A negative electrode sheet and a battery

Abstract

The application provides a negative electrode sheet and a battery, the negative electrode sheet comprising a current collector and an active material layer located on at least one side surface of the current collector, the active material layer comprising a first coating layer close to the surface of the current collector and a second coating layer away from the surface of the current collector; the first coating layer comprising first graphite particles and second graphite particles; the second coating layer comprising third graphite particles and silicon-carbon particles; and the surface of the active material layer being provided with a plurality of recesses. The negative electrode sheet of the application can inhibit the expansion problem of the silicon-based material mixed with the graphite negative electrode and the lithium precipitation problem, thereby significantly improving the cycle performance and rate performance of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a negative electrode sheet and a battery. BACKGROUND

[0002] With the increasing demand for energy density of lithium batteries, silicon-carbon material mixed graphite negative electrode as a potential alternative material has attracted attention. However, silicon-carbon material mixed graphite negative electrode faces two major problems: large expansion and easy lithium precipitation. Large expansion: silicon-containing particles will undergo severe volume expansion and contraction during lithium extraction and insertion, which can easily cause the twisting of graphite particles, resulting in the swelling and deformation of lithium ion batteries, affecting the cycle life and safety of the battery. Easy lithium precipitation: silicon-based negative electrode material is prone to lithium precipitation during charging due to slow kinetics, which can easily lead to a decrease in battery capacity. The above problems seriously limit the wide application of silicon-carbon material mixed graphite negative electrode in the field of lithium batteries. SUMMARY

[0003] Based on the above problems, the present application proposes a double-layer coated negative electrode sheet, which can inhibit the expansion and lithium precipitation problems of silicon-carbon material mixed graphite negative electrode by adjusting the spatial position of silicon-carbon particles and the particle size of upper and lower graphite particles, thereby significantly improving the cycle performance and rate performance of lithium ion batteries.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0005] The first aspect of the present application provides a negative electrode sheet, comprising a current collector and an active material layer located on at least one side surface of the current collector, the active material layer comprising a first coating layer close to the surface of the current collector and a second coating layer away from the surface of the current collector.

[0006] The first coating layer comprises first graphite particles and second graphite particles, the particle size Dv150 of the first graphite particles being 5-12 μm, the particle size Dv250 of the second graphite particles being 10-16 μm, and the particle size Dv250 of the second graphite particles being greater than the particle size Dv150 of the first graphite particles.

[0007] The second coating layer comprises third graphite particles and silicon-carbon particles, the particle size Dv350 of the third graphite particles being 4-11 μm, and the particle size Dv450 of the silicon-carbon particles being 5-12 μm.

[0008] The surface of the active material layer is provided with a plurality of recesses.

[0009] The second aspect of the present application provides a battery, comprising a negative electrode sheet and a separator, the negative electrode sheet being the negative electrode sheet of the first aspect of the present application.

[0010] Preferably, the adhesion of the negative electrode sheet to the separator is 0.284 N to 0.428 N.

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

[0012] (1) The negative electrode sheet provided by the present application can inhibit the expansion of the underlying graphite particles by allowing the silicon-carbon particles on the surface layer of the coating to expand first during charging, thereby inhibiting the overall battery expansion phenomenon, reducing the stress impact on the battery structure, and improving the cycle life of the battery.

[0013] (2) The negative electrode sheet provided by the present application can reduce lithium precipitation of silicon-carbon materials during charging and discharging by placing small-particle-size fast-charging graphite particles on the surface layer of the coating, thereby improving the stability and predictability of battery capacity.

[0014] (3) The negative electrode sheet provided by the present application helps to improve the energy density of lithium batteries by optimizing the spatial position of silicon-carbon particles and the size of graphite particles in the upper and lower coatings, thereby meeting the demand for high-energy-density batteries in modern electronic products.

[0015] (4) The active material layer on the surface of the negative electrode sheet provided by the present application is provided with a plurality of recesses, which can further solve the problem of lithium precipitation of silicon-doped negative electrode sheets.

[0016] 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 to include any and all expressed values between the end points, whether or not modifying language is used. For example, if the stated range is 1-5, the range can encompass discrete values such as 2, 3, and 4, as well as all ranges and sub-ranges beginning with a minimum of 1 up to a maximum of 5, e.g., 1-5, 1.1-5, 1.2-5, 1.3-5, 1.4-5, 1.5-5, 1.6-5, 1.7-5, 1.8-5, 1.9-5, 2-5, 3-5, 4-5, 5-5, 0.1-5.9, 0.2-5.8, 0.3-5.7, 0.4-5.6, 0.5-5.5, 0.6-5.4, 0.7-5.3, 0.8-5.2, 0.9-5.1, 1-5, 2-4, 3-4, 4-5, 5-5, 1-5.1, 2-4.2, 3-4.3, 4-4.4, 5-5.5, and so forth. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Structure diagram of the negative electrode sheet provided by an embodiment of the present application.

[0018] Figure 2 Partial enlarged view of the negative electrode sheet in an example provided by the present application.

[0019] REFERENCE NUMERALS

[0020] Current collector-1, first coating-2, second coating-3, transition layer-4, recess-5. DETAILED DESCRIPTION

[0021] 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.

[0022] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "at least one of" or "one or more of" can mean any combination of the listed terms. For example, if a list of items includes A, B, and C, then "at least one of A, B, and C" or "one or more of A, B, or C" can mean A alone; B alone; C alone; A and B together; A and C together; B and C together; or A, B, and C together. The item A can include an individual element or a combination of elements. The item B can include an individual element or a combination of elements. The item C can include an individual element or a combination of elements.

