battery

Abstract

The application relates to the technical field of batteries, in particular to a battery which comprises a negative electrode sheet, a positive electrode sheet and an electrolyte, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer located on at least one side surface of the negative electrode current collector; a conductive primer layer is arranged between the negative electrode active coating layer and the negative electrode current collector; the negative electrode active coating layer comprises a negative electrode active substance, and the negative electrode active substance comprises a spherical silicon-carbon material. The application can solve the problem that the active material in the bottom layer of the electrode sheet cannot be effectively utilized, improve the lithium precipitation on the negative electrode surface in the later stage of the cycle, and solve the problem of the expansion of the silicon-containing negative electrode, thereby improving the cycle life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery. BACKGROUND

[0002] With the advent of the 5G era and the rapid development of lithium ion battery technology, people have higher requirements for the energy density, fast charging capability and charge-discharge rate of lithium ion batteries. High-energy-density fast-charging lithium batteries are also the development trend of consumer lithium ion batteries. However, with the increase of energy density, the thickness of the positive and negative electrode sheets of lithium batteries becomes thicker, and the transmission distance of lithium ions becomes longer. In addition, after the charging speed becomes faster, lithium ions are more likely to gather and congest on the surface of the electrode sheet during the charging and discharging process. Lithium ions cannot quickly embed into the bottom layer of active materials far from the surface of the electrode sheet and close to the current collector of the electrode sheet, so that the active materials in the bottom layer of the electrode sheet cannot be effectively utilized. In addition, potential changes cause lithium to be precipitated on the surface of the electrode sheet in the later stage of the cycle, especially the silicon-doped negative electrode sheet, which is more serious with the increase of the thickness of the electrode sheet. This seriously affects the service life of the lithium ion battery. SUMMARY

[0003] Therefore, the present application is dedicated to providing a battery which can fully solve the problem that the active materials in the bottom layer of the electrode sheet cannot be effectively utilized, improve the precipitation of lithium on the surface of the negative electrode in the later stage of the cycle, and effectively solve the expansion problem of the silicon-containing negative electrode sheet, thereby improving the cycle life and cycle expansion of the battery.

[0004] The present application provides a battery, which comprises a negative electrode sheet, a positive electrode sheet and an electrolyte, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer located on at least one side surface of the negative electrode current collector; an electrically conductive primer layer is arranged between the negative electrode active coating layer and the negative electrode current collector.

[0005] The negative electrode active coating layer comprises a negative electrode active material, and the negative electrode active material comprises a spherical silicon-carbon material, the particle size Dv50 of the spherical silicon-carbon material is D.

[0006] The thickness of the negative electrode current collector is H0, the thickness of the electrically conductive primer layer is H1, and the H0 and H1 satisfy 0.1H0≤H1≤0.9H0.

[0007] After the first charge and discharge, in the battery in the full charge state, the H0, H1, H2 and D satisfy 0.20≤D / (H0+H1+H2)≤0.28, wherein H2 is the thickness of the negative electrode active coating layer.

[0008] Compared with the prior art, the present application has at least the following advantages:

[0009] (1) The battery of the present application can enhance the electron conduction of the active material close to the negative electrode current collector side (i.e. the bottom layer), fully solve the problem that the active material at the bottom of the pole piece cannot be effectively utilized, and improve the lithium precipitation on the negative electrode surface in the later cycle;

[0010] (2) The battery of the present application can avoid the influence of the conductive primer layer on the bottom of the negative electrode active coating on the expansion of the silicon negative electrode, buffer the expansion stress of the spherical silicon-carbon material, effectively solve the expansion problem of the silicon-containing negative electrode sheet, and thus improve the cycle life and cycle expansion of the battery.

[0011] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the present application. Any numerical value, however, can be expressed as a range by either adding or subtracting a small percentage (e.g., 1-10%) from the stated value to account for variations, measurement inaccuracies, and the like. For numerical ranges expressed in the format "from X to Y," it is intended that embodiments "X," "Y," and any numerical values therein can be combined with one another to achieve a new numerical range within the scope of this application. In other words, any numerical value implicit in the ranges stated herein is considered part of the disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The cross-sectional structure of the negative electrode sheet in an example of the present application is shown in the schematic diagram.

[0013] Figure 2 The schematic diagram of the lithium precipitation on the surface of the negative electrode sheet after the battery is disassembled in an example of the present application is shown. DETAILED DESCRIPTION

[0014] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0015] The present application provides a battery, which comprises a negative electrode sheet, a positive electrode sheet and an electrolyte, wherein the cross-sectional structure of the negative electrode sheet is shown in the schematic diagram Figure 1 The negative electrode sheet comprises a negative electrode current collector 100 and a negative electrode active coating 110 on at least one side surface of the negative electrode current collector 100; a conductive primer layer 120 is arranged between the negative electrode active coating 110 and the negative electrode current collector 100;

[0016] The negative electrode active coating 110 comprises a negative electrode active material, and the negative electrode active material comprises a spherical silicon-carbon material, and the particle size Dv50 of the spherical silicon-carbon material is D;

[0017] The thickness of the negative electrode current collector 100 is H0, the thickness of the conductive primer layer 120 is H1, and the H0 and H1 satisfy 0.1H0≤H1≤0.9H0, for example, 0.1H0, 0.2H0, 0.3H0, 0.4H0, 0.5H0, 0.6H0, 0.7H0, 0.8H0 or 0.9H0.

[0018] After the first charge and discharge, in the full state of the battery, the H0, H1, H2 and D satisfy 0.20≤D / (H0+H1+H2)≤0.28, for example, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27 or 0.28, wherein H2 is the thickness of the negative electrode active coating 110.

[0019] According to Figure 1 The cross-sectional structure diagram of the negative electrode sheet shown in the figure, the negative electrode sheet contains the negative electrode current collector 100 and the negative electrode active coating 110 covering one side of it, and the conductive primer coating 120 is arranged between the two. It should be noted that although the figure only shows the cross-sectional structure of the negative electrode current collector single-sided coating, this is a typical simplified expression of the schematic diagram; in actual application, based on the design requirements of the battery, the negative electrode active coating 110 and the conductive primer coating 120 can exist on the double-sided surface of the negative electrode current collector 100 (i.e. form a double-sided coating structure), or only keep single-sided coating according to specific performance requirements; the setting of the conductive primer coating 120 is not limited to the single side shown in the figure, and its double-sided coating is also applicable to the present application; in addition, the Figure 1 The display of single-sided coating is only used to clarify the relative position relationship of each layer of material, and does not constitute a limitation on the coating direction of the negative electrode sheet.

