Negative electrode sheet and battery

Abstract

A negative electrode sheet and a battery comprising the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and coating layers located on the surface of one side or two sides of the negative electrode current collector, the coating layers comprising the element Na. Taking the total weight of the coating layers as a reference, the weight content of Na is 100ppm-950ppm. The coating layers include a second coating layer and a first coating layer. The first coating layer is located between the negative electrode current collector and the second coating layer. The second coating layer comprises graphite particles, and the first coating comprises silicon-based particles and a covering substance. The weight content of the Na in the first coating layer is higher than that in the second coating layer. The negative electrode sheet has a high specific capacity, high structural stability, and a low thickness expansion rate. The battery comprising the negative electrode sheet has the advantages of high energy density, high stability in high-temperature cycling, and a low thickness expansion rate.

Description

Negative electrode sheet and battery Technical Field

[0001] The present disclosure relates to the technical field of batteries, and in particular to a negative electrode sheet and a battery including the negative electrode sheet.

[0002] Background of the Invention

[0003] In the prior art, in order to increase the energy density of lithium-ion batteries, a certain amount of silicon-based materials can be mixed with graphite. The mixing is usually carried out in the following ways: (1) the silicon-based material and graphite are uniformly mixed in the negative electrode coating; (2) the negative electrode is set to a double-coating structure, with the surface layer being a mixed coating of graphite and silicon-based materials, and the bottom layer being a graphite coating; (3) the negative electrode is set to a double-coating structure, with the surface layer being a graphite coating, and the bottom layer being a mixed coating of graphite and silicon-based materials. However, when using the above mixing methods, the problem of rapid battery high-temperature cycle capacity decay and large thickness expansion rate still exists.

[0004] Therefore, it is very important to invent a battery with advantages such as high high-temperature cycle stability and low thickness expansion rate.

[0005] Summary of the Invention

[0006] The present disclosure provides a battery with high high-temperature cycle stability and low thickness expansion rate.

[0007] The present disclosure aims to overcome the existing problem of silicon-based particles experiencing significant volume expansion and contraction during lithium insertion and delithiation, and to provide a negative electrode sheet and a battery including the negative electrode sheet. The negative electrode sheet disclosed herein can effectively reduce the impact of volume expansion and contraction of silicon-based particles during lithium insertion and delithiation, thereby providing batteries with the advantages of high high-temperature cycling stability and low thickness expansion.

[0008] To achieve the above-mentioned objectives, the first aspect of the present disclosure provides a negative electrode sheet, comprising a negative electrode current collector and a coating located on one or both surfaces of the negative electrode current collector, the coating comprising Na element, and the weight content of Na element is 100ppm-950ppm based on the total weight of the coating, the coating comprising a second coating and a first coating, the first coating being located between the negative electrode current collector and the second coating, the second coating comprising graphite particles, the first coating comprising silicon-based particles and a covering, the silicon-based particles being dispersed in the covering, and the weight content of Na element in the first coating being higher than the weight content of Na element in the second coating.

[0009] Research has found that by adjusting the weight content of Na element in the first coating to be higher than the weight content of Na element in the second coating, the impact of volume expansion and contraction of silicon-based particles during lithium insertion and delithiation on the negative electrode sheet can be effectively reduced, and the structural stability of the negative electrode sheet can be improved, thereby improving the high-temperature cycle stability of the battery and reducing the thickness expansion rate of the battery.

[0010] A second aspect of the present disclosure provides a battery, comprising the negative electrode sheet described in the first aspect of the present disclosure.

[0011] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0012] (1) The negative electrode sheet disclosed herein has high structural stability;

[0013] (2) The thickness expansion rate of the negative electrode sheet disclosed in the present invention is low;

[0014] (3) The battery disclosed herein has high high-temperature cycling stability;

[0015] (4) The thickness expansion rate of the battery disclosed herein is low.

[0016] Other features and advantages of the present disclosure will be described in detail in the following detailed description.

[0017] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a schematic structural diagram of a negative electrode sheet disclosed in the present invention.

[0019] FIG. 2 is a SEM image of a negative electrode sheet according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explain the present application and should not be construed as limiting the scope of protection of the present application. All technologies implemented based on the above content of the present application are included within the scope of protection intended by the present application.

[0021] It should be noted that the numerical expressions such as "first" and "second" in this disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0022] A first aspect of the present disclosure provides a negative electrode sheet, comprising a negative electrode current collector and a coating located on one or both surfaces of the negative electrode current collector, wherein the coating comprises a Na element, and the weight content of the Na element is 100 ppm-950 ppm based on the total weight of the coating. The coating comprises a second coating and a first coating, wherein the first coating is located between the negative electrode current collector and the second coating, the second coating comprises graphite particles, the first coating comprises silicon-based particles and a covering, the silicon-based particles are dispersed in the covering, and the weight content of the Na element in the first coating is higher than the weight content of the Na element in the second coating.

[0023] In the potential range of 5mV to 1.5V (vs. Li / Li+), the gram capacity of silicon-based particles is generally 1000 to 2000mAh / g, which is much higher than the 350 to 360mAh / g of currently commercialized graphite particles, and can help improve the energy density of lithium-ion batteries. However, the large volume expansion and contraction of silicon-based particles during the lithium insertion and removal process can lead to two unfavorable results: first, the voids in the negative electrode coating increase, the electrolyte filling degree decreases, and the contact between particles deteriorates, which increases the difficulty of electron and ion transmission between particles; second, the SEI film repeatedly ruptures and grows, consuming active lithium and electrolyte while increasing the difficulty of electrons and ions entering and exiting the silicon-based particles, resulting in the battery having problems such as rapid capacity decay and large thickness expansion rate during high-temperature cycles.

