Negative electrode sheet, battery cell and electrical device

Abstract

A negative electrode sheet (10), a battery cell and an electrical device. The electrical device comprises the battery cell. The battery cell comprises the negative electrode sheet (10). The negative electrode sheet (10) comprises a first area (11) and a second area (12), the second area (12) surrounds the first area (11), and the surface density of the active material of at least part of the second area (12) is less than that of the active material of the first area (11), thereby reducing the probability of lithium precipitation at the edge of the electrode sheet.

Description

Negative electrode sheets, battery cells and electrical equipment

[0001] This disclosure claims priority to the Chinese patent application filed with the China Patent Office on February 29, 2024, with application number 202420395079.1 and application name “Negative electrode sheet, battery cell and electrical equipment”, the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0002] The present invention and the technical field of batteries particularly relate to a negative electrode sheet, a battery cell and an electrical device. Background Art

[0003] Currently, lithium-ion batteries are widely used in people's daily lives due to their high energy density and rapid charge and discharge capabilities. In the prior art, lithium-ion batteries are frequently charged and discharged during user use. During this process, lithium at the edge of the negative electrode facing the positive electrode diffuses toward the overhang area (the protruding area refers to the area where the edge of the negative electrode extends beyond the positive electrode). As a result, during charging, the SOC (state of charge, which refers to the ratio of remaining capacity to battery capacity) near the edge of the negative electrode is lower than that in the middle, leading to lithium deposition at the edge of the electrode. Summary of the Invention

[0004] The purpose of the present invention is to provide a negative electrode sheet, a battery cell and an electrical device to solve the problem of lithium deposition at the edge of the electrode sheet.

[0005] To achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a negative electrode sheet comprising a first region and a second region, wherein the second region surrounds the first region, and the surface density of active material in at least a portion of the second region is lower than the surface density of active material in the first region.

[0007] In one embodiment, the surface density of the active material in the first region is A1, and the surface density of the active material in at least part of the second region is A2, satisfying the following: 5%≤(A1-A2) / A1≤30%.

[0008] In one embodiment, the first area is a rectangle, and the first area includes a first inner edge, a second inner edge, a third inner edge and a fourth inner edge connected in sequence, and the second area includes a first outer edge, a second outer edge, a third outer edge and a fourth outer edge connected in sequence, the first inner edge is close to and parallel to the first outer edge, the second inner edge is close to and parallel to the second outer edge, the third inner edge is close to and parallel to the third outer edge, and the fourth inner edge is close to and parallel to the fourth outer edge.

[0009] In one embodiment, the length of the second inner edge is smaller than the length of the first inner edge, the surface density of the area between the first inner edge and the first outer edge is smaller than the surface density of the first area, and the surface density of the area between the third inner edge and the third outer edge is smaller than the surface density of the first area.

[0010] In one embodiment, the width of the second region is L, which satisfies: 2 mm ≤ L ≤ 20 mm.

[0011] In one embodiment, the widths of various positions in the second region are equal.

[0012] In one embodiment, the compacted density of the active material on the negative electrode sheet is 1.2 g / cm 3 Up to 2.0g / cm 3 .

[0013] In one embodiment, the surface density of the active material on the negative electrode sheet is 50 g / m 2 Up to 200g / m 2 .

[0014] In a second aspect, the present invention further provides a battery cell comprising a positive electrode sheet and a negative electrode sheet as described in the first aspect, wherein the positive electrode sheet and the negative electrode sheet are stacked, and the four edges of the positive projection of the negative electrode sheet extend beyond the four edges of the first area and are located within the second area.

[0015] In one embodiment, the positive electrode sheet and the first region are both rectangular, the positive electrode sheet includes a first edge, the first region includes a first inner edge, the second region includes a first outer edge close to the first inner edge, the first edge, the first inner edge and the first outer edge are parallel, and the first edge is located between the first inner edge and the first outer edge.

