Negative plate and battery

Abstract

The negative plate comprises a current collector and a coating layer, the coating layer is arranged on at least one side of the current collector in the thickness direction, the coating layer comprises a first coating layer and a second coating layer, the first coating layer is arranged on at least one side of the second coating layer in the width direction of the current collector, and the second coating layer is arranged on at least one side of the second coating layer in the width direction of the current collector. The electrode plate is positioned in the edge area of the negative plate; wherein the hard carbon content of the first coating is higher than that of the second coating. The hard carbon content of the first coating is higher than the hard carbon content of the second coating, and the lithium ion diffusion coefficient of the hard carbon is obviously higher than that of the graphite, so that the charging rate of the first coating is obviously higher than that of the graphite. And the problem of lithium separation caused by lithium ion accumulation is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, in particular to a negative electrode sheet and a battery. Background Art

[0002] When charging at a high rate, the negative electrode of the lithium-ion battery is prone to lithium deposition, specifically, lithium deposition will occur at the edge of the negative electrode sheet in the width direction. To solve this problem, the relevant technology mainly adopts the following two solutions: 1. Reduce the surface density of the graphite layer of the negative electrode sheet, that is, reduce the thickness of the graphite layer; 2. Use fast-charging graphite instead of ordinary graphite. However, the former will significantly reduce the energy density, and the latter will increase the cost. At the same time, fast-charging graphite has a larger specific surface area than ordinary graphite, and the contact area with the electrolyte will be significantly increased, which is more likely to produce negative reactions with the electrolyte and reduce safety performance. Utility Model Content

[0003] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model provides a negative electrode sheet that can improve the lithium deposition problem during high-rate charging.

[0004] The utility model also provides a battery using the pole piece.

[0005] According to the first embodiment of the utility model, the negative electrode sheet comprises:

[0006] current collector;

[0007] A coating layer is disposed on at least one side of the current collector in a thickness direction, the coating layer comprises a first coating layer and a second coating layer, the first coating layer is disposed on at least one side of the second coating layer along a width direction of the current collector and is located in an edge region of the negative electrode sheet;

[0008] Wherein, the hard carbon content of the first coating layer is higher than the hard carbon content of the second coating layer.

[0009] The negative electrode sheet according to the embodiment of the utility model has at least the following beneficial effects:

[0010] The hard carbon content of the first coating layer is higher than that of the second coating layer. The lithium ion diffusion coefficient of hard carbon is significantly higher than that of graphite, so its charging rate is also significantly higher than that of graphite. In this embodiment, by setting a first coating layer with a higher hard carbon content on the side edge where lithium deposition is prone to occur, lithium ions can be quickly accepted when lithium ions are embedded, thereby reducing lithium deposition problems caused by lithium ion accumulation.

[0011] In other embodiments of the present invention, the first coating layer includes a first hard carbon layer, and the second coating layer includes a graphite layer.

[0012] In other embodiments of the present invention, the first coating includes a first hard carbon layer, the second coating includes a graphite layer and a second hard carbon layer stacked along the thickness direction of the current collector, the second hard carbon layer is arranged on the side of the graphite layer away from the current collector, and the hard carbon content of the first hard carbon layer is higher than the hard carbon content of the second hard carbon layer.

[0013] In other embodiments of the present invention, the hard carbon content of the first coating layer gradually decreases along the direction from the first coating layer to the second coating layer.

[0014] In other embodiments of the present invention, the first coating layer includes a plurality of coating regions arranged in parallel along the width direction of the current collector, and the hard carbon content of each coating region gradually decreases along the direction from the first coating layer to the second coating layer.

[0015] In other embodiments of the present invention, the width of the negative electrode sheet is defined as W1, the width of the first coating is defined as W2, the ratio of the charging rate of the first coating to the charging rate of the second coating is defined as S, the lithium precipitation parameter is defined as K, and the charging rate increase value of the battery prepared by the negative electrode sheet is defined as Fc. Then, the negative electrode sheet satisfies:

[0016] W2=K*W1*Fc / S, and the value range of K is 0.04 to 0.15.

[0017] In other embodiments of the present invention, the thickness of the first coating layer is equal to that of the second coating layer, and the surface density of the first coating layer is less than that of the second coating layer.

