Wound electrode body and battery

Abstract

The embodiment of the invention provides a winding type electrode body and a battery with the same. The wound electrode body comprises a positive plate, a negative plate and a diaphragm which are arranged in a laminated manner. The positive electrode sheet and the negative electrode sheet are wound into a wound electrode body having a flat portion and a curved portion with a separator interposed therebetween. The positive plate comprises a positive current collector and positive active material layers; the positive active material layers comprise a first positive active material layer and a second positive active material layer; along the first direction Z, the positive current collector is provided with a first surface and a second surface which are oppositely arranged; along a second direction X perpendicular to the first direction Z, the first surface is provided with a first paste coating area and a first empty foil area, the second surface is provided with a second paste coating area, the first paste coating area is provided with a first positive active material layer, and the second paste coating area is provided with a second positive active material layer. First termination glue is arranged on at least part of the first empty foil area, the distance between the side edge, close to the first pasting area, of the first termination glue and the edge of the first pasting area is d1, and d1 is larger than or equal to 0.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to a wound electrode body and a battery. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long life and environmental friendliness, making them the preferred power source in fields such as mobile electronic devices and electric vehicles.

[0003] The cell of a lithium-ion battery consists of a positive electrode, a negative electrode, an electrolyte and a separator. During the charge and discharge process, lithium ions are intercalated and deintercalated back and forth between the two electrodes: during charging, lithium ions are deintercalated from the positive electrode and intercalated into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; during discharge, the opposite is true.

[0004] At present, lithium-ion batteries have the problem of local lithium plating. Summary of the invention

[0005] In view of this, an embodiment of the present application provides a wound electrode body and a battery having the same to solve the problem of local lithium deposition in lithium-ion batteries.

[0006] On the one hand, an embodiment of the present application provides a wound electrode body. The wound electrode body includes a positive electrode sheet, a negative electrode sheet and a separator arranged in a stacked manner. The positive electrode sheet and the negative electrode sheet are wound through the separator into a wound electrode body having a flat portion and a curved portion. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer, and the positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer. Along a first direction Z, the positive electrode collector has a first surface and a second surface arranged opposite to each other. Along a second direction X perpendicular to the first direction Z, a first paste coating area and a first empty foil area are provided on the first surface, a second paste coating area is provided on the second surface, a first positive electrode active material layer is provided on the first paste coating area, and a second positive electrode active material layer is provided on the second paste coating area. A first termination glue is provided on at least part of the first empty foil area, and the spacing between the side of the first termination glue close to the first paste coating area and the edge of the first paste coating area is d1, and d1≥0.

[0007] Additionally or alternatively, a second empty foil area is further provided on the second surface along the second direction X. A second stop glue is provided on at least part of the second empty foil area, and the distance between the side of the second stop glue close to the second paste area and the edge of the second paste area is d2, d2≥0.

[0008] Additionally or alternatively, the value range of d1 and d2 is 0 mm to 3 mm; preferably, the value range of d1 and d2 is 0.5 mm to 1.5 mm.

[0009] In addition or alternatively, the first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center. At least in the bend, the surface density of the first positive electrode active material layer is less than the surface density of the second positive electrode active material layer. Preferably, at least in the bend, the surface density of the first positive electrode active material layer is 90% to 99% of the surface density of the second positive electrode active material layer. More preferably, at least in the bend, the surface density of the first positive electrode active material layer is 94% to 97% of the surface density of the second positive electrode active material layer.

[0010] Additionally or alternatively, the first surface faces the winding center of the wound electrode body, the second surface is away from the winding center, and at least in the bending portion, the thickness of the first positive electrode active material layer is less than the thickness of the second positive electrode active material layer; preferably, the difference between the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer is 0.1μm to 10μm.

[0011] In addition or alternatively, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. Along the first direction Z, the negative electrode current collector has a third surface and a fourth surface arranged opposite to each other, the third surface faces the winding center, and the fourth surface faces away from the winding center. The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer respectively arranged on the third surface and the fourth surface. At least in the bending portion, the N / P ratio of the second negative electrode active material layer to the first positive electrode active material layer is greater than the N / P ratio of the first negative electrode active material layer to the second positive electrode active material layer, and the difference between the two is 0.005 to 0.2. Preferably, the difference between the two is 0.02 to 0.08. Here, the N / P ratio is the negative electrode capacity per unit area / positive electrode capacity per unit area.

[0012] In addition or alternatively, the end of the first positive electrode active layer near the first termination glue is provided with a fillet or chamfer; and / or, the end of the second positive electrode active layer near the second termination glue is provided with a fillet or chamfer. Preferably, when the end of the first positive electrode active material layer and / or the end of the second positive electrode active material layer is provided with a fillet, the radius of the fillet is 1mm to 10mm; more preferably, the radius of the fillet is 2mm to 6mm.

[0013] Additionally or alternatively, the single-sided thickness of the positive electrode active material layer on the positive electrode sheet is 30μm to 120μm, and the thickness of the first termination glue and the second termination glue are 15μm to 30μm respectively; preferably, the single-sided thickness of the positive electrode active material layer on the positive electrode sheet is 30μm to 100μm, and the thickness of the first termination glue and the second termination glue are 20μm to 25μm respectively.

[0014] Additionally or alternatively, the first surface faces the winding center of the wound electrode body, and the second surface faces away from the winding center. At least at the bent portion, the first positive electrode active material layer is provided with holes or a concave texture structure.

[0015] Additionally or alternatively, the positive electrode active material of the first positive electrode active material layer and the positive electrode active material of the second positive electrode active material layer are the same; or, the positive electrode active material of the first positive electrode active material layer and the positive electrode active material of the second positive electrode active material layer are different.

[0016] Additionally or alternatively, the first surface faces the winding center of the wound electrode body, the second surface is away from the winding center, the first positive electrode active material layer and the second positive electrode active material layer have different positive electrode active materials, the kinetic performance of the positive electrode active material in the second positive electrode active material layer is better than the kinetic performance of the positive electrode active material in the first positive electrode active material layer, and / or the first positive electrode active material layer and the second positive electrode active material layer have the same thickness.

[0017] In a second aspect, an embodiment of the present application provides a battery, comprising the above-mentioned wound electrode body.

[0018] According to the embodiment of the present application, a wound electrode body is provided.

[0019] In order to avoid the burrs of the empty foil area at the end of the positive electrode sheet piercing the diaphragm and directly contacting the negative electrode sheet to cause a short circuit inside the battery cell, a piece of adhesive tape covering the positive electrode active material layer of the positive electrode sheet will be pasted at the end of the positive electrode sheet. During the charge and discharge cycle, the lithium ions released by the active material layer covered by the adhesive tape will migrate to the edge of the adhesive tape for enrichment, and the negative electrode active material layer corresponding to the edge of the adhesive tape cannot accept the lithium ions enriched here and cause lithium precipitation. The technical solution provided by the present application, by making the side of the first termination glue attached to the first empty foil area just contact the edge of the first positive electrode active material layer on the paste area (that is, the distance is 0) or keep a certain distance, can improve and avoid the first positive electrode active material layer in the termination glue covering area during the recycling process of the lithium ion battery. There will be some lithium ions (Li+) in the first positive electrode active material layer to diffuse to the edge of the first termination glue. Furthermore, it can reduce and avoid the lithium ion concentration at the edge of the first termination glue being higher than the remaining area of ​​the first positive electrode active material layer, resulting in a local CB value becoming smaller and producing local lithium precipitation, further improving the performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the positive electrode structure in the related technology.

