A primer slurry, a positive electrode sheet, a battery cell, and a preparation method thereof

Abstract

The application discloses a primer slurry, a positive plate, a battery cell and preparation methods of the primer slurry, the positive plate and the battery cell, and the primer slurry comprises conductive glue and functional materials, wherein the functional materials are at least one of lithium iron phosphate materials and ceramic materials; the conductive glue comprises the following raw material components in percentage by mass: epoxy resin prepolymer: 2-8%, curing agent: 1-5%, conductive filler: 3-10%, and solvent: 80-90%; the mixture of the conductive glue and the functional materials is applied to the surface of a current collector, the internal resistance of a safe battery cell is effectively reduced, the positive electrode specific capacity of the safe battery cell is improved, the conductivity of the safe battery cell is enhanced, and the internal resistance, low-temperature discharge and high-temperature cycle performance of the existing safe battery cell are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a primer slurry, a positive plate, a battery cell and a preparation method thereof. BACKGROUND

[0002] With the continuous development of 3C digital products, the demand for lithium battery capacity and voltage is getting higher and higher, and the safety problem coefficient is getting more and more difficult, which promotes the terminal market to pay high attention to and rapidly develop the demand for lithium battery safety technology. A most dangerous safety failure mode of a lithium battery is that a full-charge anode film is short-circuited with an empty aluminum foil, and this short-circuit mode can instantly generate a large amount of heat, thereby causing the battery cell to rapidly heat runaway and catch fire.

[0003] At present, the industry mainly solves this problem by the following two methods: (1) the surface of the positive current collector Al foil is coated with lithium iron phosphate; (2) the surface of the positive current collector Al foil is coated with ceramic; by the two common safety primer coating methods, the direct short-circuit of the empty Al foil and the current collector is avoided, thereby improving the safety performance. However, both methods have problems such as deteriorating internal resistance, reducing the specific capacity of the battery cell, deteriorating kinetics, deteriorating high-temperature cycle, and the safety coating being easy to fall off.

[0004] Therefore, it is urgent to develop a new type of safety primer coating method to solve the problems existing in the above methods. SUMMARY

[0005] The purpose of the application is to develop a new type of safety primer coating slurry, which can solve the problems of large internal resistance, deteriorating kinetics, low specific capacity and the like of the existing safety battery cell while ensuring the safety of the battery cell, and is a safety battery cell technology that takes into account excellent kinetics and low internal resistance.

[0006] In order to achieve the above purpose, the application adopts the following technical scheme:

[0007] A primer slurry comprises a conductive adhesive and a functional material, wherein the functional material is at least one of a lithium iron phosphate material and a ceramic material; the conductive adhesive comprises the following mass percentages of raw material components: epoxy resin prepolymer: 2-8%, curing agent: 1-5%, conductive filler: 3-10%, and solvent: 80-90%.

[0008] Preferably, the mass ratio of the conductive adhesive to the functional material is (35-45):(55-65).

[0009] Preferably, the ceramic material is at least one of aluminum oxide, zirconium oxide, boehmite, magnesium oxide, silicon oxide and calcium oxide.

[0010] Preferably, the epoxy resin prepolymer is at least one of a glycidyl ether type bisphenol A epoxy resin and a glycidyl ether type bisphenol F epoxy resin.

[0011] Preferably, the curing agent is at least one of triethylamine, 2-ethyl-4-methylimidazole and dimethylimidazole.

[0012] Preferably, the conductive filler is a mixture of single-walled carbon nanotubes and conductive carbon.

[0013] Preferably, the mass ratio of the single-walled carbon nanotubes to the conductive carbon is 1:1.

[0014] Preferably, the solvent is at least one of N-methylpyrrolidone, acetone, ethanol, propanol, isopropanol and ethylene glycol.

[0015] The application also provides a positive electrode sheet, comprising a positive electrode slurry and a positive electrode current collector, wherein the positive electrode current collector is a positive electrode current collector coated with the above-mentioned primer slurry.

[0016] The application also provides a safety battery, comprising a positive electrode sheet, a negative electrode sheet and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the above-mentioned positive electrode sheet.

