Negative electrode sheet, battery, and electric device

Abstract

The application discloses a negative electrode sheet, a battery and an electric device. The negative electrode sheet comprises: a current collector, the thickness direction of the current collector is a first direction; a negative electrode active material layer is arranged on at least one surface of the current collector; the negative electrode active material layer comprises first active coating layers and second active coating layers which are alternately arranged along a second direction perpendicular to the first direction, and the following conditions are met between the first active coating layers and the second active coating layers: Ds2 / Ds1<=0.5, D502 / D501>=1.3, and the material structure can be prevented from being damaged while the risk of segregation is reduced.

Description

TECHNICAL FIELD

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

[0002] In lithium ion secondary batteries, improving the energy density of the battery is one of the important goals. When the energy density of the battery is improved, the thickness of the active material coating of the negative electrode sheet is usually increased and the compaction density is improved. However, with the increase of the coating thickness and the improvement of the compaction density, the kinetic characteristics of the battery cell are significantly affected, which leads to the blocking of ion transmission during the charging process, increases the risk of dendrite phenomenon, and thus may damage the safety and cycle life of the battery. In the related art, in order to alleviate this problem, laser drilling technology is introduced as an innovative means, which aims to improve the kinetic performance of the battery electrode sheet through a physical method. This method forms a microporous structure by precisely ablation on the electrode sheet material with high compaction density using a laser beam. These micropores act as permeation channels for electrolyte, effectively promoting the diffusion efficiency of lithium ions, and thus optimizing the ion transmission path inside the battery.

[0003] However, the laser drilling technology also faces challenges in practical application, especially its potential destructive effect on the active material cannot be ignored. For example, the current mainstream silicon-carbon negative electrode material usually adopts a vapor deposition method, that is, embedding elemental silicon into a porous carbon matrix to improve the energy storage capacity and cycle stability of the negative electrode. However, the high temperature and high-energy laser beam generated during the laser drilling process often damages the carbon matrix structure of the silicon-carbon composite material, causing the elemental silicon originally wrapped by the carbon matrix to be directly exposed to the electrolyte. This direct exposure not only aggravates the shedding of the active material, but also may trigger a series of adverse electrochemical reactions, such as increasing the self-discharge rate of the battery, shortening the cycle life of the battery, and negatively affecting the overall performance of the battery, etc. Therefore, how to reduce the risk of dendrite phenomenon while not damaging the material structure has become a problem to be solved. SUMMARY

[0004] The embodiments of the present application provide a negative electrode sheet, a battery and an electric device, which can reduce the risk of dendrite phenomenon while not damaging the material structure.

[0005] In a first aspect, the embodiments of the present application provide a negative electrode sheet, comprising:

[0006] a current collector, a thickness direction of the current collector being a first direction;

[0007] a negative active material layer, provided on at least one surface of the current collector;

[0008] The negative electrode active material layer comprises first active coating layers and second active coating layers alternately arranged along a second direction perpendicular to the first direction, and a relationship Ds2 / Ds1≤0.5 and D502 / D501≥1.3 is met between the first active coating layers and the second active coating layers, wherein Ds2=D902-D102, Ds1=D901-D101.

[0009] D101 is a particle size corresponding to a cumulative particle size distribution percentage of 10% of active material particles in the first active coating layer, D501 is a particle size corresponding to a cumulative particle size distribution percentage of 50% of active material particles in the first active coating layer, D901 is a particle size corresponding to a cumulative particle size distribution percentage of 90% of active material particles in the first active coating layer, D102 is a particle size corresponding to a cumulative particle size distribution percentage of 10% of active material particles in the second active coating layer, D502 is a particle size corresponding to a cumulative particle size distribution percentage of 50% of active material particles in the second active coating layer, and D902 is a particle size corresponding to a cumulative particle size distribution percentage of 90% of active material particles in the second active coating layer.

[0010] The negative electrode tab provided by the first aspect of the present application has at least the following beneficial effects: by alternately arranging the first active coating layers and the second active coating layers with different particle sizes of active material particles on the surface of the current collector along the second direction, the characteristics of the first active coating layers and the second active coating layers are made different. By controlling Ds2 / Ds1≤0.5 and D502 / D501≥1.3, the particle size of the second active coating layer is relatively large, which is beneficial to the storage of electrolyte and has low ion impedance, can provide an ion channel for ion movement, can effectively improve the kinetic performance of the battery, reduce the electrolyte transport path of the first active coating layer, and improve the kinetic performance. At the same time, the particle size of the first active coating layer is relatively small, and the compaction density is large, which can improve the energy density of the battery. Therefore, the negative electrode tab provided by the embodiments of the present application can effectively reduce the risk of side reactions while not damaging the material structure.