[0016] In one embodiment, a distance between the first edge and the first inner edge is B, which satisfies: 2mm≤B≤10mm.

[0017] In one embodiment, the battery cell further includes a positive electrode tab, one end of the positive electrode tab is connected to the positive electrode sheet, and the other end extends out of the edge of the positive electrode sheet.

[0018] In a third aspect, the present invention further provides an electrical device, comprising an electrical device and the battery cell described in the second aspect, wherein the battery cell supplies power to the electrical device.

[0019] By arranging a negative electrode sheet, a battery cell and an electrical device, the electrical device includes a battery cell, the battery cell includes a negative electrode sheet, the negative electrode sheet includes a first area and a second area, the second area surrounds the first area, and the surface density of the active material in at least part of the second area is less than the surface density of the active material in the first area. During the charge and discharge process of the battery, since the surface density of the active material in at least part of the second area facing the edge of the positive electrode is less than the surface density of the active material in the first area, the SOC of the edge of the negative electrode is improved, and the difference in SOC between the edge of the electrode sheet and the middle position of the electrode sheet is reduced, thereby reducing the probability of lithium deposition at the edge of the electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] FIG1 is a schematic structural diagram of a battery cell according to an embodiment;

[0022] FIG2 is a schematic structural diagram of a negative electrode sheet according to an embodiment.

[0023] Explanation of the accompanying drawings: 10-negative electrode sheet, 11-first region, 111-first inner edge, 112-second inner edge, 113-third inner edge, 114-fourth inner edge, 12-second region, 121-first outer edge, 122-second outer edge, 123-third outer edge, 124-fourth outer edge, 125-first sub-region, 126-second sub-region, 20-positive electrode sheet, 21-first edge, 22-positive electrode tab, B-distance between the first edge and the first inner edge, L-width of the second region, X-second direction of the first region, Y-first direction of the first region. DETAILED DESCRIPTION

[0024] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only 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 are within the scope of protection of the present invention.

[0025] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may be an intermediate component. When a component is referred to as being "connected to" another component, it may be directly connected to the other component or there may be an intermediate component.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0027] The following embodiments of the present invention are described in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0028] At present, during the charging and discharging process of the battery, the lithium at the edge of the negative electrode facing the positive electrode will diffuse to the overhang area. Therefore, during the charging process, the SOC of the negative electrode near the edge is lower than that in the middle, resulting in the occurrence of lithium deposition on the electrode.

[0029] The present invention provides a negative electrode sheet 10, comprising a first region 11 and a second region 12. The second region 12 surrounds the first region 11, and the area density of the active material in at least a portion of the second region 12 is lower than the area density of the active material in the first region 11. Optionally, the negative electrode sheet 10 may be made of graphite, silicon, lithium titanate, or the like.

[0030] Specifically, the negative electrode sheet 10 includes the first region 11 and the second region 12, which means that the negative electrode sheet 10 includes the first region 11 and the second region 12 on a plane perpendicular to the thickness direction of the negative electrode sheet 10; the second region 12 surrounding the first region 11 means that the second region 12 surrounds the first region 11 on a plane perpendicular to the thickness direction of the negative electrode sheet 10.

[0031] By providing a negative electrode sheet 10, a battery cell and an electrical device, the electrical device includes a battery cell, the battery cell includes a negative electrode sheet 10, the negative electrode sheet 10 includes a first region 11 and a second region 12, the second region 12 surrounds the first region 11, and the surface density of the active material in at least a portion of the second region 12 is less than the surface density of the active material in the first region 11. During the charge and discharge process of the battery, since the surface density of the active material in at least a portion of the second region 12 facing the edge of the positive electrode on the negative electrode sheet is less than the surface density of the active material in the first region 11, the SOC of the edge of the negative electrode is improved, and the difference in SOC between the edge of the electrode sheet and the middle position of the electrode sheet is reduced, thereby reducing the probability of lithium deposition at the edge of the electrode sheet.