[0017] The application also provides a preparation method of the above-mentioned safety battery, comprising the following steps:

[0018] (1) Preparation of a positive electrode current collector containing a primer slurry: mixing a conductive adhesive and a functional material, stirring to disperse uniformly, to obtain a primer slurry, coating on both surfaces of a positive electrode current collector, and drying to obtain a positive electrode current collector containing a primer slurry;

[0019] (2) Preparation of a positive electrode sheet: dissolving a positive electrode material, a conductive agent and a binder in an N-methylpyrrolidone solution, stirring sufficiently to disperse uniformly, to obtain a positive electrode slurry, coating on both surfaces of the positive electrode current collector containing a primer slurry in step (1), and performing drying and hot pressing, so that the conductive adhesive in the primer slurry starts to be cured for the first time, to obtain a positive electrode sheet;

[0020] (3) Preparation of a negative electrode sheet: dissolving a negative electrode material, a conductive agent and a binder in deionized water, stirring to disperse uniformly, to obtain a negative electrode slurry, coating on a surface of a negative electrode current collector, and performing drying and room temperature rolling treatment, to obtain a negative electrode sheet;

[0021] (4) Obtaining a first battery by winding the positive electrode sheet in step (2) and the negative electrode sheet in step (3) and a separator;

[0022] (5) Performing first packaging, baking and liquid injection on the first battery obtained in step (4) using an aluminum plastic film, to obtain a second battery;

[0023] (6) the second electric core obtained in step (5) is subjected to formation, the conductive glue starts to be subjected to second heat curing, and then is subjected to second packaging, capacity test and edge folding, so that a safe electric core is obtained.

[0024] Preferably, in step (1), the drying temperature is 80-110 DEG C, and the drying air speed is 5-10 m / min.

[0025] Preferably, in step (1), after drying, the thickness of the primer paste coated on the surface of the positive current collector is 3-4 mu m.

[0026] Preferably, in step (2), the hot pressing mode is a hot pressing composite process.

[0027] Preferably, in step (2), the hot pressing temperature T is 130-150 DEG C, and the hot pressing pressure is 65-85T.

[0028] Preferably, in steps (2) and (3), the stirring time is 10 h, the coating speed is 4 m / min, and the drying temperature is 80-120 DEG C.

[0029] Preferably, in step (5), the baking temperature is 80-88 DEG C.

[0030] Preferably, in step (6), the formation temperature is 75-85 DEG C, and the formation air pressure is 1.2-1.4 MPa.

[0031] Compared with the prior art, the present application has at least the following beneficial effects:

[0032] 1) The present application can effectively reduce the internal resistance of the existing safe electric core; the conductive glue bonds the positive material and the current collector together, reduces the interface contact resistance of the two substances and increases the interface electron conductivity.

[0033] 2) The present application can improve the positive capacity of the existing safe electric core, thereby improving the energy density of the battery.

[0034] 3) The present application can enhance the conductivity of the safe electric core, thereby improving the performance of the existing safe electric core at low temperature; the conductive glue can increase the adhesion of the positive material and the current collector, reduce the expansion of the positive plate at high temperature, reduce the increase of the positive interface impedance, and at the same time, the conductive glue enhances the interface electron conductivity, thereby improving the discharge capacity of the electric core at low temperature. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a structure schematic view of the positive plate of the embodiment 1 of the present application.

[0036] Figure 2 It is a structure schematic view of the positive plate of the embodiment 2 of the present application.

[0037] 1 - current collector, 2 - base coating slurry, 21 - conductive adhesive, 22 - lithium iron phosphate material, 23 - ceramic material, 3 - positive electrode material, 4 - tab welding area. DETAILED DESCRIPTION

[0038] In order to make the technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] In a first aspect of the present application, the present application provides a base coating slurry, comprising a conductive adhesive and a functional material, wherein the functional material is at least one of a lithium iron phosphate material and a ceramic material; the conductive adhesive comprises the following mass percentage of raw material composition: epoxy resin prepolymer: 2-8%, curing agent: 1-5%, conductive filler: 3-10%, solvent: 80-90%.

[0040] In an embodiment according to the present application, the mass ratio of the conductive adhesive to the functional material is (35-45):(55-65), preferably 40:60.

[0041] In an embodiment according to the present application, the ceramic material is at least one of aluminum oxide, zirconium oxide, boehmite, magnesium oxide, silicon oxide and calcium oxide.

