Pole piece and battery cell

Abstract

The utility model relates to the technical field of batteries, and discloses a pole piece which comprises a current collector, a first coating layer and a second coating layer, the current collector comprises an equal-thickness area and a thinned area, the thickness of the thinned area is smaller than that of the equal-thickness area, and the current collector is provided with a first side face and a second side face which are oppositely arranged in the thickness direction of the current collector. A first coating layer is arranged on the first side face, and a second coating layer is arranged on the second side face. When the pole piece disclosed by the utility model is used for manufacturing a battery cell, the orthographic projection of the ending winding glue, the tab or the gummed paper of the battery cell along the thickness direction of the battery cell falls into the thinning area, and the adverse effect of the ending winding glue, the tab or the gummed paper on the thickness uniformity of the battery cell is reduced or even eliminated through the thinning area, so that the non-uniformity of the thickness of the battery cell is reduced; therefore, the problem that lithium is easy to separate out in the charge-discharge cycle of the battery cell due to non-uniform thickness of the battery cell is solved, and the energy density of the battery cell is favorably improved.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and in particular to an electrode sheet and a battery cell. Background Technology

[0002] Currently, in battery production, adhesive is wrapped around the beginning and end of the cell body. Some cells also require protective film to be applied to the electrodes. The thickness of this film varies from 12 to 24 μm. With the beginning and end wrapped design, the thickness of the wrapped area is increased by approximately 24 to 48 μm compared to other areas. If the protective film overlaps on the electrodes (either with the tabs), the cumulative thickness difference will be even greater. Excessive thickness differences across different areas of the cell can lead to lithium plating during charge-discharge cycles and severely reduce the cell's energy density (ED). Some existing cell designs clean a slightly larger area on the electrode coating, with a thickness similar to the adhesive film, to accommodate it. However, cleaning the electrode coating generates more dust, degrading the cell's withstand voltage (Hi-pot) and voltage drop per unit time (K-value).

[0003] Therefore, there is an urgent need for an electrode and a battery cell to solve the above problems. Utility Model Content

[0004] The purpose of this invention is to provide an electrode and a battery cell that reduce the unevenness of battery cell thickness.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] An electrode includes a current collector, a first coating layer, and a second coating layer. The current collector includes a region of equal thickness and a thinned region. The thickness of the thinned region is less than the thickness of the region of equal thickness. The current collector has a first side and a second side disposed opposite to each other along its own thickness direction. The first coating layer is disposed on the first side, and the second coating layer is disposed on the second side.

[0007] As an improvement to the above technical solution, the equal thickness region has a first side surface and a second side surface of the equal thickness region arranged opposite to each other along its own thickness direction, and the thinning region has a first side surface and a second side surface of the thinning region arranged opposite to each other along its own thickness direction. The first side surface includes the first side surface of the equal thickness region and the first side surface of the thinning region, and the second side surface includes the second side surface of the equal thickness region and the second side surface of the thinning region.

[0008] The first side of the thinning area includes a bottom surface and a transition surface. The transition surface connects the bottom surface and the first side of the equal thickness area. The second side of the thinning area is coplanar with the second side of the equal thickness area.

[0009] As an improvement to the above technical solution, the transition surface is an arc surface.

[0010] As an improvement to the above technical solution, the transition surface includes a first transition arc surface and a second transition arc surface. One end of the first transition arc surface is connected to the bottom surface, and the other end extends towards the first side surface of the equal thickness region. One end of the second transition arc surface is connected to the end of the first transition arc surface away from the bottom surface, and the other end is connected to the first side surface of the equal thickness region.

[0011] A battery cell has a first orientation and includes a cell body, tabs, and end wrapping adhesive. The cell body includes a plurality of separators and a plurality of first electrodes. The separators and the electrodes are alternately arranged along the first orientation. At least one of the plurality of first electrodes includes an electrode as described above. The cell body has a third side and a fourth side arranged opposite to each other along the first orientation. Each electrode is connected to the tab.

