Secondary battery, electrode sheet, and material strip

Abstract

A secondary battery, an electrode sheet and a material strip. The secondary battery comprises a case, a first electrode sheet and a second electrode sheet, wherein the case has an accommodating cavity; the first electrode sheet and the second electrode sheet are accommodated in the accommodating cavity; the first electrode sheet and the second electrode sheet have opposite polarities, and are stacked and wound around the same axis; the starting part of winding of the first electrode sheet is sandwiched between the innermost layer and the second inner layer of the second electrode sheet, and the end part of winding of the first electrode sheet is sandwiched between the outermost layer and the second outer layer of the second electrode sheet; the first electrode sheet comprises a substrate, and a first active material layer and a second active material layer which are respectively located on two sides of the substrate in the thickness direction; and at one end of the first electrode sheet along the winding path, the edge of the first active material layer is spaced apart from the edge of the second active material layer along the winding path, such that the thickness of the first electrode sheet gradually decreases or decreases in steps in the winding direction. In the secondary battery, the stress on the ends of the electrode sheets during charging and discharging can be reduced.

Description

Secondary batteries, electrodes and strips

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number CN202322673890.X and title “Secondary Battery, Electrode and Strip” filed with the China Patent Office on September 28, 2023, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a secondary battery, a pole piece, and a material strip. Background Art

[0004] Secondary batteries are widely used as power batteries in electric vehicles and energy storage fields.

[0005] In a secondary battery, the negative electrode sheet is wrapped around the positive electrode sheet. The positive electrode sheet includes a substrate and active material layers on both sides of the substrate. At one end of the positive electrode sheet along the winding path, the edges of the active material layers on both sides of the substrate are aligned along the winding path. During the charge and discharge process, the stress at the end of the positive electrode sheet is relatively high, causing the end of the positive electrode sheet to bend and deform. In some cases, the substrate of the positive electrode sheet breaks during deformation. In other cases, the positive electrode sheet punctures the separator and contacts the negative electrode, causing a short circuit between the positive and negative electrodes.

[0006] Application Contents

[0007] In view of this, embodiments of the present application provide a secondary battery, a pole piece, and a material strip to reduce stress at the pole piece end during charging and discharging.

[0008] In a first aspect, the present application provides a secondary battery comprising a housing, a first pole piece, and a second pole piece.

[0009] The shell has a accommodating cavity; the first pole piece and the second pole piece are accommodated in the accommodating cavity, the first pole piece and the second pole piece have opposite polarities, are stacked and wound around the same axis, the winding starting end of the first pole piece is clamped between the innermost circle and the second inner circle of the second pole piece, and the winding end of the first pole piece is clamped between the outermost circle and the second outer circle of the second pole piece. The first pole piece includes a substrate and a first active material layer and a second active material layer located on both sides of the substrate in the thickness direction; wherein, at one end of the first pole piece along the winding path, the edge of the first active material layer and the edge of the second active material layer are spaced apart along the winding path, so that the thickness of the first pole piece gradually decreases or step-wise decreases in the winding direction.

[0010] Beneficial Effect: At one end of the first electrode sheet along the winding path, the edge of the first active material layer and the edge of the second active material layer are spaced apart (staggered) along the winding path, causing the end of the first electrode sheet to gradually become thinner along the winding path. Specifically, the thickness of the end of the first electrode sheet is reduced from the sum of the thicknesses of the first active material layer, substrate, and second active material layer to the sum of the thicknesses of the first active material layer or the second active material layer and substrate, then further reduced to the thickness of the substrate, and then further reduced to zero. As a result, the stress at the end of the first electrode sheet during charge and discharge is reduced.

[0011] In an optional embodiment, at one end of the first electrode sheet along the winding path, an edge of the first active material layer and an edge of the substrate are spaced apart along the winding path, and a first blank area not coated with the first active material layer is formed on the surface of the substrate;

[0012] At one end of the first electrode sheet along the winding path, the edge of the second active material layer is spaced apart from the edge of the substrate along the winding path, and a second blank area not coated with the second active material layer is formed on the surface of the substrate.

