Negative plate, battery, battery pack and electric equipment

Abstract

The invention provides a negative plate, a battery, a battery pack and electric equipment, the negative plate comprises a negative current collector and a first negative active layer located on at least one side of the negative current collector, and the surface of the first negative active layer is provided with a groove; the first negative electrode active layer comprises a first negative electrode active material, and the first negative electrode active material comprises a carbon-based material and a silicon-based material; the negative plate meets the condition that D1 is equal to k1 * (Dsi + Dc + Dg) * (Vsi) 0.5, and k1 is greater than or equal to 5 and less than or equal to 10; wherein D1 is the depth of the groove, and the unit is metered by [mu] m; dc > = 0; when Dc is greater than 0, the silicon-based material comprises silicon particles and a carbon layer existing on the surfaces of the silicon particles, Dc is the thickness of the carbon layer in nm, and Dsi is the particle size of the silicon particles in nm; when Dc is equal to 0, Dsi is the particle size of the silicon-based material, and the unit is in nm; dg is the particle size of the carbon-based material, and the unit is micron; and Vsi is the volume ratio of the silicon-based material in the first negative electrode active material. The performance of improving the energy density, the cycle life and the like of the battery can be considered.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a negative electrode sheet, a battery, a battery pack and electrical equipment. Background Art

[0002] Traditional graphite anode materials have limited the energy density of batteries (such as lithium-ion batteries) due to their low theoretical capacity. Silicon-based materials have a higher theoretical capacity and are gradually gaining widespread attention and application. For example, silicon-carbon composites are considered one of the options for high-capacity anode materials due to their high theoretical capacity and good conductivity. For example, among battery anode materials, silicon materials with a high content in the earth's crust can reach up to 4200mAh / g when fully intercalated with lithium. They also have a low intercalation / deintercalation potential (-0.4V vs. Li / Li+) and good safety, making them one of the most promising anode materials in the field of high-energy lithium-ion batteries.

[0003] However, silicon-based materials are prone to swelling during battery cycling. Specifically, when active ions such as lithium ions are embedded in and extracted from silicon-based material particles, the volume of the silicon-based material often expands by as much as 300-400%. This generates stress within the electrode, leading to the fragmentation of silicon-based particles, loss of electrical contact, and the continuous breakdown and reformation of the solid electrolyte interface (SEI). This leads to rapid decay of electrode capacity and difficulty maintaining cycling stability, resulting in poor battery performance, such as cycle life. Therefore, how to introduce silicon-based materials into battery negative electrodes to increase battery specific capacity while also improving battery performance, such as cycle life, is a pressing technical issue in this field. Summary of the Invention

[0004] The present invention provides a negative electrode sheet, a battery, a battery pack and an electrical device, which can improve the specific capacity and cycle life of the battery.

[0005] In one aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a first negative electrode active layer located on at least one side of the negative electrode current collector, wherein a surface of the first negative electrode active layer is provided with a groove; the first negative electrode active layer comprises a first negative electrode active material, wherein the first negative electrode active material comprises a carbon-based material and a silicon-based material; the negative electrode sheet satisfies D l =k1×(D si +D c +D g )×(V si ) 0.5 , 5≤k1≤10; among them, D l is the depth of the groove, in μm; D c ≥0; when D c When D > 0, the silicon-based material includes silicon particles and a carbon layer on the surface of the silicon particles.c is the thickness of the carbon layer in nm, D si is the particle size of the silicon particles, in nm; when D c =0, D si is the particle size of the silicon-based material, in nm; D g is the particle size of the carbon-based material, in μm; V si is the volume proportion of the silicon-based material in the first negative electrode active material.

[0006] According to one embodiment of the present invention, W l =k2×(D si +D c +D g ), 0.5≤k2≤4, W l is the width of the groove, in μm.

[0007] According to one embodiment of the present invention, S l =k3×(D si +D c +D g )×(V si ) 0.5 , 50≤k3≤100, S l is the spacing between the grooves, in μm.

[0008] According to one embodiment of the present invention, the width of the groove is 5 to 50 μm; and / or the pitch of the groove is 200 to 500 μm; and / or the depth of the groove is 20 to 50 μm.

[0009] According to one embodiment of the present invention, D si 50 to 200 nm; and / or, D c 2 to 5 nm; and / or, V si is 10% to 30%; and / or, the carbon-based material includes graphite.

[0010] According to one embodiment of the present invention, the negative electrode sheet further includes a buffer layer located between the negative electrode current collector and the negative electrode active layer, and the buffer layer includes an elastic material.

[0011] According to one embodiment of the present invention, the elastic material includes an elastic polymer, and the elastic polymer includes one or more of polyetheresteramide, polyetherimide, polystyrene, and polyamide thermoplastic elastomer; and / or the mass percentage of the elastic material in the buffer layer is 60% to 80%; and / or the buffer layer also includes a conductive agent; and / or the thickness of the buffer layer is 5 to 10 μm.

[0012] According to one embodiment of the present invention, the negative electrode sheet further includes a conductive layer located between the negative electrode current collector and the buffer layer.

[0013] According to one embodiment of the present invention, the conductive layer includes a binder, and the binder contains nitrogen and / or sulfur.

[0014] According to one embodiment of the present invention, the binder in the conductive layer includes a cross-linked product of a polyacrylic binder and a tackifier containing sulfur.

[0015] According to one embodiment of the present invention, the polyacrylic acid adhesive includes a first polyacrylic acid adhesive and a second polyacrylic acid adhesive, and the molecular weight of the first polyacrylic acid adhesive is greater than the molecular weight of the second polyacrylic acid adhesive; and / or, the polyacrylic acid adhesive includes one or more of polyacrylic acid, polyacrylonitrile-polyacrylic acid copolymer, polyvinyl alcohol grafted modified polyacrylic acid, glycine amide grafted modified polyacrylic acid, alkali lignin grafted modified polyacrylic acid, and urea-pyrimidinone grafted modified polyacrylic acid; and / or, the sulfur-containing thickener includes one or more of thiourea, 2-mercaptobenzothiazole, 2-mercaptopyridine, and 2-mercaptoethane sulfonic acid.

[0016] According to one embodiment of the present invention, the conductive layer includes a second negative electrode active material, and the second negative electrode active material includes graphite; and / or the conductive layer has a thickness of 30 to 50 μm.

[0017] According to one embodiment of the present invention, the thickness of the first negative electrode active layer is 30 to 50 μm.

[0018] Another aspect of the present invention provides a battery comprising the above-mentioned negative electrode sheet.

[0019] Another aspect of the present invention provides a battery pack comprising the above-mentioned battery.

[0020] Another aspect of the present invention provides an electrical device comprising the above-mentioned battery or the above-mentioned battery pack.

