Negative electrode sheet, secondary battery, battery module, battery pack, and electric device

Abstract

The application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device, comprising a first coating layer, a second coating layer and a current collector, one side of the second coating layer is the current collector, the other side of the second coating layer is the first coating layer, the first coating layer and the second coating layer comprise a silicon-based material, the molar ratio of O element and Si element of the silicon-based material of the first coating layer is 0.5 to 1.5, and the molar ratio of O element and Si element of the silicon-based material of the second coating layer is less than or equal to 0.3. The application can improve the cycle life and energy density of the battery.

Description

Technical Field

[0001] This application relates to the field of lithium batteries, and more particularly to a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] Lithium-ion batteries are characterized by high specific energy, high operating voltage, low self-discharge rate, small size, and light weight. With the rapid development of electric vehicles, people have increasingly higher requirements for the energy density and cycle performance of lithium-ion batteries. Silicon-based materials, with their high specific capacity, have become ideal materials for the next generation of lithium-ion anode materials.

[0003] Silicon-based materials undergo significant volume changes during lithium insertion / extraction, affecting the cycle life of lithium-ion batteries. Furthermore, silicon-based materials have low initial coulombic efficiency, impacting the energy density of lithium-ion batteries. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to improve the cycle life and energy density of lithium-ion batteries.

[0005] To achieve the above objectives, this application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device.

[0006] The first aspect of this application provides a negative electrode sheet comprising a first coating, a second coating, and a current collector, wherein one side of the second coating is the current collector and the other side of the second coating is the first coating, the first coating and the second coating comprising silicon-based materials, wherein the molar ratio of O to Si in the silicon-based material of the first coating is 0.5 to 1.5, and the molar ratio of O to Si in the silicon-based material of the second coating is less than or equal to 0.3.

[0007] Therefore, this application improves the cycle life and energy density of lithium-ion batteries by synergistically controlling the molar ratio of O and Si elements in the silicon-based materials in the first and second coatings.

[0008] In any embodiment, the molar ratio of O to Si elements in the silicon-based material of the second coating is 0.05 to 0.2, which can improve the energy density of lithium-ion batteries while also improving battery cycle life.

[0009] In any embodiment, the weighted specific capacity A1 of the first coating active material and the weighted specific capacity A2 of the second coating active material satisfy the condition: 0.8 ≤ A1 ∶ A2 ≤ 1.2, which can reduce the risk of lithium-ion battery delamination during the entire battery life cycle and improve the performance and safety of lithium-ion battery.

[0010] In any embodiment, the weighted specific capacity A1 of the first coating active material is 500 mAh / g to 1000 mAh / g, and the weighted specific capacity A2 of the second coating active material is 500 mAh / g to 1000 mAh / g, thus obtaining a lithium-ion battery with good cycle life and energy density.

[0011] In any embodiment, the silicon-based material is present in the first coating at a content of 18 wt% to 55 wt%, and in the second coating at a content of 7 wt% to 21 wt%, thereby obtaining a lithium-ion battery with good cycle life and energy density.

[0012] In any embodiment, the first coating includes a first adhesive and the second coating includes a second adhesive, which can improve the interfacial bonding effect of the first coating and the second coating, further reduce the risk of delamination of the first coating and the second coating, and improve the safety of the lithium-ion battery.

[0013] In any embodiment, the first adhesive and the second adhesive each independently comprise at least one of polyacrylic acid, polyacrylate, sodium alginate, polyacrylonitrile, polyethylene glycol, carboxymethyl chitosan, and styrene-butadiene rubber.

[0014] In any embodiment, both the first adhesive and the second adhesive include polyacrylate adhesives. The content of the polyacrylate adhesive in the first coating is less than that in the second coating. This can effectively improve the energy density of the battery and reduce the cost of auxiliary materials while satisfying the bonding effect.

[0015] In any embodiment, the polyacrylate binder is present in the first coating at a content of 3 wt% to 6 wt%, and in the second coating at a content of 4 wt% to 7 wt%, which can effectively improve the energy density of the battery and reduce the cost of auxiliary materials while satisfying the bonding effect.

[0016] A second aspect of this application provides a secondary battery, including the negative electrode sheet of the first aspect of this application.

[0017] A third aspect of this application provides a battery module, including the secondary battery of the second aspect of this application.

[0018] A fourth aspect of this application provides a battery pack that includes the battery module of the third aspect of this application.

