Silicon-carbon composite material, negative plate and battery

Abstract

The invention relates to the technical field of battery materials, in particular to a silicon-carbon composite material, a negative plate and a battery, the silicon-carbon composite material comprises a porous carbon matrix and silicon particles distributed in pores in the porous carbon matrix, a coating layer is arranged on the outer surface of the porous carbon matrix, and the coating layer comprises amorphous carbon and / or a solid electrolyte material; in the 5k-time SEM image, the section contour of the silicon-carbon composite material comprises a first line segment and a second line segment, the curvature radius of the first line segment is R1, the unit is [mu] m, the curvature radius of the second line segment is R2, the unit is [mu] m, 1 / R1 is greater than or equal to 0.1, and 1 / R2 is less than 0.1; the section profile of the silicon-carbon composite material comprises a first interior angle, and the first interior angle is larger than 180 degrees. The silicon-carbon composite material disclosed by the invention is beneficial to maintaining the cycling stability of the battery, improving the dynamic performance of the battery and slowing down volume expansion; and moreover, the K value / self-discharge behavior of the battery can be managed and controlled.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a silicon-carbon composite material, a negative electrode, and a battery. Background Technology

[0002] With the rapid development of consumer electronics, electric vehicles, and energy storage systems, the market has placed higher demands on the energy density of lithium-ion batteries. The theoretical specific capacity of traditional graphite anodes is only 372 mAh / g, which is insufficient to meet the current application requirements for high energy density. Developing new high-capacity anode materials has become a key development direction for the industry.

[0003] Silicon-carbon anode materials, with their ultra-high theoretical specific capacity of 4200 mAh / g, have become a core candidate material to replace traditional graphite anodes. However, existing silicon-carbon anode technologies mostly employ a hybrid system of spherical and irregularly shaped silicon-carbon. This system is prone to systemic failure due to the combined inherent defects of the two materials, severely restricting its industrial application. Specifically, spherical silicon-carbon has fewer contact points with binders, conductive agents, and current collectors, easily leading to redundant electron conduction paths and deteriorating kinetic performance. During charge-discharge cycles, the spherical silicon-carbon expands, loosening the interparticle contacts and causing some areas to disconnect from the current collector or conductive agent. This not only exacerbates battery expansion but also creates "dead zones" that do not participate in electrochemical reactions, resulting in a sharp decline in cycle capacity.

[0004] Irregularly shaped blocky silicon-carbon has poor structural stability and is prone to breakage during electrode rolling, increasing side reactions between the electrolyte and active materials and leading to decreased battery cycle performance. Furthermore, its sharp edges can cause localized stress concentrations, potentially puncturing the battery separator and exacerbating self-discharge, posing safety hazards. Therefore, developing a silicon-carbon material that overcomes these defects is of great significance for improving the overall performance of lithium-ion batteries. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a silicon-carbon composite material, a negative electrode sheet comprising the silicon-carbon composite material, and a battery. The silicon-carbon composite material provided by this invention can overcome the systematic failures caused by the inherent shape defects of silicon-carbon materials, which is beneficial for maintaining the cycle stability of the battery, improving the dynamic performance and rate performance of the battery, and slowing down the volume expansion of the battery. It is also beneficial for controlling the K-value / self-discharge behavior of the battery and improving the safety performance of the battery.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a silicon-carbon composite material, which includes a porous carbon matrix and silicon particles distributed in the pores of the porous carbon matrix. The outer surface of the porous carbon matrix is ​​provided with a coating layer, which includes amorphous carbon and / or a solid electrolyte material. In a 5000x SEM image, the cross-sectional profile of the silicon-carbon composite material includes a first line segment and a second line segment. The radius of curvature of the first line segment is R1, in μm, and the radius of curvature of the second line segment is R2, in μm, where 1 / R1≥0.1 and 1 / R2<0.1. The cross-sectional profile of the silicon-carbon composite material includes a first interior angle, the degree of which is greater than 180 degrees.

[0007] A second aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising the silicon-carbon composite material and carbon-based material described in the first aspect of the present invention, the carbon-based material comprising at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0008] A third aspect of the present invention provides a battery comprising the negative electrode sheet described in the second aspect of the present invention.

[0009] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: The silicon-carbon composite material provided by this invention has a cross-sectional profile comprising two line segments with different curvatures, and includes a first interior angle greater than 180 degrees within the cross-section. This specific particle structure design allows the silicon-carbon composite material to have more non-curved surfaces than pure spherical silicon-carbon particles, increasing the number of non-curved contact points on the silicon-carbon surface. This effectively improves the bonding tightness between the silicon-carbon composite material and the binder and conductive agent, avoiding contact relaxation caused by the volume expansion and contraction of silicon-carbon particles during cycling, as well as the "dead zone" formed by detachment from the conductive network. This is beneficial for improving the cycle stability of the battery, enhancing its kinetic and rate performance, and reducing the need for contact bonding. The formation of voids slows down the battery's cycle volume expansion. Furthermore, compared to irregular blocky silicon-carbon particles, the silicon-carbon composite material provided by this invention has fewer sharp edges, reducing the risk of separator puncture caused by localized stress concentration from sharp edges, thus helping to reduce the battery's self-discharge (K-value) behavior. In addition, the outer surface of the porous carbon matrix of the silicon-carbon composite material provided by this invention is also provided with a coating layer containing amorphous carbon and / or solid electrolyte. The amorphous carbon effectively blocks direct contact between the silicon-carbon material and the electrolyte, reducing side reactions; while the solid electrolyte helps reduce interfacial impedance and improve ion migration rate, thereby optimizing the battery's kinetic performance. This structure comprehensively improves the battery's cycle stability while achieving a synergistic improvement in low expansion, low self-discharge, and high kinetic performance.

