Secondary battery, battery pack, and electronic device

Abstract

The utility model provides a secondary battery, a battery pack and an electronic device. The secondary battery includes: a case; the electrode assembly is accommodated in the shell and is formed by laminating a positive plate, a diaphragm and a negative plate; at least one surface of a positive current collector of the positive plate is covered with a positive active material layer, and at least one surface of a negative current collector of the negative plate is covered with a negative active material layer; a negative electrode edge region of the negative electrode active material layer exceeds a positive electrode edge region of the positive electrode active material layer along a preset direction, and the negative electrode edge region is positioned on one side, close to the positive electrode edge region, of the negative electrode current collector along a thickness direction; in the preset direction, the size of the positive electrode edge area ranges from 2 mm to 17 mm, the size of the negative electrode edge area ranges from 3 mm to 18 mm, and the ratio of the negative electrode capacity of the negative electrode edge area to the positive electrode capacity of the positive electrode edge area ranges from 1.05 to 1.1. By setting the sizes and CB values of the negative electrode marginal area and the positive electrode marginal area, the probability of lithium precipitation in the marginal areas is reduced.

Description

Technical Field

[0001] This utility model relates to the field of secondary batteries, and in particular to a secondary battery, a battery pack, and an electronic device. Background Technology

[0002] In recent years, with the rapid development of electric vehicles, consumer electronics, and new energy storage systems, battery technology has become an important factor in the development of electric vehicles.

[0003] In the development of battery technology, how to improve battery safety is a technical problem that urgently needs to be solved. Utility Model Content

[0004] The technical problem to be solved by this utility model is to overcome the above-mentioned technical problems of the prior art and provide a secondary battery, a battery pack and an electronic device.

[0005] The present invention solves the above-mentioned technical problems through the following technical solution:

[0006] A secondary battery, characterized in that the secondary battery comprises:

[0007] case;

[0008] An electrode assembly is housed within the housing. The electrode assembly is formed by stacking a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet includes a positive current collector, and the negative electrode sheet includes a negative current collector. The electrode assembly includes a first end and a second end disposed opposite to each other along the height direction. The first end is provided with a positive electrode tab and a negative electrode tab, and the direction from the second end to the first end is a preset direction.

[0009] A portion of at least one side of the positive current collector along the thickness direction is covered with a positive active material layer, and a portion of at least one side of the negative current collector along the thickness direction is covered with a negative active material layer.

[0010] The positive electrode active material layer includes a positive electrode edge region near the first end, and the negative electrode active material layer includes a negative electrode edge region near the first end. Along the preset direction, the edge of the negative electrode edge region near the first end extends beyond the edge of the positive electrode edge region near the first end, and along the thickness direction of the negative electrode current collector, the negative electrode edge region is located on the side of the negative electrode current collector near the positive electrode edge region.

[0011] Along the preset direction, the size of the positive electrode edge region is 2mm-17mm, the size of the negative electrode edge region is 3mm-18mm, and the ratio of the negative electrode capacity of the negative electrode edge region directly opposite the thickness direction to the positive electrode capacity of the positive electrode edge region is 1.05-1.1.

[0012] In this technical solution, by setting the edge of the negative electrode edge region near the first end to extend beyond the edge of the positive electrode edge region near the first end, the negative electrode edge region with lower negative electrode capacity is prevented from directly facing the positive electrode edge region. Furthermore, by setting the size range of the positive electrode edge region and the negative electrode edge region, as well as the range of the ratio of the negative electrode capacity of the negative electrode edge region directly opposite the positive electrode edge region along the thickness direction to the positive electrode capacity of the positive electrode edge region, the CB values ​​of the edge region and the middle region are made to be nearly identical, thereby reducing the probability of lithium plating in the edge region, effectively improving the safety of the cell, and increasing production yield and efficiency.

[0013] Preferably, the negative electrode current collector has a protrusion on at least one side along the thickness direction, and the edge of the negative electrode edge region near the first end is disposed close to the protrusion. The ratio of the negative electrode capacity of the negative electrode edge region directly opposite the first end along the thickness direction to the positive electrode capacity of the positive electrode edge region is 1.08-1.1.

[0014] Preferably, the thickness of the protrusion is 20%-90% of the thickness of the negative electrode active material layer.

[0015] Preferably, along the preset direction, the distance by which the edge of the negative electrode edge region near the first end extends beyond the edge of the positive electrode edge region near the first end is 1mm-1.5mm.