[0020] In the traditional negative electrode sheet, when the negative electrode current collector is in direct contact with the negative electrode active coating, the bottom layer of active material close to the negative electrode current collector is prone to low utilization rate in the charge and discharge process due to the long electron transmission path, and the potential change will cause lithium precipitation on the negative electrode surface in the later cycle; the present application introduces a conductive primer coating as an intermediate layer on the basis of the negative electrode current collector and the negative electrode active coating, which can enhance the electron conduction of the active material close to the negative electrode current collector side (i.e. the bottom layer), fully solve the problem that the bottom layer of active material of the sheet cannot be effectively utilized, and improve the lithium precipitation on the negative electrode surface in the later cycle; moreover, by further controlling the thickness relationship, the thickness H1 of the conductive primer coating and the thickness H0 of the negative electrode current collector satisfy 0.1H0≤H1≤0.9H0, which can avoid the decrease of the loading amount of active material caused by the excessive thickness of the conductive primer coating, and at the same time ensure the coating amount of the conductive primer coating, enhance the adhesion between the negative electrode active coating and the negative electrode current collector, and thus play a role in buffering the expansion stress of the spherical silicon-carbon material;

[0021] However, due to the difference in elastic modulus between the conductive coating and the negative active coating, the silicon-doped negative plate will generate internal stress during the volume expansion of charging and discharging, which may cause problems such as cracking of the conductive coating or delamination of the interface between the conductive coating and the negative active coating, thereby failing to effectively solve the expansion problem of the negative plate in the later cycle; Based on this, the present application further controls the relationship between the particle size Dv50 of the spherical silicon-carbon material in the battery after the first charging and discharging and the thickness of the plate, which satisfies 0.20≤D / (H0+H1+H2)≤0.28, wherein H0 is the thickness of the negative current collector, H1 is the thickness of the conductive bottom coating, and H2 is the thickness of the negative active coating. By reasonably reducing the particle size of the spherical silicon-carbon material, the diffusion path of lithium ions can be shortened, and the internal stress generated by the negative active coating during cycle expansion can be reduced, so that the electronic conduction of the active material on the negative current collector side (i.e. the bottom layer) is not affected, and the coating cracking or interface delamination problem in the later cycle can also be effectively alleviated. However, if the thickness of the negative plate is too thin at this time, the expansion space of the negative active coating will be compressed, which will further exacerbate the expansion of the negative plate. If the thickness of the negative plate is too thick, the coating structure stability of the negative plate will be reduced due to the too small particle size of the spherical silicon-carbon material, resulting in capacity loss of the negative active material. Therefore, by controlling the ratio of the particle size Dv50 of the spherical silicon-carbon material to the thickness of the plate within a certain range, the present application can solve the expansion problem in the later cycle caused by the setting of the conductive bottom coating, ensure the effective utilization of the active material in the bottom layer, improve the lithium precipitation problem on the negative electrode surface in the later cycle, and further improve the cycle performance of the battery, improve the cycle life and cycle expansion of the battery, and prolong the service life of the battery.

[0022] In summary, the negative plate of the present application can enhance the electronic conduction of the active material near the negative current collector side (i.e. the bottom layer), fully solve the problem that the active material in the bottom layer of the plate cannot be effectively utilized, and improve the lithium precipitation on the negative electrode surface in the later cycle; and can avoid the influence of the conductive bottom coating on the negative active coating on the expansion of the silicon negative electrode, buffer the expansion stress of the spherical silicon-carbon material, effectively solve the expansion problem of the silicon-containing negative plate, and improve the cycle life and cycle expansion of the battery.

[0023] The thickness H1 of the conductive undercoat layer is the thickness of the conductive undercoat layer on either side of the negative current collector. If the conductive undercoat layer is provided on only one side of the negative current collector, H1 is equal to the thickness of the single-sided conductive undercoat layer. If the conductive undercoat layer is provided on both sides of the negative current collector, H1 is equal to the average of the thicknesses of the conductive undercoat layers on both sides. The thickness H2 of the negative active coating layer is similarly understood. Therefore, H0+H1+H2 can be understood as the total thickness of the negative current collector, the conductive undercoat layer, and the negative active coating layer on one side of the negative current collector, which can be denoted as H, H=H0+H1+H2. In addition, the test method for the thickness H0 of the negative current collector, the thickness H1 of the conductive undercoat layer, and the thickness H2 of the negative active coating layer is as follows: after the first charge-discharge of the battery of the application, the battery is fully charged, and then the battery is disassembled in a sealed environment with an environmental humidity of less than 2%. The cross section of the negative plate along the width direction of the negative current collector is obtained, and the cross section SEM is tested in a vacuum chamber. The cross section SEM image obtained by software analysis is used to determine the thickness parameters of the negative plate of the application, including the thickness H0 of the negative current collector, the thickness H1 of the conductive undercoat layer, and the thickness H2 of the negative active coating layer. In addition, the particle size Dv50 of the spherical silicon-carbon material can also be obtained by observing and analyzing the cross section SEM image of the negative plate. In addition, it should be noted that the full charging of the battery after the first charge-discharge has little effect on the thickness H0 of the negative current collector and the thickness H1 of the conductive undercoat layer. Therefore, the thickness H0 of the negative current collector and the thickness H1 of the conductive undercoat layer provided before the first charging can be considered consistent with the thickness after the first charging.

[0024] The specific operation steps of the first charge-discharge of the battery of the application are as follows: the first charge-discharge of the battery is carried out using a blue light test device. Specifically, the battery is charged to 4.53V using 2C constant current and constant voltage, and the current cutoff is 0.05C. Then, 1C discharging to 3.0V is completed, and the first charge-discharge (one complete charge-discharge cycle) is completed. Then, 1C constant current and constant voltage charging to 4.53V is carried out, and the current cutoff is 0.05C. After the battery is fully charged, subsequent tests can be carried out. In addition, the full state of charge of the battery can be understood as 100% SOC, which means that the state of charge (SOC) of the battery reaches 100%, i.e., the battery is in a fully charged state.

[0025] In an example, 0.2H0≤H1≤0.6H0.

[0026] In an example, after 50T cycles, in the battery in a full state of charge, the H0, H1, H2, and D satisfy 0.1≤D / (H0+H1+H2)≤0.2, for example, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2.

[0027] In an example, after the cycle 200T, the H0, H1, H2 and D in the battery at full state of charge satisfy 0.05≤D / (H0+H1+H2)≤0.18, for example, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17 or 0.18.

[0028] The battery after the cycle 50T, 200T at full state of charge refers to the battery after completing 50 times, 200 times of complete charge and discharge cycles according to the specific operation steps of the first charge and discharge of the battery according to the application.

[0029] With the increase of the cycle period, the volume expansion degree of the silicon-containing negative electrode sheet will increase, and the coating cracking or interface delamination problem caused by the difference in elastic modulus between the conductive coating and the negative active coating will become more serious. Therefore, by further controlling the relationship between the particle size Dv50 of the spherical silicon-carbon material and the thickness of the electrode sheet after the cycle 50T, 200T of the battery based on the relationship between the particle size Dv50 of the spherical silicon-carbon material and the thickness of the electrode sheet after the first charge and discharge of the battery, the appropriate particle size of the spherical silicon-carbon material can be adjusted more reasonably corresponding to different cycle periods, so as to further shorten the diffusion path of lithium ions, reduce the internal stress generated in the cycle expansion of the negative active coating, and adjust the appropriate expansion space of the negative active material, improve the stability of the coating structure of the negative electrode sheet, and further solve the expansion problem in the later cycle caused by the conductive primer coating, improve the expansion problem of the negative electrode in the later cycle, improve the cycle life and cycle expansion of the battery, and prolong the service life of the battery.

[0030] In an example, 4μm≤H0≤10μm, for example, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0031] In an example, 0.4μm≤H1≤9μm, for example, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or 9μm.

[0032] In an example, 25μm≤H2≤45μm, for example, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 41μm, 42μm, 43μm, 44μm, 45μm.

[0033] In an example, the conductive primer layer comprises a conductive agent, a binder, a leveling agent, and a thickening agent.

