Battery cell and battery

Abstract

The present application provides a battery cell and a battery. The battery cell comprises a first electrode sheet, a first separator, a second electrode sheet, and a second separator which are stacked in sequence; at least one of the head and the tail of the first electrode sheet is provided with a light foil surface; the light foil surface faces the first separator; the light foil surface is provided with a bonding layer; the first separator is bonded with the first electrode sheet by means of the bonding layer. Therefore, the battery cell can be wound as a whole, thereby avoiding the problems of wrinkling, electrode sheet dislocation and the like in the processes of starting winding and finishing winding, and improving the yield rate of a product.

Description

Cells and batteries

[0001] This application claims priority to a Chinese patent application filed with the Chinese Patent Office on June 29, 2023, with application number 202321696943.3 and titled “Battery Cell and Battery,” the entire contents of which are incorporated herein by reference. This application claims priority to a Chinese patent application filed with the Chinese Patent Office on September 11, 2023, with application number 202322461015.5 and titled “An Electrode Assembly,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a battery cell and a battery. Background Art

[0003] Rechargeable batteries, also known as secondary batteries, refer to electrochemical energy devices that can be charged and discharged in cycles, such as lithium-ion batteries. They are widely used in various mobile power supply devices, including consumer electronics, new energy vehicles, and energy storage devices.

[0004] In related technologies, lithium batteries generally include a battery cell and a shell. The battery cell is arranged in the shell. The battery cell includes a positive electrode sheet and a negative electrode sheet. A separator is arranged between the positive electrode sheet and the negative electrode sheet. The stacked positive electrode sheet, negative electrode sheet and separator can be wound.

[0005] However, the negative electrode sheet of most current battery cells is longer than the positive electrode sheet, so that the negative electrode sheet covers the positive electrode sheet during the winding process. However, when the battery cell is rolled up and reeled in, the negative electrode sheet cannot be fixed to the positive electrode sheet or the diaphragm, resulting in the negative electrode sheet being in an unconstrained free state, which can easily cause poor coverage or wrinkling, affecting product yield and posing a safety risk.

[0006] Utility Model Content

[0007] In view of the above problems, the embodiments of the present application provide a battery cell and a battery to solve the technical problem that when the current battery cell is rolled up and rolled up, the electrode is in a free state without restraint, which easily causes poor coverage or wrinkling, affects product yield and poses a safety risk.

[0008] In order to achieve the above-mentioned objectives, in a first aspect, the present application provides a battery cell, which includes a first electrode sheet, a first diaphragm, a second electrode sheet, and a second diaphragm stacked in sequence.

[0009] At least one of the head and tail of the first pole piece has a plain foil surface, which faces the first diaphragm. An adhesive layer is provided on the plain foil surface, and the first diaphragm is bonded to the first pole piece via the adhesive layer.

[0010] The battery cell provided in the present application is provided with an adhesive layer at at least one end of the head and the tail, and the electrode and the diaphragm are fixed by the adhesive layer, so that the electrode and the diaphragm can be wound as a whole, thereby avoiding problems such as wrinkling and misalignment of the first electrode during the winding and rewinding process, and improving the product yield.

[0011] As an optional embodiment, the plain foil surface may include a first plain foil surface and a second plain foil surface, and the adhesive layer may include a first adhesive layer and a second adhesive layer; the first plain foil surface may be located at the head of the first pole piece, and the first adhesive layer is bonded between the first plain foil surface and the first diaphragm to form a first composite area; the second plain foil surface is located at the tail of the first pole piece, and the second adhesive layer is bonded between the second plain foil surface and the first diaphragm to form a second composite area.

[0012] As an optional embodiment, the battery cell has a third composite area, which can be located between the first composite area and the second composite area in the X direction. The first electrode, the first diaphragm, the second electrode and the second diaphragm of the third composite area are bonded in sequence.

[0013] As an optional implementation, there may be multiple third composite regions, and the multiple third composite regions are arranged at intervals along the winding direction of the battery cell.

[0014] As an optional embodiment, the battery cell has a compensation area, the length of the first electrode corresponding to the compensation area is greater than the length of the second electrode corresponding to the compensation area, and the compensation area can be located between adjacent third composite areas.

[0015] As an optional implementation manner, the spacing between two adjacent third composite regions is in an increasing arithmetic progression from the head of the first pole piece to the tail of the first pole piece.

[0016] As an optional embodiment, the battery core includes arc segments and straight segments alternately connected in sequence along the winding direction, the third composite area is located in the straight segment, and the compensation area is located in the arc segment.

[0017] As an optional embodiment, the first pole piece may include a substrate and an active layer, the active layer is coated on both side surfaces of the substrate, and the dimension T1 of the adhesive layer in the Y direction is smaller than the dimension T2 of the active layer in the Y direction, wherein 0.001mm<T1<0.5mm.

[0018] As an optional implementation, the dimension of the adhesive layer in the X direction may be greater than or equal to 2 mm.

[0019] In a second aspect, the present application provides a battery, which includes a shell and the battery cell in the above technical solution, and the battery cell is arranged in the shell or membrane shell.

[0020] The present application provides a battery cell and a battery, wherein the battery cell includes a first electrode sheet, a first diaphragm, a second electrode sheet, and a second diaphragm stacked in sequence, at least one of the head and tail of the first electrode sheet has a plain foil surface, the plain foil surface facing the first diaphragm, an adhesive layer is provided on the plain foil surface, and the first diaphragm is bonded to the first electrode sheet via the adhesive layer, thereby preventing the first electrode sheet from wrinkling and electrode sheet misalignment during the winding and rewinding process, thereby improving the product yield.

