Battery

Abstract

The utility model relates to a battery which comprises a positive plate and a negative plate, a negative current collector of the negative plate comprises a polymer layer and metal layers, and the metal layers cover two sides of the polymer layer. The polymer layer comprises a first middle region and a first redundant region; the metal layer comprises a second middle area and a second redundant area, and the thickness of the second middle area is larger than that of the second redundant area. According to the battery provided by the utility model, the second redundant region corresponds to the Overhang region. By reducing the thickness of the metal layer of the negative plate in the second redundant region, the resistance of the second redundant region is improved, the temperature of the Overhang region of the negative plate is improved, and the transmission rate of lithium ions in the Overhang region is improved. Therefore, when the battery reaches the discharge cut-off condition, discharge is more sufficient, and reversible capacity loss and lithium precipitation at the edge of the negative electrode are avoided. And on the other hand, the metal weight in the battery is reduced, the energy storage under the unit weight of the battery is increased, and the energy density is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery. Background Art

[0002] In the prior art, during the initial design stage of lithium-ion batteries, in order to minimize the risk of lithium deposition at the edge of the negative electrode during charging, the negative electrode is designed with a certain degree of redundancy (i.e., overhang) in length and width compared to the positive electrode.

[0003] Typically, when a lithium-ion battery maintains a high SOC (State of Charge), lithium ions flow from the overlapping area of ​​the positive and negative electrodes (the non-overhang area) to the overhang area. During the subsequent discharge process, especially at high current densities, the negative electrode preferentially removes lithium in the non-overhang area, resulting in different SOCs within the negative electrode, with the non-overhang area being lower and the overhang area being higher.

[0004] Due to kinetic hindrance, lithium ions in the overhang region take a long time to migrate from the overhang region to the non-overhang region, ultimately resulting in incomplete discharge when the discharge cutoff condition is reached, causing reversible capacity loss. After multiple charge and discharge cycles, lithium plating will further occur near the negative electrode area corresponding to the positive electrode edge. Utility Model Content

[0005] In view of this, the embodiments of the present application provide a battery to solve the problem of easy lithium deposition in the negative electrode sheet in the background art.

[0006] An embodiment of the present application provides a battery, comprising a positive electrode sheet and a negative electrode sheet arranged along the Z direction;

[0007] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer.

[0008] The negative electrode current collector comprises:

[0009] polymer layer;

[0010] a metal layer covering both sides of the polymer layer along the Z direction;

[0011] The polymer layer includes a first middle region and a first redundant region, wherein the first redundant region is located on both sides of the first middle region along the Y direction;

[0012] The metal layer includes a second middle region and a second redundant region, the second redundant region being located on both sides of the second middle region along the Y direction; a projection of the second middle region along the Z direction overlaps with a projection of the first middle region along the Z direction; the negative active material layer partially covers the second redundant region;

[0013] Along the Z direction, the projection of the first middle region, the projection of the second middle region, and the projection of the positive electrode active material layer overlap;

[0014] The thickness of the second intermediate region is greater than the thickness of the second redundant region.

[0015] In an optional embodiment, the width of the overhang region of the negative electrode sheet is a, and the widths of the first redundant region and the second redundant region are both b, where b=a.

[0016] In an optional embodiment, in the Y direction, the thickness of the second redundant region in a direction away from the second middle region remains unchanged, or gradually decreases, or partially gradually decreases and partially remains unchanged.

[0017] In an optional embodiment, in the Y direction, when the thickness of the second redundant region gradually decreases in a direction away from the second middle region, the thickness reduction amount of the second redundant region per unit distance remains unchanged or gradually increases.

[0018] In an optional embodiment, the thickness of the first middle region is smaller than the thickness of the first redundant region.

[0019] In an optional embodiment, along the Y direction, the thickness decrease of the first redundant area per unit distance is equal to the thickness increase of the second redundant area, and the thickness increase of the first redundant area per unit distance is equal to the thickness decrease of the second redundant area.

[0020] In an optional embodiment, the thickness of the first middle region is c, and c is 3 μm to 6 μm.

[0021] In an optional embodiment, the thickness of the first redundant region is d, and d is 4 μm to 8 μm.

[0022] In an optional embodiment, the total thickness of the polymer layer and the metal layer is e, and e is 5 μm to 10 μm.

[0023] In an optional embodiment, a is 0.2 mm to 5 mm.

