CN114142176A - Battery with a battery cell - Google Patents

Battery with a battery cell Download PDF

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Publication number
CN114142176A
CN114142176A CN202111449035.XA CN202111449035A CN114142176A CN 114142176 A CN114142176 A CN 114142176A CN 202111449035 A CN202111449035 A CN 202111449035A CN 114142176 A CN114142176 A CN 114142176A
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polymer
battery
monomer
heat
positive
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CN114142176B (en
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张祖来
李素丽
李俊义
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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
    • 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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • 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
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • 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
    • 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

Abstract

The present invention provides a battery having both long cycle and low expansion, wherein a separator in the battery comprises a polymer layer, the polymer layer comprises a first polymer and a second polymer, the first polymer and the second polymer can improve the dry-pressure adhesive force between the diaphragm and the positive and negative pole pieces, can also improve the wet-pressure adhesive force between the diaphragm and the positive and negative pole pieces, ensures that the battery has good adhesive property and avoids the deformation of the battery after circulation, ensures that the adhesive retention rate of the adhesive force between the diaphragm and the positive and negative pole pieces is more than or equal to 90 percent after the battery is circulated for 200 weeks, ensures that the positive and negative pole pieces of the battery have better interfaces so as to reduce the cyclic expansion, and further, the damage and recombination of the SEI film are reduced, so that the stability of the positive electrode material at high temperature and high voltage is improved, the cycle life of the battery is effectively prolonged, and the cycle expansion of the battery can be effectively reduced.

Description

Battery with a battery cell
Technical Field
The invention belongs to the technical field of batteries, relates to a battery, and particularly relates to a long-cycle low-expansion battery.
Background
In recent years, batteries have been widely used in the fields of smart phones, tablet computers, smart wearing, electric tools, electric vehicles, and the like. With the widespread use of batteries, consumer demands for battery life continue to increase, which requires batteries with long cycle life.
At present, the battery has potential safety hazards in the use process, for example, after the battery is used for a long time, the battery has the problems of thickness expansion and the like, and further serious safety accidents such as fire and even explosion are easily caused. The main reason for the above problems is that the interface between the separator and the pole piece is deteriorated as the cycle time of the battery increases, and the main reason for the deterioration of the interface between the separator and the pole piece is that the adhesive force between the separator and the pole piece is decreased as the cycle time increases.
Based on this situation, it is urgently required to develop a battery having a long cycle life and low swelling.
Disclosure of Invention
In order to solve the problems that the bonding force between a diaphragm and a pole piece is seriously attenuated in the using process of the existing battery, the invention provides a battery which has long cycle life and low expansibility. According to the invention, the bonding stability between the diaphragm and the pole piece is increased, so that the bonding force between the diaphragm and the pole piece is slowly attenuated along with the increase of the cycle time.
In order to achieve the purpose, the invention adopts the following technical scheme:
a battery comprising a positive electrode sheet, a negative electrode sheet, a separator interposed between the positive electrode sheet and the negative electrode sheet, and a nonaqueous electrolytic solution;
the separator includes a substrate, a heat-resistant layer disposed on a first surface of the substrate, and a polymer layer disposed on a second surface of the substrate opposite the first surface and/or on the heat-resistant layer;
the polymer layer comprises a first polymer and a second polymer; the first polymer is a copolymer of a first monomer and a second monomer; the second polymer is a copolymer of a third monomer and a fourth monomer;
the first monomer comprises at least one of vinylidene fluoride, methacrylic acid, methacrylate (such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate and isopropyl methacrylate), and acrylonitrile; the second monomer comprises at least one of perfluoropropene, chlorotrifluoroethylene, tetrafluoroethylene, vinyl chloride, styrene, vinylidene chloride and tetrachloroethylene;
the third monomer comprises at least one of vinylidene fluoride, methacrylic acid, methacrylate (such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate and isopropyl methacrylate), and acrylonitrile; the fourth monomer comprises at least one of perfluoropropene, chlorotrifluoroethylene, tetrafluoroethylene, vinyl chloride, styrene, vinylidene chloride and tetrachloroethylene;
wherein the number average molecular weight of the first polymer is less than the number average molecular weight of the second polymer.
