Electrode assembly and battery having the same

Abstract

The utility model provides an electrode assembly and a battery having the same. The electrode assembly comprises a first pole piece, a diaphragm and a second pole piece, the first pole piece, the diaphragm and the second pole piece are stacked and wound to form the electrode assembly, the first pole piece comprises a current collector, a first active material layer and a second active material layer, and the current collector is provided with a first surface and a second surface which are opposite to each other; the first surface comprises a covering area and an empty current collector area which are sequentially arranged along the winding direction of the first pole piece, the first active material layer is arranged on the covering area of the first surface, and the second active material layer is arranged on the second surface and exceeds the first active material layer along the winding direction; the first active material layer comprises a main body part and a buffer part which are sequentially arranged along the winding direction, and the thickness of the buffer part is gradually reduced along the direction of the empty current collector region. According to the electrode assembly and the battery provided by the invention, the risk of capacity loss can be effectively reduced.

Description

Technical Field

[0001] The present disclosure relates to the field of batteries, and in particular, to an electrode assembly and a battery having the same. Background Art

[0002] Some batteries include a flat, wound electrode assembly (also called a jellyroll). In terms of shape, the flat electrode assembly includes a pair of curved portions and a flat portion extending between them. However, such batteries may suffer from capacity loss. Utility Model Content

[0003] In view of this, the present disclosure provides an electrode assembly and a battery having the same to reduce the risk of capacity loss.

[0004] On the one hand, the present disclosure provides an electrode assembly. The electrode assembly includes a first pole piece, a diaphragm, and a second pole piece, and the first pole piece, the diaphragm, and the second pole piece are stacked and wound to form an electrode assembly. The first pole piece includes a current collector, a first active material layer, and a second active material layer. The current collector has a first surface and a second surface relative to each other. The first surface includes a covering area and an empty current collector area. The covering area and the empty current collector area are arranged in sequence along the winding direction of the first pole piece. The first active material layer is arranged in the covering area of ​​the first surface, and the second active material layer is arranged on the second surface. The second active material layer exceeds the first active material layer along the winding direction. The first active material layer includes a main body and a buffer part. The main body and the buffer part are arranged in sequence along the winding direction. The thickness of the buffer part decreases along the direction of the empty current collector area.

[0005] Additionally or alternatively, the buffer portion includes a plurality of steps having a plurality of first step surfaces parallel to the first surface, the plurality of first step surfaces are arranged along the winding direction, and the distances from the plurality of first step surfaces to the first surface decrease sequentially along the winding direction.

[0006] In addition or alternatively, any two adjacent step surfaces contain a second step surface perpendicular to the two first step surfaces. The second step surface forms a convex angle with one of the two first step surfaces and a concave angle with the other. At least one of the convex angle and the concave angle is provided with a chamfered right angle or a rounded angle.

[0007] In addition or alternatively, the buffer portion satisfies: L1 = 3 mm to 30 mm; and / or T1 = T2; and / or N ≥ 3; and / or W = L1 / N ± 5 mm; and / or H = T2 / N ± 10 μm. Here, L1 is the length of the buffer portion, T1 is the maximum thickness of the buffer portion, T2 is the thickness of the main body, N is the number of the plurality of first step surfaces, W is the width of any step surface, and H is the distance between any two adjacent step surfaces.

[0008] Additionally or alternatively, the buffer portion has a buffer slope, and the distance from the buffer slope to the first surface gradually decreases as it approaches the empty current collector region.

[0009] Additionally or alternatively, the buffer slope surface is an inclined plane inclined relative to the first surface.

[0010] Additionally or alternatively, the buffer portion satisfies: L1=3 mm to 30 mm; and / or T1=T2; and / or α=25° to 60°. Here, L1 is the length of the buffer portion, T1 is the maximum thickness of the buffer portion, T2 is the thickness of the main body, and α is the angle between the inclined plane and the first surface.

[0011] Additionally or alternatively, the buffer slope surface is a smooth curved surface.

[0012] Additionally or alternatively, the angle between the tangent plane of the smooth curved surface and the first surface gradually increases as it approaches the empty current collector region.

[0013] Additionally or alternatively, the buffer portion satisfies: L1 = 2 mm to 20 mm; and / or T1 = T2. Here, L1 is the length of the buffer portion, T1 is the maximum thickness of the buffer portion, and T2 is the thickness of the main body portion.

[0014] Additionally or alternatively, the electrode assembly has a width B and a thickness C, and the ratio B / C of the width B to the thickness C satisfies 1.1≤A / B≤200. The electrode assembly includes a first bend, a second bend and a flat portion, and the flat portion extends between the first bend and the second bend. The first pole piece extends sequentially along the winding direction through the first position of the flat portion and the second position of the first bend. The buffer portion has a connecting end connected to the empty current collector area, and the connecting end is located between the first position and the second position, the first position is located at the flat portion, and the second position is located at the first bend. The first position satisfies D1≤10mm, and the second position satisfies D2 / D3≤1 / 2. Here, D1 is the distance from the first position to the boundary line of the flat portion and the first bend in the width direction of the electrode assembly, D2 is the distance from the second position to the boundary line of the flat portion and the first bend in the width direction, and D3 is the size of the first bend in the width direction.

[0015] Additionally or alternatively, the abutment end is located between the boundary line and the second position.

[0016] Additionally or alternatively, the first surface is located on a side of the current collector away from the winding center of the electrode assembly, and the tail end of the first pole sheet exceeds the tail end of the second pole sheet and the tail end of the separator along the winding direction.

[0017] Additionally or alternatively, the electrode assembly has a width B and a thickness C, and a ratio B / C of the width B to the thickness C satisfies 1.1≤A / B≤200. The electrode assembly includes a first curved portion, a second curved portion, and a flat portion, and the flat portion is located between the first curved portion and the second curved portion. The first pole piece extends from the buffer portion, along the winding direction, and ends at the flat portion, and the buffer portion is located at the fourth flat area of ​​the first pole piece from the end.