[0016] Preferably, the positive current collector includes a first positive electrode surface and a second positive electrode surface disposed along the thickness direction, and the positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer. The first positive electrode active material layer covers a portion of the first positive electrode surface, and the second positive electrode active material layer covers a portion of the second positive electrode surface. The distance between the edge of the positive electrode edge region of the first positive electrode active material layer near the first end and the edge of the positive electrode edge region of the second positive electrode active material layer near the first end is less than or equal to 1 mm.

[0017] Preferably, at least one side of the positive current collector is covered with a conductive layer; the positive active material layer covers the conductive layer.

[0018] Preferably, along the preset direction, a portion of at least one side of the positive current collector along the thickness direction is covered by the conductive layer and the insulating layer;

[0019] The positive electrode active material layer at least partially covers the insulating layer, and along the thickness direction of the positive electrode current collector, the orthographic projection of the insulating layer is at least partially located outside the outer periphery of the positive electrode active material layer;

[0020] The thickness of the conductive layer is m, and the thickness of the insulating layer is n, where n ≤ m, and the units of m and n are both μm.

[0021] Preferably, the secondary battery further includes a cover assembly that covers the housing and, together with the housing, defines a receiving cavity, in which the electrode assembly is received; and / or,

[0022] The secondary battery is a square battery; and / or, the electrode assembly is a wound electrode assembly.

[0023] A battery pack characterized in that it includes a secondary battery as described above.

[0024] An electronic device characterized in that it includes a battery pack as described above.

[0025] The positive and progressive effects of this utility model are as follows:

[0026] The edge region, formed by the fluidity of the slurry during coating, has a smaller thickness than the central region. This results in insufficient CB values ​​in both the negative and positive electrode edge regions, leading to lithium plating and affecting the safety of the secondary battery. The CB value refers to the ratio of the product of the areal density and specific capacity of the negative electrode (negative electrode capacity) to the product of the areal density and specific capacity of the positive electrode (positive electrode capacity) after discharge. It can also be called the CB value or N / P ratio.

[0027] In this invention, by setting the edge of the negative electrode edge region near the first end to extend beyond the edge of the positive electrode edge region near the first end, the negative electrode edge region with lower negative electrode capacity is prevented from directly facing the positive electrode edge region. Furthermore, by setting the size range of the positive electrode edge region and the negative electrode edge region, as well as the range of the ratio of the negative electrode capacity of the negative electrode edge region directly opposite the positive electrode edge region along the thickness direction to the positive electrode capacity of the positive electrode edge region, the CB values ​​of the edge region and the middle region are made to be nearly identical, thereby reducing the probability of lithium plating in the edge region, effectively improving the safety of the cell, and increasing production yield and efficiency. Attached Figure Description

[0028] Figure 1 This is a three-dimensional exploded view of a secondary battery according to a preferred embodiment of the present invention.

[0029] Figure 2 This is a partial three-dimensional structural diagram of a secondary battery according to a preferred embodiment of the present invention.

[0030] Figure 3 This is a partial cross-sectional view of the electrode assembly of a secondary battery according to a preferred embodiment of the present invention.

[0031] Figure 4This is a partial cross-sectional view of the positive electrode of a secondary battery according to a preferred embodiment of the present invention.

[0032] Figure 5 This is a partial cross-sectional view of one embodiment of the negative electrode sheet of a secondary battery according to a preferred embodiment of the present invention.

[0033] Figure 6 This is a partial cross-sectional view of another embodiment of the negative electrode sheet of a secondary battery according to a preferred embodiment of the present invention.

[0034] Figure 7 This is a schematic diagram of the sampling position of the positive electrode small circular plate in a preferred embodiment of the present invention.

[0035] Figure 8 This is a schematic diagram of the sampling position of the negative electrode small circular plate in a preferred embodiment of the present invention.

[0036] Figure 9 This is a schematic diagram of the battery pack structure according to a preferred embodiment of the present invention.

[0037] Figure 10 This is a schematic diagram of the structure of an electronic device according to a preferred embodiment of the present invention.

[0038] Explanation of reference numerals in the attached figures

[0039] Electronic devices 1000

[0040] Battery pack 100

[0041] Work Department 300

[0042] Box 310

[0043] Box lid 320

[0044] Secondary battery 1

[0045] Casing 10

[0046] Receiving cavity 13

[0047] Electrode assembly 20

[0048] Positive electrode 21

[0049] Positive current collector 211

[0050] First positive electrode surface 2111

[0051] Second positive electrode surface 2112

[0052] Positive electrode active material layer 212

[0053] Positive edge region 2121

[0054] The positive electrode edge region is located near the first end. (21211)

