WO2008034295A1

WO2008034295A1 - A lithium ion battery electrode plate,a lithium ion battery electrode core and the preparation method of the same

Info

Publication number: WO2008034295A1
Application number: PCT/CN2006/002452
Authority: WO
Inventors: Xin Li; Xiangqian Li
Original assignee: Shenzhen Bak Battery Co., Ltd
Priority date: 2006-09-19
Filing date: 2006-09-19
Publication date: 2008-03-27

Abstract

A lithium ion battery electrode plate, a lithium ion battery electrode core comprising the said plate and the preparation method of the same, wherein the said plate is a positive electrode plate or a negative electrode plate, which is coated by a microporous layer based on PVDF. The microporous layer comprises a chemical gel formed by chemical crosslinking. The thermal shrinkage rate of the PVDF microporous layer which forms chemical gel inside by irradiation cross-linking is almost 0 under 100-200°C high temperature. The electron short circiut between the positive and negative electrode plates due to the over-shrinkage of the high-intensityshut-down polyolefin microporous separator under high temperature can be effectively avoided after the lithium ion battery electrode plate coated by the microporous layer.

Description

Lithium ion battery pole piece, battery core and battery core preparation method

The invention relates to the field of lithium ion batteries, in particular to a method for preparing a lithium ion battery pole piece, a battery core and a battery core with high safety performance.

Background technique

Lithium-ion secondary batteries are widely used in mobile phones, notebook computers, power tools, electric bicycles, etc. because of their high operating voltage, high energy density, and environmental protection.

The polymer lithium ion secondary battery usually adopts the porous polyvinylidene fluoride copolymer PVDF-HFP as the physical gel membrane. The typical process is the classic Bellcore process. See US Patent 5,540,741, which uses dibutyl phthalate DBP. As a plasticizer, DBP is removed by methanol multistage extraction. The physically crosslinked PVDF-HFP has good liquid absorption and liquid retention properties. It is used as a gel electrolyte after liquid absorption and swelling. Lithium-ion batteries are not easy to leak. However, the polyvinylidene fluoride microporous membrane layer produced by the method has low strength, and usually has a film thickness of about 50 micrometers, which still cannot meet the requirements of high-efficiency winding process, but uses positive electrode sheets, separators, and negative electrode sheets. Composite laminated structure; another disadvantage of the method is low extraction efficiency, high requirements for production safety protection, high manufacturing cost, and poor economy.

Due to the use of an organic electrolyte with a high decomposition voltage, the liquid lithium ion secondary battery may have a fire or explosion hazard in the event of an overcharge, internal electronic short circuit or external short circuit of the battery, in order to ensure the electrochemical performance of the battery. Safety, usually the battery is designed for system safety design such as cell plus protection electronic circuit and serial FTC over-current protection element. However, the protection of electronic circuit still fails, the battery itself must be safe. Redundant design, such as the use of a high-strength polyolefin microporous membrane with thermal shutdown, melts off during accidental internal heating, allowing lithium ions to stop passing through the membrane, attenuating or terminating the occurrence of thermal runaway reactions, but High-strength polyolefin microporous membranes often have 10-50% heat shrinkage due to thermal shutdown in the temperature range of 125-165 ,, which easily causes physical short circuit of the positive and negative electrodes to ignite and explode; due to high-strength polymerization The olefin microporous membrane can only be obtained by high temperature hot stretching.

1

Confirmation Therefore, the heat shrinkage due to the memory effect is unavoidable at high temperatures, and the compensation for this defect can improve the safety of the cell.

Document CN01124839, JP 178006/2000, JP212575/2004, JP093987/2004 proposes the formation of a polyamide or polyimide porous high temperature resistant film layer by a lyotropic phase separation process on the surface of a PE microporous membrane; documents CN200410067008.6, CN200410061662 .6, US 10/621234 proposes a method of combining a high temperature resistant nonwoven fabric with a polyolefin separator, and using a PVDF/DBP acetone solution as a binder and a hot press composite. The shortcoming of these methods is that the glue liquid is easy to block the micropores in the PE membrane, and it is easy to form a gas-impermeable skin layer. The uniformity and consistency of the micropores are difficult to control in production; and the polyimide porous membrane layer is polycondensed due to polycondensation. The temperature is between 180 and 320 ° C, so it cannot be formed by polycondensation at the surface of the PE separator having a melting point of 135 ° C.

The literature CN01116353.4, US 09/546266 and Degussa of Germany propose a technical method of compositeing a porous layer of a ceramic composite material and a porous layer of a polymerizable polymer, usually using a PET fiber to thermally bond the ceramic powder into a film, due to strength. Considering that the thickness of the composite ceramic porous film is often above 25 microns, it is easy to crack and drop powder during winding. Although it is theoretically possible to use the high melting point ceramic powder to prevent the short circuit of the pole piece, the internal resistance of the battery tends to be too large, electrochemical Performance is not ideal.

In order to solve the above technical problems, the inventors have proposed in the document CN03100863.1 to separately fabricate a polyimide high temperature resistant porous film layer having micron-sized pores, and then with a conventional polyolefin separator having nano-scale micropores ^: The solution is combined, but because the porous polyimide film is brittle and has insufficient strength, it is difficult to meet the winding process requirements.

Documents CN03125501.9, CN02118877.7, JP270620/2002, US10/446380, CN200410035400.2, US6322923, etc. propose a method of forming a microporous membrane of PVDF or the like on the surface of a polyolefin microporous membrane to exert a good liquid absorbing property of PVDF. The separator and the pole piece have good adhesion and uniform ion conduction, which have advantages for fully utilizing the battery capacity and improving safety; however, if the PVDF porous film layer on the polyolefin microporous membrane is too thin, the polyolefin micro at high temperature When the porous membrane is heat-shrinked, it is easy to bring PVDF to shrink, which is not enough to prevent short circuit of the inner pole piece of the battery, and the safety is not high; if the PVDF porous film layer on the polyolefin microporous membrane is too thick, due to PVDF has poor adhesion to polyolefin microporous membranes and has the disadvantage of easy peeling. This method is not conducive to mass production.

Documents US5603892 and CN01112218.8 propose to use a technique in which a composition of a polymer precursor and an electrolyte is injected into a lithium ion battery body and thermally chemically crosslinked by heating to form a thermochemical gel between the pole piece and the diaphragm to improve The adhesion between the pole piece and the diaphragm prevents uneven heating during overcharging. Thermochemical cross-linking technology has been successfully applied in the manufacture of cable insulation jackets, but on lithium-ion batteries, there are many monomers or polymer precursors, cross-linking agents, peroxide initiators, etc., and there are reactions. Incomplete, residues and impurities can easily affect the electrochemical performance of the battery, and mass production quality control is difficult.

