Pole piece and lithium ion battery

Abstract

The invention provides a pole piece and a lithium ion battery. The pole piece comprises a current collector, a first active layer and a second active layer, the first active layer is arranged on the surface of the current collector and provided with a first groove, and the second active layer is arranged on the surface of the current collector and provided with a second groove. The second active layer is divided into a first part arranged in the first groove and a second part arranged on the first active layer and far away from the surface of the current collector; wherein the first part is provided with a second groove, the tab is arranged at the second groove and is electrically connected with the current collector, and the thickness of the first part of the second active layer is smaller than the total thickness of the first active layer and the second part of the second active layer. According to the pole piece provided by the invention, by reducing the thickness of the active layer near the tab, the charging risk of the tab connection position is improved to a certain extent, and the cycle performance of the lithium ion battery is improved.

Description

[0001] This disclosure is a divisional application of the invention patent application with application number 202011628654.0 submitted to the China Patent Office, application date December 30, 2020, and the invention name is "A pole piece and lithium-ion battery". Technical Field

[0002] The present invention relates to a pole piece and a lithium ion battery, and relates to the technical field of lithium ion batteries. Background Art

[0003] With the advent of the 5G era, lithium-ion batteries are becoming increasingly important. Currently, lithium-ion batteries are developing towards higher energy density and faster charging rates. Currently, the tab connection position is being adjusted from the edge of the electrode to the middle of the electrode side to reduce the impedance of lithium-ion batteries.

[0004] However, when the tab position is changed, the current density around the tab increases, and as the lithium-ion battery cycles, lithium ions are released, resulting in poor cycling performance. Therefore, how to solve the problem of poor cycling performance of lithium-ion batteries caused by this tab connection method has attracted increasing attention. Summary of the Invention

[0005] The present invention provides a pole piece for solving the problem of poor cycle performance of lithium-ion batteries caused by this pole tab connection method.

[0006] A first aspect of the present invention provides a pole piece, comprising a current collector, a first active layer, and a second active layer, wherein the first active layer is disposed on a surface of the current collector and has a first groove, and the second active layer is divided into a first portion disposed in the first groove and a second portion disposed on the first active layer away from the surface of the current collector;

[0007] A second groove is provided on the first portion, the tab is provided at the second groove and is electrically connected to the current collector, and the thickness of the first portion of the second active layer is less than the total thickness of the first active layer and the second portion of the second active layer.

[0008] At present, the pole piece used in the prior art generally includes a current collector and an active layer arranged on the surface of the current collector, and a groove is opened in the middle of the side of the active layer. The groove is connected to the pole tab in the corresponding area on the current collector. In order to solve the problem of poor cycle performance of lithium-ion batteries caused by this pole tab connection method, the present invention reduces the thickness of the active layer around the position of the pole tab. Specifically, Figure 1a This is a front view of a pole piece provided by an embodiment of the present invention. Figure 1b A top view of a pole piece provided in one embodiment of the present invention is shown. Figure 1cThis is a left side view of a pole piece provided in one embodiment of the present invention, as shown in FIG. Figures 1a-1c As shown, the electrode includes a current collector 1, a first active layer 2, a second active layer 3 and a pole ear 4, wherein the first active layer 2 is arranged on the surface of the current collector 1, and a first groove is provided on the first active layer 2, the first part of the second active layer is arranged in the first groove and contacts the surface of the current collector 1, the second part of the second active layer is arranged on the upper surface of the first active layer 2 away from the current collector 1, and a second groove is provided in the middle of the side of the first part of the second active layer for connecting to the pole ear 4, and the thickness of the first part of the second active layer is less than the total thickness of the second part of the first active layer and the second active layer, so that the thickness of the active layer near the pole ear is lower than the thickness of the active layer away from the pole ear; wherein, the definition of the pole piece thickness in the present application is the same as that in the prior art, that is, the longest side of the pole piece is the length of the pole piece, the shortest side is the height of the pole piece, and the side between the longest side and the shortest side is the width of the pole piece, that is Figure 1a The longer side is the length of the pole piece, and the shorter side is the height of the pole piece. Figure 1b The shorter side is the width of the electrode, the longer side is the length of the electrode, the higher side is the thickness of the electrode, and the wider side is the width of the electrode. Furthermore, the first and second grooves are aligned with the length, width, and thickness of the electrode. The electrode provided by the present invention reduces the total thickness of the active layer around the tab, thereby improving the charging risk at the tab connection location and enhancing the cycling performance of the lithium-ion battery.

