Secondary battery current collector, negative pole piece and lithium ion battery

Abstract

The invention provides a secondary battery current collector, a negative pole piece and a lithium ion battery. The current collector comprises a current collector base material; the first carbon coating layer is arranged on at least one side surface along the thickness direction of the current collector base material; the second carbon coating layer is arranged on one side, far away from the current collector base material, of the first carbon coating layer; the porosity of the first carbon coating layer is 5%-25%, and the porosity of the second carbon coating layer is 35%-55%. According to the secondary battery current collector, the negative pole piece and the lithium ion battery provided by the invention, silicon particles are prevented from being embedded, and meanwhile, rapid infiltration is ensured.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a secondary battery current collector, a negative electrode sheet, and a lithium-ion battery. Background Technology

[0002] With the continuous improvement of the energy density of lithium-ion batteries, silicon-based anode materials are regarded as one of the key materials for the next generation of high-energy-density batteries due to their extremely high theoretical specific capacity. However, the high hardness and high modulus of silicon materials also bring significant challenges to the electrode manufacturing process.

[0003] During electrode rolling, high-hardness silicon particles easily embed into the current collector under high pressure, causing multiple problems: First, it damages the integrity of the copper foil structure, leading to localized thinning or even perforation of the current collector, increasing the risk of internal short circuits in the battery; second, it damages the conductive network, increasing electrode resistance and affecting battery performance; third, during cycling, the embedded silicon particles repeatedly expand and contract, generating periodic stress on the copper foil, accelerating fatigue damage to the current collector and the shedding of active material, thus causing rapid capacity decay. Forming a carbon coating layer on the current collector can enhance the bonding force between the active material and the current collector and reduce interfacial resistance, but a single carbon coating layer cannot simultaneously meet the requirements of anti-embedding, high bonding force, and wettability. Under high-pressure rolling conditions, silicon particles may still penetrate or crush the coating, ultimately embedding into the copper foil matrix, failing to fundamentally overcome the silicon embedding problem. Summary of the Invention

[0004] This invention proposes a secondary battery current collector, a negative electrode sheet, and a lithium-ion battery. By setting a first carbon coating layer and a second carbon coating layer, rapid wetting is ensured while preventing silicon particle embedding.

[0005] To solve the above-mentioned technical problems, the present invention proposes a secondary battery current collector, comprising:

[0006] Current collector substrate;

[0007] A first carbon coating layer is disposed on at least one surface along the thickness direction of the current collector substrate; and

[0008] The second carbon coating layer is disposed on the side of the first carbon coating layer away from the current collector substrate; the porosity of the first carbon coating layer is 5%-25%, and the porosity of the second carbon coating layer is 35%-55%.

[0009] In one embodiment of the present invention, the porosity ratio of the second carbon coating layer to the first carbon coating layer is greater than or equal to 2.

[0010] In one embodiment of the present invention, the first carbon coating layer includes a first conductive agent and a first binder, and the second carbon coating layer includes a second conductive agent and a second binder. The glass transition temperature of the first binder is greater than or equal to 20°C, and the glass transition temperature of the second binder is less than or equal to 0°C.

[0011] In one embodiment of the present invention, the first conductive agent includes a first conductive material and a second conductive material; the first conductive material includes at least one of hard carbon, conductive carbon black or graphite, and the second conductive material includes at least one of graphene or graphite nanosheets.

[0012] And / or, the median particle size of the first conductive material is 0.3 μm-0.7 μm, and the sheet size of the second conductive material is 0.2 μm-1.5 μm;

[0013] And / or, the mass ratio of the first conductive material to the second conductive material is (85-90):(10-15).

[0014] In one embodiment of the present invention, the second conductive agent includes a third conductive material and a fourth conductive material; the third conductive material includes at least one of hard carbon, conductive carbon black or graphite, and the fourth conductive material includes at least one of graphene or graphite nanosheets.

[0015] And / or, the median particle size of the third conductive material is 0.9 μm-2 μm, and the sheet size of the fourth conductive material is 2.5 μm-8 μm;

[0016] And / or, the mass ratio of the third conductive material to the fourth conductive material is (80-85):(15-20).

[0017] In one embodiment of the present invention, the first adhesive includes at least one of polyurethane, styrene-acrylic emulsion, or acrylate emulsion;

[0018] And / or, the second adhesive comprises one or more of styrene-butadiene rubber, acrylate rubber, or styrene-acrylic emulsion.

[0019] In one embodiment of the present invention, the second carbon coating layer further includes a thickener, the thickener including one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate or sodium polyacrylate, and the mass ratio of the second binder to the thickener is 2:1-4:1.

[0020] In one embodiment of the present invention, the current collector substrate includes at least one of copper, nickel, titanium, silver, chromium or molybdenum, and the thickness of the current collector substrate is 3.5μm-12μm;

[0021] And / or, the total thickness of the first carbon coating layer and the second carbon coating layer on one side of the current collector substrate is 1.5μm-4.5μm;

[0022] And / or, the thickness of the first carbon coating layer is 0.5μm-1.5μm;

[0023] And / or, the thickness of the second carbon coating layer is 1μm-3μm.

[0024] The present invention also provides a negative electrode sheet, comprising a current collector and a negative electrode active layer disposed on a carbon coating layer along the thickness direction of the current collector, wherein the negative electrode active layer comprises a negative electrode active material, and the negative electrode active material comprises one or more of elemental silicon, silicon-oxygen materials, silicon-carbon materials or silicon alloys;

[0025] The current collector is selected from the secondary battery current collectors described above.

[0026] The present invention also provides a lithium-ion battery, comprising:

[0027] Positive electrode sheet;

[0028] Negative electrode sheet, wherein the negative electrode sheet is selected from the negative electrode sheets described above;

[0029] A diaphragm is disposed between the positive electrode and the negative electrode.