[0032] In one embodiment, referring to FIG. 1 and FIG. 2 , the surface density of the active material in the first region 11 is A1, and the surface density of the active material in at least a portion of the second region 12 is A2, satisfying: 5%≤(A1-A2) / A1≤30%.

[0033] Optionally, the result of (A1-A2) / A1 may be, but is not limited to, 5%, 10%, 15%, 20%, 25% and 30%.

[0034] Specifically, the above arrangement reduces the probability of lithium deposition at the edge of the electrode.

[0035] In one embodiment, please refer to Figures 1 and 2, the first area 11 is a rectangle, and the first area 11 includes a first inner edge 111, a second inner edge 112, a third inner edge 113 and a fourth inner edge 114 connected in sequence, and the second area 12 includes a first outer edge 121, a second outer edge 122, a third outer edge 123 and a fourth outer edge 124 connected in sequence, the first inner edge 111 is close to and parallel to the first outer edge 121, the second inner edge 112 is close to and parallel to the second outer edge 122, the third inner edge 113 is close to and parallel to the third outer edge 123, and the fourth inner edge 114 is close to and parallel to the fourth outer edge 124.

[0036] Specifically, the first region 11 being a rectangle means that the first region 11 is a rectangle on a plane perpendicular to the thickness direction of the negative electrode sheet 10 .

[0037] Specifically, the second region 12 is the region outside the first region 11 within the pattern formed by the first outer edge 121, the second outer edge 122, the third outer edge 123, and the fourth outer edge 124. Optionally, the first inner edge 111 is closer to the center of the negative electrode sheet 10 than the first outer edge 121, the second inner edge 112 is closer to the center of the negative electrode sheet 10 than the second outer edge 122, the third inner edge 113 is closer to the center of the negative electrode sheet 10 than the third outer edge 123, and the fourth inner edge 114 is closer to the center of the negative electrode sheet 10 than the fourth outer edge 124.

[0038] Specifically, the above arrangement standardizes the first area 11 and the second area 12 , thereby enabling large-scale production and improving production efficiency.

[0039] In one embodiment, please refer to Figures 1 and 2, the length of the second inner edge 112 is less than the length of the first inner edge 111, the surface density of the area between the first inner edge 111 and the first outer edge 121 is smaller than the surface density of the first area 11, and the surface density of the area between the third inner edge 113 and the third outer edge 123 is smaller than the surface density of the first area 11.

[0040] Specifically, the second region 12 includes a first sub-region 125 and a second sub-region 126 . The first sub-region 125 refers to the region between the first inner edge 111 and the first outer edge 121 , and the second sub-region 126 refers to the region between the third inner edge 113 and the third outer edge 123 .

[0041] Specifically, the above-mentioned setting preferentially thins the long side edge region of the negative electrode sheet 10, and the area of ​​the long side edge region accounts for a larger proportion of the area of ​​the second region 12 than the area of ​​the short side edge region accounts for the area of ​​the second region 12. Compared with thinning the short side edge region, preferentially thinning the long side edge region of the negative electrode sheet 10 can increase the thinning area, further reduce the SOC difference between the edge position and the middle position of the electrode sheet, and help reduce the complexity of the process flow and improve production efficiency.

[0042] In one embodiment, referring to FIG. 1 and FIG. 2 , the width of the second region 12 is L, which satisfies: 2 mm ≤ L ≤ 20 mm.

[0043] Optionally, the width L of the second area may be, but is not limited to, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, and 20 mm.

[0044] Specifically, the distance between the first inner edge 111 and the first outer edge 121 is the width of the second area 12, the distance between the second inner edge 112 and the second outer edge 122 is the width of the second area 12, the distance between the third inner edge 113 and the third outer edge 123 is the width of the second area 12, and the distance between the fourth inner edge 114 and the fourth outer edge 124 is the width of the second area 12.