[0018] The battery according to the second embodiment of the present utility model comprises:

[0019] A battery cell, the battery cell comprising the aforementioned negative electrode sheet;

[0020] The tab is connected to the negative electrode sheet.

[0021] In other embodiments of the present invention, along the length direction of the current collector, the electrode tab is connected to the first end of the negative electrode sheet, the second side of the electrode tab facing the second end of the negative electrode sheet is provided with the first coating, the first coating extends along the length direction of the current collector, and the first end is arranged opposite to the second end;

[0022] Alternatively, along the length direction of the current collector, the electrode tab is connected to a position between the first end and the second end of the negative electrode sheet, and the first coating is provided on a first side of the electrode tab toward the first end of the negative electrode sheet and on a second side of the electrode tab toward the second end, and the first coating on both sides extends along the length direction of the current collector, and the first end is arranged opposite to the second end.

[0023] In other embodiments of the present invention, the width of the first coating layer gradually decreases in a direction away from the electrode lug.

[0024] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention is further described below with reference to the accompanying drawings and embodiments, wherein:

[0026] Figure 1 It is a cross-sectional schematic diagram of the negative electrode sheet in the first embodiment of the utility model, and the cross-sectional plane is a vertical plane and is parallel to the length direction of the negative electrode sheet;

[0027] Figure 2 It is a top view of the negative electrode sheet in the first embodiment of the utility model;

[0028] Figure 3 for Figure 2 A schematic cross-sectional view of the negative electrode sheet, wherein the cross-sectional view is a vertical plane and is parallel to the width direction of the negative electrode sheet;

[0029] Figure 4 It is a cross-sectional schematic diagram of a negative electrode sheet in another embodiment of the utility model, and the cross-sectional plane is a vertical plane and is parallel to the width direction of the negative electrode sheet;

[0030] Figure 5 A top view of a negative electrode sheet in another embodiment of the utility model;

[0031] Figure 6 It is a top view of a negative electrode sheet connected with a tab in an embodiment of the utility model;

[0032] Figure 7 It is a top view of a negative electrode sheet connected with a tab in another embodiment of the present invention.

[0033] Reference numerals:

[0034] Negative electrode sheet 100, current collector 110, coating layer 120, first coating layer 121, coating area 1211, second coating layer 122, graphite layer 1221, second hard carbon layer 1222, first end 101, second end 102;

[0035] Tab 200. DETAILED DESCRIPTION

[0036] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0037] In the description of the present invention, it should be understood that descriptions involving orientation, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0038] In the description of the present utility model, "several" means more than one, "many" means more than two, "greater than", "less than", "exceed" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used to distinguish the technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0039] In the description of the present utility model, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present utility model based on the specific content of the technical solution.

[0040] In the description of the utility model, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation 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.

[0041] As mentioned above, if the lithium-ion battery is charged at a high rate exceeding its original charging rate without modification, the lithium-ion battery is prone to lithium plating at the negative electrode due to excessive charging and discharging current. The traditional solution is to reduce the surface density of the graphite layer of the negative electrode sheet or use fast-charging graphite instead of ordinary graphite. On the basis of a certain compaction density, the lower the surface density of the graphite layer, the thinner the thickness, which is more conducive to lithium ion migration, but the energy density will be significantly reduced; fast-charging graphite has more lithium ion migration channels than ordinary graphite, but its cost will increase significantly, and fast-charging graphite has a larger specific surface area than ordinary graphite, so it is easier to produce negative reactions with the electrolyte and reduce safety performance. Based on this, the utility model proposes a negative electrode sheet 100, which can improve the lithium plating problem of the negative electrode sheet during high-rate charging, which will be explained in conjunction with specific embodiments and drawings below.

[0042] Reference Figures 1 to 3 , Figure 1 and Figure 3 All of them are cross-sectional schematic diagrams of the negative electrode sheet in the first embodiment of the present utility model, wherein: Figure 1 The section plane in is a vertical plane and is parallel to the length direction of the negative electrode sheet. Figure 1 The section plane in is a vertical plane and is parallel to the width direction of the negative electrode sheet. Figure 2 The negative electrode sheet 100 includes a current collector 110 and a coating layer 120. Figure 1 and Figure 3 In the up and down direction), at least one side of the current collector 110 is provided with a coating layer 120, specifically Figure 1 and Figure 3 In the embodiment, the coating layer 120 is disposed on both sides of the current collector 110 in the thickness direction.