[0055] Positive electrode intermediate region 2122

[0056] First positive electrode active material layer 2123

[0057] Second positive electrode active material layer 2124

[0058] Conductive layer 213

[0059] Insulation layer 214

[0060] Region 1, 2141

[0061] Second area 2142

[0062] Diaphragm 22

[0063] Negative electrode 23

[0064] Negative current collector 231

[0065] Negative electrode active material layer 232

[0066] Negative electrode edge region 2321

[0067] The negative electrode edge region is located near the edge of the first end 23211

[0068] Negative electrode intermediate region 2322

[0069] 233 protrusions

[0070] Cover assembly 40

[0071] Cover body 41

[0072] Injection hole 411

[0073] Insulating component 42

[0074] Electrode terminal 43

[0075] Top cover 50

[0076] Preset direction Q

[0077] Thickness direction T Detailed Implementation

[0078] The present invention will be described more clearly and completely below with reference to the accompanying drawings, using a preferred embodiment.

[0079] like Figure 1 and Figure 2 As shown, this embodiment provides a secondary battery 1. The secondary battery 1 includes a housing 10 and an electrode assembly 20, the electrode assembly 20 being housed within the housing 10.

[0080] like Figure 3 As shown, the electrode assembly 20 is formed by stacking a positive electrode 21, a separator 22, and a negative electrode 23. The stacking includes winding the stacked electrodes to form a wound electrode assembly 20 or stacking the stacked electrodes to form a stacked electrode assembly 20.

[0081] like Figure 4 and Figure 5 As shown, the positive electrode 21 includes a positive current collector 211, and the negative electrode 23 includes a negative current collector 231; the electrode assembly 20 includes a first end and a second end arranged opposite to each other along the height direction, the first end is provided with a positive electrode tab and a negative electrode tab, and the second end to the first end is in a preset direction Q.

[0082] A portion of at least one side of the positive current collector 211 along the thickness direction T is covered with a positive active material layer 212, and a portion of at least one side of the negative current collector 231 along the thickness direction T is covered with a negative active material layer 232.

[0083] The positive electrode active material layer 212 includes a positive electrode edge region 2121 near the first end, and the negative electrode active material layer 232 includes a negative electrode edge region 2321 near the first end. Along the preset direction Q, the edge 23211 of the negative electrode edge region near the first end extends beyond the edge 21211 of the positive electrode edge region near the first end, and along the thickness direction T of the negative electrode current collector 231, the negative electrode edge region 2321 is located on the side of the negative electrode current collector 231 near the positive electrode edge region 2121.

[0084] Along the preset direction Q, the size d1 of the positive electrode edge region 2121 is 2mm-17mm, the size d2 of the negative electrode edge region 2321 is 3mm-18mm, and the ratio of the negative electrode capacity of the negative electrode edge region 2321 directly opposite to the positive electrode edge region 2121 along the thickness direction T is 1.05-1.1.

[0085] The edge region, formed by the fluidity of the slurry during coating, has a smaller thickness. This area has a lower thickness and areal density than the central region, resulting in insufficient CB values ​​in both the negative and positive electrode edge regions. This leads to lithium plating in the edge regions, affecting the safety of the secondary battery 1. The CB value refers to the ratio of the product of the areal density and specific capacity of the negative electrode (negative electrode capacity) to the product of the areal density and specific capacity of the positive electrode (positive electrode capacity) after discharge. It can also be called the CB value or N / P ratio (Negative / Positive).

[0086] In this embodiment, by setting the edge 23211 of the negative electrode edge region 2321 near the first end to extend beyond the edge 21211 of the positive electrode edge region 2121 near the first end, the negative electrode edge region 2321 with lower negative electrode capacity is prevented from directly facing the positive electrode edge region 2121. Furthermore, by setting the size range of the positive electrode edge region 2121 and the negative electrode edge region 2321, as well as the range of the ratio of the negative electrode capacity of the negative electrode edge region 2321 to the positive electrode capacity of the positive electrode edge region 2121 (the CB value of the negative electrode edge region 2321 and the positive electrode edge region 2121) directly opposite the thickness direction T, the CB values ​​of the edge region and the middle region are made to be close to the same, thereby reducing the probability of lithium plating in the edge region, effectively improving the safety of the battery cell, and improving the production yield and efficiency.

[0087] It should be noted that the thickness direction of the positive current collector 211 is in the same direction as the thickness direction T of the negative current collector 231. The positive current collector 211 includes a first positive electrode surface 2111 and a second positive electrode surface 2112 arranged opposite to each other along the thickness direction T, and the negative current collector 231 includes a first negative electrode surface and a second negative electrode surface arranged opposite to each other along the thickness direction T.