[0045] In one embodiment, referring to FIG. 1 and FIG. 2 , the widths of various positions of the second region 12 are equal.

[0046] Specifically, the center of the first area 11 and the center of the second area 12 coincide with each other.

[0047] Specifically, the center of the first area 11 is the intersection of the diagonals of the rectangle formed by the first inner edge 111 , the second inner edge 112 , the third inner edge 113 and the fourth inner edge 114 .

[0048] Specifically, the center of the second area 12 is the intersection of the diagonals of the rectangle formed by the first outer edge 121 , the second outer edge 122 , the third outer edge 123 and the fourth outer edge 124 .

[0049] Specifically, the above arrangement standardizes the second area 12 , thereby enabling large-scale production and improving production efficiency.

[0050] In one embodiment, referring to FIG1 and FIG2 , the compacted density of the active material on the negative electrode sheet 10 is 1.2 g / cm 3 (g / cm3)-2.0g / cm 3 .

[0051] Optionally, the compaction density of the active material on the negative electrode sheet 10 may be, but is not limited to, 1.2 g / cm3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 and 2.0g / cm 3 .

[0052] In one embodiment, referring to FIG1 and FIG2 , the surface density of the active material on the negative electrode sheet 10 is 50 g / m 2 -200g / m 2 .

[0053] Optionally, the coating density of the active material on the negative electrode sheet 10 may be, but is not limited to, 50 g / m 2 , 60g / m 2 , 70g / m 2 , 80g / m 2 , 90g / m 2 , 100g / m 2 and 150g / m 2 .

[0054] Specifically, the above configuration improves the value ranges of the compaction density and the surface density of the active material of the negative electrode sheet 10 , and improves the structure of the negative electrode sheet 10 .

[0055] The present invention also provides a battery cell, comprising a positive electrode sheet 20 and the aforementioned negative electrode sheet 10, wherein the positive electrode sheet 20 and the negative electrode sheet 10 are stacked, and the four edges of the positive projection of the positive electrode sheet 20 on the negative electrode sheet 10 exceed the four edges of the first area 11 and are located within the second area 12.

[0056] Specifically, in the orthographic projection of the positive electrode sheet 20 on the negative electrode sheet 10 , the four peripheral edges thereof exceed the four peripheral edges of the first region 11 and are located within the second region 12 .

[0057] Optionally, the active material on the positive electrode sheet 20 is any one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide and lithium titanate.

[0058] Optionally, the compacted density of the active material on the positive electrode sheet 20 is 2.3 g / cm 3 -3.0g / cm 3 .

[0059] Optionally, the compaction density of the active material on the positive electrode sheet 20 may be, but is not limited to, 2.3 g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 and 3.0g / cm 3 wait.

[0060] Optionally, the coating area density of the active material on the positive electrode sheet 20 is 50 g / m 2 -300g / m 2 .

[0061] Optionally, the coating area density of the active material on the positive electrode sheet 20 may be, but is not limited to, 50 g / m 2 , 60g / m 2 , 70g / m 2 , 80g / m 2 , 90g / m 2 and 300g / m 2 wait.

[0062] Optionally, the positive electrode sheet 20 includes a positive electrode current collector having an active material thereon. The positive electrode current collector includes, but is not limited to, any one of aluminum foil, carbon-coated aluminum foil, and composite aluminum foil. The active material on the positive electrode sheet 20 also includes a conductive agent and a binder. The conductive agent includes any one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, and carbon nanotubes. The binder can be one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0063] In one embodiment, please refer to Figures 1 and 2, the positive electrode sheet 20 and the first area 11 are both rectangular, the positive electrode sheet 20 includes a first edge 21, the first area 11 includes a first inner edge 111, and the second area 12 includes a first outer edge 121 close to the first inner edge 111. The first edge 21, the first inner edge 111 and the first outer edge 121 are parallel, and the first edge 21 is located between the first inner edge 111 and the first outer edge 121.

