Preparation method of positive pole piece, positive pole piece and secondary battery

Abstract

The invention relates to a preparation method of a positive pole piece, which comprises the following steps: S1, mixing a polymer monomer, a plastic crystal compound, a lithium salt and an initiator to obtain a precursor solution; s2, mixing the positive electrode active material, a conductive agent, a binder and a solvent to obtain positive electrode active material slurry; s3, the precursor solution prepared in the step S1 and the positive active material slurry prepared in the step S2 are mixed and stirred, mixed slurry is obtained, the stirring temperature is lower than 30 DEG C, the stirring speed is lower than 500 rpm, and the stirring time is shorter than 120 min; and S4, coating a current collector with the mixed slurry, and drying to obtain the positive pole piece. According to the invention, the precursor solution of the polymer electrolyte, which is obtained by uniformly stirring the polymer monomer, the plastic crystal compound, the lithium salt and the initiator, is creatively added at low temperature and low speed in the later stage of homogenization, and is stirred for a short time, so that polymerization in the homogenization process is avoided, and subsequent preparation of the positive pole piece and application of the positive pole piece in a secondary battery are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery materials, and particularly to a method for preparing a positive electrode sheet, the positive electrode sheet, and a secondary battery. Background Art

[0002] Lithium-ion batteries occupy a large market of secondary batteries due to their advantages such as high energy density, high working voltage, and long cycle life, and are widely used in various scenarios such as electric vehicles, 3C electronics, and large-scale energy storage. With the continuous expansion of their application scope, in addition to pursuing higher energy density and faster charging speed, higher safety attributes have become the core goal of the product.

[0003] Currently, it is generally believed that the key factor for thermal runaway of lithium-ion batteries is the strong chemical reaction between the negative electrode material, the positive electrode material, and the electrolyte, releasing a huge amount of energy. Therefore, completely or partially replacing the liquid electrolyte with a solid electrolyte is considered to be able to improve the safety of the battery cell to a considerable extent. Due to the limitations of the development of basic materials and process equipment, partial solidification of the electrolyte is an effective means to improve the safety of the battery cell with application prospects at the current stage. However, how to quickly and effectively introduce it into the existing mass production process of the battery cell is still one of the difficult problems that researchers and engineers are working hard to overcome. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a method for preparing a positive electrode sheet. The positive electrode sheet prepared by the present invention containing a polymer electrolyte can effectively improve the safety, cycle performance, and rate performance of the battery cell when applied in the battery cell; and this preparation method is consistent with the existing mature lithium-ion battery cell preparation process, without significant adjustment of the process flow and equipment update, and has considerable application prospects.

[0005] In the first aspect of the present invention, the method for preparing a positive electrode sheet provided by the present invention includes

[0006] S1. Mixing a polymer monomer, a plastic crystal compound, a lithium salt, and an initiator to obtain a precursor solution;

[0007] S2. Mixing a positive electrode active material, a conductive agent, a binder, and a solvent to obtain a positive electrode active material slurry;

[0008] S3. Mixing the precursor solution prepared in step S1 with the positive electrode active material slurry prepared in step S2, and stirring to obtain a mixed slurry, wherein the stirring temperature is lower than 30 °C, the stirring speed is lower than 500 rpm, and the stirring time is less than 120 min;

[0009] S4. Coating the mixed slurry on a current collector and drying to obtain the positive electrode sheet.

[0010] In the second aspect of the present invention, the present invention provides a secondary battery, which includes a positive electrode sheet prepared by the foregoing preparation method.

[0011] In the third aspect of the present invention, the present invention provides a device, which includes the foregoing secondary battery.

[0012] Beneficial effects:

[0013] By means of the preparation method of the present invention, the precursor solution of the polymer electrolyte obtained by uniformly stirring the polymer monomer, the plastic crystal compound, the lithium salt and the initiator is added at a low temperature and low speed in the later stage of homogenization and stirred for a short time, avoiding polymerization during the homogenization process. Controlling the rotation speed, temperature and time within a small range can obtain an ideal mixed slurry, that is, the viscosity of the mixed slurry and the degree of polymerization of the polymer monomer are within a suitable range, which is beneficial to the subsequent preparation of the positive electrode sheet and its application in the secondary battery. In the positive electrode sheet containing the polymer electrolyte prepared, the electrolyte polymerizes in-situ on the surface of the positive electrode active material particles and in the particle pores of the electrode sheet. The electrode sheet prepared by this method can effectively improve the safety, cycle performance and rate performance of the battery cell. In addition, this preparation method is consistent with the existing mature lithium-ion battery cell preparation process, without significant adjustment of the process flow and equipment update, and has considerable application prospects.