[0009] In one specific embodiment, to further improve the cycling performance of lithium-ion batteries, the thickness of the first active layer should be appropriately reduced, that is, the thickness of the second active layer should be greater than that of the first active layer. Furthermore, because the first portion of the second active layer is disposed within the first groove, it is subjected to less force during the subsequent electrode sheet rolling process, resulting in a difference in thickness between the first and second portions of the second active layer. Specifically, the first portion of the second active layer is thicker than the second portion.

[0010] according to Figures 1a-1c The pole piece structure shown requires improvement of the existing coating equipment to ensure the position and area of ​​the first groove, which will not only increase the preparation cost, but also be detrimental to the preparation of other pole piece structures. Therefore, the width of the first groove can be increased to make it the same as the width of the current collector, that is, the first groove divides the first active layer into two independent parts, and the blank part in the middle is the first groove.

[0011] For example:

[0012] Figure 2a A front view of a pole piece provided in yet another embodiment of the present invention, Figure 2b A top view of a pole piece provided in another embodiment of the present invention is shown in FIG. Figure 2a-2bAs shown, the electrode sheet includes a current collector 1, a first active layer 2, a second active layer 3 and a tab 4. The first active layer 2 is provided with a first groove, and the width of the first groove is the same as the width of the current collector 1, that is, the first groove divides the first active layer 2 into two left and right parts. The first part of the second active layer 3 is arranged in the first groove, and the second part of the second active layer 3 is arranged on the upper surface of the first active layer 2 away from the current collector 1. Since the width of the first groove is the same as the width of the current collector, the second part of the second active layer 3 is also divided into two independent left and right parts.

[0013] It can be understood that, with the intersection of the diagonals of the vertical projection area of ​​the second groove on the current collector as the center, the center of the vertical projection of the second groove on the current collector is located inside the first groove.

[0014] Continue to refer Figure 1b Or 2b shows that the center of the vertical projection of the second groove on the current collector is located in the first groove. In order to further improve the cycle performance of the lithium-ion battery, the second groove can be set at the center of the first groove as much as possible so that the thickness of the active layer on both sides of the tab is the same.

[0015] The applicant's research has found that the ratio of the cross-sectional areas of the first and second grooves in the length direction significantly affects the performance of lithium-ion batteries. Specifically, the vertical projection area of ​​the second groove on the current collector is 1%-50% of the vertical projection area of ​​the first groove on the current collector. During the specific manufacturing process, those skilled in the art can determine the widths of the first and second grooves and adjust their area ratio by adjusting their length ranges.

[0016] In order to improve the fast charging performance of lithium-ion batteries, when the electrode is a negative electrode, the average particle size of the active material in the second active layer is 5-20 μm and the degree of graphitization is 90%-98%.

[0017] The electrode provided by the present invention is also applicable to positive electrode sheets, and when the electrode sheet is a positive electrode sheet, the material of the first active layer usually uses a high-viscosity substance to improve the safety performance of the lithium-ion battery. However, due to the high viscosity of the substance, when the area where the first groove is located in the first active layer is cleaned, the high-viscosity substance cannot be completely cleaned, resulting in the presence of high-viscosity substance residue in the area corresponding to the first groove, affecting the connection between the tab and the current collector, resulting in the tab being unable to connect to the middle position of the side of the current collector. Therefore, the use of the electrode structure provided by the present invention can effectively avoid this problem, that is, the first active layer uses a high-viscosity substance, and subsequently only the second active layer needs to be cleaned, without cleaning the first active layer. Specifically, the high-viscosity substance refers to the active layer material including an adhesive with a molecular weight of 800,000-2,000,000, and the mass of the adhesive is 3%-40% of the total mass of the first active layer.

