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. The secondary battery comprises an electrode assembly, and the electrode assembly comprises a first pole piece, a diaphragm and a second pole piece which are sequentially stacked. The first pole piece is provided with at least one first gap, the first gap penetrates through the first pole piece in the first direction and extends to the edge of the first pole piece, the first pole piece further comprises a first connecting part, and the first gap and the first connecting part are sequentially arranged in the third direction; in the third direction, the projection of the first connecting part falls into the projection range of the first notch, the length of the first pole piece in the third direction is S1, the effective connecting length of the first connecting part in the third direction is S2, and (S2 / S1) * 100% is larger than or equal to 1% and smaller than or equal to 50%. And the first gap is controlled to have enough length in the third direction, so that the distance of the electrolyte transmitted to the middle position of the first pole piece is effectively shortened, and the electrolyte consumed in the middle of the battery cell is quickly supplied, so that the problem of cycle failure is solved.

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] In order to improve the charging and discharging capacity of secondary batteries and meet consumers' demand for fast charging and discharging, the multi-pole structure has been favored in the fast charging and discharging system because it can significantly reduce the ohmic impedance of the battery compared to the single-pole structure, and has good ability to increase charging speed and reduce temperature rise. Among them, the stacked structure is widely used in mobile phone battery products because it has both the low impedance and high energy density performance of the multi-pole structure. Summary of the invention

[0003] For fast-charge and fast-discharge battery systems, the battery cell has high requirements for the transmission speed of the electrolyte during the cycle, and it is necessary to be able to quickly replenish the electrolyte consumed in the middle of the battery cell during the cycle. For the laminated battery cells in the related technology, especially the battery system with large length and width and high charge and discharge speed, the electrolyte replenishment speed is a big problem, which limits its application in fast-charge and fast-discharge systems. In addition, the laminated battery cells also need to be fixed by hot pressing to fix the cell structure, and hot pressing will further compress the space between the diaphragm and the pole piece, reducing the path of electrolyte transmission and worsening electrolyte replenishment. In addition, the heat problem during the use of the battery cell reduces the safety performance of the battery cell.

[0004] In view of this, the present application provides a secondary battery and an electrical device, which can increase the replenishment speed of the electrolyte and enhance the heat dissipation capacity of the electrode assembly and improve the safety of the electrode assembly.

[0005] In the first aspect, an embodiment of the present application provides a secondary battery, including an electrode assembly, the electrode assembly including a first electrode sheet, a diaphragm, and a second electrode sheet stacked in sequence. The first electrode sheet is provided with at least one first notch, the first notch penetrates the first electrode sheet along the first direction, and the first notch extends to the edge of the first electrode sheet; the first electrode sheet also includes a first connecting portion, the first notch and the first connecting portion are arranged in sequence along the third direction; along the third direction, the projection of the first connecting portion falls within the projection range of the first notch; the length of the first electrode sheet along the third direction is S1, the effective connection length of the first connecting portion along the third direction is S2, 1%≤(S2 / S1)×100%≤50%; the first direction is the thickness direction of the first electrode sheet, and the first direction, the second direction, and the third direction are perpendicular to each other.

[0006] In the above-mentioned secondary battery, the first notch on the first pole piece passes through the first pole piece along the first direction and extends to the edge of the first pole piece, which is conducive to the electrolyte at the edge of the first pole piece to penetrate into the middle position of the first pole piece through the first notch. The first pole piece also includes a first connecting portion, the first notch and the first connecting portion are arranged in sequence along the third direction, and along the third direction, the projection of the first connecting portion falls within the projection range of the first notch, wherein the ratio of the effective connection length of the first connecting portion along the third direction to the length of the first pole piece along the third 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 connecting portion along the third direction to the length of the first pole piece along the third direction is less than or equal to 50%, and the first notch is controlled to have a sufficient length in the third direction, thereby effectively shortening the distance of the electrolyte transmission 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 notch 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. In addition, the first notch is provided on the first electrode piece, which is beneficial to improving the heat dissipation capacity of the electrode assembly and improving the safety performance of the electrode assembly. It should be noted that the effective connection length of the first connection portion refers to the length of the first connection portion that can form an electron path in the third direction.

[0007] In the above embodiment, 2%≤(S2 / S1)×100%≤10%.

[0008] In the above-mentioned secondary battery, the ratio of the effective connection length of the first connecting portion along the third direction to the length of the first electrode piece along the third direction is greater than or equal to 2%, which is beneficial to further maintain the overall electronic path of the first electrode piece and further reduce the breakage of the first electrode piece; the ratio of the effective connection length of the first connecting portion along the third direction to the length of the first electrode piece along the third direction is less than or equal to 10%, and the first notch is further controlled to have a sufficient length in the third direction, thereby effectively shortening the distance for the electrolyte to be transmitted to the middle position of the first electrode piece, which is beneficial for the electrolyte to enter the middle position of the first electrode piece from the first notch to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0009] In one or more of the above embodiments, the second pole piece is provided with at least one second notch, and the second notch penetrates the second pole piece along the first direction; along the first direction, the projection of the first notch and the projection of the second notch at least partially overlap.