In order to solve the above technical problems, the inventors proposed a method for coating a PVDF porous film layer on a pole piece of a lithium ion battery core in the document CN200410081129.6, which avoids the above disadvantages, and coats the PVDF porous film layer on the pole piece. The pole piece has good adhesion and is not easy to be peeled off. In addition, the PVDF porous film layer has a low heat shrinkage rate at 100-15 CTC, which can make up for the lack of heat shrinkage of the high-strength polyolefin separator; There is a shortage of high production cost. In addition, due to the requirement of preventing thermal runaway inside the battery, it is desirable to have a high-temperature resistant and low heat-shrinkable diaphragm which can prevent short-circuiting of the positive and negative electrodes at up to 200 ° C. The method is safe in the battery and The economy of production still needs to be improved.

Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion battery pole piece, a lithium ion battery cell, and a method of manufacturing the same, which have higher safety performance, in view of the problems of the prior art.

In order to achieve the above object, the present invention employs the following technical solutions:

The invention discloses a lithium ion battery pole piece, wherein the pole piece is a positive electrode piece or a negative electrode piece, and the positive electrode piece or the negative electrode piece has a microporous film layer with polyvinylidene fluoride as a matrix, and the microporous film layer The inside has a chemical gel formed by chemical crosslinking.

The chemical gel content is from 25 to 85%, preferably from 45 to 70%.

The chemical gel is formed by irradiating a microporous layer of polyvinylidene fluoride as a matrix, and the irradiation dose is 2.5 to 25 Mrad, preferably 5 to 15 Mrad. The polyvinylidene fluoride-based microporous membrane layer has a thickness of 4 to 15 μm, preferably 5 to 10 μm; a porosity of 35 to 75%, preferably 45 to 65%; and an average pore diameter of 0.05 to 2 μm, preferably 0.1- 1 micron.

The polyvinylidene fluoride is one or a combination of a polyvinylidene fluoride homopolymer PVDF having a melting point of 163 to 175 ° C and a polyvinylidene fluoride copolymer having a melting point of 130 to 145 V, preferably both. The combination, and the polyvinylidene fluoride copolymer accounts for 5 to 75% by weight, preferably 25 to 55% by weight.

The polyvinylidene fluoride copolymer is a copolymer of vinylidene fluoride and hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene, octafluoro-1-butene or octafluoroisobutylene, preferably vinylidene fluoride and hexafluoroethylene. The copolymer of propylene PVDF-HFP has a hexafluoropropylene monomer content of 10 to 25%.

The above microporous film has a heat shrinkage ratio of less than 5% at a temperature of from 100 to 220 °C.

The invention also discloses a lithium ion battery cell comprising a positive electrode sheet, a negative electrode sheet and a separator for isolating the positive and negative electrode sheets, wherein the positive electrode sheet and/or the negative electrode sheet are the pole pieces described above.

The polyvinylidene fluoride-based microporous film layer is coated on one or both sides of the positive electrode sheet and/or the negative electrode sheet, and the one side refers to the side where the positive electrode sheet or the negative electrode sheet contacts the separator.

The separator is a turn-off polyolefin separator having a thickness of preferably 12 to 20 μm.

The shutdown polyolefin separator is a single-layer polyethylene microporous membrane having a shutdown temperature of 125 to 135 ° C or a polyethylene/polypropylene composite microporous membrane having a shutdown temperature of 125 to 165 °C.

The invention further discloses the above method for manufacturing a lithium ion battery cell, which comprises composite winding a positive electrode sheet, a separator and a negative electrode sheet, the method further comprising one or both sides of the positive electrode sheet and/or the negative electrode sheet. Coating a layer of polyvinylidene fluoride-based microporous membrane layer, and irradiating cross-linking the polyvinylidene fluoride microporous membrane layer before or after the composite winding, the side being referred to as a positive electrode sheet or a negative electrode sheet The side that is in contact with the diaphragm during winding.

The coating process includes:

A. Preparing a slurry, uniformly dissolving 2 to 25 parts of one or both of a polyvinylidene fluoride homopolymer and a polyvinylidene fluoride copolymer in 100 parts of a polar solvent, and adding 4 to 50 parts of a plasticizer. 0~ 5 parts of ceramic powder and 0~15 parts of cross-linking agent, mixed and defoamed after hooking;

B. The slurry prepared in step A is coated or sprayed on the pole piece, dried, and the polar solvent is evaporated to form a film;

C. Extract into pores, and extract the plasticizer by using a volatile solvent or by supercritical extraction. The plasticizer is a mixture of one or more of dimethyl phthalate, dibutyl phthalate, diethyl carbonate, propylene carbonate, and triethyl phosphate.

The polar solvent is a mixture of one or more of N-methylpyrrolidone, hydrazine, hydrazine-dimethylformamide, hydrazine, hydrazine-dimethylacetamide, acetone, butanone.

The crosslinking agent uses a bifunctional acrylate, including polyethylene glycol diacrylate-200, polyethylene glycol diacrylate-400, polyethylene glycol dimethacrylate-400, polypropylene glycol diacrylate. And a combination of one or more of polypropylene glycol dimethacrylate.

The ceramic powder is an ultrafine magnesium oxide, calcium oxide, cerium oxide, cerium oxide or zeolite molecular sieve having an average particle diameter of less than 2 μm, preferably an average particle diameter of less than 1 μm.

In the supercritical extraction method, the extracting agent is one or a combination of the following: propane, chlorodifluoromethane, trifluoromethane, 1,1,1,2-tetrafluoroethane, 2-chloro-1, 1,1,2-tetrafluoroethane, pentafluoroacetic acid, hexafluoroacetic acid, heptafluoropropene, octafluoropropane, octafluorocyclobutane.

The irradiation cross-linking treatment means:

Before the composite sheet, the separator, and the negative electrode sheet are compositely wound, the polyvinylidene fluoride microporous film layer is irradiated and crosslinked by electron beam irradiation; or

After the positive electrode sheet, the separator, and the negative electrode sheet are compositely wound, the polyvinylidene fluoride microporous film layer is subjected to irradiation crosslinking treatment using gamma rays having high penetrability.