[0042] In an embodiment according to the present application, the epoxy resin prepolymer is at least one of a glycidyl ether type bisphenol A epoxy resin and a glycidyl ether type bisphenol F epoxy resin, preferably a glycidyl ether type bisphenol A epoxy resin.

[0043] In an embodiment according to the present application, the curing agent is at least one of triethylamine, 2-ethyl-4-methylimidazole and dimethylimidazole, preferably triethylamine and 2-ethyl-4-methylimidazole.

[0044] In an embodiment according to the present application, the conductive filler is a mixture of single-walled carbon nanotubes and conductive carbon.

[0045] In an embodiment according to the present application, the mass ratio of the single-walled carbon nanotubes to the conductive carbon is 1:1.

[0046] In an embodiment according to the present application, the solvent is at least one of N-methylpyrrolidone, acetone, ethanol, propanol, isopropanol and ethylene glycol.

[0047] In a second aspect, the present application provides a positive electrode sheet, comprising a positive electrode slurry and a positive electrode current collector, wherein the positive electrode current collector is coated with the above-mentioned base coating slurry.

[0048] In a third aspect, the present application provides a safety battery, comprising a positive electrode sheet, a negative electrode sheet and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the above-mentioned positive electrode sheet.

[0049] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material in the negative electrode active material layer can be one or more of, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, etc. The graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys; and the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, tin alloys. The negative electrode current collector can be a copper foil, a PET copper foil or an aluminum foil.

[0050] The separator can be selected from various separators commonly used in lithium ion batteries known to those skilled in the art, such as polypropylene microporous membrane, polyethylene felt, glass fiber felt or ultra-fine glass fiber paper.

[0051] The safety battery further comprises an electrolyte, which can be various conventional 1.5C fast-charging electrolytes. The electrolyte composition comprises a solvent, a lithium salt, a film-forming additive and other additives. The solvent can be at least one of ethylene carbonate (EC), propylene carbonate (PC), polypropylene (PP) and vinylene carbonate (VC); the lithium salt can be at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6) and lithium hexafluorosilicate (LiSiF6); the film-forming additive can be at least one of fluoroethylene carbonate (FEC) and polystyrene (PS); and the other additives can be at least one of succinonitrile (SN), ethylene glycol butyl ether (EGBE), 1,3,6-hexanetricarbonitrile (HTCN), lithium difluoro(oxalato)borate (LiODFB), lithium difluoro(oxalato)phosphate (LiODFP) and 1-n-propylphosphoric anhydride (PPACA).

[0052] In a fourth aspect, the present application provides a preparation method of the above-mentioned safety battery, comprising the following steps:

[0053] (1) Preparation of the positive electrode current collector containing the base coating slurry: mix the conductive glue with the functional material, stir and disperse uniformly to obtain the base coating slurry, coat on both surfaces of the positive electrode current collector, dry to obtain the positive electrode current collector containing the base coating slurry;

[0054] (2) Production of the positive electrode sheet: the positive electrode material, the conductive agent and the binder are dissolved in an N-methylpyrrolidone solution, stirred sufficiently to disperse uniformly, to obtain a positive electrode slurry, which is coated on both surfaces of the positive electrode current collector containing the primer slurry in step (1), dried, and hot-pressed, so that the conductive adhesive in the primer slurry starts the first thermal curing, to obtain a positive electrode sheet;

[0055] (3) Production of the negative electrode sheet: the negative electrode material, the conductive agent and the binder are dissolved in deionized water, stirred to disperse uniformly, to obtain a negative electrode slurry, which is coated on the surface of the negative electrode current collector, dried, and roll-pressed at room temperature, to obtain a negative electrode sheet;

[0056] (4) The positive electrode sheet in step (2) and the negative electrode sheet in step (3) and the separator are wound to obtain a first battery cell;

[0057] (5) The first battery cell obtained in step (4) is first packaged using an aluminum plastic film, baked, and injected with electrolyte, to obtain a second battery cell;

[0058] (6) The second battery cell obtained in step (5) is formed, the conductive adhesive starts the second thermal curing, and is then second packaged, tested for capacity, and edge-folded, to obtain a safe battery cell.

