Negative electrode sheet and battery

Abstract

The present disclosure relates to the field of batteries, and in particular to a negative electrode sheet and a battery. The negative electrode sheet comprises a negative electrode current collector and a negative electrode coating. A recessed portion is formed in the surface of the negative electrode coating away from the negative electrode current collector. The negative electrode coating comprises a negative electrode active substance, and the negative electrode active substance comprises silicon-based particles. A rectangular area A is intercepted from the section of the negative electrode sheet in the depth direction of the recessed portion. The rectangular area A comprises a recess, and the depth of the recess in the section is h. Four edges of the rectangular area A are A1, A2, A3 and A4, respectively, wherein A1 is parallel to A4, A2 is parallel to A3, A1 coincides with the surface of the negative electrode coating, the midpoint of A1 is the midpoint of an orthographic projection line formed by the recess on the surface of the negative electrode coating, the lengths of A1 and A4 are both 200 µm, and the lengths of A2 and A3 are both (h+10) µm. The number of the silicon-based particles in the rectangular area A is 0-60. The negative electrode sheet of the present disclosure can mitigate the problems of lithium precipitation and expansion.

Description

Negative plate and battery Technical Field

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

[0002] With the advent of the 5G era and the rapid development of lithium-ion battery technology, people are placing higher demands on the energy density, fast charging capabilities, and charge and discharge rates of lithium-ion batteries. High-energy-density, fast-charging lithium batteries are also the development trend of consumer lithium-ion batteries. However, as energy density increases, the thickness of the positive and negative electrodes of lithium batteries becomes increasingly thicker. Coupled with faster charging speeds, lithium ions are more likely to accumulate on the electrode surfaces. This is especially true for silicon-doped negative electrodes. As the electrode thickness increases, the lithium deposition and expansion problems become more serious, seriously affecting the battery life. Summary of the Invention

[0003] The present disclosure aims to overcome the aforementioned problems of the prior art by providing a negative electrode sheet and a battery including the same. The negative electrode sheet disclosed herein comprises a recessed portion on the surface of the negative electrode coating and further controls the amount of silicon-based particles within a specific area near the recessed portion, effectively alleviating lithium deposition and expansion issues in the negative electrode sheet, thereby extending the battery's service life.

[0004] According to a first aspect of the present disclosure, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode coating on at least one surface of the negative electrode current collector, wherein a surface of the negative electrode coating away from the negative electrode current collector has a recess, the negative electrode coating comprises a negative electrode active material, and the negative electrode active material comprises silicon-based particles. On a cross section of the negative electrode sheet along the depth direction of the recess, a rectangular area A is taken, wherein the rectangular area A comprises one recess, and the depth of the recess on the cross section is h. The four sides of the rectangular area A are A1, A2, A3, and A4, respectively, wherein A1 is parallel to A4, A2 is parallel to A3, A1 coincides with the surface of the negative electrode coating, and the midpoint of A1 is the midpoint of the positive projection line formed by the recess on the surface of the negative electrode coating. The lengths of A1 and A4 are both 200 μm, and the lengths of A2 and A3 are both (h+10) μm. The number of silicon-based particles in the rectangular area A is 0-60.

[0005] A second aspect of the present disclosure provides a battery, comprising the negative electrode sheet described in the first aspect of the present disclosure.

[0006] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0007] (1) The negative electrode sheet disclosed in the present invention can improve the lithium plating problem and thickness expansion problem.

[0008] (2) The battery disclosed herein has high energy density and excellent fast charging capability and cycle life.

[0009] 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

[0010] FIG1 is a schematic cross-sectional view of a negative electrode sheet along the depth direction of a recess in an example of the present disclosure.

[0011] FIG2 is an EDS image of a cross-sectional view of a negative electrode sheet along the depth direction of a recess in an example of the present disclosure.

[0012] FIG3 is a schematic cross-sectional view of a negative electrode sheet in an example of the present disclosure.

[0013] FIG4 is a schematic diagram showing the width of the grooves of the negative electrode coating in an example of the present disclosure.

[0014] FIG5 is a schematic diagram showing the spacing of grooves in an example of the present disclosure.

[0015] FIG6 is a schematic diagram showing the morphology of a concave hole in an example of the present disclosure.

[0016] FIG. 7 is a schematic diagram of a groove in an example of the present disclosure. DETAILED DESCRIPTION

[0017] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0018] According to a first aspect of the present disclosure, a negative electrode sheet is provided, wherein the negative electrode sheet may include a negative electrode current collector and a negative electrode coating on at least one side of the negative electrode current collector, wherein the surface of the negative electrode coating away from the negative electrode current collector may have a concave portion, the negative electrode coating may include a negative electrode active material, and the negative electrode active material may include silicon-based particles; on a cross section of the negative electrode sheet along the depth direction of the concave portion, a rectangular area A is taken, wherein the rectangular area A may include one concave portion, and the depth of the concave portion on the cross section is h, and the four sides of the rectangular area A are A1, A2, and A3. A2, A3 and A4, wherein A1 is parallel to A4, A2 is parallel to A3, A1 coincides with the surface of the negative electrode coating, and the midpoint of A1 is the midpoint of the positive projection line formed by the recess on the surface of the negative electrode coating, the lengths of A1 and A4 are both 200 μm, and the lengths of A2 and A3 are both (h+10) μm; the number of the silicon-based particles in the rectangular area A can be 0-60 (for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60).

[0019] As shown in Figure 1, a schematic cross-sectional view of a negative electrode sheet along the depth direction of the recess in an example of the present disclosure is shown. The negative electrode sheet includes a negative electrode current collector 1 and a negative electrode coating 2 on at least one surface of the negative electrode current collector 1. The surface of the negative electrode coating 2 away from the negative electrode current collector 1 has a recess 3. On the cross-section of the negative electrode sheet along the depth direction of the recess 3 (that is, the thickness direction of the negative electrode sheet), a rectangular area A (dashed rectangular box in Figure 1) is taken. The rectangular area A includes a recess 3. The depth of the recess on this cross-section is h. The four sides of the rectangular area A are A1, A2, A3 and A4, respectively. A1 is parallel to A4, A2 is parallel to A3, A1 coincides with the surface of the negative electrode coating 2, and the midpoint of A1 is the midpoint 5 of the positive projection line 4 formed by the recess 3 on the surface of the negative electrode coating 2.

[0020] In the present disclosure, the number of silicon-based particles in the rectangular area A can be measured by conventional methods in the art, such as by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). The negative electrode sheet is cut along the depth direction of the recess to obtain the cross section. Five rectangular areas A are randomly selected, and the number of silicon-based particles in each rectangular area A is measured and averaged. The selection rule is: when at least 1 / 2 of the silicon-based particles are in the rectangular area A, it is counted as 1; when less than 1 / 2 of the silicon-based particles are in the rectangular area A, it is counted as 0. As shown in Figure 2, an EDS graph of a cross-section of a negative electrode sheet along the depth direction of the recess in an example of the present disclosure is shown. In the figure, the white solid line represents the recess, the white dashed rectangular box represents the rectangular area A, the gray particles are silicon-based particles, and each white dashed circle represents one silicon-based particle. It can be seen from the figure that the number of silicon-based particles in the rectangular area A is 30.

[0021] In the present disclosure, the depth h of the concave portion on the cross section refers to the vertical distance from the lowest point of the concave portion to the surface of the negative electrode coating on the cross section.

[0022] Related technologies typically increase the thickness of the electrode and use silicon-based materials with relatively high specific capacity to increase the energy density of the battery. However, as the thickness of the electrode gradually increases, lithium ions are more likely to accumulate on the electrode surface, blocking the lithium ion diffusion channel and increasing the risk of lithium plating. In particular, for silicon-doped negative electrodes, as the thickness of the electrode increases, its potential changes significantly, leading to more severe lithium plating, which in turn exacerbates volume expansion and seriously affects the battery's service life. The inventors of the present disclosure have discovered that by providing a recessed portion on the surface of the negative electrode coating, the diffusion channel for lithium ions can be increased, the diffusion efficiency of lithium ions can be improved, and the recessed portion can provide space for the volume expansion of silicon-based particles, thereby reducing its impact on the battery's service life. However, the problem of lithium deposition still occurs near silicon-based particles. After a large number of experimental studies, the inventors of the present disclosure found that the reason for this problem may be that during the battery charge and discharge cycle, compared with carbon-based materials, silicon-based particles generally embed lithium first and then de-lithium (that is, silicon-based particles embed lithium first, and carbon-based materials embed lithium later; carbon-based materials de-lithium first, and silicon-based particles de-lithium later). Therefore, the concentration of lithium ions near silicon-based particles is larger than that at other locations. In order for lithium ions to be embedded in silicon-based particles, they need to pass through the carbon-based materials around the silicon-based particles. This will cause the carbon-based materials to over-embed lithium, which in turn leads to lithium deposition from the carbon-based materials of the negative electrode of the silicon-based particles. The inventors of the present disclosure further discovered that by controlling the number of silicon-based particles in a specific area near the recess, the above-mentioned problem can be significantly improved, and the expansion of the negative electrode sheet can also be improved to a certain extent, thereby increasing the service life of the battery. The reason may be that the electrolyte in the battery can infiltrate into the interior of the negative electrode sheet through the recess on the surface of the negative electrode coating, directly shortening the transmission path of lithium ions. By controlling the number of silicon-based particles in a specific area near the recess, it is beneficial to improve the uniformity of lithium insertion of the silicon-based particles and reduce the problem of excessive lithium insertion of the carbon-based material nearby. In addition, the recess can provide space for the volume expansion of the silicon-based particles in the specific area nearby, so that the expansion part of the silicon-based particles in the vertical direction is converted into expansion in the horizontal direction, thereby improving the expansion deformation of the battery.