[0021] The negative electrode sheet, battery, battery pack and electrical equipment provided by the present invention introduce silicon-based materials into the battery negative electrode sheet, set grooves on the surface of the first negative electrode active layer, and coordinately control the depth of the grooves, the particle size and other characteristics of the silicon-based material, and the volume percentage of the silicon-based material in the first negative electrode active material to satisfy conditions such as 5≤k1≤10. Under such a negative electrode sheet structure and composition system, the specific capacity of the battery can be improved based on the high capacity properties of the silicon-based material, and the grooves on the surface of the first negative electrode active layer can provide accommodation space for the expansion of substances such as the silicon-based material, thereby suppressing the volume expansion problem of the silicon-based material during the battery cycle, thereby improving the structural stability of the negative electrode sheet, suppressing its volume expansion, and improving the cycle stability of the battery, thereby taking into account the improvement of the battery's specific capacity and cycle life and other performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present invention;

[0023] Figure 2 A schematic structural diagram of a negative electrode sheet according to another embodiment of the present invention;

[0024] Figure 3 A schematic structural diagram of a negative electrode sheet according to another embodiment of the present invention;

[0025] Figure 4 FIG. 1 is a schematic structural diagram of a negative electrode sheet according to another embodiment of the present invention.

[0026] Explanation of reference numerals: 1: negative electrode current collector; 2: negative electrode coating; 21: first negative electrode active layer; 22: groove; 23: buffer layer; 24: conductive layer. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0028] The embodiment of the present invention provides a negative electrode sheet, such as Figure 1 、 Figure 2 、 Figure 3 and Figure 4As shown, the negative electrode sheet includes a negative electrode current collector 1 and a first negative electrode active layer 21 located on at least one side of the negative electrode current collector 1. A surface of the first negative electrode active layer 21 (i.e., the surface of the first negative electrode active layer 21 facing away from the negative electrode current collector 1) is provided with a groove 22; the first negative electrode active layer 21 includes a first negative electrode active material, and the first negative electrode active material includes a carbon-based material and a silicon-based material; the negative electrode sheet meets D l =k1×(D si +D c +D g )×(V si ) 0.5 , 5≤k1≤10; among them, D l is the depth of the groove 22, in μm; D c ≥0; when D c When D > 0, the silicon-based material includes silicon particles and the carbon layer on the surface of the silicon particles. c is the thickness of the carbon layer in nm, D si is the particle size of silicon particles in silicon-based materials, D si The unit is nm; when D c =0, D si is the particle size of the silicon-based material, D si The unit is nm; D g is the particle size of the carbon-based material, in μm; V si is the volume ratio of silicon-based materials in the first negative electrode active material.

[0029] According to the inventor's research, silicon-based materials have higher capacity, but silicon-based material particles are prone to volume expansion during the battery charge and discharge cycle, thereby affecting the battery's cycle life and other performance. By using both silicon-based materials and carbon-based materials as the first negative electrode active material in the first negative electrode active layer 21, and synergistically regulating the volume proportion of silicon-based materials in the first negative electrode active material V si , the particle size of silicon-based materials (particle size D c And when there is a carbon layer on its surface, the thickness of the carbon layer D c ), and the particle size D of the carbon-based material g and the depth of the groove 22, so that it satisfies 5≤k1≤10. In this way, the first negative electrode active layer 21 contains silicon-based materials, which can ensure a high specific capacity of the negative electrode sheet. At the same time, the groove 22 (or groove) is set on the surface of the first negative electrode active layer 21 to provide accommodation space when the particles of silicon-based materials and the like expand, dispersing the stress generated by the volume change of the particles of silicon-based materials and the like during the battery charging and discharging process. At the same time, it can serve as a gas discharge channel inside the negative electrode coating 2, reducing internal gas accumulation and improving the cycle life and safety of the battery. At the same time, the depth D of the groove 22 l The proportion of silicon-based materials Vsi , the particle size and other characteristics of the silicon-based material, and the particle size and other characteristics of the carbon-based material. While suppressing the volume expansion of the negative electrode sheet, it can also reduce the loss of negative electrode material caused by the provision of the groove 22, as well as the impact on the mechanical strength and other properties of the negative electrode sheet, thereby further ensuring the high capacity and good stability of the negative electrode sheet, so that the battery has both high specific capacity and long cycle life. Therefore, the embodiment of the present invention provides a silicon-doped negative electrode sheet that can improve the capacity of the silicon-doped negative electrode sheet while also improving its structural stability and other properties, thereby improving the specific capacity and cycle life of the battery.

[0030] Illustratively, k1 may be 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range consisting of any two thereof.

[0031] In some embodiments, W l =k2×(D si +D c +D g ), 0.5≤k2≤4, W l is the width of the groove 22, measured in μm; by further coordinating the sizes of the silicon-based material particles and the carbon-based material particles and the width of the groove 22 to satisfy 0.5≤k2≤1.5, it is more conducive to the adaptation of the sizes of the groove 22 and the carbon-based material and the silicon-based material, so that the width of the groove 22 W l It is more suitable for the higher mechanical strength and electrical conductivity of the negative electrode sheet, which is conducive to further reducing the expansion rate of the negative electrode sheet and maintaining a higher capacity of the negative electrode sheet, while taking into account improving the battery's specific capacity and cycle life and other performance.

[0032] Illustratively, k2 can be 0.5, 0.7, 1, 1.3, 1.5, 1.7, 2, 2.5, 3, 3.5, 3.75, 4, or a range consisting of any two thereof.

[0033] In some embodiments, S l =k3×(D si +D c +D g )×(V si ) 0.5 , 50≤k3≤100, S l is the spacing of the grooves 22, measured in μm; so that the spacing S of the grooves 22 l It is more suitable for the stress distribution of silicon-based particles after expansion and the thermal management requirements of the battery, improves the stress distribution and current density distribution of the negative electrode during the charging and discharging process, and is conducive to further reducing the expansion rate of the negative electrode and improving the cycle stability of the negative electrode and battery.

[0034] Exemplarily, k3 is, for example, 50, 60, 70, 80, 90, 100, or a range consisting of any two thereof.

[0035] In some embodiments, the depth D of the groove 22 is l The range of 20 to 50 μm, for example, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or any two thereof, is conducive to further suppressing the expansion of the negative electrode sheet, while maintaining a higher specific capacity of the negative electrode sheet, and improving the cycle stability of the negative electrode sheet and the battery.

[0036] In some embodiments, the width W of the groove 22 is l The range of 5 to 50 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or any two thereof is beneficial to further suppress the expansion of the negative electrode sheet, while maintaining a higher specific capacity of the negative electrode sheet, and improving the cycle stability of the negative electrode sheet and the battery.

[0037] In some embodiments, the spacing S of the grooves 22 is l The thickness is 200 to 500 μm, for example, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm or any two thereof, which is beneficial to further suppress the expansion of the negative electrode sheet, while maintaining a higher specific capacity of the negative electrode sheet, and improving the cycle stability of the negative electrode sheet and the battery.

