Battery and preparation method thereof

Abstract

The invention relates to the technical field of batteries, in particular to a battery and a preparation method thereof. The battery comprises a positive plate, a diaphragm, a negative plate and an electrolyte, and the negative plate comprises a current collector; the first negative electrode coating is arranged on at least one side surface of the current collector along the thickness direction, and the first negative electrode coating comprises a first polymer and a first active material; the second negative electrode coating is arranged on the surface, far away from the current collector, of the first negative electrode coating, and the second negative electrode coating comprises a second polymer and a second active material; wherein the first polymer is positioned on the surface layer of one side, far away from the current collector, of the first negative electrode coating; the second polymer is positioned on the surface layer of one side, far away from the first negative electrode coating, of the second negative electrode coating; the first active material comprises a carbon-based active material; the second active material includes a silicon-based active material. The battery has relatively high first efficiency and relatively long quick charge cycle life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery and a preparation method thereof. BACKGROUND

[0002] In recent years, with the development of portable electronic devices and the increasing demand for electric vehicles, the current energy density of lithium ion batteries has gradually failed to meet people's needs, and developing high-energy-density lithium ion batteries is an urgent task.

[0003] Silicon negative electrode material is recognized as the next generation of lithium ion battery negative electrode material due to its high specific capacity and low potential. However, silicon-based materials have large volume expansion during charging and discharging, which easily causes structural damage to the electrode sheet, and the silicon negative electrode has poor kinetics compared to the traditional lithium ion graphite negative electrode. In view of the above defects, the prior art points out that the negative electrode sheet active material layer containing graphite material and silicon-based material can be designed in layers, and the primary particle graphite and silicon-based material are placed in the first film layer close to the negative electrode current collector, and the secondary particle graphite is placed in the second film layer. The structure damage caused by the volume expansion of the silicon-based material can be reduced. However, the silicon-based material with poor kinetics is in the lower layer, which will further worsen the negative electrode system kinetics. If the silicon-based material is placed in the upper layer, the silicon-based material can first contact the electrolyte and accept lithium ions, which can improve the negative electrode system kinetics, but due to the initial film formation of the silicon-based material on the surface of the electrode sheet, the active lithium consumption is higher, and the subsequent large volume strain effect is also more likely to damage the surface interface SEI film and cause disconnection of the inner interface connection, thereby worsening the long-term fast charging cycle performance.

[0004] Therefore, it is urgent to provide a battery to solve the defects of the existing silicon-containing battery negative electrode sheet interface connection, poor negative electrode system kinetics, low initial efficiency, and low fast charging cycle life. SUMMARY

[0005] Therefore, the present application aims to at least partially solve one of the technical problems in the related art. To this end, the present application provides a battery and a preparation method thereof, which has a higher initial efficiency and a higher fast charging cycle life.

[0006] In order to solve the above technical problems, the present application is implemented as follows: According to one aspect of the present application, the embodiments of the present application provide a battery, comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises: a current collector; a first negative electrode coating layer disposed on at least one side surface of the current collector in the thickness direction, the first negative electrode coating layer comprising a first polymer and a first active material; a second negative electrode coating layer disposed on a surface of the first negative electrode coating layer away from the current collector, the second negative electrode coating layer comprising a second polymer and a second active material; wherein the first polymer is located on a surface layer of the first negative electrode coating layer away from the current collector; the second polymer is located on a surface layer of the second negative electrode coating layer away from the first negative electrode coating layer; the first active material comprises a carbon-based active material; and the second active material comprises a silicon-based active material.

[0007] In some embodiments, the first polymer is polymerized from a first polymerization monomer.

[0008] In some embodiments, the first polymerization monomer comprises an amino group-containing and / or nitrile group-containing polymerization monomer.

[0009] In some embodiments, the second polymer is polymerized from a second polymerization monomer.

[0010] In some embodiments, the second polymerization monomer comprises a long-chain unsaturated monomer.

[0011] In some embodiments, the first polymerization monomer comprises at least one of acrylamide, N,N-dimethyl acrylamide, acrylonitrile, and isocyanate.

[0012] In some embodiments, the second polymerization monomer comprises at least one of methyl methacrylate, ethyl acrylate, and pentaerythritol acrylate.