[0018] Additionally or alternatively, the first electrode is a positive electrode.

[0019] In another aspect, the present disclosure provides a battery, which includes the electrode assembly according to the above aspect.

[0020] According to the electrode assembly and battery provided by the present disclosure, in the rolling process, when the boundary line from the double-layer segment to the single-layer segment of the first pole piece passes through the pressing roller, the buffer portion with the above structure will help the boundary line to pass through the pressing roller smoothly, preventing the pressing roller from jumping, thereby helping to prevent the current collector near the boundary line from being hit by the pressing roller and causing microcracks. Since the microcracks are eliminated or reduced, the risk of the first pole piece breaking will be significantly reduced, thereby reducing the risk of battery capacity loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of a battery according to an embodiment of the present disclosure.

[0022] Figure 2 Schematic diagram of the structure of a battery according to another embodiment of the present disclosure.

[0023] Figure 3 Schematic diagram of the structure of an electrode assembly according to an embodiment of the disclosure.

[0024] Figure 4 For along Figure 3 Schematic diagram of the cross-section taken along line BB.

[0025] Figure 5 for Figure 3 A partial schematic diagram of the lower left part of .

[0026] Figure 6 for Figure 4 Schematic diagram of the local structure of the first pole piece.

[0027] Figure 7 for Figure 6 Schematic diagram of the structure when the first pole piece passes through the pressure roller.

[0028] Figure 8 for Figure 6 Schematic diagram of the structure of the buffer part.

[0029] Fig. 9Schematic diagram of the partial structure of a buffer portion according to another embodiment of the present disclosure.

[0030] Fig.10 Schematic diagram of the partial structure of a buffer portion according to another embodiment of the present disclosure.

[0031] Fig.11 It is a schematic diagram of the partial structure of the first pole piece according to another embodiment of the present disclosure.

[0032] Fig.12 It is a schematic diagram of the partial structure of the first pole piece according to another embodiment of the present disclosure.

[0033] Fig.13 is a schematic cross-sectional view of an electrode assembly according to the related art.

[0034] Fig.14 for Fig.13 Schematic diagram of the local structure of the first pole piece.

[0035] Fig.15 for Fig.14 Schematic diagram of the structure when the first pole piece passes through the pressure roller. DETAILED DESCRIPTION

[0036] It is known that some batteries have electrode assemblies that are wound into a flat structure. However, such batteries have the problem of capacity loss, especially after a certain number of cycles. This problem has troubled technicians in the relevant field. Figures 13 to 15 , an electrode assembly 10 with a flat structure provided by the related art and the problems existing therein are illustrated.

[0037] refer to Fig.13 In terms of shape, the electrode assembly 10 has a flat structure, which includes a first curved portion 11 a, a second curved portion 11 b, and a flat portion 12, wherein the flat portion 12 is located between the first curved portion 11 a and the second curved portion 11 b.

[0038] Still refer to Fig.13 From the perspective of composition, the electrode assembly 10 may include a first electrode sheet 13, a second electrode sheet 14 and a separator 15 arranged in a stacked manner. The first electrode sheet 13 and the second electrode sheet 14 may be wound into the above-mentioned flat structure via the separator 15.

[0039] The first electrode sheet 13 and the second electrode sheet 14 are electrodes with opposite polarities. For example, the first electrode sheet 13 may be a positive electrode sheet, and the second electrode sheet 14 may be a negative electrode sheet. Regardless of whether it is the first electrode sheet 13 or the second electrode sheet 14, each electrode sheet may include a current collector and an active material layer.

[0040] For example, still refer to Fig.13The first electrode sheet 13 may include a current collector 16, a first active material layer 17 and a second active material layer 18. Fig.13 and Fig.14 , the current collector 16 may have a first surface 161 and a second surface 162. The first active material layer 17 may be disposed on the first surface 161, and the second active material layer 18 may be disposed on the second surface 162. For example, the first surface 161 may be located on the side of the current collector 16 away from the winding center A of the electrode assembly 10, and the second surface 162 may be located on the side of the current collector 16 opposite to the first surface 161, that is, the second surface 162 is located on the side of the current collector 16 close to the winding center A.

[0041] It should be noted that in the present disclosure, the winding center of the electrode assembly may refer to the winding axis of the electrode assembly. It is understood that in the winding process, the first electrode sheet, the second electrode sheet and the separator are wound around the winding axis into the above-mentioned flat structure.

[0042] Continue to refer Fig.13 and Fig.14 , the first surface 161 may include a covering area 163 and an empty current collector area 164. Along the winding direction of the first pole piece 13, the covering area 163 and the empty current collector area 164 are arranged in sequence. In other words, the empty current collector area 164 is closer to the tail end 13b of the first pole piece 13 than the covering area. The first active material layer 17 is provided in the covering area 163, while the empty current collector area 164 is not provided with an active material layer. Along the winding direction, the second active material layer 18 exceeds the first active material layer 17.

[0043] It can be understood that the first pole piece has a starting end and a tail end. In the winding process, the first pole piece is wound from the starting end to the tail end. In this article, the winding direction of the first pole piece refers to the direction from the starting end of the first pole piece to its tail end. For ease of understanding, the winding direction is indicated by an arrow X in the figure.

[0044] It can be understood that when the first electrode sheet is unfolded, the winding direction of the first electrode sheet is consistent with the length direction of the first electrode sheet. In other words, when the first electrode sheet is unfolded, the direction from the starting end to the ending end of the first electrode sheet is the length direction of the first electrode sheet. Therefore, in the view of the first electrode sheet being unfolded, for example, Figures 6 to 12 In FIGS. 13 and 15 , arrow X also indicates the length direction of the first pole piece.