[0038] Specifically, if Figures 1 to 4 As shown, the surface of the first negative electrode active layer 21 is provided with a plurality of grooves 22. These grooves 22 can be specifically distributed on the entire surface of the first negative electrode active layer 21, and can generally be distributed on the entire surface of the first negative electrode active layer 21 at substantially equal intervals along the length direction of the first negative electrode active layer 21. Each groove 22 can extend along the width direction of the first negative electrode active layer 21, but is not limited thereto.

[0039] In an embodiment of the present invention, a groove 22 can be formed on the surface of the first negative electrode active layer 21 by laser scribing. In specific implementation, the process parameters of laser scribing can be as follows: (1) Laser type: a nanosecond or picosecond pulsed fiber laser is used to avoid material damage or performance degradation caused by high temperature; (2) Laser power: a pulsed laser with a power of 10-30W can be selected to ensure that effective cutting can be achieved without overheating the material; (3) Laser frequency: set at 20-50kHz to ensure that each pulse has enough energy to carve the groove while maintaining high production efficiency; (4) Scribing speed: set between 3mm / s and 50mm / s; (5) Focal length: by adjusting the distance between the laser head and the negative electrode sheet, the laser focus falls on the surface of the material to be processed or slightly below, ensuring the best energy concentration effect; (6) Defocus: can be fine-tuned to control the width and depth of the scribing. Appropriate defocus helps to expand the melting area to form a stable groove structure, but it is necessary to prevent an excessively large heat-affected zone. Among them, the depth D of the groove 22 l is the depth of the line, the width W of the groove 22 l is the line width, the spacing S of the groove 22 l is the line spacing.

[0040] The embodiments of the present invention can use conventional laser equipment for marking, and the adjustment methods of parameters such as laser power, laser frequency, marking speed, focal length, defocus amount, etc. are all conventional operations in the field and are not particularly limited.

[0041] In an embodiment of the present invention, after obtaining the negative electrode sheet, an optical microscope can be used to observe the surface of the first negative electrode active layer 21, and the spacing (S) of the grooves 22 can be measured. The surface morphology of the laser-scribed lines can be observed by a scanning electron microscope (SEM), and features such as the width and depth of the grooves 22 can be measured (a cross-section cutting device is used to cut the sample in a direction perpendicular to the laser-scribed lines to prepare a cross section. A 3D laser scanning confocal microscope is used to scan the surface of the sample to obtain three-dimensional morphology data of the lines. Line width and depth measurement: The line width (W) and depth (D) are measured using SEM image analysis software or 3D morphology data).

[0042] In some embodiments, the silicon-based material may include one or more of silicon materials, silicon oxide materials (SiOx), and silicon carbon materials.

[0043] When D c = 0, indicating that there is no carbon layer on the surface of the silicon-based material (the silicon-based material can be specifically the above-mentioned silicon particles). c When D > 0, it indicates that there is a carbon layer on the surface of the silicon-based material (ie, the silicon-based material is a silicon-carbon material including silicon particles and a carbon layer on the surface of the silicon particles). cWhen >0, a carbon layer exists on the surface of the silicon particles, which is beneficial to further inhibit the expansion of the silicon particles and improve the conductivity of the silicon-based material, which is more conducive to the capacity of the silicon-based material and further improves the electrochemical properties of the negative electrode sheet, thereby further improving the battery's specific capacity and cycle life.

[0044] Specifically, when D c = 0, the particle size D of the silicon-based material si It can be micron or nanometer; when D c When >0, the diameter (particle size) of silicon particles in silicon-based materials is D si For example, the silicon-based material may include one or more of carbon-coated nano- or micro-silicon materials, nano- or micro-SiOx and carbon composite materials, and silicon-carbon nano- or micro-wire materials.

[0045] In some embodiments, D si The range may be 50 to 200 nm, for example, 50 nm, 70 nm, 90 nm, 100 nm, 110 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, or a range consisting of any two thereof.

[0046] In some embodiments, D c >0, the particle size D of silicon particles in silicon-based materials si Being nano-scale, the silicon-based material can be expressed as nano-silicon / carbon material (Si / C-NP).

[0047] In some embodiments, the thickness D of the carbon layer c The thickness may be in the range of 2 to 5 nm, for example, 2 nm, 3 nm, 4 nm, 5 nm, or a range consisting of any two thereof.

[0048] In the embodiment of the present invention, when D c When >0, the carbon layer in the silicon-based material can be coated on the surface of the silicon particles, which can be a conventional carbon-coated silicon-carbon material in the art, which can be commercially available or prepared by conventional methods in the art. For example, a carbon layer can be coated on the surface of silicon particles by a conventional carbon coating method in the art to prepare a silicon-carbon material (such as Si / C-NP), and there is no special limitation on this.

[0049] In some embodiments, the volume proportion of the silicon-based material in the first negative electrode active material is V si It may be in the range of 10% to 30%, for example, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30% or any two thereof.

[0050] Specifically, in the first negative electrode active material, the carbon-based material (or carbon-based active material) is used as the negative electrode active material, which may specifically include graphite.

[0051] In some embodiments, the particle size D of the carbon-based material g It can be 12 to 14 μm.

[0052] In the embodiments of the present invention, unless otherwise specified, the particle size mentioned refers to the average particle size (or median particle size D50). A laser particle size analyzer can be used to perform particle size distribution analysis to measure the particle size of each material in the negative electrode coating 2. Alternatively, an SEM or TEM can be used to measure the particle size of each material in the negative electrode coating 2. In specific implementations, the process of using an SEM or TEM to measure the particle size of a material may include: (1) scraping the coating from the negative electrode sheet and crushing the resulting coating material into fine particles using a crusher; screening the crushed particles using a screening device to separate particles of different sizes; (2) placing the sample on the sample stage of the SEM or TEM; and (3) directly measuring the diameter of the particles (the average particle size obtained by statistics) using the SEM or TEM.

[0053] For example, when testing the particle size D of the silicon-based material in the first negative electrode active layer 21, si When the coating scraped off the negative electrode sheet is crushed into particles (the crushing process will not affect the size of the original particles), the size of at least 30 particles can be measured by SEM or TEM, specifically about 100 particles can be measured, and then the average value is statistically calculated to be the final test result. c = 0, directly use SEM or TEM to measure the diameter of at least 30 particles, specifically about 100 particles, and then calculate the average value statistically, which is the particle size D of the silicon-based material. si When D c When the value of the carbon layer is greater than 0, the silicon-based material particles can be cut (specifically, focused ion beam (FIB) cutting) to obtain a cross section of the silicon-based material particles (the cross section basically passes through the center of the silicon-based material). The cross section is then examined by SEM or TEM to measure the diameter of the silicon particles and the thickness of the carbon layer. In this way, the diameters of at least 30 silicon-based material particles and the thickness of the carbon layer can be tested, specifically about 100 particles. The average value of the measured silicon particle diameters is calculated, which is the particle size D of the silicon particles. si , calculate the average value of the measured carbon layer thickness, which is the thickness of the carbon layer D c .