[0013] In some embodiments, the mass of the first polymer is 3-5% of the mass of the silicon-based active material.

[0014] In some embodiments, the mass of the second polymer is 1-3% of the mass of the silicon-based active material.

[0015] In some embodiments, the carbon-based active material comprises at least one of natural graphite and artificial graphite.

[0016] In some embodiments, the first negative electrode coating layer further comprises a first conductive agent and a first binder.

[0017] In some embodiments, the mass ratio of the first polymer, the first active material, the first conductive agent, and the first binder is (0.6-3):(92-97):(1-3):(1-2).

[0018] In some embodiments, the first negative electrode coating has an area density of 40-80 g / m 2 .

[0019] In some embodiments, the second active material has a silicon-based active material mass content of ≥20%.

[0020] In some embodiments, the silicon-based active material comprises at least one of a silicon-oxygen composite material or a silicon-carbon composite material.

[0021] In some embodiments, the second negative electrode coating further comprises a second conductive agent and a second binder.

[0022] In some embodiments, the mass ratio of the second polymer, the second active material, the second conductive agent, and the second binder is (0.2-3):(92-98):(1-3)(1-2).

[0023] In some embodiments, the second negative electrode coating has an area density of 30-60 g / m 2 .

[0024] According to another aspect of the present application, the embodiments of the present application provide a battery preparation method, comprising the following steps: sequentially arranging a positive electrode sheet, a separator, and a negative electrode sheet, injecting an electrolyte after winding, and obtaining a battery after chemical conversion and aging; In some embodiments, the electrolyte comprises an initiator.

[0025] In some embodiments, the preparation of the negative electrode sheet comprises: coating a first negative electrode slurry on at least one side surface of the current collector to obtain a first negative electrode coating; coating a second negative electrode slurry on the surface of the first negative electrode coating to obtain a second negative electrode coating; drying and cold-pressing the current collector coated with the first negative electrode coating and the second negative electrode coating.

[0026] In some embodiments, the first negative electrode coating comprises a first polymer monomer and a first active material.

[0027] In some embodiments, the second negative electrode coating comprises a second polymer monomer and a second active material.

[0028] In some embodiments, the first polymer monomer accounts for 0.6-3% of the total mass of the first negative electrode coating.

[0029] In some embodiments, the second polymer monomer accounts for 0.2-3% of the total mass of the second negative electrode coating.

[0030] In some embodiments, the initiator has a mass of 0.1-0.5% of the total mass of the first polymerizable monomer and the second polymerizable monomer in the negative electrode sheet.

[0031] In some embodiments, the initiator includes at least one of azobisisobutyronitrile, cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, or a persulfate salt.

[0032] In some embodiments, the temperature of the standing is 60-80℃ and the time is 6-12h.

[0033] The technical solutions of the present application have at least the following beneficial effects: In the embodiments of the present application, the first polymer in the first negative electrode coating layer exists in the surface layer of the first negative electrode coating layer, the carbon-based material layer is below the surface layer of the first negative electrode coating layer, the second polymer in the second negative electrode coating layer exists in the surface layer of the second negative electrode coating layer, and the silicon-based material layer is below the surface layer of the second negative electrode coating layer. The first polymer and the second polymer can coat the silicon-based material layer in the second negative electrode coating layer, thereby avoiding the low initial efficiency and SEI (solid electrolyte interface) film damage caused by the excessive activity lithium consumption and the large volume strain effect of the silicon-based material layer in the second negative electrode coating layer, and ensuring the negative electrode system kinetics and improving the fast charging cycle life. Therefore, the battery has high initial efficiency and high fast charging cycle life.

[0034] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION

[0035] The present application will be further described below in conjunction with specific examples. It should be understood that these examples of the present application are only used to illustrate the present application and not used to limit the scope of the present application.

[0036] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant variation. Various ranges of values that are explicitly delineated in the specification as supplied herein constitute examples of each individual value within that range. For numerical ranges expressed in the format "from X to Y," "X or more," or "Y or less," this is intended to include X and Y separately. For numerical ranges expressed in the format "from X to Y," this is intended to include X and Y separately, as well as X or Y. For numerical ranges expressed in the format "X... Y," this is intended to include X and Y separately, as well as X or Y.

