Secondary battery and electric device

Abstract

The invention relates to the technical field of energy storage, in particular to a secondary battery and electric equipment. A secondary battery includes an electrode assembly. The electrode assembly comprises a first pole piece, a second pole piece and a diaphragm, the diaphragm is arranged between the first pole piece and the second pole piece, and the first pole piece, the second pole piece and the diaphragm are stacked and wound to form a winding structure. In the winding direction of the electrode assembly, the first pole piece comprises a first straight section, a first bent section and a second straight section which are sequentially connected, and the first straight section and the second straight section are oppositely arranged in the first direction. The first bent section is provided with a first opening, the first opening penetrates through the first bent section in the thickness direction of the first pole piece, the first opening is provided with a first side wall and a second side wall which are oppositely arranged in the winding direction of the electrode assembly, the first side wall is located on the first straight section, and the second side wall is located on the second straight section; wherein the first direction is the thickness direction of the electrode assembly.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a secondary battery and electrical equipment. Background Art

[0002] Secondary batteries are increasingly used in the market, and users continue to pursue improvements in their battery life, requiring the energy density of secondary batteries to continue to increase. Correspondingly, the coating weight and cold pressing density of the cathode and anode electrodes of the battery are constantly increasing. For soft-pack secondary batteries with a wound structure, the corners on both sides are weak points in the interface of the battery cell. During the cycle, as the electrode continues to expand, the electrode at the corner is stretched by the main body of the battery cell and stress concentration occurs. The corner is constantly squeezed, and the space between the electrode pieces is continuously compressed, causing the electrolyte at the corner to be squeezed out, and it is impossible to provide sufficient channels for the electrolyte to flow back, resulting in insufficient electrolyte and lithium precipitation, and failure of the circulation interface. Improving the lack of electrolyte at the corners of the battery cell is an important task in the current development of secondary batteries with a wound structure. Summary of the invention

[0003] In view of this, the present application provides a secondary battery and an electrical device, which can improve the problem of insufficient electrolyte at the corners of the battery cell.

[0004] An embodiment of the present application provides a secondary battery, including an electrode assembly. The electrode assembly includes a first pole piece, a second pole piece and a diaphragm, the diaphragm is arranged between the first pole piece and the second pole piece, and the first pole piece, the second pole piece and the diaphragm are stacked and wound to form a winding structure. Along the winding direction of the electrode assembly, the first pole piece includes a first straight section, a first curved section and a second straight section connected in sequence, and the first straight section and the second straight section are arranged oppositely along the first direction. The first curved section is provided with a first opening, and the first opening penetrates the first curved section along the thickness direction of the first pole piece. Along the winding direction of the electrode assembly, the first opening has a first side wall and a second side wall arranged oppositely, and the first side wall is located on the first straight section, and the second side wall is located on the second straight section.

[0005] In the above-mentioned secondary battery, the first curved section of the first pole piece is provided with a first opening, and the first opening penetrates the first curved section along the thickness direction of the first pole piece, so that the electrolyte can enter or flow out of the electrode assembly from the first opening of the first pole piece, thereby improving the circulation efficiency of the electrolyte. The first straight section and the second straight section are arranged relatively to each other along the thickness direction of the electrode assembly, and the first opening has a first side wall and a second side wall arranged relatively to each other, the first side wall is located on the first straight section, and the second side wall is located on the second straight section, so that the first straight section and the second straight section form a pole piece similar to that in a laminated secondary battery, and the electrolyte can enter or flow out of the electrode assembly from the length direction of the electrode assembly and the width direction of the electrode assembly, so as to provide sufficient channels for the electrolyte to enter or flow back, thereby improving the problem of lithium deposition due to insufficient electrolyte and failure of the circulation interface in the secondary battery.

[0006] In the above embodiments, in the second direction, the first opening extends to the edge of the first curved segment, the first direction is the thickness direction of the electrode assembly, the second direction is the width direction of the first electrode sheet, and the first direction and the second direction are perpendicular to each other.

[0007] During the compression process of the above-mentioned secondary battery, there is a problem of uneven stress at the junction of the first straight section and the first curved section, and at the junction of the second straight section and the first curved section. During the cycle, as the pole piece continues to expand, especially at the edge of the junction along the width direction of the first pole piece, the stress of the pole piece is more concentrated after expansion, and it is more likely to break. By extending the first opening along the width direction of the first pole piece to the edge of the first curved section, the anode corresponding to this position does not undergo lithium deintercalation reaction, thereby reducing the expansion degree, relieving the stress at the corner position, and improving the problem of the first pole piece breaking from the edge due to expansion.

[0008] In one or more of the above embodiments, the first curved section is provided with a second opening, and the second opening penetrates the first curved section along the thickness direction of the first pole piece. Along the winding direction of the electrode assembly, the second opening has a fifth side wall and a sixth side wall arranged opposite to each other, and the fifth side wall is located on the first straight section, and the sixth side wall is located on the second straight section.

[0009] In the above-mentioned secondary battery, the first curved section of the first pole piece is also provided with a second opening, and the second opening penetrates the first curved section along the thickness direction of the first pole piece, so that the electrolyte can also enter or flow out of the electrode assembly from the second opening of the first pole piece, thereby further improving the circulation efficiency of the electrolyte. The second opening also has a fifth side wall and a sixth side wall, along the winding direction of the electrode assembly, the fifth side wall is located on the first straight section, and the sixth side wall is located on the second straight section, so that the electrolyte can enter or flow out of the electrode assembly from the length direction of the electrode assembly and the width direction of the electrode assembly, further improving the problem of lithium deposition and circulation interface failure caused by insufficient electrolyte in the secondary battery.

[0010] In one or more of the above embodiments, in the second direction, the second opening extends to the edge of the first curved segment.

[0011] The above-mentioned secondary battery extends the second opening along the width direction of the first electrode sheet to the edge of the first curved section so that the anode corresponding to this position does not undergo lithium insertion and extraction reaction, thereby further reducing the expansion degree, relieving the stress at the corner position on the other side of the electrode assembly, and further improving the problem of the first electrode sheet breaking from the edge due to expansion.

[0012] In one or more of the above embodiments, the first opening further has a third side wall and a fourth side wall. The third side wall and the fourth side wall are arranged opposite to each other along the second direction. The second direction is the width direction of the first pole piece. The first direction and the second direction are perpendicular to each other.

[0013] Compared with the first opening extending to the edge of the first curved section along the second direction, the electrolyte enters the center of the electrode assembly from the edge of the first curved section. In this technical solution, along the width direction of the first pole piece, the third side wall and the fourth side wall of the first opening are arranged opposite to each other, and along the thickness direction of the first pole piece, the first opening is located in the first curved section, so that the first opening is closer to the center of the electrode assembly, improving the efficiency of the electrolyte entering or flowing out of the electrode assembly, and improving the problem of lithium deposition and circulation interface failure due to insufficient electrolyte in the secondary battery.

[0014] In one or more of the above embodiments, the first pole piece includes a first edge and a second edge arranged opposite to each other along the second direction, and the third side wall is closer to the first edge than the fourth side wall; along the second direction, the distance between the third side wall and the first edge is L1, and the distance between the fourth side wall and the second edge is L2, │L1-L2│≤5mm.