[0018] In addition, the thickness of the first active layer and the second active layer in the electrode have a great influence on the performance of the lithium-ion battery. The inventors of this application have found that when the thickness ratio of the first active layer increases, the cycle performance of the lithium-ion battery will moderately decrease. Therefore, the thickness of the first active layer is 5%-80% of the total thickness of the first active layer and the second part of the second active layer.

[0019] When the electrode is a positive electrode, the thickness of the first active layer should be appropriately reduced, for example, Figure 3 A front view of a positive electrode sheet provided in one embodiment of the present invention, as shown in FIG. Figure 3 As shown, when the electrode is a positive electrode, the thickness of the first portion of the second active layer is greater than the thickness of the first active layer.

[0020] On the basis of the electrode structure provided by the present invention, those skilled in the art can combine it with the existing electrode preparation method. Specifically, first, a first active layer slurry and a second active layer slurry are prepared; secondly, the prepared first active layer slurry is coated on the surface of the current collector, and a blank coating is performed in the area corresponding to the first groove to obtain a first active layer provided with a first groove, and then the second active layer slurry is coated according to a conventional electrode coating process, wherein part of the second active layer slurry fills the first groove under the action of gravity to obtain the first part of the second active layer, and the remaining part of the second active layer slurry obtains the second part of the second active layer; finally, the active layer located in a part of the first part in the first groove is cleaned to obtain a second groove, and the electrode tab is arranged in the second groove and electrically connected to the current collector to obtain the electrode.

[0021] Those skilled in the art can select materials for the positive and negative electrode sheets in combination with existing technologies. For example, when the electrode sheet is a positive electrode sheet, the current collector can be aluminum foil, and the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium-rich manganese-based materials, and lithium nickel cobalt aluminum oxide.

[0022] When the electrode sheet is a negative electrode sheet, the current collector may be copper foil, and the negative electrode active material includes at least one of artificial graphite, natural graphite, and modified graphite;

[0023] The adhesive and conductive agent used in the positive and negative electrode sheets are the same. Specifically, the adhesive may include at least one of polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene and styrene-butadiene rubber (SBR); the conductive agent may include at least one of conductive carbon black, carbon nanotubes, conductive graphite and graphene; the negative electrode sheet may also include a thickener, which may be sodium carboxymethyl cellulose.

[0024] It can be understood that the second groove is used to connect the electrode tab, and therefore, along the width direction of the current collector, the width of the second groove is smaller than the width of the first groove.

[0025] In the actual preparation process, in order to facilitate the connection between the tab and the current collector, the vertical projection area of ​​the second groove on the current collector can be enlarged so that the vertical projection area of ​​the second groove on the current collector is larger than the area of ​​the tab connection area on the current collector.

[0026] Figure 4 A top view of a tab provided in yet another embodiment of the present invention is shown in FIG. Figure 4 As shown, the length and width of the first groove are both larger than the area of ​​the tab connection region on the current collector, so as to facilitate the connection between the tab 4 and the current collector 1 .

[0027] Furthermore, the width of the second groove is 1-2 times the width of the tab connection area, and the length of the second groove is 1-2 times the length of the tab connection area.

[0028] In summary, the present invention provides a pole piece, which improves the charging risk at the pole tab connection position to a certain extent by reducing the thickness of the active layer near the pole tab, thereby improving the cycle performance of the lithium-ion battery.

[0029] A second aspect of the present invention provides a lithium-ion battery comprising any one of the above-mentioned pole pieces.

[0030] The present invention provides a pole piece. Based on the pole piece provided by the present invention and in combination with existing technologies, a person skilled in the art can prepare a lithium-ion battery. The lithium-ion battery provided by the present invention has good cycle performance.

[0031] The implementation of the present invention has at least the following advantages:

[0032] 1. The pole piece provided by the present invention reduces the thickness of the active layer near the pole tab, thereby improving the charging risk at the pole tab connection position to a certain extent and improving the cycle performance of the lithium-ion battery.

[0033] 2. The electrode provided by the present invention is applicable to both positive and negative electrodes.