According to the invention, the number average molecular weight of the first polymer is between 5 and 50 ten thousand; the second polymer has a number average molecular weight of greater than 50 ten thousand, illustratively greater than 50 ten thousand to 200 ten thousand or less.
According to the invention, the mass of the second monomer in the first polymer is 0.5% to 20% of the total mass of the first monomer and the second monomer, for example 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18% or 20%. Within this range, the first polymer can achieve better dry-press adhesion properties.
According to the invention, the mass of the fourth monomer in the second polymer is 0.5% to 10% of the total mass of the third and fourth monomers, for example 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 9% or 10%. Within this range, the second polymer can achieve better wet-press bonding properties.
The combination of the first polymer and the second polymer can increase the bonding stability between the membrane and the pole piece, so that the bonding force between the membrane and the pole piece is slowly reduced along with the increase of the cycle time.
According to the invention, the mass ratio of the first polymer to the second polymer is (5-50): 95-50, for example 5:95, 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55 or 50: 50.
According to the invention, the thickness of the polymer layer is 0.5 μm to 2 μm, exemplary 0.5 μm, 1 μm or 2 μm.
According to the invention, the adhesive force between the polymer layer and the positive plate is more than or equal to 5N/m.
According to the invention, the adhesive force between the polymer layer and the negative plate is more than or equal to 5N/m.
According to the invention, after the battery is cycled for 200 weeks (25 ℃, 1C rate), the bonding retention rate between the polymer layer and the positive plate is more than or equal to 90%.
According to the invention, after the battery is cycled for 200 weeks (25 ℃, 1C rate), the bonding retention rate between the polymer layer and the negative plate is more than or equal to 90%.
According to the invention, the heat-resistant layer comprises a ceramic and a binder.
Preferably, the mass of the ceramic in the heat resistant layer is 20-99 wt.%, illustratively 20 wt.%, 30 wt.%, 40 wt.%, 60 wt.%, 80 wt.%, 90 wt.%, 95 wt.%, 99 wt.% or any point in the range consisting of two of the foregoing values, based on the total mass of the heat resistant layer.
Preferably, the mass of the binder in the heat resistant layer is 1 to 80 wt.%, illustratively 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, 50 wt.%, 60 wt.%, 80 wt.% or any point in the range consisting of two of the foregoing values, based on the total mass of the heat resistant layer.
According to the present invention, the ceramic in the heat-resistant layer is selected from one, two or more of alumina, boehmite, magnesium oxide, boron nitride and magnesium hydroxide.
According to the invention, the binder in the heat-resistant layer is selected from one, two or more of polytetrafluoroethylene, polyvinylidene fluoride, hexafluoropropylene-vinylidene fluoride copolymer (such as polyvinylidene fluoride-hexafluoropropylene copolymer), polyimide, polyacrylonitrile and polymethyl methacrylate.
According to the invention, the thickness of the heat-resistant layer is 0.5 μm to 5 μm, for example 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.
According to the invention, the thickness of the substrate is 3 μm to 20 μm, for example 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm or 20 μm.
According to the invention, the substrate is selected from at least one of polyethylene, polypropylene, polyethylene and polypropylene composites, polyamide, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyphenylene.
According to the present invention, the separator is disposed between the positive electrode sheet and the negative electrode sheet.
According to the invention, the first surface of the substrate is close to the negative plate, and the second surface of the substrate, which is opposite to the first surface, is close to the positive plate.
According to the invention, the battery is, for example, a lithium ion battery.
According to the invention, the positive plate comprises a positive current collector and a positive active material layer coated on one side or two sides of the positive current collector, wherein the positive active material layer comprises a positive active material, a conductive agent and a binder.
According to the invention, the positive active material is selected from lithium cobaltate (LiCoO)2) Or lithium cobaltate (LiCoO) which is doped and coated by two or more elements of Al, Mg, Mn, Cr, Ti and Zr2) The lithium cobaltate which is doped and coated by two or more elements of Al, Mg, Mn, Cr, Ti and ZrHas a chemical formula of LixCo1-y1-y2-y3-y4Ay1By2Cy3Dy4O2(ii) a X is more than or equal to 0.95 and less than or equal to 1.05, y1 is more than or equal to 0.01 and less than or equal to 0.1, y2 is more than or equal to 0.01 and less than or equal to 0.1, y3 is more than or equal to 0.1, y4 is more than or equal to 0 and less than or equal to 0.1, and A, B, C, D is selected from two or more elements of Al, Mg, Mn, Cr, Ti and Zr.