[0011] According to some embodiments of the first aspect of the present application, in the direction of the alternately arranged first active coating layers and second active coating layers, the width of the first active coating layer is W1 mm, the width of the second active coating layer is W2 mm, and W1 / W2≤5.

[0012] According to some embodiments of the first aspect of the present application, 0.1≤Ds2 / Ds1≤0.5; and / or, 1.3≤D502 / D501≤2; and / or, 1.5≤Ds2≤10.

[0013] According to some embodiments of the first aspect of the present application, in the alternating arrangement direction of the first active coating and the second active coating, the width of the first active coating is W1 mm, the width of the second active coating is W2 mm, and 1≤W1 / W2≤5; and / or, the width W2 mm of the second active coating is 1-3 mm.

[0014] According to some embodiments of the first aspect of the present application, the active substance of the first active coating and the active substance of the second active coating are independently selected from at least one of artificial graphite, natural graphite, hard carbon, and silicon-based material.

[0015] According to some embodiments of the first aspect of the present application, the active substance of the first active coating and the active substance of the second active coating are the same substance; and / or, the active substance of the first active coating and the active substance of the second active coating comprise silicon-based material.

[0016] According to some embodiments of the first aspect of the present application, the silicon-based material comprises silicon-carbon material.

[0017] According to some embodiments of the first aspect of the present application, the first active coating and the second active coating further comprise a conductive agent and a binder; the conductive agent comprises at least one of conductive carbon black, carbon nanotube, and graphene, and the binder comprises at least one of butadiene-styrene rubber, sodium carboxymethyl cellulose, and polymethyl methacrylate.

[0018] In a second aspect, the embodiments of the present application provide a battery comprising the negative electrode sheet according to the embodiments of the first aspect.

[0019] In a third aspect, the embodiments of the present application provide a power-using device comprising the battery according to the embodiments of the second aspect.

[0020] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings are included to provide a further understanding of the technical solutions of the present application, constitute a part of the specification, and are used together with the embodiments of the present application to explain the technical solutions of the present application, and do not constitute a limitation on the technical solutions of the present application.

[0022] Figure 1 is a structural schematic diagram of a negative electrode sheet provided by an embodiment of the present application;

[0023] Figure 2 is a structural schematic diagram of a negative electrode sheet provided by another embodiment of the present application. DETAILED DESCRIPTION

[0024] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0025] It can be understood that, although the functional modules are divided in the device schematic diagram, and the logical order is shown in the flowchart, in some cases, the steps shown or described can be performed in a manner different from the module division in the device or the order in the flowchart. The terms "first", "second", etc. in the specification, claims or above-described drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0026] The embodiments of the present application provide a negative electrode sheet, a battery and an electric device. The first active coating layer and the second active coating layer with different particle sizes of active material particles are alternately arranged along the second direction on the surface of the current collector, so that the characteristics of the first active coating layer and the second active coating layer are different. By controlling Ds2 / Ds1≤0.5, D502 / D501≥1.3, the particle size of the second active coating layer is relatively large, which is beneficial to the storage of electrolyte and has low ion impedance, can provide ion channels for ion movement, and can effectively improve the kinetic performance of the battery cell, and the electrolyte transport path of the first active coating layer is reduced, and the kinetic performance is improved. At the same time, the particle size of the first active coating layer is relatively small, and the compaction density is large, which can improve the energy density of the battery.

[0027] Reference Figure 1 , Figure 1 is a structure schematic diagram of a negative electrode sheet provided by the embodiments of the present application.

