Current collector, positive plate and lithium ion battery

Abstract

The utility model relates to a current collector, a positive plate and a lithium ion battery. The current collector comprises a main body area and an open pore area connected to the main body area, the open pore area is close to the edge position of the current collector, and open pores are distributed in the open pore area. The opening area is arranged at the edge of the current collector, and the openings are distributed in the opening area, so that the resistivity of the opening area is increased and the current density at the edge of the positive plate is reduced due to the existence of the openings, thereby reducing the deposition speed of lithium at the edge of the negative plate and enabling the edge of the negative active material layer of the negative plate not to have a lithium precipitation phenomenon easily; and the lithium precipitation risk is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of electrochemistry, in particular to a current collector, a positive electrode sheet and a lithium ion battery. Background Art

[0002] The positive and negative electrodes of lithium-ion batteries are formed by coating the active material slurry on the surface of the current collector and then sintering. Since the active material slurry has a certain fluidity, the coated slurry will flow and extend to the edge of the current collector and form an edge casting area at the edge of the current collector, resulting in the slurry coating thickness at the edge of the current collector being less than the designed coating thickness. This reduces the NP ratio (i.e., the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area) at the edge of the electrode after the positive and negative electrode sheets are assembled, which in turn leads to a greater risk of lithium deposition at the edge of the negative electrode sheet.

[0003] In addition, since the edge of the electrode generally has a higher current density when the battery is working, this will also speed up the deposition of lithium at the edge of the negative electrode, thereby accelerating the occurrence of lithium precipitation, which will cause the battery capacity to decay and reduce the battery's energy density. In addition, the precipitated metallic lithium will form lithium dendrites, and the continued growth of dendrites may pierce the diaphragm, thereby inducing a short circuit in the battery, which will have an irreversible impact on the life and safety of lithium-ion batteries. Utility Model Content

[0004] Based on this, it is necessary to provide a current collector, a positive electrode sheet and a lithium-ion battery to solve the problem of lithium deposition at the edge of the negative electrode sheet.

[0005] The first aspect of the utility model is to provide a current collector, the scheme is as follows:

[0006] A current collector comprises a main body region and an opening region connected to the main body region, wherein the opening region is close to an edge of the current collector and has openings distributed therein.

[0007] In one embodiment, the current collector has at least two open areas respectively connected to opposite sides of the main area.

[0008] In one embodiment, the current collector is a strip-shaped structure, and the opening area includes a first opening area and a second opening area that are oppositely arranged in the width direction of the current collector.

[0009] In one embodiment, the width of the opening area is 2 mm to 20 mm.

[0010] In one embodiment, the aperture of the opening is 5 μm to 12 μm; and / or

[0011] In one embodiment, the number of openings is 500 / cm 2~5000pcs / cm 2 .

[0012] In one embodiment, the current collector includes a metal layer and a first carbon layer stacked on a first side of the metal layer and / or a second carbon layer stacked on a second side of the metal layer.

[0013] In one embodiment, the thickness of the portion of the first carbon layer located in the opening area is smaller than that of the portion located in the main body area; or, the first carbon layer is only located in the main body area;

[0014] The thickness of the portion of the second carbon layer located in the opening area is smaller than that of the portion located in the main area; or, the second carbon layer is only located in the main area.

[0015] The second aspect of the utility model is to provide a positive electrode sheet, the scheme is as follows:

[0016] A positive electrode sheet comprises a current collector as described in any one of the above embodiments and a positive electrode active material layer arranged on the current collector.

[0017] The third aspect of the utility model is to provide a lithium ion battery, the scheme is as follows:

[0018] A lithium ion battery comprises a shell and a positive electrode sheet and a negative electrode sheet arranged in the shell, wherein the positive electrode sheet and the negative electrode sheet are arranged opposite to each other, and a diaphragm and an electrolyte are arranged between the positive electrode sheet and the negative electrode sheet.

[0019] In one embodiment, the edge of the negative electrode sheet protrudes beyond the edge of the positive electrode sheet.