[0015] In the above-mentioned secondary battery, the absolute value of the distance between the center of the first opening and the first edge and the second edge of the first electrode sheet is controlled within 5 mm, which is beneficial for controlling the first opening near the middle of the first electrode sheet, and for the electrolyte to enter from the first opening to the middle position near the first electrode sheet, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0016] In one or more of the above embodiments, the first bending section also includes a first connecting portion, the first opening and the first connecting portion are arranged in sequence along the width direction of the first pole piece, the width of the first pole piece is S1, and the effective connection length of the first connecting portion along the width direction of the first pole piece is S2, 1%≤(S2 / S1)×100%≤20%.

[0017] In the above-mentioned secondary battery, the ratio of the effective connection length of the first connection portion along the second direction to the length of the first pole piece along the second direction is greater than or equal to 1%, which is conducive to maintaining the overall electronic path of the first pole piece, and making the first pole piece have a certain strength, reducing the occurrence of the first pole piece breaking. The ratio of the effective connection length of the first connection portion along the second direction to the length of the first pole piece along the second direction is less than or equal to 20%, and the first opening is controlled to have a sufficient length in the second direction, thereby effectively shortening the distance for the electrolyte to be transmitted to the middle position of the first pole piece, which is conducive to the electrolyte entering the middle position of the first pole piece from the first opening, so as to quickly replenish the electrolyte consumed in the middle of the battery cell, improve the problem of purple spot lithium precipitation caused by ion bridge breaking, and thus lead to cycle failure.

[0018] In one or more of the above embodiments, 5%≤(S2 / S1)×100%≤10%.

[0019] In the above-mentioned secondary battery, the ratio of the effective connection length of the first connection portion along the second direction to the length of the first pole piece along the second direction is greater than or equal to 5%, which is conducive to further improving the overall electronic path of the first pole piece, and making the first pole piece have a certain strength, further reducing the occurrence of the first pole piece breaking. The ratio of the effective connection length of the first connection portion along the second direction to the length of the first pole piece along the second direction is less than or equal to 10%, and the first opening is controlled to have a sufficient length in the second direction, thereby further shortening the distance for the electrolyte to be transmitted to the middle position of the first pole piece, which is conducive to the electrolyte entering the middle position of the first pole piece from the first opening to quickly replenish the electrolyte consumed in the middle of the battery cell, further improving the problem of purple spot lithium precipitation caused by ion bridge breaking, thereby leading to cycle failure.

[0020] In one or more of the above embodiments, along the winding direction of the electrode assembly, the first pole piece includes a plurality of first bending segments, and the first opening is provided at N1 first bending segments counted from the winding starting end of the first pole piece, 1≤N1≤3.

[0021] During the cycle of the secondary battery, the stress at the junction of the first curved segment and the straight segments on both sides of the winding direction of the electrode assembly is more concentrated as the electrode sheet continues to expand, making it more prone to fracture. The first opening is set at the N1 first curved segments counted from the winding starting end of the first electrode sheet, 1≤N1≤3, so as to reduce the expansion degree, relieve the stress at the corner position, and improve the problem of the first electrode sheet breaking from the edge due to expansion.

[0022] In one or more of the above embodiments, along the winding direction of the electrode assembly, the first pole piece includes a plurality of first bending segments, and the first opening is provided at N2 first bending segments from the winding tail end of the first pole piece, 1≤N2≤3.

[0023] During the cycle of the secondary battery, the stress at the junction of the first curved segment and the straight segments on both sides of the winding direction of the electrode assembly is more concentrated as the electrode sheet continues to expand, making it more prone to fracture. The first opening is set at the N1 first curved segments counted from the winding end of the first electrode sheet, 1≤N1≤3, so as to reduce the expansion degree, relieve the stress at the corner position, and improve the problem of the first electrode sheet breaking from the edge due to expansion.

[0024] In one or more of the above embodiments, the angle of the first opening is set to be an arc shape.

[0025] In the secondary battery described above, the corner of the first opening is configured to be arc-shaped, so that the corner of the first opening remains smooth, thereby improving the problem of fracture at the corner of the first opening due to stress concentration.

[0026] In one or more of the above embodiments, the second pole piece includes a third straight segment, a second curved segment and a fourth straight segment connected in sequence, the third straight segment and the fourth straight segment are arranged relatively to each other along the first direction, the second curved segment is provided with a third opening, and the third opening penetrates the second pole piece along the thickness direction of the second pole piece.

[0027] In the above-mentioned secondary battery, the second curved section of the second electrode sheet is provided with a third opening, and the third opening penetrates the second curved section along the thickness direction of the second electrode sheet, so that the electrolyte can enter or flow out of the electrode assembly from the third opening of the second electrode sheet, thereby improving the circulation efficiency of the electrolyte.

[0028] In one or more of the above embodiments, the electrode assembly includes multiple winding layers, each winding layer includes a first electrode sheet, a second electrode sheet and a diaphragm stacked along a first direction; the first electrode sheet is a positive electrode sheet, and the second electrode sheet is a negative electrode sheet; in the same winding layer, along the third direction, the projection of the third opening falls within the projection range of the first opening; wherein the second direction is the width direction of the first electrode sheet, and the third direction is perpendicular to the first direction and the second direction.

[0029] In the above-mentioned secondary battery, the first electrode sheet is a positive electrode sheet, and the second electrode sheet is a negative electrode sheet. In the same winding layer, along the third direction, the projection of the third opening falls within the projection range of the first opening, which is beneficial for the second electrode sheet to cover the first electrode sheet to improve the lithium plating problem.

[0030] In a second aspect, an embodiment of the present application provides an electrical device, comprising a secondary battery in one or more of the above embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the overall structure of a secondary battery in one embodiment of the present application.

[0032] Figure 2 It is a schematic diagram of the disassembled structure of a secondary battery in one embodiment of the present application.

[0033] Figure 3 It is a schematic diagram of the cross-sectional structure of an electrode assembly in one embodiment of the present application.

[0034] Figure 4 It is a partial structural schematic diagram of the first pole piece in an embodiment of the present application, which shows a setting method of the first opening.

[0035] Figure 5It is a partial structural schematic diagram of the first pole piece in another embodiment of the present application, which shows another arrangement method of the first opening.

[0036] Figure 6 It is a partial structural schematic diagram of the first pole piece in another embodiment of the present application, which shows a setting method of the first opening and the second opening.

[0037] Figure 7 It is a partial structural schematic diagram of the first pole piece in another embodiment of the present application, which shows another arrangement method of the first opening and the second opening.

[0038] Figure 8 It is a partial structural schematic diagram of the first pole piece in another embodiment of the present application, which shows another arrangement method of the first opening and the second opening.

[0039] Fig. 9 It is a partial structural schematic diagram of the first pole piece and the second pole piece in an embodiment of the present application, which shows the positional relationship between the first opening and the second opening.

[0040] Fig.10 Schematic diagram of a top view of an electrode assembly in one embodiment of the present application.

[0041] Fig.11 It is a schematic diagram of the structure of an electrical device in an embodiment of the present application.

