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; in the preset direction, the positive electrode active material layer comprises a positive electrode straight area and a positive electrode thinned area which are connected, and the negative electrode active material layer comprises a negative electrode straight area and a negative electrode thinned area which are connected; in the preset direction, the edge, close to the first end, of the negative electrode straight area exceeds the edge, close to the first end, of the positive electrode straight area opposite to the negative electrode straight area, and the edge, close to the first end, of the positive electrode thinned area does not exceed the edge, close to the first end, of the negative electrode thinned area, so that the lithium precipitation probability of the thinned area 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 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] Along the preset direction, the positive electrode active material layer includes a straight positive electrode region and a thinned positive electrode region, and the negative electrode active material layer includes a straight negative electrode region and a thinned negative electrode region. Along the thickness direction of the negative electrode current collector, the thinned negative electrode region is located on the side of the negative electrode current collector closer to the thinned positive electrode region.

[0011] Wherein, along the preset direction, the edge of the negative electrode straight region near the first end extends beyond the edge of the positive electrode straight region near the first end directly opposite to it, and the edge of the positive electrode thinning region near the first end does not extend beyond the edge of the negative electrode thinning region near the first end directly opposite to it.

[0012] In the technical solution, the edge of the negative flat area close to the first end exceeds the edge of the opposite positive flat area close to the first end along the preset direction, and the edge of the positive thinning area close to the first end does not exceed the edge of the opposite negative thinning area close to the first end along the preset direction, so that the CB values of the thinning area and the flat area are close to each other, thereby reducing the probability of lithium precipitation in the thinning area, effectively improving the safety of the battery cell, and improving the production yield and efficiency.

[0013] Preferably, along the preset direction, the width of the negative thinning area is less than or equal to the width of the positive thinning area, and the width of the negative thinning area is less than or equal to 10 mm.

[0014] Preferably, along the preset direction, when the edge of the positive thinning area close to the first end is flush with the edge of the negative thinning area close to the first end, the width of the negative thinning area is 0-10 mm, and the width of the positive thinning area is 10 mm-15 mm; or,

[0015] When the edge of the negative thinning area close to the first end exceeds the edge of the opposite positive thinning area close to the first end by a distance of 5 mm-15 mm along the preset direction, the width of the negative thinning area is 10 mm-15 mm.

[0016] Preferably, at least one surface of the positive current collector is covered with a conductive layer.

[0017] The positive active material layer covers the conductive layer.

[0018] Preferably, along the preset direction, at least one surface of the positive current collector is covered with the conductive layer and an insulating layer.

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

[0020] Preferably, the thickness of the conductive layer is m, and the thickness of the insulating layer is n, then n≤m, and the units of m and n are both μm, or,

[0021] Along the preset direction, the edge of the conductive layer close to the first end exceeds the edge of the opposite negative flat area close to the first end, and does not exceed the edge of the positive active material layer close to the first end.

[0022] Preferably, the ratio of the negative capacity of the negative thinning area to the positive capacity of the positive thinning area along the opposite direction of the thickness direction is 1.05-1.1.

[0023] Preferably, the secondary battery further comprises a cover plate assembly, which is arranged on the shell and cooperates with the shell to define a receiving cavity, and the electrode assembly is received in the receiving cavity; and / or,

[0024] The secondary battery is a square battery; and / or the electrode assembly is a winding electrode assembly.

[0025] A battery pack, characterized by comprising the secondary battery as described above.

[0026] An electronic device, characterized by comprising the battery pack as described above.

[0027] The positive effect of the utility model lies in that:

[0028] Due to the flowability of the slurry in the coating process, the thickness of the thinning area at the edge is small, and the thickness and the area density of this area are lower than those of the flat area in the middle, thereby causing the CB value of the negative thinning area and the positive thinning area to be insufficient, leading to the problem of lithium precipitation in the thinning area, and affecting the safety of the secondary battery. The CB value refers to the ratio of the product of the area density and the negative gram capacity of the negative electrode sheet opposite to the positive electrode sheet (negative capacity) to the product of the area density and the positive gram capacity of the positive electrode sheet (positive capacity) when the battery is discharged. It can also be referred to as C.B. value or N / P ratio (Negative / Positive).

[0029] In the utility model, the edge of the negative flat area close to the first end exceeds the edge of the positive flat area close to the first end opposite in the preset direction, and the edge of the positive thinning area close to the first end does not exceed the edge of the negative thinning area close to the first end opposite in the preset direction, so that the CB values of the thinning area and the flat area are close to each other, thereby reducing the probability of lithium precipitation in the thinning area, effectively improving the safety of the battery cell, and improving the production yield and efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a three-dimensional explosion structure schematic view of the secondary battery of a preferred embodiment of the utility model.

[0031] Figure 2 It is a partial three-dimensional structure schematic view of the secondary battery of a preferred embodiment of the utility model.

[0032] Figure 3 It is a partial sectional view structure schematic view of an embodiment of the electrode assembly of the secondary battery of a preferred embodiment of the utility model.