[0020] Compared with the traditional solution, the above current collector, positive electrode sheet and lithium ion battery have the following beneficial effects:

[0021] The above-mentioned current collector is provided with an opening area at the edge position, and the opening area is distributed with openings. The existence of the openings increases the resistivity of the opening area, which will reduce the current density at the edge position of the positive electrode sheet, thereby reducing the deposition rate of lithium ions at the edge position of the negative electrode sheet, making it less likely for lithium deposition to occur at the edge of the negative electrode active material layer of the negative electrode sheet, thereby reducing the risk of lithium deposition.

[0022] The positive electrode sheet has the current collector, and the lithium-ion battery has the positive electrode sheet, thereby achieving corresponding beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a schematic structural diagram of a current collector according to an embodiment;

[0024] FIG2 is a cross-sectional view of a current collector according to an embodiment;

[0025] FIG3 is a cross-sectional view of a current collector according to another embodiment;

[0026] FIG4 is a schematic structural diagram of a positive electrode sheet according to an embodiment;

[0027] FIG5 is a schematic structural diagram of a lithium-ion battery according to an embodiment;

[0028] FIG. 6 is a schematic diagram showing the positional relationship between the positive electrode sheet and the negative electrode sheet in a lithium-ion battery according to an embodiment of the present invention.

[0029] Description of reference numerals:

[0030] 100. Current collector; 101. Main body region; 102. Opening region; 1021. Opening; 1022. First opening region; 1023. Second opening region; 103. Blank region; 110. Metal layer; 120. First carbon layer; 130. Second carbon layer; 121. Portion of the first carbon layer located in the main body region; 122. Portion of the first carbon layer located in the opening region; 131. Portion of the second carbon layer located in the main body region; 132. Portion of the second carbon layer located in the opening region; 200. Positive electrode sheet; 210. Positive electrode active material layer; 300. Lithium-ion battery; 310. Shell; 320. Negative electrode sheet; 330. Diaphragm. DETAILED DESCRIPTION

[0031] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively with reference to the accompanying drawings. The accompanying drawings provide preferred embodiments of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. The purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0032] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0033] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number or order of the indicated technical features.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art in the technical field of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0035] The utility model provides a current collector.

[0036] As shown in Fig. 1, a current collector 100 of an embodiment includes a main body region 101 and an opening region 102 connected to the main body region 101. The opening region 102 is close to the edge of the current collector 100, and the opening region 102 has openings 1021 distributed therein.

[0037] The current collector 100 can be used in the positive electrode sheet of a lithium-ion battery, that is, as a positive electrode current collector. In the battery cell, the positive electrode sheet and the negative electrode sheet are arranged opposite to each other. The current collector 100 is provided with an opening area 102 at the edge position, and the opening area 102 is distributed with openings 1021. The existence of the openings 1021 increases the resistivity of the opening area 102, which reduces the current density at the edge position of the positive electrode sheet, thereby reducing the deposition speed of lithium ions at the edge position of the negative electrode sheet, making it difficult for lithium to be deposited at the edge of the negative electrode active material layer of the negative electrode sheet, thereby reducing the risk of lithium deposition.

[0038] By providing the openings 1021 , the resistivity of the opening area 102 is higher than the resistivity of the main body area 101 without openings. For example, the resistivity of the opening area 102 is 5% to 200% higher than the resistivity of the main body area 101 .

[0039] In one example, the opening 1021 is a chemical etching hole, which can be formed by a chemical liquid hot etching method. In other examples, the opening 1021 can also be a mechanical opening.

[0040] In one example, a blank area 103 is provided on the outer side of the opening area 102, and the blank area serves as the pole ear of the battery cell after winding or lamination; the width of the blank area is generally related to the welding performance of the battery cell. A smaller width may easily cause cold welding, while a too long width may cause material waste.