[0042] Main component symbols

[0043] 001 Secondary battery

[0044] 100 Electrode Assembly

[0045] 110 First Pole

[0046] 111 First straight section

[0047] 112 First bend

[0048] 1121 First Opening

[0049] 1121a First side wall

[0050] 1121b Second side wall

[0051] 1121c Third side wall

[0052] 1121d Fourth side wall

[0053] 1122 Second Opening

[0054] 1122a Fifth side wall

[0055] 1122b Sixth side wall

[0056] 1122c Seventh side wall

[0057] 1122d Eighth side wall

[0058] 1123 First connection

[0059] 113 Second straight section

[0060] 114 First Edge

[0061] 115 The Second Edge

[0062] 116 Winding start end

[0063] 117 Winding end

[0064] 120 Second pole piece

[0065] 121 The third straight section

[0066] 122 Second bend

[0067] 1221 The Third Opening

[0068] 1222 The Fourth Opening

[0069] 123 Fourth straight section

[0070] 130 Diaphragm

[0071] 200 First Tab

[0072] 300 Second Tab

[0073] 400 Housing

[0074] 410 cavity

[0075] 002 Electrical equipment

[0076] X first direction

[0077] Y Second direction

[0078] Z third direction

[0079] U Winding direction DETAILED DESCRIPTION

[0080] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0081] It should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component at the same time. When a component is considered to be "provided on" another component, it can be directly provided on the other component or there may be an intermediate component at the same time.

[0082] Unless otherwise specified, the term "plurality" as used herein means two or more than two.

[0083] The terms "first", "second", etc. are only used to distinguish different objects and shall not be understood as indicating or implying relative importance or implying the quantity, specific order or primary and secondary relationship of the indicated technical features.

[0084] It should be noted that when a parameter is greater than, equal to, or less than a certain endpoint value, it should be understood that the endpoint value is allowed to have a tolerance of ±5%.

[0085] It should be recognized that the dimensions of the structures shown in the drawings are given for better understanding and more convenient description, and the present application is not limited to the dimensions shown in the drawings. In order to make the present invention clear, elements irrelevant to the description are omitted from the details of this specification.

[0086] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0087] One embodiment of the present application provides a secondary battery, including an electrode assembly. The electrode assembly includes a first pole piece, a second pole piece and a diaphragm, the diaphragm is arranged between the first pole piece and the second pole piece, and the first pole piece, the second pole piece and the diaphragm are stacked and wound to form a winding structure. Along the winding direction of the electrode assembly, the first pole piece includes a first straight section, a first curved section and a second straight section connected in sequence, and the first straight section and the second straight section are arranged oppositely along the first direction. The first curved section is provided with a first opening, and the first opening penetrates the first curved section along the thickness direction of the first pole piece. Along the winding direction of the electrode assembly, the first opening has a first side wall and a second side wall arranged oppositely, and the first side wall is located on the first straight section, and the second side wall is located on the second straight section.

[0088] In the above-mentioned secondary battery, the first curved section of the first pole piece is provided with a first opening, and the first opening penetrates the first curved section along the thickness direction of the first pole piece, so that the electrolyte can enter or flow out of the electrode assembly from the first opening of the first pole piece, thereby improving the circulation efficiency of the electrolyte. The first straight section and the second straight section are arranged relatively along the thickness direction of the electrode assembly, and the first opening has a first side wall and a second side wall arranged relatively along the winding direction of the electrode assembly, the first side wall is located on the first straight section, and the second side wall is located on the second straight section, so that the first straight section and the second straight section form a pole piece similar to that in a laminated secondary battery, and the electrolyte can enter or flow out of the electrode assembly from the length direction of the electrode assembly and the width direction of the electrode assembly, so as to provide sufficient channels for the electrolyte to enter or flow back, thereby improving the problem of lithium deposition due to insufficient electrolyte and failure of the circulation interface in the secondary battery.

[0089] Some embodiments of the present application are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the features in the following embodiments and examples can be combined with each other.

[0090] See also Figure 1 and Figure 2 The embodiment of the present application provides a secondary battery 001, which includes an electrode assembly 100 and a first pole tab 200, wherein the first pole tab 200 is connected to the electrode assembly 100. The secondary battery 001 also includes a second pole tab 300, wherein the second pole tab 300 is connected to the electrode assembly 100, and the first pole tab 200 and the second pole tab 300 have different polarities.

[0091] In some embodiments, the secondary battery 001 further includes a housing 400, the housing 400 having a cavity 410, and the electrode assembly 100 is disposed in the cavity 410 in the housing 400. A portion of the first electrode tab 200 extends out of the housing 400 and is used to be electrically connected to an external structure. A portion of the second electrode tab 300 extends out of the housing 400 and is used to be electrically connected to an external structure.

[0092] In other embodiments, the first tab 200 is connected to a conductive first adapter (not shown), the first adapter partially extends out of the housing 400 and is used to be electrically connected to an external structure. The second tab 300 is connected to a conductive second adapter (not shown), the second adapter partially extends out of the housing 400 and is used to be electrically connected to an external structure.

[0093] In some embodiments, the shell 400 includes at least one of a steel shell, a resin shell or an aluminum-plastic film. For example, when the secondary battery 001 is a hard-shell battery, the shell 400 includes a steel shell or a resin shell. When the secondary battery 001 is a soft-pack battery, the shell 400 includes an aluminum-plastic film.

[0094] See also Figure 2 and Figure 3The electrode assembly 100 includes a first electrode sheet 110, a second electrode sheet 120 and a diaphragm 130. The diaphragm 130 is disposed between the first electrode sheet 110 and the second electrode sheet 120. The first electrode sheet 110, the second electrode sheet 120 and the diaphragm 130 are stacked and wound to form a winding structure.

[0095] Figure 4 The structure of the first straight section 111 , the first curved section 112 and the second straight section 113 after being flattened is shown to illustrate the relationship between the first pole piece 110 and the first opening 1121 .

[0096] See also Figure 3 and Figure 4 In some embodiments, along the winding direction U of the electrode assembly 100 , the first electrode sheet 110 includes a first straight segment 111 , a first curved segment 112 , and a second straight segment 113 that are sequentially connected, and the first straight segment 111 and the second straight segment 113 are arranged opposite to each other along the first direction X. The first direction X is the thickness direction of the electrode assembly 100 .

[0097] The first curved section 112 is provided with a first opening 1121 which penetrates the first curved section 112 along the thickness direction of the first electrode plate 110 so that the electrolyte can enter or flow out of the electrode assembly 100 from the first opening 1121 of the first electrode plate 110, thereby improving the circulation efficiency of the electrolyte.

[0098] Along the winding direction U of the electrode assembly 100, the first opening 1121 has a first side wall 1121a and a second side wall 1121b, wherein the first side wall 1121a is located on the first straight section 111, and the second side wall 1121b is located on the second straight section 113. Thus, the first straight section 111 and the second straight section 113 form a pole piece similar to that in the laminated secondary battery 001, and the electrolyte can enter or flow out of the electrode assembly 100 from the length direction of the electrode assembly 100 and the width direction of the electrode assembly 100, so as to provide sufficient channels for the electrolyte to enter or flow back, thereby improving the problem of lithium deposition due to insufficient electrolyte and failure of the circulation interface in the secondary battery 001.