[0013] In an optional embodiment, the first blank area and the second blank area are respectively located at the starting ends of the winding of the first pole piece, the extension length of the first blank area along the winding path of the first pole piece is L1mm, and the extension length of the second blank area along the winding path of the first pole piece is L2mm, satisfying: 13≤L2≤19, 11≤L1-L2≤13.

[0014] In an optional embodiment, the first blank area and the second blank area are respectively located at the winding ends of the first pole piece, the extension length of the first blank area along the winding path of the first pole piece is L1mm, and the extension length of the second blank area along the winding path of the first pole piece is L2mm, satisfying: 6≤L1≤12, 2≤L1-L2≤4.

[0015] In an optional embodiment, at the other end of the first pole piece along the winding path, an edge of the first active material layer and an edge of the second active material layer are spaced apart along the winding path.

[0016] In an optional embodiment, the first blank area extends to both side edges of the substrate in the axial direction, and the second blank area extends to both side edges of the substrate in the axial direction; and / or the first active material layer extends to both side edges of the substrate in the axial direction, and the second active material layer extends to both side edges of the substrate in the axial direction.

[0017] In an optional embodiment, the first pole piece is a positive pole, and the second pole piece is a negative pole; and / or the secondary battery is a cylindrical battery.

[0018] In an optional embodiment, along the winding path of the first pole piece, the length of the first pole piece is L3mm, and along the winding path of the second pole piece, the length of the second pole piece is L4mm, satisfying: 1209≤L3≤1233, 1315≤L4≤1333; and / or, along the winding path of the first pole piece, the first active material layer is interrupted, and a third blank area not coated with the first active material layer is formed on the surface of the substrate, along the winding path of the first pole piece, the length of the third blank area is L5mm, and the distance between the edge of the third blank area close to the starting end of the winding of the first pole piece and the starting end of the winding is L6mm, satisfying: 6≤L5≤8, 389≤L6≤401.

[0019] In a second aspect, the present application provides a pole piece, wherein the pole piece and another pole piece have different polarities, are stacked and wound around the same axis and then accommodated in a housing cavity of a secondary battery, wherein the winding starting end of the pole piece is sandwiched between the innermost circle and the second innermost circle of the other pole piece, and the winding ending end of the pole piece is sandwiched between the outermost circle and the second outermost circle of the other pole piece;

[0020] The pole piece includes a substrate and a first active material layer and a second active material layer located on both sides of the substrate in a thickness direction;

[0021] Wherein, at one end of the electrode sheet along the winding path, an edge of the first active material layer and an edge of the second active material layer are spaced apart along the winding path.

[0022] In a third aspect, the present application provides a material strip, with a cutting direction perpendicular to the extending direction of the material strip, and the pole pieces are formed between two adjacent cutting lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0024] FIG1 is a cross-sectional view of an embodiment of a secondary battery in the related art;

[0025] FIG2 is a schematic cross-sectional view of a secondary battery according to an embodiment of the present application;

[0026] FIG3 is a cross-sectional view of a first electrode sheet in a wound state in an embodiment of a secondary battery of the present application;

[0027] FIG4 is a cross-sectional view of a first electrode sheet in a wound state in an embodiment of a secondary battery of the present application;

[0028] FIG5 is a cross-sectional view of a first electrode sheet in a wound state in an embodiment of a secondary battery of the present application, showing only the winding starting end;

[0029] FIG6 is a cross-sectional view of a first electrode sheet in a wound state in an embodiment of a secondary battery of the present application, showing only the winding end;

[0030] FIG7 is a cross-sectional view of a first electrode sheet in a flattened state in an embodiment of a secondary battery of the present application;

[0031] FIG8 is a top view of FIG7;

[0032] FIG9 is a schematic structural diagram of an embodiment of a material strip of the present application.

[0033] Description of reference numerals:

[0034] 101-shell; 102-accommodating cavity; 103-first pole piece; 105-second pole piece; 107-substrate; 109-first active material layer; 111-second active material layer; 113-first edge; 115-second edge; 117-first blank area; 119-third edge; 121-second blank area; 123-third blank area; 200-material strip; 201-cutting line; 203-foil; 205-active material layer; Q1-winding start end; Q2-winding end end; L-axis line. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of this application.

[0036] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0037] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to isolate them. The electrolyte conducts ions between the positive and negative electrodes.

