Pole piece, battery cell and battery

Abstract

The utility model discloses a pole piece, a battery cell and a battery, the pole piece comprises a current collector, a first active material layer and a second active material layer, and the current collector comprises a first surface and a second surface which are arranged back to back; the first active material layer is arranged on the first surface, and a plurality of first grooves are formed in the surface, deviating from the current collector, of the first active material layer at intervals; the first active material layer is arranged on the second surface, a plurality of second grooves are formed in the surface, away from the current collector, of the second active material layer at intervals, and the second grooves and the first grooves are arranged in a staggered mode. Through the staggered arrangement design of the first grooves and the second grooves, the thickness difference of the pole pieces can be reduced, and the risk of pole piece breakage in the battery circulation process is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, and particularly relates to an electrode sheet, a battery cell and a battery. Background Art

[0002] At present, in order to simultaneously ensure the energy density and kinetic performance of lithium-ion batteries, punched electrodes are gradually introduced, that is, holes are uniformly formed on the surface of the electrode sheet. Moreover, the punching structure designs on both surfaces of the conventional punched electrodes are the same. And to ensure the kinetic performance, the punching parameters also require deep punching, small groove width and small spacing. However, this causes the problem that the electrode sheet is prone to fracture during the battery cycling process. Summary of the Utility Model

[0003] The main object of the utility model is to propose an electrode sheet, aiming to solve the problem that the punched electrode sheet of the current battery is prone to fracture.

[0004] To achieve the above object, the utility model proposes an electrode sheet, which includes:

[0005] A current collector, the current collector includes a first surface and a second surface arranged opposite to each other;

[0006] A first active material layer, arranged on the first surface; a plurality of first grooves are arranged at intervals on the surface of the first active material layer facing away from the current collector;

[0007] A second active material layer, arranged on the second surface; a plurality of second grooves are arranged at intervals on the surface of the second active material layer facing away from the current collector; the second grooves and the first grooves are arranged in a staggered manner.

[0008] In some embodiments, the first grooves and the second grooves satisfy at least one of the following conditions:

[0009] The depth of the first grooves is less than the depth of the second grooves;

[0010] The spacing between adjacent first grooves is greater than the spacing between adjacent second grooves;

[0011] The groove width of the first grooves is greater than the groove width of the second grooves.

[0012] In some embodiments, the areal density of the first active material layer is greater than the areal density of the second active material layer.

[0013] In some embodiments, the first grooves satisfy at least one of the following conditions:

[0014] The depth of the first grooves is 5 μm to 25 μm;

[0015] The groove width of the first grooves is 50 μm to 110 μm;

[0016] The spacing between adjacent first grooves is 1 μm to 3 μm.

[0017] In some embodiments, the second groove satisfies at least one of the following conditions:

[0018] The depth of the second groove is 15 μm to 35;

[0019] The groove width of the second groove is 30 μm to 90 μm;

[0020] The spacing between adjacent second grooves is 0.3 μm to 2 μm.

[0021] In some embodiments, in a direction perpendicular to the thickness direction of the electrode tab, the center spacing between adjacent first grooves and second grooves is 1 mm to 1.5 mm.

[0022] In some embodiments, the depth of the first groove in the thickness direction of the first active material layer is less than the thickness of the first active material layer; the depth of the second groove in the thickness direction of the second active material layer is less than the thickness of the second active material layer.

[0023] In some embodiments, the length of the first active material layer in a direction perpendicular to the thickness direction of the electrode tab is less than the length of the second active material layer in a direction perpendicular to the thickness direction of the electrode tab.

[0024] The present utility model further provides an electric core, including a wound core, the wound core including a positive electrode tab, a negative electrode tab, and a separator, the separator being clamped between the positive electrode tab and the negative electrode tab, the negative electrode tab being the electrode tab as described above; in the same layer of the wound core, the first active material layer on the electrode tab is located inside and facing the winding central axis of the wound core, and the second active material layer is located outside and facing away from the winding central axis of the wound core.

[0025] The present utility model further provides a battery, the battery including a housing and an electric core disposed in the housing, the electric core being the electric core as described above.