[0059] In an embodiment according to the present application, in step (1), the drying temperature is 80-110℃, specifically 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, or 110℃, and the drying air speed is 5-10 m / min, specifically 5 m / min, 6 m / min, 7 m / min, 8 m / min, 9 m / min, or 10 m / min. When the drying temperature and the drying air speed are controlled within the above ranges, the solvent can be effectively volatilized and dried, while avoiding the premature curing of the curing agent in the conductive adhesive before the electrode sheet is compacted.

[0060] In an embodiment according to the present application, in step (1), after drying, the thickness of the primer slurry coated on the surface of the positive electrode current collector is 3-4 μm.

[0061] In an embodiment according to the present application, in step (2), the hot-pressing mode is a hot-pressing compounding process. In this hot-pressing mode, the pressure roller is heated to a certain temperature to stimulate the adhesion of the conductive adhesive, so that the conductive adhesive is heat-compounded and cured, thereby bonding the current collector, the conductive adhesive and the functional material, and lithium cobaltate together. The conductive adhesive is a flowable liquid substance under normal temperature storage conditions, and is solidified by heating to a certain temperature, thereby forming a connection with a certain strength.

[0062] In an embodiment according to the present application, in step (2), the temperature T of hot pressing is 130-150°C, and specifically can be 130°C, 135°C, 140°C, 145°C, or 150°C. When the temperature of hot pressing is controlled within the above range, the curing agent in the conductive adhesive can better play a curing role. The pressure of hot pressing is 65-85T, and specifically can be 65T, 68T, 70T, 75T, 78T, 80T, 82T, or 85T. The above pressure is used to compact the pole piece, so that the active substance after coating is more closely attached to the surface of the current collector, and at the same time, the transmission path between materials can be reduced, the conductivity can be increased, and the internal resistance can be reduced.

[0063] In an embodiment according to the present application, in step (2), the mass ratio of the positive electrode material, the conductive agent, and the binder is (96-98):(1-2):(1-2), and preferably is 97.9:1.1:1.

[0064] In an embodiment according to the present application, in step (2), the positive electrode material can be at least one of lithium cobaltate, lithium manganate, lithium nickelate, and lithium iron phosphate, and preferably is lithium cobaltate.

[0065] In an embodiment according to the present application, in steps (2) and (3), the stirring time is 10h, the coating speed is 4m / min, and the drying temperature is 80-120°C, and specifically can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C.

[0066] In an embodiment according to the present application, in steps (2) and (3), the conductive agent can be at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube, and graphene, and preferably is conductive graphite and carbon nanotube.

[0067] In an embodiment according to the present application, in steps (2) and (3), the binder can be at least one of, but not limited to, polyvinylidene fluoride, butadiene rubber, and carboxymethyl cellulose, and preferably is polyvinylidene fluoride and butadiene rubber.

[0068] In an embodiment according to the present application, in step (3), the mass ratio of the negative electrode material, the conductive agent, and the binder is (96-98):(1-2):(1-2), and preferably is 97.3:1.4:1.3.

[0069] In an embodiment according to the present application, in step (5), the baking temperature is 80-88°C, and specifically can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, or 88°C.

[0070] In one embodiment of the present invention, in step (6), the formation temperature is 75-85°C, specifically 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, or 85°C; the formation pressure is 1.2-1.4 MPa, specifically 1.2 MPa, 1.3 MPa, or 1.4 MPa. When the formation temperature and pressure are controlled within the above ranges, the specific capacity of the materials constituting the safety cell can be effectively utilized, resulting in superior overall performance of the safety cell.

[0071] The present invention will be further described below through specific embodiments.

[0072] Example 1

[0073] like Figure 1 As shown, this embodiment provides a positive electrode sheet with a centrally located tab, including a current collector 1, a base coating slurry 2, a conductive adhesive 21, a lithium iron phosphate material 22, and a positive electrode material 3. The base coating slurry 2 includes the conductive adhesive 21 and the lithium iron phosphate material 22, and the base coating slurry 2 is coated on both surfaces of the current collector 1.

[0074] (1) Preparation of positive current collector containing base coating slurry 2: The conductive adhesive 21 and lithium iron phosphate material 22 are mixed at a mass ratio of 40:60 to form a slurry. After being stirred and dispersed evenly at high speed, the slurry is coated on both surfaces of aluminum foil 1 using a gravure printing machine. The slurry is dried at a temperature of 85℃ and a wind speed of 6m / min to obtain an aluminum foil with a slurry thickness of 3μm.

