Negative electrode sheet, method for manufacturing the same, and lithium ion battery

Abstract

The application discloses a negative electrode sheet, a preparation method thereof and a lithium ion battery, and belongs to the technical field of batteries. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer; the negative electrode active material layer is attached to the surface of the negative electrode current collector; a plurality of protrusions are arranged on at least one surface of the negative electrode current collector and the negative electrode active material layer, and the protrusions are embedded in the negative electrode active material layer. The application forms micron-level protrusions on the surface of the negative electrode current collector, enhances the mechanical locking action between the active material and the current collector from the micro scale, greatly improves the adhesion of the bonding interface, effectively disperses the local stress generated in the charging and discharging process, and improves the conductivity of the electrode; the negative electrode sheet is used in a silicon negative electrode lithium ion battery, can effectively improve the energy density of the silicon negative electrode lithium ion battery, improve the cycle stability, rate performance and cycle life of the silicon negative electrode lithium ion battery, and improve the safety of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a negative electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] As a key energy source for modern portable electronic devices and electric vehicles, improving the performance of lithium-ion batteries has always been a focus of research and industry. Energy density and cycle life are two important indicators for measuring the performance of lithium-ion batteries, and the performance of the negative electrode material directly affects these two key performance characteristics.

[0003] In recent years, silicon-based anode materials have become a research hotspot due to their theoretical specific capacity, which is far higher than that of traditional graphite anode materials, and are widely considered the ideal choice for next-generation high-energy-density lithium-ion batteries. However, the challenges faced by silicon-based anode materials in practical applications cannot be ignored. The primary issue lies in the volume change of silicon materials during charge and discharge processes, which can reach 300% or higher. This dramatic expansion and contraction significantly impacts battery performance and lifespan, primarily in the following ways: Interface delamination: During the charge-discharge cycles of lithium-ion batteries, the adhesion between the silicon-based active material and the metal current collector (such as copper foil) gradually weakens due to the volume change of the silicon material. This process can cause the active material to detach from the current collector, forming interface delamination, which severely affects the battery's cycle performance and overall energy output. Localized stress concentration: Uneven expansion of the silicon material can lead to localized stress concentration within the electrode. If this stress is not effectively dispersed, it can form cracks in the electrode, accelerating the destruction of the electrode structure and thus shortening the battery's cycle life. In extreme cases, stress concentration can also trigger internal short circuits, posing a safety hazard. Insufficient electrode flexibility: Traditional electrode designs often exhibit insufficient flexibility when dealing with volume changes in silicon-based materials. The mechanical stress generated by the expansion and contraction of silicon materials is difficult to distribute evenly on the electrode, making the electrode as a whole fragile and affecting the stability and safety of the battery under high-rate charge and discharge conditions.

[0004] While existing technologies attempt to address these issues by improving the composition of silicon-based materials, adding special binders, or optimizing electrode structures, these measures often only provide partial relief and fail to fundamentally resolve the challenges posed by the drastic volume changes in silicon materials. For example, while increasing the binder content can enhance the fixation of active materials, it simultaneously reduces the conductivity and energy density of the electrode, creating a performance trade-off.

[0005] Therefore, developing a novel anode material that can effectively address volume changes in silicon-based anode materials while maintaining high energy density, ensuring a strong bond between the active material and the current collector, and uniformly dispersing local stress, is of great significance for improving the cycle life and safety of lithium-ion batteries. This aims to solve the problems of interface stability and structural integrity of silicon-based anode materials during charge and discharge processes, thereby significantly improving the cycle stability and overall performance of the battery. Summary of the Invention

[0006] The main objective of this invention is to provide a negative electrode sheet, its preparation method, and a lithium-ion battery, to solve the problems of interface delamination and localized stress concentration between the silicon-based active material and the metal current collector caused by the rapid volume change of silicon material during multiple charge-discharge cycles in existing lithium-ion batteries. It also addresses the issue of the difficulty in uniformly dispersing mechanical stress caused by the expansion and contraction of silicon material during high-rate charge-discharge cycles in traditional electrodes, which negatively impacts battery safety. The aim is to further improve the energy density of silicon negative electrode lithium-ion batteries, enhance their cycle stability, rate performance, and cycle life, and improve overall lithium-ion battery safety.

[0007] According to one aspect of this application, a negative electrode sheet is provided, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer; the negative electrode active material layer is attached to the surface of the negative electrode current collector; wherein, at least one surface of the negative electrode current collector in contact with the negative electrode active material layer is provided with a plurality of protrusions, the protrusions being embedded in the negative electrode active material layer.

[0008] Furthermore, the dry thickness of the negative electrode active material layer is t, the height of the protrusion is H, and the following relationship is satisfied: t≥H×A, A≥1.2.

[0009] Furthermore, t = H × A, A = 1.5 ~ 15.

[0010] Furthermore, t = H × A, A = 1.5 ~ 10.

[0011] Furthermore, the height of the protrusion is 2~15µm.

[0012] Furthermore, the thickness of the negative electrode active material layer is 15~200μm.

[0013] Furthermore, the thickness of the negative electrode active material layer is 15~50μm.

[0014] Furthermore, multiple protrusions are respectively provided on the two surfaces of the negative electrode current collector that are in contact with the negative electrode active material layer.

[0015] Furthermore, multiple protrusions are arranged in an array on the surface of the negative electrode current collector.

[0016] Furthermore, the length of the bottom surface of the protrusion is 2~5µm.

[0017] Furthermore, the total bottom area of ​​each protrusion accounts for 5 to 30% of the area of ​​the negative electrode current collector, preferably 8 to 25%.

[0018] Furthermore, the center distance between two adjacent protrusions is 5~15µm.

[0019] Furthermore, the radius of curvature of the raised top surface is 0.5~3μm, preferably 1~2μm.

[0020] Furthermore, the top surface of the protrusion can be hemispherical, arc-shaped, slightly arched, or frustum-shaped.

[0021] Furthermore, the protrusion and the body of the negative electrode current collector are an integrated structure.

[0022] Furthermore, the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a fibrous binder; wherein the negative electrode active material is at least one of silicon-based materials, tin, tin oxide, germanium, germanium oxide, lithium, lithium oxide, aluminum, and aluminum oxide.

[0023] Furthermore, the silicon-based material is selected from one or more of nano-silicon, silicon oxide, silicon-carbon composite, silicon-aluminum alloy, and amorphous silicon.