[0021] In addition to the technical problems solved by the present application, the technical features that constitute the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions described above, other technical problems that can be solved by the battery cells and batteries provided by the present application, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further described in detail in the specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] FIG1 is a structural schematic diagram of a battery cell according to an embodiment of the present application;

[0024] FIG2 is a schematic structural diagram of a battery cell in an expanded state according to an embodiment of the present application;

[0025] FIG3 is a schematic structural diagram of a first electrode in a battery cell provided in an embodiment of the present application;

[0026] FIG4 is a partial schematic diagram of position C in FIG3 ;

[0027] FIG5 is another structural schematic diagram of the first electrode in the battery cell provided in an embodiment of the present application;

[0028] FIG6 is a schematic diagram showing the distribution of the third composite region in the battery cell provided in an embodiment of the present application;

[0029] FIG7 is a first structural diagram of the bonding layer of the first electrode in the battery cell provided in an embodiment of the present application;

[0030] FIG8 is a second structural diagram of the bonding layer of the first electrode in the battery cell provided in an embodiment of the present application;

[0031] FIG9 is a third structural diagram of the bonding layer of the first electrode in the battery cell provided in an embodiment of the present application;

[0032] FIG10 is a partial schematic diagram of position A in FIG1 ;

[0033] FIG11 is a partial schematic diagram of a battery cell head provided in an embodiment of the present application;

[0034] FIG12 is a second structural diagram of a battery cell provided in an embodiment of the present application;

[0035] FIG13 is an enlarged structural diagram of portion D in FIG12;

[0036] FIG14 is a schematic structural diagram of a battery cell provided in an embodiment of the present application before winding;

[0037] FIG15 is an enlarged structural diagram of portion E in FIG14 ;

[0038] FIG16 is a schematic diagram of a structure of a winding needle wound around a first pole piece provided in an embodiment of the present application;

[0039] FIG17 is a schematic diagram of the structure of the first pole piece winding provided in an embodiment of the present application.

[0040] Explanation of the accompanying drawings: 10-battery cell; 11-first composite area; 12-second composite area; 13-third composite area; 14-compensation area; 15-straight segment; 16-arc segment; 17-pole tab; 17a-first pole tab; 17b-second pole tab; 100-first pole piece; 101-substrate; 102-active layer; 110-plain foil surface; 111-first plain foil surface; 112-second plain foil surface; 120-adhesive layer; 121-first adhesive layer; 122-second adhesive layer; 200-second pole piece; 300-first diaphragm; 400-second diaphragm. DETAILED DESCRIPTION

[0041] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0042] Rechargeable batteries are also called secondary batteries, which refer to electrochemical energy devices that can be used in charge and discharge cycles, such as lithium-ion batteries, etc., which are widely used in various mobile power supply devices, including consumer electronic products, new energy vehicles and energy storage devices. Lithium batteries usually include a battery cell and a shell. The battery cell is arranged in the shell. The battery cell includes a positive electrode sheet and a negative electrode sheet. A diaphragm is arranged between the positive electrode sheet and the negative electrode sheet. The stacked positive electrode sheet, negative electrode sheet and diaphragm can be wound. However, the current structure of the battery cell is in an unconstrained free state when rolling and rewinding, which easily causes poor coverage, electrode dislocation or wrinkling, affecting product yield and posing safety risks. The present application provides a battery cell and a battery. By designing the bonding structure of the second electrode sheet and the first electrode sheet in the battery cell when winding, the electrode sheet and the diaphragm are fixed so that the electrode sheet and the diaphragm can form a whole when the battery cell is wound, preventing the first electrode sheet and the second electrode sheet from wrinkling and misalignment during the rolling and rewinding of the battery cell, thereby improving the product yield.

[0043] The following describes the battery cells and batteries of the embodiments of the present application in conjunction with the accompanying drawings. It should be noted that the battery cells provided in the embodiments of the present application are used in batteries, which may be lithium batteries. Lithium batteries can be charged and discharged and recycled. The battery cells and batteries can be used in scenarios including but not limited to electronic products, energy storage devices, and transportation vehicles, such as new energy vehicles and charging stations, etc., which are not specifically limited in the embodiments of the present application.

[0044] Figure 1 is a structural schematic diagram of the battery cell provided in an embodiment of the present application, Figure 2 is a structural schematic diagram of the battery cell in the expanded state provided in an embodiment of the present application, Figure 3 is a structural schematic diagram of the first electrode in the battery cell provided in an embodiment of the present application, and Figure 4 is a partial schematic diagram of position C in Figure 3.

[0045] Referring to Figures 1 to 4, an embodiment of the present application provides a battery cell 10 that can be wound and includes a first electrode sheet 100, a first separator 300, a second electrode sheet 200, and a second separator 400 stacked in sequence. When the battery cell 10 is wound, the first electrode sheet 100, the first separator 300, the second electrode sheet 200, and the second separator 400 are alternately stacked, with the first separator 300 located between the first electrode sheet 100 and the second electrode sheet 200, and the second separator 400 located between the second electrode sheet 200 and the first electrode sheet 100.

[0046] The starting end of the battery cell 10 when it is wound is the head of the electrode sheet, and the ending end of the battery cell 10 when it is wound is the tail of the electrode sheet. The head of the electrode sheet is located at the center of the wound battery cell 10, and the tail of the electrode sheet is located outside the wound battery cell 10. It is understandable that since the battery cell 10 is formed by winding the first electrode sheet 100, the first separator 300, the second electrode sheet 200, and the second separator 400, the first electrode sheet 100, the first separator 300, the second electrode sheet 200, and the second separator 400 all have a head and a tail.

[0047] In some embodiments, at least one of the head and tail of the first electrode piece 100 has a plain foil surface 110, which faces the first diaphragm 300. That is, the plain foil surface 110 is located on the side of the first electrode piece 100 facing the first diaphragm 300. An adhesive layer 120 is provided on the plain foil surface 110, and the first diaphragm 300 is bonded to the first electrode piece 100 via the adhesive layer 120. The plain foil surface 110 is an area of ​​the current collector surface of the first electrode piece 100 that is not coated with active material.

[0048] It can be understood that before the battery cell 10 is wound, the first diaphragm 300 can be bonded to the first electrode sheet 100 through the adhesive layer 120, so as to fix the relative position of the first diaphragm 300 and the first electrode sheet 100, and then when the battery cell 10 is subsequently wound, the first electrode sheet 100 can be prevented from being misaligned or wrinkled at the position of the smooth foil surface 110 after winding.

[0049] It should be noted that the battery cell 10 provided in the present application is provided with an adhesive layer 120 at at least one end of the head and the tail, and the first electrode sheet 100 and the first diaphragm 300 are fixed by the adhesive layer 120. In the middle part of the extension direction of the battery cell 10, the first electrode sheet 100, the first diaphragm 300, the second electrode sheet 200 and the second diaphragm 400 can be all bonded together by hot pressing, so that the electrode sheet and the diaphragm can be wound as a whole, thereby avoiding problems such as wrinkling and misalignment of the first electrode sheet 100 during the rolling and winding process, thereby improving the product yield.

[0050] In addition, in an embodiment of the present application, one of the first electrode 100 and the second electrode 200 can be a positive electrode, and the other can be a negative electrode. For example, the first electrode 100 is a positive electrode and the second electrode 200 is a negative electrode, or the first electrode 100 is a negative electrode and the second electrode 200 is a positive electrode. The embodiment of the present application does not make specific limitations on this.