[0014] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given and described in detail as follows. Detailed embodiments

[0015] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as a limitation of the present application.

[0016] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0017] Terms:

[0018] In this text, the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a series of elements includes not only those elements but also other elements not expressly listed, or elements that are inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0019] In the description herein, unless otherwise specified, "above" and "below" include the number itself.

[0020] Unless otherwise specified, the terms used in the present invention have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present invention can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present invention).

[0021] The list of items connected by the terms "at least one of", "at least one in", "at least one kind in", or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single component or multiple components. Item B may include a single component or multiple components. Item C may include a single component or multiple components.

[0022] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0023] In some embodiments of the present invention, the present invention provides a method for preparing a positive electrode sheet, the method comprising:

[0024] S1. Mixing a polymer monomer, a plastic crystal compound, a lithium salt, and an initiator to obtain a precursor solution;

[0025] S2. Mixing a positive electrode active material, a conductive agent, a binder, and a solvent to obtain a positive electrode active material slurry;

[0026] S3. Mix the precursor solution prepared in step S1 with the positive electrode active material slurry prepared in step S2, and stir to obtain a mixed slurry, wherein the stirring temperature is lower than 30 °C, the stirring speed is lower than 500 rpm, and the stirring time is less than 120 min;

[0027] S4. Coating the mixed slurry on a current collector and drying to obtain the positive electrode plate.

[0028] In the present invention, a solid electrolyte is introduced into the battery by in-situ polymerization. The precursor solution is added at a low temperature and low speed in the later stage of homogenization and stirred for a short time, which can avoid polymerization during the homogenization process; during the drying process, preliminary in-situ polymerization of the polymer occurs, and in the subsequent baking process of the electrode plate in a vacuum environment, on the one hand, further polymerization occurs, and on the other hand, residual monomers are removed, thereby preparing the final positive electrode plate.

[0029] The method of the present invention avoids adding a polymer precursor, a cross-linking agent, and an initiator to the positive electrode slurry, thereby avoiding the difficult control of the degree of polymerization and the viscosity of the slurry caused by this method. Its viscosity may change over time, thereby affecting the thickness uniformity during coating.

[0030] The method of the present invention avoids post-treatment of the electrode plate, does not need to consider the problem of contamination of the electrolyte precursor solution to the electrode tab, and does not need to add processes and corresponding equipment such as electrode plate coating and heat curing.

[0031] The method of the present invention avoids in-situ polymerization in the formation stage of the battery cell. The solid components after polymerization will not affect the sufficient infiltration of the electrolyte in the battery cell to the dry battery cell, will not affect the uniformity of formation, and will not block the exhaust after formation.

[0032] When the positive electrode plate prepared by the preparation method of the present invention is applied to a secondary battery, the formed polymer electrolyte can effectively provide ion conduction, effectively bond each component in the positive electrode, has a low film resistance, and can resist the performance deterioration caused by the expansion and contraction of the electrode, thereby effectively ensuring ion and electron conduction during the cycling process and improving the cycling performance and rate performance of the prepared battery.

[0033] In addition, the in-situ generated polymer effectively binds the electrolyte, increases the liquid retention amount, and improves the safety of the prepared battery cell by reducing the free electrolyte in the positive electrode. At the same time, it prevents the electrolyte from eroding the positive electrode active material and inhibits the dissolution of transition metals to a certain extent. In summary, the application of the positive electrode plate containing a polymer electrolyte prepared by the present invention in a battery cell can effectively improve the safety, cycling, and rate performance of the battery cell. In addition, this preparation method is consistent with the existing mature lithium-ion battery cell preparation process, does not require significant adjustment of the process flow and equipment update, and has considerable application prospects.