[0024] Furthermore, the weight ratio of the negative electrode active material, conductive agent, and fibrous binder is 1:(0.02~0.12):(0.03~0.12).

[0025] Furthermore, the weight of the fibrous binder is 5 to 10% of the weight of the negative electrode active material, preferably 6 to 9%.

[0026] Furthermore, the viscosity-average molecular weight of the fibrous adhesive is 500,000 to 1,000,000.

[0027] Furthermore, the fibrous binder is selected from one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxymethyl chitosan.

[0028] Furthermore, the conductive agent is selected from one or more of Super-P, carbon black, VGCF, graphene, and carbon nanotubes.

[0029] Furthermore, the negative electrode current collector is one or more of electrolytic copper foil, rolled copper foil, nickel-plated copper foil, and porous copper foil.

[0030] According to a second aspect of this application, a method for preparing the above-mentioned negative electrode sheet is provided, comprising the following steps:

[0031] A protrusion is formed on the surface of the negative electrode current collector by laser etching;

[0032] The negative electrode active slurry is coated onto the surface of the negative electrode current collector, which includes protrusions. After curing, a negative electrode active material layer is formed, and the protrusions are embedded in the negative electrode active material layer to obtain the negative electrode sheet.

[0033] Furthermore, the laser power for laser etching is 3~15W.

[0034] Furthermore, the pulse frequency of laser etching is 20~200kHz.

[0035] Furthermore, the scanning speed of laser etching is 100~800 mm / s.

[0036] Furthermore, multiple protrusions are arranged in an array on the surface of the negative electrode current collector.

[0037] Furthermore, the dry thickness of the negative electrode active material layer is t, the height of the protrusion is H, and the following relationship is satisfied: t≥H×A, A≥1.2.

[0038] Furthermore, t = H × A, A = 1.5 ~ 15.

[0039] Furthermore, t = H × A, A = 1.5 ~ 10.

[0040] Furthermore, the height of the protrusion is 2~15µm.

[0041] Furthermore, the length of the bottom surface of the protrusion is 2~6µm.

[0042] Furthermore, the center distance between two adjacent protrusions is 5~15µm.

[0043] Furthermore, the radius of curvature of the raised top surface is 0.5~3μm, preferably 1~2μm.

[0044] Furthermore, the top surface of the protrusion can be hemispherical, arc-shaped, slightly arched, or frustum-shaped.

[0045] Furthermore, the total bottom area of ​​each protrusion accounts for 5 to 30% of the area of ​​the negative electrode current collector, preferably 8 to 25%.

[0046] Furthermore, the thickness of the negative electrode active material layer is 15~200μm.

[0047] Furthermore, the thickness of the negative electrode active material layer is 15~50μm.

[0048] Furthermore, the negative electrode active slurry includes a negative electrode active material, a conductive agent, a fibrous binder, and a solvent.

[0049] Furthermore, the solid content of the negative electrode active slurry is 20-60%.

[0050] Furthermore, the weight ratio of the negative electrode active material, conductive agent, and fibrous binder is 1:(0.02~0.12):(0.03~0.12).

[0051] Furthermore, the weight of the fibrous binder is 5 to 10% of the weight of the negative electrode active material, preferably 6 to 9%.

[0052] Furthermore, the negative electrode active material is at least one of silicon-based materials, tin, tin oxide, germanium, germanium oxide, lithium, lithium oxide, aluminum, and aluminum oxide.

[0053] Furthermore, the silicon-based material is selected from one or more of nano-silicon, silicon oxide, silicon-carbon composite, silicon-aluminum alloy, and amorphous silicon.

[0054] Furthermore, the conductive agent is selected from one or more of Super-P, carbon black, VGCF, graphene, and carbon nanotubes.

[0055] Furthermore, the viscosity-average molecular weight of the fibrous adhesive is 500,000 to 1,000,000.

[0056] Furthermore, the fibrous binder is selected from one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxymethyl chitosan.

[0057] Furthermore, the solvent is selected from one or more of NMP, deionized water, ethanol, isopropanol, acetone, dimethylformamide, dimethyl sulfoxide, PVDF, and ethyl acetate.

[0058] Furthermore, the negative electrode current collector is one or more of electrolytic copper foil, rolled copper foil, nickel-plated copper foil, and porous copper foil.

[0059] According to a third aspect of this application, a lithium-ion battery is provided, including a negative electrode sheet, wherein the negative electrode sheet is the aforementioned negative electrode sheet or a negative electrode sheet obtained by the aforementioned method for preparing the negative electrode sheet.

[0060] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0061] This application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer located on the surface of the negative electrode current collector; wherein, at least one surface of the negative electrode current collector in contact with the negative electrode active material layer is provided with a plurality of protrusions; the protrusions are embedded in the negative electrode active layer. By forming micron-level protrusions on the surface of the negative electrode current collector, the mechanical locking effect between the active material and the current collector is enhanced at the microscale, significantly improving the adhesion of the bonding interface, and effectively dispersing the local stress generated during charging and discharging, thereby improving the conductivity of the electrode. Using this negative electrode sheet in silicon anode lithium-ion batteries can effectively improve the energy density of silicon anode lithium-ion batteries, enhance the cycle stability, rate performance, and cycle life of silicon anode lithium-ion batteries, and improve the safety of lithium-ion batteries. Attached Figure Description

[0062] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0063] Figure 1 A schematic diagram of the negative electrode sheet provided in an embodiment of the present invention is shown.

[0064] Figure label:

[0065] 1. Negative electrode current collector; 2. Negative electrode active material layer; 3. Fiberized binder; 4. Protrusion. Detailed Implementation

[0066] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0067] As described in the background section, the volume expansion characteristics of silicon-based anode materials during charge and discharge not only lead to localized stress concentration in the anode sheet, thus accelerating the destruction of the electrode structure and shortening the battery's cycle life, but also result in insufficient electrode flexibility, making the electrode overall fragile and affecting the stability and safety of the battery under high-rate charge and discharge conditions. Therefore, developing a novel anode sheet that can effectively cope with the volume changes of silicon-based anode materials while maintaining high energy density, ensuring a firm bond between the active material and the current collector, and uniformly dispersing localized stress, is of great significance for improving the cycle life and safety of lithium-ion batteries.

[0068] To address the aforementioned problems, this application provides a negative electrode plate, such as... Figure 1As shown, the negative electrode sheet includes a negative current collector 1 and a negative active material layer 2; the negative active material layer 2 is attached to the surface of the negative current collector 1; wherein, at least one surface of the negative current collector 1 in contact with the negative active material layer 2 is provided with a plurality of protrusions 4, which are embedded in the negative active material layer 2.