[0054] In addition, the particle size D of the carbon-based material in the first negative electrode active layer 21 was tested. g When the first negative electrode active layer 21 scraped from the negative electrode sheet is crushed into particles (the crushing process does not affect the size of the original particles), the diameter of at least 30 carbon-based material particles is measured by SEM or TEM, specifically about 100 particles can be measured, and then the average value is statistically calculated, which is the particle size D of the carbon-based material. g .

[0055] In addition, in the first negative electrode active layer 21, the volume proportion of the silicon-based material in the first negative electrode active material is V si It can be measured by transmission X-ray, that is, by scanning the material of the first negative electrode active layer 21 by X-CT (computed tomography) imaging to obtain a three-dimensional distribution model, measuring the volume of each negative electrode active material in the three-dimensional distribution model (such as the volume of carbon-based materials and the volume of silicon-based materials), and then calculating the volume proportion V of the silicon-based material si The present invention can use conventional transmission X-ray analysis equipment in the art to perform the above-mentioned scanning, and there is no particular limitation on this.

[0056] In addition, the first negative electrode active layer 21 may further include a conductive agent and a binder. The conductive agent in the first negative electrode active layer 21 may include one or more of conductive carbon black, acetylene black, graphite, graphene, micro-nano linear conductive materials, and micro-nano tubular conductive materials. The binder may include one or more of modified phenolic resin, polyamide, polyacrylamide, polyimide, styrene-butadiene rubber, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacryloyl, polyacrylic acid (PAA), lithium polyacrylate, polyacrylate, and sodium alginate.

[0057] In addition, the first negative electrode active layer 21 may further include a thickener. The thickener may include a carboxymethyl cellulose salt, such as sodium carboxymethyl cellulose, and the like. There is no particular limitation on this.

[0058] In some embodiments, the thickness of the first negative electrode active layer 21 may be 30-50 μm, for example, 30 μm, 33 μm, 35 μm, 38 μm, 40 μm, 43 μm, 45 μm, 48 μm, 50 μm, or any two thereof.

[0059] Continue to refer Figure 1 The negative electrode sheet may further include a buffer layer 23 located between the negative electrode current collector 1 and the negative electrode active layer, wherein the buffer layer 23 comprises an elastic material. Specifically, the negative electrode sheet comprises a negative electrode current collector 1 and a negative electrode coating 2 located on the surface of the negative electrode current collector 1. The negative electrode coating 2 comprises a first negative electrode active layer 21 and a buffer layer 23 (or stress buffering intermediate layer) located between the negative electrode current collector 1. By providing the buffer layer 23 between the negative electrode current collector 1 and the first negative electrode active layer 21, effective spatial adaptability can be provided when particles such as silicon-based materials in the first negative electrode active layer 21 expand, dispersing the stress distribution of the negative electrode sheet during the battery charge and discharge process, further reducing the expansion rate of the negative electrode sheet, maintaining the structural stability of the negative electrode sheet, and improving the battery's cycle life and other performance.

[0060] In some embodiments, the thickness of the buffer layer 23 can be 5 to 10 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range composed of any two of them, which is beneficial for maintaining a relatively thin thickness of the buffer layer 23 while playing a buffering role, and further improving the specific capacity and other performance of the negative electrode sheet and the battery.

[0061] Specifically, the elastic material in the buffer layer 23 has elasticity, which can disperse the stress generated by the volume expansion of the silicon-based material in the first negative electrode active layer 21, thereby improving the structural stability and other properties of the negative electrode sheet. The elastic material in the buffer layer 23 can specifically include an elastic polymer, which can include one or more of polyetheresteramide (PEEA), polyetherimide (PEI), polystyrene (PS), and polyamide thermoplastic elastomer (TPAE).

[0062] In addition, the buffer layer 23 may also include a conductive agent. For example, the buffer layer 23 is composed of an elastic polymer matrix and a conductive agent, which is beneficial to improving the conductivity of the negative electrode coating 2, further ensuring the capacity of the negative electrode coating 2, and further improving the battery's specific capacity and cycle life.

[0063] In some embodiments, the conductive agent in the buffer layer 23 may include one or more of acetylene black (AB), conductive carbon black (SuperP), Ketjen black, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and graphene.

[0064] In some implementations, the mass percentage of the elastic material in the buffer layer 23 can be 60% to 80%, for example, 60%, 62%, 65%, 68%, 70%, 73%, 75%, 78%, 80% or a range consisting of any two thereof.

[0065] In some implementations, the mass percentage of the conductive agent in the buffer layer 23 is 20% to 40%, for example, 20%, 23%, 25%, 27%, 30%, 33%, 35%, 38%, 40% or any two thereof.

[0066] Continue to refer Figure 1 The negative electrode sheet may further include a conductive layer 24, which is located between the negative electrode current collector 1 and the buffer layer 23. The conductive layer 24 (or conductive skeleton layer) is conductive and has better stability during the battery cycle. The conductive layer 24 is provided between the negative electrode current collector 1 and the buffer layer 23. This can improve the stability of the negative electrode sheet while maintaining the capacity of the negative electrode sheet and increase its cycle life. In addition, based on the conductivity of the conductive layer 24, it is also beneficial to the electron and ion transmission between the various layers in the negative electrode coating 2 and the negative electrode current collector 1, ensuring the kinetic performance of the negative electrode sheet, thereby further improving the specific capacity and cycle life of the battery.

[0067] Therefore, in the above-mentioned negative electrode sheet, through the above-mentioned multi-layer coating structure, based on the synergistic effect of each layer, the volume expansion phenomenon of the negative electrode sheet during the battery charging and discharging process can be effectively suppressed, and the expansion rate of the negative electrode sheet can be greatly reduced, so that the negative electrode sheet has good long-term performance while having a high specific capacity, thereby improving the cycle stability and other performance of the negative electrode sheet and the battery.

[0068] In some embodiments, the conductive layer 24 may include a second negative electrode active material. In this case, the conductive layer 24 is a second negative electrode active layer, so that the conductive layer 24 can provide active capacity, further improving the battery's specific capacity and cycle life.

[0069] Specifically, the second negative electrode active material in the conductive layer 24 may include a carbon-based material, which may specifically include graphite, that is, the conductive layer 24 (the second negative electrode active layer) is a graphite negative electrode active layer, which can provide active capacity while further improving the structural stability of the negative electrode sheet and improving the cycle life and other performance of the battery.

[0070] In addition, the conductive layer 24 is located on the surface of the negative electrode current collector 1 , and specifically may be in direct contact (close contact) with the negative electrode current collector 1 . The conductive layer 24 may not contain silicon-based materials.

[0071] Specifically, the conductive layer 24 includes a conductive agent, which can be a conventional conductive material in the art. For example, the conductive agent in the conductive layer 24 includes one or more of conductive carbon black, acetylene black, graphene, carbon nanotubes, and the like.