[0034] In some embodiments of the present invention, the step S1 includes mixing a polymer monomer, a plastic crystal compound, and a lithium salt, and then adding an initiator in an inert atmosphere to obtain a precursor solution after mixing;

[0035] In some embodiments of the present invention, the inert atmosphere includes, but is not limited to, an argon atmosphere.

[0036] In some embodiments of the present invention, the step S4 includes coating the mixed slurry on a current collector, drying, and rolling to obtain the positive electrode sheet.

[0037] In some embodiments of the present invention, the step S4 includes coating the mixed slurry on a current collector, drying, rolling, and vacuum baking to obtain the positive electrode sheet.

[0038] In some embodiments of the present invention, the mass ratio of the precursor solution to the positive electrode active material is (0.5 - 10):100.

[0039] In some embodiments of the present invention, the stirring temperature is lower than 30°C. In some embodiments of the present invention, the stirring temperature is 0.01°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, or a range composed of any two of these values. If the temperature is too high, the polymerization of the monomer is initiated in advance, affecting the stability of the viscosity of the positive electrode slurry.

[0040] In some embodiments of the present invention, the stirring speed is lower than 500 rpm. In some embodiments of the present invention, the stirring speed is 0.01 rpm, 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 500 rpm, or a range composed of any two of these values. If the rotation speed is too high, the solution temperature will rise with stirring, which will initiate the polymerization of the monomer, affecting the stability of the viscosity of the positive electrode slurry.

[0041] In some embodiments of the present invention, the stirring time is less than 120 min. In some embodiments of the present invention, the stirring time is 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, or a range composed of any two of these values. If the time is too long, the reaction degree of the monomer increases, and the molecular weight increases with time, affecting the stability of the viscosity of the positive electrode slurry.

[0042] Therefore, controlling the rotational speed, temperature, and time within the above ranges can yield an ideal mixed slurry, i.e., the viscosity of the mixed slurry and the degree of polymerization of the polymer monomer are within appropriate ranges, which is beneficial to the subsequent preparation of the positive electrode sheet and its application in secondary batteries.

[0043] In some embodiments of the present invention, the drying temperature in the S4 step is 60°C - 120°C. In some embodiments of the present invention, the drying temperature in the S4 step is 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, or the range composed of any two of these values.

[0044] In some embodiments of the present invention, the drying time in the S4 step is 2 min - 300 min. In some embodiments of the present invention, the drying time in the S4 step is 2 min, 5 min, 10 min, 20 min, 40 min, 60 min, 80 min, 100 min, 200 min, 300 min, or the range composed of any two of these values.

[0045] It can be understood that if the drying temperature is too low, the solvent evaporation rate is slow, resulting in too long a preparation time; while if the drying temperature is too high, due to the fast solvent evaporation rate, the viscosity of the liquid film formed after coating the mixed slurry increases too fast, resulting in many pinholes on the surface of the formed positive electrode sheet or even a morphology similar to "orange peel", and further deteriorating the performance of the secondary battery. Controlling the drying temperature and time within the above ranges is beneficial to achieving practical applications in commerce.

[0046] In some embodiments of the present invention, the S4 step includes roll-pressing the dried positive electrode sheet. In some embodiments of the present invention, the positive electrode sheet is roll-pressed to a compaction density of 2.5 g / cm 3 - 3.8 g / cm 3 .

[0047] In some embodiments of the present invention, the S4 step includes vacuum baking the roll-pressed positive electrode sheet.

[0048] In some embodiments of the present invention, the vacuum baking temperature in the S4 step is 60°C - 120°C. In some embodiments of the present invention, the vacuum baking temperature in the S4 step is 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, or the range composed of any two of these values.

[0049] In some embodiments of the present invention, the vacuum baking time in step S4 is 1 h - 24 h. In some embodiments of the present invention, the vacuum baking time in step S4 is 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, or the range composed of any two of these values.

[0050] It can be understood that the time of vacuum baking is negatively correlated with the temperature of vacuum baking. The higher the temperature of vacuum baking, the shorter the time of vacuum baking; the lower the temperature of vacuum baking, the longer the time of vacuum baking.

[0051] In some embodiments of the present invention, the vacuum degree during baking is not greater than -95 KPa.