[0069] This application provides a negative electrode sheet with good flexibility by setting a protrusion on one side of the negative electrode sheet. When used in silicon negative electrode lithium-ion batteries, it can effectively improve the energy density of silicon negative electrode lithium-ion batteries, enhance the cycle stability, rate performance and cycle life of silicon negative electrode lithium-ion batteries, and improve the safety of lithium-ion batteries.

[0070] The reasons for the above effects can be mainly attributed to the following factors:

[0071] Firstly, the protrusions on the surface of the negative electrode current collector increase both the surface roughness and the actual contact area between the active material and the current collector. Increased surface roughness creates more microscopic irregularities, providing additional mechanical interlocking points for the negative electrode active material layer to bond with the current collector, similar to how certain organisms in nature (such as gecko toes) enhance adhesion through tiny structures. The increased actual contact area between the active material and the current collector means more bonding points, further strengthening the physical bond between them. The synergistic effect of these two aspects effectively prevents the negative electrode active material layer from detaching from the current collector surface during charging and discharging, thus better maintaining the mechanical stability of the electrode. This enhanced mechanical stability is particularly beneficial for silicon-based materials with large volume variations, significantly improving battery cycle performance and safety.

[0072] Secondly, the volume changes of negative electrode active materials, such as silicon-based materials, during charging and discharging can lead to localized stress concentration, which may cause damage to the electrode structure. The protruding structure creates a three-dimensional locking effect between the active material layer and the current collector. When the silicon-based active material expands or contracts in volume during charging and discharging, the three-dimensional protruding structure can provide sufficient space buffer, disperse localized stress, and avoid cracks and fractures caused by stress concentration. At the same time, its mechanical shape and structure maintain a tight bond between the active material and the current collector, preventing delamination in the negative electrode sheet.

[0073] Third, the distribution of protrusions promotes uniform conductivity within the active material layer. These microstructures help form a continuous conductive network, maintaining good electron transport even when the volume of the negative electrode active material layer changes significantly, thus improving the overall conductivity and energy output efficiency of the battery.

[0074] In summary, by forming micron-sized protrusions on the surface of the negative electrode current collector, the mechanical interlocking between the negative electrode active material layer and the current collector is enhanced at the microscale, significantly improving the adhesion of the bonding interface. Furthermore, by controlling the height of the protrusions, the localized stress generated in the silicon negative electrode sheet during charging and discharging can be effectively dispersed, improving the conductivity of the electrode. This design innovation demonstrates significant advantages in improving the overall performance of the battery, including cycle stability, energy density, and safety, providing strong support for the advancement of lithium-ion battery technology.

[0075] To match the thickness of the negative electrode active material layer and the height of the protrusion on the current collector, the ratio of the two is adjusted. In a preferred embodiment, the dry thickness of the negative electrode active material layer is t, and the height of the protrusion is H, satisfying the relationship: t≥H×A, A≥1.2; preferably t=H×A, A=1.5~15; the value of A is any value among 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or any value between any two; for example, t=H×A, A=1.5~10. Furthermore, the height of the protrusion is 2~15µm; for example, any value or a range between 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15µm; the thickness of the negative electrode active material layer is 15~200µm, for example, any value or a range between 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200µm; for example, 15~50µm. By controlling the ratio of protrusion height to negative electrode active layer thickness within the above range, better contact performance between the silicon-based negative electrode material and the current collector can be ensured, while also allowing the silicon-based negative electrode material to have suitable space to adapt when expanding. This is beneficial for better releasing the stress generated by the negative electrode sheet during cycling, thereby better ensuring the good structural stability of the electrode in multiple charge-discharge cycles and improving the stability and safety of lithium-ion batteries.

[0076] In a preferred embodiment, the length of the protrusion's bottom surface is 2~6µm, for example, any value among 2, 3, 4, 5, and 6µm or any range between two. Controlling the bottom surface length of the protrusions on the current collector surface within this range allows for better adhesion between the protrusions and the negative electrode active material layer, and also allows for better dispersion of stress generated by the silicon-based active material. In particular, controlling the above parameters can maximize the mechanical locking effect and adhesion strength while ensuring the overall flexibility of the electrode. Preferably, the total bottom area of ​​all protrusions accounts for 5~30% of the negative electrode current collector area, for example, any value among 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, and 30% or any range between two. By controlling the protrusion coverage on the current collector surface, on the one hand, its anchoring effect on the active material can be strengthened, controlling the interaction strength between the current collector and the negative electrode active layer; on the other hand, it can also avoid the problem of increased resistance of the negative electrode sheet caused by excessively dense distribution of protrusions on the current collector surface, which is beneficial to further improving the stability of the negative electrode sheet. More preferably, the total bottom area of ​​each protrusion accounts for 10-25% of the negative electrode current collector area. Controlling the coverage of the protrusions on the current collector surface within the above-mentioned preferred range yields even better results.

[0077] In essence, this application does not strictly limit the arrangement of the protrusions. In a preferred embodiment, multiple protrusions are arranged in an array. This array arrangement allows for a more uniform distribution of stress generated by the electrode, resulting in better electrode performance. Preferably, the center distance between adjacent protrusions is 5~15µm, for example, any value or a range between 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15µm; the radius of curvature of the tip surface of the protrusion is 0.5~3µm, preferably 1~2µm; for example, the surface of the protrusion is hemispherical, arc-shaped, micro-arched, or frustum-shaped (truncated cone). The above characteristics of the protrusions can improve the performance of the electrode; compared with sharp tips, rounded tips can effectively reduce local stress concentration and reduce the risk of crack initiation and interface delamination during the large expansion / contraction of silicon-based active materials. Furthermore, the arc / hemispherical tip facilitates wetting and continuity of the coating slurry, preventing uneven accumulation or isolated voids between the protrusions. More preferably, the protrusions and the body of the negative electrode current collector are an integrated structure, without internal pores that can accommodate active materials. Even more preferably, both surfaces of the negative electrode active current collector are coated with a negative electrode active coating, and multiple protrusions are provided on each surface. The integrated structure of the protrusions and the body of the negative electrode current collector improves the conductivity of the negative electrode sheet. Adjusting the height, bottom dimensions, and tip curvature of the protrusions within the aforementioned ranges achieves optimal anchoring and stress buffering effects.