[0023] In one example, the number of the silicon-based particles in the rectangular area A is 0-40.

[0024] In the present disclosure, the negative electrode active material may further include a carbon-based material. Based on the total mass of the negative electrode active material, the content of the silicon-based particles may be 1% - 65%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or 65%.

[0025] In one example, based on the total mass of the negative electrode active material, the content of the silicon-based particles is 1% - 45%.

[0026] When the mass content of the silicon-based particles in the negative electrode active material is within a specific range, the areal capacity of the negative electrode sheet can be increased, the amount of the negative electrode active material in the negative electrode sheet can be reduced, thereby reducing the thickness of the negative electrode sheet, improving the utilization rate of the negative electrode active material, further shortening the transmission path of lithium ions, and then improving the kinetic performance and energy density of the battery.

[0027] In the present disclosure, the carbon-based material may include at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon. The silicon-based particles may include at least one of silicon, silicon oxide, silicon carbide, and silicon alloy.

[0028] In the present disclosure, the terms "silicon oxide" and "silicon carbide" have their conventional meanings in the art. Generally, the term "silicon oxide" is considered to refer to the oxide of silicon; the term "silicon carbide" refers to a silicon carbide composite material.

[0029] In the present disclosure, the inner wall of the recess may have a protrusion. The height of the protrusion is L, where 0 < L ≤ 5 μm, such as L being 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

[0030] When the inner wall of the recess has a protrusion, the silicon-based particles can be in more direct contact with the electrolyte, enabling lithium ions to be embedded into the silicon-based particles more quickly and uniformly, improving the utilization rate of the silicon-based particles, facilitating the exertion of the battery capacity, increasing the energy density of the battery, and further improving the problem of lithium deposition; and the recess can more directly provide space for the expansion of the silicon-based particles, and thus can further improve the expansion problem. Moreover, when the height of the protrusion is within a specific range, it is beneficial to the exertion of the battery capacity. When the height of the protrusion is too large (for example, greater than 5 μm), the protrusion is likely to block the recess, which is not conducive to the infiltration of the electrolyte into the negative electrode coating, thus not conducive to the transmission of lithium ions and resulting in incomplete exertion of the battery capacity.

[0031] In this disclosure, the height of the protrusion has the conventional meaning in the art, and is generally considered to refer to the vertical distance from the apex of the protrusion to the inner wall of the recess. The height of the protrusion can be measured by conventional methods in the art, such as using an SEM or 3D microscope to measure the height of the protrusions in all recesses on the negative electrode sheet and taking the maximum value.

[0032] In the present disclosure, the silicon-based particles may be tangential to the inner wall of the recess.

[0033] When the silicon-based particles are tangent to the inner wall of the recess, lithium ions can be embedded into the silicon-based particles more quickly and evenly, thereby improving the utilization rate of the silicon-based particles, which is beneficial to the battery capacity, increasing the energy density of the battery, and further improving the lithium plating problem; and the recess can more directly provide space for the expansion of the silicon-based particles, thereby further improving the expansion problem.

[0034] In the present disclosure, the silicon-based particles may have a median particle size Dv50 of 10 μm to 17 μm, for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or 17 μm.

[0035] When the median particle size Dv50 of the silicon-based particles is too large (for example, greater than 17 μm), the height of the protrusion on the inner wall of the recess may be too large (for example, greater than 5 μm), thereby affecting the battery capacity; when the median particle size Dv50 of the silicon-based particles is too small (for example, less than 10 μm), it is not conducive to the full utilization of the silicon-based particles, which also affects the battery capacity.

[0036] The negative electrode coating may further include a negative electrode conductive agent, a negative electrode binder, and a thickener. The negative electrode conductive agent may include at least one of conductive carbon black, carbon nanotubes, and carbon fibers. The negative electrode binder may include at least one of polyvinylidene fluoride, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide. The thickener may include at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose.

[0037] Based on the total mass of the negative electrode coating, the content of the negative electrode active material may be 70%-99.7% (for example, 70%, 73%, 76%, 79%, 82%, 85%, 88%, 91%, 94%, 97% or 99.7%), the content of the negative electrode conductor may be 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1% or 0.1%), the content of the negative electrode binder may be 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1% or 0.1%), and the content of the thickener may be 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1% or 0.1%).

[0038] In one example, based on the total mass of the negative electrode coating, the content of the negative electrode active material is 88%-98%, the content of the negative electrode conductor is 0.3%-2.5%, the content of the negative electrode binder is 0.5%-5%, and the content of the thickener is 0.5%-4.5%.

[0039] In the present disclosure, the negative electrode current collector may include copper foil.

[0040] In the present disclosure, the surface density of the negative electrode sheet can be 7 mg / cm 2 -22mg / cm 2 , for example 7mg / cm 2 、10mg / cm 2 、15mg / cm 2 , 20mg / cm 2 or 22 mg / cm 2 .

[0041] When the surface density of the negative electrode sheet is within a specific range, the ability of the negative electrode sheet to receive lithium ions can be improved; at the same time, providing a recess on the outer surface of the negative electrode sheet can shorten the transmission distance of lithium ions and increase the speed at which lithium ions are embedded in the negative electrode sheet, thereby further improving the charging speed of the battery and reducing the risk of lithium plating.

[0042] In the present disclosure, the thickness of the negative electrode coating is 35 μm-70 μm, for example, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm or 70 μm.

[0043] When the thickness of the negative electrode coating is within a specific range and a recess is provided on the outer surface of the negative electrode sheet, the transmission distance of lithium ions can be shortened while increasing the energy density of the battery, the speed at which lithium ions are embedded in the negative electrode sheet can be increased, and the occurrence of lithium plating can be reduced.

[0044] In the present disclosure, the thickness of the negative electrode coating refers to the thickness of the negative electrode coating on one side of the negative electrode current collector.

[0045] In the present disclosure, the negative electrode coating may be a single-layer structure or a multi-layer structure.

[0046] <Single-layer structure>

[0047] In one example, the negative electrode coating is a single-layer structure.

[0048] When the negative electrode coating has a single-layer structure, the number of the silicon-based particles in the rectangular area A can be 2-27, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 or 27.

[0049] In one example, the number of the silicon-based particles in the rectangular area A is 3-18.

[0050] When the negative electrode coating is a single-layer structure, the negative electrode active material in the negative electrode coating includes silicon-based particles and carbon-based materials. By regulating the number of silicon-based particles in the rectangular area A within a specific range, the lithium plating and expansion problems can be further improved. When the number of silicon-based particles in the rectangular area A is too small (for example, less than 2), the transmission distance of lithium ions embedded in the silicon-based particles becomes longer, resulting in uneven lithium embedding of the silicon-based particles, and excessive lithium embedding of the carbon-based materials near the silicon-based particles, thereby increasing the risk of lithium plating, and at this time, the concave portion has a weak effect on alleviating the volume expansion of the silicon-based particles, thereby causing the negative electrode sheet to expand; when the number of silicon-based particles in the rectangular area A is too large (for example, greater than 27), it may cause the silicon-based particles to be over-embedded with lithium, and the concave portion provides limited expansion space for the silicon-based particles, which will aggravate the expansion of the negative electrode sheet and seriously affect the cycle life of the battery.

[0051] <Multi-layer structure>

[0052] In one example, the negative electrode coating is a multi-layer structure.

[0053] In one embodiment, the negative electrode coating has a double-layer structure. The negative electrode sheet includes the negative electrode current collector, a first coating layer, and a second coating layer stacked in sequence. In this case, the negative electrode coating includes the first coating layer and the second coating layer stacked in sequence, with the first coating layer being close to the negative electrode current collector and the second coating layer being further away from the negative electrode current collector.

[0054] Figure 3 shows a schematic cross-sectional view of a negative electrode sheet in one embodiment of the present disclosure. As can be seen from the figure, the negative electrode sheet comprises a negative electrode current collector 1, a first coating layer 21, and a second coating layer 22, stacked in sequence. The first coating layer 21 is located close to the negative electrode current collector 1, while the second coating layer 22 is located further away from the negative electrode current collector 1. The surface of the negative electrode coating layer 2, located further away from the negative electrode current collector 1, has a recess 3. The recess 3 may be located only in the second coating layer 22, or in both the first coating layer 21 and the second coating layer 22.