[0028] It can be understood that the negative electrode sheet includes the current collector 100 and the negative active material layer 200 coated on at least one surface of the current collector 100. Among them, the thickness direction of the current collector 100 is the first direction, and the negative active material layer 200 includes a first active coating layer 210 and a second active coating layer 220 arranged alternately along the second direction perpendicular to the first direction. That is, the negative active material layer 200 includes a plurality of first active coating layers 210 and a plurality of second active coating layers 220, the plurality of first active coating layers 210 and the plurality of second active coating layers 220 are arranged alternately, and the thickness direction of the first active coating layer 210 and the thickness direction of the second active coating layer 220 are the same as the thickness direction of the current collector 100. By arranging the first active coating layer 210 and the second active coating layer 220 alternately in a direction perpendicular to the thickness direction of the current collector 100, the electrolyte can simultaneously contact the first active coating layer 210 and the second active coating layer 220. In addition, the active material particles of the first active coating layer 210 and the active material particles of the second active coating layer 220 satisfy that the ratio of Ds2 to Ds1 is less than or equal to 0.5, and the ratio of D502 to D501 is greater than or equal to 1.3, wherein Ds2=D902-D102, Ds1=D901-D101; D101 is the particle size corresponding to the cumulative particle size distribution percentage of 10% of the active material particles of the first active coating layer 210, D501 is the particle size corresponding to the cumulative particle size distribution percentage of 50% of the active material particles of the first active coating layer 210, D901 is the particle size corresponding to the cumulative particle size distribution percentage of 90% of the active material particles of the first active coating layer 210, D102 is the particle size corresponding to the cumulative particle size distribution percentage of 10% of the active material particles of the second active coating layer 220, D502 is the particle size corresponding to the cumulative particle size distribution percentage of 50% of the active material particles of the second active coating layer 220, and D902 is the particle size corresponding to the cumulative particle size distribution percentage of 90% of the active material particles of the second active coating layer 220.

[0029] It can be understood that by controlling the active material particles of the first active coating layer 210 and the active material particles of the second active coating layer 220 to satisfy that the ratio of Ds2 to Ds1 is less than or equal to 0.5, the particle packing of the active material particles in the first active coating layer 210 is more compact than the particle packing of the active material particles in the second active coating layer 220, so that the energy density of the first active coating layer 210 is greater than the energy density of the second active coating layer 220, and because the particle size distribution of the active material particles of the second active coating layer 220 is more concentrated, it is beneficial to the storage and ion transmission of the electrolyte, thereby improving the kinetic performance of the battery.

[0030] It is understandable that the smaller the particle size of the active material particles in the active coating, the greater the compaction density of the active coating, which leads to a decrease in the battery's kinetic performance but an increase in energy density. Conversely, the larger the particle size of the active material particles in the active coating, the smaller the compaction density of the coating, the higher the ion passage efficiency, and thus the higher the battery's kinetic performance. Therefore, by controlling the active material particles of the first active coating 210 and the second active coating 220 to satisfy the ratio of D502 to D501 being greater than or equal to 1.3, it is possible to ensure the battery's kinetic performance without damaging the material structure and without reducing the battery's self-discharge performance and lifespan.

[0031] Specifically, in some embodiments, the second direction can be the length direction of the current collector 100, that is, the first active coating 210 and the second active coating 220 are alternately arranged along the length direction of the current collector 100, the total width of the plurality of first active coatings 210 and the plurality of second active coatings 220 is equal to the length of the current collector 100, and the length of the first active coating 210 and the length of the second active coating 220 are equal to the width of the current collector 100.

[0032] It should be noted that, as Figure 2 As shown, Figure 2 This is a schematic diagram of the structure of the negative electrode sheet provided in another embodiment of this application. The second direction can also be the width direction of the current collector 100, that is, the first active coating 210 and the second active coating 220 are alternately arranged along the width direction of the current collector 100. The total width of the plurality of first active coatings 210 and the plurality of second active coatings 220 is equal to the width of the current collector 100. The length of the first active coating 210 and the length of the second active coating 220 are equal to the length of the current collector 100.

[0033] It should be noted that the particle size of the active material particles in the first active coating 210 and the active material particles in the second active coating 220 are determined by screening equipment. The smaller the particle size, the more difficult the screening becomes. At the same time, the greater the dispersion of the particle size distribution of the active material particles in the active coating, the worse the improvement effect of the kinetic performance of the active coating. Therefore, the value range of Ds2 should be 1.5 to 10 (inclusive). Similarly, in order to ensure the improvement effect of the kinetic performance of the negative electrode, the ratio of Ds2 to Ds1 is preferably 0.1 to 0.5 (inclusive).