[0072] In some embodiments, the conductive layer 24 includes a binder, which contains nitrogen (N) and / or sulfur (S), which is beneficial to further improve the cycle stability and other performance of the battery. The reason for this is that the N and / or S in the binder can interact with the metal (such as copper (Cu)) between the negative electrode current collector 1, and form stable chemical bonds (such as Cu-S bonds and / or Cu-N bonds) through chemical reactions, thereby enhancing the adhesion between the negative electrode coating 2 and the negative electrode current collector 1, further avoiding the problem of shedding of the negative electrode active layer caused by the expansion-contraction process of the negative electrode coating 2 during the charge and discharge process of the battery, thereby improving the structural stability of the negative electrode sheet, and improving the cycle stability and other performance of the negative electrode sheet and the battery.

[0073] In some embodiments, the binder in the conductive layer 24 includes a cross-linked product of a polyacrylic acid binder and a thickener containing sulfur element (the cross-linked product is a polyacrylic acid binder modified by a thickener), which is beneficial to further improve the adhesion (bonding strength) between the negative electrode coating 2 and the negative electrode current collector 1, and improve the cycle stability and other performance of the negative electrode sheet and the battery.

[0074] In some embodiments, the molar ratio of the polyacrylic acid binder to the sulfur-containing thickener is 1.5:1 to 3:1, for example, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.8:1, or 3:1, which is beneficial to further improve the adhesion between the negative electrode coating 2 and the negative electrode current collector 1, and improve the performance of the negative electrode sheet and the battery such as cycle stability.

[0075] Specifically, the S in the adhesive may mainly come from the tackifier, and the N mainly comes from the polyacrylic adhesive.

[0076] In some embodiments, the binder may contain a cyano group (CN), such that the binder contains an N element.

[0077] In some specific embodiments, the polyacrylic adhesive may contain CN, so that the adhesive contains CN.

[0078] Generally, the molecular weight (average molecular weight) of the polyacrylic acid-based binder may be 400,000 to 800,000, for example, 400,000, 500,000, 600,000, 700,000 or 800,000.

[0079] Specifically, the polyacrylic binder may include polyacrylic acid and / or a polyacrylic acid derivative.

[0080] In some embodiments, the sulfur-containing thickener includes one or more of thiourea, 2-mercaptobenzothiazole, 2-mercaptopyridine, and 2-mercaptoethanesulfonic acid, which is conducive to being compatible with the polyacrylic binder to form a cross-linked product with good adhesion, and introducing S therein to further improve the adhesion between the negative electrode coating 2 and the negative electrode current collector 1, thereby improving the cycle stability and other performance of the negative electrode sheet and the battery.

[0081] Illustratively, the binder (tackifier-modified polyacrylic binder) may include a thiourea-modified polyacrylic acid-polyacrylonitrile copolymer.

[0082] In some embodiments, the polyacrylic binder may include a first polyacrylic binder and a second polyacrylic binder, the molecular weight of the first polyacrylic binder is greater than the molecular weight of the second polyacrylic binder, and by compounding the first polyacrylic binder with a high molecular weight and the second polyacrylic binder with a low molecular weight, it is beneficial to improve the adhesion (peel strength) between the negative electrode coating 2 and the negative electrode collector 1, and at the same time, it is beneficial to regulate the viscosity and other properties of the conductive slurry used to form the conductive layer 24 in the process of preparing the negative electrode sheet by the coating method, thereby being more conducive to the preparation of the negative electrode sheet.

[0083] In some embodiments, the polyacrylic binder (such as the first polyacrylic binder or the second polyacrylic binder) may include one or more of polyacrylic acid (PAA), polyacrylonitrile-polyacrylic acid copolymer (PAN-PAA), polyvinyl alcohol (PVA) grafted modified polyacrylic acid (PVA-g-PAA), glycine amide grafted modified polyacrylic acid (PAA-GA), alkali lignin grafted modified polyacrylic acid (PAL-NaPAA), and ureido pyrimidone grafted modified polyacrylic acid (PAA-UPy), which is beneficial to further improve the adhesion between the negative electrode coating 2 and the negative electrode current collector 1, and improve the cycle stability and other performance of the negative electrode sheet and the battery.

[0084] In addition, the conductive layer 24 may further include a thickener. The thickener may include carboxymethyl cellulose salt. For example, the carboxymethyl cellulose salt includes sodium carboxymethyl cellulose, etc. There is no particular limitation on this.

[0085] In a specific implementation, the formation process of the conductive layer 24 may include: mixing a tackifier and a polyacrylic acid adhesive, adding a small amount of deionized water, and then heating to a cross-linking reaction temperature for a cross-linking reaction (specifically, heating to 60±5°C and stirring for about 2h±0.5h) to prepare a pre-cross-linked binder; subsequently, the conductive agent, negative electrode active material, binder, thickener and other materials used to form the conductive layer 24 may be mixed, a solvent may be added to adjust the viscosity to a suitable coating viscosity, and the mixture may be uniformly mixed by ball milling or the like to obtain a conductive slurry; the conductive slurry may be applied to the The surface of the negative electrode current collector 1 is dried to remove the solvent to form a conductive layer 24; wherein the solvent used may include deionized water, and the drying process may include: heating the negative electrode current collector 1 with the conductive slurry coated on the surface to 100°C to 140°C under an inert atmosphere, and keeping it at this temperature for 1h±0.5h to further cure the pre-crosslinked binder to form a crosslinked product (i.e., the binder in the conductive layer 24), thereby enhancing the bonding strength between the negative electrode coating 2 and the negative electrode current collector 1, thereby forming a conductive layer 24 on the surface of the negative electrode current collector 1.

[0086] In some embodiments, the thickness of the conductive layer 24 may be 30-50 μm, for example, 30 μm, 33 μm, 35 μm, 38 μm, 40 μm, 43 μm, 45 μm, 48 μm, 50 μm, or any two thereof.

[0087] In the embodiments of the present invention, the graphite used can be conventional graphite active materials in the art. For example, the graphite in the first negative electrode active layer 21 and the conductive layer 24 can each independently include one or more of artificial graphite, natural graphite, and modified graphite, without particular limitation. Generally, the graphite in the conductive layer 24 and the first negative electrode active layer 21 is secondary graphite particles.

[0088] In the embodiment of the present invention, the negative electrode current collector 1 may be made of conventional negative electrode current collector materials in the art. For example, the negative electrode current collector 1 includes copper foil.

[0089] An embodiment of the present invention further provides a battery, comprising the above-mentioned negative electrode sheet. The battery has advantages corresponding to the above-mentioned negative electrode sheet, which will not be described in detail.

[0090] The battery may be a lithium-ion battery, but is not limited thereto.

[0091] Generally speaking, a battery includes an electrolyte, a cell, and a casing that encapsulates the cell. The electrolyte is injected into the cell within the casing, and the cell includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive and negative electrodes. The cell can be a laminated cell, where the positive electrode sheet, separator, and negative electrode sheet are stacked in an alternating pattern. Alternatively, the cell can be a wound cell, where the positive electrode sheet, separator, and negative electrode sheet are stacked and then wound.

