Positive pole piece, preparation method and secondary battery

Abstract

The invention relates to a positive pole piece and a preparation method thereof, and a secondary battery comprising the positive pole piece. The positive pole piece comprises a positive current collector; the positive electrode material layer is arranged on the surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active material and a functional polymer shown in the formula (1) # imgabs0 #, and n is equal to 10-10000. The functional polymer captures active oxygen released from the positive electrode under a high-temperature condition, so that the reaction activity of the full-electricity positive electrode and the electrolyte is reduced, the heat release power and heat release amount of the full-electricity positive electrode material and the electrolyte are greatly reduced, and the safety of the battery is improved.

Description

Technical Field

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

[0002] As electric vehicles become more and more popular, the safety of battery cells has become one of the main concerns of consumers. The main reason for the poor safety of secondary batteries is that the electrolyte used in the battery cells is carbonate as the main solvent. When there are problems such as short circuits, improper use, and heat accumulation inside the battery cells, it is easy to cause thermal runaway of the battery cells. Carbonate solvents are very flammable and explosive in the state of thermal runaway.

[0003] With the increase in energy density, it is particularly important to improve the safety of battery cells. The key factor leading to thermal runaway of battery cells is the interaction between the fully charged positive electrode material and the electrolyte. The existing positive electrode material is a transition metal oxide, which has a strong oxidizing property in the de-lithiated state. It will release singlet oxygen at high temperature, which can oxidize the electrolyte and eventually lead to thermal runaway. The commonly used method is to use solid electrolytes, which can greatly improve the safety between the fully charged positive electrode material and the electrolyte, but there are interface problems in the application process, which has been difficult to break through. There are also singlet oxygen scavengers and flame retardant additives. When the amount used is too small, the effect is relatively limited. When the amount used is relatively large, the safety improvement effect is good, but the performance degradation of the battery cell is also obvious. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a positive electrode plate. By setting a functional polymer in the positive electrode material layer, the functional polymer captures the active oxygen released in the positive electrode under high temperature conditions, reduces the reaction activity of the fully charged positive electrode and the electrolyte, greatly reduces the heat release power and heat release of the fully charged positive electrode material and the electrolyte, and improves the safety of the battery.

[0005] In a first aspect of the present invention, the positive electrode sheet provided by the present invention comprises a positive electrode current collector and a positive electrode material layer, wherein the positive electrode material layer is arranged on the surface of the positive electrode current collector, and the positive electrode material layer comprises a positive electrode active material and a polymer represented by formula (1),

[0006] Among them, n=10-10000.

[0007] In one aspect of the present invention, n=100-1000.

[0008] In a second aspect of the present invention, the present invention provides a method for preparing the above-mentioned positive electrode sheet, the method comprising:

[0009] S1: mixing a binder, a conductive agent, a positive electrode active material and a solvent to obtain a slurry;

[0010] S2: coating the slurry on the surface of the current collector, and obtaining a positive electrode sheet after drying;

[0011] S3: coating the mixed solution containing the functional polymer on the surface of the positive electrode sheet obtained in step S2 which is away from the current collector, and obtaining the positive electrode sheet after drying.

[0012] In a third aspect of the present invention, the present invention provides a secondary battery, wherein the secondary battery comprises the aforementioned positive electrode sheet or the positive electrode sheet prepared by the aforementioned method.

[0013] Beneficial effects:

[0014] The positive electrode sheet provided by the present invention has a functional polymer disposed in its positive electrode material layer, and the functional polymer is present on the surface of the positive electrode active material. The fully charged positive electrode material releases singlet oxygen at high temperature, and the singlet oxygen and the electrolyte have very strong reactivity. The functional polymer in the present invention contains a benzene ring, which gives it better steric hindrance, good stability, and good ability to capture oxygen free radicals, which reduces the reactivity of the fully charged positive electrode material and the electrolyte, that is, reduces the heat release power and heat release of the fully charged positive electrode material and the electrolyte, and improves the safety of the battery. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

[0016] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0017] the term:

[0018] In this article, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

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

[0020] Unless otherwise specified, the terms used in the present invention have the commonly known meanings generally 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 using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of the present invention).