[0010] In the above-mentioned secondary battery, the second notch arranged on the second electrode sheet passes through the second electrode sheet along the first direction, thereby effectively shortening the distance for the electrolyte to be transmitted to the middle position of the second electrode sheet, and along the first direction, the projection of the first notch and the projection of the second notch at least partially overlap, thereby widening the channel for the electrolyte to be transmitted to the first electrode sheet and the adjacent second electrode sheet in the first direction, which is beneficial for the electrolyte to enter from the first notch and the second notch to the middle position between the first electrode sheet and the adjacent second electrode sheet, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0011] In one or more of the above embodiments, the second notch extends to the edge of the second pole piece, and the second pole piece also includes a second connecting portion, and the second notch and the second connecting portion are arranged in sequence along the third direction; along the third direction, the projection of the second connecting portion falls within the projection range of the second notch.

[0012] In the above-mentioned secondary battery, the second notch extends to the edge of the second pole piece, which is conducive to the electrolyte infiltration from the edge of the pole piece to the middle position of the second pole piece; the second pole piece also includes a second connecting portion, and the second notch and the second connecting portion are arranged in sequence along the third direction, which is conducive to maintaining the overall electronic path of the second pole piece.

[0013] In one or more of the above embodiments, the first electrode piece is a cathode electrode piece, and the second electrode piece is an anode electrode piece; the first notch and the second notch are arranged correspondingly, and along the first direction, the projection of the second notch is located within the projection of the first notch.

[0014] In the above secondary battery, along the first direction, the first notch and the second notch are correspondingly arranged and the projection of the second notch is located within the projection of the first notch, which is beneficial for the second electrode sheet to cover the first electrode sheet along the first direction to improve the lithium plating problem.

[0015] In one or more of the above embodiments, the first pole piece is provided with at least one first opening, and the first opening penetrates the first pole piece along the first direction; along the third direction, the distance between the center of the first opening and the two edges of the first pole piece are L1 and L2 respectively, │L1-L2│≤5mm.

[0016] In the above-mentioned secondary battery, the absolute value of the distance between the center of the first opening and the two edges of the first electrode piece is controlled within 5 mm, which is conducive to controlling the first opening at a position close to the middle of the first electrode piece, and is conducive to the electrolyte entering from the first opening to the middle position close to the first electrode piece, so as to quickly replenish the electrolyte consumed in the middle of the battery cell. It should be noted that if the width of the first opening in the second direction is greater than or equal to the width of the first notch in the second direction, the length of the first opening in the third direction is not included in the effective connection length of the first connection portion.

[0017] In one or more of the above embodiments, the first pole piece is provided with at least one first opening, and the first opening penetrates the first pole piece along the first direction; the second pole piece is provided with at least one second opening, and the second opening penetrates the second pole piece along the first direction; along the third direction, the distances from the center of the first opening to the two edges of the first pole piece are L1 and L2 respectively, and the distances from the second opening to the two edges of the second pole piece are L3 and L4 respectively, │L1-L2│≤5mm, │L3-L4│≤5mm. It should be noted that if the width of the first opening in the second direction is greater than or equal to the width of the first notch in the second direction, the length of the first opening in the third direction is not included in the effective connection length of the first connection portion.

[0018] In the above-mentioned secondary battery, the absolute value of the distance between the center of the first opening and the two edges of the first electrode sheet is controlled within 5 mm, which is conducive to controlling the first opening at a position close to the middle of the first electrode sheet, and is conducive to the electrolyte entering from the first opening to the middle position close to the first electrode sheet, so as to quickly replenish the electrolyte consumed in the middle of the battery cell; the absolute value of the distance between the center of the second opening and the two edges of the second electrode sheet is controlled within 5 mm, which is conducive to controlling the second opening at a position close to the middle of the second electrode sheet, and is conducive to the electrolyte entering from the second opening to the middle position close to the second electrode sheet, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0019] In one or more of the above embodiments, the number of the second openings is the same as the number of the first openings, and the second openings are arranged corresponding to the first openings.

[0020] In the above-mentioned secondary battery, the number of the second openings is the same as the number of the first openings and is arranged correspondingly, which is conducive to the rapid flow of the electrolyte between the first openings and the second openings to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0021] In one or more of the above embodiments, the first pole piece is a cathode pole piece, and the second pole piece is an anode pole piece; along the first direction, the projection of the second opening is located within the projection of the first opening.

[0022] In the above-mentioned secondary battery, the projection of the second opening is located within the projection of the first opening, which is beneficial for the second electrode sheet to cover the first electrode sheet along the first direction, so as to improve the lithium plating problem.