[0088] A portion of at least one side of the positive electrode current collector 211 along the thickness direction T is covered with a positive electrode active material layer 212. That is, a portion of at least one surface of the first positive electrode surface 2111 and the second positive electrode surface 2112 is covered with the positive electrode active material layer 212. In this embodiment, a portion of both the first positive electrode surface 2111 and the second positive electrode surface 2112 is covered with the positive electrode active material layer 212. However, this is not a limitation. In other embodiments, the positive electrode active material layer 212 may be covered on a portion of one of the surfaces of the first positive electrode surface 2111 and the second positive electrode surface 2112.

[0089] At least one side of the negative electrode current collector 231 along the thickness direction T is covered with a portion of a negative electrode active material layer 232. That is, a portion of at least one of the first negative electrode surface and the second negative electrode surface is covered with a portion of a negative electrode active material layer 232. In this embodiment, portions of both the first and second negative electrode surfaces are covered with a portion of a negative electrode active material layer 232. The two negative electrode active material layers 232 are symmetrically arranged with respect to the negative electrode current collector 231. However, this is not a limitation. In other embodiments, a portion of one of the first and second negative electrode surfaces may be covered with a portion of a negative electrode active material layer 232.

[0090] Along the preset direction Q, the positive electrode active material layer 212 includes a positive electrode intermediate region 2122 and the aforementioned positive electrode edge region 2121, and the negative electrode active material layer 232 includes a negative electrode intermediate region 2322 and the aforementioned negative electrode edge region 2321.

[0091] In this embodiment, preferably, along the preset direction Q, the distance d3 by which the edge 23211 of the negative electrode edge region 2321 near the first end extends beyond the edge 21211 of the positive electrode edge region 2121 near the first end is 1mm-1.5mm. By setting this distance d3 within a certain range, on the one hand, it avoids the distance d3 being too small, thus failing to prevent lithium plating; on the other hand, it avoids the distance d3 being too large, thus affecting the energy density of the secondary battery 1.

[0092] like Figure 6 As shown, in another embodiment of this example, at least one side of the negative electrode current collector 231 along the thickness direction T is provided with a protrusion 233. The edge 23211 of the negative electrode edge region 2321 near the first end is disposed in close contact with the protrusion 233. The ratio of the negative electrode capacity of the negative electrode edge region 2321 directly opposite the first end to the positive electrode capacity of the positive electrode edge region 2121 is 1.08-1.1. Thus, by providing the protrusion 233 and ensuring that the edge 23211 of the negative electrode edge region 2321 near the first end is in close contact with the protrusion 233, the thickness of the side of the negative electrode edge region 2321 near the first end can be increased, thereby correspondingly increasing the CB value of that region and relatively improving the CB value of that region, thereby achieving the beneficial technical effect of avoiding lithium plating. In this embodiment, both the first negative electrode surface and the second negative electrode surface are provided with the protrusion 233. However, this is not the limitation; in other embodiments, the protrusion 233 may be provided on only one of the first and second negative electrode surfaces.

[0093] Preferably, the thickness of the protrusion 233 is 20%-90% of the thickness of the negative electrode active material layer 232, for example, it can be 20%, 30%, 45%, 55%, 70%, or 90%. By setting the range of values ​​for the thickness of the protrusion 233, on the one hand, it avoids the protrusion 233 being too thin, thus failing to achieve the technical effect of increasing the thickness of the side of the negative electrode edge region 2321 closer to the first end; on the other hand, it avoids the protrusion 233 being too thick, thus avoiding contact with the separator 22, piercing the separator 22 to the positive electrode plate 21, and causing safety problems.

[0094] Specifically, the positive electrode active material layer 212 includes a first positive electrode active material layer 2123 and a second positive electrode active material layer 2124. The first positive electrode active material layer 2123 covers a portion of the first positive electrode surface 2111, and the second positive electrode active material layer 2124 covers a portion of the second positive electrode surface 2112. The distance between the edge of the positive electrode edge region of the first positive electrode active material layer 2123 near its first end and the edge of the positive electrode edge region of the second positive electrode active material layer 2124 near its first end is less than or equal to 1 mm. By setting this distance range, excessive misalignment along the thickness direction T of the first positive electrode active material layer 2123 and the second positive electrode active material layer 2124 is avoided, thus preventing lithium plating.

[0095] Furthermore, at least one side of the positive current collector 211 is covered with a conductive layer 213; the positive active material layer 212 is covered with the conductive layer 213 to enhance conductivity.