[0024] In the present disclosure, as shown in Figures 1 and 2, the negative electrode sheet includes a negative electrode current collector 1 and a coating 2 located on one or both sides of the negative electrode current collector. The coating 2 includes a second coating 21 and a first coating 22. The first coating 22 is located between the negative electrode current collector and the second coating 21. The second coating 21 includes graphite particles. The first coating 22 includes silicon-based particles 221 and a covering 222. The silicon-based particles are dispersed in the covering, and the covering adheres to the surface of the negative electrode current collector. The silicon-based particles can be completely covered by the covering or partially covered by the covering (for example, the silicon-based particles are in contact with the negative electrode current collector, or the silicon-based particles are partially exposed on the surface of the first coating so that the silicon-based particles are partially covered by the covering). The covering can provide a restraining effect and a buffer space for the volume expansion and contraction of the silicon-based particles, thereby reducing the impact of the volume change of the silicon-based particles on the negative electrode sheet.

[0025] Based on the total weight of the coating, the weight content of the Na element can be 100ppm-950ppm (for example, 100ppm, 120ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 950ppm). The first coating includes the Na element, the second coating may include or exclude the Na element, the weight content of the Na element in the first coating is higher than the weight content of the Na element in the second coating, and the distribution of the Na element in the coating is non-uniform. When the content and distribution of the Na element in the coating conform to the above-mentioned specific relationship, the effect of the volume expansion and contraction of the silicon-based particles during the lithium insertion and delithiation process on the negative electrode sheet can be reduced, the structural stability of the negative electrode sheet can be improved, thereby improving the high-temperature cycle stability of the battery and reducing the thickness expansion rate of the battery. When the weight content of the Na element in the first coating layer is lower than or equal to the weight content of the Na element in the second coating layer, the weight content of the Na element in the first coating layer is too low, and the covering cannot form a uniform and complete protective layer on the surface of the silicon-based particles; or the weight content of the Na element in the second coating layer is too high, which will hinder the transmission and diffusion of lithium ions in the second coating layer, adversely affect the lithium insertion kinetics of the negative electrode coating, and deteriorate the cycle performance of the battery.

[0026] The non-uniform distribution state indicates that the mass content of the Na element in the first coating layer is not the same as the mass content of the Na element in the second coating layer. The distribution of the Na element in the first coating layer can be uniform or non-uniform, and the distribution of the Na element in the second coating layer can be uniform or non-uniform. The mass content of the Na element in the first coating layer indicates the mass content of the Na element based on the total mass of the first coating layer. The mass content of the Na element in the second coating layer indicates the mass content of the Na element based on the total mass of the second coating layer.

[0027] In the present disclosure, by designing the negative electrode sheet to have the above-mentioned specific structure, the negative electrode sheet has achieved higher structural stability and lower thickness expansion rate than the prior art. To further improve the effect, one or more of the technical features can be further optimized.

[0028] In one example, based on the total weight of the coating, the weight content of the Na element is 200 ppm-800 ppm.

[0029] In one example, the first coating layer includes a first active material, and the first active material is silicon-based particles.

[0030] In one example, the second coating layer includes a second active material, and the second active material is graphite particles.

[0031] According to a specific embodiment, the median particle size Dv50 of the silicon-based particles is 3 μm-15 μm (for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm). When the median particle size Dv50 of the silicon-based particles is limited to the above-mentioned specific range, the particle size and specific surface area of ​​the silicon-based particles can be ensured to be within a suitable range, thereby reducing the volume expansion of the silicon-based particles and reducing the side reactions with the electrolyte, thereby improving the high-temperature cycle stability of the battery. In the present disclosure, the median particle size Dv50 can be obtained by testing with a particle size analyzer.

[0032] In one embodiment, the median particle size Dv50 of the silicon-based particles is 5 μm to 12 μm. Limiting the median particle size of the silicon-based particles to the above-mentioned specific range can further reduce the volume expansion of the silicon-based particles or reduce side reactions between the silicon-based particles and the electrolyte, thereby improving the high-temperature cycling stability of the battery.

[0033] In one embodiment, the silicon-based particles include one or more of silicon-carbon particles and silicon-oxygen particles. The silicon-carbon particles are mixture particles of silicon and carbon, and the silicon-oxygen particles are oxide particles containing silicon.

[0034] In one example, the silicon-carbon particles include particles formed by mixing silicon or partially oxidized silicon with amorphous or crystalline carbon.

[0035] In one embodiment, the silicon-carbon particles include particles formed by silicon or partially oxidized silicon filling (including partial filling or complete filling) in the pores of porous amorphous carbon or porous crystalline carbon. The porous amorphous carbon or porous crystalline carbon is mainly used as a structural support and may also have a certain reversible lithium storage capacity. Silicon or partially oxidized silicon has a high reversible lithium storage capacity. Filling them in the pores of porous amorphous carbon or porous crystalline carbon can prevent silicon or partially oxidized silicon from agglomerating and breaking, thereby improving the structural stability of the silicon-based particles.

[0036] In one embodiment, the silicon-oxygen particles comprise a mixture of amorphous silicon and oxygen. Due to the oxygen element, the silicon-oxygen particles form inert or low-reactivity components such as silicates after initial lithium insertion. These components can act as a buffer matrix for silicon expansion, thereby improving the structural stability of the silicon-based particles.

[0037] In one embodiment, the silicon oxide particles include a chemical formula of M a Si b O x A substance where 0≤a<5, 0≤b<3, and 0≤x≤2.

[0038] Wherein, M includes one or more of Li and Mg. The M element, including a specific element, can combine with O and Si to form an inert or low-activity silicate, thereby reducing the amount of side reactions during the initial lithium insertion of the silicon-based particles and improving the initial coulombic efficiency of the silicon-based particles.

[0039] In one example, the silicon oxide particles include a mixture of amorphous silicon and oxygen, or one or more of Si, SiO2, Li2SiO3, Li2Si2O5, Li4SiO4, MgSiO3, Mg2SiO4, and Li2O.

[0040] In one embodiment, the silicon-oxygen particles include one or more of a mixture of amorphous silicon and oxygen, Li2SiO3 (crystalline), and Li2Si2O5 (crystalline). Li2SiO3 and Li2Si2O5 are crystalline phases formed when the silicon-oxygen particles are doped with lithium. The formation of Li2SiO3 (crystalline) and Li2Si2O5 (crystalline) can improve the first coulombic efficiency of the silicon-based particles.