[0026] In the electrode sheet of the technical solution of the present utility model, it includes a current collector, a first active material layer and a second active material layer. Among them, the current collector includes a first surface and a second surface arranged opposite to each other. The first active material layer is provided on the first surface of the current collector, and the second active material layer is provided on the second surface of the current collector. A plurality of first grooves are arranged at intervals on the surface of the first active material layer facing away from the current collector, and a plurality of second grooves are arranged at intervals on the surface of the second active material layer facing away from the current collector. The second grooves and the first grooves are arranged in a staggered manner. By arranging the positions of the first grooves on the first active material layer and the second grooves on the second active material layer in a staggered manner, the thickness difference of the electrode sheet can be reduced, and the risk of the electrode sheet breaking during the battery cycle can be reduced. Brief Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of an electrode sheet in an embodiment of the present utility model.

[0028] Explanation of the reference numerals in the drawings:

[0029] Label Name Label Name 10 Current collector 21 First groove 11 First surface 30 Second active material layer 12 Second surface 31 Second groove 20 First active material layer

[0030] The realization, functional characteristics and advantages of the object of the present utility model will be further described with reference to the embodiments and the drawings. Detailed Embodiment

[0031] Next, the solutions in the embodiments of the present utility model will be clearly and completely described with reference to the drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

[0032] It should be noted that all the directional indications (such as up, down, left, right, front, back...) in the embodiments of the present utility model are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0033] It should also be noted that when an element is referred to as being "fixed to" or "provided on" another element, it can be directly on the other element or there may be an intermediate element at the same time. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time.

[0034] In addition, the descriptions involving "first", "second", etc. in the present utility model are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between various embodiments may be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present utility model.

[0035] An embodiment of the present utility model provides a pole piece. Referring to Figure 1 , the pole piece includes a current collector 10, a first active material layer 20, and a second active material layer 30. Among them, the current collector 10 includes a first surface 11 and a second surface 12 arranged opposite to each other. The first active material layer 20 is disposed on the first surface 11 of the current collector 10, and a plurality of first grooves 21 are spaced apart on the surface of the first active material layer 20 facing away from the current collector 10; the second active material layer 30 is disposed on the second surface 12 of the current collector 10, and a plurality of second grooves 31 are spaced apart on the surface of the second active material layer 30 facing away from the current collector 10. The second grooves 31 and the first grooves 21 are arranged in a staggered manner. By designing the staggered arrangement of the first grooves 21 on the first active material layer 20 and the second grooves 31 on the second active material layer 30, the thickness difference of the pole piece can be reduced, and the risk of pole piece breakage during subsequent battery cycling can be reduced.

[0036] In some embodiments, it can be designed that the first grooves 21 penetrate the first active material layer 20, and / or the second grooves 31 penetrate the second active material layer 30, and the first grooves 21 and the second grooves 31 have side walls that are closed in the circumferential direction. Since the first grooves 21 on the first active material layer 20 and the second grooves 31 on the second active material layer 30 are arranged at intervals and the side walls are closed in the circumferential direction, even if the grooves penetrate the first active material layer 20 and the second active material layer 30, the integrity of the layer body can be ensured. The staggered arrangement design of the first grooves 21 and the second grooves 31 can prevent the pole piece from breaking during battery cycling compared with the traditional unified position design.

[0037] In order to effectively reduce the risk of pole piece breakage during cycling, it is preferably designed that the first grooves 21 on the first active material layer 20 and the second grooves 22 on the second active material layer 30 do not penetrate the corresponding active material layers, that is, the depth of the first grooves 21 in the thickness direction of the first active material layer 20 is less than the thickness of the first active material layer 20, and the depth of the second grooves 31 in the thickness direction of the second active material layer 30 is less than the thickness of the second active material layer 30.

[0038] The first groove 21 and the second groove 31 are several in number and more than two, and are arranged at intervals on the corresponding active material layer. On the basis of ensuring that the first groove 21 and the second groove 31 are arranged in a staggered manner, the specific distribution of the first groove 21 and the second groove 31 on the first active material layer 20 and the second active material layer 30 can be designed as needed, and can be arranged evenly, such as evenly arranged in a rectangular array or evenly arranged in a circular array; of course, it can also be arranged unevenly. In order to improve the uniformity of the structure and ensure the kinetic performance, preferably, the first groove 21 and the second groove 31 are arranged evenly, that is, the first groove 21 is evenly arranged on the first active material layer 20, and the second groove 31 is evenly arranged on the second active material layer 30.