[0034] In an example, the conductive agent comprises at least one of conductive carbon black, single-walled conductive carbon tubes, multi-walled conductive carbon tubes, graphene.

[0035] In an example, the binder comprises at least one of styrene butadiene rubber, PAA, polyacrylic acid, PVDF.

[0036] In an example, the leveling agent comprises thiourea.

[0037] In an example, the thickening agent comprises at least one of CMC, CMC-Li.

[0038] In an example, the mass ratio between the conductive agent, the binder, the leveling agent, the thickening agent is (10%-25%):(40%-70%):(0.2%-0.5%):(5%-15%).

[0039] In an example, the mass content of the conductive agent is 10%-25%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%.

[0040] In an example, the mass content of the binder is 40%-70%, for example, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or 70%.

[0041] In an example, the mass content of the leveling agent is 0.2%-0.5%, for example, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.4%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, or 0.5%.

[0042] In an example, the mass content of the thickening agent is 5%-15%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0043] In the conductive primer layer, the content of the conductive agent is relatively high, and the mass content accounts for 10%-25%. The main purpose is to improve the conductivity between the negative current collector and the negative active coating. At the same time, the conductive agent has a lubricating effect, which can avoid the negative active material particles in the bottom layer from extruding the negative current collector during the production process, resulting in damage to the current collector. The content of the adhesive is relatively high, and the mass content accounts for 40%-70%. The main purpose is to increase the adhesion between the negative active material and the negative current collector, that is, it can be used to improve the peeling force between the negative active coating and the negative current collector, reduce the risk of demolding, and also play a role in buffering the expansion stress of spherical silicon-carbon materials, thereby relieving the cycle expansion problem of the battery. The role of the leveling agent in the conductive primer layer is to avoid the aggregation or missing coating of the conductive primer layer during coating, so that the conductive primer layer is more gentle. The role of the thickening agent in the conductive primer layer is to increase the adhesion of the conductive primer layer and the viscosity of the slurry, making the coating more smooth.

[0044] In an example, the peeling force between the conductive primer layer and the negative current collector is 10 gf-55 gf, for example, 10 gf, 15 gf, 20 gf, 25 gf, 30 gf, 35 gf, 40 gf, 45 gf, 50 gf or 55 gf. The test method of the peeling force between the conductive primer layer and the negative current collector is as follows: the available battery is discharged to 3.0 V, the battery is disassembled, then the disassembled negative sheet is removed from the negative active coating, and the test sample sheet with a width of 3 cm and a length of 8 cm is cut. The QJ210A peeling force test equipment is used to test the peeling force between the conductive primer layer and the negative current collector of the test sample sheet. By further controlling the peeling force between the conductive primer layer and the negative current collector, the expansion stress generated during the charging and discharging process of the battery can be more effectively dispersed, further improving the cycle expansion performance of the battery. If the peeling force is too large, the stress will be concentrated at the interface between the conductive primer layer and the negative current collector, which is easy to cause the coating to crack or delaminate from the negative current collector.

[0045] In an example, the tensile strength of the negative current collector is A, and the thickness H1 of the conductive primer layer and the tensile strength A of the negative current collector satisfy 0.002A≤H1≤0.007A, for example, 0.002A, 0.003A, 0.004A, 0.005A, 0.006A or 0.007A, wherein A is 400-950 MPa, for example, 400 MPa, 450 MPa, 500 MPa, 550 MPa, 600 MPa, 650 MPa, 700 MPa, 750 MPa, 800 MPa, 850 MPa, 900 MPa or 950 MPa. The test method for the tensile strength A of the negative current collector is as follows: the available battery is discharged to 3.0 V, then the negative electrode sheet disassembled is removed of the negative active coating and the conductive primer layer, and the foil material as the negative current collector is cut into a test sample with a length of 20 cm and a width of 5 cm, and the tensile strength of the test sample foil material is tested according to ASTM standard B152M-19, with the unit of MPa and represented by A. By controlling A and H1 to satisfy the above relationship, the ductility of the negative current collector can be further improved, the brittle fracture of the negative current collector after the conductive primer layer is provided can be prevented, the risk of electrode sheet fracture can be reduced, and the safety performance of the negative electrode sheet and the battery can be improved; this is because when H1 is greater than 0.007A, the thickness of the conductive primer layer is too thick, then a large internal stress can be generated in the coating and drying process due to solvent volatilization, material shrinkage and other factors, the internal stress cannot be effectively released, and the phenomenon of cracking of the conductive primer layer can be caused, or the tensile strength A of the negative current collector is too low, which can increase the risk of electrode sheet fracture; when H1 is less than 0.002A, the thickness of the conductive primer layer is too small, which can hinder the electron conduction of the bottom active material, increase the risk of lithium precipitation of the negative electrode, or the tensile strength A of the negative current collector is too high, which can cause the ductility of the negative current collector to decrease, thereby causing the expansion stress buffering performance of the negative current collector to the negative active material to decrease.

[0046] In an example, the elongation of the negative electrode sheet is 5%-8%, for example, 5%, 6%, 7% or 8%. The test method for the elongation of the negative electrode sheet is as follows: the available battery is discharged to 3.0 V, then the negative electrode sheet disassembled is directly cut into a test sample with a length of 20 cm and a width of 5 cm, and the elongation (%) of the test sample is tested according to ASTM standard B152M-19; by testing the elongation of the negative electrode sheet, the electrode sheet ductility caused by the expansion of the negative electrode sheet can be improved, and the problems of the negative active material and the negative current collector being separated and even the current collector being broken can be avoided.

[0047] In an example, the porosity of the negative electrode sheet is P, the thickness H of the negative electrode sheet and the porosity P of the negative electrode sheet satisfy 1.7≤H / P≤2.1, for example, 1.7, 1.8, 1.9, 2 or 2.1, wherein P is 23%-48%, for example, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47% or 48%. The test method of the porosity P of the negative electrode sheet is as follows: the available battery is discharged to 3.0 V, then the negative electrode sheet taken out is taken along the cross section in the thickness direction of the electrode sheet to prepare a scanning electron microscope test sample, the cross section electron microscope image is taken, a specific length-width area, such as a 100 μm*100 μm area, is taken, color rendering is performed on the area by using Image J software, the pores between the negative electrode active materials are distinguished, then the area S of the specific length-width region taken by the negative electrode sheet can be obtained by software analysis 总 and the area sum S of the region where the pores are located 孔 ; finally, the porosity can be calculated by using the formula, porosity P(%)=S 孔 / S 总 ; the porosity P of the negative electrode sheet has the following characteristics: the unit of the porosity P is percentage, the relationship between the porosity P and the total thickness H(H=H0+H1+H2) of the negative electrode current collector, the conductive primer layer and the negative electrode active coating on one side of the negative electrode current collector satisfies 1.7≤H / P≤2.1, and the porosity P of the negative electrode sheet increases with the increase of the thickness H of the negative electrode sheet; in this way, the kinetic performance of the negative electrode sheet can be improved, and the expansion of the negative electrode sheet can be effectively inhibited, so as to further improve the cycle life of the battery; because when H / P is too large, the thickness of the electrode sheet is too large, or the porosity P of the negative electrode sheet is too small, which is not conducive to the transmission rate of lithium ions in the coating and the electrolyte, thereby leading to the decrease of the kinetic performance of the negative electrode sheet and the influence on the cycle life; when H / P is too small, the thickness of the electrode sheet is too small, which will compress the expansion space of the negative electrode active material, or the porosity P of the negative electrode sheet is too large, which will lead to the intensification of the side reaction of the negative electrode active material, and the solid by-product and gas produced by the side reaction will further compress the expansion space of the negative electrode active material, thereby affecting the cycle life and expansion performance of the battery.