[0064] Specifically, the long side of the positive electrode sheet 20 , the long side of the first region 11 , and the long side of the second region 12 are all parallel, and the short side of the positive electrode sheet 20 , the short side of the first region 11 , and the short side of the second region 12 are all parallel.

[0065] In one embodiment, referring to FIG. 1 and FIG. 2 , the center of the positive electrode sheet 20 coincides with the center of the negative electrode sheet 10 , and the distance between the first edge and the first inner edge is B, satisfying: 2 mm ≤ B ≤ 10 mm.

[0066] Optionally, the distance B between the first edge and the first inner edge may be, but is not limited to, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, and 10 mm.

[0067] In one embodiment, referring to FIG. 1 and FIG. 2 , the battery cell further includes a positive electrode tab 22 , one end of the positive electrode tab 22 is connected to the positive electrode sheet 20 , and the other end extends out of the edge of the negative electrode sheet 10 .

[0068] Optionally, one end of the positive electrode tab 22 is connected to the positive electrode sheet 20 , and the other end extends beyond the edge of the negative electrode sheet 10 by 1 mm to 10 mm.

[0069] Optionally, one end of the positive electrode tab 22 is connected to the positive electrode sheet 20 , and the other end extends beyond the edge of the negative electrode sheet 10 , which may be, but is not limited to, 1 mm, 2 mm, 3 mm, 6 mm, 8 mm, and 10 mm.

[0070] Optionally, the negative electrode sheet 10 is rectangular, the area of ​​the negative electrode sheet 10 is larger than the area of ​​the positive electrode sheet 20, the center of the negative electrode sheet 10 coincides with the center of the positive electrode sheet 20, the long side of the negative electrode sheet 10 is 2 mm longer than the long side of the positive electrode sheet 20, and the wide side of the negative electrode sheet 10 is 2 mm wider than the wide side of the positive electrode sheet 20.

[0071] The present invention also provides an electrical device, comprising an electrical device and the aforementioned battery cell, wherein the battery cell supplies power to the electrical device.

[0072] Alternatively, the battery may be a blade battery, a block battery, a cylindrical battery, a button battery, or the like, without limitation in the present invention. The battery may be manufactured using lamination or winding techniques, without limitation. The housing may be made of plastic, steel, or aluminum, without limitation.

[0073] The technical solution of this application is described in detail below through specific embodiments.

[0074] Example 1

[0075] This embodiment provides a negative electrode sheet 10, a battery cell, and an electrical device. In the battery cell, the area of ​​the negative electrode sheet 10 is larger than the area of ​​the positive electrode sheet 20. The active material of the negative electrode sheet 10 includes graphite, and the active material of the positive electrode sheet 20 includes lithium iron phosphate.

[0076] A negative electrode sheet 10 is prepared. The negative electrode sheet 10 includes a first region 11 and a second region 12. The second region 12 surrounds the first region 11. The surface density A1 of the active material in the first region 11 is 100 g / m 2 The area density A2 of the active material in the second region 12 is 95 g / m 2 , (A1-A2) / A1 is 5%, and the compaction density of the active material on the negative electrode sheet 10 is 1.6 g / cm 3 The coating density of the active material on the negative electrode sheet 10 is 100 g / m 2, L is 3 mm, the distance B between the first edge 21 and the first inner edge 111 is 2 mm, and the coating surface density of the active material on the positive electrode sheet 20 is 220 g / m 2 The compacted density of the active material on the positive electrode sheet 20 is 2.6 g / cm 3 , take the negative electrode sheet 10, the positive electrode sheet 20 and the separator to prepare a cell, and assemble the cell into a battery.

[0077] Example 2

[0078] This embodiment provides a negative electrode sheet 10, a battery cell, and an electrical device. In the battery cell, the area of ​​the negative electrode sheet 10 is larger than the area of ​​the positive electrode sheet 20. The active material of the negative electrode sheet 10 includes graphite, and the active material of the positive electrode sheet 20 includes lithium iron phosphate.