[0045] Back to Fig.13 and Fig.14Due to the existence of the empty current collector area 164, along the winding direction, the first pole piece 13 will have a double-layer segment (a portion having both the first active material layer 17 and the second active material layer 18) and a single-layer segment (a portion having only the second active material layer 18). The first active material layer 17 ends at the boundary line (also called the boundary) B1 between the double-layer segment and the single-layer segment. The boundary line B1 is also the boundary line between the cover area 163 and the empty current collector area 164.

[0046] As mentioned above, the battery with a flat electrode assembly has a capacity loss phenomenon. The inventors have found that for the battery with capacity loss phenomenon, the first pole piece 13 has a fracture phenomenon near the boundary line B1 between the single-layer segment and the double-layer segment. The occurrence of the fracture phenomenon reduces the effective length of the first pole piece 13, thereby causing the battery capacity loss.

[0047] The inventors further discovered that the structure of the first pole piece 13 at the boundary line B1 and the position of the boundary line B1 in the electrode assembly 100 are the main reasons for the fracture of the first pole piece 13. The main reasons for the fracture are described below with examples.

[0048] For some purposes, for example, to increase the bonding strength between the active material layer and the current collector, a rolling process is required to compact the active material layer. Fig.13 and Fig.14 Since the first active material layer 163 ends at the boundary line B1, the first electrode sheet 13 has a sharp change in thickness at the boundary line B1. Fig.15 When the boundary line B1 passes through a pair of rollers, the rollers will jump due to the rapid change in thickness and then hit the first pole piece 13. This will damage the current collector 16 and form microcracks on it.

[0049] After winding is completed, Fig.13 As shown, the boundary line B1 is located at the outer winding layer of the battery cell assembly 10. By way of example only, along the winding direction, from the boundary line B1, the first pole piece 13 sequentially extends through the bend 11a and the bend 11b, and then bends the bend 11a again, and then ends at the flat portion 12.

[0050] For some reasons, such as to obtain a higher energy density, the boundary line B1 is usually located in the flat portion 12 and close to the boundary line B2 between the flat portion 12 and the curved portion 11a along the width direction of the electrode assembly 10. For ease of understanding, the boundary line B2 is located at Fig.13 It is shown by a dot-dash line in the figure, which extends along the thickness direction of the electrode assembly 10.

[0051] For the convenience of explanation, the present disclosure mentions the "width direction" and "thickness direction" of the electrode assembly, and the "length direction" of the electrode assembly will also be mentioned below. Here, the "width direction" refers to the direction from one bend to another bend, indicated by arrow U in the figure; the "thickness direction" refers to the direction perpendicular to the "width direction", indicated by arrow V in the figure; the "length direction" refers to the direction parallel to the winding axis A, which is perpendicular to its "width direction" and "thickness direction", indicated by arrow R in the figure.

[0052] The wound electrode assembly 10 usually needs to undergo a formation process. During the formation process, the electrode assembly 10 needs to withstand a large pressure in its thickness direction. For example, the pressure can be provided by two pressure plates located on opposite sides of its thickness direction. During the process of the electrode assembly 10 bearing pressure, the pressure at the junction line B2 is large due to the structural characteristics of the flat electrode assembly 10, which causes the first pole piece 13 to be subjected to a large pressure at the junction line B1, which will cause the microcracks to expand.

[0053] Furthermore, according to the structural characteristics of the flat electrode assembly 100, in the outer winding layer, the closer the first pole piece 13 is to the boundary line B2, the more uneven the force is, and the expansion force from the inside to the outside is large, and the restraining force from the outside to the inside is small. This will cause the first pole piece 13 to have a more serious uneven force at the boundary line B1. Due to the more serious uneven force, the expansion of the electrode assembly 10 during the cycle will cause the microcracks to expand further, and eventually cause the first pole piece 13 to break, resulting in battery capacity loss.

[0054] In order to solve the above problems in the related art, the present disclosure provides an electrode assembly and a battery having the same. Figures 4 to 12 , the publicly provided embodiments are described.

[0055] It should be understood that the present disclosure may be implemented in many ways and should not be construed as being limited to the embodiments described herein. The embodiments described herein are merely for a more thorough and clear understanding of the present disclosure.

[0056] <Exemplary Battery>

[0057] First, it should be noted that in this disclosure, "battery" refers to a storage device that can be repeatedly charged and discharged, which can be interpreted as the concept of "secondary battery". In this disclosure, the concept of "secondary battery" can include, but is not limited to, lithium-ion secondary batteries, sodium-ion secondary batteries, and nickel-hydrogen batteries.

[0058] According to an embodiment of the present disclosure, a battery 100 is Figure 1 Reference Figure 1The battery 100 may include an electrode assembly 20 and a packaging body 30. The packaging body 30 may be provided with a cavity, and one or more electrode assemblies 20 may be accommodated in the cavity.

[0059] like Figure 1 As shown, the package 30 may be square. That is, the battery 100 may be a square battery. The material of the package 30 may be the same as that used in the past, and there is no particular limitation. For example, the package 30 may be made of metal, in particular, may be made of aluminum (alloy) or iron (alloy).

[0060] According to another embodiment of the present disclosure, a battery 100 is Figure 2 As shown in Figure 2 As shown, in this embodiment, the packaging body 30 is flat and made of a relatively soft material, such as an aluminum-plastic film. That is, in this embodiment, the battery 100 can be a soft-pack battery.

[0061] It is contemplated that in other examples of the present disclosure, the battery 100 may also be implemented as other types besides a square battery and a soft pack battery.

[0062] It should be noted that other aspects of the structure of the battery 100 may be the same as the previous battery structure, and for the purpose of brevity, this disclosure will not elaborate on this.