[0012] The finishing wrapping includes a first section, a second section, and a third section. The first section is attached to the third side, the third section is attached to the fourth side, and the second section connects the first section and the third section.

[0013] The orthographic projections of the first segment and the second segment along the first direction are both located within the thinning area.

[0014] As an improvement to the above technical solution, the battery cell has a second direction perpendicular to the first direction, and the battery cell has a first end and a second end disposed opposite to each other along the second direction. Both the first end and the second end of the battery cell are provided with a plurality of the aforementioned finishing wrapping adhesive.

[0015] A battery cell includes a battery cell body, the battery cell body being formed by winding a separator and two electrodes as described in any one of the above claims, the two electrodes being a second electrode and a third electrode, and the separator being sandwiched between the second electrode and the third electrode;

[0016] The battery cell also includes a first tab, a second tab, a first adhesive tape, and a second adhesive tape. The first tab is connected to a first side or a second side of the current collector of the second electrode, and the second tab is connected to a first side or a second side of the current collector of the third electrode. The first adhesive tape is disposed on the side of the first tab away from the current collector of the second electrode, and the second adhesive tape is disposed on the side of the second tab away from the current collector of the third electrode.

[0017] The end of the first electrode tab connected to the second electrode and the orthographic projection of the first adhesive tape along the thickness direction of the battery cell are both located within the thinning area of ​​the second electrode and / or the third electrode; the end of the second electrode tab connected to the third electrode and the orthographic projection of the second adhesive tape along the thickness direction of the battery cell are both located within the thinning area of ​​the second electrode and / or the third electrode.

[0018] As an improvement to the above technical solution, multiple thinning zones are provided on the current collectors of the second electrode and the third electrode. The orthographic projections of the first electrode tab and the first adhesive tape along the thickness direction of the battery cell body are located within the multiple thinning zones, and the orthographic projections of the second electrode tab and the second adhesive tape along the thickness direction of the battery cell body are located within the multiple thinning zones.

[0019] As an improvement to the above technical solution, it also includes a finishing wrapping adhesive. The battery cell has a fifth side and a sixth side that are arranged opposite to each other along its own thickness direction. The finishing wrapping adhesive includes a first section, a second section and a third section. The first section is attached to the fifth side, the third section is attached to the sixth side, and the second section connects the first section and the third section.

[0020] The orthographic projections of the first segment and the second segment along the thickness direction of the cell are both located within the third electrode and / or the thinned area of ​​the third electrode.

[0021] As an improvement to the above technical solution, the finishing wrapping is provided with multiple layers.

[0022] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0023] The current collector of the electrode sheet of this utility model includes a uniform thickness region and a thinning region. When using the electrode sheet of this utility model to make a battery cell, the orthogonal projection of the end wrapping, tabs, or adhesive paper of the battery cell along the thickness direction can fall within the thinning region. The thinning region reduces or even eliminates the adverse effects of the end wrapping, tabs, or adhesive paper on the uniformity of the battery cell thickness, reduces the non-uniformity of the battery cell thickness, and thus solves the problem of easy lithium deposition during the charge and discharge cycle of the battery cell caused by the non-uniformity of the battery cell thickness, which is beneficial to improving the energy density of the battery cell. Attached Figure Description

[0024] Figure 1 This is a side view of the electrode sheet provided in Embodiment 1 of this utility model;

[0025] Figure 2 This is a partial structural schematic diagram of the current collector of the electrode sheet provided in Embodiment 1 of this utility model;

[0026] Figure 3 This is a partial structural schematic diagram of the current collector of the electrode sheet provided in Embodiment 2 of this utility model;

[0027] Figure 4 This is a top view of the electrode sheet provided in Embodiment 3 of this utility model;

[0028] Figure 5 This is a schematic diagram of the structure of the battery cell before winding, provided in Embodiment 4 of this utility model;

[0029] Figure 6 This is a top view of the second electrode of the battery cell provided in Embodiment 4 of this utility model;

[0030] Figure 7 This is a top view of the third electrode of the battery cell provided in Embodiment 4 of this utility model.