[0041] In one embodiment, the surface of the silicon oxide particles comprises an amorphous carbon coating layer, which can isolate the electrolyte, thereby inhibiting side reactions on the surface of the silicon oxide particles and improving the structural stability of the silicon oxide particles.

[0042] In one embodiment, the surface of the first coating layer away from the negative electrode current collector has a protrusion (as shown in Figures 1 and 2). The first coating layer forms a protrusion close to the surface of the second coating layer based on the shape and stacking method of the silicon-based particles, that is, the surface of the first coating layer in contact with the second coating layer is uneven. This uneven surface can increase the contact area between the silicon-based particles and the second coating layer, thereby improving the uniformity of lithium ion embedding into the silicon-based particles, effectively suppressing the problem of excessive expansion caused by excessive local lithium embedding of the silicon-based particles, and improving the cycle structural stability of the negative electrode sheet.

[0043] In one embodiment, the flatness β of the first coating layer is 8 μm to 25 μm (e.g., 8 μm, 10 μm, 15 μm, 20 μm, 25 μm). When β is less than 8 μm, the first coating layer away from the current collector surface is relatively flat, the contact area between the silicon-based particles and the second coating layer is small, and the lithium insertion uniformity of the silicon-based particles is poor. When β is greater than 25 μm, the distribution of the silicon-based particles in the first coating layer becomes significantly non-uniform, which can cause excessive expansion in local areas and affect the battery cycle performance.

[0044] In one embodiment, the flatness of the first coating layer is 12 μm to 20 μm. Within this range, the silicon-based particles in the first coating layer are in sufficient contact with the second coating layer, lithium insertion is more uniform, and the silicon-based particles are more evenly distributed, resulting in less expansion of the negative electrode sheet and better cycle performance.

[0045] In the present disclosure, flatness can be obtained in the following manner: cutting in a direction perpendicular to the surface of the negative electrode sheet to obtain a cross section of the negative electrode sheet, and using SEM to observe any area of ​​the negative electrode sheet with a length of not less than 80 μm. As shown in Figure 1, along the direction perpendicular to the surface of the negative electrode sheet, draw a vertical straight line toward the negative electrode coating at any point A on the surface of the negative electrode current collector. The straight line passes through the first coating and the second coating in sequence. When the straight line has one or more intersections with the edge of the cross section of the silicon-based particles in the first coating, the intersection farthest from A is taken as B, and the length of the AB line segment is taken as the distribution width f of the silicon-based particles at point A; when the straight line has no intersection with the edge of the cross section of the silicon-based particles, the distribution width of the silicon-based particles at point A is defined as 0. The maximum value of f in the observation area is f max , the minimum value is f min , with β=f max -f min is the flatness of the first coating.

[0046] Methods for controlling the smoothness may include selecting silicon-based particles with an appropriate particle size, controlling the content of silicon-based particles, applying the second coating layer without rolling the first coating layer, and the like.

[0047] According to a specific embodiment, the ratio of the thickness of the first coating layer to the thickness of the coating layer is (0.1-0.45):1 (e.g., 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1).

[0048] In one embodiment, the ratio of the thickness of the first coating layer to the thickness of the second coating layer is (0.2-0.35):1. Within this range, the distance for lithium ions to reach the silicon-based particles from the outer surface of the coating layer is moderate, which can effectively delay the lithium insertion behavior of the silicon-based particles, making the lithium insertion process of the silicon-based particles more gentle and uniform, thereby improving the cycle stability of the silicon-based particles.

[0049] According to a specific embodiment, the coating has a thickness c of 30 μm to 100 μm (e.g., 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm). Within this range, the problem of coating scraping caused by a too thin coating thickness can be avoided, and the phenomenon of a significant decrease in lithium insertion uniformity caused by an excessively thick coating thickness can also be prevented.

[0050] In one example, the thickness c of the coating layer is 40 μm-80 μm.

[0051] In one embodiment, the thickness a of the first coating layer is 5 μm to 40 μm (e.g., 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm). Within this range, the problem of coating scraping caused by a coating layer that is too thin can be avoided; the phenomenon of silicon-based particles being too widely distributed along the thickness direction due to a first coating layer that is too thick can also be prevented, thereby improving the uniformity of lithium insertion in the silicon-based particles.

[0052] In one embodiment, the thickness b of the second coating layer is 18 μm to 90 μm (e.g., 18 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm). Within this range, the problem of coating scraping caused by a second coating layer that is too thin can be avoided; and the problem of excessive lithium polarization and uneven lithium insertion caused by a second coating layer that is too thick can also be avoided.

[0053] As shown in Figure 1, the coating thickness, the thickness of the first coating layer, and the thickness of the second coating layer can be obtained by cutting the negative electrode sheet perpendicular to the surface to obtain a cross-section of the negative electrode sheet. Using an SEM, observe any region of the negative electrode sheet with a length of not less than 80 μm. At any point A on the surface of the negative electrode current collector, a vertical straight line is drawn perpendicular to the surface of the negative electrode sheet toward the negative electrode coating layer. This straight line passes through the first coating layer and the second coating layer in sequence. This straight line intersects the edge of the cross-section of the silicon-based particles in the first coating layer at one or more points. The intersection point farthest from A is designated as B. The intersection point of this straight line with the surface of the second coating layer away from the negative electrode current collector is designated as C. The maximum length of line segment AB within the observation area is designated as the thickness a of the first coating layer. The minimum length of line segment BC is designated as the thickness b of the second coating layer. The length of line AC is designated as the coating thickness c. It can be understood that c = a + b.

[0054] According to a specific embodiment, the weight content of the covering is 15 wt%-70 wt% (e.g., 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 70 wt%), based on the total weight of the first coating layer. When the weight content of the covering in the first coating layer is limited to the above-mentioned specific range, the covering can provide sufficient buffering for the expansion or contraction of the silicon-based particles and better bind the silicon-based particles to the surface of the negative electrode current collector, thereby improving the structural stability of the negative electrode sheet and reducing the thickness expansion rate of the battery.