[0021] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, 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, 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 contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain 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 are not used to limit the scope of the present invention. Specific implementation method:

[0024] In some embodiments of the present invention, the positive electrode sheet provided by the present invention comprises a positive electrode current collector and a positive electrode material layer, wherein the positive electrode material layer comprises a positive electrode active material and a functional polymer represented by formula (1).

[0025] Wherein, n = 10-10000. In some embodiments of the present invention, n = 100-1000.

[0026] In some embodiments of the present invention, the functional polymer is present on the surface of the positive electrode active material.

[0027] In some embodiments of the present invention, based on the total mass of the positive electrode material layer, the mass content of the functional polymer 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 functional polymer 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 consisting of any two of these values. If the mass content of the functional polymer is too large, the DCR of the battery will be affected; if the content is too small, the ability to suppress the release of heat from the fully charged positive electrode material is insufficient.

[0028] In some embodiments of the present invention, based on the total mass of the positive electrode material layer, the mass content of the functional polymer is 0.5%-2%.

[0029] 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 types of positive electrode active materials are not subject to specific restrictions and can be selected according to needs. The positive electrode active material is 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.

[0030] In some embodiments of the present invention, the positive electrode active material comprises a high-nickel strong oxidizing positive electrode. In some embodiments of the present invention, the positive electrode active material comprises at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, 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 strong oxidizing active material. In some embodiments of the present invention, the positive electrode active material comprises 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 content 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 consisting of any two of these values.

[0031] In some embodiments of the present invention, the positive electrode material layer also includes a binder. In some embodiments of the present invention, non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) 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%.

[0032] In some embodiments of the present invention, the positive electrode material layer also includes a conductive agent. In some embodiments of the present invention, the conductive material may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive agents 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 nanotubes (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%.

[0033] In some embodiments of the present invention, the positive electrode current collector may 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.

[0034] In some embodiments of the present invention, the present invention provides a method for preparing the above-mentioned positive electrode sheet, the method comprising:

[0035] S1: mixing a binder, a conductive agent, a positive electrode active material and a solvent to obtain a slurry;

[0036] S2: coating the slurry on the surface of the current collector, and obtaining a positive electrode sheet after drying;

[0037] S3: coating the mixed solution containing the functional polymer on the surface of the positive electrode sheet obtained in step S2 which is away from the current collector, and obtaining the positive electrode sheet after drying.

[0038] Since conventional pole pieces contain a large number of micropores, before the solution containing the functional polymer is coated on the surface of the positive electrode material layer, the positive electrode active material and the conductive agent have formed a good conductive network, and the coated functional polymer penetrates through the micropores and finally exists on the surface of the whole formed by the positive electrode active material, the conductive agent and the binder. On the one hand, the preparation method avoids the direct mixing and contact between the functional polymer and the positive electrode active material during the preparation process, which affects the contact between the conductive agent and the positive electrode active material and greatly increases the internal resistance of the battery pole piece; on the other hand, since the functional polymer exists on the surface of the positive electrode active material in the preparation method, the functional polymer plays a wrapping role, avoiding the problem of increasing the expansion rate of the positive electrode pole piece under the infiltration of the electrolyte.

[0039] In some embodiments of the present invention, the drying temperature in step S3 is 60-110°C;

[0040] In some embodiments of the present invention, the solvent in step S1 is selected from N-methylpyrrolidone, but is not limited thereto.

[0041] In some embodiments of the present invention, the solvent in step S3 is selected from at least one of ethyl acetate, tetrahydrofuran, ethylene carbonate, vinylene carbonate, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, isopropanol, acetone and butyl acetate.

[0042] In some embodiments of the present invention, the solid content of the mixed solution in step S3 is 0.5%-2%.

[0043] 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%.

[0044] 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%.

[0045] In some embodiments of the present invention, in S2 and / or S3 of the preparation method, a rolling process is also included.

[0046] In some embodiments of the present invention, the present invention provides a secondary battery, wherein the secondary battery comprises the aforementioned positive electrode sheet or the positive electrode sheet prepared by the aforementioned method.