[0021] Figure 2 It is a schematic diagram of the three-dimensional structure of a wound electrode body provided according to one embodiment of the present application.

[0022] Figure 3 for Figure 2 Cross-sectional view along DD of the wound electrode body.

[0023] Figure 4Schematic diagram of the structure of a positive electrode sheet according to one embodiment of the present application.

[0024] Figure 5 A schematic structural diagram of a positive electrode sheet according to another embodiment of the present application.

[0025] Figure 6 A schematic structural diagram of a positive electrode sheet according to yet another embodiment of the present application.

[0026] Figure 7 Schematic diagram of a battery according to one embodiment of the present application.

[0027] Figure 8 FIG. 1 is a schematic diagram of a battery according to another embodiment of the present application.

[0028] Reference numerals:

[0029] 1000. Battery;

[0030] 100, wound electrode body; 101, bent portion; 101a, first bent portion; 101b, second bent portion; 102, flat portion;

[0031] 10 / 10', positive electrode sheet; 11, positive electrode active material layer; 11a, first positive electrode active material layer; 11b / 11b', second positive electrode active material layer; 12 / 12', positive electrode current collector; 13, positive electrode ear; 14, first paste coating area; 15 / 15', second paste coating area; 16, first empty foil area; 17 / 17', second empty foil area; 18, termination glue; 18a, first termination glue; 18b, second termination glue; 19a, first surface; 19b / 19b', second surface;

[0032] 20. Negative electrode;

[0033] 200, housing;

[0034] 30. Diaphragm. DETAILED DESCRIPTION

[0035] Lithium-ion batteries have been rapidly applied in a wide range of industries due to their advantages such as high energy density, long cycle life, low self-discharge and no memory effect. Taking the field of civil drones as an example, the energy density and power performance of the battery cells are extremely high.

[0036] Generally, the electrode body of a lithium-ion battery can be formed by stacking a positive electrode sheet, a negative electrode sheet and a separator. Taking a wound electrode body as an example, it can include a stacked positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet and the negative electrode sheet are wound with the separator to form a wound electrode body with a flat portion and a curved portion. As one of the key components of the electrode body, the structure and performance of the positive electrode sheet directly affect the overall performance of the lithium-ion battery.

[0037] The structure and performance of the positive electrode sheet, as one of the key components of the electrode body, directly affect the overall performance of the lithium-ion battery. Taking the wound electrode body as an example, along the first direction Z, i.e., the thickness direction of the electrode sheet, the positive electrode current collector of the positive electrode sheet has two surfaces arranged opposite to each other. Along the second direction X, i.e., the length direction of the electrode sheet, both surfaces are provided with an empty foil area and a paste area. For example, Figure 1 In the example, the second surface 19b' is provided with a second pasted area 15' and a second empty foil area 17' located at the tail of the positive current collector 12'. A positive active material layer is provided on the pasted area, for example, a positive active material layer 11b' is provided on the second pasted area 15'.

[0038] It should be noted that the first direction in the text is the Z direction described in the figure, that is, the thickness direction of the pole piece, and the second direction is the X direction shown in the figure, that is, the length direction of the pole piece. At the same time, the direction perpendicular to the first direction Z and the second direction X is the Y direction shown in the figure, that is, the width direction of the pole piece.

[0039] As mentioned above, taking the wound electrode body as an example, in order to avoid short circuit caused by direct contact between the empty foil area and the negative electrode sheet, a termination glue is provided on the empty foil area. Figure 1 As shown in the example, in the positive electrode sheet 10', a second stop glue 18b' is provided on the second empty foil area 17' of the second surface 19b' of the positive current collector 12', and the second stop glue 18b' will partially cover the second positive electrode active material layer 11b' provided on the second paste area 15' at the starting end. Similarly, a first stop glue is provided on the first empty foil area of ​​the first surface of the positive current collector 12', and the first stop glue will partially cover the first positive electrode active material layer provided on the first paste area at the starting end (not shown in the figure).

[0040] The inventors have found that during high-power charging, the positive electrode active material covered by the termination glue will release lithium ions. This part of the lithium ions is blocked by the substrate in the termination glue and cannot directly pass through the termination glue and the diaphragm to reach the negative electrode side. As the cycle progresses, the lithium ions in this area will gradually migrate to the edge of the termination glue, causing the lithium ions to be enriched at the edge of the termination glue, resulting in the formation of obvious strip-shaped lithium precipitation along the edge of the adhesive tape in this area. From the appearance of the battery, an obvious strip-shaped protrusion can be seen, which will affect the performance and appearance of the battery and may cause battery safety accidents.

[0041] In order to improve the above situation, the present application provides a wound electrode body and a battery. Figures 2 to 8 , the embodiments of the present application are described.

[0042] It should be understood that there may be many ways to implement the present application, and it should not be construed as being limited to the embodiments described herein. The embodiments described herein are only for a more thorough and clear understanding of the present application.

[0043] Exemplary wound electrode body

[0044] refer to Figure 2 and Figure 3 , an embodiment of the present application provides a wound electrode body 100. The wound electrode body 100 may include a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30 arranged in a stacked manner. The positive electrode sheet 10 and the negative electrode sheet 20 are wound with the separator 30 interposed therebetween to form a wound electrode body 100 having a flat portion 102 and a curved portion 101. The curved portion 101 includes a first curved portion 101a and a second curved portion 101b.

[0045] refer to Figures 4 to 6 The positive electrode sheet 10 may include a positive electrode current collector 12 and a positive electrode active material layer 11. The positive electrode active material layer 11 includes a first positive electrode active material layer 11a and a second positive electrode active material layer 11b.

[0046] The positive electrode active material layer 11 may include a positive electrode active material. In addition, the positive electrode active material layer 11 may further include one or more of a binder, a conductive agent, and a solvent.

[0047] Illustratively, the positive electrode active material includes one or more of nickel cobalt lithium manganese oxide ternary material, lithium cobalt oxide material, nickel cobalt aluminum oxide material, lithium manganese oxide material, lithium iron phosphate material and lithium-rich manganese-based material.

[0048] For example, the binder may include one or more of polyvinylidene fluoride, polytetrachloroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyimide or polyethylene.

[0049] Illustratively, the conductive agent may include one or more of conductive ceramics, carbon black, graphite, graphene, polyaniline, polypyrrole, Ketjen black, acetylene black, and carbon nanotubes.

[0050] Illustratively, the solvent may include one or more of N-methylpyrrolidone, water, ethanol and polyethylene glycol.

[0051] By way of example only, the positive electrode current collector 12 may be a strip of metal foil, such as aluminum foil.

[0052] By way of example only, the negative electrode sheet 20 may include a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector.

[0053] By way of example only, the negative electrode current collector of the negative electrode sheet 20 may be a strip of metal foil, and its active material layer may include a negative electrode active material capable of reversibly absorbing and releasing charge carriers, a binder, a dispersant, and various additives.