[0052] In some embodiments of the present invention, the polymer monomer is a nitrile compound containing an unsaturated bond. In some embodiments of the present invention, the polymer monomer is an acrylonitrile derivative. Acrylonitrile derivatives refer to a class of compounds with acrylonitrile structure derived by substituting hydrogen atoms or atomic groups in acrylonitrile with other atoms or atomic groups. In some embodiments of the present invention, the polymer monomer includes at least one of acrylonitrile, methacrylonitrile, 2-butenenitrile, (E)-1,2-dicyanoethylene.

[0053] In some embodiments of the present invention, the plastic crystal compound includes succinonitrile. In some embodiments of the present invention, based on the mass of the polymer monomer, the mass content of the plastic crystal compound is 20% - 200%.

[0054] In some embodiments of the present invention, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium tetrafluoroborate LiBF4, lithium bis(oxalato)borate LiBOB, lithium difluoro(oxalato)borate LiODFB. In some embodiments of the present invention, based on the mass of the polymer monomer, the mass content of the lithium salt is 2% - 20%.

[0055] In some embodiments of the present invention, the initiator includes at least one of 2,2'-azobisisobutyronitrile, benzoyl peroxide, bis(4-tert-butylcyclohexyl) peroxydicarbonate, lauroyl peroxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,2-dimethoxy-2-phenylacetophenone. In some embodiments of the present invention, based on the mass of the polymer monomer, the mass content of the initiator is 0.2% - 5%.

[0056] In some embodiments of the present invention, the solvent in step S2 is selected from N-methylpyrrolidone, but is not limited thereto.

[0057] In some embodiments of the present invention, the positive electrode sheet provided by the present invention includes a positive electrode current collector and a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material and a polymer electrolyte.

[0058] In some embodiments of the present invention, the polymer electrolyte is present on the surface of the positive electrode active material or in the pores of the positive electrode sheet.

[0059] In some embodiments of the present invention, based on the total mass of the positive electrode material layer, the mass content of the polymer electrolyte is 0.001%-5%. In some embodiments of the present invention, based on the total mass of the positive electrode material layer, the mass content of the polymer electrolyte is 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5% or a range composed of any two of these values.

[0060] In some embodiments of the present invention, the positive electrode active material may include a composite oxide containing lithium and at least one element selected from cobalt, manganese, and nickel. The specific type of the positive electrode active material is not specifically limited and can be selected according to requirements. The positive electrode active material is arbitrarily selected from at least one of lithium cobalt oxide LiCoO2 (LCO), lithium nickel manganese cobalt ternary material (NCM), lithium iron phosphate, and lithium manganese oxide. They can be used alone or in any combination of two or more.

[0061] In some embodiments of the present invention, the positive electrode active material includes a high-nickel and strong-oxidizing positive electrode. In some embodiments of the present invention, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, and lithium iron manganese phosphate. In some embodiments of the present invention, the positive electrode active material is a high-nickel and strong-oxidizing active material. In some embodiments of the present invention, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel manganese oxide. In some embodiments of the present invention, based on the total mass of the positive electrode material layer, the mass ratio of the positive electrode active material is 93% to 98%. In some embodiments of the present invention, based on the total mass of the positive electrode material layer, the mass content of the positive electrode active material is 93%, 94%, 95%, 96%, 97%, 98% or a range composed of any two of these values.

[0062] In some embodiments of the present invention, the positive electrode material layer further includes a binder. In some embodiments of the present invention, non-limiting examples of the binder include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto. In some embodiments of the present invention, the binder is polyvinylidene fluoride (PVDF). In some embodiments of the present invention, based on the total mass of the positive electrode material layer, the mass content of the binder is 0.3% - 5%.

[0063] In some embodiments of the present invention, the positive electrode material layer further includes a conductive agent. In some embodiments of the present invention, the conductive material can include any conductive material as long as it does not cause chemical changes. Non-limiting examples of the conductive agent include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof, but are not limited thereto. In some embodiments of the present invention, the conductive agent is carbon black (SP), carbon nanotube (CNT), vapor-grown carbon fiber reinforcement (VGCF), graphene, etc. In some embodiments of the present invention, based on the total mass of the positive electrode material layer, the mass content of the conductive agent is 0.3% - 3%.