[0010] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0011] Figure 1 The image shown is a cross-sectional SEM image of a silicon-carbon composite material provided in an embodiment of the present invention. Detailed Implementation

[0012] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0013] This invention provides a silicon-carbon composite material, comprising a porous carbon matrix and silicon particles distributed in the pores within the porous carbon matrix, wherein the outer surface of the porous carbon matrix is ​​provided with a coating layer (such as...). Figure 1 As shown in the figure, the coating layer includes amorphous carbon and / or solid electrolyte material; in a 5000x SEM image, the cross-sectional profile of the silicon-carbon composite material includes a first line segment and a second line segment, the radius of curvature of the first line segment is R1 in μm, the radius of curvature of the second line segment is R2 in μm, wherein 1 / R1≥0.1, 1 / R2<0.1; The cross-sectional profile of the silicon-carbon composite material includes a first interior angle, the degree of which is greater than 180 degrees.

[0014] "5000x" refers to the magnification of the SEM image being 5000x. In a cross-sectional SEM image magnified 5000x, such as... Figure 1 As shown, the cross-sectional profile of the silicon-carbon composite material provided by the present invention includes a first line segment and a second line segment. Using ImageJ software, 1μm long line segments are continuously cut along the interface profile line formed between the silicon-carbon composite material and the coating layer. The radius of curvature R and curvature 1 / R of different line segments can be calculated using the "circle fitting" function. When the curvature 1 / R of the line segment is ≥0.1, the line segment is a curve. When the curvature 1 / R of the line segment is <0.1, the line segment is a straight line. Therefore, by observing and calculating the curvature 1 / R of different line segments, several line segments in the cross-sectional profile of the silicon-carbon composite material can be divided into a first line segment and a second line segment. The radius of curvature of the first line segment is R1, and the curvature is 1 / R1≥0.1, so the first line segment is a curve. The radius of curvature of the second line segment is R2, and the curvature is 1 / R2<0.1, so the second line segment is a straight line.

[0015] "First interior angle" refers to the angle formed by drawing two straight lines tangent to the cross-sectional profile of a silicon-carbon composite particle in a cross-sectional SEM image. The angle between these two tangent lines is greater than 180 degrees. Figure 1 As shown (A represents the first interior angle in the figure, and A1, A2, and A3 represent different first interior angles), the cross-sectional profile of the silicon-carbon composite material of the present invention includes such interior angles. The surface of the silicon-carbon composite material corresponding to the area where such interior angles (first interior angles) are located forms a groove-like structure. This groove-like structure can increase the number of non-curved contact points on the silicon-carbon surface and reduce the sharp edges on the surface of silicon-carbon composite material particles.

[0016] The silicon-carbon composite material provided by this invention has a cross-sectional profile comprising two line segments with different curvatures, and includes a first interior angle greater than 180 degrees within the cross-section. This specific particle structure design allows the silicon-carbon composite material to have more non-curved surfaces than pure spherical silicon-carbon particles, increasing the number of non-curved contact points on the silicon-carbon surface. This effectively improves the bonding tightness between the silicon-carbon composite material and the binder and conductive agent, avoiding contact relaxation caused by the volume expansion and contraction of silicon-carbon particles during cycling, as well as the "dead zone" formed by detachment from the conductive network. This is beneficial for improving the cycle stability, kinetic performance, and rate performance of the battery. Furthermore, the presence of the first interior angle creates a larger contact area outside the interior angle, further enhancing the bonding strength between the silicon-carbon particles and the binder, conductive agent, carbon-based materials, and other silicon-carbon particles. This invention reduces voids caused by the separation of particles due to silicon expansion and contraction, thereby mitigating battery cycle volume expansion. Furthermore, compared to irregular blocky silicon-carbon particles, the silicon-carbon composite material provided by this invention has fewer sharp edges, reducing the risk of separator puncture due to localized stress concentration caused by sharp edges, thus helping to reduce battery self-discharge (K-value) behavior. In addition, the porous carbon matrix of the silicon-carbon composite material provided by this invention has a coating layer containing amorphous carbon and / or solid electrolyte on its outer surface. The amorphous carbon effectively blocks direct contact between the silicon-carbon material and the electrolyte, reducing side reactions; while the solid electrolyte helps reduce interfacial impedance and increase ion migration rate, thereby optimizing battery kinetic performance. This structure comprehensively improves battery cycle stability and achieves a synergistic improvement in low expansion, low self-discharge, and high kinetic performance.

[0017] In summary, the silicon-carbon composite material of the present invention, through a specific particle structure design (containing two line segments with different curvatures and a first interior angle greater than 180 degrees), can combine the advantages of pure spherical and irregular blocky silicon-carbon, improve battery cycle stability, kinetics and rate performance, and slow down battery volume expansion; it can also reduce the risk of separator puncture and reduce battery self-discharge behavior; in addition, the silicon-carbon composite material of the present invention is coated with a coating layer containing amorphous carbon and / or solid electrolyte on its outer surface, which can further optimize the battery cycle performance and kinetics performance.

[0018] In one specific embodiment, the surface of the silicon-carbon composite material includes a grooved structure and a non-grooved structure. The grooved structure corresponds to the region where the first interior angle is located, and the non-grooved structure corresponds to the region other than the first interior angle. The thickness of the coating layer at the grooved structure is greater than the thickness of the coating layer at the non-grooved structure.

[0019] like Figure 1 As shown, the coating layer at the grooved structure is significantly thicker than that at the non-grooved structure. This design is because the conductive pathways at the grooved structure are prone to breakage and the formation of a thick SEI film, increasing resistance. By setting the coating layer thickness at the grooved structure to be greater than that at the non-grooved structure, the overall conductivity of the silicon-carbon composite material can be improved. This is because the specific surface area at the grooved structure is larger, resulting in more side reactions and the formation of a thick and uneven SEI film, which easily leads to an increase in the impedance of the silicon-carbon material and a decrease in electronic conductivity. By controlling the thickness of the coating layer at this location to be thicker, the occurrence of side reactions at the grooved structure can be reduced, thereby improving the overall conductivity of the silicon-carbon composite material.