[0019] The fifth aspect of this application provides an electrical device including at least one selected from the second aspect of this application, the third aspect of this application, or the fourth aspect of this application.

[0020] The beneficial effects of this application are:

[0021] This application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. The negative electrode sheet includes a first coating and a second coating. By synergistically controlling the molar ratio of O and Si elements in the silicon-based materials of the first and second coatings, the first coating improves the cycle life of the lithium-ion battery after the initial lithium insertion, and the second coating improves the initial coulombic efficiency and energy density of the lithium-ion battery, thereby improving the cycle life and energy density of the lithium-ion battery. Of course, implementing any product or method of this application does not necessarily require achieving all of the above-described advantages simultaneously. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of this application and the prior art, the accompanying drawings used in the embodiments and the prior art are briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application.

[0023] Figure 1 This is a schematic diagram of the negative electrode sheet according to one embodiment of this application.

[0024] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0025] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0026] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0027] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0028] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0029] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1 First coating; 2 Second coating; 3 Current collector; 4 Battery module; 5 Secondary battery; 10 Battery pack; 11 Upper housing; 12 Lower housing; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0032] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode, positive electrode, secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0033] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] During its research on silicon-based batteries, the applicant discovered that silicon-based materials suffer from significant volume expansion during charging and discharging, resulting in a cycle life that fails to meet application requirements. The low initial coulombic efficiency of silicon-based materials also impacts the energy density of these batteries. To improve the cycle life and energy density of silicon-based batteries, enabling them to perform better in electrical devices—such as longer driving range and extended lifespan—this application provides a negative electrode, a secondary battery, a battery module, a battery pack, and an electrical device.

[0040] In one embodiment of this application, a negative electrode sheet is proposed, such as... Figure 1 As shown, it includes a first coating 1, a second coating 2, and a current collector 3. One side of the second coating 2 is the current collector 3, and the other side of the second coating 2 is the first coating 1. The first coating 1 and the second coating 2 include silicon-based materials. The molar ratio of O to Si elements in the silicon-based material of the first coating 1 is 0.5 to 1.5, preferably 0.8 to 1.2. The molar ratio of O to Si elements in the silicon-based material of the second coating 2 is less than or equal to 0.3.

[0041] Although the mechanism is not yet clear, the applicant has unexpectedly discovered that the negative electrode sheet of this application includes a first coating and a second coating. By synergistically regulating the molar ratio of O and Si elements in the silicon-based material in the first coating and the molar ratio of O and Si elements in the silicon-based material in the second coating within the scope of this application, the first coating improves the cycle life of the lithium-ion battery, and the second coating improves the first coulombic efficiency and energy density of the lithium-ion battery, thereby improving the overall cycle life and energy density of the lithium-ion battery.

[0042] The applicant has discovered, without limitation by any theory, that for silicon-based anode materials, the higher the oxygen content in the material, the greater the proportion of buffering lithium oxide and lithium silicates (e.g., Li2SiO3, Li4SiO4, Li6Si2O7, etc.) formed after the initial lithium insertion. The presence of these components effectively mitigates the volume change during the lithium insertion process in silicon-based materials, thus improving the degree of rupture and repair of the solid electrolyte interphase (SEI) film during the lithium-ion battery's lifespan, thereby improving the cycle life of the lithium-ion battery. However, the presence of these components, which lack reversible lithium insertion / extraction capabilities, reduces the reversible specific capacity of the silicon-based material, thereby affecting the initial coulombic efficiency of the lithium-ion battery and causing a certain loss in energy density. Conversely, a lower oxygen content in silicon-based materials leads to greater expansion during lithium insertion / extraction, resulting in faster capacity decay with increasing cycle count, but also a higher initial coulombic efficiency and correspondingly higher energy density.

[0043] The applicant has also discovered, without limitation to any theory, that during the charging and discharging process of porous electrodes, due to the presence of liquid phase ohmic polarization and diffusion polarization, the charging and discharging current is more concentrated on the side of the electrode sheet closer to the solution. That is, the closer the active material particles are to the surface of the electrode sheet (i.e., the electrolyte side), the greater the throughput of lithium delithiation and lithium insertion during the charging and discharging process undertaken by the active material.