[0078] In a preferred embodiment, the negative electrode active material layer further includes a conductive agent and a fibrous binder 3. On one hand, adding the fibrous binder 3 to the raw materials of the negative electrode active material layer forms a cross-linked three-dimensional fibrous network structure within the active material layer. This three-dimensional fibrous network structure firmly fixes the silicon-based active material to the current collector surface and provides the necessary flexibility when the silicon material undergoes volume changes due to charging and discharging, effectively dispersing local stress and preventing cracks and structural damage caused by stress concentration inside the electrode, thus enhancing the electrode's cycle stability. On the other hand, the micro-protrusion design on the current collector surface significantly enhances the mechanical anchoring effect and improves the interfacial bonding strength by increasing the contact area and surface roughness with the active material layer at the microscale. The three-dimensional network formed by the fibrous binder and the micro-protrusion design on the current collector surface work synergistically to strengthen the mechanical structure of the electrode. This multi-layered, all-round mechanical combination not only ensures a stable connection between the active material and the current collector but also enhances the electrode's resistance to mechanical stress during charge-discharge cycles. Through the aforementioned synergistic effect, the electrode can maintain structural stability and integrity under high energy density and high cycle rate conditions, reducing interfacial fracture and local stress concentration caused by material volume changes, significantly improving the cycle stability and safety of the battery, while maintaining high energy density. The layered synergistic effect of the three-dimensional fiber network constructed with fibrous binder and the micro-protrusion design on the current collector surface, through enhanced mechanical anchoring, dispersion of local stress, and optimization of the overall electrode structure, can more effectively improve the cycle life, energy density, and safety of lithium-ion batteries.

[0079] In a preferred embodiment, the viscosity-average molecular weight of the fibrous binder is 500,000 to 1,000,000. Controlling the viscosity-average molecular weight of the fibrous binder within this range is beneficial for forming a better three-dimensional network structure, thereby further improving the performance of the negative electrode. Besides the viscosity-average molecular weight, several structural and physicochemical properties of the fibrous binder itself significantly affect the formation of the three-dimensional network structure. For example, fiber length and branching degree determine the overlap ability of binder segments in the slurry; the degree of substitution and surface charge properties (Zeta potential) affect its adsorption and interaction with silicon-based particles; appropriate swelling capacity and viscosity facilitate the unfolding of fiber chains between particles and the formation of a continuous spatial network; furthermore, the type of functional groups, chemical reaction ability, and degree of crosslinking of the binder also affect the stability of the network. These properties collectively determine the ability of the fibrous binder to form a three-dimensional fiber network in the active material layer, thereby improving the mechanical strength of the electrode, buffering the volume expansion of silicon, and enhancing cycle stability. Preferably, the fibrous binder is selected from one or more of sodium carboxymethyl cellulose (CMC), lithium carboxymethyl cellulose, sodium alginate, polyacrylic acid (PAA), lithium polyacrylate, sodium polyacrylate, and carboxymethyl chitosan. Using the above-mentioned specific fibrous binders to prepare the negative electrode sheet of this application allows for better interaction with the convex surface of the current collector, thereby improving the electrochemical performance of the prepared negative electrode sheet.

[0080] In a preferred embodiment, the weight ratio of the negative electrode active material, the conductive agent, and the fibrous binder is 1:(0.02~0.12):(0.05~0.12). Controlling the weight ratio of the negative electrode active material, the conductive agent, and the fibrous binder in the negative electrode active material layer within the above range can improve the performance of the negative electrode sheet.

[0081] In a preferred embodiment, the weight of the fibrous binder is 5-10% of the weight of the negative electrode active material, more specifically 6-9%. As described above, the three-dimensional fiber network constructed by the fibrous binder, combined with the layered synergistic effect of the micro-protrusion design on the current collector surface, can more effectively improve the cycle life, energy density, and safety of lithium-ion batteries by enhancing mechanical anchoring, dispersing local stress, and optimizing the overall electrode structure. Controlling the weight content of the fibrous binder in the negative electrode active material layer within the above-mentioned range can better exert the above-mentioned effects and is beneficial to further improving the stability of the negative electrode sheet.

[0082] In a preferred embodiment, the negative electrode active material is a common alloy / conversion negative electrode material that undergoes significant volume expansion during lithiation. For example, the negative electrode active material is at least one selected from silicon-based materials, tin, tin oxide, germanium, germanium oxide, lithium, lithium oxide, aluminum, and aluminum oxide; preferably, the silicon-based material is selected from one or more of nano-silicon, silicon oxide, silicon-carbon composite, silicon-aluminum alloy, and amorphous silicon. The conductive agent is selected from one or more of Super-P, carbon black, VGCF, graphene, and carbon nanotubes; the negative electrode current collector is one or more of electrolytic copper foil, rolled copper foil, nickel-plated copper foil, and porous copper foil. Using the above-mentioned materials in the negative electrode active material layer of this application results in better performance of the negative electrode sheet.

[0083] According to another aspect of the present invention, a method for preparing the above-mentioned negative electrode sheet is also provided. This method includes the following steps: etching the surface of a negative electrode current collector using laser etching to form protrusions on the surface of the current collector; coating a negative electrode active slurry onto the surface of the current collector including the protrusions; curing the slurry to form a negative electrode active material layer; embedding the protrusions into the negative electrode active material layer; and thus obtaining the negative electrode sheet. In this method, the surface of the current collector may also be pretreated before subsequent laser etching. This method is simple to operate, easy to control, and enables large-scale production of current collectors.

[0084] In a preferred embodiment, the curing process includes drying the coated negative electrode active material layer at a temperature of 100-120°C. Drying removes solvents, preventing residual solvents or moisture from causing electrolyte decomposition, gas generation, or decreased electrochemical performance during battery assembly. Solvent evaporation promotes binder segment rearrangement, cross-linking, or the formation of a fibrous three-dimensional network, which is beneficial for improving the mechanical strength and anti-collapse ability of the electrode. Adjusting the drying rate and temperature affects the pore size distribution and the embedding of the surface skin and protrusions. It also avoids bulging or internal pressure problems caused by the evaporation of residual high-boiling solvents at formation / high temperatures. A suitable drying temperature can promote peel strength; by first slowly desolventizing at a low temperature and then completing the removal and stabilization of the binder network at a medium temperature, the surface skin can be avoided, the pores can be made uniform, and the fibrous structure can be protected; at the same time, in the mixing process of the negative electrode active slurry, staged mixing (protecting fiber chain length + effectively dispersing conductive agent / active particles) and coating processes that can precisely control the wet film thickness and rheology (such as slot die / blade / groove die coating or precision groove die / slot-die) can be used, along with segmented, gentle drying and timely rolling to fix the network structure.