[0096] Preferably, along the predetermined direction Q, a portion of at least one side of the positive electrode current collector 211 along the thickness direction T is covered with the aforementioned conductive layer 213 and insulating layer 214; the positive electrode active material layer 212 at least partially covers the insulating layer 214, and along the thickness direction T of the positive electrode current collector 211, the orthographic projection of the insulating layer 214 is at least partially located outside the outer periphery of the positive electrode active material layer 212; the thickness of the conductive layer 213 is m, and the thickness of the insulating layer 214 is n, where n ≤ m, and the units of m and n are both μm.

[0097] In this way, by setting a portion of one side of the positive current collector 211 to be covered with a conductive layer 213 and an insulating layer 214 along a predetermined direction Q, a positive active material layer 212 is covered on the conductive layer 213, and the positive active material layer 212 at least partially covers the insulating layer 214. That is, the conductive layer 213 and the insulating layer 214 are applied to the positive current collector 211 before the positive active material layer 212 is applied. By pre-applying the conductive and insulating layer 214, the edges of the positive active material layer 212 and the insulating layer 214 can be made clear. This is because the positive electrode active material layer 212 and the insulating layer 214 are generally applied by extrusion coating (the slurry is applied by extrusion through a gasket), so the thickness of the insulating layer 214 is uncontrollable, generally ranging from 15μm to 30μm, resulting in unclear edges between the positive electrode active material layer 212 and the insulating layer 214. In this embodiment, by pre-coating the insulating layer 214, the simultaneous extrusion coating of the positive electrode active material layer 212 and the insulating layer 214 avoids unclear edges, effectively preventing the formation of a fusion zone between the two. That is, it ensures that the edges of the positive electrode active material layer 212 are straight. After stacking or winding, the CCD can accurately identify the edge of the positive electrode active material layer 212, which facilitates the accurate identification of the spacing between the positive electrode active material layer 212 and the edges of, for example, the separator 22 and the negative electrode active material layer 232 of the negative electrode sheet 23. This controls the spacing between the electrode sheet and the separator 22 (the spacing between the edge of the positive electrode active material layer 212 of the positive electrode sheet 21 and the edge of the separator 22, and the spacing between the edge of the positive electrode active material layer 212 and the edge of the negative electrode active material layer 232 of the negative electrode sheet 23), ensuring the consistency of the electrode assembly 20 and greatly improving the yield. Furthermore, before the positive electrode sheet 21 is wound or stacked to prepare the electrode assembly 20, in order to improve the production cycle and space utilization, the positive current collector 211 is often pre-stored as a large roll (referred to as an electrode roll) before coating the positive active material layer 212. At this time, if m is less than n, that is, the thickness of the conductive layer 213 is less than the thickness of the insulating layer 214, the hardness of the area where the insulating layer 214 is set in the electrode roll is greater than that of the area where the conductive layer 213 is set. This will cause the edge where the insulating layer 214 is located to lift up, and the radial direction of the edge of the electrode roll will become more and more inclined from the center to the outer periphery. This will cause the diameter difference of the electrode roll at the corresponding positions of the conductive layer 213 and the insulating layer 214 to become larger and larger, which will easily cause the positive current collector 211 to tear, bringing safety hazards.In this embodiment, by setting the thickness m of the conductive layer 213 to be greater than or equal to the thickness n of the insulating layer 214, the radial direction of the edge of the electrode roll can be kept relatively flat from the center to the outer periphery, effectively preventing the edge of the insulating layer 214 from warping. Therefore, the diameter difference between the corresponding positions of the conductive layer 213 and the insulating layer 214 of the electrode roll is relatively close, making it less likely to tear the positive current collector 211, reducing safety hazards. Thus, when using the positive current collector 211 to coat the positive electrode sheet 21, the yield of the winding and stacking electrode assembly 20 can be greatly improved when the positive electrode sheet 21 and the separator 22 are wound or stacked. At the same time, controlling the thickness of the insulating layer 214 reduces material usage and effectively lowers production costs.

[0098] It should be noted that a conductive layer 213 and an insulating layer 214 are pre-coated on the positive current collector 211. This pre-coating includes, but is not limited to, gravure coating of the conductive layer 213 and the insulating layer 214.

[0099] Specifically, in this embodiment, a portion of the first positive electrode surface 2111 and the second positive electrode surface 2112 of the positive electrode current collector 211 are covered with a conductive layer 213 and an insulating layer 214, and a first positive electrode active material layer 2123 and a second positive electrode active material layer 2124 are respectively covered on the conductive layer 213 and the insulating layer 214 on the two surfaces. The layer structure on the first positive electrode surface 2111 and the second positive electrode surface 2112 of the positive electrode current collector 211 is symmetrically arranged with respect to the positive electrode current collector 211. However, this is not a limitation. In other embodiments, a portion of one of the first positive electrode surfaces 2111 and the second positive electrode surface 2112 of the positive electrode current collector 211 may be covered with a conductive layer 213 and an insulating layer 214, and a positive electrode active material layer 212 may be covered on the conductive layer 213 and the insulating layer 214 on that surface.