[0054] By way of example only, the metal foil mentioned in the above-mentioned negative electrode sheet 20 may be copper foil, the negative electrode active material mentioned may include one or more of graphite, soft carbon, hard carbon, intermediate phase microspheres, and silicon-based materials, the binder mentioned may be a rubber such as styrene-butadiene rubber, and the dispersant mentioned may be a cellulose such as carboxymethyl cellulose.

[0055] The separator 30 is a component that insulates the negative electrode sheet from the positive electrode sheet. As some examples, the separator 30 can be a porous belt made of a polyolefin resin such as polyethylene or polypropylene. Of course, other materials for the separator 30 are also foreseeable, and this application does not limit this, that is, no special requirements are made.

[0056] refer to Figure 5 Along the first direction Z, the positive electrode current collector 12 may have a first surface 19a and a second surface 19b that are oppositely disposed, for example Figure 5 The upper and lower surfaces of the positive electrode sheet 10 are shown in FIG. Along a second direction X perpendicular to the first direction Z, a first paste coating area 14 and a first empty foil area 16 may be provided on the first surface 19a, and a second paste coating area 15 and a second empty foil area 17 may be provided on the second surface 19b.

[0057] The length of the first pasting area 14 may be greater than that of the second pasting area 15 , and the length of the first empty foil area 16 may be less than that of the second empty foil area 17 .

[0058] The first pasting area 14 and the second pasting area 15 may be provided with a first positive electrode active material layer 11 a and a second positive electrode active material layer 11 b , respectively.

[0059] It can be understood that the first empty foil area 16 is a portion of the first surface 19a that is not provided with the positive polarity material layer 11. At this time, along the first direction Z, the second surface opposite to the first empty foil area 16 of the first surface 19a may be provided with a positive electrode active material layer, or may not be provided with an active material layer; the second empty foil area 17 is a portion of the second surface 19b that is not provided with the positive electrode active material layer 11. At this time, along the first direction Z, the first surface opposite to the second empty foil area 17 of the second surface 19b may be provided with a positive electrode active material layer, or may not be provided with an active material layer. Exemplarily, the positive current collector surfaces 12 of the first empty foil area 16 and the second empty foil area 17 may be provided with an insulating protective layer or directly exposed, respectively.

[0060] Continue to refer Figure 5, at least part of the first empty foil area 16 may be provided with a first termination glue 18a. The distance between the side of the first termination glue 18a close to the first paste area 14 and the edge of the first paste area 14 close to the first termination glue may be d1, d1 ≥ 0. That is, the first termination glue 18a may not cover the positive electrode active material layer 11. That is, along the extension direction of the positive electrode sheet 10, the first termination glue 18a does not cover the positive electrode active material layer 11, that is, it just contacts with the positive electrode active material layer 11 or maintains a certain distance.

[0061] In this way, the side of the first stop glue 18a attached to the first empty foil area 16 just contacts the edge of the positive electrode active material layer 11 (i.e., the distance between the two is 0) or maintains a certain distance. Therefore, while preventing the first empty foil area 16 of the positive electrode sheet 10 from directly contacting the negative electrode sheet 20 to cause a short circuit, the lithium ions in the area covered by the first stop glue 18a generated by the first stop glue 18a covering the positive electrode active material layer 11 can be reduced and avoided to diffuse to the edge of the first stop glue 18a. In addition, the lithium ion concentration at the edge of the first stop glue 18a is higher than that in the rest of the positive electrode active material layer 11, which causes the local CB value to become smaller and produces local lithium precipitation, thereby further improving the performance of the battery 1000.

[0062] Continue to refer Figures 4 to 6 , at least part of the second empty foil area 17 is provided with a second termination glue 18b. The spacing between the side of the second termination glue 18b close to the second paste area 15 and the edge of the second paste area 15 can be d2, d2 ≥ 0. That is, the second termination glue 18b may not cover the positive electrode active material layer 11. In other words, along the extension direction of the positive electrode sheet 10, the second termination glue 18b is just in contact with the positive electrode active material layer 11 (that is, the distance between the two is 0) or maintains a certain distance.

[0063] In this way, the side of the second stop glue 18b attached to the second empty foil area 17 just contacts the edge of the second positive electrode active material layer 11b (i.e., the distance between the two is 0) or maintains a certain distance. Therefore, while preventing the second empty foil area 17 of the positive electrode sheet 10 from directly contacting the negative electrode sheet 20 to cause a short circuit, the lithium ions in the area covered by the second stop glue 18b generated by the second stop glue 18b covering the positive electrode active material layer 11 can be reduced and avoided to diffuse to the edge of the second stop glue 18b. In addition, the lithium ion concentration at the edge of the second stop glue 18b is higher than that in the rest of the positive electrode active material layer 11, which causes the local CB value to become smaller and produces local lithium precipitation, thereby further improving the performance of the battery 1000.

[0064] The units of the above d1 and d2 may be mm.

[0065] It should be noted that d1 is the distance between the side of the first stop glue 18a close to the first paste area 14 and the edge of the first paste area 14 (the edge is adjacent to and opposite to the first stop glue 18a). It can be understood that the side of the first stop glue 18a close to the first paste area 14 may not be parallel to the edge of the first paste area 14. In addition, the edge of the first paste area 14 and the side of the first stop glue 18a close to the first paste area 14 may be irregular lines, such as oblique lines, fold lines or wavy lines.

[0066] It should also be noted that d2 is the distance between the side of the second stop glue 18b close to the second paste area 15 and the edge of the second paste area 15 (the edge is adjacent to and opposite to the second stop glue 18b). It can be understood that the side of the second stop glue 18b close to the second paste area 15 may not be parallel to the edge of the second paste area 15, and the edge of the second paste area 15 and the side of the second stop glue 18b close to the second paste area 15 may be irregular lines, such as oblique lines, fold lines or wavy lines.

[0067] As mentioned above, d1 can be 0 mm to 3 mm (e.g., 0.2 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2.0 mm, 2.5 mm or 2.8 mm, etc.). d2 can be 0 mm to 3 mm (e.g., 0.2 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2.0 mm, 2.5 mm or 2.8 mm, etc.). Alternatively, d1 can be 0 mm to 3 mm and d2 can be 0 mm to 3 mm at the same time.

[0068] The distance between the first stop glue 18a and the second stop glue 18b and the first positive electrode active material layer 11a and the second positive electrode active material layer 11b is controlled within this range, so that the stop glue 18 can maintain an appropriate distance from the positive electrode active material layer 11 while avoiding the positive electrode current collector 12 from contacting the negative electrode sheet 20 to cause a short circuit, and is convenient for operation and process implementation. If d1 and d2 are too small, it is difficult to control and the process cost will increase. If d1 and d2 are too large, the risk of a short circuit caused by direct contact between the positive electrode current collector 12 and the negative electrode sheet 20 will increase.

[0069] Preferably, d1 can be 0.5 mm to 1.5 mm. d2 can be 0.5 mm to 1.5 mm. Alternatively, d1 can be 0.5 mm to 1.5 mm and d2 can be 0.5 mm to 1.5 mm. In this way, the positive electrode current collector 12 can be better prevented from directly contacting the negative electrode sheet 20 to cause a short circuit, and the installation can be facilitated.