[0055] In the present disclosure, the silicon-based particles may be present only in the first coating layer, only in the second coating layer, or in both the first coating layer and the second coating layer. When the silicon-based particles are present in both the first coating layer and the second coating layer, the content of the silicon-based particles in the first coating layer may be equal to or different from the content of the silicon-based particles in the second coating layer. The content of the silicon-based particles in the first coating layer may be greater than the content of the silicon-based particles in the second coating layer, and the content of the silicon-based particles in the first coating layer may be less than the content of the silicon-based particles in the second coating layer.

[0056] In the present disclosure, the first coating layer may include the silicon-based particles, and the number of the silicon-based particles in the rectangular area A is 0-30, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25 or 30.

[0057] In one example, the number of the silicon-based particles in the rectangular area A is 5-18.

[0058] When the negative electrode coating is a double-layer structure, and the first coating includes silicon-based particles and the second coating includes carbon-based materials. By regulating the number of silicon-based particles in the rectangular area A within a specific range, the lithium plating and expansion problems can be further improved. The reason may be that: first, the silicon-based particles are located in the first coating close to the negative electrode current collector. At this time, the lithium ions will be preferentially embedded in the second coating located away from the negative electrode current collector, and then transferred to the first coating through the second coating and the recess. It can prevent the carbon-based materials near the silicon-based particles from being over-intercalated with lithium and the silicon-based particles from being unevenly intercalated with lithium; and the second coating located above the first coating has a certain gravity, which can suppress the volume expansion of the silicon-based particles in the thickness direction of the negative electrode sheet to a certain extent; in addition, when the number of silicon-based particles in the rectangular area A is too large (for example, greater than 30), it may cause the silicon-based particles to be over-intercalated with lithium, and the recess provides limited expansion space for the silicon-based particles, which will aggravate the expansion of the negative electrode sheet and seriously affect the cycle life of the battery.

[0059] In the present disclosure, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles can be 2%-100%, for example, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%.

[0060] In one example, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles is 30%-60%.

[0061] When the mass content of silicon-based particles in the negative electrode active material of the first coating is within a specific range, the surface capacity of the negative electrode sheet can be increased, the amount of negative electrode active material in the negative electrode sheet can be reduced, thereby reducing the thickness of the negative electrode sheet, improving the utilization rate of the negative electrode active material, further shortening the transmission path of lithium ions, and thereby improving the battery's kinetic performance and energy density.

[0062] In the present disclosure, the thickness ratio of the first coating layer to the second coating layer can be (0.2-4):1, for example, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0063] In one example, the thickness ratio of the first coating layer to the second coating layer is (0.5-1):1.

[0064] When the ratio of the thickness of the first coating layer to the thickness of the second coating layer is within a specific range, the second coating layer can better inhibit the expansion of the silicon-based particles in the first coating layer, reduce the thickness of the negative electrode sheet, and improve the utilization rate of the negative electrode active material, thereby improving the energy density and service life of the battery.

[0065] In the present disclosure, the distance from the lowest point of the recess to the negative electrode current collector is 5%-90% of the thickness of the first coating, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0066] When the distance from the lowest point of the concave portion to the negative electrode current collector is 5%-90% of the thickness of the first coating, it can not only reduce the mass loss of the silicon-based particles, but also control the lithium insertion of the silicon-based particles so that they are evenly inserted, and the service life will not be shortened due to excessive or uneven lithium insertion.

[0067] In the present disclosure, the second coating layer may include the silicon-based particles, and the number of the silicon-based particles in the rectangular area A is 5-60, for example, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60.

[0068] In one example, the number of the silicon-based particles in the rectangular area A is 6-40.

[0069] When the negative electrode coating is a double-layer structure, and the second coating includes silicon-based particles, and the first coating includes carbon-based materials. By regulating the number of silicon-based particles in the rectangular area A within a specific range, the lithium plating and expansion problems can be further improved. The reason may be that the silicon-based particles are located in the second coating away from the side of the negative electrode current collector. At this time, lithium ions will be preferentially embedded in the second coating, and because compared with carbon-based materials, silicon-based particles generally embed lithium first (that is, silicon-based particles embed lithium first, and carbon-based materials embed lithium later), by controlling the number of silicon-based particles in the rectangular area A, the uniformity of lithium embedding of silicon-based particles can be improved, and the risk of lithium plating due to excessive lithium embedding of carbon-based materials near silicon-based particles can be reduced. When the number of silicon-based particles in the rectangular area A is too small (for example, less than 5), the transmission distance of lithium ions embedded in the silicon-based particles becomes longer, which will aggravate the uneven lithium embedding of the silicon-based particles and the excessive lithium embedding of the carbon-based materials near the silicon-based particles, thereby increasing the risk of lithium precipitation; when the number of silicon-based particles in the rectangular area A is too large (for example, greater than 60), it may cause the silicon-based particles to be excessively embedded with lithium, and the concave portion provides limited expansion space for the silicon-based particles, which will aggravate the expansion of the negative electrode sheet and seriously affect the cycle life of the battery.

[0070] In the present disclosure, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles is 2%-100%, for example, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%.

[0071] In one example, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles is 30%-60%.

[0072] When the mass content of silicon-based particles in the negative electrode active material of the second coating is within a specific range, the surface capacity of the negative electrode sheet can be increased, the amount of negative electrode active material in the negative electrode sheet can be reduced, thereby reducing the thickness of the negative electrode sheet, improving the utilization rate of the negative electrode active material, further shortening the transmission path of lithium ions, and thereby improving the battery's kinetic performance and energy density.

[0073] In the present disclosure, the thickness ratio of the first coating layer to the second coating layer can be (0.2-4):1, for example, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0074] In one example, the thickness ratio of the first coating layer to the second coating layer is (0.5-2):1.

[0075] When the ratio of the thickness of the first coating layer to the thickness of the second coating layer is within a specific range, it is beneficial to reduce the thickness of the negative electrode sheet and to improve the utilization rate of the negative electrode active material, thereby improving the energy density of the battery.

[0076] In the present disclosure, both the first coating layer and the second coating layer include the silicon-based particles, and the content of the silicon-based particles in the second coating layer is greater than the content of the silicon-based particles in the first coating layer. The number of the silicon-based particles in the rectangular area A can be 3 to 40, for example, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, or 40.

[0077] In one example, the number of the silicon-based particles in the rectangular area A is 5-30.

[0078] When the negative electrode coating has a double-layer structure and the content of silicon-based particles in the second coating is greater than the content of silicon-based particles in the first coating, the lithium plating and expansion problems can be further improved by regulating the number of silicon-based particles in the rectangular area A within a specific range. When the number of silicon-based particles in the rectangular area A is too small (for example, less than 3), the transmission distance of lithium ions embedded in the silicon-based particles becomes longer, which will aggravate the uneven lithium embedding of the silicon-based particles and the excessive lithium embedding of the carbon-based materials near the silicon-based particles, thereby increasing the risk of lithium plating; when the number of silicon-based particles in the rectangular area A is too large (for example, greater than 40), it may cause the silicon-based particles to be excessively embedded in lithium, and the concave portion provides limited expansion space for the silicon-based particles, which will aggravate the expansion of the negative electrode sheet and seriously affect the cycle life of the battery.

[0079] In the present disclosure, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles can be 5%-45%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 35%, 40% or 45%.

[0080] In one example, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles is 5%-30%.

[0081] In the present disclosure, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles can be 1%-70%, for example, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%.

[0082] In one example, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles is 1%-40%.

[0083] When the mass content of silicon-based particles in the negative electrode active material of the first coating and the mass content of silicon-based particles in the negative electrode active material of the second coating are within a specific range, the surface capacity of the negative electrode sheet can be increased, and the amount of negative electrode active material in the negative electrode sheet can be reduced, thereby reducing the thickness of the negative electrode sheet, improving the utilization rate of the negative electrode active material, further shortening the transmission path of lithium ions, and thereby improving the battery's kinetic performance and energy density.

[0084] In the present disclosure, the thickness ratio of the first coating layer to the second coating layer can be (0.2-4):1, for example, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0085] In one example, the thickness ratio of the first coating layer to the second coating layer is (0.5-2):1.

[0086] When the ratio of the thickness of the first coating layer to the thickness of the second coating layer is within a specific range, it is beneficial to reduce the thickness of the negative electrode sheet and to improve the utilization rate of the negative electrode active material, thereby improving the energy density of the battery.

[0087] In the present disclosure, both the first coating layer and the second coating layer include the silicon-based particles, and the content of the silicon-based particles in the first coating layer is greater than the content of the silicon-based particles in the second coating layer. The number of the silicon-based particles in the rectangular area A can be 2 to 35, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, or 35.

[0088] In one example, the number of the silicon-based particles in the rectangular area A is 4-23.