[0048] In an example, the spherical silicon-carbon material has a particle size Dv10 of 4-6 μm, for example 4 μm, 5 μm or 6 μm, a particle size Dv50 of 6-15 μm, for example 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, and a particle size Dv90 of 13-20 μm, for example 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm. The testing method of the particle size Dv10 and Dv90 of the spherical silicon-carbon material is the same as that of the particle size Dv50 of the spherical silicon-carbon material, which is not described herein again. By controlling the particle size of the spherical silicon-carbon material at different volume distributions, the diffusion path of lithium ions can be further shortened, the electronic conduction of the active material on the negative current collector side (i.e. the bottom layer) can be improved, thereby improving the lithium precipitation problem on the surface of the negative electrode sheet, and at the same time, the internal stress generated in the cycle expansion of the negative active coating can be reduced, effectively slowing down the coating cracking or interface delamination problem in the later cycle, improving the cycle life and expansion of the battery.

[0049] In an example, in the cross section of the negative active coating on one side along the width direction of the negative current collector, the number of the spherical silicon-carbon material in the area obtained by any 100 μm x thickness of the negative active coating on one side along the width direction of the negative current collector is 3-10, for example 3, 4, 5, 6, 7, 8, 9 or 10; wherein the number of the spherical silicon-carbon material with a particle size Dv10 of 4-6 μm is 3-6, for example 3, 4, 5 or 6; the number of the spherical silicon-carbon material with a particle size Dv50 of 6-15 μm is 2-4, for example 2, 3 or 4; and the number of the spherical silicon-carbon material with a particle size Dv90 of 13-20 μm is 1-3, for example 1, 2 or 3.

[0050] The cross section of the negative active coating along the width direction of the negative current collector can be located at any side of the negative current collector; the position of the cross section of the negative active coating along the width direction of the negative current collector in the width direction of the negative current collector is arbitrary, as long as the cross section of the negative active coating along the width direction can be completely presented; further, the present application divides a detection area of the number of spherical silicon-carbon materials in the cross section, the area calculation formula of the area is = any 100 μm along the width direction of the negative current collector x the thickness of the negative active coating on one side, wherein the 100 μm along the width direction of the negative current collector can be randomly selected, in actual detection, generally 3-5 sections of 100 μm along the width direction of the negative current collector are selected, then the number of particles of the spherical silicon-carbon materials in these obtained areas is counted and averaged, so that the number of particles of the spherical silicon-carbon materials in the area is obtained, wherein the method for observing the number of particles of the spherical silicon-carbon materials is SEM. The observation method of the number of particles of the spherical silicon-carbon materials with different particle sizes is that after the total number of particles is counted, the number of particles of the spherical silicon-carbon materials with different particle sizes is analyzed by software, the selection of the detection area is the same as the above method, which will not be described here.

[0051] By controlling the number of the spherical silicon-carbon materials and the number of the spherical silicon-carbon materials with different sizes, the present application can make the spherical silicon-carbon materials more uniformly distributed in the thickness direction of the negative plate, which is more conducive to dispersing the expansion of the spherical silicon-carbon material particles in the vertical and horizontal directions of the negative plate, thereby being conducive to improving the overall expansion problem of the battery; at the same time, the problem of demolding of the negative active coating of the negative plate can also be improved.

[0052] In an example, the mass content of the spherical silicon-carbon materials in the negative active coating is 5%-35%, 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%, 31%, 32%, 33%, 34% or 35%.

[0053] In an example, the oil absorption value of the spherical silicon-carbon material is 10 mL / 100 g-30 mL / 100 g, for example, 10 mL / 100 g, 11 mL / 100 g, 12 mL / 100 g, 13 mL / 100 g, 14 mL / 100 g, 15 mL / 100 g, 16 mL / 100 g, 17 mL / 100 g, 18 mL / 100 g, 19 mL / 100 g, 20 mL / 100 g, 21 mL / 100 g, 22 mL / 100 g, 23 mL / 100 g, 24 mL / 100 g, 25 mL / 100 g, 26 mL / 100 g, 27 mL / 100 g, 28 mL / 100 g, 29 mL / 100 g, or 30 mL / 100 g; the specific surface area of the spherical silicon-carbon material is 100 m 2 / g-150 m 2 / g, for example, 100 m 2 / g, 105 m 2 / g, 110 m 2 / g, 115 m 2 / g, 120 m 2 / g, 125 m 2 / g, 130 m 2 / g, 135 m 2 / g, 140 m 2 / g, 145 m 2 / g, or 150 m 2 / g. By controlling the oil absorption value of the spherical silicon-carbon material in this range, while controlling the specific surface area in this range, the present application can effectively improve the absorption of electrolyte by the spherical silicon-carbon material, ensure sufficient wetting of the surface of the spherical silicon-carbon material particles, reduce the solid-liquid transport impedance of the surface of the spherical silicon-carbon material, and improve the kinetic performance of the battery. Moreover, after improving the wettability of the surface of the spherical silicon-carbon material particles, the diffusion speed of lithium ions in the electrolyte will also be accelerated, reducing side reactions caused by excessive or insufficient local ion concentration, thereby improving the cycle performance of the battery; in addition, sufficient wetting helps the spherical silicon-carbon material particles to be subjected to more uniform expansion stress in all directions, thereby improving the expansion performance.

[0054] In one example, after 50 cycles, in the cross section of the negative electrode active coating along the width direction of the negative electrode current collector in the full state of the battery, the number of particle broken spherical silicon carbon materials in the area of 100 μm x thickness of the negative electrode active coating on one side obtained along the width direction of the negative electrode current collector accounts for 10-30%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30% of the total number of the spherical silicon carbon materials in the area, and the broken area of a single particle broken spherical silicon carbon material accounts for 5-25%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%. The particle broken spherical silicon carbon material refers to the spherical silicon carbon material with incomplete particles or cracks on the surface of the particles, and the broken area refers to the total of the area covered by the incomplete part of the particles and the area with cracks on the surface of the particles. The test method of the percentage of the number of particle broken spherical silicon carbon materials in the total number of the spherical silicon carbon materials in the area and the percentage of the broken area of a single particle broken spherical silicon carbon material can refer to the observation method of the number of particles of the spherical silicon carbon material. First, the cross-sectional electron microscope image of the negative electrode active material layer is obtained, and then the specific area to be tested (the area obtained along the width direction of the negative electrode current collector by 100 μm x thickness of the negative electrode active coating on one side) is color rendered by using the Image J software, that is, the particle broken spherical silicon carbon material and the particle unbroken spherical silicon carbon material can be distinguished, and then the percentage of the number of particle broken spherical silicon carbon materials in the total number of the spherical silicon carbon materials in the area (%) can be counted. In addition, the actual broken area and the unbroken area of the particle broken spherical silicon carbon material can be distinguished by color rendering by using the Image J software, and then the broken area of the particle broken spherical silicon carbon material can be obtained by software analysis, and the percentage of the broken area of a single particle broken spherical silicon carbon material can be calculated = broken area of a single particle broken spherical silicon carbon material / cross-sectional area of a single spherical silicon carbon material x 100%. It should be noted that since the observed electron microscope image is a cross-sectional electron microscope image, the broken area counted is only half of the broken area of a single spherical silicon carbon material, which is used to represent the percentage of the broken area of the whole particle broken spherical silicon carbon material. By controlling the number of broken spherical silicon carbon material particles and the broken area of a single broken spherical silicon carbon material, the present application can avoid the generation of more new interfaces when there are too many broken spherical silicon carbon material particles, increase the consumption of electrolyte and form a SEI film with greater impedance, and deteriorate the cycle life of the battery.