[0039] The shapes of the first groove 21 and the second groove 31 can be designed according to actual requirements, and can be regular shapes, such as cylindrical, frustum-shaped, conical, semi-spherical, arc-shaped, prismatic, frustum-shaped, pyramidal, etc., or can be irregular shapes. In some embodiments, in order to effectively prevent the pole piece from breaking, the first groove 21 and the second groove 31 can be designed to have an arc-shaped chamfer at the bottom to reduce stress concentration and improve the stability of the pole piece structure. The shapes of the first grooves 21 on the first active material layer 20 can be the same or different; the shapes of the second grooves 31 on the second active material layer 30 can be the same or different; the shapes of the first groove 21 and the second groove 31 can be the same or different, and no limitation is made thereto. For the convenience of processing, the shapes of the first groove 21 and the second groove 31 can be designed to be the same.

[0040] In some embodiments, the length of the first active material layer 20 in the direction perpendicular to the thickness of the pole piece is less than the length of the second active material layer 30 in the direction perpendicular to the thickness of the pole piece. In the subsequent winding and core-making process, the first active material layer 20, as a short film, is configured to be the inner active material layer facing the winding central axis in the same layer of the core after winding and core-making, while the second active material layer 30, as a long film, is configured to be the outer active material layer facing the winding central axis.

[0041] The electrode of the embodiment of the present utility model can be used as a positive electrode or a negative electrode, and is preferably used as a negative electrode. When used as a negative electrode, the first active material layer 20 and the second active material layer 30 are respectively made of negative electrode active material layers; when used as a positive electrode, the first active material layer 20 and the second active material layer 30 are respectively made of positive electrode active material layers. The electrode can be applied to a wound battery. Due to the structural characteristics of the core of the wound battery, in the same layer of the core, the CB value (i.e., the ratio of the anode capacity to the cathode capacity on the directly opposite side) of the inner active material layer of the electrode facing the winding central axis of the core is usually greater than that of the outer active material layer of the electrode facing away from the winding central axis of the core. Therefore, the lithium deposition resistance of the inner active material layer is stronger than that of the outer active material layer, and the outer active material layer usually has higher requirements for the design of kinetic performance. Based on this, in some embodiments of the present utility model, the areal density of the first active material layer 20 is greater than that of the second active material layer 30. When the electrode is used to prepare the core subsequently, the first active material layer 20 is configured as the inner active material layer of the electrode facing the winding central axis in the same layer of the core after winding, and the second active material layer 30 is configured as the outer active material layer of the electrode facing the winding central axis. Based on the above design of areal density difference, when the electrode is used to make a wound core, the CB values of the inner and outer active material layers of the electrode on the core are the same, which can improve the battery performance.

[0042] On the premise of ensuring that the first groove 21 and the second groove 31 are arranged in a staggered manner, in some embodiments, the first groove 21 and the second groove 31 satisfy at least one of the following conditions: the depth L1 of the first groove 21 is less than the depth L2 of the second groove 31; the distance D1 between adjacent first grooves 21 is greater than the distance D2 between adjacent second grooves 31; the groove width W1 of the first groove 21 is greater than the groove width W2 of the second groove 31. Wherein, the groove depth is the maximum depth of the groove along the thickness direction of the pole piece, the distance between the grooves is the edge distance between adjacent grooves on the surface of the active material layer, and the groove width is the notch width of the groove on the surface of the active material layer. And, through the above-mentioned dimensional or distribution differences design of the first groove 21 and the second groove 31, the subsequent pole piece is used to make a battery core. After the first active material layer 20 is configured as the pole piece and wound into a core, the first active material layer 20 in the same layer of the core is the inner active material layer facing its winding central axis, and the second active material layer 30 is configured as the outer active material layer facing its winding central axis. Furthermore, compared with the second groove 31 on the second active material layer 30, the first groove 21 on the inner first active material layer 20 has a shallower depth, a larger groove spacing, and a larger groove width. This can effectively improve the electrolyte infiltration of the inner layer of the pole piece, reduce polarization, and at the same time reduce the loss of the electrode in the groove width direction, ensuring the energy density of the overall battery cell; in addition, a large groove width can ensure the infiltration effect of the electrolyte at the grooving position, and the inner pole piece is easily squeezed during the cycling process. The wide groove is beneficial to ensuring the maintenance degree of the groove after cycling and improving the stability of the structure and performance. Preferably, the first groove 21 and the second groove 31 simultaneously satisfy that the depth L1 of the first groove 21 is less than the depth L2 of the second groove 31, the distance D1 between adjacent first grooves 21 is greater than the distance D2 between adjacent second grooves 31, and the groove width W1 of the first groove 21 is greater than the groove width W2 of the second groove 31.