[0038] Please refer to Figure 1. Figure 1 is a cross-sectional view of an embodiment of a secondary battery in the related art. In the figure, some parts are omitted and the figure is not drawn to scale.

[0039] In the related art, the secondary battery is a cylindrical battery. The secondary battery includes a shell 101 and a winding core. The shell 101 has a receiving cavity 102. The winding core is accommodated in the receiving cavity 102. The winding core includes a first pole piece 103, a second pole piece 105 and a diaphragm (not shown). The first pole piece 103, the second pole piece 105 and the diaphragm are stacked and wound around the same axis L (spiral winding). The first pole piece 103 and the second pole piece 105 have opposite polarities. Specifically, the first pole piece 103 is the positive electrode and the second pole piece 105 is the negative electrode. The diaphragm is sandwiched between the first pole piece 103 and the second pole piece 105 to act as an electrical insulator. The winding starting end Q1 of the first pole piece 103 is sandwiched between the innermost circle and the second inner circle of the second pole piece 105. The winding end Q2 of the first pole piece 103 is sandwiched between the outermost circle and the second outer circle of the second pole piece 105. The first electrode sheet 103 includes a substrate 107 and a first active material layer 109 and a second active material layer 111 located on either side of the substrate 107 in the thickness direction. At one end of the first electrode sheet 103 along the winding path, the edge of the first active material layer 109 and the edge of the second active material layer 111 are aligned along the winding path.

[0040] The thickness of the end portion of the first electrode 103 is directly reduced from the sum of the thicknesses of the first active material layer 109 , the substrate 107 , and the second active material layer 111 to zero, that is, directly reduced from T1 + T2 + T3 to zero.

[0041] During the charge and discharge process, the stress at the end of the first electrode piece 103 is high, causing the first electrode piece 103 to bend and deform. In some cases, the substrate 107 of the first electrode piece 103 breaks during the deformation process. In other cases, the first electrode piece 103 punctures the diaphragm and contacts the second electrode piece 105, causing a short circuit between the first electrode piece 103 and the second electrode piece 105.

[0042] In order to reduce the stress at the end of the electrode during charging and discharging, in the following embodiments of the present application, the electrode is arranged at one end of the winding path, and the edges of the active material layer on both sides of the substrate 107 are spaced apart (staggered) along the winding path of the electrode.

[0043] Please refer to Figure 2. Figure 2 is a schematic cross-sectional view of a secondary battery according to an embodiment of the present application. In the figure, some components are omitted and not drawn to scale.

[0044] In some embodiments, a secondary battery includes a housing 101, a first electrode sheet 103, and a second electrode sheet 105. The housing 101 has a housing cavity 102. The first electrode sheet 103 and the second electrode sheet 105 are housed in the housing cavity 102. The first electrode sheet 103 and the second electrode sheet 105 have opposite polarities, are stacked, and are wound around the same axis L. The winding starting end Q1 of the first electrode sheet 103 is sandwiched between the innermost and second innermost turns of the second electrode sheet 105. The winding ending end Q2 of the first electrode sheet 103 is sandwiched between the outermost and second outermost turns of the second electrode sheet 105. The first electrode sheet 103 includes a substrate 107 and a first active material layer 109 and a second active material layer 111 located on either side of the substrate 107 in the thickness direction. At one end of the first electrode sheet 103 along the winding path, the edges of the first active material layer 109 and the second active material layer 111 are spaced apart along the winding path, such that the thickness of the first electrode sheet decreases gradually or in steps along the winding direction F.

[0045] Specifically, in the embodiment shown in FIG2 , the secondary battery is a cylindrical battery, and accordingly, the first pole piece 103 and the second pole piece 105 are spirally wound. In other embodiments, the secondary battery is a prismatic battery, and the first pole piece 103 and the second pole piece 105 are spirally wound and then flattened to fit into the square receiving cavity of the prismatic battery. The specific shape of the secondary battery is not limited.

[0046] Specifically, the first electrode 103 is a positive electrode, and the second electrode 105 is a negative electrode. In some other embodiments, the first electrode 103 is a negative electrode, and the second electrode 105 is a positive electrode.