[0023] In one or more of the above embodiments, the first connecting portion is also provided with a first flare, which penetrates the first connecting portion along the first direction; the first flare is provided at at least one end of the first opening along the third direction, and the first flare is connected to the first opening; along the third direction, the projection of the first opening is located within the projection of the first flare.

[0024] In the above-mentioned secondary battery, the first expansion hole passes through the first connecting portion along the first direction and is connected to the first opening. Along the third direction, the projection of the first opening is located within the projection of the first expansion hole, thereby widening at least one end of the first opening along the third direction, improving the circulation efficiency of the electrolyte, and quickly replenishing the electrolyte consumed in the middle of the battery cell.

[0025] In one or more of the above embodiments, the corner of the first notch is arranged to be arc-shaped.

[0026] In the above-mentioned secondary battery, the corner of the first notch is set to be arc-shaped, so that the corner of the first notch remains smooth, thereby improving the problem of fracture at the corner of the first notch due to stress concentration.

[0027] In one or more of the above embodiments, the angle of the first opening is set to be an arc shape.

[0028] In the above-mentioned secondary battery, the corner of the first opening is set 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.

[0029] The above-mentioned secondary battery is provided with a first notch on the first pole piece of the electrode assembly, the first notch penetrates the first pole piece along the first direction and extends to the edge of the first pole piece, the first pole piece also includes a first connecting portion, and along the third direction, the projection of the first connecting portion falls within the projection range of the first notch, wherein the ratio of the effective connection length of the first connecting portion along the third direction to the length of the first pole piece along the third direction is greater than or equal to 1%, which is beneficial to maintaining the overall electronic path of the first pole piece, and is beneficial to 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 connecting portion along the third direction to the length of the first pole piece along the third direction is less than or equal to 50%, and the first notch is controlled to have a sufficient length in the third direction, thereby effectively shortening the distance for the electrolyte to be transmitted to the middle position of the first pole piece, which is beneficial for the electrolyte to enter the middle position of the first pole piece from the first notch, 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.

[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 for Figure 1 Schematic diagram of the decomposition of the secondary battery.

[0033] Figure 3 It is a schematic diagram of the structure of the first pole piece in an embodiment of the present application.

[0034] Figure 4 It is a schematic diagram of the structure of the first pole piece in another embodiment of the present application.

[0035] Figure 5 It is a schematic diagram of the structure of the first pole piece in another embodiment of the present application.

[0036] Figure 6 It is a schematic diagram of the structure of the first pole piece in another embodiment of the present application.

[0037] Figure 7 It is a schematic diagram of the structure of the first pole piece in another embodiment of the present application.

[0038] Figure 8 It is a schematic diagram of the structure of the second pole piece and the first pole piece in one embodiment of the present application.

[0039] Fig. 9 It is a schematic diagram of the structure of the second pole piece and the first pole piece in another embodiment of the present application.

[0040] Fig.10 It is a schematic diagram of the structure of the second pole piece and the first pole piece in another 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 Shell

[0045] 110 cavity

[0046] 200 Electrode Assembly

[0047] 210 First Pole

[0048] 211 First Gap

[0049] 212 First connection

[0050] 215 First Opening

[0051] 216 First expansion

[0052] 220 Second pole piece

[0053] 221 Second Gap

[0054] 222 Second connection

[0055] 225 Second Opening

[0056] 226 Second expansion

[0057] 230 Diaphragm

[0058] 300 First Tab

[0059] 400 Second Tab

[0060] 002 Electrical equipment

[0061] X first direction

[0062] Y Second direction

[0063] Z third direction DETAILED DESCRIPTION

[0064] 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.

[0065] 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.

[0066] Unless otherwise specified, the term "plurality" as used herein means two or more than two.

[0067] 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.

[0068] 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%.

[0069] 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.

[0070] 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.

[0071] An embodiment of the present application provides a secondary battery, including an electrode assembly, the electrode assembly including a first electrode sheet, a diaphragm, and a second electrode sheet stacked in sequence. The first electrode sheet is provided with at least one first notch, the first notch penetrates the first electrode sheet along a first direction, and the first notch extends to the edge of the first electrode sheet; the first electrode sheet also includes a first connecting portion, the first notch and the first connecting portion are arranged in sequence along a third direction; along the third direction, the projection of the first connecting portion falls within the projection range of the first notch; the length of the first electrode sheet along the third direction is S1, the effective connection length of the first connecting portion along the third direction is S2, 1%≤(S2 / S1)*100%≤50%; the first direction is the thickness direction of the first electrode sheet, and the first direction, the second direction, and the third direction are perpendicular to each other.