[0030] In summary, this invention proposes a secondary battery current collector, a negative electrode sheet, and a lithium-ion battery. By sequentially depositing a first carbon coating layer and a second carbon coating layer on at least one side of the current collector substrate, with the second carbon coating layer having higher porosity, during the electrode sheet rolling process, the high-porosity porous layer of the second carbon coating layer first undergoes elastic deformation, absorbing and dispersing part of the impact force. The remaining stress is transferred to the low-porosity porous layer of the first carbon coating layer, acting as a robust physical barrier to prevent silicon particles from embedding into the copper foil. This avoids brittle damage to the current collector caused by direct hard impact while ensuring the final defensive strength of the current collector. Simultaneously, the high-porosity second carbon coating layer provides a rapid channel for the electrolyte, isolating silicon from contact with the current collector substrate, successfully resolving the inherent contradiction in traditional coatings where "increasing hardness will clog pores, and increasing porosity will decrease hardness." Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1This is a schematic diagram of a current collector in one embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram of a current collector in another embodiment of the present invention.

[0034] Label Explanation:

[0035] 10. Current collector substrate; 21. First carbon coating layer; 22. Second carbon coating layer. Detailed Implementation

[0036] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0037] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0038] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Please see Figures 1 to 2 As shown, this invention proposes a current collector comprising a current collector substrate 10, a first carbon coating layer 21, and a second carbon coating layer 22. The first carbon coating layer 21 is disposed on at least one surface along the thickness direction of the current collector substrate 10, and the second carbon coating layer 22 is disposed on the side of the first carbon coating layer 21 away from the current collector substrate 10. With the current collector provided by this application, the first carbon coating layer 21 and the second carbon coating layer 22 function synergistically, preventing silicon particle embedding while ensuring rapid wetting.

[0040] Please see Figures 1 to 2 As shown, in one embodiment of the present invention, the current collector substrate 10 is, for example, at least one of copper, nickel, titanium, silver, chromium, or molybdenum, and the thickness of the current collector substrate is 3.5 μm-12 μm to match different battery systems and meet the manufacturing requirements of lithium-ion batteries. In this embodiment, the current collector substrate 10 is, for example, copper foil.

[0041] Please see Figures 1 to 2As shown, in one embodiment of the present invention, a first carbon coating layer 21 and a second carbon coating layer 22 are sequentially disposed on one side surface along the thickness direction of the current collector substrate 10, or the first carbon coating layer 21 and the second carbon coating layer 22 are sequentially disposed on both sides surface along the thickness direction of the current collector substrate 10. The porosity of the first carbon coating layer 21 is, for example, 5%-25%, and the porosity of the second carbon coating layer 22 is, for example, 35%-55%. In one embodiment of the present invention, the porosity ratio of the second carbon coating layer 22 to the first carbon coating layer 21 is, for example, greater than or equal to 2. The second carbon coating layer 22 has a higher porosity. During electrode rolling, the high-porosity porous layer of the second carbon coating layer undergoes elastic deformation first, absorbing and dispersing a portion of the impact force. The remaining stress is transferred to the low-porosity porous layer of the first carbon coating layer, acting as a robust physical barrier to prevent silicon particles from embedding into the copper foil. This avoids brittle damage to the current collector caused by direct hard impact and ensures the final defensive strength of the current collector. Meanwhile, the second carbon coating layer 22 with high porosity provides a fast channel for the electrolyte and isolates the silicon from the current collector substrate, successfully solving the inherent contradiction in traditional coatings that "increasing hardness will block the pores, and increasing pores will reduce hardness".

[0042] Please see Figures 1 to 2 As shown, in one embodiment of the present invention, the first carbon coating layer 21 includes, for example, a first conductive agent and a first binder, and the mass ratio of the first conductive agent to the first binder is, for example, (70-75):(25-30). The first conductive agent includes, for example, a first conductive material and a second conductive material. The first conductive material includes at least one of hard carbon, conductive carbon black, or graphite, and its shape is, for example, spherical particles. The median particle size of the first conductive material is, for example, 0.3 μm-0.7 μm, where the median particle size is the particle size value corresponding to a cumulative volume distribution percentage of 50% in the volume distribution curve. The second conductive material includes, for example, at least one of graphene or graphite nanosheets, and the second conductive material is, for example, a sheet material, with a sheet diameter of, for example, 0.2 μm-1.5 μm. In one embodiment of the present invention, the mass ratio of the first conductive material to the second conductive material is (85-90):(10-15). The first conductive agent is a combination of granules and flakes. The granules can fill the spaces between the flakes, preventing them from stacking tightly and "spreading" and "bridging" them. At the same time, the flakes wrap around and connect the isolated granules, anchoring them in a unified and stable micro-framework, while also allowing for the adjustment of the porosity of the first carbon coating layer.

[0043] In one embodiment of the present invention, the glass transition temperature (Tg) of the first adhesive is, for example, greater than or equal to 20°C. The first adhesive includes, for example, at least one of waterborne polyurethane (WPU), styrene-acrylic emulsion (SAE), or acrylic emulsion (AE). To ensure the glass transition temperature of the first adhesive, for polyurethane, its molecular chain should contain a high proportion of rigid segments, such as hard segments composed of aromatic isocyanates and highly rigid polyols; for styrene-acrylic emulsion, the mass percentage of styrene monomer used in the preparation process should not be less than 50%; for acrylic emulsion, methyl methacrylate (MMA) should be used as the main monomer in the preparation process, and / or crosslinking monomers should be introduced to form a moderately crosslinked network structure. Crosslinking monomers include, for example, glycidyl methacrylate, N-hydroxymethylacrylamide, or vinyltriethoxysilane. Therefore, the first carbon coating layer has high hardness and elastic modulus, which can resist the indentation of silicon particles and act as a strong physical barrier.