Due to the adoption of the above scheme, the specific beneficial effects of the present invention are as follows:

The polyvinylidene fluoride-based microporous membrane layer of the present invention can increase the high-temperature melt strength of the polyvinylidene fluoride microporous membrane layer due to the chemical gel formed by chemical crosslinking inside; and the temperature rises to polyvinylidene fluoride (PVDF) has a heat shrinkage of almost zero before the melting point of 173 °C; even at a temperature above 173 °C of PVDF, due to the hindrance of the three-dimensional covalent bond network structure formed by chemical crosslinking, The high-temperature melt fluidity of the W polyvinylidene fluoride film layer is much lower than that of the PVDF film layer which is not chemically crosslinked; at a high temperature of 100-220 ° C, the chemical gel is formed by irradiation crosslinking. The polyvinylidene fluoride film layer has almost zero heat shrinkage rate and a heat shrinkage ratio of less than 5%. After being coated on the lithium ion battery pole piece, it can effectively prevent the electronic short circuit of the positive and negative electrodes caused by the high-strength turn-off polyolefin microporous diaphragm due to excessive shrinkage at high temperature.

Irradiation cross-linking of the polyvinylidene fluoride microporous membrane layer on the pole piece by electron beam or gamma gamma irradiation can form a large number of intermolecular chemical crosslinking points or chemical gels in the polyvinylidene fluoride film layer. Control chemical gel content above 20%, especially controlled at 45-70%, can improve the high temperature melting strength of polyvinylidene fluoride porous membrane layer; through the addition of PVDF-HFP copolymer and control chemical gel content of 80 Below %, the PVDF-HFP copolymer can exhibit the advantages of liquid absorption and liquid retention, which facilitates rapid liquid injection during cell production and maximizes the electrochemical performance of the battery, such as increased capacity and cycle life. ,

The lithium ion battery core combination of the invention adopts a microporous membrane layer which can turn off the polyolefin separator and the high temperature resistant and low heat shrinkable polyvinylidene fluoride as a collective, and can exert synergistic protection effect, can more effectively prevent the occurrence of thermal runaway, the battery Better security.

detailed description

The lithium ion battery pole piece of the present invention may be a positive electrode sheet or a negative electrode sheet, and includes a current collector generally having a positive electrode active material or a negative electrode active material thereon, and further comprising a polyvinylidene fluoride-based microparticle. A porous membrane layer having a chemical gel formed by chemical crosslinking inside the microporous membrane layer. Usually, the positive electrode or the negative electrode active material is coated on the corresponding current collector, dried and rolled, and then coated with a layer of polyvinylidene fluoride microporous film, and irradiated to form a microporous film layer. A chemical gel is formed inside. The chemical gel content is controlled at 25-85%, preferably at 45-70%.

The polyvinylidene fluoride microporous membrane layer of the present invention can be heat-shrinked to almost zero before the temperature rises to a melting point of polyvinylidene fluoride of 173 ° C, and the electron beam or gamma ray is used for the polyvinylidene fluoride on the pole piece. The microporous film layer is subjected to irradiation crosslinking treatment to form a large number of intermolecular chemical crosslinking points or chemical gels in the polyvinylidene fluoride film layer. The dose for irradiation is 2.5-25 Mrad, preferably 5-15 Mrad. Control chemical gel content above 20%, especially controlled at 45-70%, can The high temperature melting strength of the polyvinylidene fluoride porous film layer is increased. Even at the melting point of PVDF above 173 °C, the high-temperature melt fluidity of the polyvinylidene fluoride film layer is lower than that of the PVDF film layer which is not chemically crosslinked due to the hindrance of the three-dimensional covalent bond network structure formed by chemical crosslinking. Much more. The radiation-crosslinked polyvinylidene fluoride film layer has an almost zero heat shrinkage rate at a high temperature of 100-220 °. Thus, the lithium ion battery cell prepared by shutting down the polyolefin separator is used in combination with the pole piece of the present invention, and the pole piece coated polyvinylidene fluoride microporous film can effectively prevent the high-strength turn-off polyolefin microporous. The electronic short circuit of the positive and negative electrodes caused by the excessive shrinkage of the diaphragm at high temperatures. By adding and controlling a chemical copolymer such as PVDF-HFP to a chemical gel content of 80% or less, the PVDF-HFP copolymer can exhibit the advantages of liquid absorption and liquid retention, which is advantageous for rapid injection and complete injection of cells. Use the electrochemical properties of the battery, such as increased capacity and cycle life.

The polyvinylidene fluoride porous film layer on the pole piece has a single side thickness of 4-15 micrometers, preferably 5-10 micrometers, and less than 4 micrometers, it is difficult to ensure insulation performance, and above 15 micrometers, the internal resistance of the battery is increased and the material cost is increased. The porosity is too low or the pore size is too small, which affects the internal resistance. If the porosity is too large or the pore size is too large, it is not good for preventing the physical short circuit of the positive/negative electrode sheets; the porosity is 35-75%, more preferably controlled at 45-65%; 0.05-2 microns, preferably controlled at 0.1-1 microns. The content of chemical gel formed by irradiation cross-linking treatment is 25-85%, preferably controlled at 45-70%, taking into account the high-temperature melt strength of the polyvinylidene fluoride porous membrane layer and the PVDF-HFP liquid absorption property. The advantage of good liquidity is beneficial to the electrochemical performance of the battery.

In order to obtain a microporous membrane layer on the pole piece which is irradiated and crosslinked by polyvinylidene fluoride, the polyvinylidene fluoride on the pole piece is mainly made of polyvinylidene fluoride homopolymer PVDF having a melting point of 163-173 °C. The raw material is manufactured to ensure that the microporous film layer based on polyvinylidene fluoride has higher high temperature resistance. The material of polyvinylidene fluoride homopolymer can be produced by Arkema Company as 10^761, 741, 721, 711 or 760, 740 or 801 ¥ & the company's production of 8016 £ 1013, 6020 PVDF.

In order to obtain a microporous film layer on the pole piece which is irradiated and crosslinked by polyvinylidene fluoride as a matrix, the polyvinylidene fluoride on the pole piece may also be a polyvinylidene fluoride copolymer having a melting point of 130-145 为 as a raw material, wherein The comonomer can be selected from hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene, Octafluoro-1-butene, octafluoroisobutylene, etc., preferably a copolymer of hexafluoropropylene and vinylidene fluoride having a comonomer content of 10-25%, PVDF-HFP, such as KY A 2801-00 manufactured by Arkema , 2800-00 or Solva 21's PVDF-HFP from Solvay.