[0031] In the picture:

[0032] 1. Current collector;

[0033] 11. Uniform thickness zone; 12. Thinned zone;

[0034] 13. First side surface; 131. First side surface of the equal thickness region; 132. First side surface of the thinned region; 1321. Bottom surface; 1322. Transition surface; 13221. First transition arc surface; 13222. Second transition arc surface;

[0035] 14. Second side view;

[0036] 141. Second side surface of the uniform thickness zone; 142. Second side surface of the thinned zone;

[0037] 2. First coating layer; 3. Second coating layer;

[0038] 20. Second electrode; 30. Third electrode; 40. Diaphragm; 50. First tab; 60. Second tab; 70. First adhesive tape; 80. Second adhesive tape. Detailed Implementation

[0039] The specific embodiments of this utility model will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this utility model, but are not intended to limit the scope of this utility model.

[0040] In the description of this utility model, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0041] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0042] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. In addition, the terms "first" and "second" are only used for distinction in description and have no special meaning.

[0043] Example 1

[0044] like Figure 1 and Figure 2 As shown, this embodiment provides an electrode sheet, including a current collector 1, a first coating layer 2, and a second coating layer 3. The current collector 1 includes a region of equal thickness 11 and a thinning region 12. The thickness of the thinning region 12 is less than the thickness of the region of equal thickness 11. The current collector 1 has a first side surface 13 and a second side surface 14 arranged opposite to each other along its own thickness direction. The first side surface 13 is provided with the first coating layer 2, and the second side surface 14 is provided with the second coating layer 3.

[0045] The current collector 1 of the electrode sheet provided in this embodiment includes a uniform thickness region 11 and a thinning region 12. When using the electrode sheet in this embodiment to make a battery cell, the orthogonal projection of the end-wrap adhesive, tabs, or adhesive paper of the battery cell along the thickness direction can fall within the thinning region 12. The thinning region 12 reduces or even eliminates the adverse effects of the end-wrap adhesive, tabs, and adhesive paper on the uniformity of the battery cell thickness, thereby reducing the non-uniformity of the battery cell thickness and solving the problem of easy lithium deposition during the charge and discharge cycle of the battery cell caused by the non-uniformity of the battery cell thickness, which is beneficial to improving the energy density of the battery cell.

[0046] Furthermore, such as Figure 1 and Figure 2As shown, the first side surface 13 includes a first side surface 131 of uniform thickness and a first side surface 132 of thinned area, and the second side surface 14 includes a second side surface 141 of uniform thickness and a second side surface 142 of thinned area. The first side surface 132 of thinned area includes a bottom surface 1321 and a transition surface 1322, the transition surface 1322 connecting the bottom surface 1321 and the first side surface 131 of uniform thickness. The second side surface 142 of thinned area is coplanar with the second side surface 141 of uniform thickness. That is to say, in this embodiment, only the first side surface 13 of the current collector 1 is thinned to form the thinned area 12, and the area corresponding to the bottom surface 1321 on the thinned area 12 is the thinnest area of ​​the thinned area 12. By providing a transition surface 1322 between the bottom surface 1321 and the first side surface 131 of the equal thickness region, the toughness at the junction of the thinned region 12 and the equal thickness region 11 can be improved, preventing the current collector 1 from breaking at the junction of the thinned region 12 and the equal thickness region 11 after rolling. In this embodiment, the transition surface 1322 is an arc surface. Those skilled in the art will understand that the toughness of the current collector 1 of the electrode sheet has a significant impact on the service life of the soft-pack battery cell and the wound core.

[0047] This embodiment also provides a copper foil manufacturing process: copper, sulfuric acid and water - copper sulfate solution - electrolyte filtration and purification - electrolysis to generate raw foil - roughening treatment - plating with different metal layers - anti-oxidation treatment - cutting and packaging.

[0048] This embodiment also provides an aluminum foil manufacturing process: high-purity aluminum ingot - melting and casting - homogenization - hot rolling - pre-annealing - cold rolling - intermediate annealing - cold rolling - foil rolling - slitting - performance testing - packaging.