[0023] A first aspect of the present application provides a negative electrode sheet, comprising a current collector and an active material layer on at least one side surface of the current collector, wherein the active material layer comprises a first coating layer close to the surface of the current collector and a second coating layer away from the surface of the current collector. Figure 1 As shown in the structural schematic diagram of the negative electrode sheet provided by the present application, the negative electrode sheet comprises a current collector 1 and an active material layer on at least one side surface of the current collector 1, wherein the active material layer comprises a first coating layer 2 close to the surface of the current collector 1 and a second coating layer 3 away from the surface of the current collector 1.

[0024] In the present application, the first coating layer comprises first graphite particles and second graphite particles, and the particle size Dv250 of the second graphite particles is greater than the particle size Dv150 of the first graphite particles.

[0025] In the present application, the particle size Dv150 of the first graphite particles is 5 μm-12 μm, and the particle size Dv150 of the first graphite particles can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, or 12 μm, for example.

[0026] In the present application, the particle size Dv250 of the second graphite particles is 10 μm-16 μm, and the particle size Dv250 of the second graphite particles can be 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, or 16 μm, for example.

[0027] In the present application, the second coating layer comprises third graphite particles and silicon-carbon particles, the particle size Dv350 of the third graphite particles is 4-11 μm, and the particle size Dv350 of the third graphite particles may be 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, for example.

[0028] In the present application, the second coating layer comprises third graphite particles and silicon-carbon particles, the particle size Dv450 of the silicon-carbon particles is 5-12 μm, and the particle size Dv450 of the silicon-carbon particles may be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, for example.

[0029] The negative electrode sheet provided by the present application can inhibit the expansion of the underlying graphite particles by allowing the silicon-carbon particles to expand first during charging, thereby inhibiting the expansion of the overall battery, reducing the stress on the battery structure, and improving the cycle life of the battery.

[0030] Further, if the particle size of the graphite particles in the active material layer is too small, it may cause more serious side reactions, thereby affecting the cycle life of the battery; if the particle size of the graphite particles is too large, the solid-phase diffusion kinetics during charging and discharging is poor, which may affect the rate charging and discharging capacity of the battery; therefore, the present application uses graphite particles of different particle sizes in the first coating layer near the current collector, i.e., the active material of the first coating layer comprises both small-particle first graphite particles and large-particle second graphite particles, so that the cycle life and rate charging and discharging capacity of the battery can be considered, in addition, the small-particle first graphite particles can be dispersed in the gaps formed by the large-particle second graphite particles, which can provide a buffer for the cycle expansion of the small-particle first graphite particles in the later cycle stage, and can also provide a buffer for the expansion of the silicon-carbon particles in the second coating layer, which is further conducive to relieving the expansion of the overall battery and improving the cycle stability of the battery.

[0031] Further, since the reaction kinetics of the silicon-carbon particles is poorer than that of the graphite particles, the use of smaller silicon-carbon particles mixed with small third graphite particles to form the second coating layer can optimize the fast-charging kinetics of the surface layer of the active material layer to some extent, thereby ensuring that the battery meets the technical requirements for fast charging, reducing the lithium precipitation of the silicon-carbon material during charging and discharging, greatly optimizing the risk of lithium precipitation, and thereby improving the stability and predictability of the battery capacity.

[0032] In summary, the negative electrode sheet provided by the present application avoids the expansion problem of the silicon-carbon material mixed with the graphite negative electrode by optimizing the spatial position of the silicon-carbon particles and the size of the graphite particles in the upper and lower coating layers, thereby helping to improve the energy density of the lithium battery and meeting the demand for high-energy-density batteries of modern electronic products; moreover, the fast-charging kinetics of the surface layer of the active material layer is improved, thereby greatly optimizing the risk of lithium precipitation, reducing the lithium precipitation of the silicon-carbon material during charging and discharging, and thereby significantly improving the cycle performance and rate performance of the lithium ion battery.

[0033] The particle size Dv50 of each particle can be obtained by testing the particles with a particle size tester and then taking the average value, and the particle size Dv50 is the particle size of the particles accounting for 50% of the volume distribution, and the testing method is as follows: using a Malvern MS3000 particle size tester to test, and the testing conditions of the particle size tester are as follows: refractive index 2.1, absorption rate 1.0, shading degree 8-12%, dispersing agent water (or ethanol), stirring rate 2500 rpm, testing 3 times according to the above steps, and taking the average value of the 3 results to obtain the particle size Dv50 of each particle.

[0034] In addition, according to the negative electrode sheet of the present application, the surface of the active material layer is provided with a plurality of recesses. Figure 1 As shown in the figure, the surface of the active material layer is provided with a plurality of recesses, which can include holes, grooves, etc. The recess structure is generally obtained by treating the surface of the active material layer by laser wire technology, which is a technology for manufacturing micro grooves on the active material layer on the surface of the negative electrode sheet, mainly used in the production of lithium batteries. This technology can effectively improve the performance of the battery and increase the charging and discharging efficiency and cycle life of the battery.

[0035] Therefore, the present invention utilizes laser marking technology to process the active material layer on the surface of the negative electrode sheet, so that a number of recessed structures are formed on the active material layer, and specific lithium ion transmission channels can be formed in the active material layer of the negative electrode sheet. These channels contribute to the rapid transmission of lithium ions and increase the migration number of lithium ions, thereby avoiding the accumulation and precipitation of ions, and further improving the lithium precipitation problem of the silicon-doped negative electrode sheet; moreover, when a number of recessed portions are provided on the surface of the active material layer, expansion sites and expansion space can also be provided for the expansion of the active material particles in the first coating or the second coating, thereby further improving the expansion problem of the silicon-carbon material-doped negative electrode sheet and improving the cycle stability of the lithium-ion battery.