[0044] Based on this, in this application, the first coating of the negative electrode is positioned close to the electrolyte, which can handle a larger volume of lithium ions during battery use. The molar ratio of O to Si in the silicon-based material of the first coating is 0.5 to 1.5, resulting in the formation of more active materials such as lithium oxide and lithium silicate to buffer volume expansion after the initial lithium insertion, thereby improving the cycle life of the lithium-ion battery. The second coating is positioned close to the current collector, and the molar ratio of O to Si in the silicon-based material of the second coating is less than or equal to 0.3, which reduces the amount of active lithium consumed during the initial lithium insertion of the negative electrode, improving the initial coulombic efficiency and energy density of the lithium-ion battery. The negative electrode of this application includes the aforementioned first and second coatings, enabling the lithium-ion battery to possess both high energy density, high initial coulombic efficiency, and high cycle life.

[0045] In some embodiments, the silicon-based material in the first coating of this application may be a silicon-oxygen material (represented as SiO2). x The silicon-based material in the second coating can be either silicon-oxygen material or elemental silicon material.

[0046] In some embodiments, the molar ratio of O to Si in the silicon-based material of the first coating is 0.8 to 1.2, and the molar ratio of O to Si in the silicon-based material of the second coating is 0.05 to 0.2. The applicant has discovered that by controlling the molar ratio of O to Si in the silicon-based material of the first coating and the molar ratio of O to Si in the silicon-based material of the second coating within the aforementioned ranges, the energy density of lithium-ion batteries can be improved while simultaneously enhancing battery cycle life.

[0047] In some embodiments, the weighted specific capacity A1 of the first coating active material and the weighted specific capacity A2 of the second coating active material satisfy the following relationship: 0.8 ≤ A1 ∶ A2 ≤ 1.2. In this application, the weighted specific capacity A of the active material in a coating refers to the weighted value of the reversible lithium insertion / extraction specific capacity of the silicon-based material and the reversible lithium insertion / extraction specific capacity of other active components in the active material of that coating. The weighted specific capacity A is calculated using the following expression: A = ∑n i ×x i The unit is mAh / g. Where x i This represents the mass ratio of the i-th type of active ingredient in the coating to the total active material, and ∑x i =1; n i This represents the reversible specific capacity of the i-th type of active ingredient in the coating, expressed in mAh / g.

[0048] The applicant has discovered that for composite electrode sheets containing both carbon and silicon-based materials, with a fixed silicon-based material composition, the higher the proportion of silicon-based material, the higher the weighted specific capacity, but the greater the rebound of the electrode sheet under the same state of charge. When the weighted specific capacity of the first coating and the second coating differs too much, during the lithium insertion / extraction process of the electrode sheet, the expansion stress borne by the first coating and the second coating differs too much, and the interfacial compatibility between the two coatings deteriorates. Under full charge or during the battery life, the first coating and the second coating may separate and delaminate. As a result, some active materials in the first coating may be delithiated, and the conductive network may not be able to delithiate, which may lead to a mismatch in the capacity of the cathode and anode in local areas and lithium deposition, resulting in performance problems or even safety problems in lithium-ion batteries.

[0049] This application controls the ratio of the weighted specific capacity A1 of the first coating active material to the weighted specific capacity A2 of the second coating active material within the above range, so that when lithium ions are inserted and removed from the electrode under different capacity decay states, the first coating and the second coating maintain good interfacial compatibility and the stress difference between the two coatings is kept within a small range, thereby reducing the risk of lithium ion battery delamination during the entire life cycle and improving the performance and safety of lithium ion battery.

[0050] In some embodiments, the weighted specific capacity A1 of the first coating active material is 500 mAh / g to 1000 mAh / g, and the weighted specific capacity A2 of the second coating active material is 500 mAh / g to 1000 mAh / g. Without being limited to any particular theory, by synergistically controlling the weighted specific capacity A1 of the first coating active material and the weighted specific capacity A2 of the second coating active material within the aforementioned ranges, the expansion of the negative electrode sheet during cycling is controlled within a suitable range, while also achieving a high specific capacity, thereby obtaining a lithium-ion battery with good cycle life and energy density.

[0051] In some embodiments, the silicon-based material content in the first coating is 18 wt% to 55 wt%, and the silicon-based material content in the second coating is 7 wt% to 21 wt%. Without being limited to any particular theory, by synergistically controlling the silicon-based material content in the first coating and the silicon-based material content in the second coating within the aforementioned ranges, the expansion of the negative electrode during cycling is controlled within a suitable range, while also achieving a high specific capacity, thereby obtaining a lithium-ion battery with good cycle life and energy density.