[0070] The thickness of the paste on one side of the positive electrode sheet 10 is A, and the thickness of the first stop glue 18a and the second stop glue 18b are B. It should be noted that when the thickness of the paste on one side is different, A is the average, minimum or maximum value of the thickness of the paste on both sides, and this application does not limit this.

[0071] Exemplarily, A may be 30 μm to 120 μm (eg, 35 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 95 μm, 100 μm, 110 μm, etc.) Preferably, A is 30 μm to 100 μm.

[0072] Exemplarily, B can be 15 μm to 30 μm (e.g., 17 μm, 19 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm, etc.), preferably, B can be 20 μm to 25 μm. In this way, the thickness of the positive electrode active material layer 11 can be matched with the thickness of the termination glue 18, avoiding the termination glue being too thick to increase the invalid thickness and reduce the energy density of the battery.

[0073] Exemplarily, the stop glue 18 may be composed of a substrate and a glue layer. For example, the substrate may be a PET film or a BOPP film material, and the glue layer may be an acrylic pressure-sensitive adhesive or rubber.

[0074] In the design of battery cells, the N / P ratio is usually required to be greater than 1 to ensure that the reversible capacity of the negative electrode is greater than the reversible capacity of the positive electrode during the battery cycle. In this way, it is possible to minimize and avoid the deposition of excess lithium ions on the surface of the negative electrode to form lithium dendrites that reduce battery performance or puncture the diaphragm, thereby ensuring the normal performance and safety of the battery. In other words, the positive electrode active material coated on the positive electrode sheet needs to have a corresponding negative electrode active material that can accommodate lithium ions on the negative electrode sheet opposite it. If there is no or insufficient negative electrode active material, lithium will be deposited on the negative electrode sheet, thereby affecting the safety performance of the battery.

[0075] Here, the N / P (Negative / Positive) ratio (hereinafter referred to as N / P ratio) refers to the ratio of the actual capacity of the positive and negative electrode materials per unit area, and its calculation formula is: gram capacity of negative electrode active material × negative electrode surface density × negative electrode active material content ratio ÷ (gram capacity of positive electrode active material × positive electrode surface density × positive electrode active material content ratio).

[0076] The wound electrode body is widely used in the market due to its high processing efficiency and low cost. The wound electrode body will be flattened after winding, and has a flat part in the middle and curved parts at both ends. For the wound electrode body, the curvature of the inner and outer circles of the pole piece is inconsistent in the curved part, with the inner circle having a large curvature and the outer circle having a small curvature. Therefore, the N / P ratio of the inner and outer circles of the pole piece is inconsistent. If the design is improper, lithium deposition is likely to occur in the curved part.

[0077] At present, there is no good method in the industry to deal with the N / P ratio at the curved surface structure. For example, if the N / P ratio of the battery cell is designed based on the N / P ratio of the inner circle of the negative electrode sheet corresponding to the outer circle of the positive electrode sheet being greater than 1, the N / P ratio at the inner circle of the positive electrode sheet corresponding to the outer circle of the negative electrode sheet will be insufficient, and the battery cell is prone to lithium deposition at the outer circle of the negative electrode sheet with a curved surface structure, thereby affecting the cycle life and safety of the battery cell. Therefore, it is necessary to increase the N / P ratio here. In order to solve this problem, the industry now basically adopts an interference N / P ratio design to ensure that the N / P ratio of the inner and outer circles is sufficient. However, this method will cause the N / P ratio of the outer circle of the positive electrode sheet to be too large, which will reduce the initial efficiency of the battery and reduce the energy density of the battery.

[0078] The first surface 19 a faces the winding center EE of the wound electrode body 100 , and the second surface 19 b faces away from the winding center EE.

[0079] The negative electrode sheet 20 includes a negative electrode current collector and a negative electrode active material layer. Along the first direction Z, the negative electrode current collector has a third surface and a fourth surface arranged opposite to each other, the third surface faces the winding center, and the fourth surface faces away from the winding center. The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer respectively arranged on the third surface and the fourth surface.

[0080] In order to improve the above situation, at least in the curved portion 101, the surface density of the first positive electrode active material layer 11a is less than the surface density of the second positive electrode active material layer 11b, so as to at least increase the N / P ratio of the first positive electrode active material layer 11a corresponding to the curved portion 101, that is, to increase the N / P ratio of the second negative electrode active material layer to the first positive electrode active material layer 11a.

[0081] In the curved portion 101, by making the surface density of the first positive electrode active material layer 11a smaller than the surface density of the second positive electrode active material layer 11b, the N / P ratio of the second negative electrode active material layer to the first positive electrode active material layer 11a in the curved portion 101 can be adjusted. Therefore, in the curved portion 101, the N / P value of the second negative electrode active material layer to the first positive electrode active material layer 11a is increased, that is, the N / P ratio of the inner circle of the positive electrode sheet 10 corresponding to the outer circle of the negative electrode sheet 20 is increased accordingly. In this way, lithium deposition in the outer circle of the negative electrode sheet 20 in the curved portion 101 can be prevented, and the kinetic performance of the negative electrode reaction at this position can be improved, thereby reducing the risk of lithium deposition in the outer circle of the negative electrode sheet 20 in the curved portion 101, thereby improving the situation of local lithium deposition in the battery 1000. In one embodiment, in addition to such an arrangement at the bent portion, in order to further reduce the difficulty and efficiency of process manufacturing and ensure the process stability of electrode preparation, the surface density of the first positive electrode active material layer 11a on the first surface of the positive electrode sheet can also be controlled to be smaller than the surface density of the second positive electrode active material layer 11b on the first surface of the positive electrode sheet.

[0082] In some examples, at least in the curved portion 101, the surface density of the positive electrode active material layer 11 in the first pasted area 14 can be 90% to 99% of the surface density of the positive electrode active material layer 11 in the second pasted area 15. If the surface density difference on both sides of the positive electrode sheet is too large, it may cause uneven surface stress after rolling the electrode sheet, causing uneven deformation inside the battery during the cycle, increasing the risk of battery expansion. Especially at high charge and discharge rates, local expansion may cause rupture of the battery structure or leakage of the electrolyte. Exemplarily, the surface density of the first positive electrode active material layer is 8 mg / cm 2 ~25mg / cm 2 The surface density of the second positive electrode active material layer is 7.2 mg / cm 2 ~24.9mg / cm 2 Within this range, the energy density and the N / P ratio can be well balanced, and the risk of lithium plating in the outer ring of the negative electrode sheet 20 can be reduced while obtaining better performance of the battery 1000.

[0083] Preferably, at least in the curved portion 101, the surface density of the positive electrode active material layer 11 in the first paste coating area 14 can be 94% to 97% of the surface density of the positive electrode active material layer 11 in the second paste coating area 15. For example, the surface density of the first positive electrode active material layer is 12 mg / cm 2 ~17mg / cm 2 The surface density of the second positive electrode active material layer is 10.8 mg / cm 2 ~16.9mg / cm 2 . Within this range, the energy density and N / P ratio can be better balanced, and better battery 1000 performance can be obtained while reducing the risk of lithium plating in the outer ring of the negative electrode sheet 20. Similarly, in some examples, the surface density of the positive electrode active material layer 11 in the first paste coating area 14 of the first surface can be 90% to 99% of the surface density of the positive electrode active material layer 11 in the second paste coating area 15 of the first surface, preferably 94% to 97%. Exemplarily, the surface density of the first positive electrode active material layer is 12 mg / cm 2 ~17mg / cm 2 The surface density of the second positive electrode active material layer is 10.8 mg / cm 2 ~16.9mg / cm 2 .