[0072] The first notch on the first pole piece passes through the first pole piece along the first direction and extends to the edge of the first pole piece, which is conducive to the electrolyte at the edge of the first pole piece to penetrate to the middle position of the first pole piece through the first notch. The first pole piece also includes a first connecting portion, the first notch and the first connecting portion are arranged in sequence along the third direction, and along the third direction, the projection of the first connecting portion falls within the projection range of the first notch, wherein the ratio of the effective connection length of the first connecting portion along the third direction to the length of the first pole piece along the third 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 connecting portion along the third direction to the length of the first pole piece along the third direction is less than or equal to 50%, and the first notch is controlled to have a sufficient length in the third direction, thereby effectively shortening the distance of the electrolyte transmission 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 notch to quickly replenish the electrolyte consumed in the middle of the battery cell, improve the problem of purple spot lithium precipitation due to ion bridge breaking, and thus cause cycle failure. It should be noted that the effective connection length of the first connection portion refers to the length of the first connection portion that can form an electron path in the third direction.

[0073] 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.

[0074] See also Figure 1 and Figure 2The embodiment of the present application provides a secondary battery 001, which includes an electrode assembly 200 and a first pole tab 300, wherein the first pole tab 300 is connected to the electrode assembly 200. The secondary battery 001 also includes a second pole tab 400, wherein the second pole tab 400 is connected to the electrode assembly 200, and the first pole tab 300 and the second pole tab 400 have different polarities.

[0075] In some embodiments, the secondary battery 001 further includes a housing 100, the housing 100 having a cavity 110, and the electrode assembly 200 is disposed in the cavity 110 in the housing 100. A portion of the first electrode tab 300 extends out of the housing 100 and is used to be electrically connected to an external structure. A portion of the second electrode tab 400 extends out of the housing 100 and is used to be electrically connected to an external structure.

[0076] In other embodiments, the first tab 300 is connected to a conductive first adapter (not shown), which partially extends out of the housing 100 and is used to electrically connect to an external structure. The second tab 400 is connected to a conductive second adapter (not shown), which partially extends out of the housing 100 and is used to electrically connect to an external structure.

[0077] In some embodiments, the shell 100 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 100 includes a steel shell or a resin shell. When the secondary battery 001 is a soft-pack battery, the shell 100 includes an aluminum-plastic film.

[0078] See also Figure 2 and Figure 3 In some embodiments, the electrode assembly 200 includes a first electrode plate 210, a second electrode plate 220 and a diaphragm 230, the diaphragm 230 is arranged between the first electrode plate 210 and the second electrode plate 220, and the first electrode plate 210, the second electrode plate 220 and the diaphragm 230 are stacked in sequence to form a stacked structure.

[0079] In some embodiments, the first pole piece 210 is provided with at least one first notch 211 , the first notch 211 penetrates the first pole piece 210 along the first direction X, and the first notch 211 extends to the edge of the first pole piece 210 in the length direction.

[0080] The first direction X is the thickness direction of the first pole piece 210 , and the first direction X, the second direction Y and the third direction Z are perpendicular to each other.

[0081] In some embodiments, the first pole piece 210 is provided with a first notch 211 .

[0082] In some embodiments, the first pole piece 210 further includes a first connection portion 212, and the first notch 211 and the first connection portion 212 are sequentially arranged along the third direction Z. Along the third direction Z, the projection of the first connection portion 212 falls within the projection range of the first notch 211. Since the edge of the first pole piece 210 in the length direction is farther from the center of the first pole piece 210, the first notch 211 is arranged in the length direction of the first pole piece 210, which effectively shortens the distance for the electrolyte to be transmitted to the middle position of the first pole piece 210, and is conducive to the electrolyte infiltration from the first notch 211 to the middle position of the first pole piece 210.

[0083] See also Figure 4 In other embodiments, the first pole piece 210 is provided with two first notches 211, and the two first notches 211 are arranged in sequence along the third direction Z; one of the first notches 211 extends to one edge of the first pole piece 210 along the third direction Z, and the other first notch 211 extends to the other edge of the first pole piece 210 along the third direction Z; along the third direction Z, the projection of one of the first notches 211 falls within the projection range of the other first notch 211. In this case, the first connecting portion 212 is a portion connecting the two first notches 211 along the third direction Z.

[0084] See also Figure 5 In some embodiments, the first electrode 210 is provided with two first notches 211, wherein one first notch 211 extends to one edge of the first electrode 210 along the third direction Z, and the other first notch 211 extends to the other edge of the first electrode 210 along the third direction Z; along the third direction Z, the projection of one first notch 211 only partially overlaps with the projection of the other first notch 211. In this case, the first connecting portion 212 is a portion connecting the two first notches 211 along the third direction Z.

[0085] See also Figure 6 In some embodiments, the first electrode 210 is provided with two first notches 211, one of which extends to one edge of the first electrode 210 along the third direction Z, and the other first notch 211 extends to the other edge of the first electrode 210 along the third direction Z; along the third direction Z, the projection of one first notch 211 does not overlap with the projection of the other first notch 211. In this case, there are two first connecting portions 212, which are arranged in sequence with the two first notches 211 along the third direction Z respectively.