[0063] <Exemplary Electrode Assembly>

[0064] refer to Figure 3 and Figure 4 The electrode assembly 30 may include a first electrode sheet 23, a second electrode sheet 24, and a separator 25 arranged in a stacked manner. The first electrode sheet 23 and the second electrode sheet 24 have opposite polarities. For example, the first electrode sheet 23 may be a positive electrode sheet, and the second electrode sheet 24 may be a negative electrode sheet.

[0065] The first pole piece 23, the second pole piece 24 and the diaphragm 25 can be wound into a flat structure with the winding axis A as the winding center. In this article, flat means that the width is greater than the thickness. For example, the ratio B / C of the width B and the thickness C of the electrode assembly 30 can satisfy 1.1≤A / B≤200. The electrode assembly 30 may include a first curved portion 21a, a second curved portion 21b and a flat portion 22, and the flat portion 22 is located between the first curved portion 21a and the second curved portion 21b.

[0066] The first pole piece 23 may include a current collector 26, a first active material layer 27, and a second active material layer 28. The first active material layer 27 and the second active material layer 28 may be disposed on opposite sides of the current collector 26. Similarly, the second pole piece 24 may also include a current collector and two active material layers disposed on opposite sides thereof.

[0067] By way of example only, in the case where the first electrode sheet 23 is a positive electrode sheet, the current collector 26 may be a strip of metal foil, the first active material layer 27 and the second active material layer 28 may contain positive electrode active materials that can reversibly absorb and release charge carriers, and in addition, they may further include conductive materials, adhesives, and various additives.

[0068] By way of example only, the metal foil mentioned here may be aluminum foil, the positive electrode active material mentioned may be lithium transition metal composite oxides such as lithium nickel cobalt manganese composite oxide, the conductive material mentioned may be carbon materials such as acetylene black, and the adhesive mentioned may be polyvinylidene fluoride, etc.

[0069] By way of example only, when the second electrode sheet 24 is a negative electrode sheet, the current collector of the second electrode sheet 24 can be a strip of metal foil, and its active material layer can include a negative electrode active material that can reversibly absorb and release charge carriers, a binder, a dispersant, and various additives.

[0070] By way of example only, the metal foil mentioned here may be copper foil, the negative electrode active material mentioned may be carbon materials such as graphite, the binder mentioned may be rubbers such as styrene-butadiene rubber, and the dispersant mentioned may be celluloses such as carboxymethyl cellulose.

[0071] The separator 25 is a member that insulates the first pole piece 23 from the second pole piece 24. As some examples, the separator 25 may be a porous belt made of a polyolefin resin such as polyethylene or polypropylene. Of course, it is also possible to foresee that the separator 25 may be made of other materials.

[0072] refer to Figure 4 and Figure 6 , the current collector 26 may have a first surface 261 and a second surface 262 relative to each other. That is, the first surface 261 is located on the side of the current collector 26 away from the winding center A, and the second surface 262 is located on the side of the current collector 26 close to the winding center A. The first surface 261 may have a covering area 263 and an empty current collector area 264. Along the winding direction, the covering area 263 and the empty current collector area 264 may be arranged in sequence. That is, the empty current collector area 264 may be closer to the tail end 23b of the first pole piece 23 than the covering area 263. The first active material layer 27 is provided on the first surface 261 and is provided in the covering area 163. The second active material layer 28 may be provided on the second surface 262.

[0073] The empty current collector area 264 is a portion of the first surface 261 where the first active material layer 27 is not provided. It should be noted that although the empty current collector area 264 is not provided with the first active material layer 27, it does not mean that the current collector 62 is directly exposed in the empty current collector area 264.

[0074] Continue to refer Figure 4 and Figure 6 , along the winding direction, the second active material layer 28 exceeds the first active material layer 27, so that the first pole piece 23 has a double-layer segment and a single-layer segment arranged in sequence along the winding direction. Here, the double-layer segment refers to the portion of the first pole piece 23 provided with the first active material layer 27 and the second active material layer 28, and the single-layer segment refers to the portion of the first pole piece 23 provided with only the second active material layer 28. The boundary line B1 between the double-layer segment and the single-layer segment is also the boundary line between the cover area 263 and the empty current collector area 264.

[0075] Continue to refer Figure 4 and Figure 6 , the first active material layer 27 may include a main body 271 and a buffer 272. The main body 271 and the buffer 272 are arranged in sequence along the winding direction. That is, along the winding direction, one end of the buffer 272 is connected to the main body 271, and the other end is connected to the empty current collector area 264. The thickness of the buffer 272 decreases as it approaches the empty current collector area 264, that is, the thickness of the buffer decreases along the direction of the empty current collector area 264.

[0076] refer to Figure 7 In the rolling process, when the boundary line B1 of the first pole piece 23 from the double-layer section to the single-layer section passes through the pressing roller, the buffer portion 272 with the above structure will help the boundary line B1 to pass through the pressing roller smoothly, preventing the pressing roller from jumping, thereby helping to prevent the current collector 26 near the boundary line B1 from being hit by the pressing roller and causing microcracks. Since the microcracks are eliminated or reduced, the risk of the first pole piece 23 breaking will be significantly reduced, and the risk of unexpected capacity loss of the battery 100 will be reduced.

[0077] It can be understood that the first pole piece 23 has a thickness direction. The thickness of the buffer portion 272 may refer to its dimension in the thickness direction of the first pole piece 23. The thickness direction of the first pole piece 23 may be a direction from the first surface 261 to the second surface 262. When the first pole piece 23 is unfolded, the thickness direction of the first surface 261 may be perpendicular to the length direction of the first surface 261. For ease of understanding, the thickness direction of the first pole piece 23 is indicated by an arrow Y in the figure.

[0078] The present disclosure does not impose any particular limitation on the specific structure of the buffer portion 272, as long as its thickness decreases as it approaches the empty current collector region 264. Several possible implementations of the buffer portion 272 are given below.