[0051] FIG5 is another structural schematic diagram of the first electrode in the battery cell provided in an embodiment of the present application.

[0052] Referring to FIG5 in conjunction with FIG1 , in some embodiments, an adhesive portion may be provided at only one end of the head or tail of the first electrode piece 100. For example, an adhesive layer 120 may be provided at the head of the first electrode piece 100 so that the hollow foil surface at the head of the first electrode piece 100 can be bonded to the head of the first diaphragm 300 via the adhesive layer 120, thereby fixing the position of the head of the first electrode piece 100 relative to the first diaphragm 300. Of course, an adhesive layer 120 may also be provided at the tail of the first electrode piece 100 so that the hollow foil surface at the tail of the first electrode piece 100 can be bonded to the tail of the first diaphragm 300 via the adhesive layer 120, which will not be described in detail here.

[0053] Referring to Figures 1 to 4, in other embodiments, the head and tail of the first pole piece 100 can be fixed simultaneously by the adhesive layer 120, wherein the plain foil surface 110 may include a first plain foil surface 111 and a second plain foil surface 112, and the adhesive layer 120 may include a first adhesive layer 121 and a second adhesive layer 122.

[0054] It can be understood that the first plain foil surface 111 can be located at the head of the first pole piece 100, and the first adhesive layer 121 is bonded between the first plain foil surface 111 and the first diaphragm 300 to form a first composite area 11; the second plain foil surface 112 is located at the tail of the first pole piece 100, and the second adhesive layer 122 is bonded between the second plain foil surface 112 and the first diaphragm 300 to form a second composite area 12.

[0055] In an embodiment of the present application, the battery cell 10 has a third composite area 13, which can be located between the first composite area 11 and the second composite area 12 in the X direction. The first electrode 100, the first diaphragm 300, the second electrode 200, and the second diaphragm 400 of the third composite area 13 are bonded in sequence, so that the first electrode 100, the first diaphragm 300, the second electrode 200, and the second diaphragm 400 are bonded in sequence to form a whole, thereby avoiding dislocation and wrinkling during winding.

[0056] It should be noted that the first electrode 100, the first diaphragm 300, the second electrode 200, and the second diaphragm 400 can be laminated by heating and pressurizing, or by using an adhesive layer. Preferably, heating and pressurizing is used, as this can reduce the need for empty foil areas on the electrode and avoid a decrease in energy density.

[0057] The specific configuration of the third composite area 13 is described in detail below.

[0058] FIG6 is a schematic diagram showing the distribution of the third composite region in the battery cell provided in an embodiment of the present application.

[0059] Please refer to Figure 6 in combination with Figures 1 to 4. In one possible implementation, there can be multiple third composite areas 13, and the multiple third composite areas 13 are arranged at intervals along the winding direction of the battery cell 10. In this way, the third composite areas 13 can exist at different positions along the length direction of the battery cell 10, and the first electrode sheet 100, the first diaphragm 300, the second electrode sheet 200, and the second diaphragm 400 are bonded at different positions along the length direction of the battery cell 10.

[0060] Among them, the battery cell 10 has a compensation area 14, and the length of the first pole piece 100 corresponding to the compensation area 14 is greater than the length of the second pole piece 200 corresponding to the compensation area 14. The compensation area 14 can be located between adjacent third composite areas 13. When the battery cell 10 is wound, the second pole piece 200 is located on the inner side of the battery cell 10, and the first pole piece 100 is located on the outer side of the battery cell 10. The compensation area 14 can make the first pole piece 100 located on the outside of the winding direction of the battery cell 10 have a longer size to prevent the first pole piece 100 from being pulled and broken, and to prevent the second pole piece 200 from being squeezed and wrinkled.

[0061] It can be understood that when the battery cell 10 is in an unfolded state and the ends of the first pole piece 100 and the second pole piece 200 are flush, the compensation area 14 forms a raised area on the first pole piece 100, and when the battery cell 10 is wound, the position of the compensation area 14 on the first pole piece 100 can form a smooth surface.

[0062] In some embodiments, the spacing between two adjacent third composite regions 13 increases in an arithmetic progression from the head of the first electrode sheet 100 to the tail of the first electrode sheet 100, such that the spacing between the middle conforming regions gradually increases according to a certain pattern. Referring to FIG1 , when the battery cell 10 is wound, as the number of turns of the battery cell 10 increases, the length required to wind one turn on the inside of the battery cell 10 is shorter than the length required to wind one end of the battery cell 10 on the outside. Therefore, the gradually increasing spacing between the third composite regions 13 allows the third composite regions 13 and the compensation regions 14 to correspond to each other after each turn.

[0063] For example, referring to FIG6 , starting from the head of the battery cell 10 , the spacing dimension between the first third composite area 13 and the second third composite area 13 is L1, and the spacing dimension between the second third composite area 13 and the third third composite area 13 is L2. Similarly, from the head of the battery cell 10 to the tail of the battery cell 10 , the spacing support between adjacent third composite areas 13 is L1, L2, L3…Ln-1, Ln, wherein L1, L2, L3…Ln-1, Ln are an arithmetic progression.

[0064] It should be noted that the battery cell 10 includes arc segments 16 and straight segments 15 alternately connected in the winding direction, the third composite area 13 is located in the straight segment 15, and the compensation area 14 is located in the arc segment 16. In the straight segment 15, the length dimensions of the first pole piece 100 and the second pole piece 200 correspond to each other, so that the first pole piece 100, the first diaphragm 300, the second pole piece 200, and the second diaphragm 400 can be reliably bonded in sequence through the middle composite area. In the arc segment 16, the size of the first pole piece 100 located on the outside of the arc segment 16 is larger than the size of the second pole piece 200 located on the inside of the arc segment 16. Therefore, the length difference between the first pole piece 100 and the second pole piece 200 can be compensated through the compensation area 14 to prevent breakage or wrinkles during winding.

[0065] The size and structure of the adhesive layer 120 and its specific location at the head and tail of the first pole piece 100 are described in detail below.

[0066] Referring to Figures 1 to 4, in one possible implementation, the first pole piece 100 may include a substrate 101 and an active layer 102, and the active layer 102 is coated on both side surfaces of the substrate 101, wherein the position where the hollow foil surface is located has only the substrate 101 and is not coated with the active layer 102, that is, a hollow foil surface is formed in the area at the end of the first pole piece 100 that is not coated with the active layer 102.