[0079] A negative electrode sheet 10 is prepared. The negative electrode sheet 10 includes a first region 11 and a second region 12. The second region 12 surrounds the first region 11. The surface density A1 of the active material in the first region 11 is 100 g / m 2 The area density A2 of the active material in the second region 12 is 90 g / m 2 , (A1-A2) / A1 is 10%, and the compaction density of the active material on the negative electrode sheet 10 is 1.6 g / cm 3 The surface density of the active material on the negative electrode sheet 10 is 100 g / m 2 , L is 3 mm, the distance B between the first edge 21 and the first inner edge 111 is 2 mm, and the coating surface density of the active material on the positive electrode sheet 20 is 220 g / m 2 The compacted density of the active material on the positive electrode sheet 20 is 2.6 g / cm 3 , take the negative electrode sheet 10, the positive electrode sheet 20 and the separator to prepare a cell, and assemble the cell into a battery.

[0080] Example 3

[0081] This embodiment provides a negative electrode sheet 10, a battery cell, and an electrical device. In the battery cell, the area of ​​the negative electrode sheet 10 is larger than the area of ​​the positive electrode sheet 20. The active material of the negative electrode sheet 10 includes graphite, and the active material of the positive electrode sheet 20 includes lithium iron phosphate.

[0082] A negative electrode sheet 10 is prepared. The negative electrode sheet 10 includes a first region 11 and a second region 12. The second region 12 surrounds the first region 11. The surface density A1 of the active material in the first region 11 is 100 g / m 2 The area density A2 of the active material in the second region 12 is 85 g / m 2 , (A1-A2) / A1 is 15%, the compaction density of the active material on the negative electrode sheet 10 is 1.6 g / cm3, and the surface density of the active material on the negative electrode sheet 10 is 100 g / m2 , L is 3 mm, the distance B between the first edge 21 and the first inner edge 111 is 2 mm, and the coating surface density of the active material on the positive electrode sheet 20 is 220 g / m 2 The compacted density of the active material on the positive electrode sheet 20 is 2.6 g / cm 3 , take the negative electrode sheet 10, the positive electrode sheet 20 and the separator to prepare a cell, and assemble the cell into a battery.

[0083] Example 4

[0084] This embodiment provides a negative electrode sheet 10, a battery cell, and an electrical device. In the battery cell, the area of ​​the negative electrode sheet 10 is larger than the area of ​​the positive electrode sheet 20. The active material of the negative electrode sheet 10 includes graphite, and the active material of the positive electrode sheet 20 includes lithium iron phosphate.

[0085] A negative electrode sheet 10 is prepared. The negative electrode sheet 10 includes a first region 11 and a second region 12. The second region 12 surrounds the first region 11. The surface density A1 of the active material in the first region 11 is 100 g / m 2 The area density A2 of the active material in the second region 12 is 80 g / m 2 , (A1-A2) / A1 is 20%, and the compaction density of the active material on the negative electrode sheet 10 is 1.6 g / cm 3 The coating density of the active material on the negative electrode sheet 10 is 100 g / m 2 , L is 3 mm, the distance B between the first edge 21 and the first inner edge 111 is 2 mm, and the coating surface density of the active material on the positive electrode sheet 20 is 220 g / m 2 The compacted density of the active material on the positive electrode sheet 20 is 2.6 g / cm 3 , take the negative electrode sheet 10, the positive electrode sheet 20 and the separator to prepare a cell, and assemble the cell into a battery.

[0086] Example 5

[0087] This embodiment provides a negative electrode sheet 10, a battery cell, and an electrical device. In the battery cell, the area of ​​the negative electrode sheet 10 is larger than the area of ​​the positive electrode sheet 20. The active material of the negative electrode sheet 10 includes graphite, and the active material of the positive electrode sheet 20 includes lithium iron phosphate.