[0041] In one example, the width of the opening area 102 is 2 mm to 20 mm. In other words, the distance between the outer edge of the opening area 102 and the outer edge of the main body area 101 is 2 mm to 20 mm. Further, the width of the opening area 102 is 5 mm to 15 mm. In some specific examples, the width of the opening area 102 is 4 mm, 8 mm, 12 mm, 15 mm, 18 mm, 20 mm, etc.

[0042] In one example, the opening 1021 is a micropore, so that the current collector 100 maintains good mechanical properties and has good support capacity. In one example, the pore size of the opening 1021 is 5μm~12μm. Further, the pore size of the opening 1021 is 7μm~10μm. In some specific examples, the pore size of the opening 1021 is 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, etc.

[0043] In one example, the number of openings 1021 is 500 / cm 2 ~5000pcs / cm 2 Furthermore, the number of openings 1021 is 1000 / cm 2 ~4000pcs / cm 2 In some specific examples, the number of openings 1021 is 800 / cm 2 , 1000 pieces / cm 2 , 2000pcs / cm 2 , 3000 pieces / cm 2 , 4000 pieces / cm 2 , 5000pcs / cm 2 wait.

[0044] In one example, the current collector 100 has at least two open areas 102 connected to opposite sides of the main area 101 .

[0045] In one example, the current collector 100 is a strip-shaped structure. The positive electrode sheet formed by using the current collector 100 of this example is also a strip-shaped structure. The strip-shaped positive electrode sheet and negative electrode sheet can be stacked and then wound and assembled.

[0046] Further, in one example, the current collector 100 has a first opening area 1022 and a second opening area 1023 arranged opposite to each other in the width direction. The shapes, apertures, quantities, etc. of the openings 1021 in the first opening area 1022 and the second opening area 1023 may be the same or different.

[0047] In one example, the width of the main body area 101 is 40 mm to 600 mm. In one example, the width of the first opening area 1022 is 2 mm to 20 mm. The width of the second opening area 1023 is 2 mm to 20 mm. The widths of the first opening area 1022 and the second opening area 1023 may be the same or different.

[0048] It is understood that in other examples, the current collector 100 is not limited to being in a strip shape, but may also be in other shapes, such as a square, a circle, etc. The opening area 102 may also be arranged around the main body area 101, or in other arrangements.

[0049] As shown in FIG. 2 , in one example, the current collector 100 includes a metal layer 110 .

[0050] Optionally, the metal layer 110 may be, but is not limited to, at least one of an aluminum layer, a gold layer, a copper layer, a platinum layer, and a silver layer.

[0051] Furthermore, in one example, the current collector 100 further includes a first carbon layer 120 stacked on a first side of the metal layer 110 and / or a second carbon layer 130 stacked on a second side of the metal layer 110 .

[0052] In the specific example shown in FIG2 , the first carbon layer 120 includes a portion 121 located in the main region 101 and a portion 122 located in the open region 102. The portion 122 of the first carbon layer 120 located in the open region 102 has a thickness smaller than the portion 121 located in the main region 101. The second carbon layer 130 includes a portion 131 located in the main region 101 and a portion 132 located in the open region 102. The portion 132 of the second carbon layer 130 located in the open region 102 has a thickness smaller than the portion 131 located in the main region 101.

[0053] In the specific example shown in FIG3 , the first carbon layer 120 is only located in the main body region 101 . The second carbon layer 130 is only located in the main body region 101 . In other words, no carbon layer is provided in the opening region 102 .

[0054] In the above example, by setting the thickness of the carbon layer in the opening area 102 to be smaller than that in the main area 101, or only in the main area 101, the impedance of the opening area 102 is made greater than the impedance of the main area 101, so that the current density at the edge of the positive electrode sheet is reduced, lithium deposition at the edge of the negative electrode sheet is reduced, and the risk of lithium deposition is reduced.

[0055] Furthermore, the utility model also provides a positive electrode sheet.