[0024] The battery provided in the embodiment of the present application reduces the thickness of the negative electrode sheet in the second redundant area of ​​the metal layer, so that the thickness of the metal layer in the second redundant area is lower than the thickness of the metal layer in the second middle area, thereby increasing the resistance of the second redundant area. The second redundant area corresponds to the overhang area of ​​the negative electrode sheet. Therefore, it is possible to achieve higher heat generation in the overhang area of ​​the negative electrode sheet than in the middle area under the same current density, so that the temperature in the overhang area is higher than that in the middle area, thereby increasing the transmission rate of lithium ions in the overhang area and avoiding reversible capacity loss and lithium deposition at the edge of the negative electrode in the battery. On the other hand, in the battery provided in the embodiment of the present application, the thickness of the metal layer in the second redundant area is reduced, which reduces the weight of the metal, increases the energy storage per unit weight of the battery, and improves the energy density.

[0025] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0027] Figure 1 A schematic diagram showing the corresponding relationship between the positive electrode sheet and the negative electrode sheet of the battery provided in the embodiment of the present application;

[0028] Figure 2 A schematic diagram of the negative electrode composite current collector structure provided in an embodiment of the present application;

[0029] Figure 3 Schematic diagram of the Y-direction cross-sectional structure of the negative electrode composite current collector provided in the embodiments of the present application; wherein, (a) is a schematic diagram of the width-direction cross-sectional structure of the first negative electrode composite current collector, (b) is a schematic diagram of the width-direction cross-sectional structure of the second negative electrode composite current collector, (c) is a schematic diagram of the width-direction cross-sectional structure of the third negative electrode composite current collector, (d) is a schematic diagram of the width-direction cross-sectional structure of the fourth negative electrode composite current collector, and (e) is a schematic diagram of the width-direction cross-sectional structure of the fifth negative electrode composite current collector;

[0030] Figure 4 This is a schematic diagram of an uncut negative electrode sheet provided in an embodiment of the present application.

[0031] The reference numerals in the figures are:

[0032] 1. polymer layer; 3. first intermediate region; 4. first redundant region;

[0033] 2. Metal layer; 5. Second intermediate region; 6. Second redundant region;

[0034] 100, positive electrode sheet; 101, positive electrode active material layer; 103, positive electrode current collector;

[0035] 200, negative electrode sheet; 201, negative electrode active material layer; 202, overhang area; 203, negative electrode current collector. DETAILED DESCRIPTION

[0036] To make the technical solutions and beneficial effects of the present invention more clearly understood, the following detailed description is given by way of specific embodiments. The accompanying drawings are not necessarily drawn to scale, and local features may be enlarged or reduced to more clearly illustrate the details of the local features. Unless otherwise defined, the technical and scientific terms used herein have the same meanings as those in the technical field to which this application belongs.

[0037] In the description of the present invention, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "height", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and so on, indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of simplifying the description of the present invention, and do not indicate that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and should not be understood as a limitation to the present invention.

[0038] In this utility model, the terms "first" and "second" are used solely for descriptive purposes and should not be construed as indicating the relative importance of the features indicated or the number of technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly include at least one such feature. In the description of this utility model, "plurality" means at least two, such as two or three, and "several" means at least one, such as one, two, or three, unless otherwise expressly specified.

[0039] In this utility model, unless otherwise expressly defined, the terms "install," "connect," "connect," "fix," "dispose," etc. should be understood broadly. For example, "connect" can mean fixed, removable, or integrated; it can mean mechanical or electrical; it can mean direct or indirect connection through an intermediary; it can also mean internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of these terms in this utility model based on the specific circumstances.

[0040] In the present invention, unless otherwise clearly defined, when a first feature is “on,” “above,” “above,” “above,” “below,” “below,” or “below” a second feature, the first feature and the second feature may be in direct contact, or the first feature and the second feature may be in indirect contact via an intermediate medium. Moreover, when a first feature is “on,” “above,” or “above” a second feature, it may mean that the first feature is directly above or obliquely above the second feature, or simply means that the horizontal height of the first feature is higher than the horizontal height of the second feature. When a first feature is “below,” “below,” or “below” a second feature, it may mean that the first feature is directly below or obliquely below the second feature, or simply means that the horizontal height of the first feature is lower than the horizontal height of the second feature.

[0041] In this embodiment, the X direction, the Y direction, and the Z direction are based on the positional relationship among the X axis, the Y axis, and the Z axis in the three-dimensional coordinate system.