In order to obtain a microporous film layer on the pole piece which is irradiated and crosslinked by polyvinylidene fluoride as a matrix, the polyvinylidene fluoride on the pole piece may also be a polyvinylidene fluoride homopolymer PVDF having a melting point of 163-173 ° C. And a composition of a polyvinylidene fluoride copolymer PVDF-HFP having a melting point of 130-145 ° C is a raw material, wherein the PVDF-HFP copolymer is contained in an amount of 5-75% by weight, preferably 25-55% by weight of the composition. The advantage of this is that the residual portion of the uncrosslinked PVDF-HFP copolymer in the porous film after irradiation crosslinking can maintain a certain liquid swellability, and can better exert battery capacity and cycle performance.

Both sides of the positive and negative electrode sheets are coated with a porous polyvinylidene fluoride film layer, which can improve the liquid absorption and liquid retention ability of the separator, and is advantageous for the cycle performance of the battery, which fully absorbs the advantages of the polymer battery.

It is also possible to apply the polyvinylidene fluoride porous film layer only on both sides of the negative electrode sheet. Since the width of the negative electrode sheet is generally slightly larger than that of the positive electrode sheet, the high temperature resistant polyvinylidene fluoride porous film layer coated on both sides of the negative electrode sheet can be prevented. The tiny burrs generated by the strips on both sides of the positive pole piece pierce the pole piece short circuit caused by the diaphragm.

It is also possible to apply the polyvinylidene fluoride porous film layer only on both sides of the positive electrode sheet, since the negative electrode pole piece can be produced without using PVDF as a binder, and a lower cost styrene-butadiene rubber (SBR) is used. Used as the primary binder. At this time, the process can be appropriately adjusted, for example, by adding a roll-pressing and depilating step after the positive electrode sheet is cut, and then coating the polyvinylidene fluoride porous film layer or designing the widths of the positive and negative electrode sheets to be equivalent.

The polyvinylidene fluoride porous film layer may be applied only to one side of the positive and negative electrode sheets, and the polyvinylidene fluoride porous film layer may be applied to both the other electrode sheets.

The lithium ion battery cell of the present invention comprises a positive electrode sheet, a negative electrode sheet and a separator between the positive and negative electrode sheets, one or both of the positive and negative electrode sheets are prepared by using the above-mentioned pole piece, and the separator is a closed polyolefin diaphragm. For example, a high-strength, shut-off polyolefin diaphragm with a shutdown temperature of 125-135 如 Polyethylene (PE) microporous membrane, or polyethylene/polypropylene (PE/PP or PP/PE/PP three-layer structure) composite microporous membrane with a temperature of 125-165 关. This type of diaphragm can be turned off in advance after an accidental heat generation inside the battery, and the termination of heat is stopped. If the shutdown temperature is designed to be less than 125 Ό, the production of the polyethylene microporous membrane is poorly controllable, and it is easy to partially turn off in the heat setting process of the separator production; and the melting point of PP is 165 ° C, using PE/PP or The PP/PE/PP composite diaphragm can achieve a shutdown temperature range of 125-165 ° C wide. Therefore, the microporous membrane layer which can turn off the polyolefin membrane and the radiation-resistant cross-linking treatment on the high temperature and low heat shrinkage polyvinylidene fluoride can be used to synergistically protect the heat loss control. The occurrence of the battery is better.

The thickness of the polyolefin separator (single-layer polyethylene microporous membrane or polyethylene/polypropylene composite microporous membrane) can be 12-20 micrometers. If the thickness is too low, the high-strength microporous polyethylene membrane is difficult to manufacture and resistant to acupuncture. The performance is lowered. Even with the high temperature resistant and low heat shrinkable polyvinylidene fluoride microporous membrane layer proposed by the present invention, it is desirable to avoid the occurrence of micro short circuit inside the battery as much as possible; and if the thickness of the polyolefin separator is too high, the internal resistance of the battery increases. .

The method for manufacturing a lithium ion battery according to the present invention comprises the following steps: for example, coating a positive electrode or a negative electrode active material on a current collector, and then rolling to prepare a positive electrode plate or a negative electrode sheet; and the positive electrode sheet, the negative electrode sheet, and the positive and negative electrodes The separator between the pole pieces is composite wound, and then assembled, injected, formed, etc., wherein after the pole piece is rolled, one side or both sides of the pole piece (positive piece and/or negative piece) are coated. The microporous film layer is made of polyvinylidene fluoride as a matrix, and the polyvinylidene fluoride microporous film layer on the pole piece is subjected to irradiation crosslinking treatment. In order to prevent the high-strength and turn-off polyolefin microporous membrane from being over-contracted due to excessive shrinkage at high temperatures, when the pole piece is coated on the single-sided polyvinylidene fluoride microporous membrane layer, the micro-sheet The porous film layer is coated on the side of the positive electrode sheet or the negative electrode sheet that is in contact with the separator.

The microporous membrane layer on which the radiation cross-linking treatment of polyvinylidene fluoride is used as a matrix mainly comprises the following steps: A. preparing a slurry, a polyvinylidene fluoride resin or a composition thereof (polyvinylidene fluoride homopolymer) 2 to 25 parts by weight of the polyvinylidene fluoride copolymer are uniformly dissolved in 100 parts of the polar solvent, 4 to 50 parts of the plasticizer, 0 to 5 parts of the ceramic powder, 0 to 15 parts are added. Cross-linking The agent is uniformly defoamed after being mixed; B. uniformly coated or sprayed on the pole piece after rolling; drying, volatilizing and drying the polar solvent; C, extracting into a hole, using a volatile solvent or a supercritical extraction process The plasticizer is removed, and after drying, a battery pole piece with a microporous layer is obtained; D. The microporous film layer of polyvinylidene fluoride on the pole piece is irradiated and crosslinked. The C and D sequences can be adjusted as appropriate.

The binder for the positive and negative electrode sheets for applying the positive and negative active materials to the slurry is preferably a polyvinylidene fluoride homopolymer PVDF having a melting point of 163-173 ,, such that PVDF as a binder is dispersedly distributed on the pole piece. Resin and battery active material, when the slurry of the above configuration is coated thereon, the PVDF resin on the surface of the pole piece is slightly soluble in the solvent, which is equivalent to a large number of bonding points, so that the porous PVDF formed on the surface of the pole piece has Good adhesion, easy to peel off, so it is suitable for mass production.