[0036] In order to further enhance the performance improvement brought about by the particle size settings of the above-mentioned coatings, according to the negative electrode sheet of the present invention, based on the total mass of the first coating, the mass ratio of the first graphite particles to the second graphite particles is (8-12):(88-92); illustratively, the mass ratio of the first graphite particles to the second graphite particles can be 8:92, 9:91, 10:90, 11:89, 12:88, and the sum of the previous and subsequent values ​​is 100. When the mass ratio of two graphite particles of different sizes exceeds this range, it may lead to violent side reactions inside the battery during long cycles, resulting in capacity drop and accelerated expansion problems. For example, when the mass ratio of the first graphite particles is too high, the degree of side reaction between the active material layer of the negative electrode sheet and the electrolyte will become greater, which will cause the reaction to consume more electrolyte; and when the mass ratio of the second graphite particles is too high, the porosity of the first coating will increase, thereby causing the energy density of the battery to decrease; therefore, the present invention can better achieve a balance between the short-term fast charging performance and long-term cycle life of the battery by adjusting the mass ratio of the first graphite particles to the second graphite particles in the first coating.

[0037] According to the negative electrode sheet of the present invention, the mass ratio of the silicon-carbon particles to the third graphite particles is (22-38): (62-78). Exemplarily, the mass ratio of the silicon-carbon particles to the third graphite particles can be 22:78, 25:75, 30:70, 35:65, 38:62, and the sum of the preceding and following values ​​is 100. When the mass ratio of the silicon-carbon particles to the third graphite particles exceeds this range, for example, when the mass ratio of the silicon-carbon particles is too high, the expansion of the silicon-carbon particles increases, which will cause the active material layer to further squeeze the diaphragm, causing a micro-short circuit phenomenon in the negative electrode sheet; in addition, it may also cause the binder to fail, the conductive network to be disconnected, and there is a risk of capacity diving; and when the mass ratio of the third graphite particles is too high, it will cause the negative electrode active material to have a large degree of side reaction with the electrolyte, thereby consuming more electrolyte; therefore, the present invention can further achieve improvement and balance of battery fast charging performance, expansion problems and long cycle life by adjusting the mass ratio of the silicon-carbon particles and the third graphite particles in the second coating.

[0038] According to the negative electrode sheet of the present application, the specific surface area S1 of the first graphite particles is 0.1 m 2 / g-5 m 2 / g, for example, the specific surface area S1 of the first graphite particles can be 0.1 m 2 / g, 0.2 m 2 / g, 0.21 m 2 / g, 0.22 m 2 / g, 0.23 m 2 / g, 0.24 m 2 / g, 0.5 m 2 / g, 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g; in a preferred embodiment, the specific surface area S1 of the first graphite particles is 0.2 m 2 / g-0.24 m 2 / g.

[0039] According to the negative electrode sheet of the present application, the specific surface area S2 of the second graphite particles is 0.1 m 2 / g-5 m 2 / g, for example, the specific surface area S2 of the second graphite particles can be 0.1 m 2 / g, 0.13 m 2 / g, 0.14 m 2 / g, 0.15 m 2 / g, 0.16 m 2 / g, 0.17 m 2 / g, 0.5 m 2 / g, 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g. In a preferred embodiment, the specific surface area S2 of the second graphite particles is 0.13 m 2 / g-0.17 m 2 / g.

[0040] The specific surface area BET of the first graphite particles and the second graphite particles as the main material in the negative plate active material layer is too large, which can cause the contact surface between the active material layer and the electrolyte to be larger, the risk of side reaction to be larger, and the long cycle performance of the battery to be poor; and the specific surface area BET is too small, and the current distributed to the surface of the particles under the same load current is larger, which means that the particles need to bear a higher actual rate than the load rate, and the fast charging capacity is poor; therefore, by adjusting the specific surface area of the first graphite particles and the second graphite particles in the first coating, the cycle performance and the fast charging performance of the battery can be further improved.

[0041] According to the negative plate of the application, the specific surface area S3 of the third graphite particles is 0.1m 2 / g-6m 2 / g, for example, the specific surface area S3 of the third graphite particles can be 0.1m 2 / g, 0.2m 2 / g, 0.21m 2 / g, 0.22m 2 / g, 0.23m 2 / g, 0.24m 2 / g, 0.5m 2 / g, 1m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g. In a preferred embodiment, the specific surface area S3 of the third graphite particles is 0.2m 2 / g-0.24m 2 / g.

[0042] According to the negative plate of the application, the specific surface area S4 of the silicon-carbon particles is 0.2m 2 / g-5m 2 / g, for example, the specific surface area S4 of the silicon-carbon particles can be 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g. In a preferred embodiment, the specific surface area S4 of the silicon-carbon particles is 0.5 m 2 / g-1m 2 / g.

[0043] When the specific surface area of the silicon-carbon particles is too large, the volume expansion will be exacerbated, and when the specific surface area of the silicon-carbon particles is too small, the lithium ion insertion and extraction channels will be reduced, the battery reaction kinetics will be limited, and the charge and discharge rate will be reduced; therefore, by adjusting the specific surface area S4 of the silicon-carbon particles, the expansion problem of the silicon-doped graphite negative electrode can be further inhibited, and the rate performance of the battery can be improved.

[0044] The specific surface area of each particle is tested by the gas adsorption BET method, specifically, the particle sample to be tested is placed in a sample tube, nitrogen is introduced at low temperature (usually liquid nitrogen is used), the adsorption partial pressure is directly measured by controlling the equilibrium pressure in the sample tube, and then the adsorption amount is obtained. Then the monolayer adsorption amount is calculated according to the BET equation, so as to obtain the specific surface area (unit m 2 / g).

[0045] The OI value of the first coating layer is 12-18, and the OI value of the first coating layer can be 12, 13, 14, 15, 16, 17, or 18, for example. The OI value of the second coating layer is 9-13, and the OI value of the second coating layer can be 9, 10, 11, 12, or 13, for example. The OI value (Orientation Index) is a parameter for measuring the degree of orientation of graphite particles in the coating. Due to the introduction of silicon-carbon particles and the third graphite particle turning caused by the expansion of the silicon-carbon particles during formation and sorting, the OI value of the second coating layer is lower and generally smaller than the OI value of the first coating layer. However, the OI value of the second coating layer should not be too low, so it needs to be controlled within a suitable range to further improve the kinetic performance of the negative electrode.