[0042] In order to fully understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may also have other implementation methods.

[0043] This embodiment provides a battery, such as Figure 1 As shown, it includes a positive electrode sheet 100 and a negative electrode sheet 200 arranged along the Z direction. The positive electrode sheet 100 includes a positive electrode collector 103 and a positive electrode active material layer 101 , and the negative electrode sheet 200 includes a negative electrode collector 203 and a negative electrode active material layer 201 .

[0044] The negative electrode current collector 203 includes a polymer layer 1 and a metal layer 2, and the metal layer 2 covers both sides of the polymer layer 1 along the Z direction. Figure 2 As shown, the polymer layer 1 includes a first intermediate region 3 and a first redundant region 4, and the first redundant region 4 is located on both sides of the first intermediate region 3 along the Y direction; the metal layer 2 includes a second intermediate region 5 and a second redundant region 6, and the second redundant region 6 is located on both sides of the second intermediate region 5 along the Y direction; the projection of the second intermediate region 5 along the Z direction overlaps with the projection of the first intermediate region 3 along the Z direction; the negative active material layer 201 partially covers the second redundant region 6.

[0045] like Figure 1 、 Figure 2 As shown, along the Z direction, the projection of the first intermediate region 3 , the projection of the second intermediate region 5 and the projection of the positive electrode active material layer 101 overlap; the thickness of the second intermediate region 5 is greater than the thickness of the second redundant region 6 .

[0046] like Figure 1As shown, the negative electrode sheet 200 of the battery provided in this embodiment is designed with an Overhang region 202, and the second redundant region 6 corresponds to the Overhang region 202. The battery provided in this embodiment reduces the thickness of the metal layer 2 of the negative electrode sheet 200 in the second redundant region 6, so that the thickness of the metal layer in the second redundant region 6 is lower than the thickness of the metal layer in the second intermediate region 5, thereby increasing the resistance of the second redundant region 6. Therefore, it is possible to achieve that the heat generation in the Overhang region 202 of the negative electrode sheet 200 is higher than that in the intermediate region at the same current density, so that the temperature of the Overhang region 202 is higher than that in the intermediate region, and the high temperature is conducive to the movement of lithium ions, thereby increasing the transmission rate of lithium ions in the Overhang region 202. Therefore, the time required for lithium ions to migrate from the Overhang region 202 to the non-Overhang region is reduced, and the battery is discharged more fully when it reaches the discharge cut-off condition, avoiding reversible capacity loss and lithium deposition at the edge of the negative electrode. On the other hand, in the battery provided in the embodiment of the present application, the thickness of the metal layer in the second redundant region 6 is reduced, which reduces the metal weight in the battery, increases the energy storage per unit weight of the battery, and improves the energy density.

[0047] In an optional embodiment, if Figure 1 、 Figure 2 As shown, the width of the overhang region 202 of the negative electrode sheet 200 is a, and the widths of the first redundant region 4 and the second redundant region 6 are both b, where b = a. In this embodiment, the widths of the first redundant region 4 and the second redundant region 6 are designed to be consistent with the width of the overhang region 202 to ensure that the heat generation of the entire overhang region 202 is increased, while the heat generation of the non-overhang region remains unchanged. This ensures that the lithium ion transmission rate in the overhang region 202 is relatively improved.

[0048] In an optional embodiment, if Figure 3 As shown, in the Y direction, the thickness of the second redundant region 6 remains constant, gradually decreases, or partially decreases while remaining constant in another region as it moves away from the second intermediate region 5. This embodiment provides a variety of second redundant region 6 structural designs, all of which can achieve higher heat generation in the second redundant region 6 than in the second intermediate region 5, thereby ensuring a relatively improved lithium ion transmission rate in the overhang region 202.

[0049] Among them, Figure 3 As shown in (a) in the figure, in the Y direction, the thickness of the second redundant region 6 remains constant in the direction away from the second intermediate region 5. With this thickness design, the structure of the metal layer 2 is simple, the second redundant region 6 is easy to manufacture, and the process cost is reduced.

[0050] like Figure 3As shown in (b) of FIG. 2 , in the Y direction, the thickness of the second redundant region 6 gradually decreases as it moves away from the second intermediate region 5, and the amount of thickness reduction in the second redundant region 6 per unit distance gradually increases. With this thickness design, the further away from the second intermediate region 5, the more noticeable the heating of the second redundant region 6 becomes, especially at the outermost edge of the overhang region 202, thereby ensuring an enhanced lithium ion transmission rate.