The polyvinylidene fluoride microporous membrane layer on the pole piece is irradiated and crosslinked by electron beam irradiation or gamma ray irradiation at an irradiation dose of 2.5 to 25 Mrad, preferably 5 to 15 Mrad. If the dosage is too low, the crosslinking is insufficient; if the dosage is too high, the degree of crosslinking is too large, and the residual uncrosslinked PVDF-HFP is insufficient, and the porous membrane has insufficient liquid absorption and liquid retention properties, and the electrochemical performance is insufficient. The pole piece with the polyvinylidene fluoride microporous film layer may be subjected to on-line irradiation cross-linking treatment by a self-shielding electronic curtain accelerator with an accelerating voltage of 150-300 KV; or the positive electrode piece, the separator and the negative electrode piece may be compositely wound. After that, the gamma-ray ray with strong penetrating power is used for the irradiation cross-linking treatment.

In order to manufacture a polyvinylidene fluoride-based microporous membrane layer, a polyvinylidene fluoride slurry (glue) is prepared by adding a plasticizer, so that after the solvent is volatilized into a film, the plasticizer is extracted to obtain a uniform microporous layer. . The plasticizer may be a mixture of one or more of dimethyl phthalate, dibutyl phthalate (DBP), diethyl carbonate, propylene carbonate, and triethyl phosphate.

The solvent for dissolving polyvinylidene fluoride may be one or more of N-methylpyrrolidone (oxime), hydrazine, hydrazine-dimethylformamide, hydrazine, hydrazine-dimethylacetamide, acetone, butanone. A mixture, preferably a high flash point, low toxicity Ν-methylpyrrolidone.

In order to further improve the adhesion of the polyvinylidene fluoride-based microporous membrane layer to the surface of the pole piece and improve the efficiency of irradiation crosslinking, a crosslinking agent which does not affect the electrochemical performance of the battery may be added during the preparation of the slurry, for example, Bifunctional acrylates, including polyethylene glycol dipropylene Composition of one or more of ester-200, polyethylene glycol diacrylate-400, polyethylene glycol dimethacrylate-400, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate Preferably, polyethylene glycol diacrylate-400 is used.

When using lithium manganate having higher safety as the positive electrode active material, in order to better exert the performance of the spinel type lithium manganate, it is prevented that a trace amount of moisture in the electrolyte reacts with LiPF ₆ in the electrolyte to produce HF, and HF causes a poor chain reaction of dissolution of Mn ions on the surface of spinel-type lithium manganate. When manufacturing a polyvinylidene fluoride microporous membrane layer on a pole piece, a small amount of ultrafine magnesium oxide and calcium oxide having water-removing function are added. , ceramic powder such as cerium oxide, cerium oxide, zeolite molecular sieve. The ceramic powder has an average particle diameter of preferably less than 2 μm, more preferably less than 1 μm in view of coating processability and uniformity.

The traditional Bellcore process for the manufacture of PVDF-HFP separators for polymer lithium-ion batteries, the extraction and pore-forming process still has the disadvantage of high production cost. Considering the technical economy, the present invention preferably uses the following economic methods: The pores are made of a polyvinylidene fluoride-based microporous membrane layer, and a high-efficiency supercritical extraction process is adopted. Since the conventional co ₂ supercritical fluid has a lower solubility of the above-mentioned slightly higher molecular weight plasticizer, the extraction efficiency is lower. According to the invention, the extracting agent is a combination of one or more of propane or a low-toxic, non-combustible halogenated hydrocarbon refrigerant material having good solubility with the above plasticizer, and is preferably, but not limited to, the following extraction in consideration of environmental protection. ^: R22 (chlorodifluoromethane, Tc=96.2°C, Pc=4.99MPa), R23 (trifluoromethane, Tc=25.9°C, Pc=4.84MPa) R134a ( 1, 1, 1, 2-four Fluoroethane, Tc=101.1°C, Pc=4.06MPa), R124 (2-chloro-1, 1, 1, 2-tetrafluoroethane, Tc=122.3°C, Pc=3.62MPa), R125 (five Fluorine, Tc=66.2 °C, Pc=3.63MPa)> R116 (hexafluoroethane, Tc=19.9°C, Pc=3.04MPa), R227ea (sevoflurane) Propane, Tc=102.8°C, Pc=2.98MPa), R218 (octafluoropropene, Tc=71.9°C, Pc=2.68MPa), C318 (octafluorocyclobutane, Tc=115.2°C, Pc=2.78 MPa). Supercritical extraction can effectively reduce the leakage of solvent due to the use of a fully enclosed system. The plasticizer and extractant can be effectively separated and recovered in the separation tank, and the process has good environmental protection characteristics.

The main difference between the physical gel and the chemical gel proposed by the present invention is as follows: For the polyvinylidene fluoride microporous membrane layer, if hydrazine is used, hydrazine-dimethylformamide can be effectively dissolved at room temperature for 24 hours, which is regarded as Physical gels, such as PVDF-HFP polymers produced by the traditional Bellcore process The battery separator is treated with N,N-dimethylformamide under the protection of argon at 80 ° C for 24 hours while still being insoluble, and the residue on the 400 mesh sieve after filtration is regarded as a chemical gel, which is dried and sieved. The ratio of the weight of the residue to the weight before dissolution is defined as the chemical gel content, and the chemical gel content of the porous polyvinylidene fluoride film layer coated on the pole piece is tested by directly coating the same porous poly layer on the surface of the electrolytic copper foil. Comparative sample test of vinylidene fluoride film layer.

The heat shrinkage test is to sandwich a certain length and width of the microporous film separately prepared between the smooth glass plates at the corresponding temperature, heat it at this temperature for 30 minutes, take it out, and cool it to room temperature to remove the glass plate. The remaining length and width or surface area, as a percentage of the initial surface area, is considered to be the rate of thermal shrinkage at that temperature.

The present invention will be described in detail below with reference to the accompanying examples, but the invention is not limited thereto, and may be modified as appropriate without departing from the spirit and scope of the invention.

Example 1

Manufacture of positive electrode tabs

The positive active material is made of spinel-type lithium manganate LiMn ₂ 0 ₄ , the binder is mixed with KYNAR 761 PVDF, and acetylene black is used as a conductive agent in a ratio of 95:3:5 in N-methylpyrrolidone (NMP) solvent. After mixing and defoaming, the aluminum foil collector is uniformly coated, dried, and rolled on both sides, and then the porous polyvinylidene fluoride film layer is coated on both sides, and irradiated and crosslinked.