[0085] In a preferred embodiment, the laser power for laser etching is 3~15W; the pulse frequency for laser etching is 20~200kHz; and the scanning speed for laser etching is 100~800mm / s. Using the above-mentioned matched etching process parameters, a protrusion structure of the desired size can be obtained.

[0086] In a preferred embodiment, the multiple protrusions obtained by laser etching are arranged in an array; the dry thickness of the negative electrode active material layer is t, and the height of the protrusion is H, satisfying the following relationships: t≥H×A, A≥1.2; t=H×A, A=1.5~15; t=H×A, A=1.5~10; more preferably, the height of the protrusion is 2~15µm; and the bottom length of the protrusion is 2~6µm. By controlling the height and length of the protrusion, it can be matched with the thickness of the conventionally used negative electrode active coating, which helps to promote the bonding force between the current collector and the active layer.

[0087] In a preferred embodiment, the thickness of the negative electrode active material layer is 15-200 μm; preferably 15-50 μm. The solid content of the negative electrode active slurry is 20-60%; the weight ratio of the negative electrode active material, conductive agent, and fibrous binder is 1:(0.02-0.12):(0.05-0.12); preferably, the weight of the fibrous binder is 5-10% of the weight of the negative electrode active material, more preferably 6-9%; the viscosity-average molecular weight of the fibrous binder is 500,000-1,000,000; preferably, the fibrous binder is selected from one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxymethyl chitosan.

[0088] In a preferred embodiment, the negative electrode active material is at least one selected from silicon-based materials, tin, tin oxide, germanium, germanium oxide, lithium, lithium oxide, aluminum, and aluminum oxide; preferably, the silicon-based material is selected from one or more of nano-silicon, silicon oxide, silicon-carbon composite, silicon-aluminum alloy, and amorphous silicon; the conductive agent is selected from one or more of Super-P, carbon black, VGCF, graphene, and carbon nanotubes; the solvent is selected from one or more of NMP, deionized water, ethanol, isopropanol, acetone, dimethylformamide, dimethyl sulfoxide, PVDF, and ethyl acetate; the current collector is one or more of electrolytic copper foil, rolled copper foil, nickel-plated copper foil, and porous copper foil. Using the above materials as raw materials for the negative electrode active material layer can improve the performance of the prepared negative electrode sheet.

[0089] According to a third aspect of the present invention, a lithium-ion battery is also provided, the lithium-ion battery comprising a negative electrode sheet, the negative electrode sheet being the aforementioned negative electrode sheet.

[0090] According to a fourth aspect of the present invention, a battery module is also provided, the battery module comprising a plurality of the above-described lithium-ion batteries.

[0091] According to a fifth aspect of the invention, a battery pack is also provided, which contains a plurality of the aforementioned battery modules.

[0092] According to a sixth aspect of the present invention, an electrical device is also provided, the electrical device comprising the aforementioned battery pack.

[0093] According to a seventh aspect of the present invention, an energy storage system is also provided, the energy storage system comprising the above-described battery pack.

[0094] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0095] Example 1

[0096] Step S1: The negative current collector 1 (copper foil) is pretreated by cleaning; laser etching equipment is used to etch on two opposite surfaces of the copper foil. The laser power is 5W, the pulse frequency is 30kHz, and the scanning speed is 180mm / s. An array of protrusions 4 is etched on the surface of the copper foil. The bottom length of the protrusion 4 is 3µm, the height is 3µm, the distance between the two protrusions is 6.5µm, the curved surface shape of the top of the protrusion is hemispherical, and the total bottom area of ​​the protrusions covers 10% of the area of ​​the copper foil.

[0097] Step S2: Prepare the raw materials according to the following ratio: the weight ratio of nano-silicon, Super-P, and fibrous binder 3 (CMC / PAA=7 / 3) is 1:0.10:0.06; dissolve the fibrous binder in deionized water and stir at low speed planetary stirrer at 1000 rpm for 10 minutes until uniform; add the conductive agent Super-P in batches and stir at 2000 rpm for 100 seconds; add the nano-silicon in batches and premix at low speed for 5 minutes, then stir at 2000 rpm for 100 seconds; add the remaining conductive agent and mix at low speed for 5 minutes to ensure the integrity of the fibrous binder network; finally, perform vacuum degassing for 15 minutes to remove air bubbles and obtain a uniformly dispersed negative electrode active slurry with a solid content of 45%.

[0098] Step S3: The negative electrode active slurry is coated onto the copper foil surface from Step S1 using a slot-die coating method. After coating, it is pre-dried to a semi-dry state, and then rolled (compression rate 10%) to compact the particles and fix the three-dimensional network. Finally, it is dried under vacuum at 110℃ for 30 min to obtain negative electrode active material layer 2 with a thickness of 15µm. The raised structure on the copper foil surface is embedded in the negative electrode active material layer, thus obtaining the negative electrode sheet; its structure is as follows. Figure 1 As shown.

[0099] Example 2

[0100] Step S1: The negative electrode current collector 1 (copper foil) is pretreated by cleaning; laser etching equipment is used to etch on two opposite surfaces of the copper foil. The laser power is 7W, the pulse frequency is 50kHz, and the scanning speed is 160mm / s. An array of protrusions 4 is etched on the copper foil surface. The bottom length of the protrusion is 4µm, the height is 5µm, the distance between two protrusions is 6.3µm, the curved surface shape of the top of the protrusion is hemispherical, and the total bottom area of ​​the protrusions covers 15% of the copper foil area.

[0101] Step S2: Prepare the raw materials according to the following ratio: nano-silicon, Super-P, and fibrous binder 3 (CMC / PAA=7 / 3) in a weight ratio of 1:0.10:0.07; dissolve the fibrous binder in deionized water and stir at low speed planetary stirrer at 1000 rpm for 10 minutes until uniform; add the conductive agent Super-P in batches and stir at 2000 rpm for 100 seconds; add the nano-silicon in batches and premix at low speed for 5 minutes, then stir at 2000 rpm for 100 seconds; add the remaining conductive agent and mix at low speed for 5 minutes to ensure the integrity of the fibrous binder network; finally, perform vacuum degassing for 15 minutes to remove air bubbles, and obtain a uniformly dispersed negative electrode active slurry with a solid content of 48%.