[0044] In one embodiment of the present invention, the first carbon coating layer further includes, for example, a dispersant selected from one or more polymeric dispersants such as primary alcohol ethylene ether (AEO) or polyacrylate, and for example, AEO-3, AEO-7, AEO-9, sodium polyacrylate, or potassium polyacrylate. The content of the dispersant in the first carbon coating layer is, for example, 0.5 wt% to 2 wt%, to improve the formation quality of the first carbon coating layer.

[0045] Please see Figures 1 to 2As shown, in one embodiment of the present invention, the second carbon coating layer 22 includes a second conductive agent, a second binder, and a thickener, etc. In the second carbon coating layer 22, the content of the second binder is, for example, 18wt%-22wt%, and the mass ratio of the second binder to the thickener is, for example, 2:1-4:1. The second conductive agent includes, for example, a composite of a third conductive material and a fourth conductive material. The third conductive material includes at least one of hard carbon, conductive carbon black, or graphite, and the shape of the third conductive material is, for example, spherical particles, with a median particle size of, for example, 0.9μm-2μm. The fourth conductive material includes, for example, at least one of graphene or graphite nanosheets, and the fourth conductive material is, for example, a sheet material with a sheet diameter of, for example, 2.5μm-8μm. In one embodiment of the present invention, the mass ratio of the third conductive material to the fourth conductive material is (80-85):(15-20). In this application, the median particle size of the third conductive material is larger than that of the first conductive material, and the sheet diameter of the fourth conductive material is larger than that of the second conductive material. In the first carbon coating layer 21, the small carbon particles, through close packing, construct a solid base resisting the embedding stress of the silicon anode. In the second carbon coating layer 22, the large carbon particles act as support points, preventing the porous framework from being completely crushed during rolling and maintaining the elasticity of the structure. The flakes have high toughness and a large specific surface area. In the second carbon coating layer 22, the large-diameter flakes overlap to construct an open, interconnected porous network, which also improves the coating toughness. This is the microscopic basis for achieving rapid wetting and stress buffering. In the first carbon coating layer 21, the small-diameter flakes fill the spaces between the carbon particles, strengthening the toughness and bonding strength of the entire dense layer and preventing brittle cracking. Therefore, by controlling the selection of conductive materials, the constructed carbon coating layer can simultaneously achieve a microstructure of "rapid electrolyte wetting" and "efficient stress buffering".

[0046] In one embodiment of the present invention, the glass transition temperature of the second adhesive is, for example, less than or equal to 0°C. The second adhesive includes, for example, at least one of polymerized styrene-butadiene rubber (SBR), acrylic rubber (ACM), or styrene-acrylic emulsion. To ensure the glass transition temperature of the second adhesive, the styrene monomer content used in the preparation of the styrene-acrylic emulsion should not exceed 30% by mass, and the acrylate monomer used should be mainly selected from flexible monomers with a glass transition temperature below -40°C, such as n-butyl acrylate (BA) or 2-ethylhexyl acrylate (2-EHA). Therefore, the high-porosity second carbon coating layer prepared from an elastic material can provide soft cushioning, absorb the impact of rolling pressure, and provide a fast channel for the electrolyte.

[0047] In one embodiment of the present invention, the thickener includes one or more of the following: sodium carboxymethyl cellulose (CMC-Na), hydroxyethyl cellulose (HEC), sodium alginate (SA), or sodium polyacrylate (PAAS), to improve the formation quality of the second carbon coating layer.

[0048] Please see Figures 1 to 2 As shown, in one embodiment of the present invention, the total thickness of the first carbon coating layer 21 and the second carbon coating layer 22 on one side of the current collector substrate 10 is, for example, 1.5 μm-4.5 μm, the thickness of the first carbon coating layer 21 is, for example, 0.5 μm-1.5 μm, and the thickness of the second carbon coating layer 22 is, for example, 1 μm-3 μm. By controlling the thickness of each carbon coating layer, the conductivity of the current collector is ensured while also taking into account rapid electrolyte wetting and efficient stress buffering.

[0049] In one embodiment of the present invention, a method for preparing a current collector is also provided, specifically comprising: dispersing a first conductive agent and a first binder in a first solvent to obtain a first slurry; dispersing a thickener in a second solvent to obtain a glue; adding a second conductive agent to the glue and dispersing it, then adding a second binder and mixing it evenly to obtain a second slurry; coating the first slurry onto at least one surface of the current collector substrate in its thickness direction and drying it to form a first carbon coating layer; coating the second slurry onto the first carbon coating layer and drying it, and then curing it to obtain a current collector.

[0050] In one embodiment of the present invention, the first solvent and the second solvent are each selected from deionized water, high-purity water, etc. In the first slurry, the first conductive agent and the first binder are added to the first solvent, and a dispersant is added as needed. After stirring at 1000rpm-1500rpm for 40min-80min, the slurry is transferred to a pin mill and ground for 2h-4h at a shear rate of, for example, 3m / s-10m / s. At this point, the slurry particle size distribution shows D50≤0.8μm. After filtering through a 200-mesh filter, the slurry is ready for use. The solid content in the first slurry is, for example, 18%-23%.

[0051] In one embodiment of the present invention, when preparing the second slurry, a thickener is first dispersed with deionized water to prepare a glue solution. Then, the second conductive agent and the glue solution are stirred at 900 rpm-1200 rpm for 60-90 minutes, followed by short-time, low-shear grinding in a pin mill for 0.5-1 hour, wherein the shear rate is, for example, 1 m / s-5 m / s, to preserve the macroscopic network structure formed by the overlapping of large-diameter sheets. Finally, the second binder is added and stirred at 300 rpm-500 rpm for 30-60 minutes. The slurry is then degassed under vacuum, and its particle size D50 is controlled within the range of 8 μm-15 μm. After filtration through a 100-mesh sieve, it is ready for use. The solid content in the second slurry is, for example, 10%-14%.