[0099] In some embodiments, when the secondary battery 001 is compressed, there is a problem of uneven stress at the junction of the first straight section 111 and the first curved section 112, and at the junction of the second straight section 113 and the first curved section 112. When the secondary battery 001 is cycled, as the electrode sheet continues to expand, the stress at the edge of the above-mentioned junction along the width direction of the first electrode sheet 110 is more concentrated after the electrode sheet expands, and the problem of fracture is more likely to occur.

[0100] Along the second direction Y, the first opening 1121 extends to the edge of the first curved section 112, so that the anode corresponding to the position does not undergo lithium insertion and extraction reaction, thereby reducing the expansion degree, relieving the stress at the corner position, and improving the problem of the first pole piece 110 breaking from the edge due to expansion. The second direction Y is the width direction of the first pole piece 110, and the first direction X and the second direction Y are perpendicular to each other.

[0101] See also Figure 3 and Figure 5 In other embodiments, the first opening 1121 has a third side wall 1121c and a fourth side wall 1121d, and the third side wall 1121c and the fourth side wall 1121d are arranged opposite to each other along the second direction Y. Compared with the second direction Y, the first opening 1121 extends to the edge of the first curved segment 112, and the electrolyte enters the center of the electrode assembly 100 from the edge of the first curved segment 112. In this embodiment, along the width direction of the first pole piece 110, the third side wall 1121c and the fourth side wall 1121d of the first opening 1121 are arranged opposite to each other, and along the thickness direction of the first pole piece 110, the first opening 1121 is located in the first curved segment 112, so that the first opening 1121 is closer to the center of the electrode assembly 100, thereby improving the efficiency of the electrolyte entering or flowing out of the electrode assembly 100, and improving the problem of insufficient electrolyte and lithium deposition and circulation interface failure in the secondary battery 001.

[0102] In some embodiments, the first pole piece 110 includes a first edge 114 and a second edge 115 that are arranged opposite to each other along the second direction Y, and the third side wall 1121c is closer to the first edge 114 than the fourth side wall 1121d; along the second direction Y, the distance between the third side wall 1121c and the first edge 114 is L1, and the distance between the fourth side wall 1121d and the second edge 115 is L2, |L1-L2|≤5mm. The absolute value of the distance between the center of the first opening 1121 and the first edge 114 and the second edge 115 of the first pole piece 110 is controlled within 5mm, which is conducive to controlling the first opening 1121 at a position close to the middle of the first pole piece 110, and is conducive to the electrolyte entering from the first opening 1121 to the middle position close to the first pole piece 110, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0103] In some embodiments, |L1-L2| is any one of 0 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or any value therebetween.

[0104] In some embodiments, the corner of the first opening 1121 is configured to be arc-shaped, so that the corner of the first opening 1121 remains smooth, thereby improving the problem of the first opening 1121 being broken due to stress concentration at the corner.

[0105] Figure 6 The structure of the first straight section 111 , the first curved section 112 , and the second straight section 113 after being flattened is shown to illustrate the relationship between the first opening 1121 and the second opening 1122 on the first pole piece 110 .

[0106] See also Figure 3 and Figure 6 In some embodiments, the first curved section 112 is provided with a second opening 1122, and the second opening 1122 penetrates the first curved section 112 along the thickness direction of the first electrode plate 110, so that the electrolyte can enter or flow out of the electrode assembly 100 from the second opening 1122 of the first electrode plate 110, thereby further improving the circulation efficiency of the electrolyte.

[0107] In some embodiments, the first opening 1121 and the second opening 1122 are arranged along the second direction Y, and the first pole piece 110 includes a first edge 114 and a second edge 115 arranged relatively to each other along the second direction Y. The first opening 1121 extends to the first edge 114 of the first curved segment 112, and the second opening 1122 extends to the second edge 115 of the first curved segment 112, so that the anodes corresponding to the first opening 1121 and the second opening 1122 do not undergo lithium insertion and extraction reactions, thereby further reducing the degree of expansion, relieving the stress at the corner of the electrode assembly 100, and further improving the problem of the first pole piece 110 breaking from the edge due to expansion.

[0108] Along the winding direction U of the electrode assembly 100, the second opening 1122 has a fifth side wall 1122a and a sixth side wall 1122b, the fifth side wall 1122a is located on the first straight section 111, and the sixth side wall 1122b is located on the second straight section 113, so that the electrolyte can enter or flow out of the electrode assembly 100 from the length direction of the electrode assembly 100 and the width direction of the electrode assembly 100, further improving the problem of insufficient electrolyte and lithium deposition in the secondary battery 001 and the failure of the circulation interface.

[0109] See also Figure 3 and Figure 7 In other embodiments, the second opening 1122 has a seventh side wall 1122c and an eighth side wall 1122d, and the seventh side wall 1122c and the eighth side wall 1122d are arranged opposite to each other in the second direction Y. Along the thickness direction of the first pole piece 110, the second opening 1122 is located in the first curved section 112, so that the second opening 1122 is closer to the center of the electrode assembly 100, thereby improving the efficiency of the electrolyte entering or flowing out of the electrode assembly 100, and improving the problem of insufficient electrolyte in the secondary battery 001, lithium deposition, and failure of the circulation interface.

[0110] See also Figure 3 and Figure 8 In some other embodiments, two first openings 1121 are provided, and the two first openings 1121 are arranged along the second direction Y, wherein one first opening 1121 extends to the first edge 114 of the first curved section 112, and the other first opening 1121 extends to the second edge 115 of the first curved section 112. The second opening 1122 is located between the two first openings 1121, and the second opening 1122 has a seventh side wall 1122c and an eighth side wall 1122d, and the seventh side wall 1122c and the eighth side wall 1122d are arranged opposite to each other.

[0111] In some embodiments, the corner of the second opening 1122 is configured to be arc-shaped, so that the corner of the second opening 1122 remains smooth, thereby improving the problem of the second opening 1122 being broken due to stress concentration at the corner.

[0112] See also Figures 4 to 8 In some embodiments, the first curved section 112 further includes a first connecting portion 1123, the first opening 1121 and the first connecting portion 1123 are arranged in sequence along the width direction of the first pole piece 110, the width of the first pole piece 110 is S1, the effective connection length of the first connecting portion 1123 along the width direction of the first pole piece 110 is S2, 1%≤(S2 / S1)×100%≤20%. The ratio of the effective connection length of the first connecting portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is greater than or equal to 1%, which is conducive to maintaining the overall electronic path of the first pole piece 110, and making the first pole piece 110 have a certain strength, reducing the occurrence of the first pole piece 110 breaking. The ratio of the effective connection length of the first connecting portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is less than or equal to 20%. The first opening 1121 is controlled to have a sufficient length in the second direction Y, thereby effectively shortening the distance for the electrolyte to be transmitted to the middle position of the first pole piece 110, which is beneficial for the electrolyte to enter the middle position of the first pole piece 110 from the first opening 1121, so as to quickly replenish the electrolyte consumed in the middle of the battery cell, improve the problem of purple spot lithium precipitation caused by ion bridge breaking, and thus lead to cycle failure.

[0113] It is worth noting that the effective connection length of the first connection portion 1123 along the second direction Y refers to the length of the first connection portion 1123 in the second direction Y that can provide electrons with an electron path along the length direction of the first electrode 110 .