[0102] Step S3: The negative electrode active slurry is coated onto the copper foil surface from Step S1 using a slot-die coating method. After coating, it is pre-dried to a semi-dry state, and then rolled (compression rate 10%) to compact the particles and fix the three-dimensional network. Finally, it is dried under vacuum at 110℃ for 30 min to obtain negative electrode active material layer 2 with a thickness of 18µm. The raised structure on the copper foil surface is embedded in the negative electrode active material layer, thus obtaining the negative electrode sheet; its structure is as follows. Figure 1 As shown.

[0103] Example 3

[0104] Step S1: The negative electrode current collector 1 (copper foil) is pretreated by cleaning; laser etching equipment is used to etch on two opposite surfaces of the copper foil. The laser power is 9W, the pulse frequency is 80kHz, and the scanning speed is 140mm / s. An array of protrusions 4 is etched on the copper foil surface. The bottom length of the protrusion is 5µm, the height is 8µm, the distance between two protrusions is 6.2µm, the curved surface shape of the top of the protrusion is hemispherical, and the total bottom area of ​​the protrusions covers 20% of the copper foil area.

[0105] Step S2: Prepare the raw materials according to the following ratio: nano-silicon, Super-P, and fibrous binder 3 (CMC / PAA=7 / 3) in a weight ratio of 1:0.10:0.07; dissolve the fibrous binder in deionized water and stir at low speed planetary stirrer at 1000 rpm for 10 minutes until uniform; add the conductive agent Super-P in batches and stir at 2000 rpm for 100 seconds; add the nano-silicon in batches and premix at low speed for 5 minutes, then stir at 2000 rpm for 100 seconds; add the remaining conductive agent and mix at low speed for 5 minutes to ensure the integrity of the fibrous binder network; finally, perform vacuum degassing for 15 minutes to remove air bubbles, and obtain a uniformly dispersed negative electrode active slurry with a solid content of 48%.

[0106] Step S3: The negative electrode active slurry is coated onto the copper foil surface from Step S1 using a slot-die coating method. After coating, it is pre-dried to a semi-dry state, and then rolled (compression rate 10%) to compact the particles and fix the three-dimensional network. Finally, it is dried under vacuum at 110℃ for 30 min to obtain negative electrode active material layer 2 with a thickness of 30µm. The raised structure on the copper foil surface is embedded into the negative electrode active material layer to obtain the negative electrode sheet, the structure of which is as follows. Figure 1 As shown.

[0107] Example 4

[0108] Step S1: The negative electrode current collector 1 (copper foil) is pretreated by cleaning; laser etching equipment is used to etch on two opposite surfaces of the copper foil. The laser power is 12W, the pulse frequency is 100kHz, and the scanning speed is 120mm / s to etch an array of protrusions 4 on the copper foil surface; wherein, the bottom length of the protrusion is 6µm, the height is 10µm, the distance between two protrusions is 6µm, the curved surface shape of the top of the protrusion is hemispherical, and the total bottom area of ​​the protrusions covers 25% of the copper foil area;

[0109] Step S2: Prepare the raw materials according to the following ratio: nano-silicon, Super-P, and fibrous binder 3 (CMC / PAA=7 / 3) in a weight ratio of 1:0.10:0.07; dissolve the fibrous binder in deionized water and stir at low speed planetary stirrer at 1000 rpm for 10 minutes until uniform; add the conductive agent Super-P in batches and stir at 2000 rpm for 100 seconds; add the nano-silicon in batches and premix at low speed for 5 minutes, then stir at 2000 rpm for 100 seconds; add the remaining conductive agent and mix at low speed for 5 minutes to ensure the integrity of the fibrous binder network; finally, perform vacuum degassing for 15 minutes to remove air bubbles, and obtain a uniformly dispersed negative electrode active slurry with a solid content of 48%.

[0110] Step S3: The negative electrode active slurry is coated onto the copper foil surface from Step S1 using a slot-die coating method. After coating, it is pre-dried to a semi-dry state, and then rolled (compression rate 10%) to compact the particles and fix the three-dimensional network. Finally, it is dried under vacuum at 110℃ for 30 min to obtain negative electrode active material layer 2 with a thickness of 35µm. The raised structure on the copper foil surface is embedded in the negative electrode active material layer, thus obtaining the negative electrode sheet; its structure is as follows. Figure 1 As shown.

[0111] Example 5

[0112] Example 5 differs from Example 1 in that the laser etching parameters in step S1 are adjusted: the laser power is 4W, the pulse frequency is 25kHz, and the scanning speed is 200mm / s, resulting in an array of protrusions etched on the copper foil surface. The protrusions have a bottom surface length of 3μm, a height of 2μm, a spacing of 10.5µm between two protrusions, and a total bottom area of ​​5% covering the copper foil area. The other steps are the same.

[0113] Example 6

[0114] The difference between Example 6 and Example 1 is that the laser etching parameters in step S1 are adjusted: the laser power is 14W, the pulse frequency is 120kHz, and the scanning speed is 110mm / s, to etch an array of protrusions on the copper foil surface; wherein the bottom surface length of the protrusion is 6μm, the height is 12μm, the distance between two protrusions is 5µm, and the total bottom area of ​​the protrusions covers 30% of the copper foil area; the other steps are the same.

[0115] Example 7

[0116] The difference between Example 7 and Example 4 is that the height of the protrusion etched by laser in step S1 is replaced with 15 μm; the other steps are the same.

[0117] Example 8

[0118] The difference between Example 8 and Example 7 is that the thickness of the negative electrode active material layer obtained by coating and drying in step S3 is replaced with 50µm; the other steps are the same.

[0119] Example 9

[0120] The difference between Example 9 and Example 7 is that the thickness of the negative electrode active material layer obtained by coating and drying in step S3 is replaced with 200µm; the other steps are the same.

[0121] Example 10

[0122] The difference between Example 10 and Example 1 is that the nano-silicon, Super-P and fibrous binder (CMC / PAA=7 / 3) in step S2 are mixed in a weight ratio of 1:0.10:0.03, and then deionized water is added to adjust the solid content to 50% to obtain the negative electrode active slurry; the other steps are the same.

[0123] Example 11

[0124] The difference between Example 11 and Example 1 is that the nano-silicon, Super-P and fibrous binder (CMC / PAA=7 / 3) in step S2 are mixed in a weight ratio of 1:0.10:0.12, and then deionized water is added to adjust the solid content to 38% to obtain the negative electrode active slurry; the other steps are the same.