According to the invention, the conductive agent in the positive electrode active material layer is selected from acetylene black, and the amount of the conductive agent accounts for 0.01-5 wt% of the total mass of the positive electrode active material layer.
According to the invention, the binder in the positive electrode active material layer is selected from polyvinylidene fluoride (PVDF), and the amount of the binder accounts for 0.01-5 wt% of the total mass of the positive electrode active material layer.
According to the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, a conductive agent, and a binder.
According to the present invention, the negative electrode active material is selected from graphite.
According to the invention, the negative electrode active material also optionally contains SiOx/C or Si/C, wherein 0< x < 2. For example, the negative electrode active material further contains 1 to 15 wt% SiOx/C or Si/C, illustratively 1 wt%, 2 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, or any one of the foregoing ranges of values.
According to the invention, the conductive agent in the negative electrode active material layer is selected from acetylene black, and the amount of the conductive agent accounts for 0.01-5 wt% of the total mass of the negative electrode active material layer.
According to the invention, the binder in the negative electrode active material layer is selected from sodium carboxymethyl cellulose, and the amount of the binder accounts for 0.01-5 wt% of the total mass of the negative electrode active material layer.
According to the present invention, the charge cut-off voltage of the battery is 4.45V or more.
The invention has the beneficial effects that:
the present invention provides a battery having both long cycle and low expansion, wherein a separator in the battery comprises a polymer layer, the polymer layer comprises a first polymer and a second polymer, the first polymer and the second polymer can improve the dry-pressure adhesive force between the diaphragm and the positive and negative pole pieces, can also improve the wet-pressure adhesive force between the diaphragm and the positive and negative pole pieces, ensures that the battery has good adhesive property and avoids the deformation of the battery after circulation, ensures that the adhesive retention rate of the adhesive force between the diaphragm and the positive and negative pole pieces is more than or equal to 90 percent after the battery is circulated for 200 weeks, ensures that the positive and negative pole pieces of the battery have better interfaces so as to reduce the cyclic expansion, and further, the damage and recombination of the SEI film are reduced, so that the stability of the positive electrode material at high temperature and high voltage is improved, the cycle life of the battery is effectively prolonged, and the cycle expansion of the battery can be effectively reduced.
Drawings
FIG. 1: the diaphragm according to a preferred embodiment of the present invention is schematically illustrated in cross section.
Detailed Description
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 methods of making the first and second polymers used in the examples described below were made by methods known in the art.
In the description of the present invention, it should be noted that the terms "first", "second", "third", "fourth", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
Comparative examples 1 to 4 and examples 1 to 10
The lithium ion batteries of comparative examples 1 to 4 and examples 1 to 10 were each prepared according to the following preparation method, except that the first polymer and the second polymer were different in the polymer layer on the surface of the separator, with specific differences as shown in table 1.
(1) Preparation of positive plate
LiCoO as positive electrode active material2Mixing polyvinylidene fluoride (PVDF) serving as a binder and acetylene black serving as a conductive agent according to the weight ratio of 98:1.0:1.0, adding N-methylpyrrolidone (NMP), and stirring under the action of a vacuum stirrer until a mixed system becomes uniform and flowable anode slurry; uniformly coating the positive electrode slurry on an aluminum foil with the thickness of 10 mu m; baking the coated aluminum foil in 5 sections of baking ovens with different temperature gradients, drying the aluminum foil in a baking oven at 120 ℃ for 8 hours, and rolling and cutting to obtain the required positive plate.
(2) Preparation of negative plate
97% of artificial graphite negative electrode material, 0.1% of single-walled carbon nanotube (SWCNT) conductive agent, 0.8% of conductive carbon black (SP) conductive agent, 1% of sodium carboxymethyl cellulose (CMC) binder and 1.1% of Styrene Butadiene Rubber (SBR) binder are prepared into slurry by a wet process, the slurry is coated on the surface of copper foil with the thickness of 6 mu m of a negative electrode current collector, and the negative electrode sheet is obtained by drying (temperature: 85 ℃, time: 5h), rolling and die cutting.