[0033] Figure 4 It is a partial sectional view structure schematic view of the positive electrode sheet of the secondary battery of a preferred embodiment of the utility model.

[0034] Figure 5 A partial cross-sectional structure schematic view of a negative electrode sheet of a secondary battery according to a preferred embodiment of the present application.

[0035] Figure 6 A partial cross-sectional structure schematic view of another embodiment of an electrode assembly of a secondary battery according to a preferred embodiment of the present application.

[0036] Figure 7 A sampling position schematic view of a positive electrode small round sheet according to a preferred embodiment of the present application.

[0037] Figure 8 A sampling position schematic view of a negative electrode small round sheet according to a preferred embodiment of the present application.

[0038] Figure 9 A structure schematic view of a battery pack according to a preferred embodiment of the present application.

[0039] Figure 10 A structure schematic view of an electronic device according to a preferred embodiment of the present application.

[0040] BRIEF DESCRIPTION OF DRAWINGS

[0041] Electronic device 1000

[0042] Battery pack 100

[0043] Working part 300

[0044] Box body 310

[0045] Box cover 320

[0046] Secondary battery 1

[0047] Housing 10

[0048] Accommodation cavity 13

[0049] Electrode assembly 20

[0050] Positive electrode sheet 21

[0051] Positive electrode current collector 211

[0052] First positive electrode surface 2111

[0053] Second positive electrode surface 2112

[0054] Positive electrode active material layer 212

[0055] Positive electrode flat area 2121

[0056] Edge 21211 of positive electrode flat area close to the first end

[0057] Positive electrode thinning area 2122

[0058] Positive electrode thinning region edge 21221 close to first end

[0059] First positive electrode active material layer 2123

[0060] Second positive electrode active material layer 2124

[0061] Conductive layer 213

[0062] Insulating layer 214

[0063] First region 2141

[0064] Second region 2142

[0065] Separator 22

[0066] Negative electrode sheet 23

[0067] Negative electrode current collector 231

[0068] Negative electrode active material layer 232

[0069] Negative electrode flat region 2321

[0070] Negative electrode flat region edge 23211 close to first end

[0071] Negative electrode thinning region 2322

[0072] Negative electrode thinning region edge 23221 close to first end

[0073] Cover plate assembly 40

[0074] Cover plate body 41

[0075] Liquid injection hole 411

[0076] Insulating member 42

[0077] Electrode terminal 43

[0078] Top cover 50

[0079] Pre-set direction Q

[0080] Thickness direction T DETAILED DESCRIPTION

[0081] A preferred embodiment will be described below in detail with reference to the accompanying drawings.

[0082] As shown in Figure 1 and Figure 2 , the present embodiment provides a secondary battery 1. The secondary battery 1 includes a case 10 and an electrode assembly 20, which is accommodated in the case 10.

[0083] As shown in Figure 3As shown, the electrode assembly 20 is formed by stacking the positive electrode sheet 21, the separator 22, and the negative electrode sheet 23. The stacking includes stacking by winding to form a wound electrode assembly 20 or stacking by laminating to form a laminated electrode assembly 20.

[0084] As shown, the positive electrode sheet 21 includes a positive current collector 211, and the negative electrode sheet 23 includes a negative current collector 231; the electrode assembly 20 includes a first end and a second end arranged oppositely along a height direction, the first end is provided with a positive tab and a negative tab, and the second end is in a preset direction Q from the first end. Figure 4 Figure 5 As shown, the positive electrode sheet 21 includes a positive current collector 211, and the negative electrode sheet 23 includes a negative current collector 231; the electrode assembly 20 includes a first end and a second end arranged oppositely along a height direction, the first end is provided with a positive tab and a negative tab, and the second end is in a preset direction Q from the first end.

[0085] At least one surface of the positive current collector 211 along the thickness direction T is covered with a positive active material layer 212, and at least one surface of the negative current collector 231 along the thickness direction T is covered with a negative active material layer 232.

[0086] Along the preset direction Q, the positive active material layer 212 includes a positive flat area 2121 and a positive thinning area 2122 connected in sequence, and the negative active material layer 232 includes a negative flat area 2321 and a negative thinning area 2322 connected in sequence, and along the thickness direction T of the negative current collector 231, the negative thinning area 2322 is located on the side of the negative current collector 231 close to the positive thinning area 2122.

[0087] Wherein, along the preset direction Q, the edge 23211 of the negative flat area 2321 close to the first end exceeds the edge 21211 of the positive flat area 2121 close to the first end of the opposite surface, and the edge 21221 of the positive thinning area 2122 close to the first end does not exceed the edge 23221 of the negative flat area 2322 close to the first end of the opposite surface.