[0037] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0038] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0039] If not otherwise specified, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0040] If not otherwise specified, the present application refers to "comprise" and "include" as open-ended, or as closed-ended. For example, the "comprise" and "include" can mean that other components not listed can also be included or comprised, or only the listed components can be included or comprised.

[0041] In view of the defects of the existing silicon-based material applied in the negative electrode of lithium battery, the present application provides a battery comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises: a current collector; a first negative electrode coating layer arranged on at least one side surface of the current collector along the thickness direction, wherein the first negative electrode coating layer comprises a first polymer and a first active material; a second negative electrode coating layer arranged on the surface of the first negative electrode coating layer away from the current collector, wherein the second negative electrode coating layer comprises a second polymer and a second active material; wherein the first polymer is located on the surface layer of the first negative electrode coating layer away from the current collector; the second polymer is located on the surface layer of the second negative electrode coating layer away from the first negative electrode coating layer; the first active material comprises a carbon-based active material; and the second active material comprises a silicon-based active material.

[0042] The provided negative electrode sheet has a multi-layer structure, which comprises a current collector, a first negative electrode coating layer, a second negative electrode coating layer and a third negative electrode coating layer arranged in sequence, i.e. the first negative electrode coating layer is arranged on at least one side surface of the current collector, the second negative electrode coating layer is arranged on the surface of the first negative electrode coating layer, and the third negative electrode coating layer is arranged on the surface of the second negative electrode coating layer. The first negative electrode coating layer can be a silicon-based layer, the second negative electrode coating layer can be an interface enhancement layer, and the third negative electrode coating layer can be a carbon-based material layer, such as a graphite layer.

[0043] The above-mentioned "the first negative electrode coating is arranged on at least one surface of the current collector in the thickness direction" means that the first negative electrode coating can be arranged on one surface of the current collector in the thickness direction of the current collector, or can be arranged on both surfaces of the current collector in the thickness direction of the current collector. The "surface" herein can be the entire area of the current collector, or can be a partial area of the current collector. In the embodiment, the surface can be the entire area of the current collector, and the present application does not have a special limitation as long as the purpose of the present application can be achieved.

[0044] For example, the current collector has two opposite surfaces in the thickness direction of the current collector, and the first negative electrode coating is arranged on the two opposite surfaces of the current collector. Further, the second negative electrode coating is formed on the surface of the first negative electrode coating on both sides. Further, the third negative electrode coating is formed on the surface of the second negative electrode coating on both sides. It can be understood that in other embodiments, the first negative electrode coating can also be arranged on any one of the two surfaces of the current collector.

[0045] In the present application, the material of the current collector in the negative electrode sheet is not particularly limited.

[0046] In the present application, the first polymer in the first negative electrode coating exists in the surface layer of the first negative electrode coating, the carbon-based material layer is below the surface layer of the first negative electrode coating, the second polymer in the second negative electrode coating exists in the surface layer of the second negative electrode coating, and the silicon-based material layer is below the surface layer of the second negative electrode coating. The first polymer and the second polymer can coat the silicon-based material layer in the second negative electrode coating, thereby avoiding the low initial efficiency and the destruction of the SEI (solid electrolyte interface) film caused by the excessive activity lithium consumption and the excessive volume strain effect of the silicon-based material layer in the second negative electrode coating, and ensuring the kinetics of the negative electrode system and improving the fast-charging cycle life.

[0047] In some embodiments, the first polymer is obtained by polymerization of a first polymer monomer.

[0048] In some embodiments, the first polymer monomer includes an amino group-containing and / or nitrile group-containing polymer monomer. The mass of the first polymer monomer is less than the mass of the first active material, and the amino group-containing and / or nitrile group-containing polymer monomer can spontaneously float to the surface of the first coating during the coating process. After the second negative electrode coating is coated, the amino group-containing and / or nitrile group-containing polymer monomer can react with the hydroxyl group in the silicon-based active material in the second negative electrode coating to form a chemical bond, thereby improving the adverse effects of the destruction of the interface bond between the first negative electrode coating and the second negative electrode coating caused by the volume strain of the silicon-based material during fast-charging cycles. In addition, the first polymer monomer can also combine with the initiator in the subsequent electrolyte, and polymerize into the first polymer in situ on the surface layer of the first negative electrode coating through a high-temperature reaction in the early formation stage. Therefore, the surface layer of the first negative electrode coating can be connected to the second negative electrode coating based on the chemical bond, and the connection effect between the first negative electrode coating and the second negative electrode coating can be further improved, and the stability of the negative electrode as a whole in the later cycle stage can be ensured.