[0049] Example 2

[0050] like Figure 3As shown, this embodiment provides an electrode sheet, which is basically the same as that in Embodiment 1, except that the transition surface 1322 in this embodiment includes a first transition arc surface 13221 and a second transition arc surface 13222. One end of the first transition arc surface 13221 is connected to the bottom surface 1321, and the other end extends towards the first side surface 131 of the equal thickness region. One end of the second transition arc surface 13222 is connected to the first side surface 131 of the equal thickness region, and the other end extends towards the bottom surface 1321. In this embodiment, both the first transition arc surface 13221 and the second transition arc surface 13222 are circular arc surfaces. In this embodiment, the upper part of the junction between the thinned region 12 and the equal thickness region 11 of the current collector 1 is transitioned by the second transition arc surface 13222, and the lower part is transitioned by the first transition arc surface 13221, thereby further improving the toughness of the junction between the thinned region 12 and the equal thickness region 11 of the current collector 1. The first transition arc surface 13221 and the second transition arc surface 13222 are arc surfaces formed by chamfering. That is to say, the upper part of the junction between the thinned area 12 and the equal thickness area 11, and the lower part of the junction between the thinned area 12 and the equal thickness area 11, are both chamfered.

[0051] Optionally, both the first transition arc surface 13221 and the second transition arc surface 13222 are circular arc surfaces. The radius of both the first and second transition arc surfaces 13221 is not less than one-third of the difference between the thickness of the equal thickness region 11 and the thickness of the thinned region 12, and is not greater than one-half of the difference between the thickness of the equal thickness region 11 and the thickness of the thinned region 12. The height of the second transition arc surface 13222 along the thickness direction of the current collector 1 (that is, the dimension of the second transition arc surface 13222 along the thickness direction of the current collector 1) is not greater than the height of the first transition arc surface 13221 along the thickness direction of the current collector 1 (that is, the dimension of the first transition arc surface 13221 along the thickness direction of the current collector 1), and is not less than one-third of the height of the first transition arc surface 13221 along the thickness direction of the current collector 1.

[0052] Specifically, in this embodiment, the radii of the first transition arc surface 13221 and the second transition arc surface 13222 are both between 0.1μm and 0.5μm. If the chamfer radius is too small, there is no buffering effect, stress concentration easily leads to breakage, and if the chamfer radius is too large, processing is more difficult.

[0053] Example 3

[0054] like Figure 4As shown, this embodiment provides a battery cell with a first direction. The battery cell in this embodiment is a stacked battery cell, comprising a cell body, tabs, and a finishing adhesive. The cell body includes multiple separators 40 and multiple first electrodes, which are alternately arranged along the first direction. At least one of the multiple first electrodes is included, as described in Embodiment 1 or Embodiment 2. The cell body has a third side and a fourth side arranged opposite to each other along the first direction. Each first electrode is connected to a tab. The finishing adhesive is used to bond and fix the stacked separators 40 and first electrodes into a single unit. The finishing adhesive includes a first section, a second section, and a third section. The first section is attached to the third side, the third section is attached to the fourth side, and the second section connects the first and third sections. The orthographic projections of the first and second sections along the first direction are both located within the thinning area 12.

[0055] In this embodiment, the first electrode and the separator 40 are alternately arranged along the first direction, which is the thickness direction of the cell. The first and third sections of the end-wrap adhesive attached to the side of the cell body have their orthogonal projections along the first direction located within the thinning area 12. This can reduce or even eliminate the adverse effects of the first and third sections of the end-wrap adhesive on the uniformity of the cell thickness, reduce the thickness difference between different areas of the cell, and thus solve the problem of easy lithium deposition during the charge and discharge cycle of the cell caused by uneven cell thickness, which is beneficial to improving the energy density of the cell.

[0056] Furthermore, the battery cell has a first end and a second end arranged opposite to each other along the second direction. Both the first end and the second end of the battery cell are provided with a plurality of end-wrap adhesives, so that the first end and the second end of the battery cell are firmly fixed by the end-wrap adhesives.