[0088] Due to the fluidity of the slurry during the coating process, the thickness of the thinning area at the edge is small, and the thickness and the area density of this area are lower than those of the flat area in the middle, thereby causing the CB value of the negative thinning area and the positive thinning area to be insufficient, and causing the lithium precipitation problem of the thinning area, thereby affecting the safety of the secondary battery 1. The CB value refers to the ratio of the product of the area density and the negative gram capacity of the opposite negative electrode sheet (negative capacity) to the product of the area density and the positive gram capacity of the positive electrode sheet (positive capacity) when the battery is discharged, which can also be referred to as C.B. value or N / P ratio (Negative / Positive).

[0089] ​In the embodiment, the edge 23211 of the negative flat area 2321 near the first end exceeds the edge 21211 of the positive flat area 2121 opposite to the edge 23211 of the negative flat area 2321 near the first end in the preset direction Q, and the edge 21221 of the positive thinning area 2122 near the first end does not exceed the edge 23221 of the negative thinning area 2322 opposite to the edge 21221 of the positive thinning area 2122 near the first end in the preset direction Q, so that the CB values of the thinning area and the flat area are close to each other, thereby reducing the probability of lithium precipitation in the thinning area, effectively improving the safety of the battery cell, and improving the production yield and efficiency. The edge 23211 of the negative flat area 2321 near the first end exceeds the edge 21211 of the positive flat area 2121 opposite to the edge 23211 of the negative flat area 2321 near the first end in the preset direction Q, and the edge 21221 of the positive thinning area 2122 near the first end does not exceed the edge 23221 of the negative thinning area 2322 opposite to the edge 21221 of the positive thinning area 2122 near the first end in the preset direction Q, that is, at least part of the negative flat area 2321 corresponds to the positive thinning area 2122 opposite to the negative flat area 2321, so as to improve the CB value of the thinning area.

[0090] It should be noted that the thickness direction T of the positive current collector 211 is the same as the thickness direction T of the negative current collector 231. The positive current collector 211 includes the first positive surface 2111 and the second positive surface 2112 arranged opposite to each other in the thickness direction T, and the negative current collector 231 includes the first negative surface and the second negative surface arranged opposite to each other in the thickness direction T.

[0091] At least a part of the area of the positive current collector 211 in the thickness direction T is covered with the positive active material layer 212, that is, a part of the area on at least one of the first positive surface 2111 and the second positive surface 2112 is covered with the positive active material layer 212, and in the embodiment, a part of the area of the first positive surface 2111 and the second positive surface 2112 is covered with the positive active material layer 212. However, it is not limited thereto, and in other embodiments, a part of the area on one of the first positive surface 2111 and the second positive surface 2112 is covered with the positive active material layer 212.

[0092] Specifically, the positive active material layer 212 includes a first positive active material layer 2123 and a second positive active material layer 2124, the first positive active material layer 2123 covers a partial region of the first positive surface 2111, the second positive active material layer 2124 covers a partial region of the second positive surface 2112, and the distance between the edge of the positive thinning region of the first positive active material layer 2123 close to the first end and the edge of the positive thinning region of the second positive active material layer 2124 close to the first end is less than or equal to 1 mm. In this way, by setting the range of the distance, the excessive dislocation of the first positive active material layer 2123 and the second positive active material layer 2124 in the thickness direction T is avoided, thereby causing the problem of lithium precipitation.

[0093] A partial region of at least one surface of the negative current collector 231 in the thickness direction T is covered with the negative active material layer 232, that is, a partial region of at least one of the first negative surface and the second negative surface is covered with the negative active material layer 232, and in this embodiment, partial regions of the first negative surface and the second negative surface are both covered with the negative active material layer 232. The negative active material layers 232 on the first negative surface and the second negative surface are symmetrically arranged with respect to the negative current collector 231. However, this is not limiting, and in other embodiments, a partial region of one of the first negative surface and the second negative surface can be covered with the negative active material layer 232.

[0094] In this embodiment, preferably, in the preset direction Q, the width d2 of the negative thinning region 2322 is less than or equal to the width d1 of the positive thinning region 2122, and the width d2 of the negative thinning region 2322 is less than or equal to 10 mm. By setting the width d2 of the negative thinning region 2322 to be less than or equal to the width d1 of the positive thinning region 2122 and setting the range of the width d2 of the negative thinning region 2322, the CB values of the thinning region and the flat region are close to each other, thereby reducing the probability of lithium precipitation in the thinning region, effectively improving the safety of the battery cell. Furthermore, by the above setting, the width of the negative flat region 2321 corresponding to the positive flat region 2121 is larger, thereby further improving the energy density of the battery.

[0095] Please refer back to Figure 3In one embodiment of this invention, when the edge 21221 of the positive electrode thinning region 2122 near the first end is flush with the edge 23221 of the negative electrode thinning region 2322 near the first end along the preset direction Q, the width d2 of the negative electrode thinning region 2322 is 0-10mm, and the width d1 of the positive electrode thinning region 2122 is 10mm-15mm. Thus, when the edge 21221 of the positive electrode thinning region 2122 near the first end is flush with the edge 23221 of the negative electrode thinning region 2322 near the first end, by controlling the range of values ​​for the width d2 of the negative electrode thinning region 2322 and the width d1 of the positive electrode thinning region 2122, more straight negative electrode regions 2321 can correspond to the positive electrode thinning region 2122. This effectively reduces the probability of lithium plating in the thinning region, significantly improves the safety of the battery cell, and greatly reduces the coating defect rate caused by lithium plating in the thinning region, thereby improving production yield and efficiency.