[0043] On the premise of meeting the above design of the groove size / distribution difference, the specific sizes and distributions of the first groove 21 and the second groove 31 can be designed according to actual needs. In some embodiments, the first groove 21 can be designed to meet at least one of the following conditions: the depth L1 of the first groove 21 is 5 μm to 25 μm, preferably 5 μm to 15 μm; the groove width W1 of the first groove 21 is 50 μm to 110 μm, preferably 90 μm to 110 μm; the spacing D1 between adjacent first grooves 21 is 1 μm to 3 μm, preferably 2 μm to 3 μm. In some embodiments, the second groove 31 can also be designed to meet at least one of the following conditions: the depth L2 of the second groove 31 is 15 μm to 35 μm, preferably 25 μm to 35 μm; the groove width W2 of the second groove 31 is 30 μm to 90 μm, preferably 30 μm to 50 μm; the spacing D2 between adjacent second grooves 31 is 0.3 μm to 2 μm, preferably 0.3 μm to 1 μm. On the premise that the first groove 21 on the first active material layer 20 and the second groove 31 on the second active material layer 30 are arranged in a staggered manner, in some embodiments, it can also be designed that in the direction perpendicular to the thickness of the negative electrode plate, the center spacing D3 between adjacent first grooves 21 and second grooves 31 is 1 to 1.5 mm.

[0044] In the negative electrode plate of the embodiment of the present utility model, the first active material layer 20 and the second active material layer 30 can be single-layer or include multiple (such as 2, 3, 5, etc.) sub-layers respectively; if including multiple sub-layers, each sub-layer can be compounded, and the whole is used as the active material layer, and several grooves are arranged at intervals on the surface of the compounded active material layer, and the structure of the grooves is set as described above, which will not be elaborated here.

[0045] In addition, the current collector 10 can be selected according to needs. Generally, it is necessary to ensure that the current collector 10 and the first active material layer 20 and the second active material layer 30 that are in contact with it are inert to each other; in some embodiments, the current collector 10 can be made of copper foil, which can be used as the negative electrode current collector, and then the negative electrode plate is constructed according to the foregoing structure; in some embodiments, the current collector can be made of aluminum foil, which can be used as the positive electrode current collector, and then the positive electrode plate is constructed according to the foregoing structure.

[0046] An embodiment of the present utility model also provides an electrode core, which includes a wound core. The wound core includes a positive electrode plate, a negative electrode plate, and a separator that are sequentially stacked. The separator is sandwiched between the positive electrode plate and the negative electrode plate, and the negative electrode plate is the electrode plate described in the foregoing embodiment. In the same layer of the wound core, the first active material layer 20 on the electrode plate is located inside, facing the winding central axis of the wound core, and the second active material layer 30 is located outside, facing away from the winding central axis of the wound core. For the specific structure of this electrode plate, refer to the above embodiment. Since this electrode core adopts all the technical solutions of the above-mentioned embodiments, it has at least all the technical effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one. In some embodiments, it can also be designed such that both the positive electrode plate and the negative electrode plate are the electrode plates described in the foregoing embodiment; or, the positive electrode plate is the electrode plate described in the foregoing embodiment.

[0047] An embodiment of the present utility model also provides a battery, which includes a housing and an electrode core disposed in the housing. The electrode core is the electrode core described in the foregoing embodiment. For the specific structure of this electrode core, refer to the above embodiment. Since this battery adopts all the technical solutions of the above-mentioned embodiments, it has at least all the technical effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one.