[0047] In some embodiments of the present invention, the secondary battery provided by the present invention further includes a negative electrode plate, and the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed 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 negative electrode active materials are not subject to specific restrictions and can be selected according to needs. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon beads (abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon and mixtures thereof. Crystalline carbon can be amorphous or flake-shaped, platelet-shaped, spherical or fibrous natural graphite or artificial graphite. 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.

[0048] In some embodiments of the present invention, the negative electrode active material layer may include a binder. The binder improves the bonding between the negative electrode active material particles and the bonding 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, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0049] In some embodiments of the present invention, the negative electrode active material layer includes a conductive agent so that the pole piece has conductivity. The conductive agent may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials 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.

[0050] In some embodiments of the present invention, the negative electrode current collector may 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.

[0051] In some embodiments of the present invention, the electrochemical device of the present invention is provided with a separator between the positive electrode and the negative electrode 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 can be any technology disclosed in the prior art.

[0052] In some embodiments of the present invention, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present invention.

[0053] In some embodiments of the present invention, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.

[0054] Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0055] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0056] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles are selected from one or a combination of aluminum oxide, silicon oxide, magnesium oxide, 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 polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0057] 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, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene).

[0058] The secondary battery involved in the present invention further comprises an electrolyte. In some embodiments of the present invention, the electrolyte comprises a lithium salt and a solvent.

[0059] 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(oxalate borate) LiB(C2O4)2(LiBOB) or lithium di(oxalate borate) LiBF2(C2O4)(LiDFOB). In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium di(oxalate borate) LiDFOB. In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF6). In some embodiments, the mass proportion 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 consisting of any two of these values. In some embodiments, the concentration of the lithium salt in the electrolyte is 1 mol / L.

[0060] In some embodiments of the present invention, the solvent can be selected from one or more 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), cyclopentane (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.

[0061] In some embodiments of the present invention, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature performance, etc.

[0062] In some embodiments of the present invention, the secondary battery of the present invention comprises the above-mentioned positive electrode sheet, negative electrode sheet, separator, electrolyte, etc., but is not limited thereto.

[0063] In some embodiments of the present invention, as tested by differential scanning calorimetry, the electrolyte and the coating material on the surface of the positive electrode plate in a fully charged state have three exothermic peaks in the range of 80°C-350°C.

[0064] In some embodiments of the present invention, the DSC curve of the positive electrode material has an exothermic power P2 of 0.5 mW / mg-1.8 mW / mg at 150°C-250°C. In some embodiments of the present invention, the DSC curve of the positive electrode material has an exothermic power P2 of 0.5 mW / mg, 0.6 mW / mg, 0.8 mW / mg, 1.0 mW / mg, 1.2 mW / mg, 1.4 mW / mg, 1.6 mW / mg, 1.8 mW / mg, or a range consisting of any two of these values ​​at 150°C-250°C.

[0065] In some embodiments of the present invention, the DSC curve of the positive electrode material has an exothermic power P3 of 0.2 mW / mg-1.5 mW / mg at 250°C-350°C. In some embodiments of the present invention, the DSC curve of the positive electrode material has an exothermic power P3 of 0.2 mW / mg, 0.4 mW / mg, 0.6 mW / mg, 0.8 mW / mg, 1.0 mW / mg, 1.2 mW / mg, 1.4 mW / mg, 1.5 mW / mg, or a range consisting of any two of these values ​​at 250°C-350°C.

[0066] In some embodiments of the present invention, the DSC curve of the positive electrode material has an exothermic power P1 at 100°C-150°C of 0.6mW / mg-1.5mW / mg. In some embodiments of the present invention, the exothermic peak here is the exothermic peak of the reaction of the functional polymer decomposing the linear carbonate in the electrolyte. In some embodiments of the present invention, the DSC curve of the positive electrode material has an exothermic power P1 at 100°C-150°C of 0.6mW / mg, 0.8mW / mg, 1.0mW / mg, 1.2mW / mg, 1.4mW / mg, 1.5mW / mg or a range consisting of any two of these values.