[0088] A negative electrode sheet 10 is prepared. The negative electrode sheet 10 includes a first region 11 and a second region 12. The second region 12 surrounds the first region 11. The surface density A1 of the active material in the first region 11 is 100 g / m 2 The area density A2 of the active material in the second region 12 is 75 g / m 2 , (A1-A2) / A1 is 25%, and the compaction density of the active material on the negative electrode sheet 10 is 1.6 g / cm 3The coating density of the active material on the negative electrode sheet 10 is 100 g / m 2 , L is 3 mm, the distance B between the first edge 21 and the first inner edge 111 is 2 mm, and the coating surface density of the active material on the positive electrode sheet 20 is 220 g / m 2 The compacted density of the active material on the positive electrode sheet 20 is 2.6 g / cm 3 , take the negative electrode sheet 10, the positive electrode sheet 20 and the separator to prepare a cell, and assemble the cell into a battery.

[0089] Comparative Example 1

[0090] This embodiment provides a negative electrode sheet 10, a battery cell, and an electrical device. In the battery cell, the area of ​​the negative electrode sheet 10 is larger than the area of ​​the positive electrode sheet 20. The active material of the negative electrode sheet 10 includes graphite, and the active material of the positive electrode sheet 20 includes lithium iron phosphate.

[0091] A negative electrode sheet 10 is prepared. The negative electrode sheet 10 includes a first region 11 and a second region 12. The second region 12 surrounds the first region 11. The surface density A1 of the active material in the first region 11 is 100 g / m 2 The area density A2 of the active material in the second region 12 is 100 g / m 2 , the result of (A1-A2) / A1 is 0, and the compaction density of the active material on the negative electrode sheet 10 is 1.6 g / cm 3 The coating density of the active material on the negative electrode sheet 10 is 100 g / m 2 , L is 3 mm, the distance B between the first edge 21 and the first inner edge 111 is 2 mm, and the coating surface density of the active material on the positive electrode sheet 20 is 220 g / m 2 The compacted density of the active material on the positive electrode sheet 20 is 2.6 g / cm 3 , take the negative electrode sheet 10, the positive electrode sheet 20 and the separator to prepare a cell, and assemble the cell into a battery.

[0092] The battery test method is as follows:

[0093] Capacity retention rate after 500 cycles: Charge the battery at a constant current of 0.33C to 3.8V and let it sit for 30 minutes; then discharge it at a current of 0.33C to the discharge end voltage of 2.0V and let it sit for 30 minutes; repeat the above two steps for a total of 500 times, record the first discharge capacity as the battery discharge capacity C1, and the discharge capacity of the 500th cycle as C500; 500-cycle capacity retention rate (%) = (C500 / C1) × 100%.

[0094] Capacity retention rate after 1000 cycles: Charge the battery at a constant current of 0.33C to 3.8V and let it sit for 30 minutes; then discharge it at a current of 0.33C to the discharge end voltage of 2.0V and let it sit for 30 minutes; repeat the above two steps a total of 1000 times, record the first discharge capacity as the battery discharge capacity C1, and the discharge capacity of the 500th cycle as C1000; 1000-cycle capacity retention rate (%) = (C1000 / C1) × 100%.

[0095] Capacity retention rate after 1500 cycles: Charge the battery at a constant current of 0.33C to 3.8V and let it sit for 30 minutes; then discharge it at a current of 0.33C to the discharge end voltage of 2.0V and let it sit for 30 minutes; repeat the above two steps a total of 1500 times, record the first discharge capacity as the battery discharge capacity C1, and the discharge capacity of the 500th cycle as C1500; 1500 cycle capacity retention rate % = (C1500 / C1) × 100%.

[0096] Table 1 shows the values ​​of A2 / A1 of Examples 1 to 5 and Comparative Example 1, as well as the corresponding cell capacity retention rates of Examples 1 to 5 and Comparative Example 1 after 500, 1000, and 1500 cycles of charging using the above test method, respectively.