[0056] As shown in FIG4 , a positive electrode sheet 200 of an embodiment includes a current collector 100 of any of the above examples and a positive active material layer 210 disposed on the current collector 100 . More specifically, the positive active material layer 210 is disposed on the main body region 101 and the opening region 102 of the current collector 100 .

[0057] The positive electrode sheet 200 has any of the current collectors 100 described above, thereby achieving corresponding beneficial effects.

[0058] The positive electrode active material layer 210 is disposed on at least one side of the current collector 100 , and preferably disposed on both sides of the current collector 100 .

[0059] The positive electrode active material layer 210 includes a positive electrode active material. Further, the positive electrode active material layer 210 may also include a binder and / or a conductive agent. For example, the positive electrode active material layer 210 may be formed by mixing the positive electrode active material, the binder and the conductive agent with a solvent to form a slurry, coating the slurry on the current collector 100, and then drying the slurry.

[0060] Furthermore, the utility model also provides a lithium-ion battery.

[0061] As shown in FIG5 , a lithium-ion battery 300 of an embodiment includes a housing 310, the above-mentioned positive electrode sheet 200, a negative electrode sheet 320, a separator 330, and an electrolyte (not shown in the figure). The positive electrode sheet 200, the negative electrode sheet 320, the separator 330, and the electrolyte are arranged in the housing 310. The positive electrode sheet 200 and the negative electrode sheet 320 are arranged opposite to each other, and the separator 330 and the electrolyte are arranged between the positive electrode sheet 200 and the negative electrode sheet 320. Among them, the positive electrode sheet 200 and the negative electrode sheet 320 can be wound to form a wound battery cell.

[0062] The lithium-ion battery 300 has any of the positive electrode sheets 200 described above, and thus can achieve corresponding beneficial effects.

[0063] As shown in FIG6 , in one example, the edge of the negative electrode sheet 320 protrudes from the edge of the positive electrode sheet 200. Further, both the positive electrode sheet 200 and the negative electrode sheet 320 are strip-shaped structures, and the width of the negative electrode sheet 320 is greater than the width of the positive electrode sheet 200. In the width direction, the edge of the negative electrode sheet 320 protrudes from the edge of the positive electrode sheet 200. This arrangement reduces or avoids the edge area of ​​the active material layer on the negative electrode sheet 320, which is thinner due to casting, from being opposite to the positive electrode sheet 200, thereby reducing lithium deposition of the negative electrode sheet 320.

[0064] In order to ensure the normal winding of the battery cell, the width of the positive electrode sheet 200 and the negative electrode sheet 320 should not differ too much, and the width of the edge of the negative electrode sheet 320 protruding from the edge of the positive electrode sheet 200 should not be too large. For example, in one example, the width of the negative electrode sheet 320 protruding from the edge of the positive electrode sheet 200 is 1mm~4mm. Further, in one example, the width of the negative electrode sheet 320 protruding from the edge of the positive electrode sheet 200 is 2mm.

[0065] Through the coordination of the aforementioned various structural improvements and designs, the occurrence of lithium deposition at the edge of the negative electrode in lithium-ion batteries can be greatly reduced, effectively improving the energy density, safety and other performance of the battery.

[0066] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to the following specific embodiments.

[0067] Example 1

[0068] This embodiment provides a current collector, a positive electrode sheet and a lithium ion battery.

[0069] The current collector of this embodiment is made of strip-shaped aluminum foil, including a main body area, a first opening area and a second opening area. The first opening area and the second opening area are close to both sides of the main body area and close to the edge of the current collector, with a width of 10 mm. The opening area is distributed with openings, and the aperture of the openings is 7 μm. The number of openings is 1000 / cm 2 The resistivity of the first opening area and the second opening area is about twice that of the main area.

[0070] The positive electrode sheet of this embodiment includes the above-mentioned current collector and a positive electrode active material layer stacked on both sides of the current collector. The positive electrode active material layer covers the main area, the first opening area and the second opening area of ​​the current collector. The positive electrode active material layer contains the positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2, conductive agent Super-P and binder PVDF, the weight ratio is 95.5:2.5:2. The above materials are mixed with solvent NMP to form a slurry, which is coated on the above current collector and dried and solidified to form a positive electrode active material layer, and then rolled and cut to obtain a positive electrode sheet.