[0052] In one embodiment of the present invention, the first slurry is coated using, for example, a high-precision dual-microgravure coating technique. After coating, it is pre-cured by efficient hot air drying at 80℃-120℃ to obtain a first carbon coating layer. Then, a second slurry is coated onto the first carbon coating layer using, for example, a high-precision dual-microgravure coating technique. After coating, residual solvent is completely removed at 100℃-120℃, and then cross-linking and curing is performed at 150℃-180℃. This allows the binder systems in the upper and lower layers to form films synchronously and synergistically, and both reach their final physicochemical strength, thereby forming a stable double-layer composite coating structure.

[0053] The present invention also provides a negative electrode sheet, comprising a current collector and a negative electrode active layer disposed at least on one side surface of the current collector along the thickness direction of the current collector. The current collector is selected from the aforementioned current collectors. The negative electrode active layer includes, for example, a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a negative electrode thickener. The negative electrode active material includes, for example, one or more silicon-based materials such as elemental silicon, silicon-oxygen materials, silicon-carbon materials, or silicon alloys. In this embodiment, the negative electrode active material is, for example, a composite of a silicon-based material and a carbon material, and the content of the silicon-based material in the negative electrode active material is greater than or equal to 5 wt%. The carbon material is selected from, for example, at least one of artificial graphite, natural graphite, soft carbon, or hard carbon. The negative electrode binder is selected from at least one of styrene-butadiene rubber, polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinyl chloride (PVC), carboxylated polyvinyl chloride (CPVC), polyvinyl fluoride (PVF), or polyurethane (PU). The negative electrode thickener is selected from, for example, sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li). The negative electrode conductive agent is selected from, for example, one of conductive carbon black, Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, or porous carbon, or a combination of two or more in any proportion. In one embodiment of the present invention, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode binder and the negative electrode thickener in the negative electrode active layer is, for example, (91-97):(1-2):(1-5):(1-2).

[0054] In one embodiment of the present invention, the negative electrode active material is selected, for example, from a mixture of artificial graphite and silicon oxide materials, and the content of silicon oxide materials is 60 wt%. The negative electrode conductive agent is selected, for example, from conductive carbon black. The negative electrode thickener is selected, for example, from sodium carboxymethyl cellulose. The negative electrode binder is selected, for example, from polyacrylic acid. The negative electrode active material, negative electrode conductive agent, negative electrode thickener, and negative electrode binder are mixed, for example, in a mass ratio of 94:2:2:2. Deionized water is added, and the mixture is thoroughly stirred and mixed evenly under the action of a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is coated onto the above-mentioned current collector, and then vacuum dried at 120°C. After processes such as rolling, edge trimming, sheet cutting, and slitting, a negative electrode sheet is obtained. The rolling pressure is, for example, 4 T / cm-8 T / cm, the rolling speed is, for example, 4 m / min-6 m / min, the rolling temperature is, for example, room temperature, the number of times the sheet passes through the roller is, for example, once, and the target compaction density is, for example, 1.5 g / cm³. 3 -1.8g / cm 3 .

[0055] This invention also proposes a lithium-ion battery, comprising a casing and an electrode assembly disposed within the casing. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode is selected from the aforementioned negative electrode. The separator is placed between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes, allowing lithium ions to pass through. The positive electrode, separator, and negative electrode are sequentially stacked to ensure that a separator is provided between any positive and negative electrode. A multi-layered stack is obtained by winding or folding, and this stack is then installed as the electrode assembly within the battery casing. Finally, electrolyte is injected into the casing once or in multiple stages to completely immerse the electrode assembly in the electrolyte, thereby conducting ions between the positive and negative electrodes. In one embodiment of this invention, the lithium-ion battery is, for example, a primary battery or a secondary battery. A secondary battery is, for example, a pouch battery, a hard-shell battery, or a cylindrical battery. This invention does not specifically limit the type of lithium-ion battery. In this embodiment, a pouch battery is used as an example to illustrate the lithium-ion battery.

[0056] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active layer coated on at least one surface of the positive current collector. The positive current collector is, for example, a foil formed by surface treatment of materials such as nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. The thickness of the positive current collector is, for example, 8 μm-15 μm. In this embodiment, the positive current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm.

[0057] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. The positive electrode active material is selected, for example, from lithium iron phosphate (LiFePO4) and lithium manganese iron phosphate (LiFe2+). x Mn 1-xPO4, where 0 < x < 1), one or more of ternary layered oxides (NCM) or lithium manganate (LiMn2O4), etc. The cathode binder is, for example, selected from any one or more of polyvinylidene fluoride, polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile, polyacrylate (PAcr), polyvinyl ether (PVE), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene (PHFP), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer (TFE-HFP-VDF), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP), etc. The cathode conductive agent is, for example, selected from any one or more of conductive carbon black (SuperP), Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, or porous carbon, etc. Among them, the mass ratio of the cathode active material, cathode conductive agent, and cathode binder in the cathode active layer is, for example, (90 - 98):(1 - 5):(1 - 5).

[0058] In an embodiment of the present invention, the cathode active material is, for example, LiNi 0.8 Co 0.1 Mn 0.1 O2, the cathode binder is, for example, selected from polyvinylidene fluoride, and the conductive agent is, for example, selected from conductive carbon black. After mixing the cathode active material, conductive agent, and cathode binder, for example, in a mass ratio of 98:1:1, an organic solvent is added, and the mixture is stirred in a vacuum mixer until the system becomes homogeneous to obtain a cathode slurry. Among them, the organic solvent is, for example, selected from N-methylpyrrolidone (NMP). The cathode slurry is uniformly coated on an aluminum foil, then dried at room temperature and transferred to an oven for drying, and a cathode pole piece is obtained through processes such as cold pressing, edge trimming, slicing, and slitting. The present application does not limit the preparation method of the cathode pole piece. In other embodiments, the cathode pole piece can also be obtained by any other method of forming a cathode pole piece.