[0067] It can be understood that the dimension T1 of the adhesive layer 120 in the Y direction is smaller than the dimension T2 of the active layer 102 in the Y direction, that is, T1<T2. The adhesive layer 120 can cover at least part of the area of ​​the empty foil surface. The embodiment of the present application does not limit the specific coverage area of ​​the adhesive layer 120.

[0068] Illustratively, the dimension T1 of the adhesive layer 120 in the Y direction may be between 0.001 mm and 0.5 mm, that is, 0.001 mm < T1 < 0.5 mm. The specific value of the dimension T1 of the adhesive layer 120 in the Y direction may include but is not limited to 0.001 mm, 0.002 mm, 0.01 mm, 0.1 mm, 0.4 mm, 0.5 mm, etc. The embodiment of the present application does not limit the specific thickness value of the adhesive layer 120.

[0069] In some embodiments, the adhesive layer 120 can be a coating layer, and the shape coated by the adhesive layer 120 can include but is not limited to square, circular, elliptical, etc., wherein the adhesive layer 120 can form a complete coating area, or the adhesive layer 120 can form multiple separate coating areas. The embodiments of the present application do not make specific limitations on this.

[0070] Exemplarily, the material of the adhesive layer 120 can be one or more of cellulose, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyethyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, polyethylene propylene copolymer, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, carboxymethyl cellulose, polypropylene-maleic anhydride, and styrene-polyisoprene.

[0071] FIG7 is a first structural diagram of the bonding layer of the first electrode in the battery cell provided in an embodiment of the present application.

[0072] Referring to FIG. 7 , for example, the adhesive layer 120 can form a complete coating area, wherein the size of the adhesive layer 120 on the first electrode sheet 100 in the Z direction can be equal to the size of the first electrode sheet 100 in the Z direction, the two sides of the adhesive layer 120 are flush with the two sides of the first electrode sheet 100 in the Z direction, and the size of the adhesive layer 120 on the first electrode sheet 100 in the X direction can be less than or equal to the size of the empty foil surface in the X direction. For example, the distance between the edge of the adhesive layer 120 away from the active layer 102 and the edge of the empty foil surface away from the active layer 102 is D, where D ≥ 0. When D is 0, the edge of the adhesive layer 120 away from the active layer 102 is flush with the edge of the empty foil surface away from the active layer 102. When D > 0, there is a gap between the edge of the adhesive layer 120 away from the active layer 102 and the edge of the empty foil surface away from the active layer 102.

[0073] In addition, the dimension W of the adhesive layer 120 in the X direction may be greater than or equal to 2 mm, that is, W ≥ 2 mm. The specific value of the dimension W of the adhesive layer 120 in the X direction may include but is not limited to 2 mm, 2.1 mm, 3 mm, 4 mm, 5 mm, etc., as long as the value of W is less than or equal to the dimension of the empty foil surface in the X direction.

[0074] FIG8 is a second structural schematic diagram of the adhesive layer of the first electrode in the battery cell provided in an embodiment of the present application.

[0075] Please refer to Figure 8. For example, the bonding layer 120 may include multiple long strip bonding areas. The multiple bonding areas may be distributed on the empty foil surface at intervals along the width direction of the first electrode 100. The number of bonding areas may be two, three, four or more, and this embodiment of the application does not specifically limit this.

[0076] FIG9 is a third structural schematic diagram of the adhesive layer of the first electrode in the battery cell provided in an embodiment of the present application.

[0077] Please refer to Figure 9. For example, the adhesive layer 120 may include multiple adhesive points, and the multiple adhesive points may be arranged in an array on the empty foil surface. The embodiment of the present application does not specifically limit the specific number and arrangement of the adhesive points.

[0078] It should be noted that the adhesive layer 120 at the head or tail of the first pole piece 100 can adopt the size structure of the adhesive layer 120 described above, which will not be elaborated here.

[0079] FIG10 is a partial schematic diagram of position A in FIG1 .

[0080] Referring to Figure 10 , in combination with Figures 1 to 4 , in some embodiments, the distance that the tail of the first electrode piece 100 extends beyond the tail of the first diaphragm 300 is D1. When D1 is equal to 0, the first electrode piece 100 and the first diaphragm 300 are completely adhered together, and the tails of the two are flush. When D1 is greater than 0, the empty foil surface portion of the tail of the first electrode piece 100 is adhered to the first diaphragm 300 through the first adhesive layer 121, and the portion of the empty foil surface of the tail of the first electrode piece 100 that extends beyond the first diaphragm 300 is adhered to the first electrode piece 100 of the previous layer of winding through the first adhesive layer 121.

[0081] FIG11 is a partial schematic diagram of a battery cell head provided in an embodiment of the present application.

[0082] Referring to Figure 11 , in combination with Figures 1 to 4 , in some embodiments, the head of the first diaphragm 300 extends beyond the head of the first electrode piece 100 by a distance D2. When D2 is equal to 0, the first electrode piece 100 is flush with the tail of the first diaphragm 300. When D2 is greater than 0, the hollow foil surface of the head of the first electrode piece 100 is bonded to the first diaphragm 300 through the first adhesive layer 121, and the head of the first diaphragm 300 extends beyond the head edge of the first electrode piece 100 by a certain distance.

[0083] In addition, the first pole piece 100 and the second pole piece 200 may be connected to pole tabs 17 respectively, wherein one of the pole tabs 17 is a positive pole tab and the other is a negative pole tab.

[0084] The specific manufacturing process of the battery cell 10 is described below with examples.

[0085] Step 1: Manufacturing the first electrode 100, coating the active material on the upper and lower surfaces of the substrate of the first electrode 100, and reserving a blank area at least one of the head and tail of the first electrode 100 without coating the active material to form a blank foil surface according to actual needs.

[0086] Step 2: Apply the adhesive material to the hollow foil surface of the head or tail of the first electrode 100 to form the first adhesive layer 121 or the second adhesive layer 122 .

[0087] Step 3: Composite the head or tail of the first electrode 100, the first diaphragm 300, the second electrode 200 and the second diaphragm 400 into a whole according to a certain positional relationship by heating and pressurizing, or composite the head and tail into a whole simultaneously.

[0088] Step 4: The first electrode 100, the first diaphragm 300, the second electrode 200, and the middle part of the second diaphragm 400 are composited into a whole according to a certain positional relationship by heating and pressurizing to form a third composite area 13, wherein the third composite area 13 is in a discontinuous state, and the distance between two adjacent third composite areas 13 is an increasing arithmetic progression.

[0089] Step 5: Process the composite electrode sheet into a battery cell 10 by winding.