[0049] In some embodiments, the second polymer is polymerized from a second polymerization monomer.

[0050] In some embodiments, the second polymerization monomer includes a long-chain unsaturated monomer. The second polymerization monomer has a mass less than a mass of the second active material, and in the coating process, the second polymerization monomer spontaneously floats to the surface of the second coating layer. The long-chain unsaturated monomer combines with an initiator in a subsequent electrolyte, and in the pre-formation stage, the long-chain unsaturated monomer and all unsaturated bond monomers in the surface layer of the first negative electrode coating layer are polymerized through a high-temperature reaction, thereby in-situ forming a cladding layer of the silicon-based material layer, avoiding excessive active lithium consumption of the silicon-based material and damage to the SEI (solid electrolyte interface) film caused by a large volume strain effect, and ensuring the kinetics of the negative electrode system and improving the fast-charging cycle life of the battery.

[0051] In some embodiments, the first polymerization monomer includes at least one of acrylamide, N,N-dimethyl acrylamide, acrylonitrile, or isocyanate. As an example, the first polymerization monomer can be acrylamide, can be N,N-dimethyl acrylamide, or can be acrylonitrile.

[0052] In some embodiments, the second polymerization monomer includes at least one of methyl methacrylate, ethyl acrylate, or pentaerythritol acrylate. As an example, the second polymerization monomer can be methyl methacrylate or can be ethyl acrylate.

[0053] In some embodiments, the mass of the first polymer is 3-5% of the mass of the silicon-based active material. As an example, the mass of the first polymer can be 3%, 4%, 5%, or the like of the mass of the silicon-based active material, and of course can be other values within the above range, which are not specifically limited herein. If the mass of the first polymer is too low, the silicon-based material in the second negative electrode coating layer cannot be chemically linked to the surface layer of the first negative electrode coating layer. If the mass of the first polymer is too high, the capacity of the first negative electrode active material cannot be fully utilized.

[0054] In some embodiments, the mass of the second polymer is 1-3% of the mass of the silicon-based active material. As an example, the mass of the second polymer can be 1%, 2%, 3%, or the like of the mass of the silicon-based active material, and of course can be other values within the above range, which are not specifically limited herein. If the mass of the second polymer is too low, the second polymer in the surface layer of the second negative electrode coating layer cannot effectively coat the silicon-based material. If the mass of the second polymer is too high, the capacity of the second negative electrode active material cannot be fully utilized.

[0055] In some embodiments, the carbon-based active material includes at least one of natural graphite or synthetic graphite. As an example, the carbon-based active material may be natural graphite, synthetic graphite, or a mixture of both.

[0056] In some embodiments, the first negative electrode coating further includes a first conductive agent and a first binder.

[0057] In some embodiments, the mass ratio of the first polymer, the first active material, the first conductive agent, and the first binder is (0.6~3):(92~97):(1~3):(1~2). As an example, the mass ratio of the first polymer, the first active material, the first conductive agent, and the first binder can be 0.6:92:1:1, 1.6:95:2:1.5, 3:97:3:2, etc., and of course, other ratios within the above range are also possible, which are not limited here.

[0058] In some embodiments, the first conductive agent includes at least one selected from conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, or graphene. The conductive carbon black includes acetylene black, Ketjen black, etc. The conductive carbon fiber includes vapor-grown carbon fiber.

[0059] In some embodiments, the first adhesive includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, or polyacrylic acid.

[0060] In some embodiments, the areal density of the first negative electrode coating is 40-80 g / m³. 2 As an example, the areal density of the first negative electrode coating can be 40 g / m³. 2 60g / m 2 80g / m 2 "etc." can also be other values ​​within the above range, without specific limitations here.

[0061] In some embodiments, the mass content of silicon-based active material in the second active material is ≥20%. As an example, the mass content of silicon-based active material in the second active material can be 20%, 40%, 60%, 80%, etc., or other values ​​within the above range, and is not specifically limited here.