[0059] In an embodiment of the present invention, the separator is, for example, a polyethylene film (PE), polypropylene film (PP), glass fiber film, or composite film, etc., and the thickness of the separator is, for example, 9 μm - 15 μm. In an embodiment of the present invention, a polyethylene with a thickness of 8 μm - 10 μm is, for example, selected as the base film, and a nano-aluminum oxide coating with a thickness of 2 μm - 4 μm is coated on at least one side of the base film.

[0060] In one embodiment of the present invention, the electrolyte includes, for example, an organic solvent and a lithium salt. The organic solvent is selected from one or more of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC). The lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), or lithium perchlorate (LiClO4). In this embodiment, the lithium salt is, for example, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the content of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than or equal to 2 wt% to improve the operating voltage of the battery. The electrolyte may also include additives, such as any one or more selected from vinylene carbonate (VC), ethylene sulfate (1,3,2-Dioxathiolane 2,2-dioxide (DTD), lithium difluorooxalate borate (LiDFOB), or 1,3-propanesultone (1,3-PS). In this embodiment, in a glove box with an inert gas atmosphere such as argon containing less than or equal to 10 ppm of moisture and oxygen, ethylene carbonate and ethyl methyl carbonate are mixed, for example, in a mass ratio. Thoroughly dried LiPF6, LiFSI, VC, PS, and DTD are dissolved in the mixed organic solvent and mixed thoroughly to obtain the electrolyte. The electrolyte contains 24 wt% ethylene carbonate, 58 wt% ethyl methyl carbonate, 6 wt% LiPF6, 9 wt% LiFSI, 1 wt% VC, 1 wt% PS, and 1 wt% DTD.

[0061] In one embodiment of the present invention, the above-mentioned positive electrode, separator, and negative electrode are placed alternately and stacked or wound to obtain an electrode assembly. Then, an aluminum-plastic film is wrapped around the assembly, and after baking at 80°C-120°C to remove moisture, electrolyte is injected at a rate of 3.4 g / Ah and the assembly is sealed. Following this, processes such as settling, hot and cold pressing, formation, clamping, and capacity testing are performed to obtain the finished lithium-ion battery. The designed capacity of the lithium-ion battery is, for example, 1 Ah.

[0062] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the invention and all such modifications fall within the technical scope of the invention. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available or can be prepared by conventional methods in the art, and the instruments used in the tests are also commercially available.

[0063] Example 1

[0064] Preparation of the current collector: Hard carbon with a D50 of 0.5 μm and graphene with a sheet diameter of 1 μm were prepared at a mass ratio of 88:12 to obtain the first conductive agent. Polyurethane with a Tg of 45℃, the first conductive agent, and dispersant AEO-9 were prepared at a mass ratio of 30:69:1. Deionized water was added, and the mixture was premixed by stirring at 1200 rpm for 60 min. Then, it was transferred to a pin mill and ground at 5 m / s for 3 h, controlling the final solid content to be 20%. The particle size D50 of the ground slurry was 0.7 μm. After filtering through a 200-mesh filter, the first slurry was obtained.

[0065] A second conductive agent was obtained by mixing hard carbon with a D50 of 1.5 μm and graphene with a sheet diameter of 5 μm at a mass ratio of 85:15. A 1.5 wt% slurry was prepared by mixing CMC with deionized water. The second conductive agent and CMC slurry were stirred at 1000 rpm for 90 min, then transferred to a pin mill and ground at 2 m / s for 1 h. SBR with a Tg of -45℃ was slowly added, along with deionized water, and the mixture was stirred at 400 rpm for 30 min, controlling the final solid content to 12%. The slurry was degassed under vacuum, and the particle size D50 was measured to be 9.5 μm. After filtering through a 100-mesh filter, a second slurry was obtained. In the second slurry, the mass ratio of the second conductive agent, SBR, and CMC was 76:18:6.

[0066] Using a dual-microgravure coating machine, a first slurry is applied to both sides of an 8μm thick copper foil at a speed of 10m / min, and then immediately pre-cured in a 100℃ hot air oven. A second slurry is applied over the pre-cured coating, followed by a segmented curing oven. First, residual moisture is thoroughly removed at 110℃, then cross-linking and curing is performed at 170℃ for 15 minutes. After cooling, the foil is wound up to obtain the finished current collector.

[0067] Cross-sectional scanning electron microscopy (SEM) measurements showed that on one side of the copper foil, the thickness of the first carbon coating layer was 1.0 μm, the thickness of the second carbon coating layer was 2.0 μm, and the total carbon coating layer thickness was 3.0 μm. Mercury porosimetry measurements showed that the porosity of the first carbon coating layer was 18%, the porosity of the second carbon coating layer was 48%, and the porosity ratio of the second carbon coating layer to the first carbon coating layer was 2.67.

[0068] Preparation of the negative electrode sheet: The negative electrode active material is selected from a mixture of artificial graphite and silicon oxide materials, with the silicon oxide material content being 60 wt%. The negative electrode conductive agent is selected from conductive carbon black, the negative electrode thickener is selected from sodium carboxymethyl cellulose, and the negative electrode binder is selected from polyacrylic acid. The negative electrode active material, negative electrode conductive agent, negative electrode thickener, and negative electrode binder are mixed, for example, in a mass ratio of 94:2:2:2. Deionized water is added, and the mixture is thoroughly stirred and mixed evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry is coated onto the aforementioned current collector, and then vacuum dried at 120°C. After processes such as rolling, edge trimming, sheet cutting, and slitting, the negative electrode sheet is obtained. The rolling pressure is 6 T / cm, the rolling speed is 5 m / min, the rolling temperature is room temperature, the rolling is performed once, and the target compaction density is, for example, 1.67 g / cm³. 3 .