[0052] In some embodiments, the first coating includes a first adhesive, and the second coating includes a second adhesive. In this application, the first adhesive and the second adhesive may be the same or different. By adding a first adhesive to the first coating and a second adhesive to the second coating, the interfacial adhesion between the first and second coatings can be improved, further reducing the risk of delamination between the first and second coatings and improving the safety of the lithium-ion battery.

[0053] This application does not impose any particular limitations on the first and second adhesives, as long as they achieve the purpose of this application. In some embodiments, the first and second adhesives each independently include at least one of polyacrylic acid, polyacrylate, sodium alginate, polyacrylonitrile, polyethylene glycol, carboxymethyl chitosan, and styrene-butadiene rubber.

[0054] In some embodiments, both the first and second binders include polyacrylate binders, with the content of the polyacrylate binder in the first coating being less than that in the second coating. In this application, when the first and second coatings of the negative electrode sheet include silicon-based materials, and both the first and second binders include polyacrylate binders, the polyacrylate binders can form strong hydrogen bonds with the silicon-based materials, effectively coating the surface of the silicon-based materials and thus mitigating the volume expansion of the silicon-based materials during charging and discharging. The applicant has found that because the oxygen-silicon molar ratio of the silicon-based material in the first coating is high, the volume expansion during lithium-ion battery cycling is smaller than that in the second coating. Therefore, by controlling the content of the polyacrylate binder in the first coating to be less than that in the second coating, it is possible to improve the energy density of the battery and reduce auxiliary material costs while still achieving the desired bonding effect.

[0055] In some embodiments, the content of the polyacrylate binder in the first coating is 3 wt% to 6 wt%, and the content of the polyacrylate binder in the second coating is 4 wt% to 7 wt%. The applicant has found, without limitation to any theory, that by controlling the content of the polyacrylate binder in the first and second coatings within the above-mentioned ranges, it is possible to effectively improve the energy density of the battery and reduce auxiliary material costs while satisfying the bonding effect.

[0056] In this application, there are no particular restrictions on the preparation method of silicon-based materials. For example, they can be prepared by the following steps:

[0057] The silicon-based material is obtained by reacting silica powder and elemental silicon powder in a high-temperature gas phase under a non-oxidizing gas atmosphere. The ratio of oxygen to silicon in the resulting silicon-based material is adjusted by regulating the ratio of silica powder to elemental silicon powder. This application does not impose any particular limitation on the particle size of the silica powder and elemental silicon powder, as long as they meet the requirements of this application. For example, the average particle size of the silica powder is 1 μm to 10 μm, and the average particle size of the elemental silicon powder is 1 μm to 10 μm. This application does not impose any particular limitation on the non-oxidizing gas atmosphere, such as argon or hydrogen. This application does not impose any particular limitation on the temperature of the gas phase reaction, as long as it meets the requirements of this application, such as 1300℃ to 1400℃.

[0058] In some embodiments, the prepared silicon-oxygen material can also be further coated or combined with other active materials for use in lithium-ion batteries.

[0059] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0060] In one embodiment of this application, a secondary battery is provided, which includes the negative electrode sheet described in any of the above embodiments. The secondary battery in this application may refer to the lithium-ion battery described in any of the above embodiments.

[0061] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0062] [Positive electrode plate]

[0063] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0064] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0065] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0066] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0067] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0068] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0069] [Negative electrode plate]

[0070] In some embodiments, the negative current collector of the negative electrode sheet may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0071] In some embodiments, the negative electrode sheet can be prepared by: preparing a first negative electrode slurry and a second negative electrode slurry; firstly, coating the second negative electrode slurry onto the current collector to form a second coating layer, and then coating the first negative electrode slurry onto the surface of the second coating layer to form a first coating layer; or, a double-layer coating device can be used during coating to simultaneously coat the first negative electrode slurry and the second negative electrode slurry onto the current collector; after drying, cold pressing and other processes, a negative electrode sheet is obtained, wherein one side of the second coating layer of the negative electrode sheet is the current collector layer, and the other side of the second coating layer is the first coating layer.

[0072] [Electrolytes]

[0073] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0074] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0075] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0076] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0077] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0078] [Isolation membrane]

[0079] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0080] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0081] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0082] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0083] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0084] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0085] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0086] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0087] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0088] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0089] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0090] Figure 5 and Figure 6 This is a sample battery pack 10. (See reference...) Figure 5 and Figure 6 The battery pack 10 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 11 and a lower box 12, with the upper box 11 covering the lower box 12 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0091] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0092] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0093] Figure 7This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0094] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0095] Example

[0096] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0097] Example 1

[0098] <Preparation of the positive electrode>

[0099] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) are mixed in a mass ratio of 96:2:2. Then, N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred under vacuum until homogeneous, yielding a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry is uniformly coated onto one surface of a 12 μm thick aluminum foil, dried at 120°C, and cold-pressed to obtain a positive electrode sheet with a 60 μm thick active material layer. This positive electrode sheet is then formed through tab molding and slitting processes.