(3) Preparation of non-aqueous electrolyte
In a glove box filled with argon (moisture)<10ppm, oxygen content<1ppm), Ethylene Carbonate (EC), Propylene Carbonate (PC) and Propyl Propionate (PP) were mixed uniformly in a mass ratio of 2:1.5:2, and 14 wt.% of LiPF based on the total mass of the nonaqueous electrolyte was slowly added to the mixed solution6And uniformly stirring to obtain the nonaqueous electrolyte.
(4) Preparation of the separator
A first polymer and a second polymer in a specific mass ratio (relevant parameters of the first polymer and the second polymer are defined as shown in table 1) were dispersed in DMAC at a ratio of 6% solids content with stirring at a stirring speed of 1500rpm for 120min, resulting in a slurry L comprising the first polymer and the second polymer.
A polyethylene substrate having a thickness of 5 μm was coated on a first surface thereof with a 2 μm-thick aluminum oxide layer (having a composition of 92 wt% of aluminum oxide, 4 wt% of methacrylic acid, and 4 wt% of sodium polymethylcellulose), and a second surface of the polyethylene substrate opposite to the first surface and the surface of the aluminum oxide layer were coated with a 2 μm-thick polymer layer, respectively, specifically, a slurry L was coated on both sides of the polyethylene substrate having a thickness of 5 μm and the aluminum oxide layer having a thickness of 2 μm by a gravure roll coating method, and dried to obtain a separator having a polymer layer having a thickness of 2 μm on both sides, as shown in fig. 1.
(5) Preparation of lithium ion battery
Winding the prepared positive plate, the diaphragm and the negative plate to obtain a bare cell without liquid injection (wherein, a first surface of the polyethylene base material is close to one side of the negative plate, and a second surface of the polyethylene base material opposite to the first surface is close to one side of the positive plate); and (3) placing the bare cell in an outer packaging foil, injecting the prepared electrolyte into the dried bare cell, and performing vacuum packaging, standing, formation, secondary packaging, sorting and other processes to obtain the required lithium ion battery.
TABLE 1 lithium ion batteries prepared in comparative examples 1 to 4 and examples 1 to 10
Figure BDA0003385311150000071
Figure BDA0003385311150000081
The cells obtained in the above comparative examples and examples were subjected to electrochemical performance tests, as described below:
(1)25 ℃ cycling experiment:
placing the batteries obtained in the above examples and comparative examples in an environment of (25 +/-2) DEG C, standing for 2-3h, when the battery body reaches (25 +/-2) DEG C, keeping the cut-off current of the battery at 0.05C according to 1C constant current charging, standing for 5min after the battery is fully charged, then discharging to the cut-off voltage of 3.0V at 1C constant current, recording the highest discharge capacity of 3 cycles before recording as an initial capacity Q, and recording the discharge capacity Q of the last cycle of the battery when the cycle number reaches 1000 cycles1(ii) a Record cell initializationThickness T, the thickness when circulating to 1000 weeks is recorded as T1The results are reported in Table 2.
The calculation formula used therein is as follows:
capacity retention (%) ═ Q1(ii)/Q × 100%; thickness change rate (%) - (T)1-T)/T×100％。
(2) The method for measuring the adhesive force between the polymer layer on the surface of the diaphragm and the negative electrode comprises the following steps:
the batteries obtained in the above examples and comparative examples are placed in an environment of (25 +/-2) ° C, are kept stand for 2-3h, are charged according to a constant current of 0.7 ℃ when the battery body reaches (25 +/-2) ° C, the cut-off current is 0.05 ℃, when the terminal voltage of the battery reaches the charging limiting voltage, changing constant voltage charging, stopping charging and standing for 5min until the charging current is less than or equal to a cut-off current, dissecting the fully charged battery, selecting a diaphragm and a negative electrode integral sample with the length of 30mm x 15mm along the direction of a pole lug, testing the diaphragm and the negative electrode at an included angle of 180 degrees on a universal stretcher at the speed of 100mm/min and the test displacement of 50mm, and recording the test result as the bonding force N (unit N/m) between the diaphragm and the negative electrode, the bonding force tested by a fresh battery is N1 (unit N/m), and the bonding force tested by a battery circulating for 200 weeks is N2 (unit N/m);
the calculation formula used therein is as follows:
the rate of change in the adhesive force between the polymer layer on the separator surface and the negative electrode (%) (N1-N2)/N1 × 100%
TABLE 2 experimental test results of the batteries obtained in comparative examples 1 to 4 and examples 1 to 10
Figure BDA0003385311150000082
Figure BDA0003385311150000091
As can be seen from the results of table 2: according to the invention, through the synergistic effect of the first polymer and the second polymer in the diaphragm, the dry-pressure adhesive force between the diaphragm and the positive and negative pole pieces is improved, the wet-pressure adhesive force between the diaphragm and the positive and negative pole pieces is also improved, the battery is ensured to have good adhesive property so as to avoid deformation of the battery after circulation, the slow attenuation of the adhesive force between the diaphragm and the positive and negative pole pieces is ensured, the positive and negative pole pieces of the battery have better interfaces so as to reduce the cyclic expansion, and further the damage and recombination of a CEI (cellulose-rich imide) film are reduced, so that the stability of the positive pole material under high temperature and high voltage is improved, the cyclic expansion of the battery is effectively reduced while the cyclic life of the battery is effectively prolonged.