[0043] The coating layer 120 includes a first coating layer 121 and a second coating layer 122, and is disposed along the width direction (eg Figure 2 The first coating 121 is disposed on at least one side of the second coating 122, and the second coating 122 is located in the edge area of ​​the negative electrode sheet 100, that is, the area where lithium deposition is likely to occur. Figure 2 In the embodiment, the first coating layer 121 is disposed on both sides of the second coating layer 122 along the width direction of the current collector 110 .

[0044] In the present embodiment, the hard carbon content of the first coating 121 is higher than the hard carbon content of the second coating 122. The lithium ion diffusion coefficient of hard carbon is significantly higher than that of graphite, and therefore its charging rate is also significantly higher than that of graphite (specifically, the charging rate of hard carbon is more than five times that of graphite). In the present embodiment, by providing a first coating with a higher hard carbon content on the side edges where lithium plating is prone to occur, the first coating can quickly accept lithium ions when lithium ions are embedded from the side edges in a direction parallel to the electrode, thereby reducing lithium plating problems caused by lithium ion accumulation.

[0045] Based on the first embodiment, refer to Figure 3 In some embodiments of the present invention, the first coating 121 includes a first hard carbon layer, and the second coating 122 includes a graphite layer 1221. In other words, the hard carbon content of the second coating 122 in this embodiment can be as low as 0. It should be noted that although the charging rate of the graphite layer is lower than that of the hard carbon, its energy density is higher than that of the hard carbon. In this embodiment, by arranging the first hard carbon layer in the edge area and the graphite layer in the middle area, the lithium precipitation problem in the edge area can be improved, and the energy density of the negative electrode sheet can be ensured.

[0046] Based on the first embodiment, refer to Figure 4 , Figure 4 This is a cross-sectional diagram of the negative electrode sheet in the present practical embodiment. The cross-sectional plane in the figure is a vertical plane and is parallel to the width direction of the negative electrode sheet. As shown in the figure, the first coating 121 includes a first hard carbon layer, and the second coating 122 includes a graphite layer 1221 and a second hard carbon layer 1222. In other words, the second coating 122 in the present embodiment also contains a certain amount of hard carbon. The graphite layer 1221 and the second hard carbon layer 1222 are stacked along the thickness direction of the current collector 110, and the second hard carbon layer 1222 is arranged on the side of the graphite layer 1221 away from the current collector 110, that is, the side close to the adjacent positive electrode sheet. In this way, when the negative electrode sheet and the positive electrode sheet are formed into a battery cell by winding or stacking, when lithium ions migrate between the electrode sheets in a direction perpendicular to the electrode sheets, the second hard carbon layer can quickly receive lithium ions, thereby reducing the lithium precipitation problem caused by the accumulation of lithium ions. Specifically, Figure 4 In the figure, for the second coating layer 122 on the upper side, the second hard carbon layer 1222 is located above the graphite layer 1221 , and for the second coating layer 122 on the lower side, the second hard carbon layer 1222 is located below the graphite layer 1221 .

[0047] In addition, in this embodiment, the hard carbon content of the first hard carbon layer is higher than the hard carbon content of the second hard carbon layer 1222. Combined with the above, this embodiment can not only improve the lithium plating problem in the edge area, but also facilitate the migration of lithium ions within the second coating 122 along the vertical direction of the electrode.

[0048] On the basis of the first embodiment, in some embodiments of the utility model, along the direction from the first coating 121 to the second coating 122, that is, from the edge of the pole piece to the middle of the pole piece, the hard carbon content of the first coating 121 gradually decreases. For example, the first coating 121 is a mixed material of hard carbon and graphite, and the proportion of the former gradually decreases along the direction from the first coating 121 to the second coating 122. In other words, the proportion of graphite gradually increases along the direction from the first coating 121 to the second coating 122. It should be noted that, generally speaking, the closer the area is to the edge of the pole piece, the more serious the lithium precipitation problem is. This embodiment can more accurately match the change in the degree of lithium precipitation by setting the first coating 121 with a gradually changing hard carbon content. When the first coating 121 is a mixed material of hard carbon and graphite, the hard carbon content increases and the graphite content decreases in the area with more lithium precipitation, and the hard carbon content decreases and the graphite content increases in the area with less lithium precipitation. It can not only meet the needs of improving the lithium precipitation problem, but also reduce the loss of energy density caused by setting hard carbon.