[0100] <Preparation of Negative Electrode Sheets>

[0101] <Preparation of the first negative electrode slurry>

[0102] The first negative electrode active material, carbon material artificial graphite, conductive agent conductive carbon black, and binder sodium polyacrylate were mixed in a mass ratio of 18:77:2:3. Deionized water was added as a solvent, and the mixture was stirred under vacuum until the system was homogeneous, resulting in a first negative electrode slurry with a solid content of 50wt%.

[0103] <Preparation of the Second Negative Electrode Slurry>

[0104] The second negative electrode active material, carbon material artificial graphite, conductive agent conductive carbon black, and binder sodium polyacrylate were mixed in a mass ratio of 7:87:2:4. Deionized water was added as a solvent, and the mixture was stirred under vacuum until the system was homogeneous to obtain a second negative electrode slurry with a solid content of 50wt%.

[0105] <Preparation of negative electrode sheet containing first and second coatings>

[0106] A double-layer coating process is adopted, in which the first negative electrode slurry and the second negative electrode slurry are simultaneously coated on one surface of a copper foil with a thickness of 8μm. After drying at 110℃ and cold pressing, a negative electrode sheet with a first coating thickness of 25μm and a second coating thickness of 25μm is obtained. Then, the negative electrode sheet is obtained through processes such as tab forming and slitting.

[0107] <Preparation of Electrolyte>

[0108] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a volume ratio of 1:1:1 to obtain an electrolyte solvent. Then, lithium salt LiPF6 is dissolved in the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0109] <Preparation of the separating membrane>

[0110] A polyethylene film with a thickness of 9μm was selected as the separator. Before use, it was cut to a suitable width according to the size of the positive and negative electrode plates.

[0111] <Preparation of Lithium-ion Batteries>

[0112] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0113] Examples 2 to 11

[0114] In the <Preparation of Negative Electrode Sheet>, except for adjusting the molar ratio of O to Si in the first negative electrode slurry and the molar ratio of O to Si in the second negative electrode slurry as shown in Table 1; adjusting the values ​​of A1, A2, and A1:A2 as shown in Table 2; and adjusting the proportion of the first negative electrode active material in the first slurry, the proportion of the second negative electrode active material in the second slurry, the type and proportion of binder in the first slurry, the type and proportion of binder in the second slurry, the proportion of artificial graphite and conductive carbon black in the first negative electrode slurry, and the proportion of artificial graphite and conductive carbon black in the second negative electrode slurry as shown in Table 3, the rest is the same as in Example 1.

[0115] Example 12

[0116] Except for the preparation of the positive electrode sheet and the preparation of the negative electrode sheet, in which the positive electrode active material layer and the negative electrode active material layer adopt a double-sided coating process, that is, active material layers are set on both sides of the positive electrode current collector and the negative electrode current collector, the rest is the same as in Example 1. Among them, the active material layers on both sides of the negative electrode current collector each include a first coating layer and a second coating layer.

[0117] Comparative Example 1

[0118] Except for the preparation of the negative electrode sheet, which is different from Example 2, everything else is the same as Example 2.

[0119] <Preparation of Negative Electrode Sheets>

[0120] The first negative electrode slurry and the second negative electrode slurry of Example 2 were mixed at a mass ratio of 1:1 to obtain a mixed slurry. The mixed slurry was then coated on one surface of a copper foil with a thickness of 8 μm and dried at 110°C. After cold pressing, a negative electrode sheet with a negative electrode active material layer thickness of 50 μm was obtained. Then, the negative electrode sheet was obtained through processes such as tab forming and slitting.

[0121] Comparative Examples 2 to 6

[0122] In the <Preparation of Negative Electrode Sheet>, except for adjusting the molar ratio of O to Si in the first negative electrode slurry and the molar ratio of O to Si in the second negative electrode slurry as shown in Table 1; adjusting the values ​​of A1, A2, and A1:A2 as shown in Table 2; and adjusting the proportion of the first negative electrode active material in the first slurry, the proportion of the second negative electrode active material in the second slurry, the type and proportion of binder in the first slurry, the type and proportion of binder in the second slurry, the proportion of artificial graphite and conductive carbon black in the first negative electrode slurry, and the proportion of artificial graphite and conductive carbon black in the second negative electrode slurry as shown in Table 3, the rest is the same as in Example 1.