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. A battery comprising a positive electrode sheet, a negative electrode sheet, a separator interposed between the positive electrode sheet and the negative electrode sheet, and a nonaqueous electrolytic solution; characterized in that the membrane comprises a substrate, a heat-resistant layer disposed on a first surface of the substrate, and a polymer layer disposed on a second surface of the substrate opposite the first surface and/or on the heat-resistant layer;
the polymer layer comprises a first polymer and a second polymer; the first polymer is a copolymer of a first monomer and a second monomer; the second polymer is a copolymer of a third monomer and a fourth monomer;
the first monomer comprises at least one of vinylidene fluoride, methacrylic acid, methacrylate and acrylonitrile; the second monomer comprises at least one of perfluoropropene, chlorotrifluoroethylene, tetrafluoroethylene, vinyl chloride, styrene, vinylidene chloride and tetrachloroethylene;
the third monomer comprises at least one of vinylidene fluoride, methacrylic acid, methacrylate and acrylonitrile; the fourth monomer comprises at least one of perfluoropropene, chlorotrifluoroethylene, tetrafluoroethylene, vinyl chloride, styrene, vinylidene chloride and tetrachloroethylene;
wherein the number average molecular weight of the first polymer is less than the number average molecular weight of the second polymer.
2. The battery of claim 1, wherein the first polymer has a number average molecular weight of 5 to 50 ten thousand; the second polymer has a number average molecular weight of greater than 50 ten thousand.
3. The battery of claim 2, wherein the second polymer has a number average molecular weight of greater than 50 to equal to or less than 200 ten thousand.
4. The battery according to claim 1, wherein the mass of the second monomer in the first polymer is 0.5 to 20% of the total mass of the first monomer and the second monomer.
5. The battery of claim 1, wherein the second polymer comprises 0.5-10% of the total mass of the third and fourth monomers.
6. The battery according to any one of claims 1 to 5, wherein the mass ratio of the first polymer to the second polymer is (5-50): (95-50).
7. The battery of claim 1, wherein the polymer layer has a thickness of 0.5 μm to 2 μm;
and/or the thickness of the heat-resistant layer is 0.5-5 mu m.
8. The battery according to any one of claims 1, wherein the adhesion between the polymer layer and the positive electrode sheet is 5N/m or more;
and/or the adhesive force between the polymer layer and the negative plate is greater than or equal to 5N/m.
9. The battery according to claim 1, wherein the retention of adhesion between the polymer layer and the positive electrode sheet after the battery is cycled for 200 weeks (25 ℃, 1C rate) is 90% or more.
And/or the adhesion retention rate between the polymer layer and the negative plate is greater than or equal to 90% after the battery is cycled for 200 weeks (25 ℃, 1C rate).
10. The battery of any of claims 1-9, wherein the heat resistant layer comprises a ceramic and a binder.
Preferably, the mass of the ceramic in the heat-resistant layer accounts for 20 wt.% to 99 wt.% of the total mass of the heat-resistant layer, and the mass of the binder in the heat-resistant layer accounts for 1 wt.% to 80 wt.% of the total mass of the heat-resistant layer.
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Citations (8)

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