[0055] In one embodiment, the weight content of the covering is 25 wt% to 55 wt% based on the total weight of the first coating layer. Limiting the weight content of the covering in the first coating layer to the above specific range can increase the gram capacity of the negative electrode sheet, enabling the battery to have the advantages of high energy density, high cycle stability, and low thickness expansion rate.

[0056] In one example, the silicon-based particles include Si element.

[0057] According to a specific embodiment, the weight content of Si element is 30wt%-70wt% (e.g., 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%) based on the total weight of the silicon-based particles. When the weight content of Si element in the silicon-based particles is limited to the above specific range, the lithium storage capacity or stability of the silicon-based particles can be improved, thereby further improving the gram capacity or structural stability of the negative electrode sheet.

[0058] In one embodiment, the weight content of Si is 40 wt% to 65 wt% based on the total weight of the silicon-based particles. When the weight content of Si in the silicon-based particles is limited to the above specific range, the silicon-based particles have a higher specific capacity. Furthermore, the structural carrier or buffer matrix can effectively suppress structural damage caused by volume changes, further improving the lithium storage capacity or stability of the silicon-based particles, thereby further improving the specific capacity or structural stability of the negative electrode sheet.

[0059] In one embodiment, the covering includes Na element. The Na element can improve the adhesion, elasticity, and electrochemical stability of the covering on the surface of the silicon-based particles, reduce the occurrence of side reactions, and inhibit the rupture or shedding of the SEI film, thereby improving the cycle capacity retention rate of the battery and reducing the thickness expansion rate of the battery.

[0060] According to a specific embodiment, based on the total weight of the first coating, the weight content of the Na element is 0.04wt%-0.6wt% (for example, 0.04wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%).

[0061] When the weight content of Na element is less than 0.04wt%, there are two situations: first, the Na element content in the binder molecule is too low, which may lead to insufficient hydrophilicity of the binder molecule, and it cannot be fully dispersed in the commonly used aqueous slurry, and cannot be evenly adsorbed on the surface of the silicon-based material, and thus cannot form a complete and effective interface protection layer; second, the Na-containing binder content is too small, which is insufficient to form a high-strength, high-elastic bonding network, and cannot form an effective passivation layer on the surface of the silicon-based particles.

[0062] When the weight content of Na element is greater than 0.6wt%, there are also two situations: one is that the Na element content in the binder molecule is too high, which may lead to insufficient hydrophobicity of the binder molecule, and it is also impossible to fully disperse in the commonly used aqueous slurry, and cannot be evenly adsorbed on the surface of the silicon-based material, and cannot form a complete and effective interface protection layer; the other is that the Na-containing binder content is too high, which may excessively increase the difficulty of lithium ion embedding into the silicon-based material, and significantly affect the battery's rate and cycle performance.

[0063] When the weight content of the Na element in the first coating is limited to the above-mentioned specific range, the binder can be evenly dispersed in the slurry, so that the binder is more evenly distributed around the silicon-based particles, thereby forming a high-strength, high-elastic bonding network. In addition, an appropriate amount of Na element can act as a barrier to lithium ion transmission, slowing down the speed at which lithium ions are embedded in silicon-based particles, thereby improving the uniformity of lithium insertion.

[0064] In one embodiment, the weight content of the Na element is 0.15 wt% to 0.48 wt% based on the total weight of the first coating layer. Within this range, the binder is more evenly distributed around the silicon-based particles, the bonding network strength and elasticity of the first coating layer are higher, and the lithium insertion uniformity of the silicon-based particles is higher.

[0065] In one example, the first coating layer includes Si element.

[0066] According to a specific embodiment, based on the total weight of the first coating, the weight content of Si element is 10wt%-45wt% (for example, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%).

[0067] In one example, based on the total weight of the first coating layer, the weight content of the Si element is 20 wt%-40 wt%.

[0068] According to a specific embodiment, in the first coating, the ratio of the weight of the Na element to the weight of the Si element is (0.001-0.02):1 (for example, 0.001:1, 0.005:1, 0.01:1, 0.015:1, 0.019:1, 0.02:1). Through the synergistic cooperation of the Na element and the Si element, the buffering effect provided by the covering can meet the volume change requirements of the silicon-based particles while ensuring the high gram capacity of the negative electrode sheet, reduce the occurrence of side reactions, and inhibit the rupture or shedding of the SEI film, thereby further improving the energy density and high-temperature cycle stability of the battery and reducing the thickness expansion rate of the battery. The covering in the first coating includes a first binder and a first conductive agent, the first binder plays a physical bonding role, and the first conductive agent helps increase the electron transmission path. The first binder contains a certain amount of Na. When the weight ratio of Na and Si elements satisfies a certain relationship, the first binder molecules can be evenly and fully wrapped on the surface of the silicon-based particles, forming a stable interface protection layer, which is beneficial to inhibiting the repeated rupture and growth of the surface SEI film. At the same time, this interface protection layer can slow down the lithium insertion rate on the surface of the silicon-based particles to a certain extent, providing a buffer time for the uniform distribution of lithium ions within and between the silicon-based particles, avoiding excessive local expansion due to uneven lithium insertion and preventing accelerated battery performance degradation. The covering in the first coating has a strong bond with the silicon-based particles, forming a high-strength and highly elastic bonding network, which better binds the silicon-based particles to the surface of the negative electrode current collector and effectively inhibits the continuous increase of the gaps around the silicon-based particles after repeated charge and discharge.

[0069] In one embodiment, in the first coating, the weight ratio of the Na element to the Si element is (0.003-0.016):1. Within this range, the binder can be evenly and fully coated on the surface of the silicon-based particles, forming a stable interface protection layer of moderate thickness, thereby forming a high-strength and highly elastic bonding network, while also improving the uniformity of lithium insertion in the silicon-based particles and the cyclic stability of the coating.