[0096] like Figure 6 As shown, in another embodiment of this example, when the distance d3 of the negative electrode thinning area 2322 near the first end of the negative electrode thinning area 2322 extending beyond the edge 21221 of the positive electrode thinning area 2122 near the first end of the opposite positive electrode thinning area 2122 along the preset direction Q is 5mm-15mm, the width d2 of the negative electrode thinning area 2322 is 10mm-15mm. In this case, the edge 23221 of the negative electrode thinning region 2322 near the first end extends beyond the edge 21221 of the positive electrode thinning region 2122 near the first end by a distance d3 of 5mm-15mm along a preset direction Q. That is, the edge 23221 of the negative electrode thinning region 2322 near the first end is in a situation where it is moved outward relative to the edge 21221 of the positive electrode thinning region 2122 near the first end. In this case, by limiting the range of the width d2 of the negative electrode thinning region 2322, more negative electrode straight regions 2321 can correspond to the positive electrode thinning region 2122, thereby effectively reducing the probability of lithium plating in the thinning region and effectively improving the safety of the cell. Moreover, it greatly reduces the coating defect rate caused by lithium plating in the thinning region and improves the production yield and efficiency.

[0097] In this embodiment, the ratio of the negative electrode capacity of the negative electrode thinning region 2322 directly opposite to the positive electrode thinning region 2122 along the thickness direction T to the positive electrode capacity is 1.05-1.1. By setting the range of the ratio of the negative electrode capacity of the negative electrode thinning region 2322 directly opposite to the positive electrode thinning region 2122 (the CB value of the negative electrode thinning region 2322 and the positive electrode thinning region 2122), the CB values ​​of the thinned region and the flat region are made nearly identical, thereby reducing the probability of lithium plating in the thinned region, effectively improving the safety of the battery cell, and increasing production yield and efficiency.

[0098] Further, at least a partial region of at least one surface of the positive current collector 211 is covered with the conductive layer 213; the positive active material layer 212 covers the conductive layer 213 to enhance the conductive performance.

[0099] Preferably, along the preset direction Q, the edge of the conductive layer 213 near the first end exceeds the edge 23211 of the negative flat region 2321 near the first end, and does not exceed the edge 21221 of the positive active material layer 212 near the first end (i.e. the edge of the positive thinning region 2122 near the first end), that is, the width of the positive active material layer 212 along the preset direction Q is greater than the width of the conductive layer 213, so that the conductive layer 213 can provide more effective conductive effect.

[0100] Preferably, along the preset direction Q, at least a partial region of at least one surface of the positive current collector 211 in the thickness direction T is covered with the conductive layer 213 and the insulating layer 214; the positive active material layer 212 at least partially covers the insulating layer 214, and the orthographic projection of the insulating layer 214 along the thickness direction T of the positive current collector 211 is at least partially located outside the outer periphery of the positive active material layer 212; the thickness of the conductive layer 213 is m, and the thickness of the insulating layer 214 is n, then n≤m, and the units of m and n are both μm.

[0101] Thus, by setting the part area of the less side of the positive current collector 211 is covered with the conductive layer 213 and the insulating layer 214 along the preset direction Q, the conductive layer 213 is covered with the positive active material layer 212, 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 coated on the positive current collector 211 prior to the coating of the positive active material layer 212, by pre-coating the conductive and insulating layer 214, the edges of the positive active material layer 212 and the insulating layer 214 can be clear. This is because the positive active material layer 212 and the insulating layer 214 are generally coated by extrusion (the slurry is extruded through the gasket), so the thickness of the insulating layer 214 is uncontrollable, generally 15-30 μm, thereby causing the edges of the positive active material layer 212 and the insulating layer 214 to be unclear; while in the embodiment, by pre-coating the conductive and insulating layer 214, the simultaneous extrusion coating of the positive active material layer 212 and the insulating layer 214 is avoided, which causes the edges to be unclear, effectively avoiding the fusion of the two, that is, ensuring the edges of the positive active material layer 212 to be straight, so that after the stacking or winding, the CCD can accurately identify the edges of the positive active material layer 212, facilitating the accurate identification of the distance between the edges of the positive active material layer 212 and the negative active material layer 232 of the separator 22 and the negative sheet 23, controlling the distance between the sheets and the separator 22 (the distance between the edge of the positive active material layer 212 of the positive sheet 21 and the edge of the separator 22, and the distance between the edge of the positive active material layer 212 and the edge of the negative active material layer 232 of the negative sheet 23), ensuring the consistency of the electrode assembly 20, and greatly improving the yield. Moreover, before the positive sheet 21 is wound or stacked to prepare the electrode assembly 20, in order to improve the production rhythm and site utilization, the positive current collector 211 is generally pre-stored as a large roll (referred to as a pole 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, so that the hardness of the area provided with the insulating layer 214 in the pole roll is greater than the area provided with the conductive layer 213, which will cause the edge of the insulating layer 214 to be raised, so that the edge of the pole roll in the radial direction from the center to the outer periphery is more and more inclined, causing the difference in the diameter of the pole roll at the positions corresponding to the conductive layer 213 and the insulating layer 214 to be more and more different, which is easy to cause the positive current collector 211 to be torn, and brings safety hazards.In the embodiment, by setting the thickness m of the conductive layer to be greater than or equal to the thickness n of the insulating layer, the edge of the pole roll in the radial direction can be kept at a relatively flat position from the center to the periphery, effectively avoiding the edge of the insulating layer 214 from being raised, so that the diameter difference of the pole roll at the corresponding position of the conductive layer 213 and the insulating layer 214 of the pole roll is relatively close, and the positive electrode current collector 211 is not easily torn, reducing the safety hazard. Therefore, when the positive electrode current collector 211 is used to coat the positive electrode sheet 21, the yield of the wound and laminated electrode assembly 20 can be greatly improved when the positive electrode sheet 21 and the separator 22 are wound or laminated. At the same time, by controlling the thickness of the insulating layer 214, the material is reduced, and the production cost is also effectively reduced.