[0046] Further, the OI value of the first coating layer is larger than the OI value of the second coating layer, i.e., the OI value of the first coating layer is greater than the OI value of the second coating layer, because the first coating layer does not incorporate silicon-carbon particles. By setting this way, it can also prevent the negative active material layer from being detached from the current collector due to the expansion of the silicon-carbon particles, and further improve the safety and long-term cycle stability of the negative electrode sheet.

[0047] It should be noted that the OI value of the first coating or the second coating is obtained based on X-ray diffraction (XRD) technology, specifically, the active material of the first coating or the second coating to be measured is prepared into a thin film or a powder sample and placed on a sample table of an XRD instrument; then the sample is scanned by using the XRD instrument to obtain an X-ray diffraction pattern thereof, and according to the intensity ratio of specific diffraction peaks, a calculation formula and an analysis method, the OI value corresponding to the first coating or the second coating can be obtained by calculation.

[0048] According to the negative electrode sheet of the present application, the thickness of the first coating is 15 μm-27 μm, and for example, the thickness of the first coating can be 15 μm, 16 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm. In a preferred embodiment, the thickness of the first coating is 17 μm-25 μm.

[0049] According to the negative electrode sheet of the present application, the thickness of the second coating is 8 μm-20 μm, and for example, the thickness of the second coating can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 20 μm. In a preferred embodiment, the thickness of the second coating before rolling is 15 μm-19 μm.

[0050] The present application can further improve the volume expansion problem of the negative electrode sheet by adopting a double-layer coating design on the negative electrode sheet, controlling the particle size of the graphite particles and the silicon-carbon particles in the upper and lower layers respectively, and adjusting the thickness of the first coating and the second coating respectively. In the present application, a coating machine with double nozzles can be used to simultaneously coat the slurry of the first coating and the slurry of the second coating on the surface of the current collector, and by controlling the coating amount of the coating machine, the thickness of the coating can be adjusted. In addition, it should be noted that the thickness of the first coating and the second coating is the thickness of the coating in the formed negative electrode sheet after being coated by the coating machine and then being compacted by a rolling process, which can be obtained by observing the SEM image of the cross section of the negative electrode sheet.

[0051] According to the negative electrode sheet of the present application, the second coating 3 and the first coating 2 in the negative electrode sheet are embedded with each other to form a transition layer 4, the transition layer 4 is located between the first coating 2 and the second coating 3, and the thickness of the transition layer 4 is d, such as Figure 2The figure is a partial enlarged view of the negative plate in an example of the present application, a is the thickness of the second coating layer 3, b is the thickness of the first coating layer 2, d is the thickness of the transition layer 4, and the value range of d is 3 μm≤d≤4.5 μm. Exemplarily, the transition layer d can be 3 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm. After the negative plate is rolled, the silicon-carbon particles in the second coating layer will be partially embedded into the graphite particles in the first coating layer, and the graphite particles in the first coating layer will also be partially embedded into the silicon-carbon particles in the second coating layer, thus a transition layer will be formed between the first coating layer and the second coating layer due to the mutual embedding of the two coating layers, the embedding depth of the mutual embedding of the second coating layer and the first coating layer is the thickness d of the transition layer, and the thickness d of the transition layer depends on the rolling strength when the negative plate is rolled; the mutual embedding of the partial particles will not affect the effect of the first coating layer and the second coating layer, but generally the thickness d of the transition layer needs to be controlled within a proper range to avoid that the silicon-carbon particles in the second coating layer are embedded too deeply into the first coating layer, otherwise it will lead to that the thickness of the transition layer is too thick, thus the cyclic expansion of the first graphite particles and the second graphite particles in the first coating layer is intensified, affecting the long-term cycle life of the battery. In addition, it needs to be noted that since the morphology of the silicon-carbon particles in the transition layer is different from that of the three kinds of graphite particles, the position of the silicon-carbon particles in the transition layer is more convenient to observe, thus the observation and calculation method of the thickness d of the transition layer can generally be obtained by measuring the average distance of the silicon-carbon particles from the surface of the active material layer after the negative plate is rolled and the thickness of the second coating layer, and then calculating the difference between the two; wherein the average distance of the silicon-carbon particles from the surface of the active material layer after the negative plate is rolled refers to that the distance of different silicon-carbon particles from the surface of the active material layer after the negative plate is rolled is counted, and the average value of all the counted distances is calculated, which is the average distance of the silicon-carbon particles from the surface of the active material layer; when actually measuring the distances of different silicon-carbon particles, 3-5 different silicon-carbon particles can be randomly selected. It can be understood that the average distance of the silicon-carbon particles from the surface of the active material layer is calculated because the positions of different independent silicon-carbon particles embedded into the first coating layer are different after the negative plate is rolled, and thus the distances from the surface of the active material layer are different, and by calculating the average distance, the accuracy of measuring the embedding position of the silicon-carbon particles and the thickness of the transition layer can be improved.

[0052] According to the negative electrode sheet of the present application, the depth h of the recess 5 satisfies the relationship -3.5≤h-a-d≤1 (for example, -3.5, -3, -2.5, -2, -1.5, -1, -0.5, 0, 0.5, 1), where a is the thickness of the second coating layer, 8 μm≤a≤20 μm, for example, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm; and d is the thickness of the transition layer formed by the mutual embedding of the second coating layer and the first coating layer in the negative electrode sheet, 3 μm≤d≤4.5 μm, for example, 3 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm; as shown in Figure 2 .