[0067] In some embodiments of the present invention, the reduction in exothermic power (P0-P2) / P0 of the DSC curve of the electrolyte and the positive electrode material in a fully charged state at 150°C-250°C is 60%-90%, and P0 is the exothermic power of the DSC curve of the positive electrode sheet without adding functional polymer at 150°C-250°C. In some embodiments of the present invention, the reduction in exothermic power (P0-P2) / P0 of the DSC curve of the electrolyte and the positive electrode material in a fully charged state at 150°C-250°C is 60%, 63%, 75%, 78%, 80%, 83%, 85%, 88%, 90% or a range consisting of any two of these values.

[0068] In some embodiments of the present invention, the reduction in exothermic power (P0'-P3) / P0' of the DSC curve of the electrolyte and the positive electrode material in a fully charged state at 250°C-350°C is 55%-95%, and P0' is the exothermic power of the DSC curve of the positive electrode sheet without adding functional polymer at 250°C-350°C. In some embodiments of the present invention, the reduction in exothermic power (P0'-P3) / P0' of the DSC curve of the electrolyte and the positive electrode material in a fully charged state at 250°C-350°C is 55%, 58%, 60%, 63%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 93%, 95% or a range consisting of any two of these values.

[0069] In some embodiments of the present invention, the secondary battery of the present invention may include an outer package, which 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 bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0070] In some embodiments of the present invention, the present invention further provides a battery module. The battery module includes the above-mentioned secondary battery. The battery module of the present invention uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present invention can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0071] In some embodiments of the present invention, the present invention further 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.

[0072] Device:

[0073] In some embodiments of the present invention, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0074] In other embodiments of the present invention, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0075] The present application is further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0076] Embodiment and comparative example:

[0077] Example 1

[0078] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material NCM811 is added and stirred evenly to obtain the electrode slurry.

[0079] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and NCM811 are 1.548%, 1.5% and 97% respectively.

[0080] Then the functional polymer is dissolved in tetrahydrofuran to form a solution with a solid content of 1 wt%, the solution is coated on the positive electrode plate, the coating amount is controlled, and the plate is heated and dried at 80°C to finally prepare a positive electrode plate in which the functional polymer accounts for 2 wt% of the positive electrode material.

[0081] Example 2

[0082] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material NCM811 is added and stirred evenly to obtain the electrode slurry.

[0083] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and NCM811 are 1.548%, 1.5% and 97% respectively.

[0084] Then the functional polymer is dissolved in tetrahydrofuran to form a solution with a solid content of 1wt%, the solution is coated on the positive electrode plate, the coating amount is controlled, and the solution is heated and dried at 80°C to finally prepare a positive electrode plate in which the functional polymer accounts for 1wt% of the positive electrode material.

[0085] Example 3

[0086] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material NCM811 is added and stirred evenly to obtain the electrode slurry.

[0087] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and NCM811 are 1.548%, 1.5% and 97% respectively.

[0088] Then the functional polymer was dissolved in tetrahydrofuran to form a solution with a solid content of 1 wt%, and the solution was coated on the positive electrode plate, the coating amount was controlled, and the plate was heated and dried at 80°C to finally prepare a positive electrode plate in which the functional polymer accounted for 0.5 wt% of the positive electrode material.

[0089] Example 4

[0090] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material NCM811 is added and stirred evenly to obtain the electrode slurry.

[0091] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and NCM811 are 1.548%, 1.5% and 97% respectively.

[0092] The functional polymer is then dissolved in a mixed solvent of N,N-dimethylformamide and ethyl acetate, with a mass ratio of dimethylformamide to ethyl acetate being 4:1, to form a solution with a solid content of 1 wt%. The solution is coated on a positive electrode sheet, the coating amount is controlled, and the solution is heated and dried at 80°C to prepare a positive electrode sheet in which the functional polymer accounts for 1 wt% of the positive electrode material.

[0093] Example 5

[0094] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material lithium nickel manganese oxide is added. After stirring evenly, the electrode slurry is obtained.

[0095] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and lithium nickel manganese oxide are 1.5%, 1.5% and 97% respectively.