[0084] The above surface density is calculated by weighing the electrode after coating. The specific test method is to disassemble the battery, take out the positive electrode 10, and sample the single-sided coating area of ​​the positive electrode where only the first surface 19a of the positive electrode 10 has the first paste area 14. The sampled sample is recorded as A, and the sample is a circle with a diameter of 12 mm. Then weigh it as A1. After wiping off all the paste on the surface of the sampled sample A (it can be removed by soaking in an organic solvent or washing, which is not limited here), weigh it as A2. It can be understood that A2 is the weight of the positive electrode collector 12 of the sampled sample A. The surface density of the first positive active material layer 11a = (A1-A2) / circular area; it should be noted that the number of samples can be 1 or greater than or equal to 2, and the sampling positions can be evenly distributed on the electrode, which is not limited here. When the number of samples taken is greater than or equal to 2, the weight should be calculated by calculating the average weight of all sampled samples A. Similarly, when calculating the weight A2 of the positive electrode current collector, the average weight of all positive electrode current collectors should also be taken. The overlapping area of ​​the first paste coating area 14 and the second paste coating area 15 of the positive electrode sheet 10, that is, the position of the double-sided paste coating area of ​​the positive electrode sheet 10, is sampled, and the sampled sample is recorded as B. The sampled samples B are all circular with a diameter of 12 mm, and then weighed as B1. The number of samples B can be 1 or greater than or equal to 2, and the sampling positions can be evenly distributed on the positive electrode sheet 10, which is not limited here. When the number of samples taken is greater than or equal to 2, the method for calculating the weight is as described above and will not be repeated here. The surface density of the second positive electrode active material layer 11b = (B1-A2) / area-surface density of the first positive electrode active material layer 11a. The compaction density is calculated by the surface density and the thickness of the electrode sheet. The thickness of the electrode sheet can be obtained by scanning electron microscopy or micrometer testing. The compacted density is calculated from the surface density and the pole piece thickness.

[0085] In some alternative embodiments, the thickness of the positive active material layer 11 on the first surface 19a of the positive current collector 12 is h1, and the thickness of the positive active material layer 11 on the second surface 19b is h2, at least in the curved portion 101, h1<h2, so as to adjust the N / P ratio of the positive electrode and the negative electrode. Similarly, in addition to such a setting at the curved portion 101, in order to further reduce the difficulty and efficiency of process manufacturing and ensure the process stability of the electrode sheet preparation, the thickness h1 of the positive active material layer 11 on the first surface 19a of the positive current collector 12 can also be made less than the thickness h2 of the positive active material layer 11 on the second surface 19b. If the thickness difference between the two sides of the positive electrode sheet is too large, the internal resistance at different positions of the electrode sheet will be unevenly distributed, the difference will be too large, and local overheating will occur, or the battery will have uneven lithium insertion and extraction on both sides during the cycle, resulting in excessive charge and discharge of the material on one side, resulting in material degradation and peeling, which will affect the safety performance of the battery. Preferably, the difference between h1 and h2 is 0.1μm to 10μm. For example, at least at the bend 101 , the difference between h1 and h2 may be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 7 μm, 9 μm, etc.

[0086] In this way, at least in the curved portion 101, by making the thickness of the first positive electrode active material layer 11a smaller than the thickness of the second positive electrode active material layer 11b, the N / P ratio of the negative electrode to the positive electrode in the region corresponding to the first positive electrode active material layer 11a in the curved portion 101 can be adjusted. Therefore, in the curved portion 101, the N / P ratio of the negative electrode to the positive electrode in the region corresponding to the first positive electrode active material layer 11a is increased, that is, the N / P ratio of the second negative electrode active material layer to the first positive electrode active material layer 11a is increased, that is, the N / P ratio of the inner circle of the positive electrode sheet 10 corresponding to the outer circle of the negative electrode sheet 20 is increased accordingly. In this way, lithium deposition in the outer circle of the negative electrode sheet 20 can be prevented from occurring in the curved portion 101, thereby improving the situation of local lithium deposition in the battery 1000. In this way, the kinetic performance of the negative electrode reaction at this position can be improved, thereby reducing the risk of lithium deposition in the outer circle of the negative electrode sheet 20 in the curved portion 101.

[0087] It is understandable that in some embodiments, according to the needs of specific application scenarios, it can be simultaneously set at least in the curved portion 101, h1 < h2, and the surface density of the first positive electrode active material layer 11a is less than the surface density of the second positive electrode active material layer 11b. In this way, the N / P ratio of the negative electrode and the positive electrode of the curved portion 101 can be more conveniently adjusted through the cooperation of the two, and lithium precipitation can be better avoided. The specific principle is referred to the above embodiment and will not be repeated here.

[0088] As described above, at least in the curved portion 101, the N / P ratio of the second negative electrode active material layer to the first positive electrode active material layer 11a is greater than the N / P ratio of the first negative electrode active material layer to the second positive electrode active material layer 11b, and the difference between the two is 0.005-0.2 (e.g., 0.01, 0.03, 0.05, 0.08, 0.1, 0.13, 0.15 or 0.18, etc.). By setting the N / P ratio of the corresponding positions on both sides of the positive electrode sheet 10 within this range, on the one hand, it can ensure that the N / P ratio of the corresponding position of the first paste coating area 14 of the first surface 19a of the positive electrode sheet 10 is sufficient, which can reduce and avoid the occurrence of lithium deposition in the outer circle of the negative electrode sheet; on the other hand, it is not necessary to increase the N / P ratio of the corresponding position of the second paste coating area 15 of the second surface 19b of the positive electrode sheet 10, which is beneficial to improve the overall energy density, cycle life and safety of the battery 1000.

[0089] Preferably, the difference between the two is 0.02 to 0.08. Within this range, the N / P ratio and the energy density of the battery 1000 as well as the cycle life and safety can be better taken into account.

[0090] The positive electrode active materials in the first pasted area 14 and the second pasted area 15 of the positive electrode sheet 10 may be the same or different. When the positive electrode active materials in the first pasted area 14 and the second pasted area 14 are different, it is necessary to set the kinetic performance of the positive electrode active material in the second pasted area 15 to be better than that in the first pasted area 14, so as to ensure the above-mentioned N / P ratio difference.

[0091] In the curved portion 101, since the first pasted area 14 corresponds to the outer ring of the negative electrode sheet 20, the N / P value is small due to the small curvature of the outer ring of the negative electrode sheet 20, resulting in poor reaction kinetics here. Therefore, it is necessary to use a positive electrode active material with matching kinetics to prevent lithium deposition on the outer ring surface of the negative electrode sheet 20 at the corresponding position of the curved portion 101, while also ensuring the energy density of the battery. When the positive electrode active materials of the first pasted area 14 and the second pasted area 14 are different, the surface density of the positive electrode active material layer 11 of the first pasted area 14 and the second pasted area 15 can be different or the same.