[0064] In some embodiments of the present invention, the positive electrode current collector can be aluminum foil (Al), carbon-coated aluminum foil, but is not limited thereto. In some embodiments of the present invention, the positive electrode current collector is aluminum foil.

[0065] In some embodiments of the present invention, the present invention provides a secondary battery, and the secondary battery includes a positive electrode tab prepared by the foregoing method.

[0066] In some embodiments of the present invention, the secondary battery provided by the present invention further includes a negative electrode tab, and the negative electrode tab includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. In some embodiments of the present invention, the negative electrode active material layer of the present invention includes a negative electrode active material, a binder, and a conductive agent. The specific types of the negative electrode active material are not specifically limited and can be selected according to requirements. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesocarbon microbeads (abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12, one or more of Li-Al alloys. Non-limiting examples of the carbon material include crystalline carbon, amorphous carbon, and mixtures thereof. The crystalline carbon can be amorphous or in the form of flakes, small flakes, spheres, or fibers of natural graphite or artificial graphite. The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc. In some embodiments of the present invention, the negative electrode active material of the present invention is graphite.

[0067] In some embodiments of the present invention, the negative electrode active material layer may include a binder. The binder improves the binding between the negative electrode active material particles and the binding between the negative electrode active material and the current collector. In some embodiments of the present invention, non-limiting examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0068] In some embodiments of the present invention, the negative electrode active material layer includes a conductive agent, so that the electrode sheet has conductivity. The conductive agent can include any conductive material as long as it does not cause chemical changes. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0069] In some embodiments of the present invention, the negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0070] In some embodiments of the present invention, a separator is provided between the positive electrode and the negative electrode of the electrochemical device of the present invention to prevent short circuit. The material and shape of the separator used in the electrochemical device of the present invention are not particularly limited, and it can be any technology disclosed in the prior art.

[0071] In some embodiments of the present invention, the separator includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present invention, etc.

[0072] In some embodiments of the present invention, the separator may include a base material layer and a surface treatment layer. The base material layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base material layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide.

[0073] Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

[0074] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0075] The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from one or a combination of several of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from one or a combination of several of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0076] The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0077] The secondary battery according to the present invention further includes an electrolyte. In some embodiments of the present invention, the electrolyte includes a lithium salt and a solvent.

[0078] In some embodiments of the present invention, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB). In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium difluoro(oxalato)borate (LiDFOB). In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF6). In some embodiments, the mass percentage of lithium hexafluorophosphate in the lithium salt is greater than 50%. In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 mol / L - 2 mol / L. In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 mol / L - 2 mol / L or a range composed of any two of these values. In some embodiments, the concentration of the lithium salt in the electrolyte is 1 mol / L.

[0079] In some embodiments of the present invention, the solvent can be selected from one or several of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). In some embodiments of the present invention, the solvent is a linear carbonate solvent. The linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, fluoroethylene carbonate, and dipropyl carbonate. In some embodiments of the present invention, the solvent is a mixture of ethyl methyl carbonate, dimethyl carbonate, and fluoroethylene carbonate. In some embodiments of the present invention, the volume ratio of ethyl methyl carbonate, dimethyl carbonate, and fluoroethylene carbonate in the solvent is EMC:DMC:FEC = 5:2:2.

[0080] In some embodiments of the present invention, the electrolyte may optionally further include additives. For example, the additives may include negative electrode film-forming additives, or may include positive electrode film-forming additives, or may also include additives capable of improving certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature performance of the battery, and the like.

[0081] In some embodiments of the present invention, the secondary battery of the present invention includes the above-mentioned positive electrode sheet, negative electrode sheet, separator, electrolyte, etc., but is not limited thereto.

[0082] In some embodiments of the present invention, the secondary battery of the present invention may include an outer package, and the outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a pouch soft package. The material of the soft package may be plastic, such as one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0083] In some embodiments of the present invention, the present invention also provides a battery module. The battery module includes the above-mentioned secondary battery. Since the battery module of the present invention adopts the above-mentioned secondary battery, it has at least the same advantages as the secondary battery. The number of secondary batteries included in the battery module of the present invention may be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0084] In some embodiments of the present invention, the present invention also provides a battery pack, which includes the above-mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0085] In some embodiments of the present invention, the present invention also provides a device, which includes but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, energy storage systems, etc. In order to meet the high power and high energy density requirements of the device for secondary batteries, battery packs or battery modules can be used.