[0049] Based on the first embodiment, refer to Figure 5 In some embodiments of the present invention, the first coating 121 includes a plurality of coating regions 1211 arranged in parallel along the width direction of the current collector 110. Along the direction from the first coating 121 to the second coating 122, that is, from the edge of the pole piece to the middle of the pole piece, the hard carbon content of each coating region 1211 gradually decreases. Figure 5 As shown in the example, the first coating 121 includes three coating areas 1211. Along the direction from the outside to the middle of the pole piece, the outermost coating area 1211 is all hard carbon material, and the middle and inner coating areas 1211 are mixed materials of hard carbon and graphite, and the content of hard carbon in the middle coating area 1211 is greater than the hard carbon content of the inner coating area 1211. It should be noted that, generally speaking, the closer the area is to the edge of the pole piece, the more serious the lithium precipitation problem is. In this embodiment, the first coating 121 includes a plurality of coating areas 1211 with gradually changing hard carbon content, which can more accurately match the change in the degree of lithium precipitation. When at least part of the coating area 1211 is a mixed material of hard carbon and graphite, the hard carbon content in the area with more lithium precipitation increases accordingly and the graphite content decreases accordingly, and the hard carbon content in the area with less lithium precipitation decreases accordingly and the graphite content increases accordingly, which can not only meet the needs of improving the lithium precipitation problem, but also reduce the loss of energy density caused by setting hard carbon.

[0050] It should be noted that there are many ways to gradually reduce the hard carbon content of each coating area 1211. For example, the width and thickness of each coating area 1211 are the same, and the proportion of hard carbon therein is different; for another example, the thickness of each coating area 1211 is the same as the proportion of hard carbon therein, but the width is different.

[0051] On the basis of the first embodiment, in some embodiments of the utility model, the width of the negative electrode sheet is defined as W1, the width of the first coating 121 is defined as W2, the ratio of the charging rate of the first coating 121 to the charging rate of the second coating 122 is defined as S, the lithium precipitation parameter is defined as K, and the charging rate increase value of the battery prepared by the negative electrode sheet is defined as Fc, then the negative electrode sheet satisfies:

[0052] W2=K*W1*Fc / S, and the value range of K is 0.04 to 0.15

[0053] It should be noted that the lithium deposition parameter specifically refers to the ratio of the lithium deposition area to the total width of the negative electrode sheet when lithium deposition occurs in a negative electrode sheet of the same specification without the first coating 121 .

[0054] It should be noted that this embodiment describes the width of the first coating 121 that needs to be set when further improving the charging rate of an existing battery. For example, the width of the negative electrode sheet is 86mm, the value of S is 5, and when the current charging rate is increased by 1C, the lithium deposition width W2=86*(4%~15%)*1 / 5=0.688~2.58mm. Therefore, setting the first coating 121 with a width of 2.58mm can improve the problem of lithium deposition at the edge; for another example, the width of the negative electrode sheet is 86mm, the value of S is 5, and when the current charging rate is increased by 2C, the lithium deposition width W2=86*(4%~15%)*2 / 5=1.376~5.16mm. Therefore, setting the first coating 121 with a width of 5.16mm can improve the problem of lithium deposition at the edge.

[0055] The following experiments verify that the battery capacity in the comparative example and the present solution is 4900mAh, the width of the negative electrode sheet is 86mm, the negative electrode sheet in the comparative example is not provided with the first coating 121, the negative electrode sheet in the present solution is provided with the first coating, and the width of the first coating is 2.58mm, the charging rate is increased from 2C to 3C, that is, the increase in the charging rate is 1C, and relevant tests are performed, and the test results are as follows:

[0056]

[0057] From the above, it can be seen that after 100 weeks of 3C charging, the battery was disassembled. There was a lithium deposition area on the negative electrode sheet in the comparative example, but there was no lithium deposition area in this solution, and the lithium deposition problem was improved. At room temperature, after charging at a 3C rate and discharging at a 0.7C rate and cycling for 600 weeks, the retention rate of the comparative example was 82.1%, and the retention rate of this solution was 89.4%, an increase of 7.3%. The expansion rate of the comparative example was 10.4%, and the retention rate of this solution was 7.8%, a decrease of 2.6%. At 45°C, after charging at a 3C rate and discharging at a 0.7C rate and cycling for 400 weeks, the retention rate of the comparative example was 83.2%, and the retention rate of this solution was 85.5%, an increase of 2.3%. That is, the cycle performance of this solution under high rate charging is better than that of comparative example 1.