[0096] Then the functional polymer is dissolved in tetrahydrofuran to form a solution with a solid content of 1 wt%, the solution is coated on the electrode, the coating amount is controlled, and the solution is heated and dried at 80° C. to prepare a positive electrode sheet in which the functional polymer accounts for 2 wt% of the positive electrode material.

[0097] Example 6

[0098] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material lithium nickel manganese oxide is added. After stirring evenly, the electrode slurry is obtained.

[0099] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and lithium nickel manganese oxide are 1.5%, 1.5% and 97% respectively.

[0100] Then the functional polymer is dissolved in tetrahydrofuran to form a solution with a solid content of 1 wt%, the solution is coated on the electrode, the coating amount is controlled, and the solution is heated and dried at 80°C to prepare a positive electrode sheet in which the functional polymer accounts for 1 wt% of the positive electrode material.

[0101] Example 7

[0102] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material lithium nickel manganese oxide is added. After stirring evenly, the electrode slurry is obtained.

[0103] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and lithium nickel manganese oxide are 1.5%, 1.5% and 97% respectively.

[0104] Then the functional polymer was dissolved in tetrahydrofuran to form a solution with a solid content of 1 wt%, and the solution was coated on the electrode sheet, the coating amount was controlled, and the solution was heated and dried at 80° C. to prepare a positive electrode sheet in which the functional polymer accounted for 0.5 wt% of the positive electrode material.

[0105] Comparative Example 1

[0106] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material NCM811 is added and stirred evenly to obtain the electrode slurry.

[0107] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Among them, based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and NCM811 are 1.5%, 1.5% and 97% respectively. In this comparative example, P0=3.75mW / mg, P0'=3.1mW / mg.

[0108] Comparative Example 2

[0109] First, the binder PVDF is dissolved with the solvent NMP. After it is completely dissolved, the conductive agent SP is added. After it is evenly dispersed, the positive electrode material lithium nickel manganese oxide is added. After stirring evenly, the electrode slurry is obtained.

[0110] Then, the electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode material layer is formed on the surface of the current collector to obtain a conventional positive electrode sheet. Among them, based on the total mass of the positive electrode material layer, the mass contents of PVDF, SP and lithium nickel manganese oxide are 1.5%, 1.5% and 97% respectively. In this comparative example, P0=4.5mW / mg, P0'=3.9mW / mg.

[0111] Negative electrode, diaphragm, electrolyte

[0112] The negative electrode sheet is composed of graphite, carbon black (SP), sodium carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) with mass contents of 95.5%, 1%, 1.5% and 2% respectively. The negative electrode sheet is prepared according to conventional negative electrode glue application, stirring and coating process conditions.

[0113] The diaphragm is a double-sided ceramic-coated PE diaphragm;

[0114] The electrolyte is 1M LiPF6 electrolyte (volume ratio EMC:DMC:FEC=5:2:2);

[0115] DSC test method:

[0116] Take the prepared positive electrode sheet, negative electrode sheet, separator, and electrolyte, assemble them into a full battery, perform fractionation, charge to full charge, then disassemble the battery cell, take the positive electrode sheet with 100% SOC, use DMC to clean the positive electrode sheet in a glove box, and dry it in the glove box.

[0117] The heating rate during the DSC test was 5°C / min, and the sample configuration was 5 mg of fully charged positive electrode material (scraped from the positive electrode sheet after cleaning as described above), and 2 ul of 1M LiPF6 electrolyte was added (volume ratio EMC:DMC:FEC=5:2:2).

[0118] The electrochemical tests of Examples 1-7 and Comparative Examples 1-2 were performed, and the test results are shown in Table 1:

[0119] The content of the functional polymer is based on the total mass of the positive electrode material layer.

[0120] [Table 1]

[0121]

[0122]

[0123] The exothermic peak at 200°C in Table 1 corresponds to the temperature of the starting thermal runaway of the battery cell. The exothermic power here represents the severity of the thermal runaway of the battery cell. The greater the exothermic power, the faster the rate of heat release and the more severe the thermal shock. It can be seen that compared with the comparative example, by setting a functional polymer in the conventional positive electrode sheet material layer, the exothermic power of the embodiment at 200°C and 280°C is significantly reduced, the reduction is large, and the effect is very obvious; at the same time, based on the comparative example, it is found that the embodiment has an additional exothermic peak at 100°C. According to the principle of conservation of energy, heat is released in advance, which will also lead to a decrease in the energy of the two exothermic peaks at 200°C and 280°C, greatly improving the safety of the battery cell.