[0053] The wire bonding depth of the recess mainly considers the thickness design ratio of the double-layer coating and the thickness d of the transition layer formed by the mutual embedding of the second coating layer and the first coating layer. When h satisfies the relationship -3.5≤h-a-d≤1, the wire bonding depth of the recess can be ensured to just break through the second coating layer containing silicon-carbon particles (-3.5≤h-a-d). The thickness d of the transition layer can also be considered to avoid the transition layer formed by the mutual embedding of the first coating layer and the second coating layer not being broken, and to avoid the transition layer being broken too deeply (h-a-d≤1, 1 is the margin). This is because, if the wire bonding depth of the recess is too shallow (the second coating layer containing silicon-carbon particles is not broken), the ion transport kinetics brought by wire bonding will not be obviously improved, and it will still be difficult for lithium ions to transport to the first coating layer. Therefore, the main reaction zone is concentrated in the surface second coating layer, the material utilization non-uniformity is large, and adverse effects such as lithium precipitation may occur. If the wire bonding depth of the recess is too deep (the transition layer is broken, but the depth of the first coating layer into which the wire is broken is too deep), the loss of negative electrode active material will be too large, the NP ratio (the ratio of the capacity of the negative electrode of the battery to the capacity of the positive electrode) may be affected, the reaction site is reduced although the ion transport kinetics is improved, and adverse effects such as lithium precipitation may also occur. Therefore, the depth h of the recess needs to be controlled to be between the depth just breaking through the second coating layer and the depth just breaking through the transition layer, so that the problem of lithium precipitation of the negative electrode sheet containing silicon-carbon particles can be further avoided.

[0054] In addition, in a specific embodiment, as shown in Figure 2 , the thickness b of the first coating layer is 15 μm-27 μm; for example, the thickness b of the first coating layer can be 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm.

[0055] According to the negative electrode sheet of the present application, as shown in Figure 2 The depth of the recess 5 can be 12 μm-25.5 μm; for example, the depth of the recess can be 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm, 21.5 μm, 22 μm, 22.5 μm, 23 μm, 23.5 μm, 24 μm, 24.5 μm, 25.5 μm. The depth of the recess 5 refers to the vertical distance between the deepest part of the recess and the horizontal plane where the opening of the recess is located, as shown in Figure 2 The depth of the recess can reflect the loss of active material, so it should not be too deep, but if it is too shallow, the problem of lithium precipitation will not be improved significantly, therefore, it is necessary to control the depth of the recess within the above range to avoid the above problems.

[0056] In a specific embodiment, the ratio of the width to the depth of the recess is 4-6; for example, the ratio of the width to the depth of the recess can be 4, 4.1, 4.2, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5. When the ratio of the width to the depth of the recess is less than 4, it means that the width of the recess is too narrow and the depth is too deep, which will result in a large loss of active material, and the effect of accelerating the transmission of lithium ions by the narrow channel will not be obvious, the improvement of kinetics will be relatively small, which is not conducive to the overall performance. When the ratio of the width to the depth of the recess is greater than 6, it means that the width of the recess is too wide and the depth is too shallow, which will also result in an insignificant improvement of kinetics. In addition, it should be noted that the width of the recess refers to the vertical distance between the two points farthest apart in the cross-sectional view of the recess perpendicular to the surface of the negative electrode sheet. For example, when the upper and lower widths of the cross-section of the recess are not equal, i.e. the cross-section is trapezoidal, the width of the recess refers to the upper width, as shown in Figure 2 .

[0057] In the present application, the cross-sectional morphology of the recess can be any shape such as rectangular, trapezoidal, triangular, etc., which is not limited in the negative electrode sheet of the present application.

[0058] The cross-sectional morphology of the recess can be adjusted by setting the wire bonding parameters, which is not specially limited in the negative electrode sheet of the present application. However, it can be found through tests that when the cross-sectional morphology of the recess is trapezoidal and the ratio of the upper and lower widths is 2-3, compared with the recess with a rectangular cross-sectional morphology, the loss of active material can be relatively reduced, and the kinetics will not be greatly affected. Moreover, compared with the recess with a triangular cross-sectional morphology, the kinetics can be greatly improved with a slightly higher loss of active material; therefore, considering the trapezoidal cross-sectional morphology comprehensively, the loss of active material and the optimization of kinetics performance can be balanced.

[0059] Therefore, in a preferred embodiment, the cross section of the recess is trapezoidal, and the width ratio of the upper layer to the lower layer of the trapezoid is 2-3, such as shown in Figure 2 For example, the width ratio of the upper layer to the lower layer of the recess can be 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3. When the cross section of the recess is trapezoidal, the upper layer of the trapezoidal recess formed by the recess is wider than the lower layer because the recess is punched from the surface of the negative plate to the depth of the active material layer, and therefore, there is a width ratio of the upper layer to the lower layer, which can be calculated by measuring the length of the upper and lower edges of the trapezoidal cross section respectively.

[0060] In a specific embodiment, the distance between adjacent recesses is 0.5-1.5 mm, for example, the distance between adjacent recesses can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm. If the distance between adjacent recesses is small, the loss of active material is large, and if the distance between adjacent recesses is large, the radiation area is too small, and the improvement effect on kinetics is not large. In addition, it should be noted that the line distance refers to the distance between the parallel recesses formed by the laser wire forming technology, and when measuring the distance, the same point in the two recesses should be selected.

[0061] According to the negative plate of the present application, the recess is formed by laser wire forming technology; the weight loss rate of the negative plate after laser wire forming is 1.1%-2%. For example, the weight loss rate of the negative plate after laser wire forming can be 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%. If the weight loss rate is higher than 2%, the NP ratio of the battery will be reduced, which will affect the cycle performance. If the weight loss rate is higher than 1.5%, the main consideration is that the dynamics of the surface layer is poor, and the wire needs to be formed to improve it. If the weight loss rate is reduced, it will have an impact on the large rate charge and discharge. In a preferred embodiment, the weight loss rate of the negative plate after laser wire forming is 1.5%-1.8%.