[0020] In one specific embodiment, the average thickness of the coating layer is 2nm-20nm, for example, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, or within any two of the above values. The method for testing the average thickness of the coating layer is as follows: Take a small amount of silicon-carbon composite powder, disperse it in anhydrous ethanol, and ultrasonically disperse it for 10-15 minutes to ensure uniform particle dispersion; use TEM for testing, magnify the dispersed silicon-carbon composite material until multiple complete silicon-carbon particles appear in the plane, and find areas where the particles are uniformly dispersed, the coating layer is complete, and there is no overlap; randomly select at least 5-10 effective test points in different areas of a single silicon-carbon composite particle (including grooved and non-grooved structures), calibrate each point using the scale of the TEM image, and measure the vertical distance between the outer surface of the coating layer and the outer surface of the porous carbon matrix; arithmetically average the thickness data of all effective test points, and the result is the average thickness of the silicon-carbon composite coating layer.

[0021] The coating layer contains amorphous carbon, which effectively prevents direct contact between the silicon-carbon composite material and the electrolyte, reducing side reactions. Therefore, the average thickness of the coating layer should not be too low to prevent uneven distribution of the coating material, avoid exposure of active silicon which could lead to increased side reactions, and improve the cycle stability of the battery. The coating layer contains solid electrolyte, which can reduce interfacial impedance and increase ion migration rate. However, if the coating layer is too thick, it will also lead to a longer lithium-ion transport path, which is detrimental to improving the kinetic performance of the battery. Based on this, by further adjusting the average thickness of the coating layer, the battery containing the silicon-carbon composite material of this invention can simultaneously possess high rate performance and long cycle stability.

[0022] In one specific embodiment, the particle sizes Dv10, Dv50, and Dv90 of the silicon-carbon composite material respectively satisfy: 4μm≤Dv10≤8μm, for example, 4μm, 5μm, 6μm, 7μm, 8μm or within any two of the above values; 5μm≤Dv50≤14μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or within any two of the above values; and 6μm≤Dv90≤20μm, for example, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or within any two of the above values. The particle size test method for silicon-carbon composite materials is as follows: Using a laser diffraction particle size analyzer (such as Malvern Mastersizer), the silicon-carbon composite powder sample is ultrasonically dispersed in a dispersant (such as ethanol) and then pumped into the instrument. The particles are irradiated by a laser to produce a diffraction pattern, and the particle size distribution (Dv10, Dv50, Dv90) of the silicon-carbon composite material is recorded.

[0023] In one specific embodiment, (Dv90-Dv10) / Dv50≤1. In a preferred embodiment, (Dv90-Dv10) / Dv50≤0.85.

[0024] When (Dv90-Dv10) / Dv50 is within the above range, it indicates that the particle size distribution of the silicon-carbon composite material is highly concentrated, the particle size is relatively uniform, and there are few particles that are too large or too small. This uniformity allows the particles to achieve synchronous and consistent volume expansion and contraction during lithium insertion and extraction, which can reduce particle pulverization caused by stress concentration. At the same time, it helps to build a dense and stable solid electrolyte interphase (SEI) film, which can improve the battery's kinetic performance, cycle stability, and rate performance. When (Dv90-Dv10) / Dv50>1, it means that the particle size distribution is too wide, with a mixture of large and small particles. Oversized particles lengthen the lithium-ion diffusion path, which will lead to a deterioration in the battery's kinetic performance. Oversized particles have a larger specific surface area, which will continuously aggravate side reactions and consume limited electrolyte, causing the SEI film to repeatedly break, thicken, and become unstable, which can easily lead to accelerated capacity decay in the later stages of cycling.

[0025] In one specific embodiment, the Raman spectrum of the silicon-carbon composite material shows a value at 470 cm⁻¹. -1 -520cm -1 It has a first characteristic peak I1 within the displacement range, at 1300cm. -1 -1350cm -1has a second characteristic peak I2 within the displacement range of, and has a third characteristic peak I3 within the displacement range of 1590 cm -1 -1610 cm -1 The peak intensities of I1, I2, and I3 satisfy: I1 < I2, preferably 0.05 < I1 / I2 < 0.5; and / or, I2 / I3 < 1.2, preferably I2 / I3 < 1.

[0026] The Raman spectroscopy test method for the silicon-carbon composite material is as follows: It is carried out using a laser Raman spectrometer (such as WITech R300). Before the test, a small amount of the silicon-carbon composite powder sample needs to be placed between flat glass slides and compacted and flattened to ensure a flat surface. Subsequently, the sample is placed under a microscope for focusing. A 532 nm or 785 nm laser is selected, and the laser power is adjusted (usually within 70%) to avoid damaging the sample and obtain a spectrum with a good signal-to-noise ratio. During the test, it is scanned within the range of 100–4000 cm -1 range. <0x

[0027] The first characteristic peak I1 is located at 470 cm -1 -520 cm -1 , which is the characteristic vibration peak of amorphous silicon. Its intensity (the magnitude of I1, the smaller I1 is, the lower the crystallinity or the more complete the coating layer) directly reflects the crystallization state of the silicon particles in the silicon-carbon composite material; The second characteristic peak I2 (1300 cm -1 -1350 cm -1 ) is the D peak of the carbon material in the silicon-carbon composite material, corresponding to the defect sites in the carbon structure (such as edge defects. The larger I2 is, the more defect sites there are in the carbon material, which will lead to a decrease in the initial efficiency of the silicon-carbon composite material); The third characteristic peak I3 (1590 cm -1 -1610 cm -1 ) is the G peak of the carbon material, representing sp 2The ordered graphite microcrystalline structure formed by hybrid carbon reflects the regularity and crystallization quality of the carbon material (the larger I3 is, the better the regularity and crystallization quality of the carbon material). Therefore, by controlling the first characteristic peak and the second characteristic peak to satisfy 0.05 < I1 / I2 < 0.5, the low crystallinity of silicon particles and the complete coating characteristics of the carbon layer can be ensured. The low-crystalline silicon particles are uniformly dispersed in the porous carbon matrix at the nanoscale, avoiding the problem that highly crystalline silicon is prone to agglomerate to form large particles, and reducing the stress concentration and particle fragmentation caused by uneven volume expansion and contraction during the lithium insertion and extraction processes. At the same time, the complete carbon coating layer can form a physical barrier to isolate the direct contact between silicon and the electrolyte, inhibit the excessive growth, rupture and regeneration of the SEI film on the silicon surface, reduce the capacity loss caused by side reactions, and ensure the cycle stability of the battery. If I1 / I2 ≥ 0.5, it indicates that the silicon has a high crystallinity or there are defects in the carbon coating. The highly crystalline silicon particles are prone to agglomerate to form large-sized aggregates, which not only deteriorates the lithium-ion diffusion kinetics but also damages the electrode structure due to the superposition of expansion effects. The continuous side reaction between the exposed silicon surface and the electrolyte will consume the electrolyte and generate a thick and unstable SEI film, resulting in an increase in battery impedance and a sharp decline in the cycle capacity.