[0062] In some embodiments, the silicon-based active material includes at least one of a silicon-oxygen composite material or a silicon-carbon composite material. As an example, the silicon-based active material may be a silicon-oxygen composite material or a silicon-carbon composite material.

[0063] In some embodiments, the second negative electrode coating further includes a second conductive agent and a second binder.

[0064] In some embodiments, the mass ratio of the second polymer, the second active material, the second conductive agent, and the second binder is (0.2-3):(92-98):(1-3)(1-2). For example, the mass ratio of the second polymer, the second active material, the second conductive agent, and the second binder can be 0.2:92:1:1, 1.5:95:2:1.5, 3:98:3:2, or other ratios within the above ranges, without being limited thereto.

[0065] In some embodiments, the second conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube, or graphene. The conductive carbon black includes acetylene black, Ketjen black, etc. The conductive carbon fiber includes vapor grown carbon fiber.

[0066] In some embodiments, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, butadiene-styrene rubber, sodium alginate, or polyacrylic acid.

[0067] In some embodiments, the areal density of the second negative electrode coating layer is 30-60 g / m2. 2 For example, the areal density of the second negative electrode coating layer is 30 g / m2, 45 g / m2, 60 g / m2, or other values within the above ranges, without being limited thereto. 2 2 2

[0068] It can be understood that the mass ratio of the first polymer, the first active material, the first conductive agent, and the first binder, the mass ratio of the second polymer and the second conductive agent, and the mass ratio of the second conductive agent and the second binder are related to the electrochemical performance of the corresponding battery, and further affect the structural stability of the negative electrode sheet. By controlling the proportion of each substance in the first negative electrode coating layer and the second negative electrode coating layer within the above ranges, the roles of each active material and each polymer are fully played, and the cycle performance, fast charging performance, and structural stability of the negative electrode sheet are effectively improved.

[0069] It can also be understood that the areal density of the coating layer affects the electrical performance (such as energy density, cycle performance, and rate performance) of the battery, the preparation cost, and the safety performance. If the areal density of the first negative electrode coating layer, the second negative electrode coating layer, and the like is too large, the electron transport distance increases, the electron resistance increases, the rate performance decreases, which adversely affects the electrical performance of the battery, and further increases the difficulty of thermal management of the battery. However, if the areal density of the first negative electrode coating layer and the second negative electrode coating layer is too low, the structural stability of the negative electrode sheet is not obviously improved, which adversely affects the safety and long-term cycle stability of the battery.

[0070] ​​​In some embodiments, the current collector includes, but is not limited to, at least one of a copper foil, a foamed nickel, a nickel mesh, or a composite copper foil. As an example, the current collector can be a copper foil, can be a foamed copper, or can be a composite copper foil.

[0071] Based on the same inventive concept, the application provides a battery preparation method, including the following steps: The positive electrode sheet, the separator, and the negative electrode sheet are sequentially arranged, and after being wound, an electrolyte is injected and allowed to stand, and a battery is obtained after formation and aging. The electrolyte includes an initiator.

[0072] In the present application, the initiator is placed in the electrolyte, and after the battery is injected with the electrolyte, a polymerization reaction is carried out on the surface / interior interface of the upper layer of the silicon-based material in the early stage of formation through high-temperature reaction, where the surface interface refers to the surface layer of the second negative electrode coating, and the interior interface refers to the surface layer of the first negative electrode coating, thereby forming an all-encapsulating layer design of the silicon-based upper layer coating in situ, and further improving the fast-charging cycle performance of the silicon-based material.

[0073] It should be understood that all the features and advantages described above for the "battery" also apply to the "battery preparation method", which will not be repeated here.

[0074] In some embodiments, the preparation of the negative electrode sheet includes: A first negative electrode slurry is coated on at least one side surface of the current collector to obtain a first negative electrode coating; A second negative electrode slurry is coated on the surface of the first negative electrode coating to obtain a second negative electrode coating; The current collector coated with the first negative electrode coating and the second negative electrode coating is dried and cold-pressed.

[0075] In some embodiments, coating the first negative electrode slurry on at least one side surface of the current collector further includes a drying step, and the drying temperature is 80°C to 100°C.

[0076] In some embodiments, when the current collector coated with the first negative electrode coating and the second negative electrode coating is dried, the drying temperature is 80°C to 100°C.