[0051] like Figure 3 As shown in (c) in the figure, in the Y direction, the thickness of the second redundant region 6 gradually decreases as it moves away from the second intermediate region 5, and the amount of thickness reduction of the second redundant region 6 per unit distance remains constant. With this thickness design, the further away from the second intermediate region 5, the more noticeable the heating of the second redundant region 6. This can evenly increase the temperature at the edge of the overhang region 202, ensuring a uniform increase in the lithium ion transmission rate throughout the entire overhang region 202.

[0052] like Figure 3 As shown in (d) and (e), in the Y direction, the thickness of the second redundant region 6 gradually decreases as it moves away from the second intermediate region 5, and then remains unchanged. Under this thickness design, the thickness variation of the metal layer 2 is partially satisfied. The farther away from the second intermediate region 5, the more obvious the heat generation of the second redundant region 6. On the other hand, the thickness of the outermost portion of the second redundant region 6 does not change, which can reduce the process difficulty. Figure 1 As shown, the negative electrode active material layer 201 covers the outermost portion of the negative electrode current collector 203 relatively thinly, so the setting of unchanged thickness of the outermost portion of the second redundant region 6 in this embodiment does not affect its effect of promoting lithium ion transmission.

[0053] In an optional embodiment, if Figure 1-Figure 3 As shown, in this embodiment, the thickness of the first middle region 3 of the polymer layer 1 is less than the thickness of the first redundant region 4. In this embodiment, based on the thickness design of the metal layer 2, the thickness distribution of the polymer layer 1 is designed accordingly, which can help to average the overall thickness of the negative electrode current collector 203.

[0054] In an optional embodiment, if Figure 1-Figure 3 As shown, along the Y direction, the decrease in thickness of the first redundant region 4 per unit distance is equal to the increase in thickness of the second redundant region 6, and the increase in thickness of the first redundant region 4 per unit distance is equal to the decrease in thickness of the second redundant region 6. In this embodiment, the thickness changes of the first redundant region 4 and the second redundant region 6 are designed to match, one increasing and one decreasing, to ensure that the thickness of the negative electrode current collector 203 remains unchanged along the Y direction.

[0055] In an optional embodiment, in the battery of this embodiment, the thickness of the first intermediate region 3 is c, which is 3 μm to 6 μm; the thickness of the first redundant region 4 is d, which is 4 μm to 8 μm, and satisfies d>c; the total thickness of the polymer layer 1 and the metal layer 2 is e, which is 5 μm to 10 μm, and satisfies e>d. The width a of the overhang region 202 is 0.2 mm to 5 mm.

[0056] This embodiment provides a process for preparing the above-mentioned battery, comprising the following steps:

[0057] S1. Dispersing the active material, binder, and conductive agent in a solvent and mixing them uniformly to prepare a negative electrode slurry;

[0058] S2. The slurry prepared in S1 is evenly coated on the negative electrode current collector 203 to obtain Figure 4 The electrode sheet shown extends in the X direction. The negative electrode current collector 203 contained therein is any one of the negative electrode current collectors 203 of the battery provided in the above embodiments.

[0059] S3, rolling and cutting the electrode sheet in S2 (along the X direction) to obtain a plurality of negative electrode current collectors 203;

[0060] S4. Assemble the negative electrode sheet processed in step S3 with the positive electrode sheet 100, a separator, an electrolyte, etc. into a soft-pack lithium-ion battery using existing technology.

[0061] Through this preparation process, the thickness of the metal layer 2 of the negative electrode current collector 203 in the second redundant region 6 can be reduced to be lower than the thickness of the metal layer in the second intermediate region 5, so that the heat generation in the Overhang region 202 of the negative electrode sheet 200 is higher than that in the intermediate region under the same current density, so that the temperature of the Overhang region 202 is higher than that of the intermediate region, thereby improving the transmission rate of lithium ions in the Overhang region and avoiding reversible capacity loss and lithium deposition at the edge of the negative electrode.