[0055] In an example, the electrolyte contains fluoroethylene carbonate (FEC), and the mass content of the fluoroethylene carbonate is 7% to 20%, for example, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, based on the total mass of the electrolyte. Adding a certain amount of FEC in the electrolyte helps to form an SEI film on the negative electrode surface, and also improves the stability of the SEI film on the negative electrode, thereby improving the cycle performance of the battery and prolonging the cycle life.

[0056] In an example, the electrolyte contains vinylene carbonate (VC), and the mass content B of the vinylene carbonate is 0.1% to 5%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, based on the total mass of the electrolyte. Containing VC in the electrolyte and the mass content range B of VC, B satisfies: 0.1% to 5%, is beneficial to improve the interface stability between the positive active material and the electrolyte, helps to reduce the decomposition of the electrolyte, forms a more stable SEI film, reduces the dissolution of transition metals in the positive electrode material, and further improves the cycle performance of the battery and prolongs the cycle life. Further, when the content B of VC is too small, it is not conducive to the film formation of the positive electrode, and cannot effectively inhibit the dissolution of transition metals in the positive active material, thereby damaging the SEI film of the negative electrode and reducing the cycle stability of the battery; and when the content B of VC is too much, it will cause excessive reaction of the negative active material, leading to rapid decomposition of the electrolyte, and the decomposition will release gas, increasing the internal pressure of the battery. If these gases cannot be released in time, it may cause the battery to swell or thermal runaway, and in severe cases, it may cause a fire or explosion, affecting the safety performance of the battery. Therefore, by controlling the mass content B of vinylene carbonate in a suitable range, the cycle performance of the battery can be improved while avoiding safety problems.

[0057] In an example, the sphericity of the spherical silicon-carbon material is S, the mass content of the vinylene carbonate in the electrolyte is B, and S, B satisfy 0.2≤S / B≤8, wherein S is 0.6-1, for example, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or 1. When the sphericity of the spherical silicon-carbon material and the content B of the VC are simultaneously regulated to satisfy 0.2≤S / B≤8, the expansion of the negative electrode sheet and the cycle performance of the battery can be improved. This is because the more perfect the spherical structure of the spherical silicon-carbon material is, the more uniform the stress distribution will be when the stress is applied, thereby better relieving the expansion of the negative electrode. At the same time, the performance of forming a film on the positive electrode by using VC can reduce the harm of transition metal dissolution of the positive electrode material to the SEI film of the negative electrode, thereby improving the stability of the SEI film of the negative electrode, and further maintaining the structural integrity of the silicon-containing negative electrode. In general, the spherical silicon-carbon material has improved expansion uniformity, the frequency of negative electrode SEI film rupture and repair is reduced, and the harm of transition metal dissolution to the negative electrode SEI film is reduced, which is beneficial to improving the expansion and cycle of the negative electrode sheet at the same time. In addition, the addition of VC improves the film forming stability of the positive electrode material, thereby improving the cycle performance and cycle life of the battery as a whole.

[0058] In an example, the sphericity S of the spherical silicon-carbon material is 0.7-0.95.

[0059] In an example, the positive electrode sheet comprises a positive electrode active coating layer, and the positive electrode active coating layer comprises a positive electrode active material, wherein the positive electrode active material comprises a material with a chemical formula of Li a Ni x Co y Mn z M k O2, 0.9≤a≤1.1 (0.9, 0.95, 1, 1.05, 1.1 or 1.11), 0.6≤x≤0.95 (0.6, 0.65, 0.7, 0.71, 0.8, 0.85, 0.9 or 0.95), 0<y≤0.2 (0.01, 0.05, 0.1, 0.15 or 0.2), 0<z≤0.2 (0.01, 0.05, 0.1, 0.15 or 0.2), 0≤k≤0.05 (0, 0.01, 0.02, 0.03, 0.04 or 0.05), and M is selected from at least one of Al, Zr, Mg, Y, Ti, B, Sr, W, Si, La and Nb. The positive electrode active material of the present application can comprise the above-mentioned doping element M, and the stability of the positive electrode active material can be further improved by doping the M element, thereby improving the cycle performance of the battery.

[0060] In an example, the total content of Al element, Mg element and Zr element in the positive active coating ranges from 1000 ppm to 7000 ppm, for example, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm or 7000 ppm. Further, the doping of Al, Mg and Zr elements is beneficial to improve the ionic conductivity, reduce the migration resistance of the positive active material, avoid the generation of lithium precipitation on the surface of the electrode plate, and improve the cycle life of the lithium ion battery. However, the total content of Al element, Mg element and Zr element should not be too high, otherwise it will cause harm to the negative SEI film and affect the cycle life of the negative active material. The mass content of Al element, Mg element and Zr element in the positive active coating can be measured by ICP method (inductively coupled plasma method), and the specific method is as follows: the battery of the application is discharged to 3.0V and disassembled, and the positive active coating obtained by disassembly is subjected to ICP element content detection, so as to obtain the content of each element in the positive active coating.

[0061] In an example, the chemical formula is Li a Ni x Co y Mn z M k O2 includes single crystal materials and polycrystalline materials, and the mass content of the single crystal materials accounts for 0% to 100%, for example, 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%. The higher the proportion of single crystal materials, the better the structural stability of the positive electrode material on the positive electrode side, and the further improved cycle life of the battery.

[0062] In an example, the mass content of the single crystal materials accounts for 50% to 80%.

[0063] In an example, the mass content of the Ni element included in the single crystal material accounts for 85% to 99%, for example, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%. By controlling the mass content of the Ni element included in the single crystal material to account for 85% to 99%, the energy density of the positive active material is improved, and the cycle life of the battery cell is improved.

[0064] In one example, after 10T cycles, the content of Ni element in the negative active coating is 2%-7%, for example, 2%, 3%, 4%, 5%, 6% or 7%, and the content of Mn element in the negative active coating is 0.5%-5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%. The mass content of Ni element and Mn element in the negative active coating can also be measured by ICP method (inductively coupled plasma method), and the specific method is as follows: after the battery completes 50 complete charge and discharge cycles according to the above specific operation steps of the first charge and discharge of the battery of the application, it is discharged to 3.0V and disassembled, and the negative active coating obtained by disassembly is subjected to ICP element content detection, so as to obtain the content of each element in the negative active coating. The Ni element and Mn element in the negative active coating come from the transition metal elements in the positive active material which migrate to the negative electrode and participate in the generation process of SEI on the surface of the negative active material during the charge and discharge process; by controlling the element content of Ni element and Mn element in the active coating, the stability of the negative SEI can be further improved, the damage of SEI during the cycle process can be reduced, and the generation of new SEI can be avoided, the consumption of electrolyte by the negative electrode film formation is reduced, and the cycle life of the lithium battery is further improved.