[0092] Specifically, the positive electrode sheet includes a positive electrode collector and a positive electrode active layer located on at least one side surface of the positive electrode collector. Specifically, the positive electrode active layer can be provided on one side surface in the thickness direction of the positive electrode collector, or the positive electrode active layer can be provided on the surfaces of the opposite sides in the thickness direction of the positive electrode collector.

[0093] In an embodiment of the present invention, the conductive agent in the positive electrode active layer can be a conventional conductive material in the art. For example, the conductive agent in the positive electrode coating can include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0094] In an embodiment of the present invention, the binder in the positive electrode active layer may be a conventional binding material in the art. For example, the binder in the positive electrode active layer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, and the like.

[0095] The embodiment of the present invention may adopt a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes aluminum foil.

[0096] The electrolyte of the embodiment of the present invention can be a conventional electrolyte in the field. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include an organic solvent, an additive and an electrolyte salt. The organic solvent includes, for example, one or more of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and propylene carbonate (PC), the additive includes, for example, fluoroethylene carbonate (FEC) and / or vinylene carbonate (VC), and the electrolyte salt may include a lithium salt, and the lithium salt includes, for example, lithium hexafluorophosphate (LiPF6), etc., but is not limited thereto.

[0097] In the embodiment of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting. The embodiment of the present invention can adopt conventional separators in the art without special limitation.

[0098] In the embodiment of the present invention, components such as positive electrode sheets, separators and negative electrode sheets can be assembled into a battery by conventional methods in the field. For example, the positive electrode sheets, separators and negative electrode sheets can be stacked in an alternating manner to produce a laminated battery cell (or wound into a wound battery cell); the battery cell is then placed in a shell (battery shell), and after conventional processes such as liquid injection (i.e., injecting electrolyte), packaging, standing, formation, and capacity separation, a battery is obtained.

[0099] An embodiment of the present invention further provides a battery pack including the above-mentioned battery. The battery pack has advantages corresponding to those of the above-mentioned negative electrode sheet, which will not be described in detail.

[0100] Generally, a battery pack includes multiple batteries as described above, which are connected as single cells to form a battery pack. These batteries can be electrically connected using conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods, without particular limitation.

[0101] An embodiment of the present invention further provides an electrical device, comprising the above-mentioned battery or the above-mentioned battery pack. The electrical device has advantages corresponding to the above-mentioned negative electrode sheet, which will not be described in detail.

[0102] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in this field, such as power equipment (such as electric vehicles, electric cars), electronic equipment (such as mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without special restrictions.

[0103] The present invention is further described below through specific examples.

[0104] In the following examples and comparative examples, unless otherwise specified, the sources and related parameters of the polyacrylic acid-polyacrylonitrile copolymer, PAA binder for silicon-based negative electrodes, carbon-coated nanosilicon (silicon-carbon material), secondary particles of artificial graphite, and polyetheresteramide (PEEA) elastomer used are as follows:

[0105] Polyacrylic acid-polyacrylonitrile copolymer: LA132 / LA133, provided by Chengdu Yindi Le, with a solid content of 10±0.3%, a molecular weight of 960,000 g / mol, and a viscosity ≥15000 mPa.S (12 rpm / 25°C).

[0106] PAA binder specifically for silicon-based negative electrodes: BOBSive 290S3, provided by Blue Ocean Black Stone, with a solid content of 10±0.3% and a viscosity ≥15000mPa.S (12rpm / 25°C).

[0107] Carbon-coated nanosilicon (Si / C-NP): SL650B1-SC, provided by Tianmu Pioneer Battery Materials Technology Co., Ltd.

[0108] Secondary particles of artificial graphite: FSN-1, produced by Shanghai Shanshan Technology Co., Ltd.

[0109] Polyetheresteramide (PEEA) elastomer: Pebax, produced by Arkema, with an average molecular weight (weight average molecular weight (Mw)) of about 192,000 g / mol.

[0110] In the following examples and comparative examples, the laser scribing equipment used is: Baochenxin 16-path laser scribing equipment, which mainly includes 16 lasers + 16 galvanometers, a 2000W continuous fiber laser BFSC 2000P, an electro-optical conversion efficiency of more than 35%, and an output error of no more than 1% in each power segment.

[0111] Example 1

[0112] 1. Preparation of negative electrode sheet

[0113] (1-1) Si / C-NP, artificial graphite secondary particles, PAA binder for silicon-based negative electrodes, and conductive carbon black were dispersed in N-methylpyrrolidone in a mass ratio of 15:75:8:2 to obtain a negative electrode slurry; the negative electrode slurry was then coated on a copper foil surface using a doctor blade coating process. After drying and roller pressing, a first negative electrode active layer was formed to obtain a pole piece precursor;

[0114] (1-2) Using high-precision Baochenxin 16-optical path laser scribing equipment, the electrode precursor is precisely laser-scribed, and an orderly groove structure is engraved on the surface of the first negative electrode active layer of the negative electrode sheet according to preset parameters such as spacing and depth, so as to form grooves on the surface of the first negative electrode active layer to obtain a negative electrode sheet; wherein, the laser scribing parameters are a scribing width of 18μm, a scribing depth of 45μm, and a scribing spacing of 224μm.

[0115] In the prepared negative electrode sheet, the thickness of the first negative electrode active layer is about 50 μm.

[0116] 2. Preparation of positive electrode

[0117] Lithium nickel cobalt manganese oxide LiNi 0.6 Co 0.24 Mn 0.16 O2(NCM), binder PVDF, and conductive carbon black were mixed in NMP solvent at a mass ratio of 96.2:1.5:2.3 to prepare a positive electrode slurry;

[0118] The positive electrode slurry is coated on the surface of the aluminum foil, and after drying and roller pressing, the positive electrode sheet is produced.

[0119] 3. Preparation of batteries

[0120] The negative electrode sheets prepared in the examples and comparative examples were cut into 7.5 cm × 6.4 cm sheets, and corresponding ion exchange membranes (diaphragms) and positive electrode sheets were prepared. Both the positive and negative electrodes were double-sided coated with an NP ratio of 1.08. A PP film was used as the ion exchange membrane, and an aluminum-plastic film was used as the outer shell to assemble a 7+8 laminated battery (i.e., 7 positive electrode sheets and 8 negative electrode sheets). The battery was vacuum dried, the electrolyte was injected into the battery shell, packaged, allowed to stand, formed, and volume separated to obtain a lithium-ion battery. The electrolyte composition and preparation process are as follows: LiPF6 was dissolved in a ternary solvent with a mass ratio of EC, EMC, and DMC of 1:1:1, and VC and FEC additives were added as the electrolyte, wherein the LiPF6 concentration was 1 mol / L, VC accounted for 5% by mass, and FEC accounted for 1% by mass.