[0089] When the negative electrode coating has a double-layer structure and the content of silicon-based particles in the first coating is greater than the content of silicon-based particles in the second coating, the lithium plating and expansion problems can be further improved by regulating the number of silicon-based particles in the rectangular area A within a specific range. When the number of silicon-based particles in the rectangular area A is too small (for example, less than 2), the transmission distance of lithium ions embedded in the silicon-based particles becomes longer, which will aggravate the uneven lithium embedding of the silicon-based particles and the excessive lithium embedding of the carbon-based materials near the silicon-based particles, thereby increasing the risk of lithium plating; when the number of silicon-based particles in the rectangular area A is too large (for example, greater than 35), it may cause the silicon-based particles to be excessively embedded in lithium, and the concave portion provides limited expansion space for the silicon-based particles, which will aggravate the expansion of the negative electrode sheet and seriously affect the cycle life of the battery.

[0090] In the present disclosure, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles can be 1%-90%, for example, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0091] In one example, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles is 10%-40%.

[0092] In the present disclosure, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles can be 0.01%-30%, for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%.

[0093] In one example, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles is 5%-20%.

[0094] When the mass content of silicon-based particles in the negative electrode active material of the first coating and the mass content of silicon-based particles in the negative electrode active material of the second coating are within a specific range, the surface capacity of the negative electrode sheet can be increased, and the amount of negative electrode active material in the negative electrode sheet can be reduced, thereby reducing the thickness of the negative electrode sheet, improving the utilization rate of the negative electrode active material, further shortening the transmission path of lithium ions, and thereby improving the battery's kinetic performance and energy density.

[0095] In the present disclosure, the thickness ratio of the first coating layer to the second coating layer can be (0.2-4):1, for example, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0096] In one example, the thickness ratio of the first coating layer to the second coating layer is (0.5-1):1.

[0097] When the ratio of the thickness of the first coating layer to the thickness of the second coating layer is within a specific range, it is beneficial to reduce the thickness of the negative electrode sheet and to improve the utilization rate of the negative electrode active material, thereby improving the energy density of the battery.

[0098] In the present disclosure, the distance from the lowest point of the recess to the negative electrode current collector is 5%-90% of the thickness of the first coating, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0099] When the distance from the lowest point of the concave portion to the negative electrode current collector is 5%-90% of the thickness of the first coating, it can not only reduce the mass loss of the silicon-based particles, but also control the lithium insertion of the silicon-based particles so that they are evenly inserted, and the service life will not be shortened due to excessive or uneven lithium insertion.

[0100] <Concave>

[0101] In the present disclosure, the depth H of the recessed portion may be 5 μm-65 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 1 9μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm or 65μm.

[0102] In one example, the depth H of the concave portion is 8 μm-30 μm.

[0103] In one example, the depth H of the concave portion is 20 μm-40 μm.

[0104] In this disclosure, the depth of the recess has the conventional meaning in the art, and refers to the maximum vertical distance from any point within the recess to the surface of the negative electrode sheet. The depth of the recess can be measured using conventional methods in the art, such as a 3D profilometer or a scanning electron microscope (SEM). For example, 20 recesses can be randomly selected from the entire negative electrode sheet, or all recesses can be selected, and the depth of each recess can be measured and averaged.

[0105] The depth of the recess is within a specific range, which can not only improve the wettability of the electrolyte to the negative electrode active material, thereby increasing the insertion and extraction speed of lithium ions and improving the dynamic performance of the negative electrode sheet; it can also improve the utilization rate of the negative electrode active material, thereby increasing the energy density of the battery.

[0106] In the present disclosure, the recess may include a recessed hole and / or a groove.

[0107] In the present disclosure, the pore size of the concave hole can be 20μm-150μm, for example, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm or 150μm.

[0108] In one example, the diameter of the concave hole is 35 μm-90 μm.

[0109] In the present disclosure, the pitch of the recessed holes may be 50 μm-1000 μm, for example, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm or 1000 μm.

[0110] In one example, the pitch of the concave holes is 150 μm-450 μm.

[0111] In the present disclosure, the aperture and spacing of the concave holes have the conventional meanings in this field. The aperture of the concave holes is generally considered to be the diameter of the regular circle when the shape of the orthographic projection of the concave holes on the negative electrode coating is a "regular circle"; when the shape of the orthographic projection of the concave holes on the negative electrode coating is a non-"regular circle" (such as an ellipse or an irregular curved polygon), the aperture of the concave holes is the diameter of an equivalent circle with the same area as the non-"regular circle". The spacing of the concave holes refers to the shortest distance between the edges of two adjacent concave holes on the negative electrode coating.

[0112] In the present disclosure, the diameter of the concave holes can be measured by conventional means in the art, for example, by randomly selecting 50 concave holes from the entire negative electrode sheet using SEM, measuring the diameter of each concave hole, and taking the average value. The spacing between the concave holes can also be measured by conventional means in the art, for example, by randomly selecting 50 adjacent concave holes from the entire negative electrode sheet using SEM, measuring the spacing between each pair of adjacent concave holes, and taking the average value.

[0113] In the present disclosure, the width of the groove can be 35μm-185μm, for example, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm or 185μm.

[0114] In one example, the width of the groove is 40 μm-135 μm.

[0115] In one example, the width of the groove is 130 μm-170 μm.

[0116] In one example, the width of the groove is 40 μm-150 μm.

[0117] In the present disclosure, the spacing of the grooves may be 0.1 mm to 3 mm, for example, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm or 3 mm.

[0118] In one example, the spacing between the grooves is 0.5 mm to 2 mm.

[0119] In the present disclosure, the width and spacing of the grooves have the conventional meanings in the art. The width of the groove is generally considered to be the positive projection of the groove on the negative electrode coating including two long sides, and the width of the groove refers to the average distance from one long side to the other long side in the length direction or width direction of the negative electrode sheet. Figure 4 is a schematic diagram of the width of the grooves of the negative electrode coating in an example of the present disclosure, wherein the two long sides of the grooves in Figures 4(a) to 4(c) are straight lines, and the two long sides of the grooves in Figure 4(d) are curved lines. In FIG4(a) and FIG4(b), the two long sides are arranged in parallel. Therefore, in the width direction of the negative electrode sheet, the distance d from any point on one long side to the other long side is equal. In this case, the width of the groove is the distance from any point on one long side to the other long side in the length direction or width direction of the negative electrode sheet. In FIG4(c), the two long sides of the groove are straight lines, but are not arranged in parallel. Therefore, the distance d from any point on one long side to the other long side is not equal. In this case, the width of the groove can be averaged, that is, 50 points (i.e., 50 points) are selected at equal distances on one long side based on the length of the side. The distance between each point is equal, so the selection of points can make the calculation result more accurate), the width corresponding to each point is measured, and the average value is taken to obtain the width of the groove; in Figure 4 (d), the two long sides are curved, so the distance d from any point on one long side to the other long side is not equal. In this case, the width of the groove can also be taken as the average value, that is, 50 points are randomly selected on one long side (because the two long sides in Figure 4 (d) are curved, there is no relationship between the two long sides in Figure 4 (c), so 50 points can be randomly selected for measurement), the width corresponding to each point is measured, and the average value is taken to obtain the width of the groove. The spacing of the grooves is generally considered to be the average distance between the two adjacent long sides of two adjacent grooves on the negative electrode coating in the length direction or width direction of the negative electrode sheet. FIG5 is a schematic diagram of the spacing of grooves in an example of the present disclosure, wherein FIG5(a) shows a case where two adjacent long sides are straight and parallel, FIG5(b) shows a case where two adjacent long sides are straight and non-parallel, and FIG5(c) shows a case where two adjacent long sides are curved.In Figure 5(a), the two adjacent long sides are straight and parallel. Therefore, in the width direction, the distance from any point on one long side to the other long side is equal. In this case, the spacing of the grooves is the distance D from any point on one long side to the other long side in the width direction. In Figure 5(b), the two adjacent long sides are straight but not parallel. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the spacing of the grooves can be averaged, that is, on one long side, with the length of the side as the reference, 50 points are selected at equal distances (that is, the distance between each point is equal to the distance D between each point). The distances between the two points are equal, so selecting points in this way can make the calculation results more accurate), measure the distance corresponding to each point, and take the average value to get the spacing; in Figure 5(c), the two adjacent long sides are curved. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the spacing of the grooves can also be averaged, that is, 50 points are randomly selected on one long side (because the two long sides in Figure 5(c) are curved, there is no relationship between the two long sides in Figure 5(b), so 50 points can be randomly selected for measurement), measure the distance corresponding to each point, and take the average value to get the spacing.

[0120] In the present disclosure, the "groove width" can be measured by conventional means in the art, such as by SEM, selecting all grooves on the entire negative electrode sheet, measuring the width of each groove, and taking the average value. The "groove spacing" can be measured by conventional means in the art, such as by SEM, selecting all grooves on the entire negative electrode sheet, measuring the spacing between two adjacent grooves, and taking the minimum value.

[0121] In the present disclosure, there are no specific limitations on the morphology of the recessed holes. The recessed holes can be straight blind holes, meaning that the orthographic projection of the recessed holes on the negative electrode sheet is uniform throughout the thickness direction of the negative electrode sheet. The recessed holes can also be quasi-conical holes, meaning that the diameter of the recessed holes farther from the negative electrode current collector is larger than the diameter of the recessed holes closer to the negative electrode current collector. Figure 6 shows a schematic diagram of the morphology of recessed holes in an example of the present disclosure, where Figure 6(a) shows a straight through hole and Figure 6(b) shows a quasi-conical hole.