[0057] In this embodiment, the current collector uses different thicknesses depending on the cell design. For example, the thickest part of the cell is the end of the wrapping, and the thickness difference between the thickest part and other parts is δμm. The current collector area corresponding to the end of the wrapping is selectively thinned along the thickness direction of the cell. The number of current collector layers thinned (in a laminated cell, the number of current collector layers is also the number of first electrode layers, and the number of current collector layers thinned is also the number of electrodes included in the first electrode in embodiment one or embodiment two) is X. Then, the thickness h removed by each current collector layer thinning is (δ / X)μm. The length and width of the thinning are related to the length and width of the thickest part of the cell. The length L of the thinning area 12 is the length of the thickest part of the cell + (0.5~5mm); the width W of the thinning area 12 is the width of the thickest part of the cell + (0.5~5mm). Since the cathode sheet is more brittle than the anode sheet, the current collector 1 of the anode sheet is thinned first. Since the rigidity of the single-sided region of the electrode is lower than that of the double-sided region, it is recommended to prioritize thinning the current collector in the double-sided region. For cells with more than 25 layers and copper current collector thickness greater than 6 μm, prioritize thinning the anode sheet, with a thickness of 0.1 μm < thinning thickness < 3 μm. For cells with less than 25 layers, similarly prioritize thinning the anode sheet current collector, with a thickness of 0.1 μm < thinning thickness < 3 μm; the cathode sheet current collector should be thinned as needed, with a thickness of 0.1 μm < thinning thickness < 2 μm.

[0058] Example 4

[0059] like Figures 5-7 As shown, this embodiment provides a battery cell. The battery cell in this embodiment is a wound core, comprising a battery cell body. The battery cell body is formed by winding a separator 40 and two electrode sheets as described in Embodiment 1, or by winding a separator 40 and two electrode sheets as described in Embodiment 2. The two electrode sheets are a second electrode sheet 20 and a third electrode sheet 30, with the separator 40 sandwiched between the second electrode sheet 20 and the third electrode sheet 30. The battery cell also includes a first tab 50, a second tab 60, a first adhesive tape 70, and a second adhesive tape 80. The first tab 50 is connected to the first side 13 or the second side 14 of the current collector 1 of the second electrode sheet 20, and the second tab 60 is connected to the first side 13 or the second side 14 of the current collector 1 of the third electrode sheet 30. The first adhesive tape 70 is disposed on the side of the first tab 50 away from the current collector 1 of the second electrode sheet 20, and the second adhesive tape 80 is disposed on the side of the second tab 60 away from the current collector 1 of the third electrode sheet 30. The end of the first tab 50 connected to the second electrode 20 and the orthographic projection of the first adhesive tape 70 along the thickness direction of the battery cell are both located within the thinning area 12 of the second electrode 20 and / or the third electrode 30; the end of the second tab 60 connected to the third electrode 30 and the orthographic projection of the second adhesive tape 80 along the thickness direction of the battery cell are both located within the thinning area 12 of the second electrode 20 and / or the third electrode 30.

[0060] In this embodiment, the orthographic projections of the first tab 50 and the first adhesive tape 70 along the thickness direction of the battery cell are located within the thinning area 12. Similarly, the orthographic projections of the second tab 60 and the second adhesive tape 80 along the thickness direction of the battery cell are also located within the thinning area 12. This can reduce or even eliminate the adverse effects of the first tab 50, the first adhesive tape 70, the second tab 60, and the second adhesive tape 80 on the uniformity of the battery cell thickness, reduce the thickness difference between different areas of the battery cell, and thus solve the problem of easy lithium deposition during the charge and discharge cycle of the battery cell caused by uneven battery cell thickness, which is beneficial to improving the energy density of the battery cell.

[0061] Furthermore, such as Figures 5-7 As shown, multiple thinning zones 12 are provided on the current collectors 1 of the second electrode 20 and the third electrode 30. The orthographic projections of the first electrode tab 50 and the first adhesive tape 70 along the thickness direction of the battery cell body are located within the multiple thinning zones 12. The orthographic projections of the second electrode tab 60 and the second adhesive tape 80 along the thickness direction of the battery cell body are also located within the multiple thinning zones 12.