[0086] In some embodiments, the third direction Z may also be the width direction of the electrode assembly 200 , and the first electrode piece 210 is provided with at least one first notch 211 , which penetrates the first electrode piece 210 along the first direction X, and extends to the edge of the first electrode piece 210 in the width direction.

[0087] In some further embodiments, at least one first notch 211 is provided in the length direction and the width direction of the electrode assembly 200 , the first notch 211 penetrates the first electrode piece 210 along the first direction X, and the first notch 211 extends to the edge of the first electrode piece 210 in the length direction or the width direction.

[0088] In some embodiments, two or more first notches 211 have the same size.

[0089] In some other embodiments, two or more first notches 211 have different sizes.

[0090] In some embodiments, the length of the first pole piece 210 along the third direction Z is S1, and the effective connection length of the first connection portion 212 along the third direction Z is S2, 1%≤(S2 / S1)×100%≤50%. Among them, the ratio of the effective connection length of the first connection portion 212 along the third direction Z to the length of the first pole piece 210 along the third direction Z is greater than or equal to 1%, which is conducive to maintaining the overall electronic path of the first pole piece 210. The ratio of the effective connection length of the first connection portion 212 along the third direction Z to the length of the first pole piece 210 along the third direction Z is less than or equal to 50%, and the first notch 211 is controlled to have a sufficient length in the third direction Z, thereby effectively shortening the distance for the electrolyte to be transmitted to the middle position of the first pole piece 210, which is conducive to the electrolyte entering the middle position of the first pole piece 210 from the first notch 211, 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.

[0091] It is worth noting that the effective connection length of the first connection portion 212 along the third direction Z refers to the length of the first connection portion 212 in the third direction Z that can provide electrons with a path to form an electron path in the second direction Y.

[0092] In some embodiments, 2%≤(S2 / S1)×100%≤10%. The ratio of the effective connection length of the first connecting portion 212 along the third direction Z to the length of the first pole piece 210 along the third direction Z is greater than or equal to 2%, which is beneficial to further maintain the overall electronic path of the first pole piece 210, and make the first pole piece 210 have a certain strength, reducing the occurrence of the first pole piece 210 breaking. The ratio of the effective connection length of the first connecting portion 212 along the third direction Z to the length of the first pole piece 210 along the third direction Z is less than or equal to 10%, and the first notch 211 is further controlled to have a sufficient length in the third direction Z, thereby effectively shortening the distance for the electrolyte to be transmitted to the middle position of the first pole piece 210, which is beneficial for the electrolyte to enter the middle position of the first pole piece 210 from the first notch 211, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0093] See also Figure 7 In some embodiments, the first pole piece 210 is provided with at least one first opening 215 , and the first opening 215 passes through the first pole piece 210 along the first direction X.

[0094] It should be noted that if the width of the first opening 215 in the second direction Y is greater than or equal to the width of the first notch 211 in the second direction Y, the length of the first opening 211 in the third direction Z is not included in the effective connection length of the first connection portion 212 .

[0095] In some embodiments, the first pole piece 210 is provided with one first opening 215. In other embodiments, the first pole piece 210 is provided with two first openings 215, and the two first openings 215 are arranged in sequence along the third direction Z. In other embodiments, the first pole piece 210 is provided with three, four, five, etc. first openings 215.

[0096] In some embodiments, the first pole piece 210 is provided with a first opening 215. Along the third direction Z, the distances between the center of the first opening 215 and the two edges of the first pole piece 210 are L1 and L2 respectively, │L1-L2│≤5mm, and the absolute value of the distance between the center of the first opening 215 and the two edges of the first pole piece 210 is controlled within 5mm, which is conducive to controlling the first opening 215 at a position close to the middle of the first pole piece 210, and is conducive to the electrolyte entering from the first opening 215 to the middle position of the first pole piece 210, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0097] In other embodiments, the first pole piece 210 is provided with a plurality of first openings 215. Along the third direction Z, among the plurality of first openings 215, there is at least one first opening 215 whose center is respectively at a distance L1 and L2 from the two edges of the first pole piece 210, │L1-L2│≤5mm.

[0098] 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.

[0099] See also Figure 8 In some embodiments, the second pole piece 220 is provided with at least one second notch 221 , and the second notch 221 penetrates the second pole piece 220 along the first direction X.

[0100] In some embodiments, the second pole piece 220 is provided with one second notch 221. In other embodiments, the second pole piece 220 is provided with two second notches 221, and the two second notches 221 are arranged in sequence along the third direction Z. In other embodiments, the second notches 221 on the second pole piece 220 are provided with three, four, five, etc.