[0122] In the present disclosure, there is no particular limitation on the shape of the groove. The cross-section of the groove along the thickness direction of the negative electrode sheet can be rectangular or conical. FIG7 is a schematic diagram of a groove in an embodiment of the present disclosure. As can be seen from FIG7, the cross-section of the groove along the thickness direction of the negative electrode sheet can be rectangular or conical. In the present disclosure, the groove can be distributed along the length direction of the negative electrode sheet or along the width direction of the negative electrode sheet.

[0123] In the present disclosure, a vertical distance from the bottom of the recess to the negative electrode current collector is greater than 0 μm.

[0124] In the present disclosure, the concave portion can be obtained by using conventional manufacturing methods in the art, for example, etching the concave portion on the surface of the negative electrode sheet by laser engraving.

[0125] When the vertical distance from the bottom of the recess to the negative electrode current collector is greater than 0, damage to the negative electrode current collector can be avoided, thereby affecting the electrochemical performance of the battery.

[0126] A second aspect of the present disclosure provides a battery, comprising the negative electrode sheet described in the first aspect of the present disclosure.

[0127] In the present disclosure, the components of the battery other than the negative electrode sheet (such as the positive electrode sheet, separator, and electrolyte, etc.) can be conventionally selected in the art.

[0128] In one example, the lithium-ion battery further includes a positive electrode, a separator, and an electrolyte.

[0129] <Positive electrode>

[0130] In the present disclosure, the positive electrode sheet may include a positive electrode current collector and a positive electrode coating on at least one side of the positive electrode current collector. The positive electrode coating may include a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0131] The positive electrode active material may include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, and a lithium-rich manganese-based material. The positive electrode conductive agent may include at least one of conductive carbon black, carbon nanotubes, and carbon fibers. The positive electrode binder may include at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0132] In the present disclosure, based on the total mass of the positive electrode active material layer, the content of the positive electrode active material can be 80%-99.8% (for example, 80%, 85%, 90%, 95% or 99.8%), the content of the positive electrode conductor can be 0.1%-10% (for example, 10%, 7.5%, 5%, 2.5% or 0.1%), and the content of the positive electrode binder can be 0.1%-10% (for example, 10%, 7.5%, 5%, 2.5% or 0.1%).

[0133] In one example, based on the total mass of the positive electrode active material layer, the content of the positive electrode active material is 90%-99%, the content of the positive electrode conductor is 1%-5%, and the content of the positive electrode binder is 1%-5%.

[0134] In the present disclosure, the positive electrode current collector may include aluminum foil.

[0135] <Diaphragm>

[0136] In the present disclosure, the separator may include a separator commonly used in the art, for example, at least one of a polyethylene film and a polypropylene film.

[0137] <Electrolyte>

[0138] In the present disclosure, the electrolyte may include a lithium salt and an organic solvent. The lithium salt may include at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium oxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium bistrifluorosulfonylimide, and lithium bisfluorosulfonylimide. The organic solvent may include at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0139] The electrolyte may further include an additive, and the additive may include at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, methylene methanedisulfonate, propylene sultone, and succinic anhydride.

[0140] In the present disclosure, the battery can be assembled in accordance with conventional methods in the art.

[0141] In one example, the battery comprises a lithium-ion battery.

[0142] The battery disclosed herein has excellent cycle life and cycle expansion rate, and can significantly improve the problem of lithium plating.

[0143] It should be noted that the numerical expressions such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0144] 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.

[0145] In the following examples, unless otherwise specified, all materials used are commercially available analytically pure. In the following examples, silicon dioxide is used as the silicon-based particle for illustration, but other silicon-based particles (e.g., nano-silicon, silicon carbon, etc.) can achieve similar technical effects.

[0146] The following examples are provided to illustrate the batteries of the present disclosure.

[0147] Example A group

[0148] Example A1

[0149] Prepare the battery as follows:

[0150] (1) Preparation of negative electrode sheet

[0151] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite and silicon oxide is 80:20, and the median particle size Dv50 of silicon oxide is 10 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly according to the mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a negative electrode slurry with a solid content of 45%; the above-mentioned negative electrode slurry is coated on a copper foil using a coating machine, dried at 100° C., and grooves are made on the outer surface of the negative electrode coating using a laser device, wherein the depth of the groove is 10 μm, the width of the groove is 48 μm, and the spacing between the grooves is 1 mm, thereby obtaining a negative electrode sheet, wherein the width of the negative electrode sheet is 65 mm, and the height of the protrusion on the inner wall of the groove is 5 μm;

[0152] (2) Preparation of positive electrode sheet

[0153] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 97:1.5:1.5, N-methylpyrrolidone (NMP) was added, and the mixture was passed through a 200-mesh sieve to obtain a positive electrode slurry having a solid content of 72%. The positive electrode slurry was coated on aluminum foil using a coating machine and dried at 120° C. to obtain a positive electrode sheet having a width of 63 mm.

[0154] (2) Preparation of lithium-ion batteries

[0155] The negative electrode sheet obtained in step (1), the positive electrode sheet obtained in step (2) and a separator (polyethylene film, with a thickness of 9 μm) are wound to form a roll core, which is then wrapped with an aluminum-plastic film. After baking to remove moisture, an electrolyte is injected (propylene carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of 1:1:0.5:1, and 1 mol / L LiPF6 is added and mixed evenly), and a battery is obtained by a hot pressing process.

[0156] Example A2

[0157] The same procedure was followed as in Example A1, except that the negative electrode sheet was prepared as follows:

[0158] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite and silicon oxide is 80:20, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a negative electrode slurry with a solid content of 45%. The above-mentioned negative electrode slurry is coated on a copper foil using a coating machine and dried at 100°C. A laser device is used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove is 20 μm, the width of the groove is 110 μm, and the spacing between the grooves is 1 mm, to obtain a negative electrode sheet, wherein the width of the negative electrode sheet is 65 mm, and the height of the protrusion on the inner wall of the groove is 3 μm.

[0159] Example A3

[0160] The same procedure was followed as in Example A1, except that the negative electrode sheet was prepared as follows:

[0161] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite and silicon oxide is 80:20, and the median particle size Dv50 of silicon oxide is 15 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a negative electrode slurry with a solid content of 45%. The above-mentioned negative electrode slurry is coated on a copper foil using a coating machine and dried at 100°C. A laser device is used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove is 8 μm, the width of the groove is 41 μm, and the spacing between the grooves is 1 mm, to obtain a negative electrode sheet, wherein the width of the negative electrode sheet is 65 mm, and the height of the protrusion on the inner wall of the groove is 2 μm.

[0162] Example A4

[0163] The same procedure was followed as in Example A1, except that the negative electrode sheet was prepared as follows:

[0164] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite and silicon oxide is 80:20, and the median particle size Dv50 of silicon oxide is 17 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a negative electrode slurry with a solid content of 45%. The above-mentioned negative electrode slurry is coated on a copper foil using a coating machine and dried at 100°C. A laser device is used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove is 26 μm, the width of the groove is 135 μm, and the spacing between the grooves is 1 mm, to obtain a negative electrode sheet, wherein the width of the negative electrode sheet is 65 mm, and the height of the protrusion on the inner wall of the groove is 5 μm.

[0165] Example A5 group

[0166] This group of examples was carried out with reference to Example A1, except that the content of silicon-based particles in the negative electrode active material was changed. Specifically:

[0167] In Example A5a, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material is 97:3;

[0168] In Example A5b, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material is 58:42;

[0169] In Example A5c, in the negative electrode active material, the mass ratio of artificial graphite to silicon oxide is 35:65;

[0170] In Example A5d, in the negative electrode active material, the mass ratio of artificial graphite to silicon oxide is 50:50.

[0171] Example A6

[0172] The same procedure was followed as in Example A1, except that the parameters of the laser device were changed (power was adjusted to 10 W, engraving mode was changed to dot engraving mode, pulse was 0.2 s) to control the inner wall of the groove to have no protrusions.

[0173] Comparative Example 1

[0174] The same procedure was followed as in Example A1, except that no recesses were produced.

[0175] Test Case A

[0176] (1) Silicon-based particle quantity test

[0177] The negative electrode sheets prepared in Example A and Comparative Example 1 were tested for the number of silicon-based particles, and the results are recorded in Table 1.

[0178] (2) Energy density test

[0179] The batteries prepared in Example A and Comparative Example 1 were subjected to energy density testing. The specific method was as follows: the battery discharge capacity was tested by 0.5C constant current constant voltage charging / 0.2C discharge at 25°C. Energy density = discharge capacity × average voltage / (thickness × width × height). The test results are recorded in Table 1.

[0180] (3) Cycle test

[0181] The batteries prepared in Example A and Comparative Example 1 were subjected to a cycle capacity retention test. The specific method is as follows: at a test temperature of 25°C, a 2C charge to 4.5V and a 0.05C / 1C discharge to 3.0V cycle test was performed for 800T. The test results are recorded in Table 1.