[0070] In one example, the cover includes a first conductive agent and a first adhesive.

[0071] In one example, the first conductive agent includes one or more of carbon black, carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, and graphene.

[0072] In one embodiment, the first binder includes a sodium-containing binder and an optional sodium-free binder (the term "optional" means that the binder may or may not be present).

[0073] In one embodiment, the sodium-containing binder includes one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and sodium alginate. The sodium element in the covering is provided by the sodium-containing binder, that is, the sodium element in the first coating is provided by the sodium-containing binder.

[0074] In one example, the sodium-free binder includes one or more of polyacrylic acid, lithium polyacrylate, carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polytetrafluoroethylene, polypropylene, styrene-butadiene rubber and epoxy resin.

[0075] In one example, based on the total weight of the cover, the weight content of the first conductive agent is 0.1wt%-70wt% (for example, 0.1wt%, 1wt%, 5wt%, 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%), and the weight content of the first binder is 30wt%-99.9wt% (for example, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, 90wt%, 95wt%, 99.9wt%).

[0076] In one example, based on the total weight of the cover, the weight content of the first conductive agent is 30 wt %-60 wt %, and the weight content of the first binder is 40 wt %-70 wt %.

[0077] The second coating may include graphite particles.

[0078] In one example, the graphite particles include one or more of artificial graphite and natural graphite.

[0079] In one embodiment, the median particle size Dv50 of the graphite particles is 5 μm-20 μm (e.g., 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 17 μm, 20 μm). Within this range, the graphite particles have a moderate particle size, fewer surface side reactions, better lithium insertion kinetics, and higher cycling stability.

[0080] In one embodiment, the median particle size Dv50 of the graphite particles is 8 μm to 15 μm. Within this range, surface side reactions can be further reduced or lithium insertion kinetics can be improved, thereby further improving the cycle stability of the graphite particles.

[0081] In one example, the second coating layer includes a second conductive agent and a second binder.

[0082] In one example, the second conductive agent includes one or more of carbon black, carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, and graphene.

[0083] In one example, the second binder comprises one or more of carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polytetrafluoroethylene, polypropylene, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, sodium alginate, styrene-butadiene rubber and epoxy resin. The Na element in the second coating layer is provided by one or more of sodium carboxymethyl cellulose, sodium polyacrylate and sodium alginate in the second binder. Since the second binder can have different options, the Na element may or may not be included in the second coating layer.

[0084] According to a specific embodiment, based on the total weight of the second coating layer, the weight content of the Na element is 0 wt%-0.04 wt%. When the weight content of the Na element is 0 wt%, it means that the second coating layer does not contain the Na element.

[0085] In one embodiment, the weight content of the Na element is 0.003 wt% to 0.03 wt% based on the total weight of the second coating layer. When the weight content of the Na element in the second coating layer is within the above-specified range, the affinity of the second binder molecules is moderate, and the second binder is more evenly distributed in the second coating layer, thereby improving the uniformity of lithium ion transport in the second coating layer, preventing localized excessive lithium insertion or removal, and thus improving the cycling stability of the coating layer.

[0086] In one example, the first coating layer includes one or more of sodium carboxymethylcellulose, sodium polyacrylate, and sodium alginate.

[0087] In one example, the second coating layer includes sodium carboxymethylcellulose.

[0088] In one embodiment, the sodium carboxymethylcellulose content in the first coating layer is greater than the sodium carboxymethylcellulose content in the second coating layer. When this condition is met, the second coating layer exhibits better lithium ion transport kinetics than the first coating layer, which can reduce the difficulty of lithium ion insertion or diffusion in the second coating layer and improve the charging performance of the coating layer.

[0089] According to a specific embodiment, based on the total weight of the coating, the weight content of Si element is 1wt%-10wt% (for example, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%).

[0090] In one embodiment, based on the total weight of the coating, the weight content of Si element is 2 wt%-8 wt%.

[0091] According to a specific embodiment, in the coating, the weight ratio of the Na element to the Si element is (0.002-0.021):1 (for example, 0.002:1, 0.005:1, 0.01:1, 0.015:1, 0.02:1, 0.021:1).

[0092] In one example, in the coating, the ratio of the weight of the Na element to the weight of the Si element is (0.004-0.018):1.

[0093] According to a specific embodiment, based on the total weight of the coating, the weight content of the graphite particles is 50wt%-95wt% (for example, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%).

[0094] In one example, based on the total weight of the coating, the weight content of the graphite particles is 65 wt%-92 wt%.

[0095] According to a specific embodiment, based on the total weight of the coating, the weight content of the second conductive agent is 0.1wt%-2wt% (for example, 0.1wt%, 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%).

[0096] In one example, based on the total weight of the coating, the weight content of the second conductive agent is 0.3 wt%-1.2 wt%.

[0097] According to a specific embodiment, based on the total weight of the coating, the weight content of the second binder is 0.5wt%-4wt% (for example, 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%).

[0098] In one example, based on the total weight of the coating, the weight content of the second binder is 1 wt%-2.5 wt%.

[0099] According to a specific embodiment, based on the total weight of the coating, the weight content of the silicon-based particles is 2wt%-26wt% (for example, 2wt%, 5wt%, 10wt%, 15wt%, 20wt%, 23wt%, 26wt%).

[0100] In one example, based on the total weight of the coating, the weight content of the silicon-based particles is 4 wt%-16 wt%.

[0101] According to a specific embodiment, based on the total weight of the coating, the weight content of the first conductive agent is 0.05wt%-10wt% (for example, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 8wt%, 10wt%), and the weight content of the first binder is 0.2wt%-12wt% (for example, 0.2wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 8wt%, 10wt%, 12wt%).

[0102] In one example, based on the total weight of the coating, the weight content of the first conductive agent is 0.8 wt %-5.5 wt %, and the weight content of the first binder is 1 wt %-6.5 wt %.

[0103] In one example, the negative electrode current collector includes copper foil and / or a polymer current collector.