[0062] The negative electrode sheet according to the present application has a negative electrode potential of 30 mV-82 mV. For example, the negative electrode potential of the negative electrode sheet can be 30 mV, 31 mV, 32 mV, 33 mV, 34 mV, 35 mV, 36 mV, 37 mV, 38 mV, 39 mV, 40 mV, 45 mV, 50 mV, 55 mV, 60 mV, 65 mV, 70 mV, 75 mV, 80 mV, or 82 mV. The negative electrode potential of the negative electrode sheet is 100-123 mV higher than that of a conventional design. The minimum negative electrode potential of the negative electrode sheet in a conventional design is generally -60 to -50 mV under a high-rate charging condition, and there is a high risk of lithium precipitation, which leads to a rapid decline in battery performance. Compared with the conventional design, the designed negative electrode sheet can significantly increase the negative electrode potential under a high-rate charging condition, reduce the risk of lithium precipitation of the negative electrode sheet, and thus improve the capacity stability and cycle performance of the lithium ion battery.

[0063] The negative electrode sheet according to the present application has a surface resistance of 200 mΩ-290 mΩ. For example, the surface resistance of the negative electrode sheet can be 200 mΩ, 210 mΩ, 220 mΩ, 230 mΩ, 240 mΩ, 250 mΩ, 260 mΩ, 270 mΩ, 280 mΩ, or 290 mΩ. Further, the low surface resistance of the negative electrode sheet can reduce the ohmic impedance of the entire electrode sheet, reduce the polarization of the negative electrode, and improve the cycle performance of the lithium ion battery.

[0064] The second aspect of the present application provides a battery comprising a negative electrode sheet and a separator, wherein the negative electrode sheet is the negative electrode sheet according to the first aspect of the present application.

[0065] The adhesion between the negative electrode sheet and the separator is 0.1 N-2 N. For example, the adhesion between the negative electrode sheet and the separator can be 0.1 N, 0.2 N, 0.21 N, 0.22 N, 0.23 N, 0.24 N, 0.25 N, 0.26 N, 0.27 N, 0.28 N, 0.29 N, 0.3 N, 0.31 N, 0.32 N, 0.33 N, 0.34 N, 0.35 N, 0.36 N, 0.37 N, 0.38 N, 0.39 N, 0.4 N, 0.41 N, 0.42 N, 0.428 N, 0.429 N, 0.43 N, 0.5 N, 1 N, 1.5 N, or 2 N. Since the second coating layer on the surface of the present application is a silicon-containing coating layer, more silicon-carbon particles will be in contact with the separator, and the hydroxyl groups on the surface of the silicon-carbon particles will interact with the separator, so that the adhesion is 2.3 times higher than that of a graphite coating layer, thereby avoiding the problem of poor adhesion between the separator and the negative electrode, which leads to a longer lithium ion transmission path and a larger battery impedance. In a preferred embodiment, the adhesion between the negative electrode sheet and the separator is 0.2 N-0.43 N.

[0066] The battery of the present application further comprises a positive electrode sheet, and the battery of the present application can be prepared by using conventional methods in the art. Specifically, the negative electrode sheet, the separator and the positive electrode sheet can be sequentially stacked, and then the battery cell can be obtained by using a stacking or winding process. Then, the battery can be obtained by performing processes such as baking, liquid injection, formation and packaging. All the materials in the positive electrode sheet, the negative electrode sheet and the separator can be prepared according to methods known in the art or obtained by commercial channels.

[0067] The present application will be further described in detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology achieved based on the above description of the present application is encompassed within the scope of protection intended by the present application.

[0068] The experimental methods used in the following examples are conventional methods unless otherwise specified. The reagents, materials and the like used in the following examples can be obtained by commercial channels unless otherwise specified.

[0069] Example 1

[0070] Preparation of the battery

[0071] 1) Preparation of the negative electrode sheet: the first graphite particles and the second graphite particles and the silicon-carbon particles and the third graphite particles are mixed according to a certain ratio to form a slurry, the slurry of the first graphite particles and the second graphite particles is placed in the bottom nozzle of the coating machine, and the slurry of the silicon-carbon particles and the third graphite particles is placed in the top nozzle of the coating machine, and then the first coating layer and the second coating layer are formed on the 5 μm copper foil, dried, rolled and cut into small pieces of 73 mm*1458 mm.

[0072] The thickness d of the transition layer formed by the mutual embedding of the second coating layer and the first coating layer is 3.5 μm, the thickness b of the first coating layer is 25 μm, and the thickness a of the second coating layer is 11 μm, then laser wire is punched, the wire punching power is set to 50%, the cross-sectional morphology of the recess is trapezoidal (the width ratio of the upper layer to the lower layer is 2.5, the upper layer is 70 μm wide, and the lower layer is 28 μm wide), the width of the recess / the depth of the recess h is 5 (70 μm / 14 μm), and the recess spacing is 1 mm.

[0073] 2) Preparation of the positive electrode sheet:

[0074] LiCoO2: conductive carbon black: PVDF are mixed in a mass ratio of 9.8:0.1:0.1, and then stirred in a planetary mixer for 12 h; the positive electrode paste is uniformly coated on an aluminum foil with a diameter of 8 um thick, dried in an oven at 60°C for 24 h, and then the positive electrode is cut into a size of 71 mm*1456 mm to obtain the positive electrode sheet.

[0075] 3) Preparation of the electrolyte:

[0076] An electrolyte was prepared by dissolving 1 M LiPF6in EC / DMC (1 / 1 mass ratio), and 15% of FEC was additionally added.

[0077] 4) Preparation of lithium ion batteries

[0078] After the positive and negative electrode sheets and the separator were wound to form an electrode assembly, the electrode assembly was stacked and pressed using a hot press at a temperature of about 90°C and a pressure of 250 kgf for 100 seconds. Subsequently, the electrode assembly was accommodated in a case, electrolyte was injected thereinto, and then vacuum-sealed.