[0034] 3. When the electrode is a positive electrode, the electrode structure provided by the present invention can avoid the problem of being unable to connect the electrode tab to the center of the side of the current collector due to the presence of highly viscous substances in the first active layer.

[0035] 4. The lithium-ion battery provided by the present invention has good cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1aA front view of a pole piece provided in one embodiment of the present invention;

[0037] Figure 1b A top view of a pole piece provided in one embodiment of the present invention;

[0038] Figure 1c A left side view of a pole piece provided in one embodiment of the present invention;

[0039] Figure 2a A front view of a pole piece provided in yet another embodiment of the present invention;

[0040] Figure 2b A top view of a pole piece provided in yet another embodiment of the present invention;

[0041] Figure 3 A front view of a pole piece provided in yet another embodiment of the present invention;

[0042] Figure 4 A top view of a pole piece provided in yet another embodiment of the present invention.

[0043] Description of reference numerals:

[0044] 1: Current collector;

[0045] 2: first active layer;

[0046] 3: second active layer;

[0047] 4: Tab. DETAILED DESCRIPTION

[0048] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0049] Example 1

[0050] The electrode provided in this embodiment is a positive electrode, and its main view is as follows: Figure 3 As shown, the top view is Figure 4 As shown, the left view is as follows Figure 1c As shown, where:

[0051] The current collector is aluminum foil with a width of 79 mm;

[0052] The first groove has a width of 79 mm and a length of 15 mm;

[0053] The second groove has a width of 25 mm and a length of 10 mm;

[0054] The thickness of the first active layer is 10 μm, and the thickness of the second active layer is 80 μm;

[0055] The material used for the first active layer is a highly viscous substance including lithium cobalt oxide, conductive carbon and polyvinylidene fluoride. The molecular weight of the polyvinylidene fluoride is 800,000, and the mass of the polyvinylidene fluoride accounts for 20% of the total mass of the first active layer.

[0056] Example 2

[0057] The electrode provided in this embodiment is a negative electrode, and its structural front view is as follows: Figure 2a As shown, the top view is Figure 4 As shown, the left view is as follows Figure 1c As shown, where:

[0058] The current collector is copper foil with a width of 81 mm;

[0059] The first groove has a width of 81 mm and a length of 50 mm;

[0060] The second groove has a width of 25 mm and a length of 10 mm;

[0061] The thickness of the first active layer is 50 μm, and the thickness of the second active layer is 50 μm;

[0062] The active material used in the second active layer is graphite. The average particle size of the graphite is 15 μm and the degree of graphitization is 94%.

[0063] Example 3

[0064] The electrode provided in this embodiment is a negative electrode, and its structural front view is as follows: Figure 3 As shown, the top view is Figure 4 As shown, the left view is as follows Figure 1c As shown, where:

[0065] The current collector is copper foil with a width of 81 mm;

[0066] The first groove has a width of 81 mm and a length of 50 mm;

[0067] The second groove has a width of 25 mm and a length of 10 mm;

[0068] The thickness of the first active layer is 30 μm, and the thickness of the second active layer is 70 μm;

[0069] The active material used in the second active layer is graphite. The average particle size of the graphite is 15 μm and the degree of graphitization is 94%.

[0070] Example 4

[0071] The electrode provided in this embodiment is a negative electrode, and its structural front view is as follows: Figure 3 As shown, the top view is Figure 4 As shown, the left view is as follows Figure 1c As shown, where:

[0072] The current collector is copper foil with a width of 81 mm;

[0073] The first groove has a width of 81 mm and a length of 50 mm;

[0074] The second groove has a width of 25 mm and a length of 10 mm;

[0075] The thickness of the first active layer is 40 μm, and the thickness of the second active layer is 60 μm;

[0076] The active material used in the second active layer is graphite. The average particle size of the graphite is 15 μm and the degree of graphitization is 94%.