[0075] (2) Preparation of positive electrode sheet: Lithium cobalt oxide 3, conductive carbon black, carbon nanotubes and polyvinylidene fluoride are dissolved in N-methylpyrrolidone solution at a mass ratio of 97.9:0.5:0.6:1 and stirred thoroughly for 10 hours to disperse them evenly and obtain positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil at a speed of 4 m / min and dried at a temperature of 100℃. The sheet is pressed using a hot-pressing composite process. The conductive adhesive in the bottom coating slurry begins to undergo the first heat curing to obtain the positive electrode sheet.

[0076] (3) Preparation of negative electrode sheet: Graphite, conductive carbon black, carboxymethyl cellulose and styrene-butadiene rubber are dissolved in deionized water at a mass ratio of 97.3:0.3:1.1:1.3 and stirred for 10 hours to disperse them evenly to obtain negative electrode slurry. The negative electrode slurry is coated on the surface of copper foil at a speed of 4 m / min and dried at 100°C and rolled at room temperature to obtain negative electrode sheet;

[0077] (4) The positive electrode sheet in step (2) and the negative electrode sheet and separator in step (3) are wound together to obtain the first battery cell;

[0078] (5) The first battery cell obtained in step (4) is first packaged using an aluminum plastic film, baked in a vacuum oven at 85°C, and injected with liquid to obtain a second battery cell;

[0079] (6) The second battery cell obtained in step (5) is subjected to formation at a temperature of 80°C and a pressure of 1.2 MPa, the conductive adhesive begins to be secondarily heat-cured, and then the second packaging, capacity testing, and edge folding are performed to obtain a safety battery cell.

[0080] Example 2

[0081] As shown in Figure 2 , the present embodiment provides a positive electrode sheet with the tab in the middle, which includes a current collector 1, a primer paste 2, a conductive adhesive 21, a ceramic material 23, and a positive electrode material 3. The primer paste 2 includes the conductive adhesive 21 and the ceramic material 23, and is coated on both surfaces of the current collector 1.

[0082] The difference between the present embodiment and Example 1 is that the functional material in the primer paste of the present embodiment is the ceramic material 23. The rest is the same as Example 1, which will not be repeated here.

[0083] Comparative Example 1

[0084] The difference between the present comparative example and Example 1 is that the primer paste of the present comparative example does not contain the conductive adhesive 21. The rest is the same as Example 1, which will not be repeated here.

[0085] Comparative Example 2

[0086] The difference between the present comparative example and Example 2 is that the primer paste of the present comparative example does not contain the conductive adhesive 21. The rest is the same as Example 2, which will not be repeated here.

[0087] Comparative Example 3

[0088] The difference between the present comparative example and Example 1 is that the present comparative example does not contain the primer paste 2. The rest is the same as Example 1, which will not be repeated here.

[0089] The safety battery cells obtained in Examples 1-2 and Comparative Examples 1-3 are subjected to needle puncture test, high temperature cycle test, and discharge at 0°C with 0.2C, and the test results are shown in the following table:

[0090]

[0091]

[0092] From the test results in the table, it can be seen that the qualified rate of the battery cell of the application is 100% when the needle test is carried out, the capacity of the battery cell is larger, the capacity retention rate is still higher than 87% after 500 cycles under high temperature conditions, the expansion rate of the battery cell is relatively small, the battery cell of the application has a lower internal resistance, and the discharge capacity of the battery cell is stronger when discharged at 0.2C under 0℃.

[0093] From the test results of examples 1-2 and comparative examples 1-3, it can be seen that the safety and high temperature resistance of the battery cell of the application are higher, and the capacity is larger; further, from the test results of examples 1, 2 and comparative examples 1, 2, it can be seen that examples 1, 2 using conductive glue and lithium iron phosphate material or ceramic material to bottom coat the current collector have higher safety performance and battery cell capacity than comparative examples 1, 2 using only lithium iron phosphate material or ceramic material to bottom coat the current collector, the battery capacity retention rate after 500 cycles under high temperature is much higher, the expansion rate of the battery cell is much smaller, and the internal resistance of the battery cell is greatly reduced, and the discharge capacity of the battery cell is stronger when discharged at 0.2C under 0℃.