[0101] In some embodiments, along the first direction X, the projection of the first notch 211 and the projection of the second notch 221 at least partially overlap, thereby widening the channel for electrolyte transmission to the first pole piece 210 and the adjacent second pole piece 220 in the first direction X, which is beneficial for the electrolyte to enter from the first notch 211 and the second notch 221 to the middle position between the first pole piece 210 and the adjacent second pole piece 220, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0102] In some embodiments, the second notch 221 is located inside the second pole piece 220 , and the projection of the first notch 211 and the projection of the second notch 221 at least partially overlap.

[0103] In some embodiments, the second notch 221 extends to the edge of the second pole piece 220. The second pole piece 220 further includes a second connecting portion 222. The second notch 221 and the second connecting portion 222 are sequentially arranged along the third direction Z. Along the third direction Z, the projection of the second connecting portion 222 falls within the projection range of the second notch 221.

[0104] In some embodiments, the first pole piece 210 is a cathode pole piece, and the second pole piece 220 is an anode pole piece.

[0105] In some embodiments, the first notch 211 and the second notch 221 are arranged correspondingly, and along the first direction X, the projection of the second notch 221 is located within the projection of the first notch 211, which is beneficial for the second electrode 220 to cover the first electrode 210 along the first direction X to improve the lithium plating problem.

[0106] See also Fig. 9 In some embodiments, the second connection portion 222 is provided with at least one second opening 225 , and the second opening 225 passes through the second connection portion 222 along the first direction X.

[0107] In some embodiments, the second connection portion 222 is provided with one second opening 225. In other embodiments, the second connection portion 222 is provided with two second openings 225, and the two second openings 225 are arranged in sequence along the third direction Z. In other embodiments, the second connection portion 222 is provided with three, four, five, etc. second openings 225.

[0108] In some embodiments, the second connecting portion 222 is provided with a second opening 225. Along the third direction Z, the distances between the second opening 225 and the two edges of the second pole piece 220 are L3 and L4 respectively, │L3-L4│≤5mm, and the absolute value of the distance between the center of the second opening 225 and the two edges of the second pole piece 220 is controlled within 5mm, which is conducive to controlling the second opening 225 at a position close to the middle of the second pole piece 220, and is conducive to the electrolyte entering from the second opening 225 to the middle position of the second pole piece 220, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0109] In other embodiments, the second connecting portion 222 is provided with a plurality of second openings 225. Along the third direction Z, among the plurality of second openings 225, there is at least one second opening 225, whose center is respectively at a distance of L3 and L4 from the two edges of the second pole piece 220, │L3-L4│≤5mm.

[0110] In some embodiments, |L3-L4| 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.

[0111] In some embodiments, the number of second openings 225 is the same as the number of first openings 215 , and the second openings 225 are arranged corresponding to the first openings 215 , which is conducive to the rapid flow of electrolyte between the first openings 215 and the second openings 225 to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0112] In some embodiments, along the first direction X, the projection of the second opening 225 is located within the projection of the first opening 215 , which is beneficial for the second pole piece 220 to cover the first pole piece 210 along the first direction X to improve the lithium plating problem.

[0113] See also Fig.10 In some embodiments, the first connection portion 212 is further provided with a first expansion opening 216, and the first expansion opening 216 penetrates the first connection portion 212 along the first direction X. Along the third direction Z, the projection of the first opening 215 is located within the projection of the first expansion opening 216, thereby widening the first opening 215 and improving the circulation efficiency of the electrolyte, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0114] In some embodiments, the first flare 216 is disposed at at least one end of the first opening 215 along the third direction Z, and the first flare 216 is connected to the first opening 215. In other embodiments, the first flare 216 is disposed at both ends of the first opening 215 along the third direction Z.

[0115] In some embodiments, in the second pole piece 220, the second connection portion 222 is further provided with a second flared opening 226, and the second flared opening 226 penetrates the second connection portion 222 along the second direction Y. Along the third direction Z, the projection of the second opening 225 is located within the projection of the second flared opening 226, thereby widening the second opening 225 and improving the circulation efficiency of the electrolyte, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0116] In some embodiments, the second flare 226 is disposed at at least one end of the second opening 225 along the third direction Z, and the second flare 226 is connected to the second opening 225. In other embodiments, the second flare 226 is disposed at both ends of the second opening 225 along the third direction Z.

[0117] In some embodiments, the first expansion opening 216 and the second expansion opening 226 are arranged correspondingly, and along the first direction X, the projection of the second expansion opening 226 is located within the projection of the first expansion opening 216, which is beneficial for the second pole piece 220 to cover the first pole piece 210 along the first direction X to improve the lithium plating problem.

[0118] In some embodiments, the angle of the first notch 211 is set to an arc shape. In some embodiments, the angle of the second notch 221 is set to an arc shape. In some embodiments, the angle of the first opening 215 is set to an arc shape. In some embodiments, the angle of the second opening 225 is set to an arc shape. In some embodiments, the angle of the first flare 216 is set to an arc shape. In some embodiments, the angle of the second flare 226 is set to an arc shape.