[0182] (4) Expansion rate test

[0183] The batteries prepared in Example A and Comparative Example 1 were subjected to an expansion rate test. The specific method is as follows: referring to the cycle test method, a PPG thickness tester was used to test the thickness of the first fully charged battery and the thickness of the fully charged battery after completing 800T cycles. The expansion rate = (thickness of the fully charged battery after 800T cycles - thickness of the first fully charged battery) / thickness of the first fully charged battery. The results are recorded in Table 1.

[0184] (5) Lithium deposition test

[0185] The batteries prepared in Example A and Comparative Example 1 were subjected to a room temperature lithium deposition test. The specific method is as follows: at 25°C, the charging process is: first charging at a constant current of 4C to 4.48V, and then charging at a constant voltage until the current drops to 0.05C; the discharging process is: discharging at a constant current of 1C to 3.0V; and finally fully charging at 0.3C; after repeating 20 cycles, the battery is disassembled and the lithium deposition on the negative electrode sheet is observed. The results are recorded in Table 1, where the degree of lithium deposition is ranked from light to heavy as no lithium deposition, slight lithium deposition, lithium deposition, and severe lithium deposition.

[0186] Table 1

[0187] As can be seen from Table 1, compared with the comparative example, the battery prepared from the negative electrode sheet of the present invention has an improved cycle capacity retention rate, a reduced expansion rate, and improved lithium plating. The battery of the present invention has an excellent cycle life.

[0188] Example Group B

[0189] Example B1

[0190] Prepare the battery as follows:

[0191] (1) Preparation of negative electrode sheet

[0192] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 40:60, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0193] The negative electrode active material (artificial graphite), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0194] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto a copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the groove depth was 38 μm, the groove width was 170 μm, and the groove spacing was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating layer to the second coating layer was 0.5:1, the distance from the lowest point of the groove to the negative electrode current collector was 15% of the thickness of the first coating layer, the height of the protrusion on the inner wall of the groove was 3 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%;

[0195] (2) Preparation of positive electrode sheet

[0196] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 97:1.5:1.5, N-methylpyrrolidone (NMP) was added, and the mixture was passed through a 200-mesh sieve to obtain a positive electrode slurry having a solid content of 72%. The positive electrode slurry was coated on aluminum foil using a coating machine and dried at 120° C. to obtain a positive electrode sheet having a width of 63 mm.

[0197] (2) Preparation of lithium-ion batteries

[0198] The negative electrode sheet obtained in step (1), the positive electrode sheet obtained in step (2) and a separator (polyethylene film, with a thickness of 9 μm) are wound to form a roll core, which is then wrapped with an aluminum-plastic film. After baking to remove moisture, an electrolyte is injected (propylene carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of 1:1:0.5:1, and 1 mol / L LiPF6 is added and mixed evenly), and a battery is obtained by a hot pressing process.

[0199] Example B2

[0200] The same procedure was followed as in Example B1, except that the negative electrode sheet was prepared as follows:

[0201] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 51.4:48.6, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0202] The negative electrode active material (artificial graphite), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0203] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove was 32 μm, the width of the groove was 151 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 0.7:1, the distance from the lowest point of the groove to the negative electrode current collector was 49% of the thickness of the first coating, the height of the protrusion on the inner wall of the groove was 4 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0204] Example B3

[0205] The same procedure was followed as in Example B1, except that the negative electrode sheet was prepared as follows:

[0206] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 57.8:42.2, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0207] The negative electrode active material (artificial graphite), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0208] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove was 25 μm, the width of the groove was 130 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 0.9:1, the distance from the lowest point of the groove to the negative electrode current collector was 79% of the thickness of the first coating, the height of the protrusion on the inner wall of the groove was 2 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0209] Example B4

[0210] The same procedure was followed as in Example B1, except that the negative electrode sheet was prepared as follows:

[0211] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 60:40, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0212] The negative electrode active material (artificial graphite), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0213] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove was 30 μm, the width of the groove was 143 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 1:1, the distance from the lowest point of the groove to the negative electrode current collector was 50% of the thickness of the first coating, the height of the protrusion on the inner wall of the groove was 5 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0214] Example B5 group

[0215] This group of examples was carried out with reference to Example B4, except that the content of silicon-based particles in the negative electrode active material in the first negative electrode slurry was changed. Specifically:

[0216] In Example B5a, in the negative electrode active material in the first negative electrode slurry, the mass ratio of artificial graphite to silicon oxide is 80:20, and the mass content of silicon-based particles in the negative electrode active material is 10%;

[0217] In Example B5b, in the negative electrode active material in the first negative electrode slurry, the mass ratio of artificial graphite to silicon oxide is 20:80, and the mass content of silicon-based particles in the negative electrode active material is 40%;

[0218] In Example B5c, the negative electrode active material in the first negative electrode slurry is entirely silicon oxide, and the mass content of silicon-based particles in the negative electrode active material is 50%.

[0219] Example B6

[0220] The same procedure was followed as in Example B4, except that the parameters of the laser equipment were changed (power was adjusted to 10 W, engraving mode was changed to point engraving mode, pulse was 0.2 s) to control the inner wall of the groove to have no protrusions.

[0221] Example B7 group

[0222] The method was carried out with reference to Example B4, except that the thickness ratio of the first coating layer to the second coating layer was changed, specifically:

[0223] In Example B7a, the thickness ratio of the first coating layer to the second coating layer was 0.3:1, and the distance from the lowest point of the groove to the negative electrode current collector was 22% of the thickness of the first coating layer. (To control the mass content of silicon-based particles in the negative electrode active material to 20%, the mass ratio of artificial graphite to silicon oxide in the first negative electrode slurry was adjusted to 13.3:86.7).

[0224] In Example B7b, the thickness ratio of the first coating layer to the second coating layer is 4:1, and the distance from the lowest point of the groove to the negative electrode current collector is 6% of the thickness of the first coating layer; (in order to control the mass content of silicon-based particles in the negative electrode active material to 20%, the mass ratio of artificial graphite and silicon oxide in the first negative electrode slurry is adjusted to 75:25).

[0225] Comparative Example 2

[0226] The same procedure was followed as in Example B1, except that no recesses were produced.

[0227] Test Case B

[0228] The results are shown in Table 2.

[0229] Table 2

[0230] As can be seen from Table 2, compared with the comparative example, the battery prepared from the negative electrode sheet of the present invention has an improved cycle capacity retention rate, a reduced expansion rate, and improved lithium plating. The battery of the present invention has an excellent cycle life.

[0231] Example C group

[0232] Example C1

[0233] Prepare the battery as follows:

[0234] (1) Preparation of negative electrode sheet

[0235] The negative electrode active material (artificial graphite), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are uniformly mixed in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0236] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 70:30, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0237] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto a copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the groove depth was 30 μm, the groove width was 145 μm, and the groove spacing was 1 mm, to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating layer to the second coating layer was 0.5:1, the height of the protrusion on the inner wall of the groove was 5 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%;

[0238] (2) Preparation of positive electrode sheet

[0239] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 97:1.5:1.5, N-methylpyrrolidone (NMP) was added, and the mixture was passed through a 200-mesh sieve to obtain a positive electrode slurry having a solid content of 72%. The positive electrode slurry was coated on aluminum foil using a coating machine and dried at 120° C. to obtain a positive electrode sheet having a width of 63 mm.

[0240] (2) Preparation of lithium-ion batteries

[0241] The negative electrode sheet obtained in step (1), the positive electrode sheet obtained in step (2) and a separator (polyethylene film, with a thickness of 9 μm) are wound to form a roll core, which is then wrapped with an aluminum-plastic film. After baking to remove moisture, an electrolyte is injected (propylene carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of 1:1:0.5:1, and 1 mol / L LiPF6 is added and mixed evenly), and a battery is obtained by a hot pressing process.

[0242] Example C2

[0243] The same procedure was followed as in Example C1, except that the negative electrode sheet was prepared as follows:

[0244] The negative electrode active material (artificial graphite), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are uniformly mixed in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0245] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 60:40, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0246] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the grooves was 20 μm, the width of the grooves was 112 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 1:1, the height of the protrusion on the inner wall of the groove was 3 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0247] Example C3

[0248] The same procedure was followed as in Example C1, except that the negative electrode sheet was prepared as follows:

[0249] The negative electrode active material (artificial graphite), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are uniformly mixed in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0250] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 50:50, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0251] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the grooves was 13 μm, the width of the grooves was 60 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 1.5:1, the height of the protrusion on the inner wall of the groove was 4 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0252] Example C4

[0253] The same procedure was followed as in Example C1, except that the negative electrode sheet was prepared as follows:

[0254] The negative electrode active material (artificial graphite), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are uniformly mixed in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0255] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 40:60, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0256] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the grooves was 10 μm, the width of the grooves was 45 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 2:1, the height of the protrusion on the inner wall of the groove was 3 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0257] Example C5

[0258] This group of examples was carried out with reference to Example C1, except that the content of silicon-based particles in the negative electrode active material in the second negative electrode slurry was changed. Specifically:

[0259] In Example C5a, in the negative electrode active material of the second negative electrode slurry, the mass ratio of artificial graphite to silicon oxide is 85:15, and the mass content of silicon-based particles in the negative electrode active material is 10%;

[0260] In Example C5b, in the negative electrode active material of the second negative electrode slurry, the mass ratio of artificial graphite to silicon oxide is 40:60, and the mass content of silicon-based particles in the negative electrode active material is 40%;

[0261] In Example C5c, in the negative electrode active material in the second negative electrode slurry, the mass ratio of artificial graphite to silicon oxide is 25:75, and the mass content of silicon-based particles in the negative electrode active material is 50%;

[0262] In Example C5d, in the negative electrode active material in the second negative electrode slurry, the mass ratio of artificial graphite to silicon oxide is 10:90, and the mass content of silicon-based particles in the negative electrode active material is 60%.