[0114] In some embodiments, 5%≤(S2 / S1)×100%≤10%. In the above-mentioned secondary battery 001, the ratio of the effective connection length of the first connecting portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is greater than or equal to 5%, which is conducive to further improving the overall electronic path of the first pole piece 110, and making the first pole piece 110 have a certain strength, further reducing the occurrence of the first pole piece 110 breaking. The ratio of the effective connection length of the first connecting portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is less than or equal to 10%, and the first opening 1121 is controlled to have a sufficient length in the second direction Y, thereby further shortening the distance for the electrolyte to be transmitted to the middle position of the first pole piece 110, which is conducive to the electrolyte entering the middle position of the first pole piece 110 from the first opening 1121, so as to quickly replenish the electrolyte consumed in the middle of the battery cell, further improving the problem of purple spot lithium precipitation caused by ion bridge breaking, thereby causing cycle failure.

[0115] In some embodiments, along the winding direction U of the electrode assembly 100, the first pole piece 110 includes a plurality of first curved segments 112, and the first opening 1121 is provided at N1 first curved segments 112 counted from the winding starting end 116 of the first pole piece 110, 1≤N1≤3. That is, as the pole piece continues to expand, the stress at the junction of the three first curved segments 112 and the straight segments on both sides of the winding direction U of the electrode assembly 100 is more concentrated, and the problem of fracture is more likely to occur. The first opening 1121 is provided at N1 first curved segments 112 counted from the winding starting end 116 of the first pole piece 110, 1≤N1≤3, thereby reducing the expansion degree, relieving the stress at the corner position, and improving the problem of the first pole piece 110 breaking from the edge due to expansion.

[0116] In other embodiments, along the winding direction U of the electrode assembly 100, the first pole piece 110 includes a plurality of first curved segments 112, and the first opening 1121 is provided at N2 first curved segments 112 from the winding tail end 117 of the first pole piece 110, 1≤N2≤3. That is, as the pole piece continues to expand, the stress at the junction of the three first curved segments 112 and the straight segments on both sides of the winding direction U of the electrode assembly 100 is more concentrated, and the problem of fracture is more likely to occur. The first opening 1121 is provided at N1 first curved segments 112 from the winding tail end 117 of the first pole piece 110, 1≤N1≤3, thereby reducing the expansion degree, relieving the stress at the corner position, and improving the problem of the first pole piece 110 breaking from the edge due to expansion. For ease of expression, the portion within three folds of the winding starting end 116 close to the first pole piece 110 is defined as the head of the first pole piece 110, the portion within three folds of the winding ending end 117 close to the first pole piece 110 is defined as the tail, and the portion located at the head and middle of the first pole piece 110 is defined as the middle.

[0117] In some other embodiments, the first opening 1121 is located in the middle of the first pole piece 110 .

[0118] See also Figure 2 and Fig. 9 In some embodiments, the second pole piece 120 includes a third straight segment 121, a second curved segment 122 and a fourth straight segment 123 which are connected in sequence, and the third straight segment 121 and the fourth straight segment 123 are arranged opposite to each other along the first direction X.

[0119] The second curved section 122 is provided with a third opening 1221 which penetrates the second electrode sheet 120 along the thickness direction of the second electrode sheet 120 so that the electrolyte can enter or flow out of the electrode assembly 100 from the third opening 1221 of the second electrode sheet 120, thereby improving the circulation efficiency of the electrolyte.

[0120] In some embodiments, the first pole piece 110 is a positive pole piece, and the second pole piece 120 is a negative pole piece.

[0121] In some embodiments, the electrode assembly 100 includes a plurality of winding layers, each of which includes a first electrode sheet 110 , a second electrode sheet 120 , and a separator 130 stacked along a first direction X.

[0122] In the same winding layer, along the third direction Z, the projection of the third opening 1221 falls within the projection range of the first opening 1121, which is conducive to the second pole piece 120 covering the first pole piece 110 to improve the lithium deposition problem. The third direction Z is perpendicular to the first direction X and the second direction Y, and the third direction Z is the width direction of the secondary battery 001.

[0123] In some embodiments, the corner of the third opening 1221 is configured to be arc-shaped, so that the corner of the third opening 1221 remains smooth, thereby improving the problem of the third opening 1221 being broken due to stress concentration at the corner.

[0124] It is worth noting that the angular positions of the first opening 1121 , the second opening 1122 , and the third opening 1221 refer to the ends of the first opening 1121 , the second opening 1122 , and the third opening 1221 close to the first connection portion 1123 .

[0125] See also Figure 2 and Fig.10 In some embodiments, the first pole piece 110 in each winding layer is configured as follows: two first openings 1121 are provided, and the two first openings 1121 are arranged along the second direction Y, wherein one first opening 1121 extends to the first edge 114 of the first curved section 112, and the other first opening 1121 extends to the second edge 115 of the first curved section 112. The second opening 1122 is located between the two first openings 1121, and the second opening 1122 has a seventh side wall 1122c and an eighth side wall 1122d, and the seventh side wall 1122c and the eighth side wall 1122d are arranged opposite to each other. A third opening 1221 and a fourth opening 1222 are correspondingly arranged on the second electrode sheet 120, and the second electrode sheet 120 covers the first electrode sheet 110, so that the first electrode sheet 110 and the second electrode sheet 120 form a electrode sheet similar to that in the stacked secondary battery 001, and the electrolyte can enter or flow out of the electrode assembly 100 from the length direction of the electrode assembly 100 and the width direction of the electrode assembly 100, so as to provide sufficient channels for the electrolyte to enter or flow back, thereby improving the problem of insufficient electrolyte and lithium deposition in the secondary battery 001 and the failure of the circulation interface.

[0126] See also Fig.11 An embodiment of the present application further provides an electric device 002, comprising the secondary battery 001 in one or more of the above embodiments.

[0127] In order to verify the effect of setting an opening on the electrode sheet on the electrolyte replenishment efficiency in the middle of the secondary battery 001, the following test was conducted:

[0128] (1) Cycle test: Take 10 secondary batteries 001 for each comparative example and each example for testing, place each secondary battery 001 in a 25°C environment for 30 minutes, and then charge and discharge according to the following steps. Charge to 4.2V at 5C constant current, then charge to 4.3V at 4C constant current, then charge to 4.45V at 3C constant current, then charge to 0.05C at 4.45V constant voltage, let stand for 5 minutes, discharge to 3V at 1C constant current, let stand for 5 minutes, this is one cycle. Cycle 1000 times according to the above cycle steps. After the cycle test, calculate the capacity retention rate of a single secondary battery 001. The capacity retention rate is the ratio of the discharge capacity after 1000 cycles to the discharge capacity in the first cycle. Record the capacity retention rate of 10 secondary batteries 001 in each comparative example and each example after 1000 cycles, and calculate its average value.

[0129] (2) 80°C storage test: 10 secondary batteries 001 were tested in each comparative example and each example. Each secondary battery 001 was placed in a 25°C environment for 30 minutes, and then charged and stored in the following steps: The thickness of the secondary battery 001 at the initial voltage was measured using a micrometer, and then the secondary battery 001 was fully charged, that is, charged to 4.45V at a constant current of 0.7C, and then charged to 0.02C at a constant voltage of 4.45V, and then the secondary battery 001 was placed in an 80°C constant temperature furnace for 8h. After 8h, the thickness of the secondary battery 001 after storage was measured using a micrometer, and the expansion rate of the secondary battery 001 was calculated. The expansion rate of the secondary battery 001: [(the thickness of the secondary battery 001 after high temperature storage-the thickness of the secondary battery 001 at the initial voltage) / the thickness of the secondary battery 001 at the initial voltage]×100%. The average expansion rate of the 10 secondary batteries 001 in each comparative example and each example was calculated.