[0119] It is worth mentioning that the corner positions of the first notch 211, the second notch 221, the first opening 215, the second opening 225, the first expansion 216 and the second expansion 226 refer to the ends of the first notch 211, the second notch 221, the first opening 215, the second opening 225, the first expansion 216 and the second expansion 226 close to the first connecting portion 212. The corner positions are kept smooth, which is conducive to improving the problem of fracture due to stress concentration at the corner positions.

[0120] See also Fig.11 One embodiment of the present application further provides an electric device 002, comprising the secondary battery 001 in one or more of the above embodiments.

[0121] In order to verify the effect of setting a notch / opening on the electrode on the electrolyte replenishment efficiency in the middle of the secondary battery 001, the following test was conducted:

[0122] (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.

[0123] (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.

[0124] (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: Fully charge the secondary battery 001 at 25°C, i.e. charge it to 4.45V at a constant current of 0.7C, and then charge it to 0.02C 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.

[0125] The specific implementation of the secondary battery 001 in the embodiment and the comparative example is described below.

[0126] Embodiment 1:

[0127] A secondary battery 001, the assembly process is as follows:

[0128] (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 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 of the anode current collector in the width direction, 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 in the thickness direction, and an empty foil area without an anode active material layer is reserved at one end of the anode current collector in the width direction, to obtain an anode pole piece substrate coated with an anode active material layer on both sides, wherein the weight of the active material layer per unit area is 100mg / 1540mm 2 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 7 As shown, along the length direction (third direction Z) of the anode electrode sheet (second electrode sheet 220), a second notch 221 is punched out at both ends of the anode electrode sheet using a die cutter, and the second notch 221 penetrates the second electrode sheet 220 along the first direction X. Then a second opening 225 is punched out in the second electrode sheet 220, and the absolute value of the distance difference between the center of the second opening 225 and the two edges of the second electrode sheet 220 along the third direction Z is 3mm. Among them, along the third direction Z, the projection of the second connecting portion 222 falls within the projection range of the second notch 221, and the ratio of the effective connection length of the second connecting portion 222 along the third direction Z to the length of the second electrode sheet 220 along the third direction Z is 5%.

[0129] (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. A single cathode electrode sheet is obtained by punching the cathode electrode sheet substrate using a mold and a die cutter, wherein the cathode electrode ear is formed at the empty foil area where the cathode active material layer is not provided. A first notch 211 is punched out at both ends of the cathode electrode sheet along the length direction (third direction Z) of the cathode electrode sheet (first electrode sheet 210), and the first notch 211 penetrates the first electrode sheet 210 along the first direction X. Then a first opening 215 is punched out in the first electrode sheet 210, and the absolute value of the distance difference between the center of the first opening 215 and the two edges of the first electrode sheet 210 along the third direction Z is 3 mm. Among them, along the third direction Z, the projection of the first connecting portion 212 falls within the projection range of the first notch 211, and the ratio of the effective connection length of the first connecting portion 212 along the third direction Z to the length of the first electrode sheet 210 along the third direction Z is 5%.

[0130] (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.

[0131] (4) Preparation of the diaphragm 230: The diaphragm 230 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.

[0132] (5) Preparation of electrode assembly 200: stacking the cathode electrode sheet, the separator 230 and the anode electrode sheet.

[0133] (6) Assembly of the electrode assembly 200: Place the aluminum-plastic film with the holes punched and formed in an assembly fixture, with the holes facing upward, and place the electrode assembly 200 in the holes, and apply external force to press it. Then, cover the electrode assembly 200 with another aluminum-plastic film with the holes punched and formed, 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 200.

[0134] (7) Liquid injection and packaging: The electrolyte is injected into the assembled electrode assembly 200, and the secondary battery 001 is obtained through processes such as vacuum packaging, static standing, hot pressing, and shaping.

[0135] Comparative Example 1: The difference from Example 1 is that both the anode electrode sheet and the cathode electrode sheet are conventionally configured without notches / openings.

[0136] Comparative Example 2: The difference from Comparative Example 1 is that the weight of the active material layer per unit area on the anode current collector copper foil (the second electrode sheet 220) is set to 90 mg / 1540 mm 2 .

[0137] Comparative Example 3: The difference from Comparative Example 1 is that the conductivity of the electrolyte is set to 9.0 S / m.

[0138] Comparative Example 4: The difference from Comparative Example 1 is that the thickness of the diaphragm 230 is set to 7 um.

[0139] Embodiment 2: The difference from Embodiment 1 is that the anode electrode plate is conventionally arranged without a notch / opening.

[0140] Example 3: The difference from Example 1 is that the second notch 221 and the second opening 225 are arranged along the width direction (second direction Y) of the anode current collector copper foil (second pole piece 220), and the first notch 211 and the first opening 215 are arranged along the width direction (second direction Y) of the cathode current collector aluminum foil (first pole piece 210).