[0071] The lithium-ion battery of this embodiment includes a shell, the above-mentioned positive electrode sheet, negative electrode sheet, separator and electrolyte. The positive electrode sheet, negative electrode sheet, separator and electrolyte are arranged in the shell. Among them, the negative electrode sheet is prepared by mixing the negative electrode active material graphite, the conductive agent Super-P, the thickener CMC and the binder SBR in pure water at a weight ratio of 95.5:1.5:1:2 to obtain a slurry, and then applying the slurry to the negative electrode collector, drying, rolling and cutting to obtain it. The positive electrode sheet and the negative electrode sheet are arranged opposite to each other and wound, and a separator and electrolyte are arranged between the positive electrode sheet and the negative electrode sheet. The edge of the negative electrode sheet protrudes from the edge of the positive electrode sheet, and the width of the edge of the negative electrode sheet protruding from the edge of the positive electrode sheet is 2mm.

[0072] Example 2

[0073] This embodiment provides a current collector, a positive electrode sheet and a lithium ion battery.

[0074] The current collector of this embodiment is made of strip-shaped aluminum foil, including a main body area, a first opening area and a second opening area. The first opening area and the second opening area are close to both sides of the main body area and close to the edge of the current collector, with a width of 10 mm. The opening area is distributed with openings, and the aperture of the opening is 5 μm. The number of openings is 500 / cm 2 The resistivity of the first opening area and the second opening area is about 1.5 times that of the main area.

[0075] The positive electrode sheet of this embodiment includes the above-mentioned current collector and a positive electrode active material layer stacked on both sides of the current collector. The positive electrode active material layer covers the main area, the first opening area and the second opening area of ​​the current collector. The positive electrode active material layer contains the positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2, conductive agent Super-P and binder PVDF, the weight ratio is 95.5:2.5:2. The above materials are mixed with solvent NMP to form a slurry, which is coated on the above current collector and dried and solidified to form a positive electrode active material layer, and then rolled and cut to obtain a positive electrode sheet.

[0076] The lithium-ion battery of this embodiment includes a shell, the above-mentioned positive electrode sheet, negative electrode sheet, separator and electrolyte. The positive electrode sheet, negative electrode sheet, separator and electrolyte are arranged in the shell. Among them, the negative electrode sheet is prepared by mixing the negative electrode active material graphite, the conductive agent Super-P, the thickener CMC and the binder SBR in pure water at a weight ratio of 95.5:1.5:1:2 to obtain a slurry, and then applying the slurry to the negative electrode collector, drying, rolling and cutting to obtain it. The positive electrode sheet and the negative electrode sheet are arranged opposite to each other and wound, and a separator and electrolyte are arranged between the positive electrode sheet and the negative electrode sheet. The edge of the negative electrode sheet protrudes from the edge of the positive electrode sheet, and the width of the edge of the negative electrode sheet protruding from the edge of the positive electrode sheet is 2mm.

[0077] Example 3

[0078] This embodiment provides a current collector, a positive electrode sheet and a lithium ion battery.

[0079] The current collector of this embodiment is in the shape of a strip, including aluminum foil, a first carbon layer and a second carbon layer. The current collector includes a main body area, a first opening area and a second opening area. The first opening area and the second opening area are close to both sides of the main body area and close to the edge of the current collector, with a width of 15 mm. The aluminum foil is close to the main body area, the first opening area and the second opening area. The first carbon layer and the second carbon layer are only close to the main body area and are stacked on opposite sides of the aluminum foil. The opening area is distributed with openings, and the pore size of the openings is 5 μm. The number of openings is 500 / cm 2 The resistivity of the first opening area and the second opening area of ​​the aluminum foil is about 1.5 times that of the main area.