[0079] Example 2 group:

[0080] Example 2 group was prepared in the same manner as Example 1, except that the particle size of the particles in the first coating layer or the second coating layer was changed, as shown in Tables 1-3.

[0081] Example 3 group:

[0082] Example 3 group was prepared in the same manner as Example 1, except that the mass ratio of the first graphite particles and the second graphite particles in the first coating layer slurry was changed, specifically:

[0083] Example 3-1, the mass ratio of the first graphite particles and the second graphite particles in the first coating layer slurry was changed to 8:92;

[0084] Example 3-2, the mass ratio of the first graphite particles and the second graphite particles in the first coating layer slurry was changed to 12:88;

[0085] Example 3-3, the mass ratio of the first graphite particles and the second graphite particles in the first coating layer slurry was changed to 5:95;

[0086] Example 3-4, the mass ratio of the first graphite particles and the second graphite particles in the first coating layer slurry was changed to 20:80.

[0087] Example 4 group:

[0088] Example 4 group was prepared in the same manner as Example 1, except that the mass ratio of the silicon-carbon particles and the third graphite particles in the second coating layer slurry was changed, specifically:

[0089] Example 4-1, the mass ratio of the silicon-carbon particles and the third graphite particles in the second coating layer slurry was changed to 22:78;

[0090] Example 4-2, the mass ratio of the silicon-carbon particles and the third graphite particles in the second coating layer slurry was changed to 38:62;

[0091] Example 4-3, the mass ratio of silicon-carbon particles and third graphite particles in the second coating slurry is changed to 10:90;

[0092] Example 4-4, the mass ratio of silicon-carbon particles and third graphite particles in the second coating slurry is changed to 50:50.

[0093] Example 5 group:

[0094] Example 5 group is conducted according to Example 1, the only difference is that the parameter setting of the laser wire processing technology is changed so that the depth h of the recess is changed, see Table 1-3.

[0095] Example 6:

[0096] Example 6 is conducted according to Example 1, the only difference is that the parameter setting of the laser wire processing technology is changed so that the cross-sectional shape of the recess is changed, see Table 1-3.

[0097] Example 7 group:

[0098] Example 7 group is conducted according to Example 1, the only difference is that the thickness of the first coating and the second coating is changed, see Table 1-3.

[0099] Comparative Example 1 group:

[0100] Comparative Example 1 group is conducted according to Example 1, the only difference is that the particle size in the first coating or the second coating is changed, see Table 1-3.

[0101] Comparative Example 2:

[0102] Comparative Example 2 is conducted according to Example 1, the only difference is that the slurry in the bottom layer nozzle is changed to silicon-carbon particles and second graphite particles, see Table 1-3.

[0103] Comparative Example 3:

[0104] Comparative Example 3 is conducted according to Example 1, the only difference is that no wire processing is performed, and the surface of the active material layer is not provided with a recess, see Table 1-3.

[0105] Table 1

[0106]

[0107]

[0108] Table 2

[0109]

[0110]

[0111] Table 3

[0112]

[0113]

[0114] In Table 3, the active material layer in Comparative Example 2 does not contain a transition layer between the first coating layer and the second coating layer because the same composition is used for both coating layers, and thus the thickness of the transition layer is represented by " / " in the table.

[0115] Negative electrode sheet test examples

[0116] The negative electrode sheets prepared in the above examples and comparative examples were subjected to the following tests, and the test results are shown in Table 4.

[0117] 1) Weight loss rate of the negative electrode sheet: The negative electrode sheets prepared in the above examples and comparative examples were cut into small pieces and weighed, and then weighed again after laser wire bonding. The weight loss rate of the negative electrode sheet was calculated as follows: weight loss rate of the negative electrode sheet (%) = (weight after wire bonding / weight before wire bonding) x 100%.

[0118] 2) Negative electrode potential of the negative electrode sheet: The negative electrode sheets prepared in the above examples and comparative examples were subjected to charge-discharge with a conventional lithium sheet, and the voltage displayed was the potential of the negative electrode sheet (mv).

[0119] 3) Adhesion test between the negative electrode sheet and the separator: The lithium ion batteries prepared in the above examples and comparative examples were charged to 4.5 V, and then disassembled. The position where the negative electrode sheet and the separator were well adhered was cut into a strip having a width of 15 mm and a length of 5 cm, and then placed in a peeling force tester to measure the adhesion between the negative electrode sheet and the separator (N).

[0120] 4) Surface resistance test of the negative electrode sheet: The lithium ion batteries prepared in the above examples and comparative examples were disassembled, and the negative electrode sheets were taken out. A surface resistance meter was used to measure the surface resistance of the negative electrode sheet (mΩ) under a pressure of 0.2 N.

[0121] Lithium ion battery test examples

[0122] The lithium ion batteries prepared in the above examples and comparative examples were subjected to the following tests, and the test results are shown in Table 4.

[0123] 4) Rate test: The lithium ion batteries prepared in the above examples and comparative examples were subjected to 0.1 C and 1 C discharge tests at 25°C for 10 min in the voltage range of 4.5-3.0 V to measure the rate performance of the lithium ion batteries. The amount of electricity discharged at 1 C discharge rate was measured based on the amount of electricity discharged at 0.1 C discharge rate, and the rate performance (%) was calculated as follows: rate performance (%) = (amount of electricity discharged at 1 C discharge rate / amount of electricity discharged at 0.1 C discharge rate) x 100%.