[0069] Example 2

[0070] In preparing the current collector, the solid content of the second slurry is 10%, and the porosity of the obtained second carbon coating layer is 55%. The remaining steps are the same as in Example 1.

[0071] Example 3

[0072] In preparing the current collector, the solid content of the second slurry was 14%, and the porosity of the obtained second carbon coating layer was 35%. The remaining steps were the same as in Example 1.

[0073] Example 4

[0074] In preparing the current collector, the solid content of the first slurry is 35%, the porosity of the first carbon coating layer is 5%, and the remaining steps are the same as in Example 1.

[0075] Example 5

[0076] In preparing the current collector, the solid content of the first slurry was 18%, and the porosity of the first carbon coating layer was 25%. The remaining steps were the same as in Example 1.

[0077] Example 6

[0078] In preparing the current collector, the first slurry had a solid content of 19%, resulting in a first carbonized layer with a porosity of 20%; the second slurry had a solid content of 13%, resulting in a second carbonized layer with a porosity of 40%. The porosity ratio of the second carbonized layer to the first carbonized layer was 2.0. The remaining steps were the same as in Example 1.

[0079] Example 7

[0080] In preparing the current collector, the first binder is SAE with a Tg of 22°C, wherein the styrene content in the SAE preparation is 55%-60% by mass. The second binder is an acrylic emulsion with a Tg of -2°C, which is obtained by copolymerizing methyl methacrylate and n-butyl acrylate at a mass ratio of 30:70 and contains 0.5%-1% of the crosslinking monomer glycidyl methacrylate. The thickener is HEC, and the remaining steps are the same as in Example 1.

[0081] Example 8

[0082] In preparing the current collector, the first conductive agent has a D50 of 0.3 μm for hard carbon and a sheet diameter of 0.2 μm for graphene. The remaining steps are the same as in Example 1.

[0083] Example 9

[0084] In preparing the current collector, the first conductive agent has a D50 of 0.7 μm for hard carbon and a sheet diameter of 1.5 μm, and the remaining steps are the same as in Example 1.

[0085] Example 10

[0086] In preparing the current collector, the hard carbon in the second conductive agent has a D50 of 0.9 μm and the graphene sheet diameter is 2.5 μm. The remaining steps are the same as in Example 1.

[0087] Example 11

[0088] In preparing the current collector, the hard carbon in the second conductive agent has a D50 of 2 μm and the graphene sheet diameter is 8 μm. The remaining steps are the same as in Example 1.

[0089] Comparative Example 1

[0090] In preparing the current collector, hard carbon (D50 2 μm), acrylate, and AEO-9 were mixed in a mass ratio of 30:69:1, and deionized water was added and mixed thoroughly to control the solid content at 16%, thus obtaining a carbon coating slurry. The carbon coating slurry was coated onto both sides of an 8 μm thick copper foil and dried in a 100°C hot air oven. The thickness of the carbon coating layer was 3.0 μm, and the porosity of the carbon coating layer was 30%. The remaining steps were the same as in Example 1.

[0091] Comparative Example 2

[0092] When preparing the current collector, the solid content of the second slurry is 8%, and the porosity of the obtained second carbon coating layer is 60%. The remaining steps are the same as in Example 1.

[0093] Comparative Example 3

[0094] In preparing the current collector, the solid content of the second slurry is 16%, and the porosity of the obtained second carbon coating layer is 30%. The remaining steps are the same as in Example 1.

[0095] Comparative Example 4

[0096] In preparing the current collector, the solid content of the first slurry was 38%, and the porosity of the first carbon coating layer was 3%. The remaining steps were the same as in Example 1.

[0097] Comparative Example 5

[0098] In preparing the current collector, the solid content of the first slurry is 15%, and the porosity of the first carbon coating layer is 30%. The remaining steps are the same as in Example 1.

[0099] Comparative Example 6

[0100] When preparing the current collector, the second slurry is first coated on the copper foil, and then the first slurry is coated. That is, the positions of the first carbon coating layer and the second carbon coating layer are interchanged. The remaining steps are the same as in Example 1.

[0101] In this invention, some conditions for preparing current collectors in Examples 1-11 and Comparative Examples 1-6 are shown in Table 1. The performance of the negative electrode sheets obtained in Examples 1-11 and Comparative Examples 1-6 was tested, and the test results are shown in Table 1.

[0102] In one embodiment of the present invention, in order to test the wetting time of the electrolyte, an electrolyte wettability test is performed. Specifically, a contact angle measuring instrument equipped with a precision syringe and a high-speed camera is used. The unrolled negative electrode sheet is flattened and fixed on the sample stage. Electrolyte is drawn with a syringe, and a standard volume (set to 1 μL) of electrolyte is dropped onto the sample surface. The time required from the droplet contacting the surface until it is completely spread out and absorbed is measured by a stopwatch or high-speed video recording.

[0103] In one embodiment of the present invention, in order to obtain the maximum embedding depth, mechanical strength performance tests are conducted. Specifically, a cross-sectional sample is made by cold mounting and polishing (CP) the rolled negative electrode sheet, and the maximum depth of silicon particles pressed into the copper foil surface is observed and measured by scanning electron microscopy.

[0104] In one embodiment of the present invention, to obtain the porosity of the carbon coating layer, a fully automated mercury porosimeter (Micromeritics AutoPore V) was used. The test conditions included: pressure range of 0.5 psi-33000 psi, contact angle of 130°, mercury surface tension of 485 dynes / cm, and equilibrium time of 10 s. A 1 cm × 1 cm sample was precisely cut from the current collector and dried in a vacuum oven at 105 °C for 4 h to remove moisture. The type of sample after drying was then weighed. Based on the capillary phenomenon, mercury was permeated into the pores of the material by applying external pressure. The pore size distribution was calculated using the Washburn equation: porosity = (total volume of mercury permeated / apparent volume of sample) × 100%. A layer-by-layer peeling technique was used to calculate the porosity of the upper and lower layers separately.