[0263] Example C6

[0264] The same procedure was followed as in Example C1, except that the parameters of the laser device were changed (power was adjusted to 10 W, engraving mode was changed to point engraving mode, pulse was 0.2 s) to control the inner wall of the groove to have no protrusions.

[0265] Example C7 group

[0266] The method was carried out with reference to Example C1, except that the thickness ratio of the first coating layer to the second coating layer was changed, specifically:

[0267] In Example C7a, the thickness ratio of the first coating layer to the second coating layer was 0.2:1; (in order to control the mass content of silicon-based particles in the negative electrode active material to 20%, the mass ratio of artificial graphite to silicon dioxide in the second negative electrode slurry was adjusted to 76:24);

[0268] In Example C7b, the thickness ratio of the first coating layer to the second coating layer is 4:1; (in order to control the mass content of silicon-based particles in the negative electrode active material to 20%, the negative electrode active material in the first negative electrode slurry is completely replaced with silicon dioxide).

[0269] Comparative Example 3

[0270] The same procedure was followed as in Example C1, except that no recesses were produced.

[0271] Test Case C

[0272] Refer to Test Example A and the results are recorded in Table 3.

[0273] Table 3

[0274] As can be seen from Table 3, compared with the comparative example, the battery prepared by the negative electrode sheet of the present invention has an improved cycle capacity retention rate, a reduced expansion rate, and improved lithium plating. The battery of the present invention has an excellent cycle life.

[0275] Example D group

[0276] Example D1

[0277] Prepare the battery as follows:

[0278] (1) Preparation of negative electrode sheet

[0279] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 85:15, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0280] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 77.5:22.5, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0281] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto a copper foil using a coating machine and dried at 100°C. A laser device was used to create grooves on the outer surface of the negative electrode coating, wherein the groove depth was 30 μm, the groove width was 145 μm, and the groove spacing was 1 mm, to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating layer to the second coating layer was 0.5:1, the height of the protrusion on the inner wall of the groove was 2 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%;

[0282] (2) Preparation of positive electrode sheet

[0283] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 97:1.5:1.5, N-methylpyrrolidone (NMP) was added, and the mixture was passed through a 200-mesh sieve to obtain a positive electrode slurry having a solid content of 72%. The positive electrode slurry was coated on aluminum foil using a coating machine and dried at 120° C. to obtain a positive electrode sheet having a width of 63 mm.

[0284] (2) Preparation of lithium-ion batteries

[0285] The negative electrode sheet obtained in step (1), the positive electrode sheet obtained in step (2) and a separator (polyethylene film, with a thickness of 9 μm) are wound to form a roll core, which is then wrapped with an aluminum-plastic film. After baking to remove moisture, an electrolyte is injected (propylene carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of 1:1:0.5:1, and 1 mol / L LiPF6 is added and mixed evenly), and a battery is obtained by a hot pressing process.

[0286] Example D2

[0287] The same procedure was followed as in Example D1, except that the negative electrode sheet was prepared as follows:

[0288] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 90:10, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0289] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 70:30, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0290] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the grooves was 20 μm, the width of the grooves was 112 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 1:1, the height of the protrusion on the inner wall of the groove was 1 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0291] Example D3

[0292] The same procedure was followed as in Example D1, except that the negative electrode sheet was prepared as follows:

[0293] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 90:10, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0294] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 65:35, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0295] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the grooves was 13 μm, the width of the grooves was 60 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 1.5:1, the height of the protrusion on the inner wall of the groove was 4 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0296] Example D4

[0297] The same procedure was followed as in Example D1, except that the negative electrode sheet was prepared as follows:

[0298] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 88:12, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0299] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 64:36, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0300] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the grooves was 10 μm, the width of the grooves was 45 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 2:1, the height of the protrusion on the inner wall of the groove was 3 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0301] Example D5 group

[0302] This group of examples was carried out with reference to Example D1, except that the content of silicon-based particles in the negative electrode active material in the first negative electrode slurry and the second negative electrode slurry was changed. Specifically:

[0303] In Example D5a, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the first negative electrode slurry was 94:6, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the second negative electrode slurry was 88:12, and the mass content of silicon-based particles in the negative electrode active material was 10%;

[0304] In Example D5b, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the first negative electrode slurry was 76:24, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the second negative electrode slurry was 70:30, and the mass content of silicon-based particles in the negative electrode active material was 40%;

[0305] In Example D5c, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the first negative electrode slurry is 70:30, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the second negative electrode slurry is 55:45, and the mass content of silicon-based particles in the negative electrode active material is 50%;

[0306] In Example D5d, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the first negative electrode slurry is 55:45, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the second negative electrode slurry is 32.5:67.5, and the mass content of silicon-based particles in the negative electrode active material is 60%.

[0307] Example D6

[0308] The same procedure was followed as in Example D1, except that the parameters of the laser device were changed (power was adjusted to 10 W, engraving mode was changed to dot engraving mode, pulse was 0.2 s) to control the inner wall of the groove to have no protrusions.

[0309] Example D7 group

[0310] This group of examples was carried out with reference to Example D1, except that the thickness ratio of the first coating layer to the second coating layer was changed. Specifically:

[0311] In Example D7a, the thickness ratio of the first coating layer to the second coating layer was 0.2:1. (To control the mass content of silicon-based particles in the negative electrode active material to 20%, the mass ratio of artificial graphite to silicon oxide in the first negative electrode slurry was adjusted to 94:6, and the mass ratio of artificial graphite to silicon oxide in the second negative electrode slurry was adjusted to 77.2:22.8).

[0312] In Example D7b, the thickness ratio of the first coating layer to the second coating layer is 4:1; (in order to control the mass content of silicon-based particles in the negative electrode active material to 20%, the mass ratio of artificial graphite and silicon oxide in the first negative electrode slurry is adjusted to 85:15, and the mass ratio of artificial graphite and silicon oxide in the second negative electrode slurry is adjusted to 60:40).

[0313] Comparative Example 4

[0314] The same procedure was followed as in Example D1, except that no recesses were produced.

[0315] Test Case D

[0316] The results were recorded in Table 4.

[0317] Table 4

[0318] As can be seen from Table 4, compared with the comparative example, the battery prepared by the negative electrode sheet of the present invention has an improved cycle capacity retention rate, a reduced expansion rate, and improved lithium plating. The battery of the present invention has an excellent cycle life.

[0319] Example E group

[0320] Example E1

[0321] Prepare the battery as follows:

[0322] (1) Preparation of negative electrode sheet

[0323] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 70:30, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0324] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 85:15, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0325] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto a copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the groove depth was 38 μm, the groove width was 170 μm, and the groove spacing was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating layer to the second coating layer was 0.5:1, the distance from the lowest point of the groove to the negative electrode current collector was 15% of the thickness of the first coating layer, the height of the protrusion on the inner wall of the groove was 5 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%;

[0326] (2) Preparation of positive electrode sheet

[0327] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 97:1.5:1.5, N-methylpyrrolidone (NMP) was added, and the mixture was passed through a 200-mesh sieve to obtain a positive electrode slurry having a solid content of 72%. The positive electrode slurry was coated on aluminum foil using a coating machine and dried at 120° C. to obtain a positive electrode sheet having a width of 63 mm.

[0328] (2) Preparation of lithium-ion batteries

[0329] The negative electrode sheet obtained in step (1), the positive electrode sheet obtained in step (2) and a separator (polyethylene film, with a thickness of 9 μm) are wound to form a roll core, which is then wrapped with an aluminum-plastic film. After baking to remove moisture, an electrolyte is injected (propylene carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of 1:1:0.5:1, and 1 mol / L LiPF6 is added and mixed evenly), and a battery is obtained by a hot pressing process.