[0028] When I2 / I3 < 1.2, it indicates that the sp 2 hybridized ordered graphite microcrystalline region dominates in the carbon material, and the proportion of defect sites is low. The ordered graphite structure can construct an efficient electron transport channel, significantly reduce the electrode electron impedance, and improve the battery kinetic performance. At the same time, a small number of defect sites can reduce the side reaction active centers between the carbon layer and the electrolyte, avoid side reactions from consuming lithium sources and electrolytes, and are beneficial to maintaining the stability and integrity of the SEI film, thereby improving the first Coulomb efficiency of the battery. If I2 / I3 ≥ 1.2, there are too many defect sites in the carbon material. On the one hand, it will block the electron transport path, resulting in a decrease in electrode conductivity. On the other hand, a large number of defect sites will intensify side reactions, causing intense side reactions during the first charge and discharge processes, increasing irreversible capacity loss, directly reducing the first Coulomb efficiency, and the SEI film formed at the defect sites is prone to fall off and rupture, continuously consuming the electrolyte during the cycle process, further deteriorating the cycle stability and capacity retention rate of the battery.

[0029] In a specific embodiment, the solid electrolyte includes at least one of lithium phosphate, lithium metaaluminate, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, lithium phosphorus sulfur, lithium germanium phosphorus sulfur, polyethylene oxide, and polyacrylonitrile.

[0030] A second aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising the spherical silicon-carbon composite material and carbon-based material described in the first aspect of the present invention, the carbon-based material comprising at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0031] In one specific embodiment, the carbon-based material includes graphite material, which includes at least one of artificial graphite and natural graphite. The particle size Dv50 of the graphite material is smaller than the particle size Dv50 of the silicon-carbon composite material, and the difference in particle size between the two is less than 2 μm.

[0032] In one specific embodiment, the particle size Dv50 of the graphite material satisfies: 3μm≤Dv50≤12μm, for example, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm or within any two of the above values.

[0033] The method for testing the particle size of graphite materials is as follows: Disperse the graphite material sample in a dispersion reagent, use a laser diffraction particle size analyzer (such as Malvern Mastersizer), irradiate the particles with a laser to produce a diffraction pattern, and record the particle size Dv50 of the graphite material.

[0034] Controlling the particle size of graphite materials to be smaller than that of silicon-carbon composite materials allows all or part of the graphite particles to effectively fill the grooved structure of the silicon-carbon composite material, which is beneficial for increasing the packing density between the graphite and silicon-carbon composite particles and improving the energy density of the battery. Furthermore, since graphite has higher electronic conductivity than silicon-carbon composite materials, controlling the particle size of the silicon-carbon composite material can increase the contact between particles, further optimizing the rate performance of the battery. If the particle size Dv50 of the graphite material is less than 3 μm, or the difference between the particle size Dv50 of the graphite material and that of the silicon-carbon composite material is greater than 2 μm, it indicates that the particle size of the carbon-based material is too small, which may lead to an increase in specific surface area, resulting in more side reactions and deteriorating cycle stability. When the particle size Dv50 of the graphite material is larger than the above range, it will cause the lithium-ion transport path to become longer, increasing battery polarization and leading to poorer kinetics.

[0035] In one specific embodiment, the OI value of the negative electrode is 10-80, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or within any two of the above values. OI value test of negative electrode: The OI value of the electrode was tested using an X-ray diffractometer. The electrode was placed horizontally on the sample stage, and a Cu-Kα X-ray source (wavelength λ=1.5406 Å) was used. The scanning range was set to 10°–80° (2θ angle), the step size was 0.02°, and the scanning speed was 5° / min. The diffraction peak intensities of the (004 crystal plane (corresponding to the graphite layer parallel to the electrode) and the 110 crystal plane (corresponding to the graphite layer perpendicular to the electrode) were collected, and the orientation degree OI value was calculated: OI = I(004) / I(110). When the OI value of the negative electrode is within the above range, the graphite material undergoes lattice expansion in multiple directions, which helps to disperse the expansion of the battery in the thickness direction and alleviate the volume expansion effect of silicon. If the OI value is too low, the initial expansion of the battery in the thickness direction is small, but the excessive lateral extension leads to battery deformation. If the OI value is too high, the expansion may be more concentrated in the thickness direction, which is not conducive to alleviating the overall expansion of the battery.

[0036] In one specific embodiment, the negative electrode active layer further comprises carbon nanotubes. The diameter of the carbon nanotubes is 2nm-50nm, for example, 2nm, 3nm, 4nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, or any two of the above values. The length is 0.2μm-50μm, for example, 0.2μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, or any two of the above values. In a preferred embodiment, the aspect ratio of the carbon nanotubes is 100-1000. The method for testing the aspect ratio of carbon nanotubes is as follows: The aspect ratio of carbon nanotubes is tested using electron microscopes such as SEM / TEM. The carbon nanotube sample is uniformly dispersed on the sample stage, and the same area is photographed from multiple angles using a scanning electron microscope. Multiple carbon nanotubes are selected, and their total length and outer diameter are measured using software tools. The average length and the average diameter are calculated respectively. The ratio of the average length to the average diameter is recorded as the aspect ratio of the carbon nanotube.