[0090] As shown in Figures 12 to 15 , this embodiment provides a battery cell comprising a first electrode sheet 100, a second electrode sheet 200, a first separator 300, and a second separator 400 that are stacked and wound. The first separator 300 and the second separator 400 are respectively located on either side of the second electrode sheet 200, and the first separator 300 is located between the first electrode sheet 100 and the second electrode sheet 200. The first separator 300 and the second separator 400 can isolate the second electrode sheet 200 to prevent the second electrode sheet 200 and the first electrode sheet 100 from contacting and causing a short circuit. In this embodiment, the number of first separators 300 can be one or at least two; the number of second separators 400 can be one or at least two, and the number of first separators 300 and second separators 400 can be the same or different, which is not further limited in this embodiment.

[0091] Along the length direction of the first pole piece 100 (i.e., the x-axis direction in Figure 14), the first pole piece 100, the second pole piece 200, the first diaphragm 300 and the second diaphragm 400 are connected to form at least one third composite area B, and a non-third composite area A is formed between any two adjacent third composite areas B; in the third composite area B, the first pole piece 100, the second pole piece 200, the first diaphragm 300 and the second diaphragm 400 are composited together to prevent the first pole piece 100 from moving, shifting, etc.; in the non-third composite area A, the first pole piece 100, the second pole piece 200, the first diaphragm 300 and the second diaphragm 400 are not composited together to avoid the first pole piece 100 from breaking due to tension or the second pole piece 200 from bulging. As an optional embodiment, the first electrode piece 100, the second electrode piece 200, the first diaphragm 300 and the second diaphragm 400 can be bonded together by thermal bonding to achieve the bonding between the first electrode piece 100, the second electrode piece 200, the first diaphragm 300 and the second diaphragm 400; the first electrode piece 100, the second electrode piece 200, the first diaphragm 300 and the second diaphragm 400 can also be bonded and fixed by adhesive tape, glue or an adhesive layer to achieve the bonding between the first electrode piece 100, the second electrode piece 200, the first diaphragm 300 and the second diaphragm 400. The first electrode piece 100, the second electrode piece 200, the first diaphragm 300 and the second diaphragm 400 are not bonded together, which means that the first electrode piece 100, the second electrode piece 200, the first diaphragm 300 and the second diaphragm 400 are not bonded into one piece.

[0092] Along the length of the first electrode sheet 100, the first electrode sheet 100 includes a plurality of bending regions C and a plurality of straight regions (the region between the bending regions C) that are alternately arranged and sequentially connected. The bending regions C are regions where the first electrode sheet 100 bends when it is wound to form a battery cell, and the straight regions are regions where the first electrode sheet 100 does not bend when it is wound to form a battery cell. The third composite regions B are all located within the straight regions. Preferably, in this embodiment, the first electrode sheet 100, the second electrode sheet 200, the first separator 300, and the second separator 400 are connected to form a plurality of third composite regions B, and a non-third composite region A is formed between any two adjacent third composite regions B.

[0093] The battery cell in this embodiment includes a plurality of third composite areas B and non-third composite areas A that are alternately arranged and sequentially connected between the first pole piece 100 and the first diaphragm 300 along the length direction of the first pole piece 100. In the third composite area B, the first pole piece 100, the second pole piece 200, the first diaphragm 300 and the second diaphragm 400 are connected, which can avoid the first pole piece 100 from moving and shifting, and the first pole piece 100, the first diaphragm 300, the second pole piece 200 and the second diaphragm 400 are composited into one body, which can not only improve the bonding strength between the first pole piece 100, the second pole piece 200, the first diaphragm 300 and the second diaphragm 400, but also reduce the risk of battery assembly failure due to drop. , it can also simplify the correction and feeding mechanisms of the winding setting, realize the simplification of the winding device, and help reduce production costs; in addition, in the non-third composite area A, the first pole piece 100, the second pole piece 200, the first diaphragm 300 and the second diaphragm 400 are not connected, and the third composite area B is all located in the straight area to avoid the third composite area B being located in the bending area C, so that the length deviation between the first pole piece 100 and the second pole piece 200 at the bending area C can alleviate the first pole piece 100 and the second pole piece 200 from being broken due to the influence of tension or the second pole piece 200 from bulging during the winding process, which is beneficial to improving the safety performance of the battery cell.

[0094] In this embodiment, the first electrode sheet 100 may include a first current collector and a first active material layer disposed on both sides of the first current collector. The first current collector may be made of, but is not limited to, metal foil, alloy foil, or a metal-polymer composite foil. For example, the first current collector may be made of aluminum, nickel, or titanium. The active material in the first active material layer may include, but is not limited to, lithium-transition metal composite oxides.

[0095] The second pole piece 200 may include a second current collector and a second active material layer disposed on both sides of the second current collector. The second current collector may be made of, but is not limited to, metal foil, alloy foil, or a metal-polymer composite foil. For example, the second current collector may be made of copper, nickel, or stainless steel. The active material in the second active material layer is selected from one or more of graphite, hard carbon, soft carbon, lithium titanate, and silicon-based materials.

[0096] In this embodiment, along the length of the first pole piece 100, the spacing between any two adjacent third composite regions B is equal. As shown in FIG14 , along the length of the first pole piece 100, the spacing between the first and second third composite regions B is L1, the spacing between the second and third third composite regions B is L2, and so on. The spacing between the (N-1)th and (N)th third composite regions B is Ln, where L1 = L2 = ... = Ln.

[0097] Based on the above embodiment, half of the outer circumference of the winding needle used for winding the battery cell is Lw, that is, as shown in Figure 16, Lw = Lw' + π × Rw', then L1 = L2 = ... = Ln = Lw, so as to avoid the third composite area B appearing in the bending area C and ensure that the third composite area B is located in the straight area.

[0098] In this embodiment, the lengths of the plurality of third composite regions B are all equal along the length direction of the first pole piece 100. The length of the third composite region B can be set to a fixed value, and those skilled in the art can adjust the length according to actual conditions. As an optional embodiment, the length of the third composite region B is 5 mm to 10 mm. For example, the length of the third composite region B is 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm.