[0092] When the positive electrode active material of the first pasted area 14 and the second pasted area 15 is the same, it is necessary to set the surface density of the positive electrode active material layer 11 of the first pasted area 14 and the second pasted area 15 to be different, so as to compensate for the small curvature of the outer circle of the negative electrode sheet 20, resulting in a small N / P value and poor kinetic performance leading to lithium deposition.

[0093] Preferably, the positive electrode active material in the first pasted area 14 and the second pasted area 15 of the positive electrode sheet 10 is the same, so as to simplify the preparation process.

[0094] In some embodiments, at least at the curved portion 101, the positive electrode active material layer 11 of the first pasted area 14 is provided with holes or a concave texture structure (not shown in the figure), so as to increase the compaction density of the first pasted area 14 through the holes or the concave texture structure, reduce the lithium ion deintercalation ability and speed of the positive electrode material at this position, or reduce the positive electrode active material in the first pasted area 14, thereby increasing the negative electrode and positive electrode N / P ratio at the corresponding position of the first pasted area 14, thereby reducing and avoiding lithium precipitation in the outer circle of the negative electrode sheet 20. In addition, the holes and the concave texture structure can also store electrolyte, which is conducive to the transmission of lithium ions and improves the cycle performance of the battery.

[0095] It is understandable that the pores may be formed by mechanical pore making or laser pore making on the positive electrode active material layer 11 or the positive electrode sheet, or may be formed by adding a pore-forming agent to the positive electrode active material layer 11 during the electrode sheet molding, which is not limited here. Similarly, the concave texture structure may be formed by rolling the positive electrode active material layer 11 with a roller having a concave-convex structure, or may also be formed on the positive electrode sheet, which is not limited in this application.

[0096] Continuing to refer to the figure, at the end of the first paste coating area 14 and / or the second paste coating area 15, that is, at one end of the paste coating area close to the empty foil area, the positive electrode active material layer 11 can be provided with a rounded corner R, a chamfer or a corrugated edge. The positive electrode active material layer 11 is designed with an R angle, a chamfer or a corrugated edge at the end, which can prevent the sharp corners of the sharp positive electrode active material layer 11 from falling off, thereby preventing dust and foreign matter from piercing the diaphragm 30 and contacting the negative electrode to cause a short circuit. At the same time, the positive electrode active material layer 11 at the edge of the positive electrode sheet 10 adopts an R angle, a chamfer or a corrugated edge design, which can also alleviate the stress concentration caused by the thickness difference on both sides of the positive electrode sheet 10, avoid stress concentration on one line, and thus improve the battery expansion during the cycle, resulting in excessive stress on the outside of the winding core and the breakage of the positive electrode sheet.

[0097] Preferably, when fillets are provided at the end of the first positive electrode active material layer 11a and / or the end of the second positive electrode active material layer 11b, the radius of the fillet R is 1 mm to 10 mm (e.g., 1.5 mm, 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, etc.), so as to better avoid powder loss, relieve stress concentration caused by the thickness difference between the two sides of the positive electrode sheet 10, avoid stress concentration on one line, and better improve the fracture of the electrode sheet. More preferably, the radius of the fillet R is 2 mm to 6 mm, so as to better avoid powder loss, relieve stress concentration caused by the thickness difference between the two sides of the positive electrode sheet 10, avoid stress concentration on one line, and further improve the fracture of the electrode sheet.

[0098] Exemplary Battery 1000

[0099] refer to Figure 7 and 8 As shown, the embodiment of the present application further provides a battery 1000. The battery 1000 includes the wound electrode body 100 described above.

[0100] refer to Figure 7 and Figure 8 The battery 1000 may include a wound electrode body 100 and a housing 200. The housing 200 may be provided with a receiving cavity, and one or more wound electrode bodies 100 may be received in the receiving cavity.

[0101] like Figure 7 As shown, the housing 200 may be square, for example. That is, the battery 1000 may be a square battery 1000. The material of the housing 200 may be the same as that used in the past, and there is no particular limitation. For example, the housing 200 may be made of metal, in particular, may be made of aluminum (alloy) or iron (alloy).

[0102] like Figure 8 As shown, illustratively, the housing 200 is flat and made of a relatively soft material, such as an aluminum-plastic film. That is, in this embodiment, the battery 1000 can be a soft-pack battery 1000.

[0103] It is foreseeable that in other examples of the embodiments of the present application, the battery 1000 may also be implemented as other types besides the square battery 1000 and the soft-pack battery 1000 .

[0104] It should be noted that other aspects of the structure of the battery 1000 may be the same as the structure of the conventional battery 1000 , and for the purpose of brevity, this embodiment of the present application will not be described in detail.

[0105] The battery 1000 can be made into a wound electrode body 100 by making the positive electrode sheet 10, the negative electrode sheet 20 and the separator 30 according to a conventional winding structure, and then the battery 1000 is made through packaging, liquid injection, formation, secondary sealing, capacity division and other steps. The electrolyte is a commercially available conventional electrolyte, and this application does not make any special requirements for this.

[0106] The battery 1000 provided according to the embodiment of the present application has the corresponding effects of the above-mentioned wound electrode body 100 , and the details are referred to above and will not be repeated here.

[0107] It should be noted that in the present disclosure, "battery 1000" refers to a power storage device that can be repeatedly charged and discharged, which can be interpreted as the concept of "secondary battery 1000". In the embodiment of the present application, the concept of "secondary battery 1000" can include lithium-ion secondary battery 1000 and the like.

[0108] It should be understood that the term "including" and its variations used in the embodiments of the present application are open inclusions, i.e., "including but not limited to". The term "according to" means "at least in part according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "plurality" means "more than one", which is intended to cover two, three or more situations.

[0109] It should be understood that although the terms "first" or "second" etc. may be used in the embodiments of the present application to describe various elements, for example, the first positive electrode active material layer and the second positive electrode active material layer, these elements are not defined by these terms, which are only used to distinguish one element from another.

[0110] The protection scope of the embodiments of the present application is not limited to the above embodiments. Any changes or substitutions that can be imagined by any technician familiar with the technical field within the technical scope disclosed in the embodiments of the present application should be included in the protection scope of the embodiments of the present application. Therefore, the protection scope of the embodiments of the present application should be based on the protection scope of the claims.

[0111] The present application is described in detail below in conjunction with specific embodiments, which are used to understand rather than limit the present application.

[0112] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources. The processing procedures and techniques involved are conventional technical means unless otherwise specified.

[0113] Example 1

[0114] Preparation of negative electrode sheet 20: Disperse negative electrode active substance (i.e., negative electrode active material), sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black in a solvent of deionized water (or water) in a mass percentage of 93:2.5:1.5:3, and mix them evenly to obtain slurry. The prepared negative electrode slurry is evenly coated on a copper foil, dried at 100°C, and rolled and cut to obtain a negative electrode sheet 20. The negative electrode active material is graphite. The thickness of the negative electrode active layer is 27 μm.