[0123] The relevant parameters of Examples 1-12 and Comparative Examples 1-6 are shown in Tables 1 to 3 below. Specifically, the molar ratio of O to Si in the first negative electrode slurry and the molar ratio of O to Si in the second negative electrode slurry are shown in Table 1; the values ​​of A1, A2, and A1:A2 are shown in Table 2; and the proportions of the first negative electrode active material in the first slurry, the second negative electrode active material in the second slurry, the type and proportion of binder in the first slurry, the type and proportion of binder in the second slurry, the proportions of artificial graphite and conductive carbon black in the first negative electrode slurry, and the proportions of artificial graphite and conductive carbon black in the second negative electrode slurry are shown in Table 3.

[0124] Table 1. Relevant parameters of Examples 1-12 and Comparative Examples 1-6

[0125]

[0126]

[0127] Table 2. Relevant parameters of Examples 1-12 and Comparative Examples 1-6

[0128] <![CDATA[A1∶A2]]> <![CDATA[A1(mAh / g)]]> <![CDATA[A2(mAh / g)]]> Example 1 1.01 549 546 Example 2 1.01 605 601 Example 3 1.01 860 853 Example 4 1.02 964 941 Example 5 1.02 565 553 Example 6 1.03 690 672 Example 7 0.81 605 743 Example 8 1.20 686 574 Example 9 1.00 605 602 Example 10 1.01 605 601 Example 11 1.02 607 598 Example 12 1.01 549 546 Comparative Example 1 1.01 605 601 Comparative Example 2 1.00 605 605 Comparative Example 3 0.99 601 605 Comparative Example 4 0.99 460 467 Comparative Example 5 0.64 549 853 Comparative Example 6 1.58 860 546

[0129] Table 3. Relevant parameters of Examples 1-12 and Comparative Examples 1-6

[0130]

[0131] In addition, the lithium-ion batteries prepared in Examples 1-12 and Comparative Examples 1-6, as well as coin cells made using the negative electrode active materials of Examples 1-12 and Comparative Examples 1-6, were subjected to performance tests. The test results are shown in Table 4 below.

[0132] Energy density test:

[0133] The test temperature was 25℃. The lithium-ion batteries prepared in each example and comparative example were first charged at a constant current rate of 0.33C to 4.25V, then charged at a constant voltage rate to 0.05C. After standing for 5 minutes, they were discharged at 0.33C to 2.8V, and their discharge energy was recorded. Then, the 0.33C discharge energy density was calculated according to the following formula: Energy density (Wh / kg) = Discharge energy (Wh) / Weight of electrochemical device (kg).

[0134] Cyclic life test:

[0135] The test temperature was 25℃. The lithium-ion batteries prepared in each example and comparative example were charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 0.05C, and after resting for 10 minutes, discharged at 0.33C to 2.8V. The capacity obtained in this step was taken as the initial capacity. Cyclic tests were performed using a cycle of charging at a constant current of 0.33C to 4.25V, charging at 4.25V to 0.05C, and discharging at 0.33C to 2.8V. The capacity decay curve was obtained by comparing the capacity at each step with the initial capacity. The cycle life of the battery was defined as the number of cycles at 25℃ until 80% capacity retention was achieved.

[0136] First charge / discharge efficiency test:

[0137] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to charge-discharge tests using the Neware CT-4000 power battery testing system, and the initial charge-discharge efficiency of the lithium-ion batteries was calculated.

[0138] The initial efficiency is calculated as (C1 / C2)×100%, where C1 is the capacity of the lithium-ion battery during the first charge, and the charging process is constant current charging at 0.33C to 4.25V, and then constant voltage charging at 4.25V to 0.05C; C2 is the capacity of the lithium-ion battery after the first charge according to the above process, with a discharge cutoff voltage of 2.8V at 0.33C.