[0102] It should be noted that the conductive layer 213 and the insulating layer 214 are pre-coated on the positive electrode current collector 211, and the pre-coating includes but is not limited to the way of gravure coating the conductive layer 213 and the insulating layer 214.

[0103] Specifically, in the embodiment, part of the area on the first positive electrode surface 2111 and the second positive electrode surface 2112 of the positive electrode current collector 211 is covered with the conductive layer 213 and the insulating layer 214, and the conductive layer 213 and the insulating layer 214 on the two surfaces are respectively covered with the first positive electrode active material layer 2123 and the second positive electrode active material layer 2124. 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, it is not limited thereto, and in other embodiments, part of the area on one of the first positive electrode surface 2111 and the second positive electrode surface 2112 of the positive electrode current collector 211 can be covered with the conductive layer 213 and the insulating layer 214, and the conductive layer 213 and the insulating layer 214 on the surface can be covered with the positive electrode active material layer 212.

[0104] In the embodiment, 0.5 μm≤m<1 μm, for example, can be 0.5 μm, 0.6 μm, 0.75 μm, 0.8 μm or 0.99 μm, etc. Or, 0.5 μm<n<1 μm, for example, can be 0.55 μm, 0.6 μm, 0.75 μm, 0.8 μm or 0.99 μm. In this way, by controlling the value range of the thickness m of the conductive layer, on the one hand, the thickness m of the conductive layer is avoided to be too small, which cannot improve the conductive performance of the positive current collector 211; on the other hand, the thickness m of the conductive layer is avoided to be too large, which leads to the overall volume of the electrode assembly 20 being too large, thereby affecting the overall energy density. By controlling the thickness n of the insulating layer, on the one hand, the thickness n of the insulating layer is avoided to be too small, thereby not playing the insulation role; on the other hand, the thickness n of the insulating layer is avoided to be too large to affect the flexibility of the insulating layer 214. It should be noted that the pre-coating method of gravure coating can realize the thickness of the conductive layer 213 and the insulating layer 214 being less than or equal to 1 μm, while the thickness of the coating formed by the extrusion coating method is thicker, and the minimum thickness is about 10 μm.

[0105] The insulating layer 214 includes a first region 2141 not covered by the positive active material layer 212 and a second region 2142 covered by the positive active material layer 212, the width of the first region 2141 is w1, and the width of the second region 2142 is w2; wherein 3 mm≤w1+w2≤20 mm, for example, can be 3 mm, 5 mm, 7 mm, 10 mm, 14 mm or 20 mm, etc.; or, 0.1≤w1 / (w1+w2)≤1, for example, can be 0.1, 0.4, 0.5, 0.75, 0.9 or 1, etc. In this way, by setting the value range of the width of the insulating layer 214, the flexibility of the insulating layer 214 can be effectively ensured. By setting the proportion range of the width of the first region 2141 to the width of the insulating layer 214, it can be ensured that the first region 2141 always exceeds the edge of the positive active material layer 212 of the opposite surface by a certain width along the preset direction Q, thereby it can ensure the flexibility of the insulating layer 214 while ensuring the insulation function of the insulating layer 214, in the case of wide coating of the insulating layer 214, the tab of the positive plate 21 can still be normally bent; and the tab of the positive plate 21 will not directly contact the negative plate 23 in the extreme environment, for example, when the tab is inserted upside down.