[0047] When the first electrode sheet 103 is a positive electrode, in some embodiments, the substrate 107 is an aluminum foil, and the first active material layer 109 and the second active material layer 111 are slurries containing lithium ions.

[0048] When the first electrode 103 is a negative electrode, in some embodiments, the substrate 107 is a copper foil, and the first active material layer 109 and the second active material layer 111 are a slurry containing graphite.

[0049] Specifically, in the embodiment shown in FIG. 2 , the aforementioned “winding path” is a spiral path.

[0050] At one end of the first electrode sheet 103 along the winding path, the edge of the first active material layer 109 and the edge of the second active material layer 111 are spaced apart (staggered) along the winding path, so that the end of the first electrode sheet 103 gradually becomes thinner along the winding path. Specifically, the thickness of the end of the first electrode sheet 103 is reduced from the sum of the thicknesses of the first active material layer 109, the substrate 107, and the second active material layer 111 (T1+T2+T3) to the sum of the thicknesses of the first active material layer 109 or the second active material layer 111 and the substrate 107 (T1+T2, or T3+T2), then further reduced to the thickness of the substrate 107 (T2), and then further reduced to zero. As a result, the stress at the end of the first electrode sheet 103 during charging and discharging is reduced.

[0051] In some embodiments, at the other end of the first electrode sheet 103 along the winding path, an edge of the first active material layer 109 and an edge of the second active material layer 111 are spaced apart along the winding path.

[0052] Specifically, the aforementioned “one end” may be one of the winding starting end Q1 and the winding ending end Q2 of the first pole piece 103 , and the aforementioned “other end” may be the other of the winding starting end Q1 and the winding ending end Q2 of the first pole piece 103 .

[0053] In some embodiments, as shown in FIG2 , both the winding starting end Q1 and the winding ending end Q2 of the first pole piece 103 have the improved structure of the present proposal. Therefore, both the winding starting end Q1 and the winding ending end Q2 of the first pole piece 103 can reduce stress during the charge and discharge process.

[0054] In other embodiments, the first pole piece 103 has the improved structure of the present proposal only at the winding starting end Q1 , so the winding starting end Q1 of the first pole piece 103 can reduce stress during the charging and discharging process.

[0055] In other embodiments, the first pole piece 103 has the improved structure of the present proposal only at the winding end Q2 , so that the winding end Q2 of the first pole piece 103 can reduce stress during the charging and discharging process.

[0056] Please refer to FIG. 3 , which is a cross-sectional view of the first electrode 103 in a wound state in an embodiment of the secondary battery of the present application.

[0057] In some embodiments, blank areas are formed on both the inner and outer sides of one end of the first pole piece 103 along the winding path.

[0058] Specifically, at one end of the first electrode sheet 103 along the winding path, the first edge 113 of the first active material layer 109 and the second edge 115 of the substrate 107 are spaced apart along the winding path, and a first blank area 117 not coated with the first active material layer 109 is formed on the surface of the substrate 107. At one end of the first electrode sheet 103 along the winding path, the third edge 119 of the second active material layer 111 and the first edge 113 of the substrate 107 are spaced apart along the winding path, and a second blank area 121 not coated with the second active material layer 111 is formed on the surface of the substrate 107. In the embodiment shown in FIG3 , the winding starting end Q1 and the winding ending end Q2 of the first electrode sheet 103 both adopt this structure. Please refer to FIG4 , which is a cross-sectional view of the first electrode sheet 103 in a wound state in one embodiment of the secondary battery of the present application.

[0059] In some other embodiments, a blank area is formed on only one side of one end of the first pole piece 103 along the winding path.

[0060] Specifically, at one end of the first electrode sheet 103 along the winding path, the first edge 113 of the first active material layer 109 and the second edge 115 of the substrate 107 are spaced apart along the winding path, forming a first blank area 117 on the surface of the substrate 107 where the first active material layer 109 is not applied. At one end of the first electrode sheet 103 along the winding path, the third edge 119 of the second active material layer 111 is flush with the first edge 113 of the substrate 107 along the winding path. In the embodiment shown in FIG4 , this structure is employed at both the winding start end Q1 and the winding end end Q2 of the first electrode sheet 103.