[0139] Weighted capacity test:

[0140] The weighted specific capacity of the different coatings on the negative electrode sheets in Examples 1-12 and Comparative Examples 1-6 was obtained in the following manner:

[0141] A negative electrode active material (e.g., silicon-based material, artificial graphite material) is mixed with conductive carbon black (conductive agent) and PVDF (polyvinylidene fluoride) (binder) in a ratio of 80:10:10. After adding deionized water and stirring, a slurry with a solid content of 50 wt% is formed. A 50 μm thick coating is then applied to the current collector surface using a doctor blade. After drying in a vacuum drying oven at 85°C for 12 hours, the coating is cut into 1 cm diameter discs using a stamping machine in a dry environment. A coin cell is assembled using a lithium metal sheet as the counter electrode and a PE (polyethylene) composite membrane as the separator, along with electrolyte. The reversible specific capacity of the tested active components is calculated using a charge-discharge test. The weighted specific capacity of the active material in the first or second coating is calculated using the following expression: A = x1 × n1 + x2 × n2 (mAh / g). Where x1 and x2 are the mass ratios of silicon-based materials and carbon materials in the active material, respectively, and x1+x2=1, n1 represents the reversible specific capacity of silicon-based materials in mAh / g, and n2 represents the reversible specific capacity of artificial graphite materials in mAh / g.

[0142] Table 4: Performance test results of Examples 1-12 and Comparative Examples 1-6

[0143] First charge / discharge efficiency Energy density (Wh / kg) Cycle life (cycles) Example 1 90％ 280 1300 Example 2 88％ 300 1000 Example 3 86％ 330 700 Example 4 84％ 360 550 Example 5 83％ 270 1400 Example 6 89％ 320 850 Example 7 88％ 300 900 Example 8 88％ 300 950 Example 9 90％ 305 950 Example 10 88％ 300 850 Example 11 88％ 300 900 Example 12 90％ 285 1300 Comparative Example 1 88％ 300 550 Comparative Example 2 72％ 250 1050 Comparative Example 3 88％ 300 200 Comparative Example 4 76％ 250 1200 Comparative Example 5 87％ 300 600 Comparative Example 6 85％ 300 550

[0144] Based on the above results, the negative electrode of the lithium-ion battery in Examples 1-12 includes a first coating and a second coating, i.e., it has a multilayer structure. One side of the second coating is the current collector, and the other side of the second coating is the first coating. The molar ratio of O to Si elements in the silicon-based material in the first and second coatings is within the range of this application. The lithium-ion battery has better energy density and initial coulombic efficiency, while also having a good cycle life.

[0145] As can be seen from Examples 1 to 4, once the oxygen-silicon element ratio of the silicon-based material in each coating of the negative electrode is determined, the weighted specific capacity of the negative electrode will be improved as the content of silicon-based material in the negative electrode increases, thereby improving the energy density of the lithium-ion battery.

[0146] As can be seen from Examples 2, 5, 6, and 9, when the proportion of silicon-based material in each coating of the negative electrode is relatively fixed, as the molar ratio of oxygen and silicon elements in the silicon-based material in the first and second coatings increases, the cycle life of the lithium-ion battery is improved, while the energy density and initial coulombic efficiency show a decreasing trend, but the decrease is not significant.

[0147] As can also be seen from Examples 1 to 12, by controlling the proportion of silicon-based material in each coating, and making the ratio A1:A2 of the weighted specific capacity A1 of the first coating and the weighted specific capacity A2 of the second coating within the scope of this application, lithium-ion batteries can achieve a balance of high energy density, high initial coulombic efficiency, and long cycle life.

[0148] Examples 1-9 and 11-12 also show that when both the first and second coatings use polyacrylate binders (e.g., sodium polyacrylate), the lithium-ion battery will have a better cycle life when the content of the polyacrylate binder in the first coating is less than that in the second coating.

[0149] The type and content of binders in the first and second coatings also usually affect the performance of lithium-ion batteries. As can be seen from Examples 1 to 12, as long as the type and content of binders are within the scope of this application, lithium-ion batteries with better energy density and first coulombic efficiency, while also taking into account good cycle life, can be obtained.

[0150] In contrast, the negative electrode of Comparative Example 1 was obtained by uniformly mixing the slurry of the first coating and the slurry of the second active coating of Example 2 and then coating them. The type and composition of the silicon-based material in the direction perpendicular to the current collector are the same in this negative electrode. Therefore, the energy density and initial coulombic efficiency of Comparative Example 1 are basically the same as those of Example 2. However, since it does not have the dual-coating structure of this application, the reversible capacity of the silicon-based material (i.e., the second negative electrode active material) with an oxygen-silicon element ratio of 0.1:1 near the current collector surface will rapidly decay during the cycle. As a result, the cycle life of the lithium-ion battery in Comparative Example 1 is only 550 cycles. The cycle life has not been effectively improved, which is difficult to meet the requirements of lithium-ion battery life in many application scenarios.