[0125] Example 12

[0126] The difference between Example 12 and Example 1 is that the fibrous binder in step S2 is replaced with sodium alginate and lithium polyacrylate in a weight ratio of 7:3; all other operations are the same.

[0127] Example 13

[0128] The difference between Example 13 and Example 1 is that the fibrous binder in step S2 is replaced with sodium carboxymethyl cellulose and lithium polyacrylate in a weight ratio of 7:3; all other operations are the same.

[0129] Comparative Example 1

[0130] The difference between Comparative Example 1 and Example 1 is that the copper foil surface in step S1 is smooth and has no protruding structure; the other steps are the same.

[0131] Application examples

[0132] The negative electrode sheets prepared in each embodiment and comparative example were used to prepare lithium-ion batteries.

[0133] (1) Positive electrode sheet: NCM811, PVDF and Super-P are mixed in a weight ratio of 95:3:2; NMP is added to adjust the solid content to 60% to obtain positive electrode active slurry; the slurry is coated on aluminum foil with a wet film thickness of 100μm; dried at 120℃ for 20min; and rolled to compaction density.

[0134] (2) Negative electrode sheet: negative electrode sheets prepared in each embodiment and comparative example;

[0135] (3) Lithium-ion battery assembly: The prepared negative electrode, positive electrode, and PP separator are wound or stacked and assembled into a standard battery casing; electrolyte is injected (the electrolyte lithium salt is LiPF6, the mixed solvent is ethylene carbonate EC, ethyl methyl carbonate EMC and dimethyl carbonate DMC, with a volume ratio of 1:1:1; the electrolyte concentration is 1.0 mol / L, and it contains 5 wt% fluoroethylene carbonate additive; after injection, it is allowed to stand and wet for 12 hours, and then formation and capacity testing are performed (2 cycles of 0.1C charge and discharge, and 0.2C stable SEI) to complete the battery preparation.

[0136] Performance testing:

[0137] (1) Peel strength test of negative electrode sheet at 180°: The test was conducted using an electronic universal testing machine (Instron5943) in accordance with GB / T2790-1995 standard.

[0138] The prepared negative electrode sheet was cut into 10mm×60mm samples, bonded with adhesive tape, and then subjected to a 180° peel test at a speed of 50mm / min. The average peel force during the peel process was recorded and converted into peel strength (N / m).

[0139] (2) Battery cycle performance and rate performance test: The battery test system (Neware Technology Limited BTS series battery test equipment) was used to conduct cycle tests in accordance with the test method of GB / T31484-2015.

[0140] The assembled lithium-ion batteries were tested under a constant temperature of 25°C: charged at a 1C rate to the cutoff voltage; then discharged at a 1C rate to the cutoff voltage; this constituted one charge-discharge cycle; after 500 consecutive cycles, the battery capacity retention rate was recorded. Subsequently, a rate performance test was performed: the battery was discharged at a 5C rate, the battery capacity was recorded, and the capacity retention rate relative to 0.33C was calculated.

[0141] (3) Electrochemical impedance spectroscopy (EIS): The test was performed using an electrochemical workstation (Bio-Logic Science Instruments VMP3 electrochemical workstation) and the relevant test methods in GB / T36276-2018 were followed.

[0142] Test conditions: frequency range 100kHz–0.01Hz; perturbation voltage 5mV; charge transfer impedance Rct obtained by fitting Nyquist plot.

[0143] (4) Safety performance test (needle penetration test): The power battery needle penetration tester is used; refer to the needle penetration test method of GB / T31485-2015.

[0144] Test conditions: Use a 5mm diameter steel needle; needle penetration speed 10mm / s; insert the needle vertically into the center of the battery and observe whether the battery ignites, explodes, or experiences thermal runaway, and record the test results.

[0145] The test results are shown in Table 1.

[0146] Table 1

[0147]

[0148] As shown in Table 1, compared with the negative electrode sheet with no protrusions on the copper foil surface in Comparative Example 1, the lithium-ion battery assembled in Example 1 of this application exhibits significantly improved cycle performance and reduced interfacial impedance. Example 2 shows enhanced anchoring effect, with a peel strength of approximately 210 N / m. Example 3 demonstrates improved rate performance, with a 2C / 1C capacity retention rate of 78%. Example 4 exhibits the highest expansion suppression rate and significantly improved safety. In Comparative Example 1, the material layer is easily peeled off, with only 58% capacity retention after 500 cycles. The negative electrode sheets prepared in Examples 1-13 of this application all show significant improvements in cycle stability, rate performance, interfacial impedance, and structural stability.

[0149] Specifically, regarding structural optimization, in Examples 1-4, the electrochemical performance continuously improved with the gradual optimization of key structural parameters. Specifically, the capacity retention increased from 85% to 93%, and the capacity retention at 5C rate increased from 70% to 80%. Simultaneously, the interfacial charge transfer impedance Rct decreased from 52Ω to 32Ω, indicating that the constructed negative electrode composite structure effectively improved interfacial stability and promoted lithium-ion transport.

[0150] Regarding the coating coverage, Example 5 (5%) had limited protective layer formation due to insufficient coverage, resulting in relatively low cycle performance and rate performance. When the coverage was increased to 10-25% (Examples 2-4), the material exhibited the best overall performance. When the coverage was further increased to 30% (Example 6), although the cycle stability remained at a high level, the rate performance decreased slightly and the interfacial impedance increased slightly, indicating that excessively high coverage had a certain hindering effect on ion transport, but the overall performance was still better than that of Comparative Example 1.

[0151] Regarding structural stability, in Examples 7-9, by increasing the thickness of the negative electrode active material layer and adjusting its ratio with the protrusion height, the embedding degree of the protrusion structure in the active material layer can be further enhanced, thereby forming a more stable three-dimensional mechanical interlocking structure. As the coating thickness increases, the protrusion structure is more fully covered, and the interface contact area increases significantly, which helps to build a continuous and stable interface bonding network, thereby improving the overall structural integrity of the electrode. At the same time, a larger thickness-to-protrusion height ratio can effectively buffer the volume change of the active material during charging and discharging, reduce the risk of particle shedding and interface failure, thereby significantly improving the structural stability and interface reliability of the electrode during long-cycle processes. In addition, this structure helps to maintain the continuity of the conductive network, enabling the electrode to maintain a good electrical contact state during repeated cycles, further improving the cycle life performance of the battery.

[0152] Regarding the binder content, Example 10 (low binder content) exhibited lower bond strength; while Example 11 (high binder content) showed significantly improved bond performance and slightly improved rate performance, but its overall performance was still better than Comparative Example 1.