[0097] By comparing the values ​​of (A1-A2) / A1 of Examples 1 to 5 and Comparative Example 1, as well as the corresponding capacity retention rates of cyclic charging, the data in the above table illustrate that during the charge and discharge process of the battery, since the surface density of the active material in at least a portion of the second region 12 facing the edge of the positive electrode is thinner than the surface density of the active material in the first region 11, the probability of lithium deposition at the edge of the electrode is reduced.

[0098] In the description of the embodiments of the present invention, it should be noted that the orientations or positional relationships of indicators such as terms such as "first direction", "second direction", "first distance", "second distance", "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" are orientations or positional relationships based on the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0099] The above disclosure is only a preferred embodiment of the present invention, and certainly cannot be used to limit the scope of the rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the present invention still fall within the scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The method comprises a first region and a second region, wherein the second region surrounds the first region, and the surface density of the active material in at least a portion of the second region is lower than the surface density of the active material in the first region.

2. The negative electrode sheet according to claim 1, characterized in that: The surface density of the active material in the first region is A1, and the surface density of the active material in at least a portion of the second region is A2, satisfying the following: 5%≤(A1-A2) / A1≤30%.

3. The negative electrode sheet according to claim 1, characterized in that: The first area is a rectangle, and the first area includes a first inner edge, a second inner edge, a third inner edge and a fourth inner edge connected in sequence. The second area includes a first outer edge, a second outer edge, a third outer edge and a fourth outer edge connected in sequence. The first inner edge is close to and parallel to the first outer edge, the second inner edge is close to and parallel to the second outer edge, the third inner edge is close to and parallel to the third outer edge, and the fourth inner edge is close to and parallel to the fourth outer edge.

4. The negative electrode sheet according to claim 3, characterized in that: The length of the second inner edge is smaller than that of the first inner edge, the surface density of the area between the first inner edge and the first outer edge is smaller than that of the first area, and the surface density of the area between the third inner edge and the third outer edge is smaller than that of the first area.

5. The negative electrode sheet according to claim 3, characterized in that: The width of the second area is L, which satisfies: 2mm≤L≤20mm.

6. The negative electrode sheet according to claim 5, characterized in that: The widths of various positions in the second region are equal.

7. The negative electrode sheet according to claim 1, characterized in that: The compaction density of the active material on the negative electrode sheet is 1.2 g / cm 3 Up to 2.0g / cm 3 .

8. The negative electrode sheet according to claim 1, characterized in that: The surface density of the active material on the negative electrode sheet is 50 g / m 2 Up to 200g / m 2 .

9. A battery cell, characterized in that: It comprises a positive electrode sheet and a negative electrode sheet as claimed in any one of claims 1 to 8, wherein the positive electrode sheet and the negative electrode sheet are stacked, and the four edges of the positive projection of the positive electrode sheet on the negative electrode sheet exceed the four edges of the first area and are located in the second area.

10. The battery cell according to claim 9, characterized in that: The positive electrode sheet and the first region are both rectangular, the positive electrode sheet includes a first edge, the first region includes a first inner edge, the second region includes a first outer edge close to the first inner edge, the first edge, the first inner edge and the first outer edge are parallel, and the first edge is located between the first inner edge and the first outer edge.

11. The battery cell according to claim 10, characterized in that: A distance B between the first edge and the first inner edge satisfies: 2 mm ≤ B ≤ 10 mm.

12. The battery cell according to claim 9, characterized in that The battery cell further includes a positive electrode tab, one end of which is connected to the positive electrode sheet, and the other end of which extends out of the edge of the negative electrode sheet.

13. An electrical device, characterized in that: The invention comprises an electric device and the battery cell according to any one of claims 9 to 12, wherein the battery cell supplies power to the electric device.

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