[0077] In some embodiments, the cold-pressed compacted density is 1.3 to 1.7 g / cm 3 .

[0078] In some embodiments, the first negative electrode coating includes a first polymerized monomer and a first active material.

[0079] In some embodiments, the second negative electrode coating includes a second polymerized monomer and a second active material.

[0080] In some embodiments, the first polymer monomer accounts for 0.6-3% of the total mass of the first negative electrode coating. For example, the first polymer monomer can account for 0.6%, 1%, 2%, 3%, or the like, of the total mass of the first negative electrode coating, and can also be other values within the above range, which are not specifically limited herein. If the content of the first polymer monomer is too low, it will not be able to be chemically linked with the silicon-based material in the second negative electrode coating, thereby failing to effectively improve the adverse effects of the destruction of the interface link between the first negative electrode coating and the second negative electrode coating caused by the volume strain of the silicon-based material in fast charging cycles. If the proportion of the first polymer monomer is too high, the content of the first active material will be relatively low, thereby affecting the battery capacity.

[0081] In some embodiments, the second polymer monomer accounts for 0.2-3% of the total mass of the second negative electrode coating. For example, the second polymer monomer can account for 0.2%, 1%, 2%, 3%, or the like, of the total mass of the second negative electrode coating, and can also be other values within the above range, which are not specifically limited herein. If the content of the second polymer monomer is too low, the integrity of the surface layer of the second negative electrode coating cannot be guaranteed, and it cannot withstand the volume strain of the silicon-based active material; if the content of the second polymer monomer is too high, the polarization effect of the battery will be increased.

[0082] In some embodiments, the mass of the initiator is 0.1-0.5% of the total mass of the first polymer monomer and the second polymer monomer in the negative electrode sheet. For example, the mass of the initiator can be 0.1%, 0.3%, 0.5%, or the like, of the total mass of the first polymer monomer and the second polymer monomer in the negative electrode sheet, and can also be other values within the above range, which are not specifically limited herein.

[0083] In some embodiments, the initiator includes at least one of azobisisobutyronitrile, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, or persulfate.

[0084] In some embodiments, the temperature for the standing is 60-80°C, and the time is 6-12h. For example, the temperature for the standing can be 60°C, 70°C, 80°C, or the like, and can also be other values within the above range, which are not specifically limited herein. The time for the standing can be 6h, 8h, 10h, 12h, or the like, and can also be other values within the above range, which are not specifically limited herein. It can be understood that the standing process is the process of polymerization of the polymer monomers under the action of the initiator, and when polymerization is performed at a low temperature, a relatively long standing time is required.

[0085] In this embodiment, the positive electrode sheet does not have limitations on the positive electrode current collector, the conductive agent, the binder, and other materials in the positive electrode active material layer, and the structure thereof, and any positive electrode sheet structure and composition known in the art that can be used in a secondary battery can be selected.

[0086] In this embodiment, the specific material or type of the diaphragm is not limited, and the diaphragm that can be used for the secondary battery known in the art can be selected.

[0087] It should be further pointed out that the battery of the present application is not limited to the specific material or type of the electrolyte, and the components and types known in the art that can be used for the secondary battery can be selected as long as the purpose of the present application can be achieved.

[0088] Therefore, based on the above scheme, the present application proposes a full-coating design of silicon-based material coating to solve the problems of the surface interface and the inner interface caused by the double-layer coating of the silicon-based material in the fast-charging design requirement. The coating layer can connect the inner interface of the bottom layer based on chemical bonds to ensure the stability of the negative electrode as a whole in the later cycle. The coating layer in-situ constructs a uniform and thin surface interface, which can be initially polymerized into a film on the surface layer of the pole piece in the early formation stage, thereby reducing the consumption of active lithium. The in-situ polymerized interface protection film can better withstand the volume strain effect of the silicon-based material, protect the interface integrity and stability, and thus improve the initial efficiency and fast-charging capacity. Therefore, the battery of the present application has a high initial efficiency and a high fast-charging cycle life.

[0089] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explaining the present application only and cannot be understood as a limitation of the present application. In the embodiments, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents, materials or instruments not mentioned by the manufacturer are all conventional products that can be obtained by purchase.