[0086] In some embodiments of the present invention, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device usually requires being thin and light, and a secondary battery can be used as the power source.

[0087] The following further elaborates on the present application in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0088] Examples and comparative examples:

[0089] Example 1

[0090] The monomer of the polymer electrolyte, acrylonitrile, the plastic crystal compound, succinonitrile, and the lithium salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), were successively added to a stirring tank in a mass ratio of 20:20:7, stirred evenly at room temperature, purged with an inert atmosphere to remove oxygen for 2 h, and then 1.5% of the initiator, azobisisobutyronitrile (AIBN), based on the mass of the monomer was added and stirred evenly to obtain a precursor solution of the polymer electrolyte;

[0091] The high-nickel ternary material (Ni = 90%), the conductive agent (SP), and the binder, polyvinylidene fluoride (PVDF), were stirred evenly in a solvent (NMP) in a ratio of 97.8%:1.2%:1% to obtain a positive electrode active material slurry;

[0092] 0.5% of the precursor solution of the polymer electrolyte based on the mass of the positive electrode active material was added to the prepared positive electrode active material slurry, stirred at a low speed at a rate of 200 rpm for 30 min, and the temperature of the stirring tank was maintained at 25 °C to obtain a mixed positive electrode slurry;

[0093] The mixed positive electrode slurry was coated on an aluminum foil and dried at 115 °C for 4 min to preliminarily prepare a positive electrode plate of a lithium-ion battery containing a solid electrolyte; after the preliminarily prepared positive electrode plate containing the solid electrolyte was roll-pressed, it was baked in a vacuum at 115 °C for 12 h to obtain a positive electrode plate with a final compaction density of 3.65 g / cm 3 ³.

[0094] Example 2

[0095] The difference from Example 1 was that 5% of the precursor solution of the polymer electrolyte based on the mass of the positive electrode active material was added to the prepared positive electrode active material slurry, stirred at a low speed at a rate of 300 rpm for 30 min, and the temperature of the stirring tank was maintained at 20 °C to obtain a mixed positive electrode slurry.

[0096] Example 3

[0097] The difference from Example 1 was that 2% of the precursor solution of the polymer electrolyte based on the mass of the positive electrode active material was added to the prepared positive electrode active material slurry, stirred at a low speed at a rate of 400 rpm for 20 min, and the temperature of the stirring tank was maintained at 30 °C to obtain a mixed positive electrode slurry.

[0098] Example 4

[0099] The difference from Example 2 was that the monomer of the polymer electrolyte, acrylonitrile, the plastic crystal compound, succinonitrile, and the lithium salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), were successively added to a stirring tank in a ratio of 20:10:7.

[0100] Stir at a low speed of 300 rpm for 30 min, and keep the temperature of the stirring tank at 20 °C to obtain the mixed positive electrode slurry.

[0101] Example 5

[0102] The difference from Example 2 is that the monomer acrylonitrile of the polymer electrolyte, the plastic crystal compound succinonitrile, and the lithium salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are sequentially added to the stirring tank in a ratio of 20:30:7.

[0103] Stir at a low speed of 200 rpm for 30 min, and keep the temperature of the stirring tank at 25 °C to obtain the mixed positive electrode slurry.

[0104] Example 6

[0105] The difference from Example 2 is that 2-butenenitrile of the polymer electrolyte, the plastic crystal compound succinonitrile, and the lithium salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are sequentially added to the stirring tank in a ratio of 20:20:7.

[0106] Stir at a low speed of 300 rpm for 60 min, and keep the temperature of the stirring tank at 10 °C to obtain the mixed positive electrode slurry.