[0121] Examples 2 to 9, 13 and 14, and Comparative Examples 1 to 2: The differences from Example 1 are that the binder in the conductive layer, the width of the grooves on the surface of the first negative electrode active layer, W l , groove depth D l , groove spacing S l , and K1, K2, K3 and other conditions are different, see Table 1 for details. Except for the differences shown in Table 1, the other conditions are the same.

[0122] Example 9: The difference from Example 2 is that a buffer layer is provided between the first negative electrode active layer and the negative electrode current collector (copper foil) in the negative electrode sheet. The other conditions are the same as those in Example 2. The preparation process of the negative electrode sheet of Example 11 is as follows:

[0123] (1) Formation of buffer layer (stress buffering intermediate layer)

[0124] A composite of polyetheresteramide (PEEA) and acetylene black (AB) was coated on the surface of the copper foil by a coating method to form a buffer layer; wherein the mass ratio of PEEA to AB was 70:30;

[0125] (2) Si / C-NP, artificial graphite secondary particles, PAA binder for silicon-based negative electrode, and conductive carbon black were dispersed in N-methylpyrrolidone in a mass ratio of 15:75:8:2, and then a doctor blade coating process was used to coat the surface of the stress buffer intermediate layer to form a first negative electrode active layer to obtain a pole piece intermediate;

[0126] (5) Roll-pressing (sheeting) the pole piece intermediate to obtain a pole piece precursor;

[0127] (6) Using a high-precision Baochenxin 16-optical path laser scribing device, the electrode precursor is precisely laser-scribed, and an orderly groove structure is engraved on the surface of the first negative electrode active layer of the negative electrode sheet according to preset parameters such as spacing and depth, so as to form a groove on the surface of the first negative electrode active layer to obtain a negative electrode sheet; wherein, the laser scribing parameters are a scribing width of 18μm, a scribing depth of 54μm, and a scribing spacing of 224μm.

[0128] In the prepared negative electrode sheet, the buffer layer has a thickness of about 10 μm, and the first negative electrode active layer has a thickness of about 50 μm.

[0129] Example 10: The difference from Example 9 is that in the negative electrode sheet, a conductive layer is provided between the buffer layer and the negative electrode current collector (copper foil). Other conditions are the same as those of Example 9. The preparation process of the negative electrode sheet of Example 10 is as follows:

[0130] (1) Preparation of a pre-crosslinked binder: polyacrylic acid-polyacrylonitrile copolymer and thiourea were stirred and dissolved in deionized water, and the resulting solution was vacuum dried at 40° C. to obtain a pre-crosslinked binder (polyacrylonitrile-polyacrylic acid + thiourea binder);

[0131] (2) Formation of the conductive layer (first conductive skeleton layer):

[0132] Disperse artificial graphite secondary particles, conductive carbon black, pre-crosslinked binder, and sodium carboxymethyl cellulose in pure water at a mass ratio of 90:1:8:1, and stir evenly to obtain a conductive slurry;

[0133] The conductive paste is evenly coated on the surface of the copper foil by a coating machine and kept at 100-140°C for 1 hour (heat treatment) to form a conductive layer. The pre-crosslinked binder forms a thiourea-modified polyacrylic acid-polyacrylonitrile copolymer after heat treatment;

[0134] (3) Formation of buffer layer (stress buffering intermediate layer)

[0135] A composite of polyetheresteramide (PEEA) and acetylene black (AB) is coated on the surface of the conductive layer by a coating method to form a buffer layer covering the conductive layer; wherein the mass ratio of PEEA to AB is 70:30;

[0136] (4) Dispersing Si / C-NP, artificial graphite secondary particles, PAA binder for silicon-based negative electrode, and conductive carbon black in N-methylpyrrolidone in a mass ratio of 15:75:8:2, and then coating the surface of the stress buffer intermediate layer with a doctor blade coating process to form a first negative electrode active layer to obtain a pole piece intermediate;

[0137] (5) Roll-pressing (sheeting) the pole piece intermediate to obtain a pole piece precursor;

[0138] (6) Using a high-precision Baochenxin 16-optical path laser scribing device, the electrode precursor is precisely laser-scribed, and an orderly groove structure is engraved on the surface of the first negative electrode active layer of the negative electrode sheet according to preset parameters such as spacing and depth, so as to form a groove on the surface of the first negative electrode active layer to obtain a negative electrode sheet; wherein, the laser scribing parameters are a scribing width of 18μm, a scribing depth of 54μm, and a scribing spacing of 224μm.

[0139] In the prepared negative electrode sheet, the thickness of the conductive layer is about 50 μm, the thickness of the buffer layer is about 10 μm, and the thickness of the first negative electrode active layer is about 50 μm.

[0140] Example 11: The difference from Example 10 is that when preparing the pre-cross-linked adhesive, a high molecular weight polyacrylic acid-polyacrylonitrile copolymer (molecular weight 960,000 g / mol) and a low molecular weight polyacrylic acid-polyacrylonitrile copolymer (molecular weight 80,000 g / mol) are mixed and compounded in a mass ratio of 1:1 to replace the polyacrylic acid-polyacrylonitrile copolymer. The other conditions are the same as those in Example 10.

[0141] The preparation process of the pre-crosslinked adhesive in Example 11 is as follows: a high molecular weight polyacrylic acid-polyacrylonitrile copolymer (molecular weight 960,000 g / mol) and a low molecular weight polyacrylic acid-polyacrylonitrile copolymer (molecular weight 80,000 g / mol) are mixed in a mass ratio of 1:1, stirred and dissolved in deionized water with thiourea, and the resulting solution is vacuum dried at 40°C to obtain a pre-crosslinked adhesive.

[0142] Example 12: The difference from Example 10 is that in the negative electrode sheet, no buffer layer is provided between the conductive layer and the first negative electrode active layer (that is, in the preparation process of the negative electrode sheet, after the conductive layer is formed according to step (2), step (3) is not performed, but step (4) is directly performed to form the first negative electrode active layer on the conductive layer). The other conditions are the same as those in Example 10.

[0143] Comparative Example 3: The difference from Example 2 is that no grooves are provided on the surface of the first negative electrode active layer (that is, in the preparation process of the negative electrode sheet, step (1-2) is not performed, and the electrode sheet precursor prepared in step (1-1) is used as the negative electrode sheet), and the other conditions are the same as those in Example 2.

[0144] Specifically, in Examples 1 to 14 and Comparative Examples 1 to 3, D si =100nm, D c =2nm; D in Examples 1 to 14, Comparative Example 1 and Comparative Example 3 g =12μm, D in Comparative Example 2 g =11μm.

[0145] The performance of the batteries of each embodiment and comparative example was tested according to the following process:

[0146] (1) Capacity retention rate test:

[0147] Cycling performance test: At room temperature of 25°C, use a fixture to fix the soft-pack battery, with the starting and ending voltages of 2.8V and 4.2V, respectively. Charge to 4.2V at 0.5C, then charge at 4.2V constant voltage until the current drops to 0.05C, and discharge to 2.8V at 0.2C. Record the capacity retention rate under different cycle numbers. The results are shown in Table 2.