[0151] In Comparative Example 2, the molar ratio of oxygen to silicon in the first and second coatings of the silicon-based materials was 1:1. The initial coulombic efficiency of the resulting lithium-ion battery was reduced to 72%, and the energy density of the lithium-ion battery could only reach 250Wh / kg. Compared with lithium-ion batteries that do not use silicon-based materials in the negative electrode, there was no significant advantage in energy density, making it difficult to meet the needs of high energy density scenarios.

[0152] The oxygen-silicon molar ratio of the first and second coatings used in the negative electrode of Comparative Example 3 is opposite to that of Example 2. The resulting lithium-ion battery exhibits rapid capacity decay during cycling, and its cycle life is only 200 cycles. The cycle life has not been effectively improved, making it difficult to meet the life requirements of lithium-ion batteries in many application scenarios.

[0153] In Comparative Example 4, the oxygen-silicon ratio of the silicon-based material in the first coating was 1.85:1, resulting in a lithium-ion battery with extremely low initial coulombic efficiency and an energy density of only 250Wh / kg. This is no better than lithium-ion batteries that do not use silicon-based materials and cannot meet the needs of high energy density applications.

[0154] The weighted specific capacity A1 of the first coating to the weighted specific capacity A2 of the second coating in the negative electrode sheets of Comparative Examples 5 and 6 is outside the scope of this application, resulting in a decrease in the cycle life of the lithium-ion battery. This may be because during the lithium-ion battery deintercalation and deintercalation process in Comparative Examples 5 and 6, the expansion stress difference between the first coating and the second coating is large, the interfacial compatibility between the first coating and the second coating is poor, and even some areas of the first coating detach from the second coating. This may cause some active material in the first coating to detach from the conductive network during cycling, affecting the cycle life of the lithium-ion battery.

[0155] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode sheet, characterized by, It includes a first coating, a second coating, and a current collector. The second coating is disposed on at least one side surface of the current collector, and the first coating is disposed on the side surface of the second coating away from the current collector. The first coating and the second coating include silicon-based materials. The molar ratio of O to Si in the silicon-based material of the first coating is 0.5 to 1.5, and the molar ratio of O to Si in the silicon-based material of the second coating is less than or equal to 0.

3.

2. The negative electrode sheet according to claim 1, characterized by, The molar ratio of O to Si elements in the silicon-based material of the second coating is 0.05 to 0.

2.

3. The negative electrode sheet according to claim 1, wherein The weighted specific capacity A1 of the first coating active material and the weighted specific capacity A2 of the second coating active material satisfy the following condition: 0.8 ≤ A1 ∶ A2 ≤ 1.

2.

4. The negative electrode sheet according to claim 3, characterized in that, The weighted specific capacity A1 of the first coating active material is 500 mAh / g to 1000 mAh / g, and the weighted specific capacity A2 of the second coating active material is 500 mAh / g to 1000 mAh / g.

5. The negative electrode sheet according to claim 1, wherein The silicon-based material is present in the first coating at a content of 18 wt% to 55 wt%, and in the second coating at a content of 7 wt% to 21 wt%.

6. The negative electrode sheet according to claim 1, wherein The first coating includes a first adhesive, and the second coating includes a second adhesive.

7. The negative electrode sheet according to claim 6, characterized in that, The first adhesive and the second adhesive each independently comprise at least one of polyacrylic acid, polyacrylate, sodium alginate, polyacrylonitrile, polyethylene glycol, carboxymethyl chitosan, and styrene-butadiene rubber.

8. The negative electrode sheet according to claim 6, characterized by Both the first adhesive and the second adhesive include polyacrylate adhesives, and the content of the polyacrylate adhesive in the first coating is less than that in the second coating.

9. The negative electrode sheet according to claim 8, characterized by, The polyacrylate adhesive is present in the first coating at a content of 3 wt% to 6 wt%, and in the second coating at a content of 4 wt% to 7 wt%.

10. A secondary battery characterized by comprising: It includes the negative electrode sheet as described in any one of claims 1 to 9.

11. A battery module, characterized by It includes the secondary battery as described in claim 10.

12. A battery pack, characterized by, It includes the battery module as described in claim 11.

13. An electrical device, characterized by It includes at least one selected from the secondary battery of claim 10, the battery module of claim 11, or the battery pack of claim 12.

Images