[0062] This embodiment provides a method for testing and comparing battery performance, as follows:

[0063] Example 1:

[0064] This embodiment provides a process for preparing the above-mentioned battery, comprising the following steps:

[0065] S1. Dispersing graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black in a solvent of deionized water in a mass ratio of 95:1.5:1.5:2, and mixing them uniformly to prepare a negative electrode slurry;

[0066] S2. The slurry prepared in S1 is evenly coated on the negative electrode current collector 203, with a coating surface density of 9.2 mg / cm 2, and dried at 90℃ to form Figure 4 The electrode piece shown. The negative electrode current collector 203 included in the electrode piece is Figure 3 Medium type, its parameters are: a = 4 mm; the parameters of the negative electrode current collector 203 are: b = 4 mm, c = 3 μm, d = 4 μm, e = 5 μm;

[0067] S3, rolling and cutting the electrode sheets in S2 to obtain a plurality of negative electrode sheets 200;

[0068] S4. Assemble the negative electrode sheet 200 processed in step S3 with the positive electrode sheet 100, a separator, an electrolyte, etc. using existing technology to form a soft-pack lithium-ion battery with a capacity of 2.2 Ah.

[0069] Example 2:

[0070] The difference from Example 1 is that the parameters of the negative electrode current collector 203 in S2 are: b=4 mm, c=3 μm, d=7 μm, and e=8 μm.

[0071] Example 3:

[0072] The difference from Example 1 is that the parameters of the negative electrode current collector 203 in S2 are: b=4 mm, c=3 μm, d=8 μm, and e=10 μm.

[0073] Example 4:

[0074] The difference from Example 1 is that the parameters of the negative electrode current collector 203 in S2 are: b=4 mm, c=4 μm, d=7 μm, and e=8 μm.

[0075] Example 5:

[0076] The difference from Example 1 is that the parameters of the negative electrode current collector 203 in S2 are: b=4 mm, c=6 μm, d=7 μm, and e=8 μm.

[0077] Comparative Example 1:

[0078] The difference from Example 1 is that the negative electrode current collector parameters in S2 are: b=4 mm, c=d=3 μm, e=5 μm.

[0079] The following electrical performance tests were performed on Examples 1 to 5 and Comparative Example 1:

[0080] 1. Discharge capacity test:

[0081] Test method a:

[0082] 1. Discharge at a constant voltage of 2.7 V for 100 h (ensure that the negative electrode is fully discharged and no active lithium ions exist in the overhang region 202);

[0083] 2. Charge at a constant current of 2.5C to 4.2V;

[0084] 3. Discharge at a constant current of 2.5C to 2.7V, and record the discharge capacity at this time as the discharge constant current capacity Q CC ;

[0085] 4. Discharge at 2.7V constant voltage for 50h (to recover the capacity loss caused by polarization). The discharge capacity at this time is recorded as the constant voltage discharge capacity Q. CV .

[0086] Test method b:

[0087] 1. Charge at a constant current of 2.5C to 4.2V;

[0088] 2. 4.2V constant voltage charging until the current is less than 0.01C (ensuring that the SOC of the overhang area 202 and the non-overhang area of ​​the negative electrode sheet 200 is the same);

[0089] 3. Discharge at a constant current of 2.5C to 2.7V, and record the discharge capacity at this time as the discharge constant current capacity Q CC ;

[0090] 4. Discharge at 2.7V constant voltage for 50h (to ensure that all active lithium ions in the overhang area 202 of the negative electrode 200 are released), and record the discharge capacity at this time as the discharge constant voltage stage capacity Q CV .

[0091] Examples 1-5 and Comparative Example 1 were tested using both methods to determine reversible capacity loss. Test method a aims to determine the reversible capacity loss caused by polarization during discharge. Therefore, the reversible capacity loss due to overhang region 202 is calculated by subtracting the constant-voltage capacity obtained by test method a from the constant-voltage capacity obtained by test method b.

[0092] The reversible capacity loss caused by the overhang region 202 is shown in Table 1:

[0093]

[0094] Table 1

[0095] Q in the table 总 is the total CC-CV discharge capacity (Q 总 =Q CC +Q CV ), Q CC is the capacity of the constant current discharge stage, Q CV is the capacity of the constant voltage discharge stage, Q OHIt is the reversible capacity loss caused by the Overhang region 202.

[0096] As can be seen from the data in Table 1, the reversible capacity loss caused by the overhang region 202 in Examples 1 to 5 ranges from 0.9% to 1.8%, significantly lower than the 4.2% in Comparative Example 1. This indicates that the design of the negative electrode current collector 203 provided in this embodiment, in which the thickness of the second intermediate region 5 of the metal layer 2 is greater than the thickness of the second redundant region 6, helps reduce the reversible capacity loss caused by the negative electrode overhang region 202.