[0034] It should be noted that the smaller the particle size of the active material particles in the active coating, the more difficult the screening is, and the larger the particle size of the active material particles in the active coating, the lower the energy density of the battery is, in addition, the larger the particle size of the active material particles in the active coating, the higher the risk of the active coating being broken in the rolling process, therefore, the ratio of D502 / D501 is preferably in the range of 1.3 to 2 (including 1.3 and 2).

[0035] Specifically, in some embodiments, the first active coating 210 and the second active coating 220 satisfy any one of the conditions of 0.1≤Ds2 / Ds1≤0.5, 1.3≤D502 / D501≤2 and 1.5≤Ds2≤10.

[0036] Specifically, in some embodiments, the first active coating 210 and the second active coating 220 satisfy any two of the conditions of 0.1≤Ds2 / Ds1≤0.5, 1.3≤D502 / D501≤2 and 1.5≤Ds2≤10.

[0037] Specifically, in some embodiments, the first active coating 210 and the second active coating 220 satisfy all of the conditions of 0.1≤Ds2 / Ds1≤0.5, 1.3≤D502 / D501≤2 and 1.5≤Ds2≤10.

[0038] It can be understood that, since the particle size of the active material of the second active coating 220 is larger than that of the first active coating 210, the larger the width of the first active coating 210, the larger the energy density of the battery is, but since the width of the first active coating 210 is increased, the width of the second active coating 220 is reduced under the condition that the length of the current collector 100 is unchanged, and the reduction of the width of the second active coating 220 reduces the ion diffusion rate and the storage space of the electrolyte, thereby causing the kinetic performance of the battery to decrease. Therefore, the ratio of W1 to W2 should be less than or equal to 5, wherein the width of the first active coating 210 is W1 mm, and the width of the second active coating 220 is W2 mm.

[0039] Specifically, in order to ensure the energy density of the battery while providing a higher ion diffusion rate and more electrolyte storage space, the width W2 of the second active coating 220 can be controlled in the range of 1 millimeter to 3 millimeters and / or the ratio of the width W1 of the first active coating 210 to the width W2 of the second active coating 220 is less than or equal to 5 but greater than or equal to 1.

[0040] It can be understood that the active material of the first active coating 210 and the active material of the second active coating 220 can be at least one of artificial graphite, natural graphite, hard carbon, and silicon-based materials, wherein the active material of the first active coating 210 and the active material of the second active coating 220 are the same substance. The conductive agent is at least one of conductive carbon black, carbon nanotubes, and graphene; and the binder is at least one of butadiene rubber, sodium carboxymethyl cellulose, and polymethyl methacrylate. In some embodiments, the active material includes a silicon-carbon material with a core-shell structure or a silicon-carbon material with porous carbon deposited silicon.

[0041] Specifically, in some embodiments, the active material used in the active coating includes a silicon-carbon material with a core-shell structure or a silicon-carbon material with porous carbon deposited silicon. If the laser drilling method is used to improve the kinetic performance of the battery, the carbon matrix around the nano-silicon and the coating layer on the surface of the composite material will be damaged during the laser drilling process, thereby directly exposing the active nano-silicon to the air and electrolyte environment, and reducing the service life of the battery. However, the technical solution of the present application, in which the plurality of first active coatings 210 and the plurality of second active coatings 220 are alternately arranged, and the ratio of Ds2 to Ds1 is less than or equal to 0.5, and the ratio of D502 to D501 is greater than or equal to 1.3, will not damage the carbon matrix around the nano-silicon and the coating layer on the surface of the composite material.

[0042] In order to further illustrate the present application, the present application will be further illustrated by specific examples. Unless otherwise specified, the experimental methods used in the examples of the present application are conventional methods; and unless otherwise specified, other materials and reagents used in the examples of the present application are commercially available.

[0043] Example 1

[0044] The present embodiment provides a battery, which includes an electrode assembly formed by winding a positive electrode sheet and a negative electrode sheet, and a separator is further arranged between the positive electrode sheet and the negative electrode sheet, and an electrolyte is further filled in the battery.

[0045] The preparation method is as follows:

[0046] (1) Preparation of the positive electrode sheet: the positive electrode active material, the conductive agent acetylene black, and the binder polyvinylidene fluoride are mixed uniformly in a mass ratio of 95:3:2 in an N-methylpyrrolidone solvent system, and then coated on a positive electrode current collector, the material of the positive electrode current collector is aluminum foil, and then dried, cold-pressed, and slitted to obtain the positive electrode sheet.