Coating the porous polyvinylidene fluoride film layer includes:

A, ingredients, 2.5 parts of KY AR 761 PVDF, 1.25 parts of KYNAR 2801 PVDF-HFP, dissolved in 96.25 parts of N-methylpyrrolidone (NMP) solvent, added 7.5 parts of DBP, continue to mix evenly, defoaming;

B. coating the slurry (glue) on both sides of the positive electrode sheet after rolling, and controlling the thickness of the polyvinylidene fluoride film after drying: 10 μm;

C. Extracting DBP, the above-mentioned pole piece is wound into a roll together with a PP nonwoven fabric having an areal density of 35 g, and placed in a high-pressure extraction autoclave of supercritical extraction, using R125 as an extractant, an extraction pressure of 4.0 MPa, extraction heating Temperature: 80 ° C, extraction time 75-120 min, extraction and vacuum drying, microporous membrane layer porosity of 55%, average pore diameter of about 0.4 microns; D. Irradiation cross-linking, using a self-shielding electronic curtain accelerator with an accelerating voltage of 250KV, the positive electrode piece with polyvinylidene fluoride microporous film layer was subjected to on-line irradiation cross-linking treatment, the irradiation dose was 15Mrad, and the chemical gel content test value was used. At 70%, the microporous film layer has a heat shrinkage ratio of less than 3% at a temperature of from 100 ° C to 220 ° C.

Manufacture of negative pole pieces

The negative electrode active material is made of artificial graphite, and an aqueous solution of SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose) is used as an adhesive. The three are prepared according to the weight ratio of 97:1.5丄5, and are coated. Both sides of the copper foil current collector are dried, rolled, and slit.

Can turn off the diaphragm

Biaxially stretched ultrahigh molecular weight polyethylene UHMWPE microporous separator with a thickness of 16 microns, the membrane porosity is 50%, the Gurley value is 8-15s/10cc, the tensile strength at room temperature is more than 80MPa in both directions, and the shutdown temperature is 135 °C.

Battery manufacturing

The above positive electrode piece / UHMWPE separator / negative electrode piece is wound into a core, inserted into a stainless steel casing with an explosion-proof membrane, vacuum-dried at 80 ° C, and then poured into a non-aqueous electrolyte, and the injection hole is pasted with adhesive tape. The opening in the drying room is formed, and the steel ball is pressed and sealed.

Battery safety test

The battery prepared above was prepared in a conventional manner, and 100 batteries were placed in a hot box, and the hot box was temperature-programmed to 220 ° C at 3 ° C / _m in 15 min. battery. The test results showed that a total of 10 batteries exploded, and the other batteries were intact, with a pass rate of 90%. Example 2

In the same manner as in the first embodiment, a porous polyvinylidene fluoride film layer and a radiation crosslinking treatment step were separately coated on both sides of the negative electrode tab, and the thickness of the polyvinylidene fluoride film after drying was controlled to be 10 μm.

The same method was used for battery safety testing with a pass rate of 92%.

Example 3

In the same manner as in Example 2, only the thickness of the porous polyvinylidene fluoride film layer coated on the positive and negative electrode sheets was adjusted to 4 μm. The same method was used for battery safety testing with a pass rate of 85%.

Example 4 .

The remainder was the same as in Example 2 except that the thickness of the porous polyvinylidene fluoride film layer coated on the positive and negative electrode sheets was adjusted to 15 μm.

The same method was used for battery safety testing with a pass rate of 93%.

Example 5

The rest of the same example 2, the irradiation dose is 2.5 Mrad, the chemical gel content test value is 25%, and the microporous film layer has a heat shrinkage rate of less than 4% at a temperature of 100 ° C to 220 ° C.

The same method was used for battery safety testing with a pass rate of 83%.

Example 6

The rest of the same example 2, irradiation dose 25Mmd, chemical gel content test value of 85%, microporous membrane layer at 100 ° C -220 ° C temperature heat shrinkage rate of less than 3%.

The same method was used for battery safety testing with a pass rate of 91%.

Example 7

The rest of the same example 2, the irradiation dose is 5 Mrad, the chemical gel content is 45%, and the microporous membrane layer is at 100 °C-22 (the heat shrinkage rate at TC temperature is less than 3%).

The same method was used for battery safety testing with a pass rate of 88%.

Example 8 '

The rest is the same as in Example 2, changing the ratio of PVDF-HFP used in coating the porous polyvinylidene fluoride film layer. Ingredients: KYNAR 761 PVDF 2.5 parts, KYNAR 2801 PVDF-HFP 0.14 parts, dissolved in 97.37 parts of N-methylpyrrole In the solvent of fluorenone (NMP), 5 parts of DBP was added, and the mixture was uniformly mixed and defoamed. The DBP was extracted as in Example 1, the irradiation dose was 15 Mrad, and the chemical gel content was 55%. The microporous membrane layer was The heat shrinkage rate at a temperature of from 100 ° C to 220 ° C is less than 3%.

The same method was used for battery safety testing with a pass rate of 87%.

Example 9

The rest is the same as in the second embodiment, the negative active material is made of artificial graphite, and KYNAR 761 PVDF is used. As an adhesive, N-methylpyrrolidone (MP) is used as a solvent. The uniformly stirred slurry is applied to both sides of the copper foil current collector, dried and rolled, and the surface of the negative and negative electrode sheets are coated on both sides. The fluoroethylene film layer is subjected to irradiation crosslinking treatment to control the thickness of the dried polyvinylidene fluoride film on one side: 10 μm, and slit.

Battery manufacturing

The same method was used for battery safety testing with a pass rate of 92%. three

Example 10

Manufacture of positive electrode tabs

The positive electrode active material is made of spinel-type lithium manganate LiMn ₂ 0 ₄ , the binder is KYNAR 761 PVDF, and acetylene black is used as a conductive agent in a ratio of 95:3:5 to be dissolved in N-methylpyrrolidone (NMP). In the solvent, after defoaming, the aluminum foil collector is uniformly coated, dried, rolled, and coated on both sides with a porous polyvinylidene fluoride film layer to control the thickness of the dried polyvinylidene fluoride film on one side: S micron , Irradiation cross-linking treatment.

Manufacture of negative pole pieces

The anode active material is made of artificial graphite, KYNAR 761PVDF is used as the adhesive, N-methylpyrrolidone (NMP) is used as the solvent, and the slurry is uniformly stirred and applied to both sides of the copper foil current collector, dried, rolled, and the surface of the pole piece. The polyvinylidene fluoride film layer was coated on both sides, and the thickness of the polyvinylidene fluoride film after drying was controlled to be 8 μm, irradiated and crosslinked.