[0105] In one embodiment of the present invention, when testing the D50 of the slurry, an appropriate amount of slurry sample is taken at 25°C, diluted with deionized water to a suitable concentration, and 0.1% sodium hexametaphosphate solution is added as a dispersant. The sample is ultrasonically dispersed at 200W for 3 minutes to ensure that the particles are fully deagglomerated. The sample is then added to the sample cell of the laser particle size analyzer. After the signal stabilizes, the measurement is started. The measurement is repeated 3 times, and the average D50 value is taken as the final result. The particle size distribution curve and characteristic particle size value are recorded.

[0106] Table 1 shows some characteristics of the current collector and the performance of the negative electrode in Examples 1-11 and Comparative Examples 1-6.

[0107]

[0108] The negative electrode sheet prepared using the embodiments of the present invention exhibits excellent performance, specifically satisfying the following conditions: immersion time ≤ 7s, maximum embedding depth ≤ 3μm. A shorter immersion time indicates better electrode wettability, which is more conducive to lithium-ion transport, effectively reducing battery resistance and improving fast-charging performance. A smaller maximum embedding depth indicates higher current collector structure integrity and higher electrode hardness, making the electrode less prone to breakage during battery cycling and helping to extend battery cycle life. Referring to Table 1, comparing Example 1 and Comparative Example 1, it can be seen that, compared to setting a conventional single-layer carbon coating on copper foil, this application, by setting a first carbon coating layer and a second carbon coating layer with different porosities, can increase the electrolyte immersion time and reduce the maximum embedding depth of silicon particles. This is because a conventional single-layer carbon coating layer, increasing hardness clogs pores (slow immersion), while increasing pores reduces hardness (deep embedding), resulting in failure due to the inherent contradiction between "hardness and pores." Example 1 achieves functional decoupling through a double-layer carbon coating. The compactness of the first carbon coating provides an anti-embedding function with high elastic modulus, while the porous second carbon coating provides wetting and stress buffering functions, thus breaking through the performance bottleneck of traditional single-layer materials from a physical perspective.

[0109] Please refer to Table 1. Comparing Example 1 and Comparative Example 6, it can be seen that when the first and second carbon coating layers are replaced, the electrolyte wetting time and maximum embedding depth are not improved. When the first and second carbon coating layers are replaced, during rolling, stress is first applied to the hard top layer. Due to its poor plastic deformation ability, it cannot effectively buffer the stress, leading to stress concentration and direct transmission to the loose bottom layer, causing plastic damage to the copper foil. At the same time, the electrolyte is completely blocked by the dense top layer, and the wetting path is cut off. Therefore, setting the carbon coating layer to "loose on top and dense on bottom" has a decisive effect on performance improvement and cannot be reversed.

[0110] Please refer to Table 1. Comparing Example 1 and Comparative Example 2, it can be seen that when the porosity of the second carbon coating layer is large, such as exceeding 55%, the maximum embedding depth increases. This is because when the porosity of the second carbon coating layer is large, the bulk density and cohesive strength of the second carbon coating layer are significantly reduced. During rolling, excessive pore structure collapse prevents it from effectively dispersing stress, deteriorates the buffering function, and allows more stress to penetrate into the first carbon coating layer, resulting in deeper embedding. However, the electrolyte wetting ability has certain advantages.

[0111] Referring to Table 1, a comparison of Example 1 and Comparative Example 3 shows that when the porosity of the second carbon coating layer is low, the electrolyte wetting time is prolonged. This is because when the porosity of the second carbon coating layer is too low, effective capillary channels cannot be formed throughout the second carbon coating layer. The electrolyte mainly relies on slow diffusion within a narrow space, rather than rapid penetration driven by capillary force, resulting in a prolonged wetting time. Therefore, controlling the porosity of the second carbon coating layer can improve the balance between the electrolyte wetting time and the maximum embedding depth.

[0112] Please refer to Table 1. Comparing Example 1 and Comparative Example 4, it can be seen that when the porosity of the first carbon coating layer is small, the first carbon coating layer is almost non-porous. Although the hardness is extremely high, it sacrifices the only longitudinal channel for electrolyte to replenish from the copper foil substrate to the second carbon coating layer, thus disrupting the overall wetting kinetics. Therefore, setting the lower limit of the porosity of the first carbon coating layer is the key to balancing "absolute density".

[0113] Please refer to Table 1. Comparing Example 1 and Comparative Example 5, it can be seen that when the porosity of the first carbon coating layer is large, the maximum embedding depth increases. This is because the elastic modulus and indentation hardness of the first carbon coating layer are insufficient to resist the impact of silicon particles under high pressure. Its structure yields under stress, thus losing its significance as a final line of defense, leading to uncontrolled embedding depth. Therefore, it is necessary to control the porosity of the first carbon coating layer to achieve a balance between the "physical barrier" and the "wetting channel".

[0114] Please refer to Table 1. Comparing Examples 1-6, it can be seen that when the porosity of the first and second carbon coating layers is within a set range, both the electrolyte wetting time and maximum embedding depth are improved. Furthermore, when the porosity ratio is greater than or equal to 2, the overall performance of wetting time and maximum embedding depth is optimal. Therefore, controlling the porosity of the first and second carbon coating layers and their porosity ratio can achieve the best possible improvement in the performance of electrolyte wetting time and maximum embedding depth.

[0115] Please refer to Table 1. Comparing Examples 1 and 7, it can be seen that by controlling the glass transition temperature of the first and second adhesives, the hardness and elastic modulus of the first carbon coating layer can be ensured within the set range to resist the indentation of silicon particles. At the same time, the obtained second carbon coating layer can provide soft buffering, absorb the impact force of rolling, and provide a fast channel for the electrolyte, thereby improving the electrolyte wetting time and maximum embedding depth of the current collector.