[0104] A second aspect of the present disclosure provides a battery, comprising the negative electrode sheet described in the first aspect of the present disclosure.

[0105] The materials of the battery except the negative electrode sheet can be prepared according to the methods in the art, and can achieve the effects of high high-temperature cycle stability and low thickness expansion rate.

[0106] The battery may be a lithium-ion battery.

[0107] Since the battery of the present disclosure includes the negative electrode sheet of the present disclosure, the high-temperature cycle stability of the battery is improved and the thickness expansion rate is reduced.

[0108] The present disclosure will be described in detail below through examples. The examples described in this disclosure are only a portion of the examples of the present disclosure, not all of the examples. Based on the examples in this disclosure, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this disclosure.

[0109] The following examples are used to illustrate the negative electrode sheet of the present disclosure.

[0110] Example 1

[0111] (1) Preparation of ingredients

[0112] Negative electrode current collector: copper foil, thickness of 6 μm;

[0113] First coating: silicon-based particles (silicon-carbon particles, particles formed by completely filling the pores of porous amorphous carbon with silicon, wherein the average pore size of the pores of the porous amorphous carbon is 2 nm, the median particle size Dv50 of the porous amorphous carbon is 7.0 μm, the median particle size Dv50 of the silicon-carbon particles is 7.0 μm, the weight content of Si element in the silicon-carbon particles is 48%, and the specific surface area of ​​the silicon-carbon particles is 4.1 m 2 / g) 64 parts by weight, a first conductive agent (carbon black) 16 parts by weight, a first binder (wherein, a sodium-containing binder (sodium carboxymethyl cellulose, the sodium content of the sodium element in the sodium carboxymethyl cellulose being 6.4%) 5 parts by weight, a sodium-free binder (5 parts by weight of lithium carboxymethyl cellulose, 10 parts by weight of styrene-butadiene rubber)) 20 parts by weight;

[0114] Second coating: 97 parts by weight of graphite particles (artificial graphite, wherein the median particle size Dv50 is 12.0 μm), 0.8 parts by weight of a second conductive agent (carbon black), and 2.2 parts by weight of a second binder (0.1 parts by weight of sodium carboxymethyl cellulose, 1 part by weight of lithium carboxymethyl cellulose, and 1.1 parts by weight of styrene-butadiene rubber).

[0115] (2) Preparation of negative electrode sheet

[0116] The silicon-based particles, the first conductive agent and the first binder are mixed and stirred evenly to obtain a first coating slurry; the first coating slurry is coated with a surface density of 1.4 mg / cm 2 The first coating is evenly coated on both sides of the negative electrode current collector to form a first coating, which is then rolled and dried until the compaction density of the first coating is 0.85 g / cm 3 , obtaining a negative electrode sheet including a first coating layer;

[0117] The graphite particles, the second conductive agent and the second binder are mixed and stirred evenly to obtain a second coating slurry; the second coating slurry is mixed and stirred at a surface density of 8.3 mg / cm 2 uniformly coating the surface of the first coating to form a second coating, and drying to obtain a negative electrode sheet including the first coating and the second coating;

[0118] The negative electrode sheet including the first coating layer and the second coating layer was rolled to a compact density of the negative electrode coating layer of 1.73 g / cm 3 , then cut the electrode sheets and weld the tabs to obtain the negative electrode sheets.

[0119] Example 2 group

[0120] This group of examples was carried out with reference to Example 1, except that the weight content of the Na element was changed. In Example 2a, the sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the first coating layer were 2.5 parts by weight and 7.5 parts by weight, respectively; in Example 2b, the sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the first coating layer were 1 part by weight and 9 parts by weight, respectively; in Example 2c, the sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the first coating layer were 7 parts by weight and 3 parts by weight, respectively; in Example 2d, the sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the first coating layer were 9 parts by weight and 1 part by weight, respectively; and in Example 2e, the sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the second coating layer were 0 parts by weight and 1.1 parts by weight, respectively. It should be noted that when the weight content of the Na element is changed, the flatness of the first coating layer and the ratio of the thickness of the first coating layer to the thickness of the coating layer will inevitably fluctuate within a reasonably small range.

[0121] Example 3 group

[0122] This example group was carried out with reference to Example 1, except that the median particle size Dv50 of the silicon-based particles was changed. The median particle size of the silicon-carbon particles in Example 3a was 3.3 μm, and the median particle size of the silicon-carbon particles in Example 3b was 14.2 μm. For details, see Table 1-1 and Table 1-2.

[0123] Example 4 Group

[0124] This example group was carried out in accordance with Example 1, except that the flatness of the first coating layer was changed by roller pressing. In Example 4a, before applying the second coating layer, the negative electrode sheet including the first coating layer was roller pressed to make the compaction of the first coating layer 1.24 g / cm 3 In Example 4b, the negative electrode sheet including the first coating was rolled to a compaction of 0.65 g / cm 3 In Example 4c, the negative electrode sheet including the first coating was rolled to a compaction of 0.5 g / cm 3 For details, see Table 1-1 and Table 1-2.

[0125] Example 5 Group

[0126] This example group was carried out with reference to Example 1, except that the weight content of the covering material in the first coating layer was changed. In Example 5a, the silicon-carbon particles, carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber in the first coating layer were 82 parts by weight, 8 parts by weight, 5 parts by weight, and 5 parts by weight, respectively; in Example 5b, the silicon-carbon particles, carbon black, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and styrene-butadiene rubber in the first coating layer were 38.8 parts by weight, 27.2 parts by weight, 5 parts by weight, 12 parts by weight, and 17 parts by weight, respectively. See Table 1-1 and Table 1-2 for details.

[0127] Example 6

[0128] This example group was carried out with reference to Example 1, except that the weight content of Si element in the silicon-based particles was changed. The weight content of Si element in the silicon-carbon particles of Example 6a was 35%, and the weight content of Si element in the silicon-carbon particles of Example 6b was 68%. For details, see Table 1-1 and Table 1-2.