Positive and negative electrode sheets coated on both sides of the porous polyvinylidene fluoride film layer include -

A, ingredients, 2.5 parts of KYNAR 761 PVDF, 1.25 parts of KYNAR 2801 PVDF-HFP, 1.0 part of polyethylene glycol diacrylate-400, 1 part of anhydrous magnesium oxide powder with an average particle size of less than 1 micron, dissolved in 95 parts 7.5 parts of DBP was added to the solvent of N-methylpyrrolidone (NMP), and the mixture was uniformly mixed and defoamed;

B. coating the above slurry (glue) on both sides of the pole piece after rolling; C. Extracting DBP, the above-mentioned pole piece is wound into a roll together with a PP melt-blown nonwoven fabric having an areal density of 50 g, and then placed in a high-pressure extraction autoclave of supercritical extraction, using R125 as an extractant, and an extraction pressure of 4.5 MPa. Extraction heating temperature: 80 ° C, extraction time 60-90 min, extraction and vacuum drying, microporous membrane layer porosity of 50%, average pore diameter of about 0.2 microns;

D. Irradiation cross-linking, using a self-shielding electronic curtain accelerator with an accelerating voltage of 250KV, the pole piece with the polyvinylidene fluoride microporous film layer is subjected to on-line irradiation cross-linking treatment, the irradiation dose is 8Mrad, and the chemical gel content test value is 65%, the microporous membrane layer has a heat shrinkage ratio of less than 3% at 100 ° C-22 (TC temperature).

Can turn off the diaphragm

A biaxially oriented ultrahigh molecular weight polyethylene UHMWPE separator having a thickness of 16 μm is preferred, and the Gurley value is 8-15 s/10 cc. The tensile strength at room temperature is more than 80 MPa in both directions, and the shutdown temperature is 135 ° C.

Battery manufacturing

The above positive electrode piece / UHMWPE membrane / negative electrode piece is wound into a core, inserted into a stainless steel casing with an explosion-proof membrane, vacuum-dried at 80 ° C, and then injected into a non-aqueous electrolyte. After the injection hole is affixed with adhesive tape, The opening in the drying room is formed, and the steel ball is pressed and sealed.

Battery safety test

The battery prepared above was prepared in a conventional manner, and 100 batteries were placed in a hot box, and the hot box was temperature-programmed to 220 ° C at 3 ° C/min for 15 minutes, and finally the battery was taken out. . The test results showed that a total of 7 batteries exploded, and the other batteries were intact, with a pass rate of 93%. Example 11-18

Examples 11-18 are substantially the same as Example 1, and the differences are listed in the following table.

Example 11 12 13 14 15 16 17 18

PVDF (parts) 2. 0 10 — 15 4. 5 7. 5 9. 5 3

PVDF-HFP (parts) 1. 75 15 10 5. 5 2. 5 0. 5 7 Type I II IV V III IV+VII Polar Solvent ¹

Dosage (parts) 100 100 100 100 100 100 100 100 Type 3 1 C 1 +3 4 5 1 2 Plasticizer ²

Dosage (parts) 4 10 20 45 30 10 10 15 Type (2) (1) — (3) (4) (5) Ceramic powder ³

Dosage (parts) 5 2 — 4 3 · 3 Type ca — ebd crosslinker ⁴

Dosage (parts) 15 10 — 5 10 10 Extractant R23 R22 R134a R124 R116 R125 C318 R218 Poly single-sided thickness (μ πι) 12 10 14 15 8 4 10 10 Partial porosity 55% 35% 45% 50% 65% 55 % 75% 50% Fluorine average pore diameter (μ πι) 0. 4 1 0. 5 0. 6 0. 5 0. 4 0. 1 1. 5 B irradiation dose (Mrad) 15 12 10 20 15 15 5 5 Chemistry: «Content 70% 65% 55% 75% 65% 70% 45% 50% Micro heat shrinkage rate <3% <3% <3% <3 <3% <3% <3% <3% Multi-positive film Coated double-sided double-sided single-sided single-sided single-faced face

Negative film coating, silent surface, double-sided, single-sided, silent surface, single-sided film

Can cut off diaphragm thickness (μ ΐη) 12 20 16 18 14 16 16 16 Battery safety test pass rate 90% 93% 91% 94% 89% 90% 85% 86% Note: ¹ : I refers to N in polar solvent -methylpyrrolidone; II finger

Ν, Ν-dimethylacetamide; IV means acetone; V means butanone.

: 1 refers to dimethyl phthalate in plasticizer; 2 refers to dibutyl phthalate; 3 refers Diethyl carbonate; 4 refers to propylene carbonate; 5 refers to triethyl phosphate.

³ : In the ceramic powder, (1) refers to ultrafine magnesium oxide; (2) refers to calcium oxide; (3) refers to cerium oxide; (4) refers to cerium oxide; (5) refers to zeolite molecular sieve.

⁴ : in the crosslinking agent, a refers to polyethylene glycol diacrylate-200; b refers to polyethylene glycol diacrylate-400; c refers to polyethylene glycol dimethacrylate-400; d refers to polypropylene glycol diacrylate Ester; e refers to polypropylene glycol dimethacrylate.

Further, in the above embodiments 11-14, the radiation crosslinking is carried out in the same manner as in the first embodiment, that is, the pole piece having the polyvinylidene fluoride microporous film layer is subjected to a self-shielding electronic curtain accelerator with an acceleration voltage of 250 kV. In the radiation irradiation cross-linking treatment, in the embodiment 15-18, the radiation cross-linking method is to combine the positive electrode tab, the separator and the negative electrode tab, and then use the gamma ray with strong penetrating power to irradiate and crosslink. deal with. And Example 13, the positive electrode active material in place of LiCo0 ₂ LiMn0 _4.

Comparative example

The positive and negative electrode sheets were prepared in the same manner as in Example 1, but the polyvinylidene fluoride microporous film layer was not coated on the pole piece, and the irradiation cross-linking treatment was not performed; and the same cut-off separator and positive and negative electrodes were used. The sheets are prepared together with a battery. The obtained battery was prepared in a conventional manner, and the same safety performance test was carried out: 100 batteries were placed in a hot box, and the temperature was programmed to 220 ° C at 3 ° C/min for 15 min. , finally remove the battery. The test results showed that a total of 60 batteries exploded.

Claims

A lithium ion battery pole piece, wherein the pole piece is a positive electrode piece or a negative electrode piece, characterized in that - the positive electrode piece or the negative electrode piece has a microporous film layer having polyvinylidene fluoride as a matrix, and the microporous layer The inside of the film layer has a chemical gel formed by chemical crosslinking.

A lithium ion battery pole piece according to claim 1, wherein said chemical gel content is 25 to 85%.