[0094] From the test results of comparative example 3 and example 2, it can be seen that the current collector and the positive electrode material without bottom coating are made into a positive electrode sheet, and the battery cell made of the positive electrode sheet has a higher battery cell capacity and a lower internal resistance, but its safety performance is poor, the high temperature cycle capacity retention rate is low, and the expansion rate of the high temperature cycle battery cell is high.

[0095] In summary, the new bottom coating slurry of the application can take into account the safety performance of the battery cell, and solve the problems of large internal resistance, poor kinetics, low specific capacity and the like of the existing safety battery cell, and is a safety battery cell technology taking into account excellent kinetics and low internal resistance.

[0096] Based on the disclosure and teaching of the above description, those skilled in the art of the present application can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the above specific embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art on the basis of the present application all fall within the protection scope of the present application. In addition, although some specific terms are used in the present specification, these terms are only for convenience of description and do not constitute any limitation on the present application.

Claims

1. A primer slurry, characterized in that, It includes conductive adhesive and functional materials, wherein the functional materials are ceramic materials; the conductive adhesive comprises the following raw materials in the following mass percentages: epoxy resin prepolymer: 2-8%, curing agent: 1-5%, conductive filler: 3-10%, solvent: 80-90%; The curing agent in the conductive adhesive exerts its curing effect at a temperature of 130–150°C.

2. The primer slurry according to claim 1, characterized in that, The mass ratio of the conductive adhesive to the functional material is (35-45):(55-65).

3. The primer slurry according to claim 1, characterized in that, The ceramic material is at least one of alumina, zirconium oxide, boehmite, magnesium oxide, silicon oxide, and calcium oxide.

4. The primer slurry according to claim 1, characterized in that, The epoxy resin prepolymer is at least one of glycidyl ether bisphenol A type epoxy resin and glycidyl ether bisphenol F type epoxy resin.

5. A primer slurry according to claim 1, characterized in that, The curing agent is at least one of triethylamine, 2-ethyl-4-methylimidazole and dimethylimidazole; the conductive filler is a mixture of single-walled carbon nanotubes and conductive carbon.

6. A primer slurry according to claim 5, characterized in that, The mass ratio of the single-walled carbon nanotubes to the conductive carbon is 1:

1.

7. A primer slurry according to claim 1, characterized in that, The solvent is at least one selected from N-methylpyrrolidone, acetone, ethanol, propanol, isopropanol, and ethylene glycol.

8. A positive electrode plate, characterized in that, It includes a positive electrode slurry and a positive electrode current collector, wherein the positive electrode current collector is a positive electrode current collector coated with the primer slurry according to any one of claims 1-7.

9. A safety battery cell, characterized in that, It includes a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode as described in claim 8.

10. A method for preparing a safe battery cell according to claim 9, characterized in that, Includes the following steps: (1) Preparation of positive current collector containing primer slurry: The conductive adhesive and functional material are mixed and stirred to disperse evenly to obtain primer slurry. The primer slurry is coated on both surfaces of the positive current collector and dried to obtain positive current collector containing primer slurry. (2) Preparation of positive electrode sheet: Dissolve the positive electrode material, conductive agent and binder in N-methylpyrrolidone solution, stir thoroughly to disperse them evenly, and obtain positive electrode slurry. Coat the two surfaces of the positive electrode current collector containing the base coating slurry in step (1), dry and hot press, and the conductive adhesive in the base coating slurry begins to undergo the first heat curing to obtain positive electrode sheet. (3) Fabrication of negative electrode sheet: Dissolve negative electrode material, conductive agent and binder in deionized water, stir to disperse them evenly to obtain negative electrode slurry, coat it on the surface of negative electrode current collector, dry it and roll it at room temperature to obtain negative electrode sheet; (4) The positive electrode sheet in step (2) and the negative electrode sheet and separator in step (3) are wound together to obtain the first battery cell; (5) The first battery cell obtained in step (4) is first encapsulated, baked and injected with electrolyte using aluminum-plastic film to obtain the second battery cell; (6) The second battery cell obtained in step (5) is formed, the conductive adhesive is thermally cured for the second time, and then it is encapsulated, capacity divided and folded for the second time to obtain a safe battery cell.

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