[0058] On the basis of the first embodiment, in some embodiments of the utility model, the thickness of the first coating 121 and the second coating 122 are equal, so that the roller can roll the first coating 121 and the second coating 122 of the negative electrode sheet synchronously to roll the first coating 121 and the second coating 122 to the same thickness. In addition, in this embodiment, the surface density of the first coating 121 is less than the surface density of the second coating 122, that is, the compaction density of the first coating 121 is less than the compaction density of the second coating 122, and the limit compression amount of the first coating 121 during rolling is less than the limit compression amount of the second coating 122. In this way, when coating, the coating thickness of the first coating 121 is less than the coating thickness of the second coating 122, so that the hard carbon particles can be prevented from being fractured during rolling and losing the lithium insertion ability.

[0059] The second embodiment of the present invention further provides a battery, which includes a positive electrode sheet, a positive electrode ear, a separator, a negative electrode ear 200 and the negative electrode sheet 100 of the above-mentioned embodiments, wherein the positive electrode sheet, the separator and the negative electrode sheet 100 are wound or stacked to form a battery cell, the positive electrode ear is connected to the positive electrode sheet, and the negative electrode ear 200 is connected to the negative electrode sheet 100, such as Figure 6 , Figure 7 shown.

[0060] Based on the second embodiment, refer to Figure 6 , along the length direction of the current collector 110, that is, Figure 6 In the left-right direction, the tab 200 is connected to the first end 101 of the negative electrode sheet 100. Specifically, the first end 101 of the negative electrode sheet 100 is provided with an empty foil area, and the tab 200 is connected to the empty foil area of ​​the negative electrode sheet 100 by welding or the like.

[0061] In this embodiment, a first coating 121 is provided on the second side of the pole tab 200 facing the second end 102 of the negative electrode sheet 100, and the first coating 121 extends along the length direction of the current collector 110. The first end 101 and the second end 102 are arranged opposite to each other. For example, the first end 101 is the left end of the negative electrode sheet 100, and the second end 102 is the right end of the negative electrode sheet 100. The pole tab 200 is arranged at the left end of the negative electrode sheet 100, and the first coating 121 is provided on the right side of the pole tab 200, and the first coating 121 extends from the first end 101 to the direction of the second end 102.

[0062] In this embodiment, since the pole tab 200 is arranged at the end of the negative electrode sheet 100, the current mainly flows on one side of the pole tab 200, so the lithium deposition area is also mainly formed on one side of the pole tab 200. In this embodiment, the first coating 121 is arranged on one side of the pole tab 200 to match the lithium deposition area.

[0063] Based on the second embodiment, refer to Figure 7 , along the length direction of the current collector 110, that is, Figure 6 In the left and right directions, the tab 200 is connected to a position between the first end 101 and the second end 102 of the negative electrode sheet 100. The present embodiment does not limit the specific position of the tab 200, which may be in the middle of the negative electrode sheet 100, or at any position biased toward the first end 101, or at any position biased toward the second end 102.

[0064] In this embodiment, the first side of the pole tab 200 facing the first end 101 of the negative electrode sheet 100 and the second side facing the second end 102 are both provided with a first coating 121, and the first coating 121 on both sides extends along the length direction of the current collector 110, and the first end 101 and the second end 102 are arranged opposite to each other. For example, the first end 101 is the left end of the negative electrode sheet 100, and the second end 102 is the right end of the negative electrode sheet 100. The pole tab 200 is arranged between the left end and the right end of the negative electrode sheet 100, then the left and right sides of the pole tab 200 are provided with the first coating 121, and the first coating 121 on the left side extends from the second end 102 to the first end 101, and the first coating 121 on the right side extends from the first end 101 to the second end.