[0048] During the research process, the inventors conducted a large number of research experiments, especially on the influence of the size / distribution difference of the grooves on the active material layers on both sides of the current collector on the battery performance of the electrode plate. Taking the negative electrode plate as an example, the inventors fabricated negative electrode plates with different structures during the specific experimental process, and further manufactured finished lithium-ion batteries, and then verified the performance of the product batteries. Some experimental methods, cases, and performance test results are listed as follows:

[0049] (I) Fabrication of the positive electrode plate: The active material LiCoO 2 , conductive agent acetylene black, conductive carbon nanotubes, and binder polyvinylidene fluoride (PVDF) were uniformly dispersed in an N-methylpyrrolidone solvent system according to a weight ratio of 97.6:0.7:0.5:1.2, and then coated onto an aluminum current collector, and then cold-pressed and cut into strips to obtain the positive electrode plate.

[0050] (II) Fabrication of the negative electrode plate: The active material graphite, Super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber (SBR) emulsion were mixed in deionized water according to a weight ratio of 96.8:0.5:1.1:1.6, uniformly dispersed, and then coated onto a copper current collector, and then cold-pressed and cut into strips to obtain the negative electrode plate body. Laser drilling was performed on the active material layers on both sides of the copper current collector of the obtained negative electrode plate body to form grooves on the surfaces of the active material layers on both sides, thereby obtaining the negative electrode plate. The structure of this negative electrode plate is similar to Figure 1The shown electrode includes a current collector 10, and a first active material layer 20 and a second active material layer 30 disposed on both surfaces of the current collector 10. On the surface of the first active material layer 20 facing away from the current collector 10, a plurality of first grooves 21 are provided. On the surface of the second active material layer 30 facing away from the current collector 10, a plurality of second grooves 31 are provided at intervals. The first grooves 21 and the second grooves 31 are arranged in a staggered manner. Among them, the thicknesses of the first active material layer 20 and the second active material layer 30 are 40um. Specifically, refer to the size and distribution parameters in Table 1 below to open holes and prepare different negative electrodes.

[0051] (III) Battery assembly preparation: Take the positive electrode, negative electrode, and separator prepared above, stack the positive electrode, separator, and negative electrode in sequence, and wind them into a bare battery cell. In the bare battery cell, the first active material layer 20 on the negative electrode is located on the inner side facing the winding central axis in the same layer of the bare battery cell, and the second active material layer 30 is located on the outer side facing away from the winding central axis; then, encapsulate the bare battery cell into a housing and inject electrolyte to obtain a finished lithium-ion battery.

[0052] Use the different negative electrodes prepared above to obtain different finished lithium-ion batteries according to the above method.

[0053] (IV) Performance testing

[0054] Charge the battery at a constant current density of 3C to 4.5V, and the constant voltage cut-off current is 0.05C; discharge it at a constant current density of 0.5C to 3V, and perform cycling with this process step. The first cycle is the first discharge capacity.

[0055] Charge the battery at a constant current density of 3C / 3.2C / 3.4C / 3.6C / 3.8C / 4C / 4.2C / 4.4C / 4.6C / 4.8C / 5C to 4.5V, and the constant voltage cut-off current is 0.05C; discharge it at a constant current density of 0.5C to 3V, and perform cycling for 20 weeks with this process step to obtain the lithium plating window data of the battery.

[0056] At the same time, calculate the material loss etched by laser drilling during the preparation of the negative electrode. Since the shape after etching is similar to a cone, the material loss can be calculated through the cone formula.

[0057] Use the above method to test the performance of each battery, and the obtained results are shown in Table 1.

[0058] Table 1

[0059]

[0060]

[0061] By comparing Examples 1 to 15 with Comparative Example 1, it can be seen that through the differential design of the size / distribution of the grooves on the active material layers on both sides of the current collector on the negative electrode sheet, in the same layer of the battery cell, compared with the second grooves on the second active material layer in the outer layer, the depth of the first grooves on the first active material layer in the inner layer is shallower, the groove pitch is larger, and the groove width is larger. This can effectively improve the electrolyte infiltration in the inner layer of the electrode sheet, reduce polarization, further improve the kinetic performance, increase the lithium plating window and cycle life, and relieve the swelling of the battery cell.