[0062] Furthermore, the battery cell in this embodiment also includes a finishing wrapping adhesive. The battery cell has a fifth side and a sixth side arranged opposite to each other along its own thickness direction. The finishing wrapping adhesive includes a first section, a second section, and a third section. The first section is attached to the fifth side, the third section is attached to the sixth side, and the second section connects the first section and the third section. The orthographic projections of the first section and the second section along the thickness direction of the battery cell are both located within the third electrode 30 and / or the thinning area 12 of the third electrode 30. This reduces or even eliminates the adverse effects of the first and third sections of the finishing wrapping adhesive on the uniformity of the battery cell thickness. In this embodiment, multiple finishing wrapping adhesives are provided to ensure that the battery cell can be firmly fixed by the finishing wrapping adhesive.

[0063] The core provided in this embodiment has a thickness difference of δμm between the thickest part and the surrounding area. The number of layers of thinned current collector (the number of current collector layers in the core formed after the separator 40 and the two electrode sheets are wound is generally much greater than two layers) is X (no need to distinguish between positive and negative electrode current collectors). The thickness of each thinned current collector layer is h=(δ / X)μm. The width W of the thinned area 12 is W=(width of the thickest part of the core)+(0.5~5)mm. The length of the thickest part of the core +(0.5~5mm)≤ the length L of the thinned area 12≤ the electrode width W1.

[0064] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present utility model, and these improvements and substitutions should also be considered within the protection scope of the present utility model.

[0065] The experimental data for the battery cell (wound core) provided in this embodiment four under different thinning and chamfering schemes are as follows:

[0066]

[0067]

[0068]

[0069] By comparing Embodiment 1, Embodiment 4 and Comparative Example 1, it can be seen that thinning the aluminum foil (cathode current collector) can effectively improve energy density and improve lithium plating, and setting a chamfer can reduce the frequency of cathode band breakage.

[0070] By comparing Embodiment 2, Embodiment 5 and Comparative Example 1, it can be seen that thinning the copper foil (anode current collector) can effectively improve energy density and improve lithium plating, and setting a chamfer can reduce the frequency of cathode breakage.

[0071] By comparing embodiments 1-6, it can be found that simultaneously thinning copper foil and aluminum foil can effectively improve energy density and improve lithium plating. However, the cathode sheet has poorer toughness than the anode sheet, so thinning copper foil can be given priority.

Claims

1. A pole piece, characterized in that, The application relates to a current collector (1), a first coating layer (2) and a second coating layer (3), wherein the current collector (1) comprises an equal-thickness area (11) and a thinned area (12), the thickness of the thinned area (12) is smaller than that of the equal-thickness area (11), the current collector (1) has a first side (13) and a second side (14) oppositely arranged along the thickness direction of the current collector (1), the first side (13) is provided with the first coating layer (2), and the second side (14) is provided with the second coating layer (3).

2. The pole piece of claim 1, wherein The equal-thickness area (11) has an equal-thickness area first side (131) and an equal-thickness area second side (141) oppositely arranged along the thickness direction of the equal-thickness area (11), the thinned area (12) has a thinned area first side (132) and a thinned area second side (142) oppositely arranged along the thickness direction of the thinned area (12), the first side (13) comprises the equal-thickness area first side (131) and the thinned area first side (132), and the second side (14) comprises the equal-thickness area second side (141) and the thinned area second side (142). The thinned area first side (132) comprises a bottom surface (1321) and a transition surface (1322), the transition surface (1322) connects the bottom surface (1321) and the equal-thickness area first side (131), and the thinned area second side (142) is coplanar with the equal-thickness area second side (141).

3. The pole piece of claim 2, wherein The transition surface (1322) is an arc surface.

4. The pole piece of claim 2, wherein The transition surface (1322) comprises a first transition arc surface (13221) and a second transition arc surface (13222), one end of the first transition arc surface (13221) is connected with the bottom surface (1321), and the other end extends towards the equal-thickness area first side (131), one end of the second transition arc surface (13222) is connected with the equal-thickness area first side (131), and the other end extends towards the bottom surface (1321).