[0107] Comparative Example 1

[0108] Stir the high-nickel ternary material (Ni = 90%), the conductive agent SP, and the polyvinylidene fluoride (PVDF) binder evenly in the NMP solvent in a ratio of 97.8%:1.2%:1% to prepare the positive electrode active material slurry;

[0109] Coat the positive electrode active material slurry on the aluminum foil and dry it at 115 °C for 4 min to preliminarily prepare the positive electrode plate of the lithium-ion battery without the solid electrolyte;

[0110] After rolling the positive electrode plate without the solid electrolyte, perform vacuum baking of the electrode plate at 115 °C for 12 h to prepare the positive electrode plate with a final tap density of 3.65 g / cm 3 of the positive electrode plate.

[0111] Comparative Example 2

[0112] The difference from Example 2 is that the polymer electrolyte precursor solution accounting for 5% of the mass of the positive electrode active material is added to the prepared positive electrode active material slurry, stirred at a rate of 3000 rpm for 60 min, and the temperature of the stirring tank is kept at 30 °C to obtain the mixed positive electrode slurry.

[0113] Comparative Example 3

[0114] The difference from Example 2 is as follows: A polymer electrolyte precursor solution accounting for 5% of the mass of the positive electrode active material is added to the prepared positive electrode active material slurry, stirred at a rate of 500 rpm for 60 min, and the temperature of the stirring tank is maintained at 50 °C to obtain a mixed positive electrode slurry.

[0115] Comparative Example 4

[0116] The difference from Example 2 is as follows: A polymer electrolyte precursor solution accounting for 5% of the mass of the positive electrode active material is added to the prepared positive electrode active material slurry, stirred at a rate of 500 rpm for 400 min, and the temperature of the stirring tank is maintained at 30 °C to obtain a mixed positive electrode slurry.

[0117] Comparative Example 5

[0118] The difference from Example 2 is as follows: A polymer electrolyte precursor solution accounting for 5% of the mass of the positive electrode active material is added to the prepared positive electrode active material slurry, stirred at a rate of 2000 rpm for 300 min, and the temperature of the stirring tank is maintained at 60 °C to obtain a mixed positive electrode slurry.

[0119] Negative electrode sheet, separator, electrolyte

[0120] The mass contents of graphite, carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in the negative electrode sheet are 95.5%, 1%, 1.5%, and 2% respectively. The negative electrode sheet is prepared according to the conventional negative electrode sizing, stirring, and coating and sheet-making process conditions.

[0121] The separator is a double-sided ceramic-coated PE separator;

[0122] The electrolyte is 1 M LiPF6 electrolyte (volume ratio EMC:DMC:FEC = 5:2:2);

[0123] Testing method:

[0124] 1. Rate performance of the lithium battery

[0125] Rate discharge capacity test:

[0126] (1) At 25 ± 2 °C, stand for 5 min;

[0127] (2) At 25 ± 2 °C, charge at 1 / 10C rated CC-CV to 4.25 V, with the cut-off current being 1 / 20C rated;

[0128] (3) At 25 ± 2 °C, stand for 10 min;

[0129] (4) At 25 ± 2 °C, discharge at 1 / 10C rated to 2.5 V;

[0130] (5) At 25 ± 2 °C, stand for 10 min;

[0131] (6) Repeat steps (2) to (5) twice;

[0132] (7) At 25 ± 2 °C, charge in CC-CV mode at 1 / 10C rated current up to 4.25 V, with the cut-off current being 1 / 20C rated current;

[0133] (8) At 25 ± 2 °C, let it stand for 10 min;

[0134] (9) At 25 ± 2 °C, discharge at 1 / 5C rated current down to 2.5 V;

[0135] (10) At 25 ± 2 °C, let it stand for 10 min;

[0136] (11) Repeat steps (7) to (10) twice;

[0137] (12) At 25 ± 2 °C, charge in CC-CV mode at 1 / 10C rated current up to 4.25 V, with the cut-off current being 1 / 20C rated current;

[0138] (13) At 25 ± 2 °C, let it stand for 10 min;

[0139] (14) At 25 ± 2 °C, discharge at 1 / 3C rated current down to 2.5 V;

[0140] (15) At 25 ± 2 °C, let it stand for 10 min;

[0141] (16) Repeat steps (12) to (15) twice;

[0142] Under each rate condition, repeat the above cycle. Charging: Charge in CC-CV mode at 1 / 10C rated current up to 4.25 V, with the cut-off current being 1 / 20C rated current; Discharging: Record the discharge capacity under the conditions of different discharge currents of 1 / 2C, 1C, 2C, and 1 / 10C respectively.