[0061] According to the embodiments shown in Figures 3 and 4, the first edge 113 and the third edge 119 can be staggered, and the relative positional relationship between the first edge 113 and the second edge 115 is not limited, and the relative positional relationship between the third edge 119 and the second edge 115 is not limited.

[0062] In the case where blank areas are formed on both the inner and outer sides of one end of the first pole piece 103 along the winding path, the present application further refines the relevant dimensions.

[0063] Please refer to FIG. 5 , which is a cross-sectional view of the first electrode piece 103 in a wound state in an embodiment of the secondary battery of the present application, showing only the winding starting end Q1 .

[0064] In some embodiments, the first blank area 117 and the second blank area 121 are respectively located at the winding starting end Q1 of the first pole piece 103, the extension length of the first blank area 117 along the winding path of the first pole piece 103 is L1mm, and the extension length of the second blank area 121 along the winding path of the first pole piece 103 is L2mm, satisfying: 13≤L2≤19, 11≤L1-L2≤13.

[0065] For example, L1 is 24, L2 is 13; L1 is 26, L2 is 13; L1 is 26, L2 is 15; L1 is 28, L2 is 15; L1 is 30, L2 is 19; L1 is 32, L2 is 19.

[0066] Please refer to FIG. 6 , which is a cross-sectional view of the first electrode 103 in a wound state in an embodiment of the secondary battery of the present application, showing only the winding end Q2 .

[0067] In some embodiments, the first blank area 117 and the second blank area 121 are respectively located at the winding end Q2 of the first pole piece 103, the extension length of the first blank area 117 along the winding path of the first pole piece 103 is L1mm, and the extension length of the second blank area 121 along the winding path of the first pole piece 103 is L2mm, satisfying: 6≤L2≤12, 2≤L1-L2≤4.

[0068] For example, L1 is 8, L2 is 6; L1 is 10, L2 is 6; L1 is 11, L2 is 9; L1 is 13, L2 is 9; L1 is 14, L2 is 12; L1 is 16, L2 is 12.

[0069] In one inspection scenario, the secondary battery is disassembled, and the first electrode piece 103 is taken out. After the first electrode piece 103 is dried and flattened, a ruler is used to inspect the extension lengths of the first blank area 117 and the second blank area 121 .

[0070] Please refer to FIG. 7 and FIG. 8 . FIG. 7 is a cross-sectional view of the first electrode 103 in a flattened state in an embodiment of the secondary battery of the present application. FIG. 8 is a top view of FIG. 7 .

[0071] At the winding starting end Q1 of the first pole piece 103 , the first blank area 117 a extends to both side edges of the substrate 107 in the axis L direction, and the second blank area 121 a extends to both side edges of the substrate 107 in the axis L direction.

[0072] At the winding end Q2 of the first pole piece 103 , the first blank area 117 b extends to both side edges of the substrate 107 in the axis L direction, and the second blank area 121 b extends to both side edges of the substrate 107 in the axis L direction.

[0073] The first active material layer 109 extends to both side edges of the substrate 107 in the axis L direction, and the second active material layer 111 extends to both side edges of the substrate 107 in the axis L direction.

[0074] Please continue to refer to Figures 7 and 8. In some embodiments, along the winding path of the first pole piece 103, the length of the first pole piece 103 is L3 mm, and along the winding path of the second pole piece 105, the length of the second pole piece 105 is L4 mm, satisfying the following: 1209 ≤ L3 ≤ 1233, 1315 ≤ L4 ≤ 1333. For example, L3 = 1209, L4 = 1351; L3 = 1215, L4 = 1320; L3 = 1233, L4 = 1333; L3 = 1209, L4 = 1333; L3 = 1233, L4 = 1315.

[0075] In one detection scenario, the secondary battery is disassembled, and the first electrode piece 103 and the second electrode piece 105 are taken out. After the first electrode piece 103 and the second electrode piece 105 are dried and flattened, a tape measure is used to measure the length.