[0065] The application will be described in detail below through examples. The examples described in the application are only part of the examples of the application, not all examples. Based on the examples in the application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0066] In the following examples, the materials used are commercially available analytical pure unless otherwise specified.

[0067] The following examples are used to illustrate the application.

[0068] Example 1

[0069] Prepared according to the following method:

[0070] (1) Preparation of positive electrode sheet

[0071] The ternary material powder (chemical formula LiNi 0.9 Co 0.01 Mn 0.1 M 0.02O2, the mass content ratio of single crystal material in the ternary material is 60%, and the mass content ratio of Ni element in the single crystal material is 90%), polyvinylidene fluoride, acetylene black, and carbon nanotubes are put into a vacuum stirrer in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) is added, and they are fully mixed under the action of the vacuum stirrer until a uniform and flowable positive electrode active coating slurry is formed; the positive electrode active coating slurry is uniformly coated on an aluminum foil, dried, rolled, slitted, and punched to obtain the positive electrode sheet of Example 1.

[0072] (2) Preparation of the negative electrode sheet

[0073] Preparation of the negative electrode active coating slurry

[0074] Artificial graphite, spherical silicon-carbon material (particle size Dv50, D=10 μm, Dv10=5 μm, Dv90=15 μm; oil absorption value of the spherical silicon-carbon material is 15 mL / 100 g; specific surface area of the spherical silicon-carbon material is 122 m 2 / g; sphericity S of the spherical silicon-carbon material is 0.9), styrene-butadiene rubber (SBR), lithiumated polyacrylic acid (PAA), and acetylene black are put into a vacuum stirrer in a mass ratio of 86.5:10:1:1:1.5, deionized water is added, and they are fully mixed under the action of the vacuum stirrer to finally form a uniform and flowable negative electrode active coating slurry;

[0075] Preparation of the conductive primer coating slurry

[0076] Conductive carbon black, styrene-butadiene rubber (SBR), thiourea, and CMC-Li are put into a vacuum stirrer in a mass ratio of 25:64.7:0.3:10, and they are fully mixed under the action of the vacuum stirrer to finally form a uniform and flowable conductive primer coating slurry;

[0077] The conductive primer coating slurry is uniformly coated on a copper foil with a thickness of 8 μm (H0=8 μm), wherein the conductive primer coating slurry is coated on both sides of the copper foil, the coating thickness of the conductive primer coating on one side is 2.4 μm (H1=2.4 μm), then drying is performed, after drying, the negative electrode active coating slurry is uniformly coated on the surfaces of the conductive primer coatings on both sides, the coating thickness of the negative electrode active coating on one side is 35 μm (H2=35 μm), then drying, rolling, and die cutting are performed to obtain the negative electrode sheet of Example 1.

[0078] The peeling force between the conductive primer coating and the negative current collector is 30 gf, the tensile strength A of the negative current collector is 500 MPa, and the porosity P of the negative electrode sheet is 23%;

[0079] The particle size Dv10 of the spherical silicon-carbon material is measured to be 5 μm, and the particle size Dv90 of the spherical silicon-carbon material is measured to be 15 μm;

[0080] In the cross section of the negative electrode active coating on one side along the width direction of the negative electrode current collector, the number of spherical silicon-carbon materials in the area of any 100 μm x single-side negative electrode active coating thickness along the width direction of the negative electrode current collector is measured to be 5, wherein the number of spherical silicon-carbon materials with a particle size Dv10 of 4 μm-6 μm is 2, the number of spherical silicon-carbon materials with a particle size Dv50 of 6 μm-15 μm is 2, and the number of spherical silicon-carbon materials with a particle size Dv90 of 13 μm-20 μm is 1; the number of particle-damaged spherical silicon-carbon materials accounts for 20% of the total number of spherical silicon-carbon materials in the area, and the damaged area of a single particle-damaged spherical silicon-carbon material accounts for 8%.

[0081] (3) Preparation of electrolyte

[0082] In an argon glove box with a water content <0.1 ppm and an oxygen content <0.1 ppm, fluoroethylene carbonate (FEC), PC, PP, and EP are mixed uniformly at a mass ratio of 15:25:30:10, and fully dried lithium hexafluorophosphate (LiPF6) is added and stirred to dissolve, the mass of LiPF6 added is 16.5% of the total mass of the electrolyte, 3.5% of the total mass of the electrolyte is added as vinylene carbonate (VC), and the mixture is stirred uniformly. After passing the physical property test, the electrolyte of Example 1 is obtained.

[0083] (4) Preparation of battery

[0084] The positive electrode sheet obtained in step (1), the negative electrode sheet obtained in step (2), and the separator film (PP) are obtained in a winding manner to obtain a bare battery cell; the electrolyte prepared in step (3) is injected into the dry qualified battery cell, and after standing, aging, formation, exhaust, aging, and sorting processes, a battery is obtained.

[0085] The total content of Al, Mg, and Zr elements in the positive electrode active coating of the obtained battery is measured to be 6100 ppm; after 10T cycles, the battery is disassembled after discharging to 3.0V, the content of Ni element in the negative electrode active coating is 5%, and the content of Mn element in the negative electrode active coating is 2%.

[0086] Example 2 group

[0087] The preparation method of the battery in this group of examples is referred to Example 1, the only difference is that the thickness H1 of the conductive primer coating is changed, see Tables 1-3 for details.

[0088] Example 3 group

[0089] The preparation method of the battery in this group of examples refers to Example 1, the only difference is that the thickness H2 of the negative electrode active coating is changed, see Table 1-3 for details.

[0090] Example 4 group

[0091] The preparation method of the battery in this group of examples refers to Example 1, the only difference is that the thickness H2 of the negative electrode active coating is changed, see Table 1-3 for details.

[0092] Example 4-1, particle size Dv50, D = 6 μm, Dv10 = 4 μm, Dv90 = 13 μm;

[0093] Example 4-2, particle size Dv50, D = 15 μm, Dv10 = 6 μm, Dv90 = 20 μm;

[0094] See Table 1-3 for details.

[0095] Comparative Example 1 group

[0096] The preparation method of the battery in this group of examples refers to Example 1, the only difference is that the thickness H2 of the negative electrode active coating is changed, see Table 1-3 for details.

[0097] Comparative Example 2 group

[0098] The preparation method of the battery in this group of examples refers to Example 1, the only difference is that the thickness H2 of the negative electrode active coating is changed, see Table 1-3 for details.

[0099] Comparative Example 2-1, particle size Dv50, D = 5 μm, Dv10 = 3 μm, Dv90 = 12 μm;

[0100] Comparative Example 2-2, particle size Dv50, D = 17 μm, Dv10 = 7 μm, Dv90 = 22 μm;

[0101] See Table 1-3 for details.

[0102] Comparative Example 3

[0103] The preparation method of the battery in this group of examples refers to Example 1, the only difference is that the thickness H2 of the negative electrode active coating is changed, see Table 1-3 for details.

[0104] Example 5 group

[0105] The preparation method of the battery in this group of examples refers to Example 1, the only difference is that the thickness H2 of the negative electrode active coating is changed, see Table 1-3 for details.