[0130] (3) Hot box test: Take 10 secondary batteries 001 for each comparative example and each example for testing. Place each secondary battery 001 in a 25°C environment and let it stand for 30 minutes. Then perform a hot box test in the following steps: Under a 25°C environment, fully charge the secondary battery 001, that is, charge it to 4.45V at a constant current of 0.5C, and then charge it to 0.05C at a constant voltage of 4.45V. Then place the secondary battery 001 in a high temperature box and heat it to (130+n)±2°C at a heating rate of 5±2°C / min and keep it for 60 minutes; (n is an integer such as 0, 1, 2... and -1, -2...), and observe whether the secondary battery 001 explodes or catches fire. Record the temperature at which each secondary battery 001 starts to smoke, and record it as its maximum tolerance temperature. Calculate the average maximum tolerance temperature of the 10 secondary batteries 001 in each comparative example and each example.

[0131] The specific implementation of the secondary battery 001 in the embodiment and the comparative example is described below.

[0132] Embodiment 1:

[0133] A secondary battery 001, the assembly process is as follows:

[0134] (1) Preparation of anode pole piece: The anode active material artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) are mixed in a weight ratio of 96:1.5:2.5, and deionized water is added as a solvent to prepare an anode active material slurry with a weight percentage of 70wt%, and stirred evenly for use. A copper foil with a thickness of 10μm is used as the anode current collector, and the above-mentioned anode active material slurry is evenly coated on one surface of the anode current collector along its thickness direction using a slit coater, wherein an empty foil area without an anode active material layer is reserved at one end in the width direction of the anode current collector, and dried at 110°C to obtain an anode pole piece substrate coated with an anode active material layer on one side. Then, the above steps are repeated on the other side of the anode current collector along its thickness direction, and an empty foil area without an anode active material layer is reserved at one end in the width direction of the anode current collector to obtain an anode pole piece substrate coated with an anode active material layer on both sides, wherein the compression of the anode active material layer is 1.70g / cm 3 The anode plate substrate is punched out using a mold and a die cutter to obtain a single anode plate, wherein the empty foil area where the anode active material layer is not provided forms the anode ear. Figure 8 As shown, along the width direction of the anode electrode sheet (second electrode sheet 120), in the same second curved section 122, two third openings 1221 and a fourth opening 1222 are punched out on both sides of the anode electrode sheet using a die cutter, wherein the two third openings 1221 are arranged along the second direction Y, wherein one third opening 1221 extends to one edge of the second curved section 122, and the other third opening 1221 extends to the other edge of the second curved section 122. The fourth opening 1222 is located between the two third openings 1221. The absolute value of the distance difference between the center of the fourth opening 1222 and the first edge 114 and the second edge 115 of the second electrode sheet 120 is 3 mm. In addition, each curved section of the anode electrode sheet adopts the above-mentioned setting, hereinafter referred to as all corner edges and internal openings of the anode.

[0135] (2) Preparation of cathode pole piece: The cathode active material lithium cobalt oxide (Li CoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a cathode active material slurry with a solid content of 75wt%, and stirred evenly for use. A 10μm thick aluminum foil is used as a cathode current collector, and the above cathode active material slurry is evenly coated on one surface of the cathode current collector along its thickness direction using a slit coater, wherein an empty foil area without a cathode active material layer is reserved at one end in the width direction of the cathode current collector, and dried at 90°C to obtain a cathode pole piece substrate coated with a cathode active material layer on one side. Then repeat the above steps on the other side of the cathode current collector along its thickness direction, and reserve an empty foil area without a cathode active material layer at one end in the width direction of the cathode current collector to obtain a cathode pole piece substrate coated with a cathode active material layer on both sides. The cathode plate substrate is punched out using a mold and a die cutter to obtain a single cathode plate, wherein the empty foil area where the cathode active material layer is not provided forms a cathode ear. Along the width direction of the cathode plate (first plate 110), in the same first curved section 112, two first openings 1121 and one second opening 1122 are punched out on both sides of the cathode plate using a die cutter, wherein the two first openings 1121 are arranged along the second direction Y, wherein one first opening 1121 extends to the first edge 114 of the first curved section 112, and the other first opening 1121 extends to the second edge 115 of the first curved section 112. The second opening 1122 is located between the two first openings 1121. The absolute value of the distance difference between the center of the second opening 1122 and the first edge 114 and the second edge 115 of the second plate 120 is 3 mm. Moreover, each curved section of the cathode plate adopts the above-mentioned setting, and the cathode is referred to as the corner edge and the internal opening below.

[0136] The ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is 7%.

[0137] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L, wherein the conductivity of the electrolyte was 8.0 S / m.

[0138] (4) Preparation of the diaphragm 130: The diaphragm 130 has a three-layer structure and a thickness of 5 μm, and includes a first adhesive layer, a first substrate layer, and a second adhesive layer stacked in layers. The first substrate layer is made of polyethylene (PE), and both the first adhesive layer and the second adhesive layer contain a first adhesive and boehmite.

[0139] (5) Preparation of the electrode assembly 100: A first electrode sheet 110, a separator 130 and a second electrode sheet 120 are stacked along a first direction X to form a winding layer, and then the winding layer is wound to form a winding structure.

[0140] (6) Assembly of the electrode assembly 100: Place the aluminum-plastic film with the holes punched and formed in an assembly fixture, with the holes facing upward, place the electrode assembly 100 in the holes, and apply external force to press it. Then, place another aluminum-plastic film with the holes punched and formed on the electrode assembly 100 with the holes facing downward, and heat-seal the four sides of the two aluminum-plastic films by hot pressing to obtain an assembled electrode assembly 100.

[0141] (7) Liquid injection packaging: The electrolyte is injected into the assembled electrode assembly 100, and the secondary battery 001 is obtained through processes such as vacuum packaging, static standing, hot pressing, and shaping.

[0142] Comparative Example 1: The difference from Example 1 is that both the anode electrode plate and the cathode electrode plate are conventionally arranged without openings.

[0143] Comparative Example 2: The difference from Comparative Example 1 is that the density of the anode active material layer on the anode current collector copper foil (the second electrode sheet 120) is set to 1.60 g / cm 3 .

[0144] Comparative Example 3: The difference from Comparative Example 1 is that the conductivity of the electrolyte is set to 9.0 S / m.

[0145] Comparative Example 4: The difference from Comparative Example 1 is that the thickness of the diaphragm 130 is set to 7 um.

[0146] Embodiment 2: The difference from Embodiment 1 is that the anode electrode plate is conventionally arranged without openings.

[0147] Embodiment 3: The difference from Embodiment 1 is that the first opening 1121 and the second opening 1122 are both provided as one, and along the thickness direction of the first pole piece 110, the first opening 1121 and the second opening 1122 are both located in the first curved section 112. The third opening 1221 and the fourth opening 1222 are both provided as one, and along the thickness direction of the second pole piece 120, the third opening 1221 and the fourth opening 1222 are both located in the second curved section 122, hereinafter referred to as all corner embedded openings.