[0090] Example 1 Preparation of negative electrode sheet The artificial graphite, conductive carbon black Super P (SP), single-walled carbon nanotube (SWCNT), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and acrylamide (AM) were mixed in a mass ratio of 94.2:1.42:0.08:1.9:0.9:1.5, deionized water was added, and stirring was performed to obtain a uniform slurry, thereby obtaining a first active slurry. The first active slurry was uniformly coated on the side of the negative electrode current collector (8 μm copper foil), and after drying (drying temperature: 90°C), a first negative electrode coating layer was obtained.

[0091] The silicon-oxygen composite material, SP, PAA, SBR, and methyl methacrylate (MMA) were mixed in a mass ratio of 96.5:1:1.3:0.7:0.5, deionized water was added, and stirring was performed to obtain a uniform slurry, thereby obtaining a second active slurry. The second active slurry was coated on the surface of the first negative electrode coating layer, and after drying (drying temperature: 90°C), cold pressing (compaction density: 1.5 g / cm 3 ) was performed to obtain a negative electrode sheet.

[0092] Preparation of positive electrode sheet The positive electrode active material (lithium nickel cobalt manganese oxide LiNi) 0.8 Co 0.1 Mn 0.1 SP, carbon nanotubes, and polyvinylidene fluoride (PVDF5130) binder are mixed in a ratio of 97:1.6:0.4:1. N-methylpyrrolidone (NMP) is added and stirred to form a uniform and stable positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector (13μm aluminum foil), dried, and cold-pressed to obtain the positive electrode sheet.

[0093] Separating membrane A polyethylene (PE) membrane with a thickness of 12μm was selected as the separator.

[0094] Preparation of electrolyte In a glove box filled with inert gas, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. Then, lithium salt LiPF6 was dissolved in the organic solvent at a concentration of 1.2 mol / L, and an initiator of 0.2% of the total mass of the monomers was added to obtain the electrolyte.

[0095] Battery manufacturing The positive electrode, separator, and negative electrode are arranged in sequence and assembled by winding. The electrolyte is injected into the dry cell and immersed at room temperature for 12 hours. After standing at 70°C for 10 hours, formation is carried out at 45°C. The formation process is as follows: charge at 0.05C to 3.4V, then charge at 0.2C to 3.75V. After aging at room temperature for 24 hours, capacity testing is performed: charge at 1C to 4.25V, then discharge at 1C to 2.5V to obtain the battery.

[0096] Examples 2-10 The differences between Examples 2-10 and Example 1 are shown in Table 1. All contents not mentioned in the table are the same as those in Example 1.

[0097] Comparative Examples 1-11 The differences between Comparative Examples 1-11 and Example 1 are shown in Table 1. All contents not mentioned in the table are the same as those in Example 1.

[0098] Table 1 Note: In Table 1, AM refers to acrylamide, MMA refers to methyl methacrylate, PETA refers to pentaerythritol acrylate, and " / " indicates that the substance was not added or that the step was not involved.

[0099] Performance testing (1) First Coulomb efficiency test: Record the total charge C1 and total discharge C2 during the capacity formation stage, and obtain the first Coulomb efficiency test = C2 / C1*100%.

[0100] (2) Fast charging cycle test: 1) 30 min static in 25℃ constant temperature box, charged to 4.25V with 2C constant current; 2) after 30 min static, discharged to 2.5V with 1C constant current, record initial discharge capacity C1; 3) cycle 1)~2) until the discharge capacity of the battery is lower than 80% of the initial discharge capacity C1, stop the test, record the discharge capacity Cn, wherein n is the cycle number.

[0101] The test results of each embodiment and comparative example are shown in Table 2.

[0102] Table 2 Note: The silicon-based material layer refers to the silicon-based material layer in the second negative electrode material.

[0103] The part of the present application not described in detail is the technology known to the person skilled in the art.

[0104] The above describes the basic principles of the present application in combination with specific embodiments, but it should be pointed out that the advantages, advantages, effects and the like mentioned in the present application are only examples and not limitations, and these advantages, advantages, effects and the like cannot be considered as the must-have of each embodiment of the present application. In addition, the above specific details disclosed are only for the purpose of example and for the purpose of understanding, and the above details do not limit the present application to the above specific details.

[0105] It should be noted that the term "and / or" or " / " used herein is only to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the existence of A alone, the existence of A and B, and the existence of B alone. The singular form "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural form, unless the context clearly indicates otherwise.