[0079] As an implementation of the buffer unit 272, refer to Figure 8, the buffer portion 272 may include a plurality of steps, and the plurality of steps include a plurality of step surfaces 272a parallel to the first surface 261. The plurality of step surfaces 272a may be arranged along the winding direction. Along the winding direction, the distances from the plurality of step surfaces 272a to the first surface 261 decrease in sequence. For example, for any two adjacent step surfaces 272a, the step surface 272a closer to the tail end 23b is closer to the first surface 261 than the step surface 272a farther from the tail end 23b.

[0080] According to this implementation of the buffer portion 272, when the buffer portion 272 passes the pressing roller, the pressing roller will successively fall on multiple step surfaces 272a that descend in sequence, thereby helping the buffer portion 272 to pass the pressing roller smoothly and avoiding the current collector 26 from being damaged by the jumping of the pressing roller.

[0081] Continue to refer Figure 8 , the buffer portion 272 may have a length L1. For example, the length L1 may be equal to the sum of the lengths of the plurality of step surfaces 272a. The length L1 may range from 3 mm to 30 mm, preferably from 3 mm to 15 mm. Exemplarily, the length L1 may be 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, or 14 mm.

[0082] An excessively long buffer portion 272 will excessively reduce the energy density of the battery 100, while an excessively short buffer portion 272 will cause a sharp change in thickness and fail to effectively prevent the roller from jumping. The length L1 within the above value range can effectively eliminate or reduce the generation of cracks without significantly reducing the energy density of the battery 100, so that the risk of the first pole piece 23 breaking is significantly reduced, thereby reducing the risk of unexpected capacity loss of the battery 100.

[0083] Continue to refer Figure 8 , the buffer portion 272 may have a maximum thickness T1. For example, the maximum thickness T1 of the buffer portion 272 is the distance from the step surface 272a closest to the body 271 to the first surface 261. The maximum thickness T1 of the buffer portion 272 may be equal to the thickness T2 of the body portion 272. That is, the step surface 272a closest to the body 271 may be flush with the surface of the body 271 facing away from the current collector 26.

[0084] Continue to refer Figure 8 , the number of the plurality of step surfaces 272a may be greater than or equal to three.

[0085] Since the number of step surfaces 272a is large, that is, the number of step surfaces 272a is greater than or equal to 3, the thickness change of the buffer portion 272 will be relatively gentle, which can help the buffer portion 272 pass through the pressing roller smoothly, thereby reducing the risk of the pressing roller jumping. This effectively eliminates or reduces the generation of cracks, and significantly reduces the risk of breakage of the first pole piece 23, thereby reducing the risk of unexpected capacity loss of the battery 100.

[0086] Considering that the flatness of the buffer portion 272 is affected not only by the number of the step surfaces 272a but also by the thickness T2 of the main body portion 271. Therefore, when determining the number of the plurality of step surfaces 272a, the thickness T2 of the main body portion 271 should be considered.

[0087] For example, when the thickness T2 of the main body 271 is less than or equal to 45 μm, in order to make the thickness of the buffer portion 272 change smoothly enough, the number of the plurality of step surfaces 272 a needs to be greater than or equal to 3. For another example, when the thickness T2 of the main body 271 is greater than 45 μm, in order to make the thickness of the buffer portion 272 change smoothly enough, the number of the plurality of step surfaces 272 a needs to be greater than or equal to 4.

[0088] Continue to refer Figure 8 , the step surface 272a has a width W, and the width W is the size of the step surface 272a in the winding direction. That is, the width direction of the step surface 272a is consistent with the length direction of the buffer portion 272. The width W of any step surface 272a satisfies W=L1 / N±5mm. Here, L1 is the length of the buffer portion 272, and N is the number of the plurality of step surfaces 272a. It should be understood that the widths W of different step surfaces 272a are not necessarily the same.

[0089] Since the width W of each step surface 272a satisfies W=L1 / N±5mm, the difference in the width W of different step surfaces 272a will be small. In this way, the thickness of the buffer portion 272 will change more smoothly, and the risk of roller jumping will be reduced. This will effectively eliminate or reduce the generation of cracks, significantly reduce the risk of the first pole piece 23 breaking, and further reduce the risk of unexpected capacity loss of the battery 100.

[0090] Continue to refer Figure 8 , two adjacent step surfaces 272a have a spacing H, and the spacing H refers to the distance between them in the thickness direction Y. The spacing H between any two adjacent step surfaces 272a satisfies H=T2 / N±5μm. Here, T2 is the thickness of the main body 271, and N is the number of the plurality of step surfaces 272a.

[0091] Since the distance H between any two adjacent step surfaces 272a satisfies H=T2 / N±10 μm, the spacing difference between different step surfaces 272a will be small. In this way, the thickness change of the buffer portion 272 will be relatively gentle, and the risk of roller jumping will be reduced.

[0092] Continue to refer Figure 8 As a specific example, the buffer portion 272 can simultaneously meet the above conditions, that is, the buffer portion 272 can simultaneously meet: L1 = 3mm ~ 30mm, T1 = T2, N ≥ 3, W = L1 / N ± 5mm, and H = T2 / N ± 5μm. The study found that the buffer portion 272 that meets the above conditions can effectively eliminate or reduce the generation of cracks without significantly reducing the energy density of the battery 100, so that the risk of the first pole piece 23 breaking is significantly reduced, thereby reducing the risk of unexpected capacity loss of the battery.

[0093] As a variation of the above implementation, refer to Fig. 9 and Fig.10 Any two adjacent step surfaces 272a may contain a step surface (also called an extension surface) 272b perpendicular to the two step surfaces 272a. The step surface 272b forms a convex angle 272c with one of the step surfaces 272a, and forms a concave angle 272d with the other step surface 272b. At least one of the convex angle 272c and the concave angle 272d may be provided with a chamfered right angle 272e or a rounded angle 272f.