[0106] As Figure 7 and Figure 8As shown in the figure, the surface density of the positive electrode thinning area 2122 of the positive electrode sheet 21 and the negative electrode thinning area 2322 of the negative electrode sheet 23 is measured according to the positions shown in the figure, the weight of the small disc (marked as positive electrode small disc) with a distance a1 of 2mm-17mm from the edge 21221 of the positive electrode thinning area 2122 and the weight of the small disc (marked as negative electrode small disc) with a distance a2 of 3mm-18mm from the edge 23221 of the negative electrode thinning area 2322 are tested respectively, the surface density of the active material on the small disc is the surface density of the area, and the CB value of the negative electrode thinning area 2322 and the positive electrode thinning area 2122 is calculated according to the surface density of the two. The positive electrode small disc is sampled at the position with a distance a1 from the edge 21221 of the positive electrode thinning area 2122, and the negative electrode small disc is sampled at the position with a distance a2 from the edge 23221 of the negative electrode thinning area 2322, so as to identify and sample the monitoring while ensuring the performance of the battery.

[0107] In this example, experimental data is cited to demonstrate that the structure of the secondary battery 1 of the embodiment can better avoid the problem of lithium precipitation. The 72173 hard shell wound lithium iron phosphate battery is taken as the test object, the battery adopts the winding process, the positive electrode sheet 21 mainly consists of lithium iron phosphate (LFP), SP (Super P, conductive carbon black) and PVDF (polyvinylidene fluoride); the negative electrode sheet 23 mainly consists of artificial graphite, SP, CMC (carboxymethyl cellulose) and SBR (styrene butadiene rubber); the electrolyte mainly consists of solvent, lithium salt and additive; and the separator 22 is selected from PE (polyethylene), ceramic and rubber-coated composite membrane with rubber coating layer.

[0108] Example one: along the preset direction Q, when the edge 21221 of the positive electrode thinning area 2122 close to the first end is flush with the edge 23221 of the negative electrode thinning area 2322 close to the first end, the width of the negative electrode thinning area 2322 is 5mm-10mm, and the width of the positive electrode thinning area 2122 is 10mm-15mm.

[0109] Example two: the difference from example one is that the width of the negative electrode thinning area 2322 is 0-5mm, and other conditions and parameters are completely the same as those of example 1.

[0110] Example three: the difference from example one is that the edge 23221 of the negative electrode thinning area 2322 close to the first end exceeds the edge 21221 of the positive electrode thinning area 2122 close to the first end opposite to it by a distance of 5mm along the preset direction Q, the width of the negative electrode thinning area 2322 is 10mm-15mm, and other conditions and parameters are completely the same as those of example 1.

[0111] Example four: the difference from example one is that the edge 23221 of the negative thinning area 2322 near the first end exceeds the edge 21221 of the positive thinning area 2122 opposite to it by a distance d1 of 10 mm in the preset direction Q, and the width of the negative thinning area 2322 is 10 mm-15 mm, and other conditions and parameters are the same as example one.

[0112] Example five: the difference from example one is that the edge 23221 of the negative thinning area 2322 near the first end exceeds the edge 21221 of the positive thinning area 2122 opposite to it by a distance of 15 mm in the preset direction Q, and the width of the negative thinning area 2322 is 10 mm-15 mm, and other conditions and parameters are the same as example one.

[0113] Comparative example: the difference from example one is that the width of the negative thinning area 2322 is 10 mm-15 mm, and other conditions and parameters are the same as example one.

[0114] Test the small samples of positive and negative small round sheets from example one to example five and the comparative example respectively, and the sampling method is as described above.

[0115] Under the same test conditions, the ratio of the negative capacity of the negative thinning area 2322 opposite to the positive thinning area 2122 in the thickness direction T to the positive capacity of the positive thinning area 2122 in example one is 1.04-1.06, the probability of lithium precipitation in the thinning area is 2.6%, and the coating failure rate caused by lithium precipitation in the thinning area is 1.2%; the ratio of the negative capacity of the negative thinning area 2322 opposite to the positive thinning area 2122 in the thickness direction T to the positive capacity of the positive thinning area 2122 in example two is 1.06-1.08, the probability of lithium precipitation in the thinning area is 0.1%, and the coating failure rate caused by lithium precipitation in the thinning area is 0.05%; the ratio of the negative capacity of the negative thinning area 2322 opposite to the positive thinning area 2122 in the thickness direction T to the positive capacity of the positive thinning area 2122 in example three is 1.05-1.07, the probability of lithium precipitation in the thinning area is 0.8%, and the coating failure rate caused by lithium precipitation in the thinning area is 0.34%; the ratio of the negative capacity of the negative thinning area 2322 opposite to the positive thinning area 2122 in the thickness direction T to the positive capacity of the positive thinning area 2122 in example four is 1.06-1.08, the probability of lithium precipitation in the thinning area is 0.1%, and the coating failure rate caused by lithium precipitation in the thinning area is 0.05%; the ratio of the negative capacity of the negative thinning area 2322 opposite to the positive thinning area 2122 in the thickness direction T to the positive capacity of the positive thinning area 2122 in example five is 1.08-1.10, the probability of lithium precipitation in the thinning area is 0%, and the coating failure rate caused by lithium precipitation in the thinning area is 0%; the ratio of the negative capacity of the negative thinning area 2322 opposite to the positive thinning area 2122 in the thickness direction T to the positive capacity of the positive thinning area 2122 in the comparative example is 1.02-1.04, the probability of lithium precipitation in the thinning area is 5.5%, and the coating failure rate caused by lithium precipitation in the thinning area is 3.2%.