[0153] Furthermore, by optimizing the interface composition, Examples 12-13 can further reduce interface impedance and improve cycle stability.

[0154] The negative electrode sheet applied in this application enhances the mechanical interlocking between the active material and the current collector at the microscale by creating micron-level protrusions on the surface of the negative electrode current collector. This significantly improves the adhesion of the bonding interface and effectively disperses the localized stress generated during charging and discharging, thereby improving the conductivity of the electrode. Using this negative electrode sheet in silicon anode lithium-ion batteries can effectively improve the energy density of silicon anode lithium-ion batteries, enhance their cycle stability, rate performance, and cycle life, and improve the safety of lithium-ion batteries.

[0155] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer; the negative electrode active material layer is attached to the surface of the negative electrode current collector; In this embodiment, at least one surface of the negative electrode current collector that is in contact with the negative electrode active material layer is provided with a plurality of protrusions, and the protrusions are embedded in the negative electrode active material layer.

2. The negative electrode sheet according to claim 1, characterized in that, The dry thickness of the negative electrode active material layer is t, and the height of the protrusion is H, satisfying the relationship: t≥H×A, A≥1.2; Preferably, t = H × A, where A = 1.5~15; More preferably, t = H × A, where A = 1.5 ~ 10; More preferably, the height of the protrusion is 2~15µm; More preferably, the thickness of the negative electrode active material layer is 15~200μm, and even more preferably 15~50μm.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, Multiple protrusions are respectively provided on the two surfaces of the negative electrode current collector that are in contact with the negative electrode active material layer; And / or, multiple of the protrusions are arranged in an array on the surface of the negative electrode current collector; And / or, the bottom surface length of the protrusion is 2~6µm; preferably, the total bottom area of ​​all the protrusions accounts for 5~30% of the area of ​​the negative electrode current collector, more preferably 10~25%; And / or, the center distance between two adjacent protrusions is 5~15µm; And / or, the radius of curvature of the top surface of the protrusion is 0.5~3μm, preferably 1~2μm; more preferably, the top surface of the protrusion is hemispherical, arc-shaped, slightly arched or frustum-shaped; And / or, the protrusion and the body of the negative electrode current collector are an integrated structure.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that, The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a fibrous binder; wherein the negative electrode active material is at least one of silicon-based materials, tin, tin oxide, germanium, germanium oxide, lithium, lithium oxide, aluminum, and aluminum oxide. Preferably, the silicon-based material is selected from one or more of nano-silicon, silicon oxide, silicon-carbon composite, silicon-aluminum alloy, and amorphous silicon.

5. The negative electrode sheet according to claim 4, characterized in that, The weight ratio of the negative electrode active material, the conductive agent, and the fibrous binder is 1:(0.02~0.12):(0.03~0.12); preferably, the weight of the fibrous binder is 5~10% of the weight of the negative electrode active material, and more preferably 6~9%; And / or, the viscosity-average molecular weight of the fibrous adhesive is 500,000 to 1,000,000.

6. The negative electrode sheet according to claim 4 or 5, characterized in that, The fibrous binder is selected from one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxymethyl chitosan; And / or, the conductive agent is selected from one or more of Super-P, carbon black, VGCF, graphene, and carbon nanotubes; And / or, the negative electrode current collector is one or more of electrolytic copper foil, rolled copper foil, nickel-plated copper foil, and porous copper foil.

7. A method for preparing a negative electrode sheet according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: A protrusion is formed on the surface of the negative electrode current collector by laser etching; The negative electrode active slurry is coated onto the surface of the negative electrode current collector including the protrusions, and after curing, a negative electrode active material layer is formed. The protrusions are embedded in the negative electrode active material layer, thereby obtaining the negative electrode sheet.

8. The method for preparing the negative electrode sheet according to claim 7, characterized in that, The laser power for the laser etching is 3~15W; And / or, the pulse frequency of the laser etching is 20~200kHz; And / or, the scanning speed of the laser etching is 100~800mm / s; And / or, multiple of the protrusions are arranged in an array on the surface of the negative electrode current collector; And / or, the dry state thickness of the negative electrode active material layer is t, the height of the protrusion is H, and the following relationship is satisfied: t≥H×A, A≥1.2; preferably, t=H×A, A=1.5~15; even more preferably, t=H×A, A=1.5~10; And / or, the height of the protrusion is 2~15µm; And / or, the length of the bottom surface of the protrusion is 2~6µm; And / or, the center distance between two adjacent protrusions is 5~15µm; And / or, the radius of curvature of the top surface of the protrusion is 0.5~3μm; preferably, the top surface of the protrusion is hemispherical, arc-shaped, slightly arched or frustum-shaped; And / or, the total bottom area of ​​each of the protrusions accounts for 5-30% of the area of ​​the negative electrode current collector; And / or, the thickness of the negative electrode active material layer is 15~200μm, preferably 15~50μm; And / or, the negative electrode active slurry includes a negative electrode active material, a conductive agent, a fibrous binder, and a solvent; And / or, the solid content of the negative electrode active slurry is 20-60%.

9. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The weight ratio of the negative electrode active material, the conductive agent, and the fibrous binder is 1:(0.02~0.12):(0.03~0.12); preferably, the weight of the fibrous binder is 5~10% of the weight of the negative electrode active material, and more preferably 6~9%; And / or, the negative electrode active material is at least one selected from silicon-based materials, tin, tin oxide, germanium, germanium oxide, lithium, lithium oxide, aluminum, and aluminum oxide; preferably, the silicon-based material is selected from one or more selected from nano-silicon, silicon oxide, silicon-carbon composite, silicon-aluminum alloy, and amorphous silicon. And / or, the conductive agent is selected from one or more of Super-P, carbon black, VGCF, graphene, and carbon nanotubes; And / or, the viscosity-average molecular weight of the fibrous binder is 500,000 to 1,000,000; preferably, the fibrous binder is selected from one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxymethyl chitosan. And / or, the solvent is selected from one or more of NMP, deionized water, ethanol, isopropanol, acetone, dimethylformamide, dimethyl sulfoxide, PVDF, and ethyl acetate; And / or, the negative electrode current collector is one or more of electrolytic copper foil, rolled copper foil, nickel-plated copper foil, and porous copper foil.

10. A lithium-ion battery, comprising a negative electrode, characterized in that, The negative electrode sheet is the negative electrode sheet prepared by any one of claims 1 to 6 or any one of claims 7 to 9.

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