[0076] Please continue to refer to Figures 7 and 8. In some embodiments, along the winding path of the first electrode 103, the first active material layer 109 is interrupted, and a third blank area 123 is formed on the surface of the substrate 107 where the first active material layer 109 is not coated. Along the winding path of the first electrode 103, the length of the third blank area 123 is L5mm, and the distance between the edge of the third blank area 123 close to the winding starting end Q1 of the first electrode 103 and the winding starting end Q1 is L6mm, satisfying: 6≤L5≤8, 389≤L6≤401. For example, L5=6, L6=389; L5=7, L6=395; L5=8, L6=401; L5=6, L6=401; L5=8, L6=389.

[0077] Specifically, the third blank area 123 can be used for welding connection tabs (not shown), so that the first electrode sheet 103 is electrically connected to the electrode column (not shown) of the secondary battery through the tabs.

[0078] Please refer to Figure 2. The application embodiment also provides a pole piece (first pole piece 103) and another pole piece (second pole piece 105) with different polarities, which are stacked and wound around the same axis L and then accommodated in the accommodating cavity 102 of the housing 101 of the secondary battery. The winding starting end Q1 of the pole piece is sandwiched between the innermost circle and the second inner circle of the other pole piece, and the winding ending end Q2 of the pole piece is sandwiched between the outermost circle and the second outer circle of the other pole piece. The pole piece includes a substrate 107 and a first active material layer 109 and a second active material layer 111 located on both sides of the substrate 107 in the thickness direction;

[0079] At one end of the electrode sheet along the winding path, the edge of the first active material layer 109 and the edge of the second active material layer 111 are spaced apart along the winding path. The electrode sheet is the first electrode sheet 103 in each embodiment of the secondary battery described above and will not be described in detail here.

[0080] Please refer to Figure 9, which is a schematic structural diagram of an embodiment of a material strip 200 of the present application. The drawing is not to scale.

[0081] The embodiment of the present application further provides a material strip 200 , with a cutting direction perpendicular to the extending direction of the material strip 200 , and the first electrode 103 in each of the above-mentioned secondary battery embodiments is formed between two adjacent cutting lines 201 .

[0082] Specifically, in the embodiment shown in FIG9 , the material strip 200 extends along the Y axis. The material strip 200 is coated using a continuous coating method. The material strip 200 includes a foil 203 and an active material layer 205 coated on the surface of the foil 203 .

[0083] The size of the foil 203 along the X-axis is the length of the first pole piece 103 along the winding path. According to the design parameters of the first pole piece 103, a first baffle (not shown) and a second baffle (not shown) are placed in the slurry tank of the coating equipment, and the first baffle and the second baffle are spaced apart along the X-axis. There is no slurry between the first baffle and the second baffle, and a blank area parallel to the coating direction can be left on the foil 203 during coating. The size of the blank area on the X-axis can be controlled by adjusting the position of the first baffle and the second baffle in the slurry tank. During subsequent cutting, cutting is performed in a direction perpendicular to the coating direction according to the width of the first pole piece 103 to obtain the first pole piece 103.

[0084] By adopting the above-mentioned cutting method, the thickness consistency of the first pole piece 103 can be high, and the material strip 200 is not cut and discarded, which can save costs.

[0085] In summary, the embodiments of the present application can reduce the stress at the ends of the electrode during the charging and discharging process.

[0086] Although the embodiments of the present application have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present application, and such modifications and variations shall fall within the scope defined by the appended claims. Industrial Applicability

[0087] A secondary battery includes a housing, a first electrode, and a second electrode. The housing has a housing cavity; the first and second electrode sheets are housed in the housing cavity. The first and second electrode sheets have opposite polarities, are stacked, and are wound around the same axis. The winding start of the first electrode sheet is sandwiched between the innermost and second innermost circles of the second electrode sheet, and the winding end of the first electrode sheet is sandwiched between the outermost and second outermost circles of the second electrode sheet. The first electrode sheet includes a substrate and a first active material layer and a second active material layer located on either side of the substrate in the thickness direction. At one end of the first electrode sheet along the winding path, the edges of the first active material layer and the edges of the second active material layer are spaced apart along the winding path, so that the thickness of the first electrode sheet decreases gradually or in steps along the winding direction. Specifically, the thickness of the end of the first electrode sheet decreases from the sum of the thicknesses of the first active material layer, the substrate, and the second active material layer to the sum of the thicknesses of the first active material layer or the second active material layer and the substrate, further decreases to the thickness of the substrate, and further decreases to zero. This reduces the stress on the end of the first electrode sheet during charging and discharging.