[0065] In this embodiment, since the pole tab 200 is arranged between the first end 101 and the second end 102 of the negative electrode sheet 100, the current flows on both sides of the pole tab 200, so lithium deposition areas are formed on both sides of the pole tab 200. In this embodiment, a first coating 121 is arranged on both sides of the pole tab 200 to match the lithium deposition area.

[0066] It should be noted that when referring to the first end 101 and the second end 102 , the description is made based on the negative electrode sheet 100 being in an unfolded state.

[0067] Based on the second embodiment, refer to Figure 6 , the width of the first coating 121 gradually decreases in the direction away from the pole ear 200. Generally speaking, the width of the lithium deposition area is larger as it is closer to the pole ear 200, so the lithium deposition area is roughly triangular. In this embodiment, the width of the first coating 121 is set to gradually decrease, which can accurately match the lithium deposition area, so that other areas can remain as the second coating 122, thereby reducing the loss of energy density caused by the setting of hard carbon.

[0068] It should be noted that although this embodiment is based on Figure 6 for illustration, but can also be applied to Figure 7 In addition, this embodiment does not limit the specific shape of the first coating layer 121, which may also be a triangle, a right-angled trapezoid, or a shape similar to these.

[0069] The embodiments of the utility model are described in detail above in conjunction with the accompanying drawings, but the utility model is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the utility model. In addition, the embodiments of the utility model and the features in the embodiments can be combined with each other without conflict.

Claims

1. A negative electrode sheet, characterized in that: include; current collector; A coating layer is disposed on at least one side of the current collector in a thickness direction, the coating layer comprises a first coating layer and a second coating layer, the first coating layer is disposed on at least one side of the second coating layer along a width direction of the current collector and is located in an edge region of the negative electrode sheet; Wherein, the hard carbon content of the first coating layer is higher than the hard carbon content of the second coating layer.

2. The negative electrode sheet according to claim 1, characterized in that: The first coating layer includes a first hard carbon layer, and the second coating layer includes a graphite layer.

3. The negative electrode sheet according to claim 1, characterized in that: The first coating includes a first hard carbon layer, and the second coating includes a graphite layer and a second hard carbon layer stacked along the thickness direction of the current collector, the second hard carbon layer is arranged on the side of the graphite layer away from the current collector, and the hard carbon content of the first hard carbon layer is higher than the hard carbon content of the second hard carbon layer.

4. The negative electrode sheet according to claim 1, characterized in that: The hard carbon content of the first coating layer gradually decreases along the direction from the first coating layer to the second coating layer.

5. The negative electrode sheet according to claim 1, characterized in that: The first coating layer includes a plurality of coating regions arranged in parallel along a width direction of the current collector, and the hard carbon content of each coating region gradually decreases along a direction from the first coating layer to the second coating layer.

6. The negative electrode sheet according to claim 1, characterized in that: The width of the negative electrode sheet is defined as W1, the width of the first coating is defined as W2, the ratio of the charging rate of the first coating to the charging rate of the second coating is defined as S, the lithium precipitation parameter is defined as K, and the charging rate increase value of the battery prepared by the negative electrode sheet is defined as Fc. Then, the negative electrode sheet satisfies: W2=K*W1*Fc / S, and the value range of K is 0.04 to 0.

15.

7. The negative electrode sheet according to claim 1, characterized in that: The thickness of the first coating layer is equal to that of the second coating layer, and the surface density of the first coating layer is smaller than that of the second coating layer.

8. A battery, characterized in that include: A battery cell, comprising the negative electrode sheet according to any one of claims 1 to 7; The tab is connected to the negative electrode sheet.

9. The battery according to claim 8, characterized in that Along the length direction of the current collector, the electrode tab is connected to the first end of the negative electrode sheet, the second side of the electrode tab facing the second end of the negative electrode sheet is provided with the first coating, the first coating extends along the length direction of the current collector, and the first end is arranged opposite to the second end; Alternatively, along the length direction of the current collector, the electrode tab is connected to a position between the first end and the second end of the negative electrode sheet, and the first coating is provided on a first side of the electrode tab toward the first end of the negative electrode sheet and on a second side of the electrode tab toward the second end, and the first coating on both sides extends along the length direction of the current collector, and the first end is arranged opposite to the second end.

10. The battery according to claim 9, characterized in that Along the direction away from the electrode ear, the width of the first coating layer gradually decreases.

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