[0037] When the aspect ratio of carbon nanotubes is within the aforementioned range, a highly efficient three-dimensional conductive network can be formed, significantly reducing the electronic impedance of the electrode. This network structure can also encapsulate and immobilize the active material, buffering its volume expansion during charging and discharging and maintaining the structural integrity of the electrode. If the aspect ratio of the carbon nanotubes is too small, a continuous three-dimensional cross-linked electronic conductive pathway cannot be formed, resulting in poor electronic conductivity. If the aspect ratio of the carbon nanotubes is too large, they are prone to entanglement and aggregation, making it difficult to disperse uniformly in the slurry and easily forming conductive agent-rich areas and non-conductive areas in the electrode. Therefore, by further controlling the aspect ratio of the carbon nanotubes within a suitable range, the rate performance of the battery can be improved, and electrode expansion can be reduced.

[0038] In one specific embodiment, the negative electrode active layer further includes an adhesive, which includes a water-based polyurethane adhesive, and the peel force of the negative electrode sheet is >5 N / m. The peel force test method for the negative electrode sheet is as follows: cut the negative electrode sheet sample into a standard test strip (15 mm wide); use the 180° peel method (refer to GB / T 2790-1995 or ASTM D903), stretch it at a rate of 50 mm / min on a tensile testing machine, record the average force required to peel the negative electrode active layer from the negative electrode current collector, and convert it into peel strength (unit: N / m), which is the peel force of the negative electrode sheet.

[0039] Waterborne polyurethane adhesives, due to their low glass transition temperature, maintain high elasticity and toughness during cycling, effectively buffering the massive volume expansion and contraction of silicon particles and preventing electrode structure breakage. They also possess moderate swelling properties, facilitating closer contact between the adhesive and the active material surface, better wetting the electrolyte, enhancing electrolyte retention, and promoting ion transport. When the peel force of the negative electrode sheet is within the aforementioned range, it indicates a strong interaction between the negative electrode active layer and the negative electrode current collector, preventing gaps and disconnection between silicon carbon and the conductive network during cycling. Conversely, when the peel force of the negative electrode sheet is too low, powder shedding easily occurs during electrode fabrication, reducing process yield. Furthermore, during cycling, the active material may detach from the current collector, leading to a sharp decrease in cycle capacity and abnormal expansion.

[0040] In one specific embodiment, the waterborne polyurethane adhesive includes at least one of sulfonic acid-based waterborne polyurethane, carboxylic acid-based waterborne polyurethane, internally crosslinked waterborne polyurethane, silicone-modified waterborne polyurethane, acrylate-modified waterborne polyurethane (polyurethane-acrylate composite emulsion), and composite waterborne polyurethane with a three-dimensional network structure.

[0041] In one specific embodiment, the surface of the negative electrode active layer is provided with a plurality of grooves.

[0042] In one specific embodiment, the width of the groove is 20μm-150μm, for example, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, or within any two of the above values.

[0043] In one specific embodiment, the depth of the groove is 5μm-50μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, or within any two of the above values.

[0044] In one specific embodiment, the spacing between two adjacent grooves is 0.5mm-5mm, for example, 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, or within any two of the above values.

[0045] In this invention, the width, depth, and spacing between two adjacent grooves can be tested using the following method: A laser confocal microscope / 3D profilometer is used to scan the area containing multiple grooves on the surface of the negative electrode active layer, measuring the line width and averaging the values ​​to obtain the groove width; a clear cross-sectional profile perpendicular to the laser drilling direction is generated in the software, and the height of the surface of the negative electrode active layer and the height of the lowest point at the bottom of the groove are determined. The difference between the surface height of the negative electrode active layer and the height of the lowest point at the bottom of the groove is calculated as the groove depth; on the acquired top-view image or 3D topographic height map, an area containing multiple clear grooves is selected, and the distance between the center lines of two adjacent grooves or between the same edge (e.g., the right edge) of the groove is measured. Five sets of measurements are taken, and the average value is used as the groove spacing.

[0046] Using a laser light source to ablate the active layer of the negative electrode creates several parallel groove structures with consistent depth, width, and spacing. This directly increases the surface area and depth of electrolyte wetting, allowing the electrolyte to penetrate more fully into the negative electrode. This shortens the diffusion distance of lithium ions, improves ionic conductivity, and reduces charge transfer impedance, further enhancing the battery's dynamic performance and rate performance.

[0047] In this invention, the negative electrode active layer may also include other adhesives, including at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0048] In the present invention, the negative electrode active layer may further include a negative electrode conductive agent, and the negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, metal powder, and carbon fiber.

[0049] A third aspect of the present invention provides a battery, and the battery includes the negative electrode sheet described in the second aspect of the present invention.

[0050] In a specific embodiment, the battery further includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on any one or both sides of the positive electrode current collector.

[0051] It can be understood that the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0052] The positive electrode current collector in the present invention may be a conventional current collector in the art. For example, aluminum foil is selected as the positive electrode current collector.

[0053] The positive electrode active material in the present invention includes lithium cobaltate and / or a substance with the chemical formula Li a Ni x Co y M k O2, where 0.85 ≤ a ≤ 1.1, 0.3 < x ≤ 0.9, 0 ≤ y ≤ 0.5, 0.1 ≤ z ≤ 0.5, 0 ≤ k ≤ 0.15; M is at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0054] The present invention does not specifically limit the sources of the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent, and products commercially available to those skilled in the art or products prepared by conventional preparation methods can be used.

[0055] In the present invention, the battery further includes an electrolyte and a separator. Products commercially available to those skilled in the art or products prepared by conventional preparation methods can be used. <&

[0056] The following will further describe the present invention in more detail with reference to specific embodiments. It should be understood that the following embodiments are only illustrative of and explanatory of the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0057] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified; the reagents, materials, etc. used in the following embodiments can be obtained from commercial sources unless otherwise specified.