[0047] (2) Preparation of the negative electrode sheet: The artificial graphite and porous carbon silicon-deposited silicon-carbon material were mixed in a mass ratio of 9:1 and sieved by a sieving device to obtain a first negative electrode active material with D101 of 5.5 μm, D501 of 13.5 μm, and D901 of 28.5 μm. The artificial graphite and porous carbon silicon-deposited silicon-carbon material were mixed in a mass ratio of 9:1 and sieved by a sieving device to obtain a second negative electrode active material with D102 of 18.5 μm, D502 of 21.6 μm, and D902 of 24.7 μm.

[0048] The first negative electrode active material, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose were mixed in a mass ratio of 96:1:1.5:1.5 in a deionized water solvent system, and stirred sufficiently to obtain a first active coating slurry. The second negative electrode active material, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose were mixed in a mass ratio of 96:1:1.5:1.5 in a deionized water solvent system, and stirred sufficiently to obtain a second active coating slurry. The first active coating slurry and the second active coating slurry were alternately coated on the surface of the negative current collector in the length direction of the electrode sheet by electrostatic spraying, and then dried, cold-pressed, and slitted to obtain a negative electrode sheet with the first active coating and the second active coating alternately arranged in the length direction of the electrode sheet. In this embodiment, the negative current collector was a copper foil with a thickness of 6 μm, and the two surfaces of the current collector were both coated with the first active coating and the second active coating alternately arranged in the length direction of the electrode sheet. In this embodiment, the width W1 of the first active coating formed by the first active coating slurry in the length direction of the electrode sheet was 1 mm, and the width W2 of the second active coating formed by the second active coating slurry in the length direction of the electrode sheet was 1 mm. Alternatively, the first active coating slurry and the second active coating slurry can be alternately coated on the surface of the negative current collector in the length direction of the electrode sheet by 3D printing or extrusion die.

[0049] (3) Selection of the separator film

[0050] A polyethylene (PE) porous polymer film was used as the separator film.

[0051] (4) Preparation of the electrolyte

[0052] Lithium salt LiPF6 was added to a non-aqueous organic solvent (ethylene carbonate (EC): fluoroethylene carbonate (FEC): diethyl carbonate (DEC): propylene carbonate (PC): dimethyl carbonate (DMC) = 1:1:1:1:1, weight ratio), and the concentration of LiPF6 was 1 mol / L, and the mixture was uniformly mixed.

[0053] (5) Preparation of the lithium ion secondary battery

[0054] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a safety isolation, and the electrode assembly is obtained by winding. The electrode assembly is placed in a packaging shell, electrolyte is injected and packaged, and a lithium ion secondary battery is obtained.

[0055] Example 2

[0056] Example 1 and Example 2 differ only in that the first active coating formed by the first active coating slurry in Example 2 has a width W1 of 3 mm in the length direction of the electrode sheet, and the second active coating formed by the second active coating slurry has a width W2 of 3 mm in the length direction of the electrode sheet. The others are the same as in Example 1 and will not be repeated.

[0057] Example 3

[0058] Example 1 and Example 3 differ only in that the first active coating formed by the first active coating slurry in Example 3 has a width W1 of 5 mm in the length direction of the electrode sheet, and the second active coating formed by the second active coating slurry has a width W2 of 1 mm in the length direction of the electrode sheet. The others are the same as in Example 1 and will not be repeated.

[0059] Example 4

[0060] Example 1 and Example 4 differ only in that the D102 of the second active material in the negative electrode sheet of Example 4 is 14.8 μm, the D502 is 18 μm, and the D902 is 21.2 μm, and the active material of the above particle size is obtained by screening equipment. The others are the same as in Example 1 and will not be repeated.

[0061] Example 5

[0062] Example 1 and Example 5 differ only in that the D102 of the second active material in the negative electrode sheet of Example 5 is 18.5 μm, the D502 is 19.85 μm, and the D902 is 21.2 μm, and the active material of the above particle size is obtained by screening equipment. The others are the same as in Example 1 and will not be repeated.