[0099] The battery cell includes multiple winding coils. During the process of winding the first pole piece 100 and the second pole piece 200 into the battery cell, in the same winding coil, there is a difference in the radius of the first pole piece 100 and the second pole piece 200 at the bending zone C. This difference may cause the first pole piece 100 to break due to the influence of tension or the second pole piece 200 to bulge during the winding process. In order to further alleviate this problem, in combination with Figures 13 and 14, on the basis of the above embodiment, along the length direction of the first pole piece 100, between any two adjacent third composite areas B, the length of the first pole piece 100 is greater than the length of the second pole piece 200. Therefore, the length of the first pole piece 100 is greater than the length of the second pole piece 200, which can achieve length compensation for the first pole piece 100, reduce the length deviation of the first pole piece 100 and the second pole piece 200 at the bending zone C, and avoid the first pole piece 100 from breaking due to the influence of tension or the second pole piece 200 from bulging. Preferably, along the length direction of the first pole piece 100, between any two adjacent third composite regions B, the length difference between the first pole piece 100 and the second pole piece 200 is La, La = π × a, wherein a = R2 - R1, R1 is the radius of the center of the second pole piece 200 of the N-1th winding at the bending zone C, and R2 is the radius of the center of the first pole piece 100 of the N-1th winding at the bending zone C, that is, a is the sum of half the thickness of the first pole piece 100, half the thickness of the second pole piece 200, and the thickness of the first diaphragm 300. Therefore, limiting the compensation length of the first pole piece 100 to La can further prevent the first pole piece 100 from breaking due to tension or the second pole piece 200 from bulging.

[0100] As shown in FIG17 , the battery cell includes N windings, where N is greater than or equal to 1 and is an integer. Two third composite areas B are provided on each winding. The battery cell is divided by the center line (i.e., the dotted line in FIG17 ) in the thickness direction of the battery cell (i.e., the z-axis direction in FIG17 ). The battery cell includes an upper side (i.e., the second side) and a lower side (i.e., the second side). Each winding has a third composite area B located on the upper side of the battery cell and another third composite area B located on the lower side of the battery cell. The projections of the two third composite areas B of each winding in the thickness direction of the battery cell do not overlap. To facilitate the description of the technical solutions of the embodiments of the present application, the third composite area B of each winding located on the upper side of the battery cell is referred to as the first side composite area B1, and the third composite area B of each winding located on the lower side of the battery cell is referred to as the second side composite area B2. The projections of the first side composite area B1 and the second side composite area B2 of each winding turn in the thickness direction of the battery cell do not overlap, which is beneficial to improving the thickness consistency of the battery cell, thereby reducing the thickness of the battery cell and improving the energy density of the battery cell.

[0101] It should be noted that a winding circle refers to a point on the battery cell as the starting end, and a circle along the winding direction to another point as the ending end. The ending end, the starting end and the center of the circle are on a straight line, and the starting end is between the ending end and the center of the circle.

[0102] In this embodiment, the upper side of the battery cell includes N first side composite areas B1; the lower side of the battery cell includes N second side composite areas B2. When the first electrode 100 is wound to form the battery cell, as the number of winding turns increases, the winding radius of the bending area of ​​the first electrode 100 increases, and the length of the bending area C of the first electrode 100 increases, while the spacing between any two adjacent third composite areas B is equal. Therefore, as the number of winding turns increases, the positions of the first side composite area B1 and the second side composite area B2 on different winding turns will change.

[0103] Specifically, the first pole piece 100 includes a first winding coil wound at least one turn along the length direction from its winding head end, and an Nth winding coil wound at least one turn along the length direction to its winding tail end, wherein the first winding coil includes a first bending area C1 and a second bending area C2, wherein the first bending area C1 is the area where the first pole piece 100 is bent for the first time, and the second bending area C2 is the area where the first pole piece 100 is bent for the second time. On the upper side of the battery cell, the first side composite area B1 located on the first winding coil is arranged near the first bending area C1, and the distance between the first side composite area B1 and the first bending area C1 gradually increases from the first winding coil to the Nth winding coil. As shown in Figure 17, on the upper side of the battery cell, from the first winding coil to the Nth winding coil, as the number of windings increases, the first side composite area B1 gradually moves to the left. On the lower side of the cell, the second side lamination region B2, located on the first winding, is positioned near the second bending region C2. From the first winding to the Nth winding, the distance between the second side lamination region B2 and the second bending region C2 gradually increases. As shown in Figure 17 , on the lower side of the cell, from the first winding to the Nth winding, the second side lamination region B2 gradually shifts to the right as the number of windings increases.

[0104] Based on the above embodiment, on the upper side of the battery cell, the first side composite area B1 located on the first winding has a first end, and the first end is arranged close to the first bending area C1. The distance between the end of the first side composite area B1 close to the first bending area C1 on the Nth winding satisfies the following relationship: An = (N-1)2×π×B

[0105] Among them, An is the distance between one end of the first side composite area B1 on the Nth winding turn close to the first bending area C1 and the first end, B = R3-R2, R3 is the radius of the center of the first pole piece 100 of the Nth winding turn at the bending area C, R2 is the radius of the center of the first pole piece 100 of the N-1th winding turn at the bending area C, that is, B is the sum of the thicknesses of the first pole piece 100, the second pole piece 200 and the first diaphragm 300.

[0106] Based on the above embodiment, on the lower side of the battery cell, the second side composite area B2 located on the first winding has a second end, and the second end is arranged close to the second bending area C2. The distance between the end of the second side composite area B2 close to the second bending area C2 on the Nth winding satisfies the following relationship: An'=(N-1)×N×π×B

[0107] An′ is the distance between one end and the second end of the second side composite region B2 close to the second bending region C2 on the Nth winding, and B is the sum of the thicknesses of the first pole piece 100 , the second pole piece 200 and the first diaphragm 300 .

[0108] In this embodiment, limiting An and An' to the above range is beneficial to further improving the consistency of the thickness of the battery cell, thereby further reducing the thickness of the battery cell and improving the energy density of the battery cell.

[0109] For example, as shown in FIG17 , when the winding needle winds the battery cell, the first winding circle of the first electrode sheet 100 is in contact with the winding needle, and the first end of the first side composite area B1 on the first winding circle is A1, and the second end of the second side composite area B2 on the first winding circle is A1′;

[0110] An end of the first side composite area B1 on the second winding coil close to the first bending area C1 is A2, and an end of the second side composite area B2 on the second winding coil close to the second bending area C2 is A2';

[0111] An end of the first side composite area B1 on the third winding coil close to the first bending area C1 is A3, and an end of the second side composite area B2 on the third winding coil close to the second bending area C2 is A3';

[0112] An end of the first side composite area B1 on the fourth winding coil close to the first bending area C1 is A4, and an end of the second side composite area B2 on the fourth winding coil close to the second bending area C2 is A4';

[0113] By analogy, the end of the first side composite region B1 on the Nth winding coil closest to the first bending region C1 is An, and the end of the second side composite region B2 on the Nth winding coil closest to the second bending region C2 is An'. Then: A1 = 0; A1' = 0; A2 = π × B; A2' = A2 + π × B = 2 × π × B = 1 × 2 × π × B; A3 = A2' + 2 × π × B = 4 × π × B = 22 × π × B; A3' = A3 + 2 × π × B = 6 × π × B = 2 × 3 × π × B; A4 = A3' + 3 × π × B = 9 × π ​​× B = 32 × π × B; A4' = A4 + 3 × π × B = 12 × π × B = 3 × 4 × π × B; ... An=(N-1)2×π×B; An’=(N-1)×N×π×B.