[0116] Referring to Table 1, a comparison of Examples 1 and 8-11 shows that the smaller the size of the particles and sheets in the first and second conductive agents, the lower the porosity of the carbon coating layer under the same solid content, thus affecting the wetting time and maximum embedding depth of the electrolyte. By controlling the size of the particles and sheets in the first and second conductive agents, the wetting time and maximum embedding depth of the electrolyte can be improved within a set range. This is because the size of the conductive agent affects the structure and morphology of the carbon coating layer, thereby causing changes in the wetting time and maximum embedding depth of the electrolyte. Therefore, controlling the size of the particles and sheets in the first and second conductive agents balances the wetting time and maximum embedding depth of the electrolyte.

[0117] This invention also provides an electronic device comprising at least one of the aforementioned lithium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the aforementioned lithium-ion battery, and therefore the advantages of including the aforementioned lithium-ion battery are not elaborated here.

[0118] In summary, this invention proposes a secondary battery current collector, a negative electrode sheet, and a lithium-ion battery. By setting a first carbon coating layer and a second carbon coating layer, with the second carbon coating layer having higher porosity, during the electrode sheet rolling process, the high-porosity porous layer of the second carbon coating layer first undergoes elastic deformation, absorbing and dispersing part of the impact force. The remaining stress is transferred to the low-porosity porous layer of the first carbon coating layer, acting as a robust physical barrier to prevent silicon particles from embedding into the copper foil. This avoids brittle damage to the current collector caused by direct hard impact while ensuring the final defensive strength of the current collector. Simultaneously, the high-porosity second carbon coating layer provides a rapid channel for the electrolyte and isolates the silicon from contact with the current collector substrate, successfully resolving the inherent contradiction in traditional coatings where "increasing hardness will clog pores, and increasing porosity will decrease hardness." The conductive agent is a combination of granular and sheet-like particles. The particles fill the spaces between the sheets, preventing them from stacking tightly and instead "spreading" and "bridging" them. Simultaneously, the sheets encapsulate and connect the isolated particles, anchoring them within a unified and stable microstructure. This results in a carbon coating layer that simultaneously achieves a microstructure of "rapid electrolyte wetting" and "efficient stress buffering." By controlling the glass transition temperature of the binder, the elastic properties of the carbon coating layer are controlled, ensuring rapid wetting while preventing silicon particle embedding.

[0119] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0120] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A current collector for a secondary battery, characterized in that, include: Current collector substrate; The first carbon coating layer is disposed on at least one side surface along the thickness direction of the current collector substrate; as well as The second carbon coating layer is disposed on the side of the first carbon coating layer away from the current collector substrate; the porosity of the first carbon coating layer is 5%-25%, and the porosity of the second carbon coating layer is 35%-55%.

2. The secondary battery current collector according to claim 1, characterized in that, The porosity ratio of the second carbon coating layer to the first carbon coating layer is greater than or equal to 2.

3. The secondary battery current collector according to claim 1, characterized in that, The first carbon coating layer includes a first conductive agent and a first binder, and the second carbon coating layer includes a second conductive agent and a second binder. The glass transition temperature of the first binder is greater than or equal to 20°C, and the glass transition temperature of the second binder is less than or equal to 0°C.

4. The secondary battery current collector according to claim 3, characterized in that, The first conductive agent includes a first conductive material and a second conductive material; the first conductive material includes at least one of hard carbon, conductive carbon black or graphite, and the second conductive material includes at least one of graphene or graphite nanosheets. And / or, the median particle size of the first conductive material is 0.3 μm-0.7 μm, and the sheet size of the second conductive material is 0.2 μm-1.5 μm; And / or, the mass ratio of the first conductive material to the second conductive material is (85-90):(10-15).

5. The secondary battery current collector according to claim 3, characterized in that, The second conductive agent includes a third conductive material and a fourth conductive material; the third conductive material includes at least one of hard carbon, conductive carbon black or graphite, and the fourth conductive material includes at least one of graphene or graphite nanosheets. And / or, the median particle size of the third conductive material is 0.9 μm-2 μm, and the sheet size of the fourth conductive material is 2.5 μm-8 μm; And / or, the mass ratio of the third conductive material to the fourth conductive material is (80-85):(15-20).

6. The secondary battery current collector according to claim 3, characterized in that, The first adhesive includes at least one of polyurethane, styrene-acrylic emulsion, or acrylate emulsion; And / or, the second adhesive comprises one or more of styrene-butadiene rubber, acrylate rubber, or styrene-acrylic emulsion.

7. The secondary battery current collector according to claim 3, characterized in that, The second carbon coating layer also includes a thickener, which includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate or sodium polyacrylate, and the mass ratio of the second binder to the thickener is 2:1 to 4:

1.

8. The secondary battery current collector according to claim 1, characterized in that, The current collector substrate includes at least one of copper, nickel, titanium, silver, chromium or molybdenum, and the thickness of the current collector substrate is 3.5μm-12μm; And / or, the total thickness of the first carbon coating layer and the second carbon coating layer on one side of the current collector substrate is 1.5μm-4.5μm; And / or, the thickness of the first carbon coating layer is 0.5μm-1.5μm; And / or, the thickness of the second carbon coating layer is 1μm-3μm.

9. A negative electrode sheet, characterized in that, It includes a current collector and a negative electrode active layer disposed on a carbon coating layer along the thickness direction of the current collector. The negative electrode active layer includes a negative electrode active material, which includes one or more of elemental silicon, silicon-oxygen materials, silicon-carbon materials, or silicon alloys. The current collector is selected from the secondary battery current collectors described in any one of claims 1-8.

10. A lithium-ion battery, characterized in that, include: Positive electrode sheet; The negative electrode sheet is selected from the negative electrode sheet according to claim 9; A diaphragm is disposed between the positive electrode and the negative electrode.

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