[0106] Example 6 group

[0107] The preparation method of the battery in this group of examples is referred to Example 1, the only difference is that the sphericity S of the spherical silicon-carbon material is changed, see Tables 1-3 for details.

[0108] Test Example 1

[0109] The batteries prepared in each of the above examples and comparative examples are prepared, and several batteries are prepared for each example / comparative example, and then the several batteries prepared in each group of examples / comparative examples are divided into three batches, the first batch is subjected to first charge-discharge, and then the thickness parameters (including H0, H1, H2) in the negative electrode sheet under full charge state are measured, which are the average values of the test results of all batteries in the same batch; the second batch is subjected to 50T cycles, and then the thickness parameters (including H0, H1, H2) in the negative electrode sheet under full charge state are measured, which are also the average values; the third batch is subjected to 200T cycles, and then the thickness parameters (including H0, H1, H2) in the negative electrode sheet under full charge state are measured, which are also the average values. All test results are recorded in Tables 1-3.

[0110] Table 1

[0111]

[0112] D / (H0+H1+H2) in Table 1 首充 represents the relationship between the thickness parameters in the negative electrode sheet under full charge state after the first charge-discharge of the above first batch of batteries and the particle size Dv50 of the spherical silicon-carbon material, D / (H0+H1+H2) 50T , D / (H0+H1+H2) 200T Similarly, D / (H0+H1+H2) and D / (H0+H1+H2) respectively represent the relationship between the thickness parameters in the negative electrode sheet under full charge state after 50 times and 200 times charge-discharge of the above second and third batches of batteries and the particle size Dv50 of the spherical silicon-carbon material. It should be noted that the thickness H0+H1+H2 of the electrode sheet and the particle size Dv50 of the spherical silicon-carbon material will change with the increasing number of cycles, the thickness of the electrode sheet will thicken, and the particle size of the spherical silicon-carbon material will increase, and the thickness and particle size after the first charge-discharge will also be different from the thickness and particle size of the electrode sheet and the spherical silicon-carbon material set during battery preparation, therefore, when the formula D / (H0+H1+H2) 首充 , D / (H0+H1+H2) 50T and D / (H0+H1+H2) 200T are substituted, attention should be paid to the thickness (H0+H1+H2) of the electrode sheet and the corresponding particle size Dv50 of the spherical silicon-carbon material of the same cycle.

[0113] Table 2

[0114]

[0115] Table 3

[0116]

[0117]

[0118] Test Example 2

[0119] (1) Lithium precipitation test on the surface of the negative electrode

[0120] The observation method of the lithium precipitation on the surface of the negative electrode is as follows: the batteries obtained in the above examples and comparative examples are first subjected to constant current discharge at 25°C ± 2°C, 0.2C discharge to the lower limit voltage, and stand for 5 min; then constant current constant voltage charging, 0.5C charging to the upper limit voltage, cutoff 0.025C, stand for 10 min, 0.2C discharge to the lower limit voltage, and then repeat the charging and discharging cycle process 800T, after which the battery is fully charged, the battery cell is disassembled in a dry environment, and the lithium precipitation on the surface of the negative electrode is observed, as shown in Figure 2 , which is a schematic diagram of the lithium precipitation on the surface of the negative electrode after the battery is disassembled. The degree of lithium precipitation is divided into four grades: no lithium precipitation, slight lithium precipitation at the edge, lithium precipitation at the edge, and severe lithium precipitation at the edge. No lithium precipitation means that no gray or silver lithium is produced on the surface of the negative electrode, such as Example 1 in Figure 2 ; slight lithium precipitation at the edge means that lithium precipitation appears as a line on the edge of the negative electrode, the lithium precipitation area accounts for less than 10% of the area of the negative electrode, and appears gray; lithium precipitation at the edge means that the lithium precipitation area has spread to the center of the negative electrode on the basis of slight lithium precipitation at the edge, the lithium precipitation area accounts for 10-30% of the area of the negative electrode, and also appears gray; severe lithium precipitation at the edge means that the lithium precipitation has spread to the center of the negative electrode on the basis of lithium precipitation at the edge, the lithium precipitation area accounts for more than 30% of the area of the negative electrode, and the lithium precipitated at the edge appears silver, such as Comparative Example 3 in Figure 2 .

[0121] (2) Cycle capacity retention rate and cycle expansion rate test of the battery

[0122] The cycle capacity retention rate and cycle expansion rate of the batteries obtained in the examples and comparative examples are tested, and the specific test method is as follows: before testing, the thickness M0 of the full battery cell is first measured; at 25°C, constant current charging is performed at a charge rate of 2C to 4.53V, and the cutoff current is 0.05C, then discharging is performed at a discharge rate of 1C to 3.0V; cycle according to the foregoing charging and discharging mechanism, the number of cycles is 800, and then the battery is fully charged, the battery cell is taken out, and the thickness M1 of the battery cell at full charge is tested again after standing at room temperature for 1h;

[0123] The discharge capacity of the last cycle is divided by the first discharge capacity to obtain the 800T cycle capacity retention rate of the battery, which is recorded in Table 4.

[0124] The expansion rate of the battery after 800 cycles is calculated according to the following formula: battery cycle 800T expansion rate (%) = (M1-M0) / M0*100%, which is recorded in Table 4.

[0125] The test results are recorded in Table 4.

[0126] Table 4

[0127]

[0128] In Example 2, the thickness H1 of the conductive undercoat layer is changed. When H1 is close to 0.1H0, the thickness of the conductive undercoat layer becomes lower, which can cause the utilization rate of the underlayer active material to decrease, resulting in slight lithium precipitation at the edge of the negative electrode sheet in the later cycle stage, as shown in Example 2-3. When H1 is close to 0.9H0, the thickness of the conductive undercoat layer becomes thicker, which can cause the load of the negative electrode active material to decrease, the cycle capacity retention rate to decrease, and the expansion rate to increase, as shown in Example 2-4. In contrast, if H1 is less than 0.1H0, the thickness of the conductive undercoat layer is too thin, and the lithium precipitation problem at the edge of the negative electrode will be exacerbated, as shown in Comparative Example 1-1. If H1 is greater than 0.9H0, the thickness of the conductive undercoat layer is too thick, and the impact on the cycle capacity retention rate and the expansion rate of the battery will also be greater, as shown in Comparative Example 1-2.

[0129] According to Example 1, Example 2-4 group, Comparative Example 2-1, 2-2, controlling the value of D / (H0+H1+H2) within the above range after the first charge-discharge, 50 cycles and 200 cycles can solve the expansion problem in the later cycle stage caused by the setting of the conductive undercoat layer, ensure the effective utilization of the underlayer active material, improve the lithium precipitation problem at the negative electrode surface in the later cycle stage, and further improve the cycle performance of the battery, effectively improve the cycle life and cycle expansion of the battery, and prolong the service life of the battery.

[0130] Comparative Example 3 does not set the conductive undercoat layer, and the lithium precipitation problem at the edge of the negative electrode sheet in the later cycle stage will be even more serious. The utilization rate of the underlayer active material is not high, and the cycle performance and expansion problem will also be affected by the charge-discharge of the battery, which seriously affects the service life of the lithium ion battery.