[0124] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present invention and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principle and scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet comprises a positive electrode current collector; and A positive electrode material layer, the positive electrode material layer is arranged on the surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active material and a functional polymer represented by formula (1), Among them, n=10-10000.

2. The positive electrode sheet according to claim 1, characterized in that: in, n=100-1000; and / or Based on the total mass of the positive electrode material layer, the mass content of the functional polymer is 0.001%-5%.

3. The positive electrode sheet according to claim 1, characterized in that: Based on the total mass of the positive electrode material layer, the mass content of the functional polymer is 0.5%-2%.

4. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet satisfies at least one of the conditions 1) to 2): 1) The positive electrode active material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel manganese oxide; 2) Based on the total mass of the positive electrode material layer, the mass content of the positive electrode active material is 93%-98%.

5. A method for preparing the positive electrode sheet according to any one of claims 1 to 4, characterized in that: The method comprises S1: mixing a binder, a conductive agent, a positive electrode active material and a solvent to obtain a slurry; S2: coating the slurry on the surface of the current collector, and obtaining a positive electrode sheet after drying; S3: coating the mixed solution containing the functional polymer on the surface of the positive electrode sheet obtained in step S2 which is away from the current collector, and obtaining the positive electrode sheet after drying.

6. The method for preparing a positive electrode sheet according to claim 5, characterized in that: The step S3 satisfies at least one of the conditions 1) to 3): 1) The drying temperature is 60°C-110°C; 2) the mixed solution comprises a solvent, and the solvent comprises at least one of ethyl acetate, tetrahydrofuran, ethylene carbonate, vinylene carbonate, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, isopropanol, acetone and butyl acetate; 3) The solid content of the mixed solution is 0.5%-2%.

7. A secondary battery, characterized in that: The secondary battery comprises an electrolyte and a positive electrode sheet according to any one of claims 1 to 4 or a positive electrode sheet prepared by the method according to any one of claims 5 to 6.

8. The secondary battery according to claim 7, characterized in that: The electrolyte includes a solvent and a lithium salt, wherein the solvent includes at least one of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate and fluoroethylene carbonate; and the mass proportion of lithium hexafluorophosphate in the lithium salt is greater than 50%.

9. The secondary battery according to claim 8, characterized in that: Through the test using differential scanning calorimetry, the DSC curves of the electrolyte and the positive electrode material in a fully charged state have three exothermic peaks in the range of 80° C.-350° C.

10. The secondary battery according to claim 9, characterized in that: The DSC curve of the electrolyte and the positive electrode material in a fully charged state has an exothermic power P2 of 0.5 mW / mg to 1.8 mW / mg at 150° C. to 250° C.; and / or The DSC curve of the electrolyte and the positive electrode material in a fully charged state has an exothermic power P3 of 0.2 mW / mg to 1.5 mW / mg at 250° C. to 350° C.; and / or The DSC curves of the electrolyte and the positive electrode material in a fully charged state have a heat release power P1 of 0.6 mW / mg to 1.5 mW / mg at 100° C. to 150° C.

11. The secondary battery according to claim 9 or 10, characterized in that: The reduction in the exothermic power (P0-P2) / P0 of the DSC curves of the electrolyte and the positive electrode material in the fully charged state at 150°C-250°C is 60%-90%, and P0 is the exothermic power of the DSC curve of the positive electrode sheet without adding the functional polymer at 150°C-250°C; and / or The reduction in exothermic power (P0'-P3) / P0' of the DSC curves of the electrolyte and the fully charged positive electrode material at 250°C-350°C is 55%-95%, and P0' is the exothermic power of the DSC curve of the positive electrode sheet without adding functional polymer at 250°C-350°C.

Images