[0143] Perform electrochemical tests on Examples 1 - 6 and Comparative Examples 1 - 5, and the test results are shown in Table 1:

[0144] Among them, the content of the polymer electrolyte is based on the total mass of the positive electrode active material.

[0145] [Table 1]

[0146]

[0147] Compared with Comparative Examples 2-5, it can be seen from the data of Examples 1-6 that the electrodes prepared with different raw material ratios of the precursor solution and different mass ratios of the precursor solution to the cathode active material exhibit better electrical properties under the conditions of low-speed, low-temperature, and short-time stirring. It can be seen from Comparative Example 1 and Comparative Examples 3, 4, and 5 that when inappropriate stirring process conditions are adopted, the performance of the final electrode will be deteriorated instead, although Comparative Examples 3, 4, and 5 use a precursor solution with a higher mass ratio.

[0148] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be construed as limiting the present invention, and changes, substitutions, and modifications can be made to the embodiments without departing from the spirit, principles, and scope of the present invention.

Claims

1. A method for preparing a positive electrode plate, characterized in that, The method includes S1. Mixing a polymer monomer, a plastic crystal compound, a lithium salt, and an initiator to obtain a precursor solution; S2. Mixing a positive electrode active material, a conductive agent, a binder, and a solvent to obtain a positive electrode active material slurry; S3. Mixing the precursor solution prepared in step S1 with the positive electrode active material slurry prepared in step S2, and stirring to obtain a mixed slurry, wherein the stirring temperature is lower than 30°C, the stirring speed is lower than 500 rpm, and the stirring time is less than 120 min; S4. Coating the mixed slurry on a current collector, and drying to obtain the positive electrode sheet.

2. The method for preparing a positive electrode plate according to claim 1, characterized in that, The mass ratio of the precursor solution to the positive electrode active material is (0.5-10):

100.

3. The method for preparing a positive electrode plate according to claim 1, characterized in that, Step S4 includes rolling the dried positive electrode sheet.

4. The method for preparing a positive electrode plate according to claim 3, characterized in that, The drying temperature is 60°C - 120°C; and / or The drying time is 2 min - 300 min; and / or Roll press the positive electrode sheet until the tap density of the positive electrode sheet is 2.5 g / cm 3 - 3.8 g / cm 3 ; 5. The method for preparing a positive electrode plate according to claim 3, characterized in that, Step S4 includes vacuum baking the rolled positive electrode sheet.

6. The method for preparing a positive electrode plate according to claim 5, characterized in that, The baking temperature is 60°C - 120°C; and / or The baking time is 1 h - 24 h; and / or The vacuum degree during baking is not greater than -95 KPa.

7. The method for preparing a positive electrode plate according to claim 1, characterized in that, The polymer monomer is a nitrile compound containing an unsaturated bond; and / or The plastic crystal compound includes succinonitrile; and / or The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide salt LiFSI, lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium tetrafluoroborate LiBF4, lithium bis(oxalato)borate LiBOB, and lithium difluoro(oxalato)borate LiODFB; and / or The initiator includes at least one of 2,2'-azobisisobutyronitrile, benzoyl peroxide, bis(4-tert-butylcyclohexyl), peroxydicarbonate, lauroyl peroxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2,2-dimethoxy-phenylacetophenone.

8. The method for preparing a positive electrode plate according to claim 1, characterized in that, The polymer monomer includes at least one of acrylonitrile, methacrylonitrile, 2-butenenitrile, and (E)-1,2-dicyanoethylene; and / or Based on the mass of the polymer monomer, the mass content of the plastic crystal compound is 20% - 200%; and / or Based on the mass of the polymer monomer, the mass content of the lithium salt is 2% - 20%; and / or Based on the mass of the polymer monomer, the mass content of the initiator is 0.2% - 5%.

9. A secondary battery, characterized in that, The secondary battery includes a positive electrode sheet prepared by the method according to any one of claims 1-8.

10. A device, characterized in that, The device includes the secondary battery according to claim 9.

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