[0094] Due to the presence of the chamfered right angle 272e or the rounded corner 272f, the convex corner portion 272c and / or the concave corner portion 272d will not form sharp edges, which can help the convex corner portion 272c and / or the concave corner portion 272d pass through the pressure roller more smoothly, further reducing the risk of the pressure roller jumping. This effectively eliminates or reduces the generation of cracks, thereby significantly reducing the risk of breakage of the first pole piece 23, thereby reducing the risk of unexpected capacity loss of the battery 100.

[0095] As another implementation of the buffer unit 272, refer to Fig.11 The buffer portion 272 may have a buffer slope 2721 , and the distance from the buffer slope 2721 to the first surface 261 gradually decreases along the direction of the empty current collector area.

[0096] According to this implementation method of the buffer portion 272, when the buffer portion 272 passes through the pressing roller, the buffer slope 2721 can support and guide the pressing roller, helping the buffer portion 272 to pass through the pressing roller smoothly, and avoiding the current collector 26 from being damaged by the jumping of the pressing roller. This effectively eliminates or reduces the generation of cracks, and significantly reduces the risk of breakage of the first pole piece 23, thereby reducing the risk of unexpected capacity loss of the battery 100.

[0097] In one example of the buffer slope 2721, continue to refer to Fig.11 , the buffer slope 2721 can be implemented as an inclined plane 2721 inclined relative to the first surface 261.

[0098] Continue to refer Fig.11 The buffer portion 272 may have a maximum thickness T1. The maximum thickness T1 of the buffer portion 272 is the thickness of the portion where the buffer portion 272 is connected to the main body portion 172. The maximum thickness T1 of the buffer portion 272 may be equal to the thickness T2 of the main body portion 271.

[0099] Continue to refer Fig.11 The buffer portion 272 may have a length L1. The length L1 may range from 3 mm to 30 mm, preferably from 3 mm to 15 mm. For example, the length L1 may be 4 mm, 6 mm, 8 mm, 10 mm, 12 mm or 14 mm.

[0100] An excessively long buffer portion 272 will excessively reduce the energy density of the battery 100, while an excessively short buffer portion 272 will cause a sharp change in thickness, thereby failing to effectively prevent the roller from jumping. The length L1 within the above value range can not significantly reduce the energy density of the battery 100, and effectively eliminate or reduce the generation of cracks, so that the risk of the first pole piece 23 breaking is significantly reduced, thereby reducing the risk of unexpected capacity loss of the battery 100.

[0101] Continue to refer Fig.11 The inclined plane 2721 has an angle α relative to the first surface 261, and the angle α may range from 25° to 60°. For example, the angle α may range from 30°, 35°, 40°, 45°, 50° or 55°.

[0102] If the angle α is too large, the inclined plane 2721 will be too steep, which will lead to a greater risk of roller jumping. If the angle α is too small, the length L1 of the inclined plane 2721 will be too long, which will excessively reduce the energy density of the battery 100. The angle α within the above value range can not significantly reduce the energy density of the battery 100, and effectively eliminate or reduce the generation of cracks, so that the risk of the first pole piece 23 breaking is significantly reduced, thereby reducing the risk of unexpected capacity loss of the battery 100.

[0103] Continue to refer Fig.11As a specific example, the buffer portion 272 can simultaneously meet the above conditions, that is, the buffer portion 272 simultaneously meets: L1 = 3mm ~ 30mm, T1 = T2, and α = 25° ~ 60°. Studies have found that the buffer portion 272 that simultaneously meets the above conditions can more effectively eliminate or reduce the generation of cracks without significantly reducing the energy density of the battery 100, so that the risk of the first pole piece 23 breaking is significantly reduced, thereby reducing the risk of unexpected capacity loss of the battery 100.

[0104] In another example of the buffer slope 2721, reference Fig.12 , the buffer slope 2721 can be implemented as a smooth curved surface 2721. It should be noted that although Fig.12 In the embodiment, the smooth curved surface 2721 has an outwardly convex structure, but in other examples of the present disclosure, the smooth curved surface 2721 may also have an inwardly concave structure.

[0105] Further, continue to refer to Fig.12 , the angle between the tangent plane of the smooth curved surface 2721 and the first surface 261 can gradually increase along the winding direction. Fig.11 As shown, for points P1 and P2 spaced apart along the winding direction on the first surface 261 , the angle between the tangent plane F1 at point P1 and the first surface 261 is smaller than the angle between the tangent plane F2 at point P2 and the first surface 261 .

[0106] According to this structure, along the winding direction, the smooth curved surface 2721 will gradually change from a relatively smooth structure to an increasingly steep structure, so that the buffer portion 272 has a relatively short length L1 while ensuring that the buffer portion 272 can smoothly pass through the pressure roller.

[0107] Further, continue to refer to Fig.12 The cross section of the smooth curved surface 2721 may be a quarter ellipse or an approximately ellipse. The major axis of the ellipse or the approximately ellipse may extend along the winding direction, and the minor axis thereof may extend along the thickness direction of the buffer portion 272. According to this configuration, the buffer portion 272 can pass through the pressing roller more smoothly, thereby more effectively preventing the pressing roller from jumping.

[0108] Continue to refer Fig.12 The buffer portion 272 may have a maximum thickness T1. The maximum thickness T1 of the buffer portion 272 is the thickness of the portion where the buffer portion 272 is connected to the main body portion 172. The maximum thickness T1 of the buffer portion 272 may be equal to the thickness T2 of the main body portion 271.

[0109] Continue to refer Fig.12The buffer portion 272 may have a length L1. The length L1 may range from 2 mm to 20 mm, preferably from 3 mm to 10 mm. For example, the length L1 may be 4 mm, 5 mm, 6 mm, 7 mm, 8 mm or 9 mm.