[0131] Compared with Example 1, Example 5-1: the mass content B of vinylene carbonate in the electrolyte is too small, and S / B is too large, which is not conducive to the film formation of the positive electrode, and cannot effectively inhibit the dissolution of transition metals in the positive electrode active material, thereby damaging the negative electrode SEI film and reducing the cycle stability of the battery; compared with Example 1, Example 5-2: the mass content B of vinylene carbonate in the electrolyte is too large, and S / B is too small, which will cause excessive reaction of the negative electrode active material, and the battery will expand and become larger. In addition, as can be seen from the comparison between Example 6-1 and Example 1, the sphericity of the spherical silicon-carbon material particles is too low, which will cause the frequency of the rupture and repair of the SEI film formed by vinylene carbonate in the negative electrode to rise, S / B is too small, and it is also not conducive to improving the expansion and cycle of the battery at the same time.

[0132] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A battery, characterized by, The battery comprises a negative electrode sheet, a positive electrode sheet and an electrolyte, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer located on at least one side surface of the negative electrode current collector; an electrically conductive primer layer is arranged between the negative electrode active coating layer and the negative electrode current collector; The negative electrode active coating layer comprises a negative electrode active material, and the negative electrode active material comprises a spherical silicon-carbon material, and the particle size Dv50 of the spherical silicon-carbon material is D; The thickness of the negative electrode current collector is H0, the thickness of the electrically conductive primer layer is H1, and the H0 and H1 satisfy 0.1H0≤H1≤0.9H0; After the first charge-discharge, in the battery in the full charge state, the H0, H1, H2 and D satisfy 0.20≤D / (H0+H1+H2)≤0.28, wherein H2 is the thickness of the negative electrode active coating layer; wherein the specific operation steps of the first charge-discharge of the battery are as follows: using a blue test device to perform the first charge-discharge on the battery, using 2C constant current and constant voltage to charge the battery to 4.53V, and the current cutoff is 0.05C; then discharging at 1C to 3.0V, completing the first charge-discharge, that is, one complete charge-discharge cycle; then charging to 4.53V at 1C constant current and constant voltage, and the current cutoff is 0.05C, and the battery is in the full charge state, that is, the subsequent test can be performed.

2. The battery of claim 1, wherein, 0.2H0≤H1≤0.6H0; And / or, after 50T cycles, in the battery in the full charge state, the H0, H1, H2 and D satisfy 0.1≤D / (H0+H1+H2)≤0.2, wherein the battery in the full charge state after 50T cycles refers to that, after completing 50 complete charge-discharge cycles according to the specific operation steps of the first charge-discharge of the battery, the battery is charged to 4.53V at 1C constant current and constant voltage, and the current cutoff is 0.05C, and the battery is in the full charge state; And / or, after 200T cycles, in the battery in the full charge state, the H0, H1, H2 and D satisfy 0.05≤D / (H0+H1+H2)≤0.18, wherein the battery in the full charge state after 200T cycles refers to that, after completing 200 complete charge-discharge cycles according to the specific operation steps of the first charge-discharge of the battery, the battery is charged to 4.53V at 1C constant current and constant voltage, and the current cutoff is 0.05C, and the battery is in the full charge state.

3. The battery according to claim 1 or 2, characterized in that, The electrically conductive primer layer comprises an electrically conductive agent, a binder, a leveling agent and a thickening agent, wherein The electrically conductive agent comprises at least one of electrically conductive carbon black, single-walled electrically conductive carbon tube, multi-walled electrically conductive carbon tube and graphene; The binder comprises at least one of butadiene styrene rubber, PAA, polyacrylic acid and PVDF; The leveling agent comprises thiourea; The thickening agent comprises at least one of CMC and CMC-Li; The mass ratio among the electrically conductive agent, the binder, the leveling agent and the thickening agent is (10%-25%):(40%-70%):(0.2%-0.5%):(5%-15%).

4. The battery according to claim 1 or 2, characterized by The peeling force between the conductive primer layer and the negative current collector is 10 gf-55 gf; And / or, the tensile strength of the negative current collector is A, the thickness H1 of the conductive primer layer and the tensile strength A of the negative current collector satisfy 0.002A≤H1≤0.007A, wherein A is 400MPa-950MPa; And / or, the porosity of the negative sheet is P, the thickness H of the negative sheet and the porosity P of the negative sheet satisfy 1.7≤H / P≤2.1, wherein P is 23%-48%.

5. The battery according to claim 1 or 2, characterized by The particle size Dv10 of the spherical silicon-carbon material is 4μm-6μm, the particle size Dv50 of the spherical silicon-carbon material is 6μm-15μm, and the particle size Dv90 of the spherical silicon-carbon material is 13μm-20μm; And / or, in the cross section of the negative active coating on one side along the width direction of the negative current collector, the number of the spherical silicon-carbon material in any 100μm×single side thickness of the negative active coating along the width direction of the negative current collector is 3-10, wherein the number of the spherical silicon-carbon material with particle size Dv10 of 4μm-6μm is 3-6, the number of the spherical silicon-carbon material with particle size Dv50 of 6μm-15μm is 2-4, and the number of the spherical silicon-carbon material with particle size Dv90 of 13μm-20μm is 1-3.

6. The battery according to claim 1 or 2, characterized by The mass content of the spherical silicon-carbon material in the negative active coating is 5%-35%; and / or the oil absorption value of the spherical silicon-carbon material is 10 mL / 100 g-30 mL / 100 g, and the specific surface area of the spherical silicon-carbon material is 100 m 2 / g-150 m 2 / g.

7. The battery according to claim 1 or 2, characterized by After 50T cycles, in the cross section of the negative active coating on one side along the width direction of the negative current collector in the battery under full charge state, the number of particle-damaged spherical silicon-carbon material in any 100μm×single side thickness of the negative active coating along the width direction of the negative current collector accounts for 10%-30% of the total number of the spherical silicon-carbon material in the area, and the damage area ratio of a single particle-damaged spherical silicon-carbon material is 5%-25%.

8. The battery of claim 1, wherein, The electrolyte contains fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate in the electrolyte is 7%-20% based on the total mass of the electrolyte; And / or, the electrolyte contains vinylene carbonate, and the mass content B of the vinylene carbonate in the electrolyte is 0.1%-5% based on the total mass of the electrolyte; And / or, the sphericity of the spherical silicon-carbon material is S, the mass content of the vinylene carbonate in the electrolyte is B, and S / B satisfies 0.2≤S / B≤8, wherein S is 0.6-1.

9. The battery of claim 1, wherein, The positive electrode sheet includes a positive electrode active coating layer containing a positive electrode active material including a substance of a chemical formula of Li a Ni x Co y Mn z M k O2, 0.9≤a≤1.1, 0.6≤x≤0.95, 0<y≤0.2, 0<z≤0.2, 0≤k≤0.05, M is selected from at least one of Al, Zr, Mg, Y, Ti, B, Sr, W, Si, La, and Nb.

10. The battery of claim 9, wherein, The total content of Al, Mg and Zr elements in the positive active coating ranges from 1000ppm to 7000ppm; and / or, the chemical formula is Li a Ni x Co y Mn z M k The substance containing O2 includes single crystal material and polycrystalline material, the mass content of the single crystal material accounts for 0-100%; the mass content of the Ni element included in the single crystal material accounts for 85-99%. And / or, after 10T cycles, the content of Ni element in the negative active coating is 2%-7% and the content of Mn element in the negative active coating is 0.5%-5% when discharged to 3.0V.

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