[0116] From the experimental results, it can be seen that, as the width of the negative thinning area 2322 decreases, the CB values of the negative thinning area 2322 and the positive thinning area 2122 continuously increase, and the probability of lithium precipitation in the thinning area continuously decreases, thereby greatly reducing the probability and risk of lithium precipitation in the thinning area; as the edge 23221 of the negative thinning area 2322 near the first end moves outward in the direction close to the first end more and more, the corresponding negative flat area 2321 of the positive thinning area 2122 increases, thereby the CB values of the negative thinning area 2322 and the positive thinning area 2122 continuously increase, gradually reaching a level comparable to the CB values (1.06-1.08) of the negative flat area 2321 and the positive flat area 2121, or even reaching a higher value than the CB values of the negative flat area 2321 and the positive flat area 2121, thereby reducing the probability of lithium precipitation in the thinning area, and the probability of lithium precipitation in the thinning area is reduced to 0%. It is proved that, by setting the edge 23211 of the negative flat area 2321 near the first end to exceed the edge 21211 of the positive flat area 2121 opposite to it in the preset direction Q, and setting the edge 21221 of the positive thinning area 2122 near the first end to not exceed the edge 23221 of the negative thinning area 2322 opposite to it in the preset direction Q, the safety of the battery cell can be effectively improved, and the coating failure rate caused by lithium precipitation in the thinning area is reduced, thereby improving the production yield and efficiency.

[0117] Please refer to Figure 1 and Figure 2 In an embodiment of the present embodiment, the secondary battery 1 is a square battery. However, it is not limited thereto, and in other embodiments, the secondary battery 1 can also be a cylindrical battery or other shaped battery.

[0118] The electrode assembly 20 is a wound electrode assembly, or the electrode assembly 20 is a stacked electrode assembly.

[0119] The specific setting mode of the edge 23211 of the negative flat area 2321 near the first end exceeding the edge 21211 of the positive flat area 2121 opposite to it in the preset direction Q, and the edge 21221 of the positive thinning area 2122 near the first end not exceeding the edge 23221 of the negative thinning area 2322 opposite to it in the preset direction Q, can be applied to a square battery, which can effectively improve the safety of the battery cell, and reduce the coating failure rate caused by lithium precipitation in the thinning area, thereby improving the production yield and efficiency.

[0120] The secondary battery 1 further comprises a cover plate assembly 40, which is covered on the shell 10 and cooperates with the shell 10 to define a containing cavity 13, and the electrode assembly 20 is contained in the containing cavity 13. The cover plate assembly 40 comprises a cover plate body 41 and an insulating piece 42. The cover plate body 41 is provided with a through liquid injection hole 411 along the thickness direction of the cover plate body 41. The insulating piece 42 is located between the cover plate body 41 and the electrode assembly 20.

[0121] The cover plate assembly 40 further comprises electrode terminals 43. One end of the electrode terminals 43 is electrically connected with the tab led out by the electrode assembly 20, and the other end is sequentially arranged in the first electrode leading-out hole on the insulating piece 42 and the second electrode leading-out hole on the cover plate body 41. The tab led out by the positive plate 21 is a positive tab, and the tab led out by the negative plate 23 is a negative tab, and the positive tab and the negative tab are respectively electrically connected with the corresponding electrode terminals 43.

[0122] The secondary battery 1 further comprises a top cover 50 covered on the cover plate assembly 40.

[0123] As shown in Figure 9 The utility model further provides a battery pack 100, the battery pack 100 includes above-mentioned secondary battery 1, in an embodiment of the utility model battery pack 100, the battery pack 100 includes box 310, box lid 320 and multiple secondary batteries 1, multiple secondary batteries 1 are placed in the box 310, and are connected in series or parallel with each other, or series and parallel hybrid, and the box lid 320 is covered on the box 310 to protect multiple secondary batteries 1. It needs to be explained that the battery pack 100 can also include battery pack 100 heat management system, circuit board and other parts in addition to the secondary battery 1 of the utility model, and the battery pack 100 can be a battery module or a battery pack, and can be an energy storage cabinet, etc. Here, it will not be expanded one by one.