[0058] In the following specific examples, A will be used to represent the preparation example of silicon-carbon composite material, and B will be used to represent the example of preparing battery.

[0059] Preparation Example A1 Used in the preparation of silicon-carbon composite materials: (1) Phenol and formaldehyde aqueous solution (molar ratio 1:2) were reacted at 85°C for 24h under sodium hydroxide catalysis to obtain phenolic resin microspheres; SiO2−SO3H was used as catalyst (mass ratio of phenolic resin microspheres 1:20) to catalyze the reaction of phenolic resin and PEG (molar ratio 6:1) at 60°C to obtain modified resin microspheres; the modified resin was dispersed in ethanol / water mixed solvent (volume ratio 2:1), a small amount of ammonia water (mass ratio of modified resin 1:20) was added, and the mixture was reacted at 60°C for 12h, and then subjected to hydrothermal reaction (120°C, 12h) to obtain spherical phenolic resin microspheres; the microspheres were mixed with KOH at a mass ratio (1:1 to 1:3), and carbonized at 300°C for 2h under an inert atmosphere, and then heated to 700-900°C at 5°C / min and held for 2-12h to finally obtain spherical porous carbon matrix material.

[0060] (2) The spherical porous carbon matrix material is transferred to a fluidized bed reactor, silane gas (SiH4) is introduced, the temperature is raised to 550℃ and held for 5h, so that the silane is pyrolyzed to generate nano-silicon particles, which are uniformly embedded in the pores of the spherical porous carbon matrix material to obtain the silicon-carbon composite material prepared in this invention. (3) After purging the silane gas, hydrocarbon gases such as ethylene are introduced, and the mixture is pyrolyzed at 600°C for 3 hours to coat with amorphous carbon. After coating, the amorphous carbon is uniformly dispersed in a solvent containing lithium nitrate and ammonium dihydrogen phosphate (mass ratio 2:1), and reacted at 75°C for 3 hours. Impurities are then washed away to obtain the silicon-carbon composite material with the coating layer. The coating layer material includes amorphous carbon and the solid electrolyte material lithium phosphate.

[0061] In the 5kx SEM image, the cross-sectional profile of the silicon-carbon composite material with coating prepared above can be observed to include a first line segment with curvature (1 / R1≥0.1) and a second line segment (1 / R2<0.1), such as... Figure 1 As shown; and, the cross-sectional profile of the silicon-carbon composite material includes a first interior angle with a degree greater than 180 degrees, as shown. Figure 1 As shown, A1=252°, A2=256°, A3=258°; in addition, through SEM images, it can be observed that the coating thickness at the groove-like structure corresponding to the first inner angle is greater than the coating thickness at the non-groove structure, and the average thickness of the coating layer on the surface of the silicon-carbon composite material can be obtained by measurement as 12nm.

[0062] The particle size distribution of the silicon-carbon composite material, as measured by a laser diffraction particle size analyzer, is as follows: Dv10=6μm, Dv50=8μm, Dv90=12.8μm, (Dv90-Dv10) / Dv50=0.85.

[0063] Among them, the silicon-carbon composite material was measured at 470 cm⁻¹ using laser Raman spectroscopy. -1 -520cm -1 The peak intensity of the first characteristic peak I1 within the displacement range is 101, and it is at 1300 cm⁻¹. -1 -1350cm -1 The peak intensity of the second characteristic peak I2 within the displacement range is 520, and it is at 1590 cm⁻¹. -1 -1610cm -1 The peak intensity of the third characteristic peak I3 within the displacement range is 611, I1 / I2=0.19, I2 / I3=0.85.

[0064] Comparative Example A1 The comparative example refers to the preparation method of silicon-carbon composite material in Example A1. The difference is that the spherical porous carbon matrix material is replaced by spherical porous carbon (commercially available) as the matrix material for silicon particle deposition. Steps (2) and (3) are the same as in Example 1. Finally, a spherical silicon-carbon composite material with a coating layer is prepared. The cross-sectional profile of the composite material does not include the first line segment and the second line segment, nor does it have a first interior angle.

[0065] Comparative Example A2 The comparative example refers to the preparation method of silicon-carbon composite material in Example A1. The difference is that the spherical porous carbon matrix material is replaced by block porous carbon (commercially available) as the matrix material for silicon particle deposition. Steps (2) and (3) are the same as in Example A1. Finally, a block silicon-carbon composite material with a coating layer is prepared. The cross-sectional profile of the composite material does not include the first line segment, but includes the second line segment. There are interior angles, but the interior angles are all less than or equal to 180 degrees, that is, there are no first interior angles.

[0066] Preparation Example A2 Group The examples in this group refer to the preparation method of silicon-carbon composite material in Example A1. The difference is that the amount of reactant material added to the reaction between amorphous carbon and solid electrolyte material lithium phosphate, or the reaction time and temperature, are changed, so that the average thickness of the coating layer is changed. See Table 1-1 for details.

[0067] Preparation Example A3 Group The examples in this group refer to the preparation method of silicon-carbon composite material in Example A1. The difference is that the reaction conditions of the porous carbon matrix material in step (1) are changed, so that the particle size of the prepared silicon-carbon composite material is changed. See Table 1-1 for details.