[0100] In this embodiment, 0.5μm ≤ m < 1μm, for example, it can be 0.5μm, 0.6μm, 0.75μm, 0.8μm, or 0.99μm, etc. Alternatively, 0.5μm < n < 1μm, for example, it can be 0.55μm, 0.6μm, 0.75μm, 0.8μm, or 0.99μm. Thus, by controlling the range of the thickness m of the conductive layer 213, on the one hand, it avoids the thickness m of the conductive layer 213 being too small, thus failing to improve the conductivity of the positive current collector 211; on the other hand, it avoids the thickness m of the conductive layer 213 being too large, resulting in an excessively large overall volume of the electrode assembly 20, thereby affecting the overall energy density. By controlling the thickness n of the insulating layer 214, on the one hand, it avoids the thickness n of the insulating layer 214 being too small, thus failing to provide insulation; on the other hand, it avoids the thickness n of the insulating layer 214 being too large, thus affecting the flexibility of the insulating layer 214. It should be noted that the pre-coating method, which is not limited to gravure coating, can achieve a thickness of less than or equal to 1 μm for the conductive layer 213 and the insulating layer 214, while the coating formed by extrusion coating is thicker, with a minimum thickness of about 10 μm.

[0101] The insulating layer 214 includes a first region 2141 not covered by the positive electrode active material layer 212 and a second region 2142 covered by the positive electrode active material layer 212. The width of the first region 2141 is w1, and the width of the second region 2142 is w2. Wherein, 3mm ≤ w1 + w2 ≤ 20mm, for example, it can be 3mm, 5mm, 7mm, 10mm, 14mm, or 20mm, etc.; or, 0.1 ≤ w1 / (w1 + w2) ≤ 1, for example, it can be 0.1, 0.4, 0.5, 0.75, 0.9, or 1, etc. Thus, by setting the range of values ​​for the width of the insulating layer 214, the flexibility of the insulating layer 214 can be effectively guaranteed. By setting the ratio range between the width of the first region 2141 and the width of the insulating layer 214, it can be ensured that the first region 2141 always extends beyond the edge of the positive electrode active material layer 212 by a certain width along the preset direction Q. This ensures that the insulating layer 214 has the insulating function while maintaining its flexibility. Even with a wide coating of the insulating layer 214, the tab of the positive electrode 21 can still be bent normally. Furthermore, it prevents the tab of the positive electrode 21 from directly contacting the negative electrode 23 in extreme environments, such as when the tab is inserted upside down.

[0102] like Figure 7 and Figure 8As shown in the figure, the areal density of the positive electrode edge region 2121 of the positive electrode 21 and the negative electrode edge region 2321 of the negative electrode 23 are measured at the positions shown in the figure. The weights of small discs (denoted as positive electrode discs) at distances a1 from the edge of the positive electrode edge region 2121 (2mm-17mm) and at distances a2 from the edge of the negative electrode edge region 2321 (3mm-18mm) are measured respectively. The areal density of the active material on the discs is calculated as the areal density of that region. The CB values ​​of the negative electrode edge region 2321 and the positive electrode edge region 2121 are calculated based on the areal densities of both. Samples are taken from the positive electrode discs at a distance a1 from the edge of the positive electrode edge region 2121 and from the negative electrode discs at a distance a2 from the edge of the negative electrode edge region 2321 to facilitate identification and sampling monitoring while ensuring battery performance.

[0103] Experimental data is presented here to demonstrate that the structure of the secondary battery 1 in this embodiment can better avoid the lithium plating problem. A 72173 hard-shell wound lithium iron phosphate battery is used as the test object. The battery adopts a winding process. The positive electrode 21 is mainly composed of lithium iron phosphate (LFP), SP (Super P, conductive carbon black), and PVDF (polyvinylidene fluoride); the negative electrode 23 is mainly composed of artificial graphite, SP, CMC (carboxymethyl cellulose), and SBR (styrene-butadiene rubber); the electrolyte is mainly composed of solvent, lithium salt, and additives; the separator 22 is a composite membrane made of PE (polyethylene), ceramic, and an adhesive layer. Example 1: No protrusion 233 is provided on the negative electrode current collector 231, and the ratio of the negative electrode capacity of the opposite negative electrode edge region 2321 to the positive electrode capacity of the positive electrode edge region 2121 is 1.06-1.1; Example 2: A protrusion 233 is provided on the negative electrode current collector 231, and the ratio of the negative electrode capacity of the opposite negative electrode edge region 2321 to the positive electrode capacity of the positive electrode edge region 2121 is 1.08-1.1; Comparative Example: No protrusion 233 is provided on the negative electrode current collector 231, and the ratio of the negative electrode capacity of the opposite negative electrode edge region 2321 to the positive electrode capacity of the positive electrode edge region 2121 is 1.02-1.04. The sampling methods for the positive and negative electrode discs are as described above.