[0129] Example 7

[0130] This example is carried out in accordance with Example 1, except that silicon-oxygen particles are used instead of silicon-carbon particles. The silicon-oxygen particles include a mixture of amorphous silicon and oxygen, crystalline Li2SiO3, and crystalline Li2Si2O5. The surface of the silicon-oxygen particles contains an amorphous carbon coating layer. The median particle size Dv50 of the silicon-oxygen particles is 7 μm, the weight content of Si element in the silicon-oxygen particles is 61%, and the specific surface area of ​​the silicon-carbon particles is 2.3 m 2 / g.

[0131] Example 8

[0132] This example is carried out with reference to Example 1, except that sodium carboxymethyl cellulose is replaced by sodium polyacrylate in equal parts by weight, wherein the weight content of the sodium element in the sodium polyacrylate is 6.4%.

[0133] Table 1-1

[0134] Table 1-2

[0135] *Same as Example 1.

[0136] - means it does not exist.

[0137] Comparative Example 1

[0138] The negative electrode sheet was processed in the same manner as in Example 1, except that the negative electrode sheet had only one coating layer: 9.2 parts by weight of silicon carbon particles, 83 parts by weight of graphite particles, 3 parts by weight of carbon black, 0.82 parts by weight of sodium carboxymethyl cellulose, 1.58 parts by weight of lithium carboxymethyl cellulose, and 2.4 parts by weight of styrene-butadiene rubber. The coating layer had an areal density of 9.7 mg / cm 2 .

[0139] Comparative Example 2

[0140] The process was carried out with reference to Example 1, except that the sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the first coating were 1 part by weight and 9 parts by weight, respectively, and the sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the second coating were 0 parts by weight and 1.1 parts by weight, respectively, and the weight content of the Na element in the coating was 92 ppm.

[0141] Comparative Example 3

[0142] The process was carried out with reference to Example 1, except that the amounts of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the first coating layer were 10 parts by weight and 0 parts by weight, respectively, and the weight content of the Na element in the coating layer was 978 ppm.

[0143] Comparative Example 4

[0144] The process was carried out with reference to Example 1, except that the amounts of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the first coating layer were 1.1 parts by weight and 8.9 parts by weight, respectively; the amounts of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the second coating layer were 1.1 parts by weight and 0 parts by weight, respectively; and the mass content of Na element in the first coating layer was equal to the mass content of Na element in the second coating layer.

[0145] Comparative Example 5

[0146] The process was carried out with reference to Example 1, except that the amounts of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the first coating layer were 0.8 parts by weight and 9.2 parts by weight, respectively, and the amounts of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose in the second coating layer were 1.1 parts by weight and 0 parts by weight, respectively, and the mass content of the Na element in the first coating layer was lower than the mass content of the Na element in the second coating layer.

[0147] Preparation Example

[0148] Batteries were prepared using the negative electrode sheets obtained in the examples and comparative examples in the following manners.

[0149] (1) Positive electrode

[0150] The positive electrode active material (lithium cobalt oxide, 96 parts by weight), the binder (polyvinylidene fluoride, 2 parts by weight) and the conductive agent (carbon black, 2 parts by weight) were mixed and stirred at high speed to obtain a uniformly dispersed positive electrode slurry. The positive electrode slurry was evenly coated on both sides of the positive electrode current collector (aluminum foil, 9 μm thick), dried and compacted by a roller press to obtain a positive electrode sheet. The single-sided surface density of the positive electrode sheet is 24.3 mg / cm 2 , the compacted density is 4.1g / cm 3 .

[0151] (2) Negative electrode

[0152] The negative electrode sheets obtained in the above embodiments and comparative examples were used respectively.

[0153] (3) Diaphragm

[0154] The separator is a polyethylene separator with a thickness of 8 μm.

[0155] (4) Electrolyte

[0156] The electrolyte is a mixed solution including EC, PC, PP, LiPF6, FEC, and PS in a weight ratio of 12:12:47:15:10:4.

[0157] (4) Preparation of lithium-ion batteries

[0158] The positive electrode sheet of step (1), the diaphragm of step (3), and the negative electrode sheet of step (2) are stacked in the above order, so that the diaphragm is located between the positive electrode sheet and the negative electrode sheet and plays an isolating role. The battery core is wound to obtain a battery core, and the battery core is placed in an aluminum-plastic film shell. After drying the moisture, the electrolyte of step (4) is injected. After the steps of packaging, aging, formation, secondary sealing, and sorting, a lithium-ion battery is obtained.

[0159] Test Case

[0160] The batteries obtained in the examples and comparative examples were tested as follows:

[0161] (1) High temperature cycle stability test

[0162] The test temperature is 45°C, discharged at 0.5C to 3V, and allowed to stand for 10 minutes; charged at 1C constant current to 4.45V, charged at constant voltage to 0.05C, allowed to stand for 10 minutes, discharged at 0.5C to 3V, and allowed to stand for 10 minutes. The cycle test is carried out with this charge and discharge procedure, and the capacity of the nth discharge divided by the capacity of the first discharge is the nth capacity retention rate.

[0163] (2) Thickness expansion rate test

[0164] The test temperature is 45°C, discharged at 0.5C to 3V, and allowed to stand for 10 minutes; charged at a constant current of 1C to 3.83V, charged at a constant voltage to 0.05C, and allowed to stand for 10 minutes, and the battery thickness is measured, which is taken as the initial thickness; charged at a constant current of 1C to 4.45V, charged at a constant voltage to 0.05C, and allowed to stand for 10 minutes, discharged at 0.5C to 3V, and allowed to stand for 10 minutes. This charge and discharge procedure is used for 600 cycles, and a full charge thickness test is performed every 100 cycles. The growth rate of this thickness relative to the initial thickness is the thickness expansion rate of the battery.

[0165] (3) Energy density test

[0166] 1) The dimensions of the battery cell model are: H (mm, thickness) * 63 (mm, width, W) * 84 (mm, height, L), that is, the volume of the battery cell V = thickness * width * height;

[0167] 2) Place the battery cell in an environment of 25±3℃ and let it stand for 2 hours. Then charge the battery cell to full power using a constant current and constant voltage rate of 0.5C, set the cutoff current to 0.025C, let it stand for 5 minutes, and then discharge the battery cell to 3.0V using a rate of 0.2C. Record the discharge energy E.