[0062] The specific design intention of the differential size / distribution of the grooves on the inner and outer layer active material layers in this application is as follows: on the basis that the first grooves on the first active material layer in the inner layer and the second grooves on the second active material layer in the outer layer are arranged in a staggered manner, the first grooves and the second grooves satisfy at least one of the following conditions: ① the depth of the first grooves is less than the depth of the second grooves; ② the spacing between adjacent first grooves is greater than the spacing between adjacent second grooves; ③ the groove width of the first grooves is greater than the groove width of the second grooves, so as to improve the electrolyte infiltration in the inner layer of the electrode sheet, reduce polarization, further improve the kinetic performance, increase the lithium plating window and cycle life, and relieve the swelling of the battery cell. In Example 16, in the same layer of the battery cell, compared with the second grooves on the first active material layer in the outer layer, the depth of the first grooves on the first active material layer in the inner layer is deeper, the groove pitch is smaller, and the groove width is smaller, which is contrary to the above design intention. Therefore, the battery kinetic performance, lithium plating window, cycle life and the swelling situation of the battery cell in Example 16 under this structure have not been improved compared with Comparative Example 1; however, based on the staggered arrangement design of the first grooves and the second grooves on the active material layers on both sides of the electrode sheet current collector in Example 16, the thickness difference of the electrode sheet can be reduced, and the risk of the electrode sheet breaking during battery cycling can be reduced. In this regard, it has more advantages compared with the scheme of the consistent design of the grooves on the active material layers on both sides of the electrode sheet current collector in Comparative Example 1.

[0063] The above are only partial or preferred embodiments of the present invention. Whether in terms of text or drawings, the scope of protection of the present invention cannot be limited thereby. All equivalent structural transformations made under the overall concept of the present invention by using the content of the specification and drawings of the present invention, or directly / indirectly applied in other related technical fields are included in the scope of protection of the present invention.

Claims

1. A pole piece, characterized in that: include: A current collector, the current collector comprising a first surface and a second surface disposed opposite to each other; A first active material layer is disposed on the first surface; a plurality of first grooves are disposed on the surface of the first active material layer away from the current collector; A second active material layer is disposed on the second surface; a plurality of second grooves are arranged at intervals on the surface of the second active material layer away from the current collector, and the second grooves are arranged in a staggered manner with the first grooves.

2. The pole piece according to claim 1, characterized in that: The first groove and the second groove satisfy at least one of the following conditions: The depth of the first groove is smaller than the depth of the second groove; The spacing between adjacent first grooves is greater than the spacing between adjacent second grooves; The groove width of the first groove is greater than the groove width of the second groove.

3. The pole piece according to claim 2, characterized in that: The surface density of the first active material layer is greater than the surface density of the second active material layer.

4. The pole piece according to claim 2, characterized in that: The first groove satisfies at least one of the following conditions: The depth of the first groove is 5 μm to 25 μm; The width of the first groove is 50 μm to 110 μm; The distance between adjacent first grooves is 1 μm to 3 μm.

5. The pole piece according to claim 4, characterized in that: The second groove satisfies at least one of the following conditions: The depth of the second groove is 15 μm to 35 μm; The width of the second groove is 30 μm to 90 μm; The distance between adjacent second grooves is 0.3 μm to 2 μm.

6. The pole piece according to claim 1, characterized in that: In a thickness direction perpendicular to the pole piece, a center distance between adjacent first grooves and second grooves is 1 mm to 1.5 mm.

7. The pole piece according to claim 1, characterized in that: The depth of the first groove along the thickness direction of the first active material layer is less than the thickness of the first active material layer; the depth of the second groove along the thickness direction of the second active material layer is less than the thickness of the second active material layer.

8. The pole piece according to any one of claims 1 to 7, characterized in that: A length of the first active material layer along a direction perpendicular to the thickness of the pole piece is smaller than a length of the second active material layer along a direction perpendicular to the thickness of the pole piece.

9. A battery cell, characterized in that: The invention comprises a winding core, wherein the winding core is formed by winding a positive electrode sheet, a separator and a negative electrode sheet which are stacked in sequence, the separator is sandwiched between the positive electrode sheet and the negative electrode sheet, and the negative electrode sheet is a sheet according to any one of claims 1 to 8; In the same coil layer of the winding core, the first active material layer on the pole piece is located on the inner side of the winding center axis of the winding core, and the second active material layer is located on the outer side of the winding center axis opposite to the winding core.

10. A battery, characterized in that: The invention comprises a shell and a battery cell arranged in the shell, wherein the battery cell is the battery cell as claimed in claim 9.

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