[0114] Based on the above embodiment, the distance between the first end of the first side composite area B1 and the second end of the second side composite area B2 is W, that is, the distance between A1 and A1' is W, then An ≤ W, An' ≤ W. This ensures that the first side composite area B1 and the second side composite area B2 are both located in the straight area, preventing the first side composite area B1 and the second side composite area B2 from being located in the bending area C. This allows for length compensation of the first electrode sheet 100 in the bending area C, preventing the first electrode sheet 100 from breaking due to tension or the second electrode sheet 200 from bulging, thereby improving the safety performance of the battery cell. Furthermore, the first side composite area B1 and the second side composite area B2 located in the straight area can improve the coverage stability of the first electrode sheet 100 and the second electrode sheet 200, and enhance the bonding strength between the first electrode sheet 100, the first separator 300, the second electrode sheet 200, and the second separator 400.

[0115] In this embodiment, on the upper side of the battery cell, from the first winding turn to the Nth winding turn, as the number of winding turns increases, the distance between the first side composite area B1 and the first bending area C1 gradually increases. Then, from the first winding turn to the Nth winding turn, as the number of winding turns increases, the overlapping area of ​​the projections of the first side composite areas B1 on two adjacent winding turns in the thickness direction of the battery cell gradually decreases. For example, the overlapping area of ​​the projections of the first side laminated region B1 on the first winding and the first side laminated region B1 on the second winding in the thickness direction of the battery cell is S1, the overlapping area of ​​the projections of the first side laminated region B1 on the second winding and the first side laminated region B1 on the third winding in the thickness direction of the battery cell is S2, and so on. The overlapping area of ​​the projections of the first side laminated region B1 on the Nth winding and the first side laminated region B1 on the N-1th winding in the thickness direction of the battery cell is Sn-1. Then, S1>S2>…>Sn-1, where Sn-1 can be zero, i.e., the projections of the first side laminated region B1 on the Nth winding and the first side laminated region B1 on the N-1th winding in the thickness direction of the battery cell do not overlap at all. In this embodiment, the number of the projections of the first side laminated region B1 on two adjacent windings in the thickness direction of the battery cell that do not overlap at all is not further limited, and those skilled in the art can set it according to actual conditions.

[0116] On the lower side of the battery cell, from the first winding turn to the Nth winding turn, as the number of winding turns increases, the distance between the second side composite area B2 and the second bending area C2 gradually increases. From the first winding turn to the Nth winding turn, as the number of winding turns increases, the overlapping area of ​​the projections of the second side composite areas B2 on two adjacent winding turns in the thickness direction of the battery cell gradually decreases. Illustratively, the overlapping area of ​​the projections of the second side composite area B2 on the first winding turn and the second side composite area B2 on the second winding turn in the thickness direction of the battery cell is S1', the overlapping area of ​​the projections of the second side composite area B2 on the second winding turn and the second side composite area B2 on the third winding turn in the thickness direction of the battery cell is S2', and so on, the overlapping area of ​​the projections of the second side composite area B2 on the Nth winding turn and the second side composite area B2 on the N-1th winding turn in the thickness direction of the battery cell is Sn-1', then S1'>S2'>…>Sn-1', where Sn-1' can be zero, that is, the projections of the second side composite area B2 on the Nth winding turn and the second side composite area B2 on the N-1th winding turn in the thickness direction of the battery cell do not overlap at all. In this embodiment, there is no further limitation on the number of completely non-overlapping projections of the second side composite areas B2 on two adjacent windings in the thickness direction of the battery cell, and those skilled in the art can set it according to actual conditions.

[0117] Based on the above embodiment, the battery cell also includes an insulating layer 500. When the first pole piece 100 and the second pole piece 200 are wound to form a battery cell, the first pole piece 100 is located at the outermost circle of the battery cell, and the insulating layer 500 is attached to the winding tail end of the first pole piece 100, which can insulate and protect the winding tail end of the first pole piece 100, thereby improving the safety of the battery cell.

[0118] As an optional embodiment, the projection of the insulating layer 500 in the thickness direction of the battery cell overlaps at least partially with the projection of at least one third composite region B, that is, the projection of the insulating layer 500 in the thickness direction of the battery cell may overlap with the projection of at least one third composite region B in the thickness direction of the battery cell, or the projection of the insulating layer 500 in the thickness direction of the battery cell may completely overlap with the projection of at least one third composite region B in the thickness direction of the battery cell.

[0119] In this embodiment, there is no specific limit on the number of third composite areas B and non-third composite areas A. Those skilled in the art can set the number of third composite areas B and non-third composite areas A according to actual conditions, and this embodiment does not impose any further limit on this.

[0120] In this embodiment, the first pole piece 100 further includes a first pole tab 17a, which is connected to the first current collector and is used to lead to an electrode of the battery cell. The second pole piece 200 further includes a second pole tab 17b, which is connected to the second current collector and is used to lead to another electrode of the battery cell.

[0121] An embodiment of the present application further provides a battery, which includes a housing and the battery cell 10 in the above technical solution. The battery cell 10 is arranged in the housing or membrane shell, and the interior of the housing can be injected with electrolyte.

[0122] An embodiment of the present application provides a battery cell 10 and a battery, wherein the battery cell 10 can be wound and includes a first electrode sheet 100, a first diaphragm 300, a second electrode sheet 200, and a second diaphragm 400 stacked in sequence. At least one of the head and tail of the first electrode sheet 100 has a smooth foil surface 110, and the smooth foil surface 110 faces the first diaphragm 300. An adhesive layer 120 is provided on the smooth foil surface 110. The first diaphragm 300 is bonded to the first electrode sheet 100 through the adhesive layer 120, so that the battery cell 10 can be wound as a whole, avoiding problems such as wrinkling and electrode sheet misalignment during the winding and rewinding process, and improving the product yield.

[0123] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to a fixed connection, an indirect connection via an intermediate medium, internal communication between two components, or an interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0124] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0125] The terms "first," "second," "third," "fourth," and so on (if any) in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can, for example, be implemented in orders other than those illustrated or described herein.