[0115] Preparation of positive electrode sheet 10: Mix the positive electrode active material lithium nickel cobalt manganese oxide (NCM), the binder polyvinylidene fluoride, and the conductive agent carbon black in a mass percentage ratio of 97:2:1, add an appropriate amount of N-methylpyrrolidone as a solvent, stir evenly, and form a uniformly dispersed electrode slurry with a solid content of 65wt%. The prepared positive electrode slurry is evenly coated on aluminum foil, and rolled and cut to form a positive electrode sheet 10. The surface density of the positive electrode active material layer 11 on the first surface 19a of the aluminum foil is 15.9mg / cm 2The surface density of the first positive electrode active material layer 11a is 96% of the surface density of the second positive electrode active material layer 11b, which is 16.6 mg / cm 2 , the surface density is controlled by controlling the rolling pressure. The thickness of the first positive electrode active material layer 11a is 70μm, the thickness of the second positive electrode active material layer 11b is 73μm, and the N / P ratio of the negative electrode and the positive electrode at the corresponding position of the first paste coating area 14 is 0.04 greater than the N / P ratio of the negative electrode and the positive electrode at the corresponding position of the second paste coating area 15, that is, the N / P ratio of the second negative electrode active material layer 21b to the first positive electrode active material layer 11a is greater than the N / P ratio of the first negative electrode active material layer 21a to the second positive electrode active material layer 11b by 0.04. The length of the first positive electrode active material layer 11a is greater than the length of the second positive electrode active material layer 11b.

[0116] The distances d1 and d2 between the stop glue 18 and the positive electrode active material layer 11 are 1 mm. The fillet R of the positive electrode active material layer 11 at the end of the first paste coating area 14 and the second paste coating area 15 is R4 mm.

[0117] Then, according to the conventional winding structure, the positive electrode sheet 10, the negative electrode sheet 20 and the separator 30 are made into a wound battery 1000, and then the battery 1000 is made through the steps of packaging, liquid injection, formation, secondary sealing, and capacity division. Here, the electrolyte is a conventional commercially available electrolyte.

[0118] Example 2

[0119] This embodiment is carried out with reference to Embodiment 1, except that the surface density of the first positive electrode active material layer is 95% of the surface density of the second positive electrode active material layer, which is 15.77 mg / cm2, the thickness of the first positive electrode active material layer is 70 μm, the thickness of the second positive electrode active material layer is 73.7 μm, and the N / P ratio of the second negative electrode active material layer 21b to the first positive electrode active material layer 11a is greater than the N / P ratio of the first negative electrode active material layer 21a to the second positive electrode active material layer 11b, which is 0.05.

[0120] Example 3

[0121] This embodiment is carried out in accordance with the embodiment 1, except that the surface density of the first positive electrode active material layer is 93% of the surface density of the second positive electrode active material layer, which is 15.44 mg / cm 2 The thickness of the first positive electrode active material layer 11a is 70 μm, the thickness of the second positive electrode active material layer 11b is 75.2 μm, and the N / P ratio of the second negative electrode active material layer 21b to the first positive electrode active material layer 11a is greater than the N / P ratio of the first negative electrode active material layer 21a to the second positive electrode active material layer 11b of 0.07.

[0122] Example 4 Group

[0123] This group of embodiments is used to illustrate the influence of changes in d1 and d2.

[0124] Example 4a

[0125] This embodiment is carried out with reference to the embodiment 1, except that d1 is 0.1 mm.

[0126] Example 4b

[0127] This embodiment is carried out with reference to the embodiment 1, except that d1 is 4.1 mm.

[0128] Example 4c

[0129] This embodiment is carried out in accordance with the embodiment 1, except that the surface density of the first positive electrode active material layer 11a and the second positive electrode active material layer is 16.6 mg / cm 2 The thickness of the first positive electrode active material layer 11a and the second positive electrode active material layer is 70 μm respectively, and the N / P ratio of the second negative electrode active material layer 21b to the first positive electrode active material layer 11a is the same as the N / P ratio of the first negative electrode active material layer 21a to the second positive electrode active material layer 11b. The second stopper 18b covers the second positive electrode active material layer 11b.

[0130] Example 5 Group

[0131] This group of embodiments is used to illustrate the influence caused by the change in the relative proportion between the surface density of the positive electrode active material layer 11 on the first surface 19 a of the positive electrode current collector 12 and the surface density of the positive electrode active material layer 11 on the second surface 19 b.

[0132] Example 5a

[0133] This embodiment is carried out with reference to the embodiment 1, except that the surface density of the positive active material layer 11 on the first surface 19a of the positive current collector 12 is 87.8% of the surface density of the positive active material layer 11 on the second surface 19b, which is 14.57 mg / cm 2 The thickness of the first positive electrode active material layer 11a is 70 μm, the thickness of the second positive electrode active material layer 11b is 79.7 μm, and the N / P ratio of the second negative electrode active material layer 21b to the first positive electrode active material layer 11a is greater than the N / P ratio of the first negative electrode active material layer 21a to the second positive electrode active material layer 11b of 0.14.

[0134] Example 5b

[0135] This embodiment is carried out with reference to the embodiment 1, except that the surface density of the positive active material layer 11 on the first surface 19a of the positive current collector 12 is 99.6% of the surface density of the positive active material layer 11 on the second surface 19b, which is 16.53 mg / cm 2The thickness of the first positive electrode active material layer 11a is 70 μm, the thickness of the second positive electrode active material layer 11b is 70.3 μm, and the N / P ratio of the second negative electrode active material layer 21b to the first positive electrode active material layer 11a is greater than the N / P ratio of the first negative electrode active material layer 21a to the second positive electrode active material layer 11b of 0.004.

[0136] Example 5c

[0137] This embodiment is carried out with reference to the embodiment 1, except that the surface density of the positive active material layer 11 on the first surface 19a of the positive current collector 12 is 97.3% of the surface density of the positive active material layer 11 on the second surface 19b, which is 16.15 mg / cm 2 The thickness of the first positive electrode active material layer 11a is 70 μm, the thickness of the second positive electrode active material layer 11b is 71.9 μm, and the N / P ratio of the second negative electrode active material layer 21b to the first positive electrode active material layer 11a is greater than the N / P ratio of the first negative electrode active material layer 21a to the second positive electrode active material layer 11b of 0.027.

[0138] Example 6

[0139] This embodiment is carried out with reference to the embodiment 1, except that no rounded corners are provided at the ends of the first paste coating area and the second paste coating area.

[0140] Example 7

[0141] This embodiment is carried out with reference to the embodiment 1, except that the first positive electrode active material layer and the second positive electrode active material layer adopt a wavy tail design, such as Figure 6 shown.

[0142] Example 8

[0143] This embodiment is carried out with reference to the embodiment 1, except that the ratio of the positive electrode active material is lithium cobalt oxide, conductive carbon black (Super P, SP) and polyvinylidene fluoride (PVDF) mixed in a mass percentage of 97.6:1.4:1, and the weight of Li2NiO2 accounts for 1% of the weight of lithium cobalt oxide.

[0144] Comparative Example 1

[0145] The first stop glue 18 a covers the first positive electrode active material layer 11 a , and the second stop glue 18 b covers the second positive electrode active material layer 11 b .

[0146] Material performance testing

[0147] Energy density: The batteries prepared in Comparative Example 1 and Example were calibrated at 0.5C / 0.5C capacity and weighed to calculate the weight energy density.