[0097] 2. Cycle test:

[0098] Examples 1 to 5 and Comparative Example 1 were cycled 400 times (the specific test process is as follows: step 1, 2.5C constant current charging to 4.2V; step 2, 4.2V constant voltage charging to a current of ≤0.05C; step 3, 2.5C constant current discharge to 2.7V; step 4, repeat steps 1 to 3 400 times), and the negative electrode edge was disassembled to observe the lithium deposition. The results are shown in Table 2 below:

[0099] Lithium deposition at the edge of the negative electrode Example 1 No lithium plating Example 2 No lithium plating Example 3 No lithium plating Example 4 No lithium plating Example 5 No lithium plating Comparative Example 1 lithium deposition

[0100] Table 2

[0101] It can be seen from the data in Table 2 that, compared with Comparative Example 1, after 400 charge and discharge cycles, the lithium deposition at the edge of the negative electrode in Examples 1 to 5 is significantly improved, indicating that the negative electrode current collector 203 provided in this embodiment makes the temperature of the overhang region 202 of the negative electrode sheet 200 higher than that of the middle region, which can improve the lithium ion transmission efficiency and thus avoid lithium deposition at the edge of the negative electrode.

[0102] It should be understood that the above embodiments are exemplary and are not intended to encompass all possible implementations of the claims. Various modifications and variations may be made to the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form additional embodiments of the present application that may not be explicitly described. Therefore, the above embodiments merely illustrate several implementations of the present application and do not limit the scope of protection of the patent application.

Claims

1. A battery, characterized in that: It comprises a positive electrode sheet (100) and a negative electrode sheet (200) arranged along the Z direction; The positive electrode sheet (100) comprises a positive electrode current collector (103) and a positive electrode active material layer (101), and the negative electrode sheet (200) comprises a negative electrode current collector (203) and a negative electrode active material layer (201). The negative electrode current collector (203) comprises: a polymer layer (1); a metal layer (2) covering both sides of the polymer layer (1) along the Z direction; The polymer layer (1) comprises a first middle region (3) and a first redundant region (4), wherein the first redundant region (4) is located on both sides of the first middle region (3) along the Y direction; The metal layer (2) comprises a second middle region (5) and a second redundant region (6), wherein the second redundant region (6) is located on both sides of the second middle region (5) along the Y direction; a projection of the second middle region (5) along the Z direction overlaps with a projection of the first middle region (3) along the Z direction; and the negative electrode active material layer (201) partially covers the second redundant region (6); Along the Z direction, the projection of the first intermediate region (3), the projection of the second intermediate region (5) and the projection of the positive electrode active material layer (101) overlap; The thickness of the second intermediate region (5) is greater than the thickness of the second redundant region (6).

2. The battery according to claim 1, characterized in that The width of the overhang region (202) of the negative electrode sheet (200) is a, and the widths of the first redundant region (4) and the second redundant region (6) are both b, where b=a.

3. The battery according to claim 1, characterized in that In the Y direction, the thickness of the second redundant region (6) in the direction away from the second intermediate region (5) remains unchanged, or gradually decreases, or partially decreases and remains unchanged.

4. The battery according to claim 3, characterized in that In the Y direction, when the thickness of the second redundant region (6) gradually decreases in a direction away from the second intermediate region (5), the thickness reduction amount of the second redundant region (6) per unit distance remains unchanged or gradually increases.

5. The battery according to any one of claims 1 to 4, characterized in that: The thickness of the first intermediate region (3) is smaller than the thickness of the first redundant region (4).

6. The battery according to claim 5, characterized in that Along the Y direction, the thickness reduction of the first redundant area (4) per unit distance is equal to the thickness increase of the second redundant area (6), and the thickness increase of the first redundant area (4) per unit distance is equal to the thickness reduction of the second redundant area (6).

7. The battery according to any one of claims 1 to 4, characterized in that: The thickness of the first middle region (3) is c, and c is 3 μm to 6 μm.

8. The battery according to any one of claims 1 to 4, characterized in that: The thickness of the first redundant region (4) is d, and d is 4 μm to 8 μm.

9. The battery according to any one of claims 1 to 4, characterized in that: The total thickness of the polymer layer (1) and the metal layer (2) is e, and e is 5 μm to 10 μm.

10. The battery according to any one of claims 2 to 4, characterized in that: a is 0.2mm~5mm.

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