[0126] In addition, the terms "comprises" and "having" and any variations thereof are intended to cover a non-exclusive inclusion. For example, a process, method, system, product or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, product or apparatus.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A battery cell, characterized in that: The battery cell comprises a first pole piece, a first diaphragm, a second pole piece and a second diaphragm which are stacked in sequence, the first diaphragm and the second diaphragm are respectively located on both sides of the second pole piece, and the first diaphragm is located between the first pole piece and the second pole piece; At least one of the head and the tail of the first pole piece has a smooth foil surface, the smooth foil surface faces the first diaphragm, an adhesive layer is provided on the smooth foil surface, and the first diaphragm is bonded to the first pole piece through the adhesive layer.

2. The battery cell according to claim 1, characterized in that: The smooth foil surface includes a first smooth foil surface and a second smooth foil surface, and the adhesive layer includes a first adhesive layer and a second adhesive layer; the first smooth foil surface is located at the head of the first pole piece, and the first adhesive layer is bonded between the first smooth foil surface and the first diaphragm to form a first composite area; the second smooth foil surface is located at the tail of the first pole piece, and the second adhesive layer is bonded between the second smooth foil surface and the first diaphragm to form a second composite area.

3. The battery cell according to claim 2, characterized in that: The battery cell has a third composite area, which is located between the first composite area and the second composite area in the X direction, and the first pole piece, the first diaphragm, the second pole piece, and the second diaphragm of the third composite area are bonded in sequence.

4. The battery cell according to claim 3, characterized in that: There are a plurality of the third composite regions, and the plurality of the third composite regions are arranged at intervals along the winding direction of the battery core.

5. The battery cell according to claim 4, characterized in that: Along the length direction of the first pole piece, the spacing between any two adjacent third composite regions is equal.

6. The battery cell according to claim 4, characterized in that: The lengths of the plurality of third composite regions are all equal.

7. The battery cell according to claim 4, characterized in that: The battery cell has a compensation area, the length of the first pole piece corresponding to the compensation area is greater than the length of the second pole piece corresponding to the compensation area, and the compensation area is located between adjacent third composite areas.

8. The battery cell according to claim 4, characterized in that: Between any two adjacent third composite regions, the difference between the length of the first pole piece and the length of the second pole piece satisfies the following relationship: La = π × a Wherein, La is the difference between the length of the first pole piece and the length of the second pole piece, and a is the sum of half the thickness of the first pole piece, half the thickness of the second pole piece, and the thickness of the first diaphragm.

9. The battery cell according to claim 4, characterized in that: The spacing between two adjacent third composite regions is in an increasing arithmetic progression from the head of the first pole piece to the tail of the first pole piece.

10. The battery cell according to claim 9, characterized in that: The battery core comprises arc segments and straight segments which are alternately connected in sequence along a winding direction, the third composite area is located in the straight segment, and the compensation area is located in the arc segment.

11. The battery cell according to claim 4, characterized in that: The battery core comprises N windings, N≥1, and N is an integer, and each winding is provided with two third composite areas, and the two third composite areas are respectively a first side composite area and a second side composite area; The battery core comprises a first side and a second side, and along the thickness direction of the battery core, the first side and the second side are respectively arranged on both sides of the battery core, the first side composite area of ​​each winding coil is located on the first side, and the second side composite area of ​​each winding coil is located on the second side; Projections of the first side composite region and the second side composite region in a thickness direction of the battery cell do not overlap.

12. The battery cell according to claim 11, characterized in that: The first pole piece includes a first winding circle wound at least one circle along the length direction from the winding head end thereof, and an Nth winding circle wound at least one circle along the length direction to the winding tail end thereof, wherein the first winding circle includes a first bending area and a second bending area; On the first side, the first side composite area located in the first winding circle is close to the first bending area, and the distance between the first side composite area and the first bending area gradually increases from the first winding circle to the Nth winding circle; And / or, on the second side, the second side composite area located in the first winding turn is close to the second bending area, and the distance between the second side composite area and the second bending area gradually increases from the first winding turn to the Nth winding turn.

13. The battery cell according to claim 12, characterized in that: On the first side, from the first winding turn to the Nth winding turn, the overlapping area of ​​the projections of the first side composite areas on two adjacent winding turns in the thickness direction of the battery core gradually decreases; and / or, on the second side, from the first winding circle to the Nth winding circle, two adjacent winding circles The overlapping area of ​​the projection of the second side composite region on the battery core in the thickness direction gradually decreases.

14. The battery cell according to claim 12, characterized in that: On the first side, there are N first side composite areas, the first side composite area located in the first winding circle has a first end, the first end is close to the first bending area, and the distance between one end of the first side composite area close to the first bending area on the Nth winding circle and the first end satisfies the following relationship: An = (N-1)2×π×B Wherein, An is the distance between one end of the first side composite area close to the first bending area and the first end on the Nth winding turn, and B is the sum of the thicknesses of the first pole piece, the second pole piece and the first diaphragm.

15. The battery cell according to claim 14, characterized in that: On the second side, N second side composite areas are included, the second side composite area located in the first winding circle has a second end, the second end is close to the second bending area, and the distance between one end of the second side composite area close to the second bending area on the Nth winding circle and the second end satisfies the following relationship: An'=(N-1)×N×π×B Wherein, An' is the distance between one end of the second side composite area close to the second bending area and the second end on the Nth winding turn, and B is the sum of the thicknesses of the first pole piece, the second pole piece and the first diaphragm.

16. The battery cell according to claim 15, characterized in that: The distance between the first end and the second end is W, An≤W, and / or An′≤W.

17. The battery cell according to any one of claims 1 to 16, characterized in that: The first pole piece includes a substrate and an active layer, wherein the active layer is coated on both side surfaces of the substrate, and a dimension T1 of the adhesive layer in the Y direction is smaller than a dimension T2 of the active layer in the Y direction, wherein 0.001 mm<T1<0.5 mm.

18. The battery cell according to any one of claims 1 to 16, characterized in that: The dimension of the adhesive layer in the X direction is greater than or equal to 2 mm.

19. The battery cell according to any one of claims 1 to 16, characterized in that: The winding tail end of the first pole piece is also covered with an insulating layer, and the projection of the insulating layer in the thickness direction of the battery core at least partially overlaps with at least one of the composite regions.

20. A battery, characterized in that: It comprises a shell and a battery cell as described in any one of claims 1 to 19, wherein the battery cell is arranged in the shell or the membrane shell.

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