Claims

1. A secondary battery, characterized in that: include: A housing having a receiving cavity; A first pole piece and a second pole piece, the first pole piece and the second pole piece are accommodated in the accommodation cavity, the first pole piece and the second pole piece have opposite polarities, are stacked and wound around the same axis, the winding start end of the first pole piece is sandwiched between the innermost circle and the second inner circle of the second pole piece, the winding end end of the first pole piece is sandwiched between the outermost circle and the second outer circle of the second pole piece, and the first pole piece includes a substrate and a first active material layer and a second active material layer located on both sides of the substrate in a thickness direction; Among them, at one end of the first pole piece along the winding path, the edge of the first active material layer and the edge of the second active material layer are spaced apart along the winding path, so that the thickness of the first pole piece gradually decreases or decreases in steps in the winding direction.

2. The secondary battery according to claim 1, characterized in that: At one end of the first electrode sheet along the winding path, the edge of the first active material layer and the edge of the substrate are spaced apart along the winding path, and a first blank area not coated with the first active material layer is formed on the surface of the substrate; At one end of the first pole piece along the winding path, the edge of the second active material layer and the edge of the substrate are spaced apart along the winding path, and a second blank area not coated with the second active material layer is formed on the surface of the substrate.

3. The secondary battery according to claim 2, characterized in that: The first blank area and the second blank area are respectively located at the starting ends of the winding of the first pole piece. The extension length of the first blank area along the winding path of the first pole piece is L1mm, and the extension length of the second blank area along the winding path of the first pole piece is L2mm, satisfying: 13≤L2≤19, 11≤L1-L2≤13.

4. The secondary battery according to claim 2, characterized in that: The first blank area and the second blank area are respectively located at the winding ends of the first pole piece. The extension length of the first blank area along the winding path of the first pole piece is L1mm, and the extension length of the second blank area along the winding path of the first pole piece is L2mm, satisfying: 6≤L1≤12, 2≤L1-L2≤4.

5. The secondary battery according to claim 1, characterized in that: At the other end of the first pole piece along the winding path, an edge of the first active material layer and an edge of the second active material layer are spaced apart along the winding path.

6. The secondary battery according to claim 2, characterized in that: The first blank area extends to both side edges of the substrate in the axial direction, and the second blank area extends to both side edges of the substrate in the axial direction; And / or the first active material layer extends to both side edges of the substrate in the axial direction, and the second active material layer extends to both side edges of the substrate in the axial direction.

7. The secondary battery according to claim 1, characterized in that: The first pole piece is a positive pole, and the second pole piece is a negative pole; and / or the secondary battery is a cylindrical battery.

8. The secondary battery according to claim 1, characterized in that: Along the winding path of the first pole sheet, the length of the first pole sheet is L3mm, and along the winding path of the second pole sheet, the length of the second pole sheet is L4mm, satisfying: 1209≤L3≤1233, 1315≤L4≤1333; and / or, along the winding path of the first pole sheet, the first active material layer is interrupted, and a third blank area not coated with the first active material layer is formed on the surface of the substrate, and along the winding path of the first pole sheet, the length of the third blank area is L5mm, and the distance between the edge of the third blank area close to the starting end of the winding of the first pole sheet and the starting end of the winding is L6mm, satisfying: 6≤L5≤8, 389≤L6≤401.

9. A pole piece, characterized in that: The pole piece and the other pole piece have different polarities, are stacked and wound around the same axis and then placed in the accommodating cavity of the secondary battery housing, the winding start end of the pole piece is sandwiched between the innermost circle and the second inner circle of the other pole piece, and the winding end end of the pole piece is sandwiched between the outermost circle and the second outer circle of the other pole piece; The pole piece comprises a substrate and a first active material layer and a second active material layer located on both sides of the substrate in a thickness direction; Wherein, at one end of the pole piece along the winding path, an edge of the first active material layer and an edge of the second active material layer are spaced apart along the winding path.

10. A material strip, characterized in that: The cutting direction is perpendicular to the extending direction of the material strip, and the pole piece as claimed in claim 9 is formed between two adjacent cutting lines.

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