[0106] In the detailed description and claims, a list of items connected by the term "at least one of", "at least one", "at least one of" or other similar terms means any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, 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 can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0107] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, characterized in that, The negative electrode includes: current collector; A first negative electrode coating is disposed on at least one side surface of the current collector along the thickness direction, and the first negative electrode coating comprises a first polymer and a first active material; A second negative electrode coating is disposed on the surface of the first negative electrode coating away from the current collector, and the second negative electrode coating includes a second polymer and a second active material; Wherein, the first polymer is located on the surface layer of the first negative electrode coating on the side away from the current collector; The second polymer is located on the surface of the second negative electrode coating on the side away from the first negative electrode coating; The first active material includes a carbon-based active material; the second active material includes a silicon-based active material.

2. The battery according to claim 1, characterized in that, The first polymer is obtained by polymerization of a first polymeric monomer; Preferably, the first polymeric monomer comprises an amino- and / or nitrile-containing polymeric monomer; And / or, the second polymer is obtained by polymerization of a second polymerizing monomer; Preferably, the second polymerizable monomer comprises a long-chain unsaturated monomer.

3. The battery according to claim 2, characterized in that, The first polymerizing monomer includes at least one of acrylamide, N,N-dimethylacrylamide, acrylonitrile, and isocyanate; And / or, the second polymerizing monomer includes at least one of methyl methacrylate, ethyl acrylate, and pentaerythritol acrylate.

4. The battery according to claim 1, characterized in that, Based on the mass of the silicon-based active material, the mass of the first polymer is 3-5% of the mass of the silicon-based active material; And / or, based on the mass of the silicon-based active material, the mass of the second polymer is 1 to 3% of the mass of the silicon-based active material.

5. The battery according to claim 1, characterized in that, The first negative electrode coating satisfies at least one of the following features (1) to (3): (1) The carbon-based active material includes at least one of natural graphite and artificial graphite; (2) The first negative electrode coating further includes a first conductive agent and a first binder; Preferably, the mass ratio of the first polymer, the first active material, the first conductive agent, and the first binder is (0.6~3):(92~97):(1~3):(1~2); (3) The areal density of the first negative electrode coating is 40-80 g / m³. 2 .

6. The battery according to claim 1, characterized in that, The second negative electrode coating satisfies at least one of the following features (1) to (4): (1) The mass content of silicon-based active material in the second active material is ≥20%; (2) The silicon-based active material includes at least one of silicon-oxygen composite material or silicon-carbon composite material; (3) The second negative electrode coating further includes a second conductive agent and a second binder; Preferably, the mass ratio of the second polymer, the second active material, the second conductive agent, and the second binder is (0.2~3):(92~98):(1~3):(1~2); (4) The areal density of the second negative electrode coating is 30-60 g / m³. 2 .

7. The method for preparing the battery according to any one of claims 1 to 6, characterized in that, Includes the following steps: The positive electrode, separator, and negative electrode are arranged in sequence, wound up, injected with electrolyte, left to stand, and then formed and aged to obtain the battery. The electrolyte contains an initiator.

8. The method for preparing a battery according to claim 7, characterized in that, The preparation of the negative electrode includes: A first negative electrode slurry is coated on at least one side of the current collector to obtain a first negative electrode coating. A second negative electrode slurry is coated on the surface of the first negative electrode coating to obtain a second negative electrode coating. The current collector coated with the first negative electrode coating and the second negative electrode coating is dried and cold-pressed; Preferably, the first negative electrode coating comprises a first polymeric monomer and a first active material; Preferably, the second negative electrode coating comprises a second polymer monomer and a second active material; Preferably, the first polymeric monomer accounts for 0.6% to 3% of the total mass of the first negative electrode coating; Preferably, the second polymeric monomer accounts for 0.2% to 3% of the total mass of the second negative electrode coating; And / or, the mass of the initiator is 0.1 to 0.5% of the total mass of the first and second polymerizing monomers in the negative electrode.

9. The method for preparing a battery according to claim 7, characterized in that, The initiator includes at least one of azobisisobutyronitrile, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, or persulfate.

10. The method for preparing a battery according to claim 7, characterized in that, The settling temperature is 60~80℃, and the time is 6~12h.

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