[0148] Embodiment 4: The difference from Embodiment 3 is that the anode electrode piece is conventionally set without openings. Three first curved sections 112 are set in the middle of the cathode electrode piece, and in each first curved section 112, the first opening 1121 and the second opening 1122 are both set as one, and along the thickness direction of the first electrode piece 110, the first opening 1121 and the second opening 1122 are both located in the first curved section 112, hereinafter referred to as the cathode middle three-fold corner embedded opening.

[0149] Embodiment 5: The difference from Embodiment 4 is that three first bent sections 112 are provided at the head of the cathode electrode piece, hereinafter referred to as the cathode head three-fold corner embedded opening.

[0150] Embodiment 6: The difference from Embodiment 4 is that three first bent sections 112 are provided at the tail of the cathode electrode piece, hereinafter referred to as the cathode tail three-fold corner embedded opening.

[0151] Embodiment 7: The difference from Embodiment 1 is that the ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is 3%.

[0152] Embodiment 8: The difference from Embodiment 1 is that the ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is 15%.

[0153] Embodiment 9: The difference from Embodiment 1 is that the ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is 0.8%.

[0154] Embodiment 10: The difference from Embodiment 1 is that the ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is 55%.

[0155] The main parameter control and test results of each embodiment and comparative example are shown in Table 1:

[0156] Table 1

[0157]

[0158]

[0159] Note: “ / ” means no value.

[0160] In Comparative Example 1, both the cathode and anode pole pieces use a conventional integral structure, with no openings at the corners, and are matched with a conventional coating weight and a conventional 5um thick diaphragm 130 substrate. The electrolyte uses a matching system charge and discharge rate design, and the conductivity is 8.0S / m. Under this design, the speed at which the electrolyte is transmitted from the periphery to the center during the cycle cannot match the system charge and discharge rate requirements. In the middle and late stages of the normal temperature cycle, the electrolyte in the middle of the pole piece is insufficient, and purple spots on the interface precipitate lithium, resulting in rapid cycle decay.

[0161] Comparative Example 2, based on Comparative Example 1, lowered the density of the anode pole piece, increased the porosity of the pole piece, improved the electrolyte transmission channel inside the corner external pole piece, and improved the interface and circulation level at the corner position. However, this design significantly reduced the surface density of the pole piece, and the energy density of the battery cell decreased by about 2.08%, which was difficult to meet customer requirements.

[0162] Comparative Example 3, based on Comparative Example 1, the conductivity of the electrolyte is increased from 8.0 to 9.0, and the transmission speed of the electrolyte is accelerated by reducing the viscosity of the electrolyte. Under this design, the dynamic performance of the battery cell is significantly improved, and the normal temperature cycle is significantly improved. However, the increased activity of the electrolyte causes a significant deterioration in the high-temperature stability of the entire battery cell, and its high-temperature storage level and hot box window are significantly deteriorated, and cannot meet the requirements.

[0163] Comparative Example 4 thickens the thickness of the diaphragm 130 substrate on the basis of Comparative Example 1, thereby widening the electrolyte transmission channel between the pole pieces, thereby increasing the electrolyte transmission speed. Based on this, the room temperature cycle performance is significantly improved, basically meeting the requirement of achieving ≥80% capacity retention rate, and the high temperature performance remains the same. However, the increase in the thickness of the diaphragm 130 significantly deteriorates the energy density of the battery cell, and its volume energy density decreases by about 3% compared with the comparative example, which cannot meet the requirements.

[0164] Embodiment 1, on the basis of comparative example 1, the cathode electrode piece and the anode electrode piece are provided with a first opening 1121, a second opening 1122, a third opening 1221 and a fourth opening 1222 distributed along the second direction Y. Among them, the two first openings 1121 are arranged along the second direction Y, one of the first openings 1121 extends to the first edge 114 of the first curved section 112, and the other first opening 1121 extends to the second edge 115 of the first curved section 112. The second opening 1122 is located between the two first openings 1121. The two third openings 1221 are arranged along the second direction Y, one of the third openings 1221 extends to the first edge 114 of the second curved section 122, and the other third opening 1221 extends to the second edge 115 of the second curved section 122. The fourth opening 1222 is located between the two third openings 1221. A connecting portion is retained between the cathode electrode piece and the anode electrode piece as an electron transmission channel. Under this design, the energy density of the battery cell decreases slightly by about 1% due to the loss of active materials at the opening position, but the design of the opening basically opens up the corners on both sides of the original winding structure, which is close to the stacking structure. The active materials at the corners are basically removed, and there will be no interface shortcomings. In addition, the newly added electrolyte transmission pathways on both sides have significantly improved the electrolyte transmission speed of the main body, which is beneficial to the improvement of the main body interface. Under the action of the two, the cycle performance is significantly improved to meet customer requirements. In addition, the opening can be used as an exhaust and heat dissipation channel, which is conducive to the discharge of heat inside the battery cell and gases generated by side reactions in a high temperature environment, and can significantly increase the hot box window of the battery cell by about 4°C.

[0165] In Example 2, based on Example 1, only the cathode electrode piece is designed with a corner opening, that is, two first openings 1121 are arranged along the second direction Y, one of the first openings 1121 extends to the first edge 114 of the first curved section 112, and the other first opening 1121 extends to the second edge 115 of the first curved section 112, and the second opening 1122 is located between the two first openings 1121. The anode electrode piece maintains the non-opening design morphology of Example 1. Under this design, because the active material lost by the cathode electrode piece is the same as that of Example 1, the energy density is at the same level as that of Example 1, and the circulation level and the hot box window are significantly improved compared with Example 1. However, due to the non-opening design of the anode electrode piece, its liquid storage, electrolyte transmission, heat dissipation and gas transmission channels are reduced compared with Example 1, and the improvement of circulation and hot box will be less than that of Example 1.

[0166] In Example 3, compared with Example 1, the shape of the corner opening is changed from an opening that opens through the head and tail edges of the pole piece to an embedded opening that does not open through the head and tail, that is, the first opening 1121 and the second opening 1122 are both set as one, and along the thickness direction of the first pole piece 110, the first opening 1121 and the second opening 1122 are both located in the first curved section 112. The third opening 1221 and the fourth opening 1222 are both set as one, and along the thickness direction of the second pole piece 120, the third opening 1221 and the fourth opening 1222 are both located in the second curved section 122. The overall design is basically equivalent to the improvement of the interface, circulation and hot box window in Example 1, and the energy density level is also basically the same, which further illustrates that the shape of the corner opening is not limited, and the desired effect can be achieved.

[0167] In Example 4, compared with Example 3, the design of all the embedded openings at the corners of the cathode and anode plates is changed to embedded openings only at the three-fold corners in the middle of the cathode, that is, three first curved sections 112 are set in the middle of the cathode plate, and in each first curved section 112, the first opening 1121 and the second opening 1122 are set as one, and along the thickness direction of the first plate 110, the first opening 1121 and the second opening 1122 are both located in the first curved section 112. Under this system, the middle corner position is a severely squeezed area. This design solves the corner failure problem at a fixed point, and also has obvious improvements on the cycle and interface, but is slightly inferior to Example 1 and Implementation 3. On the other hand, the energy density loss of the battery is further reduced.