[0063] Example 6

[0064] Example 1 and Example 6 differ only in that the D102 of the second active material in the negative electrode sheet of Example 6 is 14.8 μm, the D502 is 19.78 μm, and the D902 is 24.7 μm, and the active material of the above particle size is obtained by screening equipment. The others are the same as in Example 1 and will not be repeated.

[0065] Example 7

[0066] The difference between Example 1 and Example 7 is only that the first active coating layer formed by the first active coating slurry of Example 7 has a width W1 of 5 mm in the length direction of the pole piece, and the second active coating layer formed by the second active coating slurry has a width W2 of 5 mm in the length direction of the pole piece. The others are the same as Example 1, and will not be repeated here.

[0067] Example 8

[0068] The difference between Example 1 and Example 8 is only that the first active coating layer formed by the first active coating slurry of Example 8 has a width W1 of 7 mm in the length direction of the pole piece, and the second active coating layer formed by the second active coating slurry has a width W2 of 1 mm in the length direction of the pole piece. The others are the same as Example 1, and will not be repeated here.

[0069] Comparative Example 1

[0070] The difference between Example 1 and Comparative Example 1 is only that the D102 of the second active material in the negative pole piece of Comparative Example 1 is 14.8 μm, the D502 is 16.65 μm, and the D902 is 18.5 μm, and the active material of the above particle size is obtained by screening the screening equipment. The others are the same as Example 1, and will not be repeated here.

[0071] Comparative Example 2

[0072] The difference between Example 1 and Comparative Example 2 is only that the D102 of the second active material in the negative pole piece of Comparative Example 2 is 10.6 μm, the D502 is 20.15 μm, and the D902 is 29.7 μm, and the active material of the above particle size is obtained by screening the screening equipment. The others are the same as Example 1, and will not be repeated here.

[0073] Comparative Example 3

[0074] The difference between Comparative Example 3 and Example 1 is only that the active material layer of the negative pole piece of Comparative Example 3 is formed by the first active coating slurry, and does not contain the second active coating layer. The others are the same as Example 1, and will not be repeated here.

[0075] Comparative Example 4

[0076] The difference between Comparative Example 4 and Example 1 is only that the active material layer of the negative pole piece of Comparative Example 4 is formed by the first active coating slurry, and does not contain the second active coating layer. And the surface of the active material layer of Comparative Example 4 is laser punched, and the punching depth is 20% of the coating thickness. The others are the same as Example 1, and will not be repeated here.

[0077] The parameters of Example 1 to Example 8 and Comparative Example 1 to Comparative Example 4 are shown in Table 1.

[0078]

[0079] Table 1

[0080] The batteries provided in Examples 1 to 8 and Comparative Examples 1 to 4 were subjected to lithium precipitation tests, and the lithium precipitation test method was as follows:

[0081] At room temperature, the following steps were performed:

[0082] 1. XC rate constant current charging to 4.5V, 4.5V constant voltage charging to current less than 0.05C;

[0083] 2. Standby for 10 min;

[0084] 3. 0.7C constant current discharging to 3.0V;

[0085] 4. Standby for 10 min;

[0086] 5. Repeat steps 1 to 4 for a total of 20 times;

[0087] 6. 0.5C constant current charging to 4.5V, 4.5V constant voltage charging to current less than 0.05C.

[0088] Wherein, X is respectively 2.5, 3, 3.5, 4, 4.5.

[0089] The results are shown in Table 2:

[0090]

[0091]

[0092] Table 2

[0093] Wherein, slight lithium precipitation is only slight lithium precipitation at the head and tail of the pole piece, and no lithium precipitation at other places; moderate lithium precipitation is lithium precipitation at the head and tail of the pole piece and the tab, and no lithium precipitation on the large surface; severe lithium precipitation is lithium precipitation at the head and tail of the pole piece, the tab and the large surface.

[0094] As can be seen from Table 2, under the condition that Ds2 / Ds1≤0.5 and D502 / D501≥1.3 between the first active coating and the second active coating, the laser drilling lithium precipitation improvement effect can be achieved.

[0095] The batteries provided in Examples 1 to 8 and Comparative Examples 1 to 4 were subjected to self-discharge tests, and the self-discharge test method was as follows:

[0096] Charged at 0.5C rate constant current to voltage reaches 4.0V at room temperature, further charged at 4.0V constant voltage to current less than 0.05C, then put into 45℃ environment for 24h, then into 25℃ environment for 24h, record the voltage after storage as OCV1, finally put the battery in 25℃ for 48h, record the voltage after storage as OCV2, and calculate K value. Wherein, K value=(OCV2-OCV1) / 48h, unit: mV / h.