[0068] Table 1-1 Preparation Example A4 Group The examples in this group refer to the preparation method of silicon-carbon composite material in Example A1, except that the reaction conditions of the porous carbon matrix material in step (1) are changed, so that the peak intensity of the characteristic peaks of the prepared silicon-carbon composite material changes in different displacement ranges. Specifically: Preparation Example A4-1: By changing the amount, time, and deposition temperature of silane gas during the preparation of the silicon-carbon composite material, the deposition temperature of the silicon-carbon composite material at 470 cm⁻¹ was determined using laser Raman spectroscopy. -1 -520cm -1 The peak intensity of the first characteristic peak I1 within the displacement range is 320, and it is at 1300 cm⁻¹. -1 -1350cm -1 The peak intensity of the second characteristic peak I2 within the displacement range is 480, and it is at 1590 cm⁻¹. -1 -1610cm -1 The peak intensity of the third characteristic peak I3 within the displacement range is 650, I1 / I2=0.67, I2 / I3=0.74; Preparation Example A4-2: By changing the coating temperature of amorphous carbon during the preparation of the silicon-carbon composite material, the silicon-carbon composite material at 470 cm⁻¹ was measured using laser Raman spectroscopy. -1 -520cm -1 The peak intensity of the first characteristic peak I1 within the displacement range is 98, and it is at 1300 cm⁻¹. -1 -1350cm -1 The peak intensity of the second characteristic peak I2 within the displacement range is 612, and it is at 1590 cm⁻¹. -1 -1610cm -1 The peak intensity of the third characteristic peak I3 within the displacement range is 460, I1 / I2=0.16, I2 / I3=1.33.

[0069] Example B1 Used in the preparation of negative electrode sheets and batteries: (1) Preparation of negative electrode: The silicon-carbon composite material with a coating layer prepared in Example A1, artificial graphite, lithium carboxymethyl cellulose, waterborne polyurethane adhesive (sulfonic acid type waterborne polyurethane), and carbon nanotubes were mixed in a mass ratio of 19.2:76.8:1.5:2:0.5. Deionized water was added and stirred to form a negative electrode slurry. The slurry was then uniformly coated onto both sides of a copper foil using a coating machine to obtain the negative electrode active layer. The surface density of the coating on one side was controlled at 4.5 mg / cm². 2 After drying, cold pressing, and slitting, negative electrode sheets are obtained. The particle size Dv50 of the artificial graphite material in the negative electrode active layer was measured to be 7 μm using a laser diffraction particle size analyzer, which is 1 μm different from the particle size Dv50 of the silicon-carbon composite material. The OI value of the negative electrode sheet is 35. The carbon nanotubes have a diameter of 20 nm, a length of 10 μm, and an aspect ratio of 500. The peeling force between the negative electrode active layer and the negative electrode current collector is 40 N / m.

[0070] (2) Preparation of the positive electrode: Lithium cobalt oxide (CCO), polyvinylidene fluoride (PVDF), acetylene black (HCO3), and carbon nanotubes were mixed in a mass ratio of 97.2:1.7:0.6:0.5 and added to N-methylpyrrolidone (NMP) solvent. The mixture was stirred under vacuum to form a CCO slurry, which was then coated onto the surface of a 9 μm thick aluminum foil current collector. The slurry was dried in a vacuum drying oven at 120 °C for 8 hours and then rolled and slit to obtain the CCO sheet.

[0071] (3) Preparation of electrolyte: Under an argon atmosphere and in an environment with a water content of less than 10 ppm, lithium hexafluorophosphate was mixed with a non-aqueous organic solvent (ethylene carbonate (EC): propylene carbonate (PC): polypropylene (PP): diethyl carbonate (DEC) = 1:1:1:1, mass percentage) to prepare an electrolyte with a lithium salt concentration of 1.05 mol / L. Fluoroethylene carbonate (15% by mass of the total electrolyte) and succinate (2.5% by mass of the total electrolyte) were then added. After stirring until homogeneous, the electrolyte was obtained after passing the tests for moisture and free acid.

[0072] (4) Preparation of lithium-ion batteries: The positive electrode sheet and separator (a polyethylene separator with a porosity of 35% and a thickness of 7.5μm) of step (2) and the negative electrode sheet of step (1) are stacked and wound in sequence. The wound core is put into an aluminum-plastic film of matching size and sealed. The electrolyte of step (3) is injected under vacuum conditions and vacuum sealed. The battery is obtained through standing, formation and sorting processes.

[0073] Examples B2-B4 and Comparative Examples B1 and B2 refer to the preparation methods of negative electrode sheets and batteries in Example B1, except that the silicon-carbon composite material in the negative electrode active material is the silicon-carbon composite material prepared in Examples A2-A4 and Comparative Examples A1 and A2, respectively. For the specific correspondence between each example and the preparation examples, please refer to Table 1-2.

[0074] Table 1-2 Example B5 group The embodiments in this group refer to the preparation method of the negative electrode and battery in Embodiment B1, except that the particle size Dv50 of the artificial graphite material is changed, or the particle size Dv50 of the silicon-carbon composite material is changed at the same time, so that the particle size difference between the particle size Dv50 of the artificial graphite material and the particle size Dv50 of the silicon-carbon composite material is changed, as detailed in Tables 1-3.

[0075] Example B6 group The embodiments in this group refer to the preparation method of the negative electrode and battery in Embodiment B1, except that the diameter and length of the carbon nanotubes are changed to change their aspect ratio, as detailed in Tables 1-3.

[0076] Table 1-3 Example B7 group This set of embodiments refers to the preparation method of the negative electrode sheet and battery in Embodiment B1, except that several linear grooves are obtained by laser drilling on the surface of the negative electrode active layer. The width, depth, and spacing between adjacent grooves are changed according to the laser parameters. Specifically: In Example B7-1, the width of the groove is 50μm, the depth of the groove is 25μm, and the distance between two adjacent grooves is 3mm. In Example B7-2, the width of the groove is 20μm, the depth of the groove is 5μm, and the distance between two adjacent grooves is 0.5mm; In Example B7-3, the width of the groove is 150μm, the depth of the groove is 50μm, and the distance between two adjacent grooves is 5mm.

[0077] Example B8 group This set of embodiments refers to the preparation method of the negative electrode sheet and battery in Embodiment B1, except that the areal density and cold pressing process conditions in the preparation of the negative electrode sheet are changed, so that the OI value of the negative electrode sheet is changed. Specifically: Example B8-1: The OI value of the negative electrode is 15; Example B8-2: The OI value of the negative electrode is 40.

[0078] Test case The lithium-ion batteries prepared in Example B and Comparative Example B were subjected to the following tests.