[0077] Example 5

[0078] The electrode provided in this embodiment is a negative electrode, and its structural front view is as follows: Figure 2a As shown, the top view is Figure 4 As shown, the left view is as follows Figure 1c As shown, where:

[0079] The current collector is copper foil with a width of 81 mm;

[0080] The first groove has a width of 81 mm and a length of 50 mm;

[0081] The second groove has a width of 25 mm and a length of 10 mm;

[0082] The thickness of the first active layer is 50 μm, and the thickness of the second active layer is 50 μm;

[0083] The active material used in the second active layer is graphite. The average particle size of the graphite is 10 μm and the degree of graphitization is 92%.

[0084] Example 6

[0085] The electrode provided in this embodiment is a negative electrode, and its structural front view is as follows: Figure 2a As shown, the top view is Figure 4 As shown, the left view is as follows Figure 1c As shown, where:

[0086] The current collector is copper foil with a width of 81 mm;

[0087] The first groove has a width of 81 mm and a length of 50 mm;

[0088] The second groove has a width of 25 mm and a length of 10 mm;

[0089] The thickness of the first active layer is 50 μm, and the thickness of the second active layer is 50 μm;

[0090] The active material used in the second active layer is graphite, the average particle size of the graphite is 10 μm, and the degree of graphitization is 95%.

[0091] Example 7

[0092] The electrode provided in this embodiment is a negative electrode, and its structural front view is as follows: Figure 2a As shown, the top view is Figure 4 As shown, the left view is as follows Figure 1c As shown, where:

[0093] The current collector is copper foil with a width of 81 mm;

[0094] The first groove has a width of 81 mm and a length of 50 mm;

[0095] The second groove has a width of 25 mm and a length of 10 mm;

[0096] The thickness of the first active layer is 50 μm, and the thickness of the second active layer is 50 μm;

[0097] The active material used in the second active layer is graphite. The average particle size of the graphite is 15 μm and the degree of graphitization is 92%.

[0098] Example 8

[0099] The electrode provided in this embodiment is a negative electrode, and its structural front view is as follows: Figure 2a As shown, the top view is Figure 4 As shown, the left view is as follows Figure 1c As shown, where:

[0100] The current collector is copper foil with a width of 81 mm;

[0101] The first groove has a width of 81 mm and a length of 50 mm;

[0102] The second groove has a width of 25 mm and a length of 10 mm;

[0103] The thickness of the first active layer is 50 μm, and the thickness of the second active layer is 50 μm;

[0104] The active material used in the second active layer is graphite, the average particle size of the graphite is 15 μm, and the degree of graphitization is 95%.

[0105] Comparative Example 1

[0106] The electrode provided in this comparative example is a positive electrode, comprising a current collector and an active layer disposed on the surface of the current collector, with the tab connected to the outermost edge of the current collector, wherein:

[0107] The current collector is aluminum foil with a width of 79 mm;

[0108] The thickness of the active layer is 90 μm.

[0109] Comparative Example 2

[0110] The electrode sheet provided in this comparative example is a negative electrode sheet, comprising a current collector and a first active layer and a second active layer disposed on the surface of the current collector. A groove is disposed between the sides of the first active layer and the second active layer, and the electrode tab is connected to the groove, wherein:

[0111] The current collector is copper foil with a width of 81 mm;

[0112] The groove has a width of 25 mm and a length of 10 mm;

[0113] The total thickness of the first active layer and the second active layer is 100 μm.

[0114] Based on the electrode sheets provided in Examples 1-8 and Comparative Examples 1-2 of the present invention, lithium-ion batteries were prepared by combining negative electrode sheets / positive electrode sheets, separators, and electrolytes with the same structure. For example, if Example 1 and Comparative Example 1 are positive electrode sheets, the structure of the corresponding negative electrode sheets is the same as that of the positive electrode sheets; if Examples 2-8 and Comparative Example 2 are negative electrode sheets, the structure of the corresponding positive electrode sheets is the same as that of the negative electrode sheets, and the cycle performance of the lithium-ion batteries was tested.

[0115] Among them, the positive electrode material was purchased from Xiamen Xiatung New Energy Materials Co., Ltd., the negative electrode material was purchased from Shanghai Shanshan Technology Co., Ltd., the diaphragm was purchased from Dongguan Zhuogao Electronic Technology Co., Ltd., and the electrolyte was purchased from Shenzhen Xinzhoubang Technology Co., Ltd.