[0148] (2) First discharge specific capacity test (lithium removal):

[0149] Using metallic lithium as the counter electrode, the negative electrode sheets prepared in the above examples and comparative examples were cut into 14mm diameter discs. A separator (PP film) and electrolyte were then assembled into button cells, and the mass of the corresponding negative electrode active material (negative electrode active substance) was calculated. Test conditions: At 25°C ± 2°C, the cells were charged at a rate of 0.1C to 1.5V, allowed to stand for 10 minutes, and then discharged at a rate of 0.1C to 0.005V. The discharge capacity of the button cells was measured. The formula for calculating the initial discharge specific capacity is: specific capacity (mAh / g) = discharge capacity (mAh) / mass of negative electrode active material (g). Results are shown in Table 2. The electrolyte composition and preparation process are as follows: LiPF6 was dissolved in a ternary solvent containing EC, EMC, and DMC in a 1:1:1 mass ratio. VC and FEC additives were added to form the electrolyte. The LiPF6 concentration was 1 mol / L, the VC accounted for 5% by mass, and the FEC accounted for 1% by mass.

[0150] Table 1

[0151]

[0152]

[0153] Table 2

[0154] Example 100-cycle capacity retention rate (%) 500-cycle capacity retention rate (%) Specific capacity (mAh / g) Example 1 96 90 573 Example 2 93 88 575 Example 3 92 87 573 Example 4 95 89 572 Example 5 96 91 569 Example 6 96 91 565 Example 7 95 89 573 Example 8 93 85 574 Example 9 97 91 571 Example 10 98 92 569 Example 11 98 93 570 Example 12 97 91 572 Example 13 96 92 577 Example 14 84 79 760 Comparative Example 1 88 82 572 Comparative Example 2 86 78 563 Comparative Example 3 84 72 580

[0155] It can be seen from Table 1 that, compared with Comparative Examples 1 to 3, Examples 1 to 14 can improve both the cycle life and specific capacity of the battery by controlling 5≤k1≤10.

[0156] It can be further seen from Examples 1 to 9 that Examples 1, 2, 4, 5, 7 and 13 can further improve both the cycle life and specific capacity of the battery by further controlling 0.5≤k2≤4 and / or 50≤k3≤100.

[0157] In addition, it can be further seen from Example 14 that increasing the silicon doping content of the negative electrode sheet can significantly improve the specific capacity of the battery while maintaining a high cycle life of the battery. Compared with Comparative Examples 1 to 3, Example 14 achieves both improved cycle life and specific capacity of the battery.

[0158] It can be further seen from Example 1 and Examples 9 to 12 that Examples 9 to 12 further improve the cycle life and specific capacity of the battery by further providing a buffer layer and / or a conductive layer between the negative electrode active layer and the current collector.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The invention comprises a negative electrode current collector and a first negative electrode active layer located on at least one side of the negative electrode current collector, wherein a surface of the first negative electrode active layer is provided with a groove; the first negative electrode active layer comprises a first negative electrode active material, and the first negative electrode active material comprises a carbon-based material and a silicon-based material; The negative electrode sheet satisfies D l =k1×(D si +D c +D g )×(V si ) 0.5 , 5≤k1≤10; Among them, D l is the depth of the groove, in μm; D c ≥0； When D c When D > 0, the silicon-based material includes silicon particles and a carbon layer on the surface of the silicon particles. c is the thickness of the carbon layer in nm, D si is the particle size of the silicon particles, in nm; When D c =0, D si is the particle size of the silicon-based material, in nm; D g is the particle size of the carbon-based material, in μm; V si is the volume proportion of the silicon-based material in the first negative electrode active material.

2. The negative electrode sheet according to claim 1, characterized in that: W l =k2×(D si +D c +D g ), 0.5≤k2≤4, W l is the width of the groove, in μm.

3. The negative electrode sheet according to claim 1, characterized in that: S l =k3×(D si +D c +D g )×(V si ) 0.5 , 50≤k3≤100, S l is the spacing between the grooves, in μm.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The width of the groove is 5 to 50 μm; and / or, the spacing between the grooves is 200 to 500 μm; And / or, the depth of the groove is 20-50 μm.

5. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: D si 50~200nm; and / or, D c 2~5nm; and / or, V si 10% to 30%; And / or, the carbon-based material includes graphite.

6. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The negative electrode sheet further includes a buffer layer located between the negative electrode current collector and the negative electrode active layer, and the buffer layer includes an elastic material.

7. The negative electrode sheet according to claim 6, characterized in that: The elastic material comprises an elastic polymer, and the elastic polymer comprises one or more of polyetheresteramide, polyetherimide, polystyrene, and polyamide thermoplastic elastomer; And / or, the mass percentage of the elastic material in the buffer layer is 60% to 80%; And / or, the buffer layer further comprises a conductive agent; And / or, the buffer layer has a thickness of 5 to 10 μm.

8. The negative electrode sheet according to claim 6, characterized in that: The negative electrode sheet further includes a conductive layer located between the negative electrode current collector and the buffer layer.

9. The negative electrode sheet according to claim 8, characterized in that: The conductive layer includes a binder containing nitrogen and / or sulfur.

10. The negative electrode sheet according to claim 9, characterized in that: The binder in the conductive layer includes a cross-linked product of a polyacrylic binder and a tackifier containing sulfur.

11. The negative electrode sheet according to claim 10, characterized in that: The polyacrylic acid adhesive comprises a first polyacrylic acid adhesive and a second polyacrylic acid adhesive, wherein the molecular weight of the first polyacrylic acid adhesive is greater than the molecular weight of the second polyacrylic acid adhesive; And / or, the polyacrylic acid binder includes one or more of polyacrylic acid, polyacrylonitrile-polyacrylic acid copolymer, polyvinyl alcohol grafted modified polyacrylic acid, glycine amide grafted modified polyacrylic acid, alkali lignin grafted modified polyacrylic acid, and ureido pyrimidone grafted modified polyacrylic acid; And / or, the sulfur-containing viscosity enhancer includes one or more of thiourea, 2-mercaptobenzothiazole, 2-mercaptopyridine, and 2-mercaptoethanesulfonic acid.

12. The negative electrode sheet according to any one of claims 8 to 11, characterized in that: The conductive layer includes a second negative electrode active material, and the second negative electrode active material includes graphite; And / or, the thickness of the conductive layer is 30-50 μm.

13. The negative electrode sheet according to any one of claims 1 to 12, characterized in that: The thickness of the first negative electrode active layer is 30 to 50 μm.

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

15. A battery pack, characterized in that: Including the battery according to claim 14.

16. An electrical device, characterized in that: Comprising the battery according to claim 14 or the battery pack according to claim 15.

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