[0097] The results are shown in Table 3:

[0098] K value Percent change in K value Example 1 0.0229 -5.80％ Example 2 0.0233 -4.10％ Example 3 0.0239 -1.60％ Example 4 0.0238 -2.10％ Example 5 0.0231 -4.90％ Example 6 0.0233 -4.10％ Example 7 0.0235 -3.30％ Example 8 0.0242 -0.40％ Comparative Example 1 0.0241 -0.80％ Comparative Example 2 0.0239 -1.60％ Comparative Example 3 0.0243 0.00％ Comparative Example 4 0.0311 28％

[0099] Wherein, the larger the K value, the higher the self-discharge rate, the K value change percentage=(the K value of each group of examples or comparative examples-the K value of comparative example 3) / the K value of comparative example 3*100%, the smaller the K value change percentage, the smaller the K value, and the better the self-discharge performance.

[0100] As can be seen from Table 2, both the application and laser drilling can improve the dynamic performance of the battery and reduce the risk of lithium precipitation. However, as can be seen from Table 3, laser drilling will have a greater impact on self-discharge while improving the dynamic performance of the battery, while the application can effectively improve the self-discharge performance while improving the dynamic performance of the battery. The higher the self-discharge rate of the battery, the faster it will lose its capacity during storage, which not only affects the battery's endurance, but also may cause the battery to fail to meet the expected power demand after a long period of non-use, resulting in a decrease in the battery's service life.

[0101] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0102] The above is a specific description of the preferred embodiments of the present application, but the present application is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or replacements without departing from the spirit of the present application, and these equivalent modifications or replacements are all included in the scope defined by the claims of the present application.

Claims

1. A negative electrode sheet, characterized by, include: A current collector, wherein the thickness direction of the current collector is a first direction; A negative electrode active material layer is disposed on at least one surface of the current collector; The negative electrode active material layer includes a first active coating and a second active coating alternately arranged along a second direction perpendicular to the first direction. The first active coating and the second active coating satisfy the following conditions: 0.1≤Ds2 / Ds1≤0.5, 1.3≤D502 / D501≤2, 1.5≤Ds2≤10, where Ds2= D902-D102, Ds1= D901-D101. D101 is the particle size corresponding to a cumulative particle size distribution percentage of 10% in the active material particles of the first active coating; D501 is the particle size corresponding to a cumulative particle size distribution percentage of 50% in the active material particles of the first active coating; D901 is the particle size corresponding to a cumulative particle size distribution percentage of 90% in the active material particles of the first active coating; D102 is the particle size corresponding to a cumulative particle size distribution percentage of 10% in the active material particles of the second active coating; D502 is the particle size corresponding to a cumulative particle size distribution percentage of 50% in the active material particles of the second active coating; and D902 is the particle size corresponding to a cumulative particle size distribution percentage of 90% in the active material particles of the second active coating. The active material in the first active coating and the active material in the second active coating are the same substance.

2. The negative electrode sheet according to claim 1, characterized by In the alternating arrangement direction of the first active coating and the second active coating, the width of the first active coating is W1 mm, the width of the second active coating is W2 mm, and W1 / W2≤5.

3. The negative electrode sheet according to claim 1, characterized by In the alternating arrangement direction of the first active coating and the second active coating, the width of the first active coating is W1 mm, the width of the second active coating is W2 mm, and 1≤W1 / W2≤5; And / or, the width W2 mm of the second active coating is 1-3 mm.

4. The negative electrode sheet according to claim 1, wherein The active material of the first active coating and the active material of the second active coating are at least one of artificial graphite, natural graphite, hard carbon and silicon-based materials.

5. The negative electrode sheet according to claim 4, characterized by The active materials of the first active coating and the second active coating include silicon-based materials.

6. The negative electrode sheet according to claim 5, characterized by The silicon-based materials include silicon-carbon materials.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein The first active coating and the second active coating further include a conductive agent and a binder; the conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene, and the binder includes at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, and polymethyl methacrylate.

8. A battery, characterized by Includes the negative electrode sheet as described in any one of claims 1-7.

9. An electric device, characterized by Includes the battery as described in claim 8.

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