[0104] Under the same test conditions, the probability of lithium deposition in the edge region of Example 1 was 0.1%; the coating defect rate caused by lithium deposition in the edge region was 0.05%; the probability of lithium deposition in the edge region of Example 2 was 0%; the coating defect rate caused by lithium deposition in the edge region was 0%; the probability of lithium deposition in the edge region of the comparative example was 5.5%; the coating defect rate caused by lithium deposition in the edge region was 3.2%.

[0105] Experimental results show that by increasing the ratio of the negative electrode capacity of the opposite negative electrode edge region 2321 to the positive electrode capacity of the positive electrode edge region 2121, the probability of lithium plating in the edge region can be greatly reduced, thus improving safety. Furthermore, by setting protrusions 233 on the negative electrode current collector 231, the thicknesses of the positive and negative electrodes in the edge region and the middle region are essentially the same. This results in the CB values ​​of the negative electrode edge region 2321 and the positive electrode edge region 2121 being consistent with the CB values ​​of the negative electrode middle region 2322 and the positive electrode middle region 2122, thereby reducing the probability of lithium plating in the edge region to 0%. This demonstrates that the secondary battery 1 of this embodiment, by setting the size range of the positive electrode edge region 2121 and the negative electrode edge region 2321, and the range of the ratio of the negative electrode capacity of the opposite negative electrode edge region 2321 to the positive electrode capacity of the positive electrode edge region 2121 along the thickness direction T, can effectively improve the safety of the battery cell and reduce the coating defect rate caused by lithium plating in the edge region, thereby improving production yield and efficiency.

[0106] Please refer to the following: Figure 1 and Figure 2 In one embodiment of this invention, the secondary battery 1 is a square battery. However, it is not limited to this; in other embodiments, the secondary battery 1 may also be a cylindrical battery or other types of batteries.

[0107] Electrode assembly 20 is a wound electrode assembly, or electrode assembly 20 is a stacked electrode assembly.

[0108] Applying the specific setting of the size range of the positive electrode edge region 2121 and the negative electrode edge region 2321 in this embodiment, as well as the range of the ratio of the negative electrode capacity of the negative electrode edge region 2321 to the positive electrode capacity of the positive electrode edge region 2121 directly opposite to the thickness direction T, to square batteries can effectively improve the safety of the cell and reduce the coating defect rate caused by lithium plating in the edge region, thereby improving the production yield and efficiency.

[0109] The secondary battery 1 also includes a cover assembly 40, which covers the housing 10 and, together with the housing 10, defines a receiving cavity 13, in which the electrode assembly 20 is received. The cover assembly 40 includes a cover body 41 and an insulating member 42. The cover body 41 has a through-hole 411 along its thickness direction. The insulating member 42 is located between the cover body 41 and the electrode assembly 20.

[0110] The cover plate assembly 40 also includes electrode terminals 43. One end of the electrode terminal 43 is electrically connected to the tabs leading out from the electrode assembly 20, and the other end passes through the first electrode lead-out hole on the insulating member 42 and the second electrode lead-out hole on the cover plate body 41 in sequence. The tabs leading out from the positive electrode plate 21 are positive electrode tabs, and the tabs leading out from the negative electrode plate 23 are negative electrode tabs. The positive electrode tabs and negative electrode tabs are electrically connected to the corresponding electrode terminals 43, respectively.

[0111] The secondary battery 1 also includes a top cover 50 disposed on the cover assembly 40.

[0112] like Figure 9 As shown, this utility model also provides a battery pack 100, which includes the aforementioned secondary battery 1. In one embodiment of the battery pack 100, the battery pack 100 includes a housing 310, a cover 320, and multiple secondary batteries 1. The multiple secondary batteries 1 are placed in the housing 310 and are connected in series, parallel, or a combination of series and parallel connections. The cover 320 seals the housing 310 to protect the multiple secondary batteries 1. It should be noted that, in addition to the secondary battery 1 of this utility model, the battery pack 100 may also include a battery pack thermal management system, circuit board, etc. The battery pack 100 can be a battery module, a battery pack, an energy storage cabinet, etc.; these will not be described in detail here.