[0124] 5) Cycle and lithium precipitation test: the lithium ion battery prepared in the above examples and comparative examples is charged at 3.5C to 4.35V (1.8C cut-off voltage for constant voltage), 1.8C to 4.4V (1.5C cut-off voltage for constant voltage), 1.5C to 4.53V (1.2C cut-off voltage for constant voltage), 1.2C to 4.58V (0.24C cut-off voltage for constant voltage), 1C to 3.5V, 0.7C to 3V after 10 minutes of standing at ambient temperature of 25℃, and the above capacity test process is cycled to obtain the capacity retention rate at 800 cycles = discharge capacity at 800 cycles / initial discharge capacity; then when the lithium ion battery is cycled for 800 cycles, it is charged to 50% SOC at 1.1C rate, and then charged to 4.5V at 0.5C, and the cut-off voltage for constant voltage charging is 0.05C, and after 10 minutes of standing, the full battery is dissected, the state of the outermost and innermost negative electrode sheets is observed, and whether lithium precipitation occurs and the severity of lithium precipitation are determined, which can be divided into four degrees: no lithium precipitation, slight lithium precipitation, lithium precipitation and severe lithium precipitation.

[0125] 6) Full-to-full expansion rate test: the lithium ion battery prepared in the above examples and comparative examples is fully charged, and the PPG thickness is tested under a force of 600g, and after 800T cycles, the thickness is measured, and the full-to-full expansion rate = 1-initial full charge thickness / cycled full charge thickness

[0126] 7) Charge transfer resistance: the lithium ion battery prepared in the above examples and comparative examples is charged at 3.5C to 4.35V (1.8C cut-off voltage for constant voltage), 1.8C to 4.4V (1.5C cut-off voltage for constant voltage), 1.5C to 4.53V (1.2C cut-off voltage for constant voltage), 1.2C to 4.58V (0.24C cut-off voltage for constant voltage), 1C to 3.5V, and 0.7C to 3V after 10 minutes of standing.

[0127] Table 4

[0128]

[0129]

[0130] As can be analyzed from Table 4, by adopting the double-layer coated negative electrode sheet and regulating the spatial position of the silicon-carbon particles and the particle size of the upper and lower graphite particles, the expansion problem and the lithium precipitation problem of the silicon-carbon material mixed with the graphite negative electrode can be inhibited, the full-to-full expansion rate of the lithium ion battery is significantly reduced compared with the comparative examples, and the rate performance and the cycle capacity retention rate can also be maintained at a high level, so that the cycle performance and the rate performance of the lithium ion battery can be simultaneously improved, and the expansion problem is effectively improved.

[0131] The preferred embodiments of the present application are described in detail above, 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 that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A negative electrode sheet, characterized in that: The invention comprises a current collector and an active material layer located on at least one side of the current collector, wherein the active material layer comprises a first coating layer close to the surface of the current collector and a second coating layer away from the surface of the current collector; The first coating layer comprises first graphite particles and second graphite particles, wherein the particle size Dv150 of the first graphite particles is 5 μm-12 μm, the particle size Dv250 of the second graphite particles is 10 μm-16 μm, and the particle size Dv250 of the second graphite particles is greater than the particle size Dv150 of the first graphite particles; The second coating layer comprises third graphite particles and silicon-carbon particles, wherein the particle size Dv350 of the third graphite particles is 4 μm-11 μm; the particle size Dv450 of the silicon-carbon particles is 5 μm-12 μm; The surface of the active material layer is provided with a plurality of concave portions; the thickness of the second coating layer is 8 μm-20 μm; and the depth of the concave portions is 12 μm-25.5 μm.

2. The negative electrode sheet according to claim 1, characterized in that: Based on the total mass of the first coating layer, the mass ratio of the first graphite particles to the second graphite particles is (8-12):(88-92); And / or, based on the total mass of the second coating layer, the mass ratio of the silicon-carbon particles to the third graphite particles is (22-38):(62-78).

3. The negative electrode sheet according to claim 1, characterized in that: The specific surface area S1 of the first graphite particles is 0.1 m² / g-5 m² / g, and the specific surface area S2 of the second graphite particles is 0.1 m² / g-5 m² / g; And / or, the specific surface area S3 of the third graphite particles is 0.1 m² / g-6 m² / g, and the specific surface area S4 of the silicon-carbon particles is 0.2 m² / g-5 m² / g.

4. The negative electrode sheet according to claim 1, characterized in that: The OI value of the first coating layer is 12-18, and the OI value of the second coating layer is 9-13; The OI value of the first coating layer is greater than the OI value of the second coating layer.

5. The negative electrode sheet according to claim 1, characterized in that: The thickness of the first coating layer is 15 μm-27 μm.

6. The negative electrode sheet according to claim 1, characterized in that: The second coating layer and the first coating layer in the negative electrode sheet are embedded in each other to form a transition layer. The transition layer is located between the first coating layer and the second coating layer. The thickness of the transition layer is d, 3μm≤d≤4.5μm.

7. The negative electrode sheet according to claim 1, characterized in that: The depth of the recess is h, satisfying the relationship -3.5≤had≤1, where a is the thickness of the second coating layer, 8μm≤a≤20μm; d is the thickness of the transition layer formed by the second coating layer and the first coating layer in the negative electrode sheet being embedded in each other, 3μm≤d≤4.5μm.

8. The negative electrode sheet according to claim 1, characterized in that: The ratio of the width to the depth of the recess is 4-6.

9. The negative electrode sheet according to claim 1, characterized in that: The cross section of the concave portion is trapezoidal, and the width ratio of the upper layer to the lower layer of the trapezoid is 2-3.

10. The negative electrode sheet according to claim 1, characterized in that: The distance between adjacent recesses is 0.5 mm to 1.5 mm.

11. The negative electrode sheet according to claim 1, characterized in that: The negative electrode potential of the negative electrode sheet is 30mv-82mv; And / or, the surface resistance of the negative electrode sheet is 200mΩ-290mΩ.

12. A battery, characterized in that: The battery comprises a negative electrode sheet and a separator, and the negative electrode sheet is the negative electrode sheet according to any one of claims 1 to 11.

13. The battery according to claim 12, characterized in that The bonding strength between the negative electrode sheet and the separator is 0.1N-2N.

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