[0168] 3) Volume energy density of the battery cell ED = E / (H*W*L).

[0169] (4) Gram capacity test of negative electrode

[0170] Pair the negative electrode sheet with lithium foil to form a button cell. Discharge at 0.05C to 0.005V to obtain the first discharge capacity. Let it rest for 10 minutes, then discharge at 0.01C to 0.005V to obtain the second discharge capacity. Let it rest for 10 minutes, and charge at 0.05C to 0.8V to obtain the charge capacity. Divide the charge capacity by the mass of the negative electrode coating to obtain the gram capacity of the negative electrode sheet.

[0171] The obtained results are recorded in Table 2.

[0172] Table 2

[0173] As can be seen from Table 2, by comparing the comparative example with the embodiment, the battery made from the negative electrode sheet of the embodiment has a significantly improved high-temperature cycle capacity retention rate and a significantly reduced thickness expansion rate, indicating that the negative electrode sheet and the battery including the negative electrode sheet of the present disclosure, by designing the negative electrode sheet into a specific structure, reduces the impact of the volume expansion and contraction of silicon-based particles during lithium insertion and delithiation on the negative electrode sheet and the battery, so that the battery has the advantages of high high-temperature cycle stability and low thickness expansion rate.

[0174] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet includes a negative electrode current collector and a coating located on one side or both sides of the negative electrode current collector, the coating includes Na element, and the weight content of Na element is 100ppm-950ppm based on the total weight of the coating, the coating includes a second coating and a first coating, the first coating is located between the negative electrode current collector and the second coating, the second coating includes graphite particles, the first coating includes silicon-based particles and a covering, the silicon-based particles are dispersed in the covering, and the weight content of Na element in the first coating is higher than the weight content of Na element in the second coating.

2. The negative electrode sheet according to claim 1, wherein: Based on the total weight of the coating, the weight content of the Na element is 200ppm-800ppm; and / or, the first coating comprises a first active material, the first active material being silicon-based particles; And / or, the second coating layer includes a second active material, and the second active material is graphite particles.

3. [Corrected 19.12.2024 in accordance with Rule 26] A negative electrode sheet according to claim 1 or 2, wherein: The median particle size Dv50 of the silicon-based particles is 3 μm-15 μm, preferably 5 μm-12 μm; And / or, the cover comprises a first conductive agent and a first binder, wherein the first binder comprises a sodium-containing binder and optionally a sodium-free binder.

4. The negative electrode sheet according to claim 3, wherein: The sodium-containing binder includes one or more of sodium carboxymethyl cellulose, sodium polyacrylate and sodium alginate.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein: The first coating layer includes one or more of sodium carboxymethyl cellulose, sodium polyacrylate and sodium alginate; and / or, the second coating comprises sodium carboxymethyl cellulose; And / or, the content of sodium carboxymethyl cellulose in the first coating layer is greater than the content of sodium carboxymethyl cellulose in the second coating layer.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The ratio of the thickness of the first coating layer to the thickness of the coating layer is (0.1-0.45):1, preferably (0.2-0.35):1; and / or, the coating has a thickness of 30 μm-100 μm, preferably 40 μm-80 μm; And / or, the thickness of the first coating layer is 5 μm-40 μm, and the thickness of the second coating layer is 18 μm-90 μm.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: The first coating layer has a protrusion on its surface away from the negative electrode current collector; And / or, the flatness β of the first coating layer is 8 μm to 25 μm.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein: The first coating layer includes Na element, and the weight content of the Na element is 0.04wt%-0.6wt%, preferably 0.15wt%-0.48wt%, based on the total weight of the first coating layer; And / or, the first coating layer comprises Si element, and based on the total weight of the first coating layer, the weight content of Si element is 10wt%-45wt%, preferably 20wt%-40wt%.

9. The negative electrode sheet according to claim 8, wherein: In the first coating layer, the weight ratio of the Na element to the Si element is (0.001-0.02):1, preferably (0.003-0.016):

1.

10. The negative electrode sheet according to any one of claims 1 to 9, wherein: Based on the total weight of the first coating, the weight content of the covering is 15wt%-70wt%, preferably 25wt%-55wt%; And / or, based on the total weight of the silicon-based particles, the weight content of Si element is 30wt%-70wt%, preferably 40wt%-65wt%.

11. The negative electrode sheet according to any one of claims 1 to 10, wherein: Based on the total weight of the coating, the weight content of Si element is 1wt%-10wt%, preferably 2wt%-8wt%; And / or, in the coating, the weight ratio of the Na element to the Si element is (0.002-0.021):1, preferably (0.004-0.018):1; And / or, based on the total weight of the coating, the weight content of the silicon-based particles is 2wt%-26wt%, preferably 4wt%-16wt%.

12. The negative electrode sheet according to any one of claims 1 to 11, wherein: The graphite particles include one or more of artificial graphite and natural graphite; And / or, the silicon-based particles include one or more of silicon-carbon particles and silicon-oxygen particles.

13. The negative electrode sheet according to claim 12, wherein: The silicon carbon particles include particles formed by silicon or partially oxidized silicon filling the pores of porous amorphous carbon or porous crystalline carbon; And / or, the silicon-carbon particles include particles formed by mixing silicon or partially oxidized silicon with amorphous carbon or crystalline carbon; And / or, the silicon oxide particles include a chemical formula of M a Si b Ox substances, wherein 0≤a<5, 0≤b<3, 0≤x≤2, wherein M includes one or more of Li and Mg; And / or, the surface of the silicon oxide particles contains an amorphous carbon coating layer.

14. A battery, characterized in that: The battery comprises the negative electrode sheet according to any one of claims 1 to 13.

15. The battery according to claim 14, wherein The battery is a lithium-ion battery.

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