[0110] An excessively long buffer portion 272 will excessively reduce the energy density of the battery 100, while an excessively short buffer portion 272 will cause a sharp change in thickness, thereby failing to effectively prevent the roller from jumping. The length L1 within the above value range can not significantly reduce the energy density of the battery 100, and effectively eliminate or reduce the generation of cracks, so that the risk of the first pole piece 23 breaking is significantly reduced, thereby reducing the risk of unexpected capacity loss of the battery 100.

[0111] Continue to refer Fig.12 As a specific example, the buffer portion 272 can simultaneously satisfy the above conditions, that is, the buffer portion 272 simultaneously satisfies: L1 = 2 mm to 20 mm, and T1 = T2.

[0112] The buffer portion 272 that satisfies the above conditions can more effectively prevent the roller from jumping without significantly reducing the energy density of the battery 100 .

[0113] The above is an example of the structure of the buffer portion. It should be noted that the buffer portion provided by the present disclosure is not limited to the above description. For example, in a foreseeable example, the buffer portion may also be in a wavy shape that gradually becomes thinner along the winding direction.

[0114] Next, back to Figure 4 and Figure 5 , the overall structure of the electrode assembly 20 is further illustrated.

[0115] refer to Figure 4 and Figure 5 , the first pole piece 23 extends in the winding direction sequentially through the first position P3 of the flat portion 22 and the second position P4 of the first curved portion 21a. The buffer portion 272 has a connecting end 2720 connected to the empty current collector area 264. The first position is located in the flat portion, and the second position is located in the first curved portion. The first position and the second position define the range where the connecting end 2720 is located. The connecting end 2720 is located between the first position P3 and the second position P4 in the width direction of the electrode assembly 20. The first position P3 satisfies D1≤10mm, and the second position P4 satisfies D2 / D3≤1 / 2. Here, D1 is the distance from the first position P3 to the boundary line B2 between the flat portion 22 and the first curved portion 21a in the width direction of the electrode assembly 20, D2 is the distance from the second position P4 to the boundary line B2 in the width direction, and D3 is the size of the first curved portion 21a in the width direction.

[0116] The connecting end 2720 of the buffer portion 272 is the end of the first active material layer 27, and its position affects the energy density of the battery 100. On the one hand, if the connecting end 2720 is located at the flat portion 22 and the distance to the boundary line B2 is large, the space from the connecting end 2720 to the boundary line B2 will be wasted, which will reduce the energy density. On the other hand, if the connecting end 2720 is located at the curved portion 21a and the distance from the boundary line B2 exceeds half of the dimension D3 of the first curved portion 21a in the width direction, the width of the electrode assembly 20 will be increased, which will also reduce the energy density.

[0117] According to the present disclosure, the connecting end 2720 is located between the first position P3 and the second position P4, the first position P3 satisfies D1≤10mm, and the second position P4 satisfies D2 / D3≤1 / 2. In this way, the end 2720 of the buffer portion 272 will be located at a suitable position relative to the boundary line B2 to obtain a larger energy density.

[0118] Further, continue to refer to Figure 4 and Figure 5 , the tail end 2720 of the buffer portion 272 may be located between the boundary line B2 and the second position P4.

[0119] According to the structural characteristics of the flat battery cell assembly 20, compared with the portion of the first pole piece 23 located in the flat portion 22, the portion of the first pole piece 23 located in the first curved portion 21a is subjected to less uneven force and is subjected to less pressure during the formation process, which helps to further reduce the risk of breakage of the first pole piece 23 and thereby reduce the risk of unexpected capacity loss of the battery 100.

[0120] Therefore, the tail end 2720 of the buffer portion 272 is disposed between the boundary line B2 and the second position P4, so that the portion of the first pole piece 23 that is easily broken is located in the first bend 21a, which helps to prevent it from being subjected to more serious uneven force and greater pressure, which helps to further reduce the risk of breakage of the first pole piece 23.

[0121] refer to Figure 4 , the electrode assembly 20 can be outsourced by the first electrode sheet 23. Specifically, the tail end 23b of the first electrode sheet 23 can exceed the tail end of the second electrode sheet 24 and the tail end of the separator 25 along the winding direction, and the first surface 261 can be located on the side of the current collector 26 away from the winding center A, so that the part of the first surface 261 of the current collector 26 in the empty current collector area 264 defines the outer surface of the electrode assembly 20, so as to realize the outsourcing of the electrode assembly 20. Further, as Figure 4 As shown, a fixing tape 291 may be adhered to the tail end 23 b of the first electrode sheet 23 to ensure that the electrode assembly 20 remains tightly wound.

[0122] Further, continue to refer to Figure 4 , starting from the buffer portion 272, along the winding direction, the first pole piece 23 can extend through the first curved portion 21a, the second curved portion 21b and the first curved portion 21a in sequence and end at the flat portion 22. In other words, along the direction from the end end 23b to the start end 23a, the buffer portion 272 is located near the third to last curved portion 21, that is, near the fourth to last flat portion 22. Here, the first curved portion 21a and the second curved portion 21b are collectively referred to as the curved portion 21.

[0123] Continue to refer Figure 4 The electrode assembly 20 may include a first electrode tab 292 and a second electrode tab 293. The first electrode tab 292 may be a part of the current collector 26 or an independent component fixed to the current collector 26. Correspondingly, the second electrode tab 293 may be a part of the current collector of the second electrode sheet 24 or an independent component fixed to the current collector of the second electrode sheet 24.

[0124] It should be noted that although Figure 4 In the embodiment, the electrode assembly 20 adopts a structure in which the tabs are placed in the middle. However, in other examples, the electrode assembly 20 may also adopt a structure in which the tabs are placed in the middle. The present disclosure does not impose any particular limitation on the arrangement of the tabs.