5. The pole piece of claim 4, wherein The first transition arc surface (13221) and the second transition arc surface (13222) are both circular arc surfaces, the radius of the first transition arc surface (13221) and the radius of the second transition arc surface (13222) are both not less than one-third of the difference between the thickness of the equal-thickness area (11) and the thickness of the thinned area (12), and both are not greater than one-half of the difference between the thickness of the equal-thickness area (11) and the thickness of the thinned area (12), the height of the second transition arc surface (13222) along the thickness direction of the current collector (1) is not greater than the height of the first transition arc surface (13221) along the thickness direction of the current collector (1), and is not less than one-third of the height of the first transition arc surface (13221) along the thickness direction of the current collector (1).

6. An electric cell having a first direction, characterized by The battery cell comprises a cell body, a tab and a tailing winding adhesive, the cell body comprises a plurality of separators (40) and a plurality of first pole pieces, the separators (40) and the first pole pieces are arranged alternately along the first direction, at least one of the plurality of first pole pieces is the pole piece of any one of claims 1-5, the cell body has a third side and a fourth side oppositely arranged along the first direction, and each first pole piece is connected with the tab. The tailing winding adhesive comprises a first segment, a second segment and a third segment, the first segment is attached to the third side, the third segment is attached to the fourth side, and the second segment connects the first segment and the third segment. The first segment and the second segment are both located in the thinning area (12) in the orthogonal projection along the first direction.

7. The battery cell of claim 6, having a second direction perpendicular to the first direction, wherein, The battery cell has a first end and a second end oppositely arranged along the second direction, and the first end and the second end of the battery cell are both provided with a plurality of tailing winding adhesives.

8. An electric cell characterized by The battery cell comprises a cell body, the cell body is wound by a separator (40) and two pole pieces according to any one of claims 1-5, the two pole pieces are a second pole piece (20) and a third pole piece (30) respectively, and the separator (40) is arranged between the second pole piece (20) and the third pole piece (30). The battery cell further comprises a first tab (50), a second tab (60), a first adhesive paper (70) and a second adhesive paper (80), the first tab (50) is connected to the first side (13) or the second side (14) of the current collector (1) of the second pole piece (20), the second tab (60) is connected to the first side (13) or the second side (14) of the current collector (1) of the third pole piece (30), the first tab (50) is provided with the first adhesive paper (70) on the side away from the current collector (1) of the second pole piece (20), and the second tab (60) is provided with the second adhesive paper (80) on the side away from the current collector (1) of the third pole piece (30). The orthogonal projection of the first tab (50) and the first adhesive paper (70) along the thickness direction of the battery cell is located in the thinning area (12) of the second pole piece (20) and / or the third pole piece (30); and the orthogonal projection of the second tab (60) and the second adhesive paper (80) along the thickness direction of the battery cell is located in the thinning area (12) of the second pole piece (20) and / or the third pole piece (30).

9. The electric cell of claim 8, wherein, The current collector (1) of the second pole piece (20) and the third pole piece (30) is provided with a plurality of thinning areas (12), the orthogonal projection of the first tab (50) and the first adhesive paper (70) along the thickness direction of the cell body is located in the plurality of thinning areas (12), and the orthogonal projection of the second tab (60) and the second adhesive paper (80) along the thickness direction of the cell body is located in the plurality of thinning areas (12).

10. The cell of claim 8 or 9, wherein, The winding end adhesive tape also includes a first section, a second section and a third section, the first section is attached to the fifth side surface, the third section is attached to the sixth side surface, and the second section connects the first section and the third section. The first section and the second section are both in the third pole piece (30) and / or the thinning area (12) of the third pole piece (30) in the orthographic projection along the thickness direction of the battery cell.

11. The electric cell of claim 10, wherein, The winding end adhesive tape is provided with a plurality of.

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