[0148] Battery performance test: After calculating the energy density, charge at a constant current of 2C rate at 25℃±3℃, with a cut-off current of 0.05C rate, and then discharge at a constant current of 4C rate. The voltage range is 2.0V~4.3V. This is one charge and discharge cycle. For each comparative example and embodiment, 30 cells are tested, and the capacity retention rate of the cell after 300 cycles (i.e., 300 heavy discharge cycles) is recorded (the average value of 30 cells is taken).

[0149] Battery abnormality test: After calculating the energy density, charge at a constant current rate of 2C at 25℃±3℃, cut-off current of 0.05C, and then discharge at a constant current rate of 4C, with a voltage range of 2.0V to 4.3V. This is one charge and discharge cycle. Take 30 cells for each comparative example and embodiment for testing. Disassemble the cells after the cycle to confirm whether lithium deposition and fracture occur. If one of them has lithium deposition and fracture, it is considered that lithium deposition and fracture occur. The data is shown in Table 1.

[0150] Determination of the degree of lithium deposition: No lithium deposition: After 300 cycles and disassembly, the surface of the negative electrode sheet is golden yellow; Slight lithium deposition: Gray-black areas appear locally on the surface of the negative electrode sheet, and the ratio of the lithium deposition area of ​​the fully charged negative electrode sheet (gray-black area) to the area of ​​the negative electrode sheet is ≤15%; Lithium deposition: Gray-black areas appear locally on the surface of the negative electrode sheet, and the ratio of the lithium deposition area of ​​the fully charged negative electrode to the area of ​​the negative electrode sheet is greater than 15% and less than 30%; Severe lithium deposition: Gray-black areas appear locally on the surface of the negative electrode sheet, and the ratio of the lithium deposition area of ​​the fully charged negative electrode to the area of ​​the negative electrode sheet is >30%.

[0151] Table 1

[0152]

[0153]

[0154] From the above data, it can be seen that the glue sticking method of the cover paste tape at the end of the positive electrode paste coating of the wound battery is changed to sticking on the empty foil, and the interval with the paste is 0 to 3mm, which can significantly improve the lithium deposition problem on the edge of the tape caused by the end tape. In addition, the different N / P ratio active materials set in the paste coating area on the first surface of the positive electrode and the paste coating area on the second surface significantly improve the lithium deposition problem of the outer circle of the negative electrode caused by the inconsistent curvature of the inner and outer ring pole pieces of the wound battery cell, and also improve the energy density of the battery by 3Wh / kg to 4Wh / kg, which has a good improvement effect. In addition, the R angle design is adopted at the end of the pole piece, which can significantly reduce the problem of pole piece breakage caused by expansion in the later stage of the pole piece cycle.

Claims

1. A wound electrode body, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a separator which are stacked, wherein the positive electrode sheet and the negative electrode sheet are wound with the separator interposed therebetween to form the wound electrode body having a flat portion and a curved portion; wherein, The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, along a first direction Z, the positive electrode collector has a first surface and a second surface arranged opposite to each other, along a second direction X perpendicular to the first direction Z, a first paste coating area and a first empty foil area located at the tail of the first surface and adjacent to the first paste coating area are arranged on the first surface, a second paste coating area is arranged on the second surface, the first paste coating area is arranged with the first positive electrode active material layer, the second paste coating area is arranged with the second positive electrode active material layer, a first termination glue is arranged on at least part of the first empty foil area, and the distance between the side of the first termination glue close to the first paste coating area and the edge of the first paste coating area close to the first termination glue is d1, and d1≥0.

2. The wound electrode body according to claim 1, characterized in that: Along the second direction X, a second empty foil area is also provided on the second surface, located at the tail of the second surface and adjacent to the second paste coating area, and a second termination glue is provided on at least part of the second empty foil area, and the distance between the side of the second termination glue close to the second paste coating area and the edge of the second paste coating area is d2, and d2≥0.

3. The wound electrode body according to claim 2, characterized in that: The value range of d1 and d2 is 0 mm to 3 mm; preferably The value range of d1 and d2 is 0.5 mm to 1.5 mm.

4. The wound electrode body according to claim 1, characterized in that: The first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center. At least in the bending portion, the surface density of the first positive electrode active material layer is less than the surface density of the second positive electrode active material layer. Preferably, At least in the bent portion, the surface density of the first positive electrode active material layer is 90% to 99% of the surface density of the second positive electrode active material layer; more preferably, At least in the bent portion, the surface density of the first positive electrode active material layer is 94% to 97% of the surface density of the second positive electrode active material layer.

5. The wound electrode body according to claim 1, characterized in that: The first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center. At least in the bending portion, the thickness of the first positive electrode active material layer is less than the thickness of the second positive electrode active material layer. The difference between the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer is 0.1 μm to 10 μm.

6. The wound electrode body according to claim 1, characterized in that: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer. Along the first direction Z, the negative electrode current collector has a third surface and a fourth surface arranged opposite to each other, the third surface faces the winding center, and the fourth surface faces away from the winding center. The negative electrode active material layer comprises a first negative electrode active material layer and a second negative electrode active material layer respectively arranged on the third surface and the fourth surface. At least in the bending portion, the N / P ratio of the second negative electrode active material layer to the first positive electrode active material layer is greater than the N / P ratio of the first negative electrode active material layer to the second positive electrode active material layer, and the difference between the two is 0.005 to 0.2; Preferably, the difference between the two is 0.02 to 0.08; wherein, The N / P ratio is the negative electrode capacity per unit area / positive electrode capacity per unit area.

7. The wound electrode body according to claim 2, characterized in that: The end of the first positive electrode active layer close to the first termination glue is provided with a rounded corner, a chamfered corner or a corrugated edge; and / or, the end of the second positive electrode active layer close to the second termination glue is provided with a rounded corner, a chamfered corner or a corrugated edge; Preferably, when the rounded corner is provided at the end of the first positive electrode active material layer close to the first empty foil area and / or the end of the second positive electrode active material layer close to the second empty foil area, the radius of the rounded corner is 1 mm to 10 mm; more preferably, the radius of the rounded corner is 2 mm to 6 mm.

8. The wound electrode body according to claim 2, characterized in that: The thickness of the single side of the positive electrode active material layer on the positive electrode sheet is 30 μm to 120 μm, and the thickness of the first termination glue and the second termination glue are 15 μm to 30 μm respectively; Preferably, the single-sided thickness of the positive electrode active material layer on the positive electrode sheet is 30 μm to 100 μm, and the thicknesses of the first termination glue and the second termination glue are 20 μm to 25 μm, respectively.

9. The wound electrode body according to claim 1, characterized in that: The first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center. At least at the bending portion, the first positive electrode active material layer is provided with holes or a concave texture structure.

10. The wound electrode body according to claim 1, characterized in that: The first positive electrode active material layer and the second positive electrode active material layer have the same positive electrode active material; or The first positive electrode active material layer and the second positive electrode active material layer have different positive electrode active materials.

11. The wound electrode body according to claim 1, characterized in that: The first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center; the positive electrode active material in the first positive electrode active material layer and the second positive electrode active material layer are different; the kinetic performance of the positive electrode active material in the second positive electrode active material layer is better than the kinetic performance of the positive electrode active material in the first positive electrode active material layer, and / or, The first positive electrode active material layer and the second positive electrode active material layer have the same thickness.

12. A battery, characterized in that: The invention comprises the wound electrode body according to any one of claims 1 to 11.

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