[0330] Example E2

[0331] The same procedure was followed as in Example E1, except that the negative electrode sheet was prepared as follows:

[0332] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 76:24, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0333] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 83:17, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0334] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove was 32 μm, the width of the groove was 151 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 0.7:1, the distance from the lowest point of the groove to the negative electrode current collector was 49% of the thickness of the first coating, the height of the protrusion on the inner wall of the groove was 3 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0335] Example E3

[0336] The same procedure was followed as in Example E1, except that the negative electrode sheet was prepared as follows:

[0337] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 68:32, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0338] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 90.5:9.5, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly according to the mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0339] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove was 25 μm, the width of the groove was 130 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 0.9:1, the distance from the lowest point of the groove to the negative electrode current collector was 79% of the thickness of the first coating, the height of the protrusion on the inner wall of the groove was 2 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0340] Example E4

[0341] The same procedure was followed as in Example E1, except that the negative electrode sheet was prepared as follows:

[0342] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 70:30, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a first negative electrode slurry with a solid content of 45%;

[0343] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 90:10, and the median particle size Dv50 of silicon oxide is 12 μm), the negative electrode conductive agent (conductive carbon black and carbon nanotubes, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1), the negative electrode binder (styrene-butadiene rubber) and the thickener (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 96.5:0.5:1.5:1.5, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a second negative electrode slurry with a solid content of 45%;

[0344] The first negative electrode slurry and the second negative electrode slurry were sequentially coated onto copper foil using a coating machine and dried at 100°C. A laser device was used to make grooves on the outer surface of the negative electrode coating, wherein the depth of the groove was 30 μm, the width of the groove was 143 μm, and the spacing between the grooves was 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet was 65 mm, the thickness ratio of the first coating and the second coating was 1:1, the distance from the lowest point of the groove to the negative electrode current collector was 50% of the thickness of the first coating, the height of the protrusion on the inner wall of the groove was 4 μm, and the mass content of silicon-based particles in the negative electrode active material was 20%.

[0345] Example E5 group

[0346] This group of examples was carried out with reference to Example E1, except that the content of silicon-based particles in the negative electrode active material in the first negative electrode slurry and the second negative electrode slurry was changed. Specifically:

[0347] In Example E5a, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the first negative electrode slurry was 85:15, and the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the second negative electrode slurry was 92.5:7.5. The content of silicon-based particles in the negative electrode active material was 10% by mass.

[0348] In Example E5b, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the first negative electrode slurry was 16:84, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the second negative electrode slurry was 82:18, and the mass content of silicon-based particles in the negative electrode active material was 40%;

[0349] In Example E5c, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the first negative electrode slurry is 10:90, the mass ratio of artificial graphite to silicon oxide in the negative electrode active material in the second negative electrode slurry is 70:30, and the mass content of silicon-based particles in the negative electrode active material is 50%.

[0350] Example E6

[0351] The same procedure was followed as in Example E1, except that the parameters of the laser device were changed (power was adjusted to 10 W, engraving mode was changed to dot engraving mode, pulse was 0.2 s) to control the inner wall of the groove to have no protrusions.

[0352] Example E7 group

[0353] This group of examples was carried out with reference to Example E1, except that the thickness ratio of the first coating layer to the second coating layer was changed. Specifically:

[0354] In Example E7a, the thickness ratio of the first coating layer to the second coating layer was 0.2:1, and the distance from the lowest point of the groove to the negative electrode current collector was 22% of the thickness of the first coating layer. (To control the mass content of silicon-based particles in the negative electrode active material to 20%, the mass ratio of artificial graphite to silicon oxide in the first negative electrode slurry was adjusted to 60:40, and the mass ratio of artificial graphite to silicon oxide in the second negative electrode slurry was adjusted to 87:13).

[0355] In Example E7b, the thickness ratio of the first coating layer to the second coating layer is 4:1, and the distance from the lowest point of the groove to the negative electrode current collector is 6% of the thickness of the first coating layer; (in order to control the mass content of silicon-based particles in the negative electrode active material to 20%, the mass ratio of artificial graphite and silicon oxide in the first negative electrode slurry is adjusted to 78.7:21.3, and the mass ratio of artificial graphite and silicon oxide in the second negative electrode slurry is adjusted to 85:15).

[0356] Comparative Example 5

[0357] The same procedure was followed as in Example E1, except that no recesses were produced.

[0358] Test Case E

[0359] The results were recorded in Table 5.

[0360] Table 5

[0361] As can be seen from Table 5, compared with the comparative example, the battery prepared by the negative electrode sheet of the present invention has an improved cycle capacity retention rate, a reduced expansion rate, and improved lithium plating. The battery of the present invention has an excellent cycle life.

[0362] 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 negative electrode coating on at least one side of the negative electrode current collector, wherein the negative electrode coating has a concave portion on a side away from the negative electrode current collector, and the negative electrode coating includes a negative electrode active material, and the negative electrode active material includes silicon-based particles; On the cross section of the negative electrode sheet along the depth direction of the recess, a rectangular area A is taken, wherein the rectangular area A includes one recess, and the depth of the recess on the cross section is h. The four sides of the rectangular area A are A1, A2, A3 and A4, respectively, wherein A1 is parallel to A4, A2 is parallel to A3, A1 coincides with the surface of the negative electrode coating, and the midpoint of A1 is the midpoint of the positive projection line formed by the recess on the surface of the negative electrode coating. The lengths of A1 and A4 are both 200 μm, and the lengths of A2 and A3 are both (h+10) μm; the number of silicon-based particles in the rectangular area A is 0-60.

2. The negative electrode sheet according to claim 1, wherein: The number of the silicon-based particles in the rectangular area A is 0-40; And / or, based on the total mass of the negative electrode active material, the content of the silicon-based particles is 1%-65%, preferably 1%-45%.

3. The negative electrode sheet according to claim 1 or 2, wherein: The inner wall of the recess has a protrusion; Preferably, the height of the protrusion is L,0 <L≤5μm。 4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The median particle size Dv50 of the silicon-based particles is 10 μm to 17 μm; Preferably, the surface density of the negative electrode sheet is 7 mg / cm 2 -22mg / cm 2 ; Preferably, the thickness of the negative electrode coating is 35 μm-70 μm.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein: The negative electrode coating has a single-layer structure, and the number of the silicon-based particles in the rectangular area A is 2-27, preferably 3-18.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The negative electrode sheet includes the negative electrode current collector, a first coating layer, and a second coating layer stacked in sequence.

7. The negative electrode sheet according to claim 6, wherein: The first coating layer includes the silicon-based particles, and the number of the silicon-based particles in the rectangular area A is 0-30, preferably 5-18; Preferably, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles is 2%-100%; more preferably 30%-60%; Preferably, the thickness ratio of the first coating layer to the second coating layer is (0.2-4):1; more preferably (0.5-1):1; Preferably, the distance from the lowest point of the concave portion to the negative electrode current collector is 5%-90% of the thickness of the first coating layer.

8. The negative electrode sheet according to claim 6, wherein: The second coating layer includes the silicon-based particles, and the number of the silicon-based particles in the rectangular area A is 5 to 60, preferably 6 to 40; Preferably, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles is 2%-100%; more preferably 30%-60%; Preferably, the thickness ratio of the first coating layer to the second coating layer is (0.2-4):1; more preferably (0.5-2):

1.

9. The negative electrode sheet according to claim 6, wherein: The first coating layer and the second coating layer both include the silicon-based particles, the content of the silicon-based particles in the second coating layer is greater than the content of the silicon-based particles in the first coating layer, and the number of the silicon-based particles in the rectangular area A is 3 to 40, preferably 5 to 30; Preferably, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles is 5%-45%; more preferably 5%-30%; Preferably, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles is 1%-70%, more preferably 1%-40%.

10. The negative electrode sheet according to claim 9, wherein: The thickness ratio of the first coating layer to the second coating layer is (0.2-4):1, preferably (0.5-2):

1.

11. The negative electrode sheet according to claim 6, wherein: The first coating layer and the second coating layer both include the silicon-based particles, the content of the silicon-based particles in the first coating layer is greater than the content of the silicon-based particles in the second coating layer, and the number of the silicon-based particles in the rectangular area A is 2 to 35, preferably 4 to 23; Preferably, based on the total mass of the negative electrode active material in the first coating layer, the content of the silicon-based particles is 1%-90%; more preferably 10%-40%; Preferably, based on the total mass of the negative electrode active material in the second coating layer, the content of the silicon-based particles is 0.01%-30%; more preferably 5%-20%.

12. The negative electrode sheet according to claim 11, wherein: The thickness ratio of the first coating layer to the second coating layer is (0.2-4):1; preferably (0.5-1):1; Preferably, the distance from the lowest point of the concave portion to the negative electrode current collector is 5%-90% of the thickness of the first coating layer.

13. The negative electrode sheet according to any one of claims 1 to 12, wherein: The depth H of the concave portion is 5 μm-65 μm; Preferably, the recess comprises a recessed hole and / or a groove; Preferably, the diameter of the concave holes is 20 μm-150 μm; the spacing between the concave holes is 50 μm-1000 μm; Preferably, the width of the groove is 35 μm-185 μm; the spacing between the grooves is 0.1 mm-3 mm.

14. The negative electrode sheet according to any one of claims 1 to 13, wherein: The vertical distance from the bottom of the recess to the negative electrode current collector is greater than 0 μm; Preferably, the silicon-based particles include at least one of silicon-carbon, silicon-oxygen, silicon and silicon alloy; Preferably, the negative electrode active material further includes a carbon-based material, and the carbon-based material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon.

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

Images