[0113] like Figure 10 As shown, this utility model also provides an electronic device 1000, which includes the aforementioned battery pack 100. A working part 300 is electrically connected to the battery pack 100 to obtain electrical power. As an example, the electronic device 1000 is a vehicle, which can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, but are not limited thereto. The working part 300 is the vehicle body, and the battery pack 100 is located at the bottom of the vehicle body, providing electrical power for the vehicle's operation or the operation of its internal electrical components. However, in other embodiments, the electronic device 1000 can also be a mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; the working part 300 can be a unit component capable of obtaining electrical power from the battery pack 100 and performing corresponding work, such as a fan blade rotation unit or a vacuum cleaner suction unit. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the aforementioned electronic device 1000.

[0114] While specific embodiments of this utility model have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of this utility model is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of this utility model, but all such changes and modifications fall within the scope of protection of this utility model.

Claims

1. A secondary battery, characterized in that, The secondary battery includes: case; An electrode assembly is housed within the housing. The electrode assembly is formed by stacking a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet includes a positive current collector, and the negative electrode sheet includes a negative current collector. The electrode assembly includes a first end and a second end disposed opposite to each other along the height direction. The first end is provided with a positive electrode tab and a negative electrode tab, and the direction from the second end to the first end is a preset direction. A portion of at least one side of the positive current collector along the thickness direction is covered with a positive active material layer, and a portion of at least one side of the negative current collector along the thickness direction is covered with a negative active material layer. The positive electrode active material layer includes a positive electrode edge region near the first end, and the negative electrode active material layer includes a negative electrode edge region near the first end. Along the preset direction, the edge of the negative electrode edge region near the first end extends beyond the edge of the positive electrode edge region near the first end, and along the thickness direction of the negative electrode current collector, the negative electrode edge region is located on the side of the negative electrode current collector near the positive electrode edge region. Along the preset direction, the size of the positive electrode edge region is 2mm-17mm, the size of the negative electrode edge region is 3mm-18mm, and the ratio of the negative electrode capacity of the negative electrode edge region directly opposite the thickness direction to the positive electrode capacity of the positive electrode edge region is 1.05-1.

1.

2. The secondary battery as described in claim 1, characterized in that, The negative electrode current collector has a protrusion on at least one side along the thickness direction, and the edge of the negative electrode edge region near the first end is disposed close to the protrusion. The ratio of the negative electrode capacity of the negative electrode edge region directly opposite the first end along the thickness direction to the positive electrode capacity of the positive electrode edge region is 1.08-1.

1.

3. The secondary battery as described in claim 2, characterized in that, The thickness of the protrusion is 20%-90% of the thickness of the negative electrode active material layer.

4. The secondary battery as described in claim 1, characterized in that, Along the preset direction, the distance by which the edge of the negative electrode edge region near the first end extends beyond the edge of the positive electrode edge region near the first end is 1mm-1.5mm.

5. The secondary battery as described in claim 1, characterized in that, The positive electrode current collector includes a first positive electrode surface and a second positive electrode surface disposed along the thickness direction. The positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer. The first positive electrode active material layer covers a portion of the first positive electrode surface, and the second positive electrode active material layer covers a portion of the second positive electrode surface. The distance between the edge of the positive electrode edge region of the first positive electrode active material layer near the first end and the edge of the positive electrode edge region of the second positive electrode active material layer near the first end is less than or equal to 1 mm.

6. The secondary battery as described in claim 1, characterized in that, At least one side of the positive current collector is covered with a conductive layer; the positive active material layer covers the conductive layer.

7. The secondary battery as described in claim 6, characterized in that, Along the predetermined direction, a portion of at least one side of the positive current collector along the thickness direction is covered by the conductive layer and the insulating layer; The positive electrode active material layer at least partially covers the insulating layer, and along the thickness direction of the positive electrode current collector, the orthographic projection of the insulating layer is at least partially located outside the outer periphery of the positive electrode active material layer; The thickness of the conductive layer is m, and the thickness of the insulating layer is n, where n ≤ m, and the units of m and n are both μm.

8. The secondary battery as described in any one of claims 1 to 7, characterized in that, The secondary battery further includes a cover assembly that covers the housing and, together with the housing, defines a receiving cavity, in which the electrode assembly is received; and / or... The secondary battery is a square battery; and / or, the electrode assembly is a wound electrode assembly.

9. A battery pack, characterized in that, The secondary battery includes any one of claims 1 to 8.

10. An electronic device, characterized in that, Includes the battery pack as described in claim 9.

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