[0116] The performance test method for lithium-ion batteries is:

[0117] The lithium-ion batteries prepared in Example 1 and Comparative Example 1 were subjected to a 2C / 0.7C charge-discharge cycle test at 25°C, and their cycle retention (%) was calculated. The surface temperature of the battery cell was monitored using a temperature sensor, and the difference between the maximum value and the initial temperature was recorded as the temperature rise (°C) of the lithium-ion battery. The test results are shown in Table 1.

[0118] The lithium-ion batteries prepared based on Examples 2-8 and Comparative Example 2 were subjected to 2C / 0.7C charge-discharge cycle tests at 25°C / 10°C, and their cycle retention rates (%) were calculated. The test results are shown in Table 2.

[0119] Table 1 Performance test results of lithium ion batteries provided in Example 1 and Comparative Example 1

[0120] 25℃ cycle retention rate Battery cell surface temperature rise Example 1 84.80％ 13℃ Comparative Example 1 83.90％ 16℃

[0121] Table 2 Cycling performance test results of lithium ion batteries provided in Examples 2-8 and Comparative Example 2

[0122] 25℃ cycle retention rate 10℃ cycle retention rate Example 2 85.10％ 83.00％ Example 3 86.10％ 84.00％ Example 4 85.50％ 83.00％ Example 5 86.00％ 84.50％ Example 6 84.90％ 83.30％ Example 7 85.30％ 83.50％ Example 8 83.00％ 82.60％ Comparative Example 2 82.00％ 81.00％

[0123] As can be seen from Table 1-2, the lithium-ion batteries provided in Examples 1-8 all have good cycle performance; according to the data provided in Examples 2-4, as the proportion of the first active layer to the total thickness of the active layer increases, the performance of the lithium-ion battery will moderately decrease, and therefore, the thickness of the first active layer should be controlled; according to the data provided in Examples 5-8, in the negative electrode sheet, as the average particle size and degree of graphitization of the negative electrode active material in the second active layer increase, the cycle retention rate of the lithium-ion battery will decrease.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pole piece, characterized in that: The pole piece includes a current collector, a first active layer, and a second active layer. The first active layer is arranged on the surface of the current collector and is provided with a first groove. The second active layer is divided into a first portion arranged in the first groove and a second portion arranged on the first active layer away from the current collector surface. A second groove is provided on the first portion, the tab is provided at the second groove and is electrically connected to the current collector, and the thickness of the first portion of the second active layer is less than the total thickness of the first active layer and the second portion of the second active layer.

2. The pole piece according to claim 1, characterized in that: The thickness of the second active layer is greater than the thickness of the first active layer; and / or the thickness of the first portion of the second active layer is greater than the thickness of the second portion.

3. The pole piece according to claim 1, characterized in that: The width of the first groove is the same as the width of the current collector.

4. The pole piece according to claim 1, characterized in that: A vertical projection area of ​​the second groove on the current collector is 1% to 50% of a vertical projection area of ​​the first groove on the current collector.

5. The pole piece according to any one of claims 1 to 4, characterized in that: The pole piece is a negative pole piece, the average particle size of the negative electrode active material in the second active layer is 5-20 μm, and the graphitization degree is 90%-98%.

6. The pole piece according to any one of claims 1 to 4, characterized in that: The first portion contacts a portion of the surface of the current collector in the first groove.

7. The pole piece according to claim 1, characterized in that: The thickness of the first active layer is 5%-80% of the total thickness of the first active layer and the second portion of the second active layer.

8. The pole piece according to claim 1, characterized in that: Along the width direction of the current collector, the width of the second groove is smaller than the width of the first groove.

9. The pole piece according to claim 1, characterized in that: The width of the second groove is 1-2 times the width of the tab connection area, and the length of the second groove is 1-2 times the length of the tab connection area.

10. A lithium ion battery, characterized in that: The pole piece comprises any one of claims 1 to 9.

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