[0168] In Example 5, compared with Example 4, the position of the corner opening is changed from the middle three-fold to the head three-fold. Because the head three-fold is not the most serious corner failure position in this system, the corresponding cycle improvement effect is slightly reduced, but it still shows an improvement effect compared with the comparative example. This design will have a better improvement effect on other systems where the corner failure is serious at the head and tail positions, and the fixed point design is based on the actual situation.

[0169] In Example 6, compared with Example 4, the position of the corner opening is changed from the middle three-fold to the tail three-fold, because the tail three-fold is not the most serious corner failure position in this system, and the corresponding cycle improvement effect is slightly reduced, but it still shows an improvement effect compared with the comparative example. This design will have a better improvement effect on other systems where the corner failure is serious at the head and tail positions, and the fixed point design is based on the actual situation.

[0170] In addition, embodiments 4, 5, and 6 are more suitable for high expansion systems with risk of fracture at corners. The cathode corner openings are correspondingly arranged at the positions where the stress at the corners is most concentrated, which can effectively solve the fracture problem of the pole pieces.

[0171] Example 7 Based on Example 1, the ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is adjusted from 7% to 3%, and other parameters remain unchanged. Due to the increase in the area of ​​the opening, the energy density is slightly reduced, but due to the shortening of the connection portion retained between the cathode pole piece and the anode pole piece, the overall electron path of the pole piece is narrowed, the cycle performance is significantly reduced, the expansion rate is increased, and the average maximum tolerance temperature is reduced.

[0172] Example 8 Based on Example 1, the ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is adjusted from 7% to 15%, and other parameters remain unchanged. Due to the reduction in the area of ​​the opening, the energy density is slightly improved, but due to the increase in the area of ​​the connection portion retained between the cathode pole piece and the anode pole piece, the electrolyte transmission path is narrowed, the cycle performance is reduced, the expansion rate is increased, and the average maximum tolerance temperature is reduced.

[0173] Example 9 Based on Example 1, the ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is adjusted from 7% to 0.8%, and other parameters remain unchanged. As the area of ​​the opening is further increased, the energy density is not significantly improved, but as the connection portion retained between the cathode pole piece and the anode pole piece is further shortened, the overall electron path of the pole piece is further narrowed, the cycle performance is significantly reduced, the expansion rate is increased, and the average maximum tolerance temperature is reduced.

[0174] Example 10 Based on Example 1, the ratio of the effective connection length of the first connection portion 1123 along the second direction Y to the length of the first pole piece 110 along the second direction Y is adjusted from 7% to 55%, and other parameters remain unchanged. Due to the reduction in the area of ​​the opening, the energy density is slightly improved, but due to the further increase in the area of ​​the connection portion retained between the cathode pole piece and the anode pole piece, the electrolyte transmission path is narrowed, the cycle performance is reduced, the expansion rate is increased, and the average maximum tolerance temperature is reduced.

[0175] In addition, for ordinary technicians in this field, various other corresponding changes and modifications can be made according to the technical concept of this application, and all these changes and modifications should fall within the protection scope of the claims of this application.

Claims

1. A secondary battery, comprising an electrode assembly, wherein the electrode assembly comprises a first electrode sheet, a second electrode sheet and a diaphragm, wherein the diaphragm is disposed between the first electrode sheet and the second electrode sheet, and the first electrode sheet, the second electrode sheet and the diaphragm are stacked and wound to form a winding structure, characterized in that: Along the winding direction of the electrode assembly, the first electrode sheet includes a first straight section, a first curved section, and a second straight section which are sequentially connected, and the first straight section and the second straight section are arranged opposite to each other along the first direction; The first curved section is provided with a first opening, and the first opening penetrates the first curved section along the thickness direction of the first pole piece. Along the winding direction of the electrode assembly, the first opening has a first side wall and a second side wall that are oppositely arranged, and the first side wall is located on the first straight section, and the second side wall is located on the second straight section; wherein the first direction is the thickness direction of the electrode assembly.

2. The secondary battery according to claim 1, wherein: In the second direction, the first opening extends to the edge of the first curved section. The second direction is the width direction of the first pole piece. The first direction and the second direction are perpendicular to each other.

3. The secondary battery according to claim 1 or 2, characterized in that: The first curved section is provided with a second opening, and the second opening penetrates the first curved section along the thickness direction of the first pole piece. Along the winding direction of the electrode assembly, the second opening has a fifth side wall and a sixth side wall arranged opposite to each other, and the fifth side wall is located on the first straight section, and the sixth side wall is located on the second straight section.

4. The secondary battery according to claim 3, characterized in that: In the second direction, the second opening extends to an edge of the first curved segment.

5. The secondary battery according to claim 1, wherein: The first opening further has a third side wall and a fourth side wall. The third side wall and the fourth side wall are arranged opposite to each other along a second direction. The second direction is the width direction of the first pole piece. The first direction and the second direction are perpendicular to each other.

6. The secondary battery according to claim 5, characterized in that: The first pole piece includes a first edge and a second edge arranged opposite to each other along the second direction, and the third side wall is closer to the first edge than the fourth side wall; along the second direction, the distance between the third side wall and the first edge is L1, and the distance between the fourth side wall and the second edge is L2, │L1-L2│≤5mm.

7. The secondary battery according to claim 1, wherein: The first curved section also includes a first connecting portion, the first opening and the first connecting portion are arranged in sequence along the width direction of the first pole piece, the width of the first pole piece is S1, and the effective connection length of the first connecting portion along the width direction of the first pole piece is S2, 1%≤(S2 / S1)×100%≤20%.

8. The secondary battery according to claim 7, characterized in that 5%≤(S2 / S1)×100%≤10%.

9. The secondary battery according to claim 1, wherein: Along the winding direction of the electrode assembly, the first pole piece includes a plurality of the first curved segments, and the first opening is provided at N1 of the first curved segments counted from the winding starting end of the first pole piece, where 1≤N1≤3.

10. The secondary battery according to claim 1, wherein: Along the winding direction of the electrode assembly, the first pole piece includes a plurality of the first curved segments, and the first opening is provided at N2 first curved segments from the winding tail end of the first pole piece, where 1≤N2≤3.

11. The secondary battery according to claim 1, wherein The corner of the first opening is arranged to be in an arc shape.

12. The secondary battery according to claim 1, wherein: The second pole piece includes a third straight section, a second curved section and a fourth straight section which are connected in sequence, the third straight section and the fourth straight section are arranged opposite to each other along the first direction, the second curved section is provided with a third opening, and the third opening penetrates the second pole piece along the thickness direction of the second pole piece.

13. The secondary battery according to claim 12, characterized in that: The electrode assembly includes multiple winding layers, each of which includes a first electrode sheet, a second electrode sheet and a diaphragm stacked along the first direction; the first electrode sheet is a positive electrode sheet, and the second electrode sheet is a negative electrode sheet; in the same winding layer, along the third direction, the projection of the third opening falls within the projection range of the first opening; wherein the second direction is the width direction of the first electrode sheet, and the third direction is perpendicular to the first direction and the second direction.

14. An electrical device, characterized in that: Comprising the secondary battery according to any one of claims 1 to 13.

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