 1 or 2, wherein in the negative active layer, D50 of the silicon material is 4-10 μm.
5. The lithium ion battery according to claim 1 or 2, wherein a mass ratio of the carbon material to the silicon material is (99.5:0.5) - (0.5: 99.5).
6. The lithium ion battery according to claim 1 or 2, wherein the total thickness H of the negative active layer is 40 to 160 μm.
7. The lithium ion battery according to claim 2, wherein the first negative active layer comprises carbon tubes, and the mass of the carbon tubes is 0.001% to 10% of the total mass of the first negative active layer.
8. The lithium ion battery of any of claims 1-7, wherein the negative active layer comprises a binder selected from one or more of PAA, SBR, polyacrylamide, polyacrylonitrile.
9. The lithium ion battery of claim 2, wherein the first negative active layer comprises, by mass, 95% to 97.5% of a negative active material, 0.5% to 2.5% of a conductive agent, 1.2% to 2.5% of a binder, and 0.5% to 1.5% of a dispersant;
the second negative active layer comprises 95-98% of carbon material, 0-2% of conductive agent, 1-2% of binder and 1-2% of dispersant by mass percentage.
10. The lithium ion battery according to any one of claims 1 to 9, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer arranged on at least one functional surface of the positive electrode current collector, and the positive electrode active layer comprises, by mass, 91.0% to 99.8% of a positive electrode active material, 0.05% to 3.0% of a conductive agent, and 0.05% to 3.0% of a binder.
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