[0079] (1) Battery cycle retention rate and thickness expansion rate test: Step 1: At 25℃, charge the battery at a constant current of 0.5C to 4.53V, then charge it at a constant voltage of 0.02C, and let it stand for 10 minutes; record the initial discharge capacity of the battery and measure the initial thickness of the battery. Step 2: Discharge to 3 V at 0.2C and let stand for 10 minutes; Step 3: Repeat steps 1 and 2 500 times. On the 500th cycle, after step 1, measure the battery thickness after cycling, and then perform step 2 to record the remaining capacity of the battery after cycling.

[0080] The battery capacity retention rate (%) was obtained by calculating the ratio of the remaining capacity after 500 cycles to the initial capacity. The battery thickness expansion rate (%) was obtained by measuring and calculating the difference between the battery thickness after 500 cycles and the initial thickness, and then dividing it by the initial thickness. The test results are recorded in Table 2.

[0081] (2) Ratio performance test: The lithium-ion batteries prepared in Example B and Comparative Example B were subjected to rate discharge capability tests. The specific test methods are as follows: The battery was charged at a constant current density of 0.2C to 4.53V, and then charged at a constant voltage of 4.53V to 0.02C. After resting for 10 minutes, it was discharged to 3.0V at current densities of 0.2C and 1C respectively. The percentage of the capacity discharged at 1C to the capacity discharged at 0.2C is the battery's rate discharge capability, expressed as a percentage. The test results are recorded in Table 2.

[0082] (3) Self-discharge behavior (K value) test: The lithium-ion batteries prepared in the above-mentioned Example B group and Comparative Example B group were charged to 4.53V at a constant current density of 0.2C, and then charged at a constant voltage of 4.53V with a cutoff current of 0.02C. After standing for 10 minutes, the open circuit voltage V1 of the battery was recorded. Then, the battery was kept standing for 24 hours, and the open circuit voltage V2 of the battery was recorded after the standing period. The self-discharge degree K value of the battery (mV / h) = (V1-V2) / 24 (unit is mV / h). The test results are recorded in Table 2.

[0083] Table 2 The silicon-carbon composite material provided by this invention can overcome the systematic failure caused by the inherent shape defects of traditional silicon-carbon materials, which is beneficial to maintaining the cycle stability and rate performance of the battery and can slow down the battery volume expansion; it is also beneficial to control the K value / self-discharge behavior of the battery and improve the safety performance of the battery.

[0084] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes a porous carbon matrix and silicon particles distributed in the pores inside the porous carbon matrix. The outer surface of the porous carbon matrix is ​​provided with a coating layer, which includes amorphous carbon and / or solid electrolyte material. In a 5000x SEM image, the cross-sectional profile of the silicon-carbon composite material includes a first line segment and a second line segment. The radius of curvature of the first line segment is R1, in μm, and the radius of curvature of the second line segment is R2, in μm, where 1 / R1≥0.1 and 1 / R2<0.

1. The cross-sectional profile of the silicon-carbon composite material includes a first interior angle, the degree of which is greater than 180 degrees.

2. The silicon-carbon composite material according to claim 1, characterized in that, The surface of the silicon-carbon composite material includes a grooved structure and a non-grooved structure. The grooved structure corresponds to the area where the first interior corner is located, and the non-grooved structure corresponds to the area outside the first interior corner. The thickness of the coating layer at the grooved structure is greater than the thickness of the coating layer at the non-grooved structure. And / or, the average thickness of the coating layer is 2nm-20nm.

3. The silicon-carbon composite material according to claim 1, characterized in that, The particle sizes Dv10, Dv50 and Dv90 of the silicon-carbon composite material satisfy the following conditions: 4μm≤Dv10≤8μm, 5μm≤Dv50≤14μm, 6μm≤Dv90≤20μm; and / or, (Dv90-Dv10) / Dv50≤1, preferably (Dv90-Dv10) / Dv50≤0.

85.

4. The silicon-carbon composite material according to claim 1, characterized in that, In the Raman spectrum of the silicon-carbon composite material, there is a first characteristic peak I1 within the displacement range of 470 cm -1 -520 cm -1 , a second characteristic peak I2 within the displacement range of 1300 cm -1 -1350 cm -1 , and a third characteristic peak I3 within the displacement range of 1590 cm -1 -1610 cm -1 . The peak intensities of I1, I2, and I3 satisfy: I1 < I2, preferably 0.05 < I1 / I2 < 0.5; and / or, I2 / I3 < 1.2, preferably I2 / I3 < 1.

5. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector. The negative electrode active layer contains a negative electrode active material, which includes silicon-carbon composite material and carbon-based material as described in any one of claims 1-4. The carbon-based material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

6. The negative electrode sheet according to claim 5, characterized in that, The carbon-based material includes graphite material, which includes at least one of artificial graphite and natural graphite. The particle size Dv50 of the graphite material is smaller than the particle size Dv50 of the silicon-carbon composite material, and the difference in particle size between the two is less than 2 μm. Preferably, the particle size Dv50 of the graphite material satisfies: 3μm≤Dv50≤12μm.

7. The negative electrode sheet according to claim 5, characterized in that, The OI value of the negative electrode is 10-80.

8. The negative electrode sheet according to claim 5, characterized in that, The negative electrode active layer also contains carbon nanotubes, the diameter of which is 2nm-50nm and the length is 0.2μm-50μm; preferably, the aspect ratio of the carbon nanotubes is 100-1000. And / or, the negative electrode active layer further includes an adhesive, the adhesive including an aqueous polyurethane adhesive, and the peel force of the negative electrode sheet is >5 N / m.

9. The negative electrode sheet according to claim 5, characterized in that, The surface of the negative electrode active layer is provided with a plurality of grooves, wherein the width of the grooves is 20μm-150μm; And / or, the depth of the groove is 5μm-50μm; And / or, the spacing between two adjacent grooves is 0.5mm-5mm.

10. A battery, characterized in that, The battery includes the negative electrode sheet as described in any one of claims 5-9.

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