[0125] In addition, despite the Figure 4 Not shown, the electrode assembly 20 may further include a termination tape, a portion of which may be pasted on the buffer portion 272 and another portion of which may be pasted on the empty current collector region 264, so as to define the effective boundary of the first active material layer 27, and ensure that the tail end of the second electrode sheet 24 serving as the negative electrode exceeds the effective boundary along the winding direction to avoid the occurrence of lithium plating.

[0126] It should be understood that the term "including" and its variations used in the present disclosure 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 cases.

[0127] It should be understood that although the terms “first” or “second” etc. may be used in the present disclosure to describe various elements, for example, a first surface and a second surface, these elements are not defined by these terms, and these terms are only used to distinguish one element from another.

[0128] The protection scope of the present disclosure is not limited to the above-mentioned embodiments. Any changes or substitutions that can be conceived by any person skilled in the art within the technical scope disclosed in the present disclosure should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.

Claims

1. An electrode assembly, characterized in that: The electrode assembly includes a first electrode sheet, a separator, and a second electrode sheet layer. The first electrode sheet, the separator, and the second electrode sheet are stacked and wound to form an electrode assembly. The first electrode sheet includes a current collector, a first active material layer, and a second active material layer. The current collector has a first surface and a second surface relative to each other in a thickness direction. The first surface includes a covering area and an empty current collector area sequentially arranged along the winding direction of the first electrode sheet. The first active material layer is arranged in the covering area of ​​the first surface, and the second active material layer is arranged in the second surface and exceeds the first active material layer along the winding direction. The first active material layer includes a main body and a buffer portion sequentially arranged along the winding direction, and the thickness of the buffer portion decreases along the direction of the empty current collector area.

2. The electrode assembly according to claim 1, characterized in that: The buffer portion includes a plurality of steps, the plurality of steps having a plurality of first step surfaces parallel to the first surface, the plurality of first step surfaces are arranged along the winding direction, and distances from the plurality of first step surfaces to the first surface decrease sequentially along the winding direction.

3. The electrode assembly according to claim 2, characterized in that: A second step surface perpendicular to the two first step surfaces is contained between any two adjacent first step surfaces, the second step surface forms a convex angle with one of the two first step surfaces and a concave angle with the other, and at least one of the convex angle and the concave angle is provided with a chamfered right angle or a rounded angle.

4. The electrode assembly according to claim 2, characterized in that: The buffer portion satisfies: L1 = 3 mm to 30 mm; and / or T1 = T2; and / or N ≥ 3; and / or W=L1 / N±5mm;and / or H=T2 / N±10μm, Among them, L1 is the length of the buffer part, T1 is the maximum thickness of the buffer part, T2 is the thickness of the main body, N is the number of the multiple first step surfaces, W is the width of any step surface, and H is the distance between any two adjacent step surfaces.

5. The electrode assembly according to claim 1, characterized in that: The buffer portion has a buffer slope, and the distance from the buffer slope to the first surface gradually decreases along the direction of the empty current collector area.

6. The electrode assembly according to claim 5, characterized in that: The buffer slope surface is an inclined plane inclined relative to the first surface.

7. The electrode assembly according to claim 6, characterized in that: The buffer portion satisfies: L1 = 3 mm to 30 mm; and / or T1 = T2; and / or α＝25°～60°， Wherein, L1 is the length of the buffer portion, T1 is the maximum thickness of the buffer portion, T2 is the thickness of the main body portion, and α is the angle between the inclined plane and the first surface.

8. The electrode assembly according to claim 5, characterized in that: The buffer slope is a smooth curved surface, and the angle between the tangent plane of the smooth curved surface and the first surface gradually increases as it approaches the empty current collector.

9. The electrode assembly according to claim 8, characterized in that: The buffer portion satisfies: L1 = 2 mm to 20 mm; and / or T1 = T2, Wherein, L1 is the length of the buffer portion, T1 is the maximum thickness of the buffer portion, and T2 is the thickness of the main body portion.

10. The electrode assembly according to any one of claims 1 to 9, characterized in that: The electrode assembly has a width B and a thickness C, and a ratio B / C of the width B to the thickness C satisfies 1.1≤A / B≤200. The electrode assembly includes a first curved portion, a second curved portion, and a flat portion, and the flat portion is located between the first curved portion and the second curved portion. The buffer portion has a connecting end connected to the empty current collector region, and the connecting end is located between a first position and a second position, wherein the first position is located at the flat portion, and the second position is located at the first curved portion. The first position satisfies D1≤10mm, and the second position satisfies D2 / D3≤1 / 2. Among them, D1 is the distance from the first position to the boundary line between the flat portion and the first curved portion in the width direction of the electrode assembly, D2 is the distance from the second position to the boundary line in the width direction, and D3 is the size of the first curved portion in the width direction.

11. The electrode assembly according to claim 10, characterized in that: The connecting end is located between the boundary line and the second position.

12. The electrode assembly according to any one of claims 1 to 9, characterized in that: The first surface is located on a side of the current collector away from a winding center of the electrode assembly, and a tail end of the first pole sheet exceeds a tail end of the second pole sheet and a tail end of the separator along the winding direction.

13. The electrode assembly according to claim 12, characterized in that: The electrode assembly has a width B and a thickness C, a ratio B / C of the width B to the thickness C satisfies 1.1≤A / B≤200, the electrode assembly includes a first curved portion, a second curved portion and a flat portion, the flat portion is located between the first curved portion and the second curved portion, The first pole piece starts from the buffer portion, extends along the winding direction and ends at the flat portion, and the buffer portion is located at the fourth flat area from the end of the first pole piece.

14. The electrode assembly according to any one of claims 1 to 9, characterized in that: The first electrode is a positive electrode.

15. A battery, characterized in that: The battery comprises the electrode assembly according to any one of claims 1 to 14.

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