[0080] The positive electrode sheet of this embodiment includes the above-mentioned current collector and a positive electrode active material layer stacked on both sides of the current collector. The positive electrode active material layer covers the main area, the first opening area and the second opening area of ​​the current collector. The positive electrode active material layer contains the positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3O2, conductive agent Super-P and binder PVDF, the weight ratio is 95.5:2.5:2. The above materials are mixed with solvent NMP to form a slurry, which is coated on the above current collector and dried and solidified to form a positive electrode active material layer, and then rolled and cut to obtain a positive electrode sheet.

[0081] The lithium-ion battery of this embodiment includes a shell, the above-mentioned positive electrode sheet, negative electrode sheet, separator and electrolyte. The positive electrode sheet, negative electrode sheet, separator and electrolyte are arranged in the shell. Among them, the negative electrode sheet is prepared by mixing the negative electrode active material graphite, the conductive agent Super-P, the thickener CMC and the binder SBR in pure water at a weight ratio of 95.5:1.5:1:2 to obtain a slurry, and then applying the slurry to the negative electrode collector, drying, rolling and cutting to obtain it. The positive electrode sheet and the negative electrode sheet are arranged opposite to each other and wound, and a separator and electrolyte are arranged between the positive electrode sheet and the negative electrode sheet. The edge of the negative electrode sheet protrudes from the edge of the positive electrode sheet, and the width of the edge of the negative electrode sheet protruding from the edge of the positive electrode sheet is 2mm.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that no perforated area is provided on the edge of the current collector.

[0084] The lithium ion batteries prepared in Examples 1 to 3 and Comparative Example 1 were tested for capacity retention and lithium deposition, and the results are shown in Table 1.

[0085] Table 1 Capacity retention and lithium deposition of lithium ion batteries prepared in Examples and Comparative Examples

[0086]

[0087] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The above-mentioned embodiments only express several implementation methods of the utility model, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the utility model patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the utility model, which all belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent shall be based on the attached claims.

Claims

1. A current collector, characterized in that: It comprises a main body region and an opening region connected to the main body region, wherein the opening region is close to the edge of the current collector and has openings distributed therein.

2. The current collector according to claim 1, characterized in that The current collector has at least two open areas respectively connected to opposite sides of the main area.

3. The current collector according to claim 2, characterized in that: The current collector is a strip-shaped structure, and the opening area includes a first opening area and a second opening area that are oppositely arranged in the width direction of the current collector.

4. The current collector according to any one of claims 1 to 3, characterized in that The width of the opening area is 2 mm to 20 mm.

5. The current collector according to any one of claims 1 to 3, characterized in that The aperture of the opening is 5 μm to 12 μm; and / or The number of openings is 500 / cm 2 ~5000pcs / cm 2 .

6. The current collector according to any one of claims 1 to 3, characterized in that The current collector includes a metal layer and a first carbon layer stacked on a first side of the metal layer and / or a second carbon layer stacked on a second side of the metal layer.

7. The current collector according to claim 6, characterized in that The thickness of the portion of the first carbon layer located in the opening area is smaller than that of the portion located in the main body area; or, the first carbon layer is only located in the main body area; The thickness of the portion of the second carbon layer located in the opening area is smaller than that of the portion located in the main area; or, the second carbon layer is only located in the main area.

8. A positive electrode sheet, characterized in that: The invention comprises a current collector according to any one of claims 1 to 7 and a positive electrode active material layer arranged on the current collector.

9. A lithium ion battery, characterized in that: The invention comprises a shell and the positive electrode sheet and the negative electrode sheet as claimed in claim 8 arranged in the shell, the positive electrode sheet and the negative electrode sheet are arranged opposite to each other, and a diaphragm and an electrolyte are arranged between the positive electrode sheet and the negative electrode sheet.

10. The lithium ion battery according to claim 9, characterized in that The edge of the negative electrode sheet protrudes from the edge of the positive electrode sheet.

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