[0124] As shown in Figure 10As shown, the utility model further provides an electronic device 1000, electronic device 1000 includes battery pack 100 described above. Working part 300 is electrically connected with battery pack 100 to obtain electric energy support. As an example, electronic device 1000 is vehicle, and vehicle can be fuel automobile, gas automobile or new energy automobile, and new energy automobile can be pure electric vehicle, hybrid vehicle or extended range vehicle, but is not limited. Working part 300 is vehicle body, and battery pack 100 is arranged at the bottom of vehicle body and provides electric energy support for the running of vehicle or the operation of electrical element in vehicle. However, in some other embodiments, electronic device 1000 can also be mobile phone, portable device, notebook computer, ship, spacecraft, electric toy and electric tool and the like. Spacecraft includes airplane, rocket, space shuttle and spacecraft and the like, and working part 300 can be unit component that can obtain the electric energy of battery pack 100 and make corresponding work, for example, fan blade rotating unit of fan, dust absorption working unit of dust collector and the like. Electric toy includes fixed or mobile electric toy, for example, game machine, electric car toy, electric ship toy and electric plane toy and the like, and electric tool includes metal cutting electric tool, grinding electric tool, assembly electric tool and railway electric tool, for example, electric drill, electric grinder, electric wrench, electric screwdriver, electric hammer, impact drill, concrete vibrator and electric planer and the like. The embodiment of the application does not specially limit the above-mentioned electronic device 1000.

[0125] Although the specific embodiments of the utility model are described above, those skilled in the art should understand that this is only an example, and the protection scope of the 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 the utility model, and these changes and modifications all fall within the protection scope of the utility model.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises: a housing; an electrode assembly accommodated in the housing, the electrode assembly being formed by stacking a positive electrode sheet, a separator, and a negative electrode sheet; the positive electrode sheet comprising a positive electrode current collector, and the negative electrode sheet comprising a negative electrode current collector; the electrode assembly comprising a first end and a second end in a height direction, the first end being provided with a positive electrode tab and a negative electrode tab, and the second end being in a preset direction from the first end; at least one surface of the positive electrode current collector in a thickness direction is partially covered with a positive electrode active material layer, and at least one surface of the negative electrode current collector in the thickness direction is partially covered with a negative electrode active material layer; in the preset direction, the positive electrode active material layer comprises a positive electrode flat area and a positive electrode thinning area connected in sequence, the negative electrode active material layer comprises a negative electrode flat area and a negative electrode thinning area connected in sequence, and in the thickness direction of the negative electrode current collector, the negative electrode thinning area is located on a side of the negative electrode current collector close to the positive electrode thinning area; wherein, in the preset direction, an edge of the negative electrode flat area close to the first end exceeds an edge of the positive electrode flat area close to the first end on the opposite side, and an edge of the positive electrode thinning area close to the first end does not exceed an edge of the negative electrode thinning area close to the first end on the opposite side.

2. The secondary battery according to claim 1, wherein In the preset direction, the width of the negative electrode thinning area is less than or equal to the width of the positive electrode thinning area, and the width of the negative electrode thinning area is less than or equal to 10 mm.

3. The secondary battery according to claim 1, wherein In the preset direction, when the edge of the positive electrode thinning area close to the first end is flush with the edge of the negative electrode thinning area close to the first end, the width of the negative electrode thinning area is 0-10 mm, and the width of the positive electrode thinning area is 10 mm-15 mm; or, In the preset direction, when the edge of the negative electrode thinning area close to the first end exceeds the edge of the positive electrode thinning area close to the first end on the opposite side by a distance of 5 mm-15 mm, the width of the negative electrode thinning area is 10 mm-15 mm.

4. The secondary battery according to claim 1, wherein At least one surface of the positive electrode current collector is partially covered with a conductive layer; The positive electrode active material layer covers the conductive layer.

5. The secondary battery according to claim 4, wherein In the preset direction, at least one surface of the positive electrode current collector is partially covered with the conductive layer and an insulating layer; The positive electrode active material layer at least partially covers the insulating layer, and a positive projection of the insulating layer in the thickness direction of the positive electrode current collector is at least partially located outside the outer periphery of the positive electrode active material layer.

6. The secondary battery according to claim 5, wherein the positive electrode is provided on the surface of the positive electrode substrate. The thickness of the conductive layer is m, and the thickness of the insulating layer is n, then n≤m, the units of m and n are both μm, or In the preset direction, the edge of the conductive layer close to the first end exceeds the edge of the negative electrode flat area close to the first end on the opposite side, and does not exceed the edge of the positive electrode active material layer close to the first end.

7. The secondary battery of any one of claims 1 to 6, wherein The ratio of the negative electrode capacity of the negative electrode thinning area to the positive electrode capacity of the positive electrode thinning area on the opposite side in the thickness direction is 1.05-1.

1.

8. The secondary battery of any one of claims 1 to 6, wherein The secondary battery further comprises a cover plate assembly, which is covered on the shell and cooperates with the shell to define a receiving cavity, and the electrode assembly is received in the receiving cavity; and / or, The secondary battery is a square battery; and / or, the electrode assembly is a winding electrode assembly.

9. A battery pack characterized by comprising: A secondary battery comprising any one of claims 1 to 8.

10. An electronic device, comprising: A battery pack comprising claim 9.

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