3. A lithium ion battery pole piece according to claim 2, wherein the chemical gel content is 45 to 70%.

The invention relates to a lithium ion battery pole piece according to any one of claims 1 to 3, wherein the chemical gel is irradiated and crosslinked by a microporous layer comprising polyvinylidene fluoride as a matrix. Formed by treatment, the irradiation dose is 2.5 to 25 Mrad.

5. A lithium ion battery pole piece according to claim 4, wherein: said irradiation dose is 5 to 15 Mrad.

The lithium ion battery pole piece according to claim 4, wherein the polyvinylidene fluoride-based microporous film layer has a thickness of 4 to 15 μm.

The lithium ion battery pole piece according to claim 6, wherein the polyvinylidene fluoride-based microporous film layer has a thickness of 5 to 10 μm.

The lithium ion battery pole piece according to claim 4, wherein the polyvinylidene fluoride-based microporous film layer has a porosity of 35 to 75%.

The lithium ion battery pole piece according to claim 8, wherein the polyvinylidene fluoride-based microporous film layer has a porosity of 45 to 65%.

The lithium ion battery pole piece according to claim 4, wherein the polyvinylidene fluoride-based microporous film layer has an average pore diameter of 0.05 to 2 μm.

The lithium ion battery pole piece according to claim 10, wherein the polyvinylidene fluoride-based microporous film layer has an average pore diameter of 0.1 to 1 μm.

The lithium ion battery pole piece according to claim 4, wherein the polyvinylidene fluoride is a polyvinylidene fluoride homopolymer having a melting point of 163 to 175 ° C, and has a melting point of 130 to 145 ° C. One or a combination of two of the polyvinylidene fluoride copolymers.

The lithium ion battery pole piece according to claim 12, wherein the polyvinylidene fluoride is a polyvinylidene fluoride homopolymer having a melting point of 163 to 175 ° C and a melting point of 130 to 145 ° C. A combination of polyvinylidene fluoride copolymers, and the polyvinylidene fluoride copolymer accounts for 5 to 75% by weight of the two.

A lithium ion battery pole piece according to claim 13, wherein the polyvinylidene fluoride copolymer accounts for 25 to 55% by weight.

The lithium ion battery pole piece according to claim 13 or 14, wherein the polyvinylidene fluoride copolymer is vinylidene fluoride and hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene, a copolymer of octafluoro-1-butene or octafluoroisobutylene.

The lithium ion battery pole piece according to claim 15, wherein the polyvinylidene fluoride copolymer is a copolymer of vinylidene fluoride and hexafluoropropylene, and the content of the hexafluoropropylene monomer is 10~25%.

A lithium ion battery cell comprising a positive electrode sheet, a negative electrode sheet, and a separator for isolating the positive and negative electrode sheets, wherein the positive electrode sheet and/or the negative electrode sheet are the pole pieces according to any one of claims 1 to 16.

18. The lithium ion battery cell according to claim 17, wherein: the polyvinylidene fluoride-based microporous film layer is coated on one or both sides of the positive electrode sheet and/or the negative electrode sheet. The one side refers to the side of the positive electrode sheet or the negative electrode sheet that is in contact with the separator.

19. A lithium ion battery cell according to claim 18, wherein: said diaphragm is a turn-off polyolefin membrane having a thickness of 12 to 20 microns.

20. A lithium ion battery cell according to claim 19, wherein: said switchable polyolefin membrane is a single layer polyethylene microporous membrane or shutdown temperature at a shutdown temperature of 125 to 135 °C. Polyethylene/polypropylene composite microporous membrane at 125 to 165 °C.

21. The method of manufacturing a lithium ion battery cell according to claim 17, wherein the method comprises The positive electrode sheet, the separator and the negative electrode sheet are compositely wound, and the method further comprises: coating a microporous film layer of polyvinylidene fluoride as a matrix on one or both sides of the positive electrode sheet and/or the negative electrode sheet, The polyvinylidene fluoride microporous film layer is subjected to irradiation crosslinking treatment before or after the composite winding, and the one side refers to the side of the positive electrode sheet or the negative electrode sheet which is in contact with the separator at the time of winding.

22. The method of manufacturing a lithium ion battery cell according to claim 21, wherein: said coating process comprises

A. Preparing a slurry, uniformly dissolving 2 to 25 parts of one or both of a polyvinylidene fluoride homopolymer and a polyvinylidene fluoride copolymer in 100 parts of a polar solvent, and adding 4 to 50 parts of a plasticizer. , 0~5 parts of ceramic powder and 0~15 parts of cross-linking agent, and uniformly defoamed after being mixed;

B. uniformly coating or spraying the prepared slurry of step A on the pole piece, drying it, and evaporating the polar solvent to form a film;

C. Extract into pores, and extract the plasticizer by using a volatile solvent or by supercritical extraction.

The method for manufacturing a lithium ion battery cell according to claim 22, wherein the plasticizer is dimethyl phthalate, dibutyl phthalate, diethyl carbonate, A mixture of one or more of propylene carbonate and triethyl sulphate.

The method of manufacturing a lithium ion battery cell according to claim 22, wherein the polar solvent is N-methylpyrrolidone, N,N-dimethylformamide, hydrazine, hydrazine- A mixture of one or more of dimethylacetamide, acetone, butanone.

The method for manufacturing a lithium ion battery cell according to claim 22, wherein the crosslinking agent is a bifunctional acrylate, including polyethylene glycol diacrylate-200, polyethylene glycol II. A combination of one or more of acrylate-400, polyethylene glycol dimethacrylate-400, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate.

The method of manufacturing a lithium ion battery cell according to claim 22, wherein the ceramic powder is an ultrafine magnesium oxide, calcium oxide, cerium oxide, cerium oxide or zeolite molecular sieve.

A method of manufacturing a lithium ion battery cell according to claim 22, characterized in that In the supercritical extraction method, the extracting agent is one or a combination of the following: propane, chlorodifluoromethane, trifluoromethane, 1,1,1,2-tetrafluoroacetamidine, 2-chloro- 1,1,1,2-tetrafluoroethane, pentafluoroacetic acid, hexafluoroethane, heptafluoropropane, octafluoropropene, octafluorocyclobutane.

27. The method of manufacturing a lithium ion battery cell according to claim 21, wherein: said irradiation crosslinking treatment means that

After the positive electrode sheet, the separator, and the negative electrode sheet are compositely wound, the polyvinylidene fluoride microporous film layer is subjected to irradiation crosslinking treatment using gamma gamma rays having high penetrating ability.