[0141] Comparative Example 5: The difference from Example 1 is that, along the length direction of the anode current collector copper foil (second pole piece 220), only the second opening 225 is punched out in the second connection part 222, and the absolute value of the distance between the center of the second opening 225 and the two edges of the second pole piece 220 is controlled at 3 mm. Among them, the ratio of the effective connection length of the first connection part 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is 66.66%. Along the length direction of the cathode current collector aluminum foil (first pole piece 210), only the first opening 215 is punched out in the first connection part 212, and the absolute value of the distance between the center of the first opening 215 and the two edges of the first pole piece 210 is controlled at 3 mm. Among them, the ratio of the effective connection length of the first connection part 212 along the third direction Z to the length of the first pole piece 210 along the third direction Z is 66.66%.

[0142] Comparative Example 6: The difference from Example 4 is that, along the length direction of the anode current collector copper foil (second pole piece 220), circular second expansions 226 are punched out at both ends of the second opening 225, and along the length direction of the cathode current collector aluminum foil (first pole piece 210), circular first expansions 216 are punched out at both ends of the first opening 215.

[0143] Embodiment 4: The difference from Embodiment 1 is that the ratio of the effective connection length of the first connection portion 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is 1.5%.

[0144] Embodiment 5: The difference from Embodiment 1 is that the ratio of the effective connection length of the first connection portion 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is 20%.

[0145] Comparative Example 7: The difference from Example 1 is that the ratio of the effective connection length of the first connecting portion 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is 0.8%.

[0146] Comparative Example 8: The difference from Example 1 is that the ratio of the effective connection length of the first connecting portion 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is 55%.

[0147] The main parameter control and test results of each embodiment and comparative example are shown in Table 1:

[0148] Table 1

[0149]

[0150]

[0151]

[0152] Note: “ / ” means no value.

[0153] In Comparative Example 1, both the cathode and anode plates use a conventional integral structure, with no notch in the middle, with a conventional coating weight and a conventional 5um thick diaphragm 230 substrate, and the electrolyte uses a matching system charge and discharge rate design, with a conductivity of 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, and in the middle and late stages of the normal temperature cycle, the electrolyte in the middle of the plate is insufficient, and purple spots on the interface precipitate lithium, resulting in rapid cycle decay.

[0154] Comparative Example 2, based on Comparative Example 1, the unit area weight of the coating of the anode electrode was reduced, the electrolyte transmission path in the thickness direction of the electrode was shortened, and the normal temperature cycle level was improved. However, this design significantly reduced the surface density of the electrode, and the energy density of the secondary battery 001 decreased by about 2%, which was difficult to meet customer requirements.

[0155] 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 secondary battery 001 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 secondary battery 001, and its high-temperature storage level and hot box window are significantly deteriorated, and cannot meet the requirements.

[0156] Comparative Example 4 thickens the thickness of the diaphragm 230 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 230 significantly deteriorates the energy density of the secondary battery 001, and its volume energy density decreases by about 3% compared with the comparative example, which cannot meet the requirements.

[0157] Embodiment 1, on the basis of comparative example 1, the cathode electrode piece and the anode electrode piece are provided with a first notch 211, a first opening 215, a second notch 221 and a second opening 225 in the third direction Z, and the first connecting portion 212 and the second connecting portion 222 are retained in the middle as an electron transmission channel. Under this design, the energy density of the secondary battery 001 decreases by about 1% due to the loss of active materials at the positions of the first notch 211, the first opening 215, the second notch 221 and the second opening 225, but the first notch 211, the first opening 215, the second notch 221 and the second opening 225 can be used for liquid storage purposes, and the original whole electrode piece is basically divided into two parts on the left and right, the transmission path of the electrolyte is greatly shortened, and the cycle performance is significantly improved, meeting customer requirements. In addition, the notch can be used as an exhaust heat dissipation channel, which is conducive to the discharge of heat inside the secondary battery 001 and the gas generated by the side reaction in a high temperature environment, and can significantly increase the hot box window of the secondary battery 001 by about 4°C.

[0158] Example 2, on the basis of Example 1, only the cathode electrode plate is provided with a first notch 211 and a first opening 215 in the third direction Z, and the anode electrode plate maintains the notch-free design morphology of Example 1. Under this design, because the active material lost by the cathode electrode plate is the same as that in Example 1, the energy density is at the same level as that in Example 1, and the circulation level and the hot box window are significantly improved compared with Example 1. However, due to the notch-free design of the anode electrode plate, its liquid storage, electrolyte transmission, heat dissipation and gas transmission channels are reduced compared with Example 1, and the improvement of the circulation performance and the hot box is less than that of Example 1.

[0159] In Example 3, compared with Example 1, the setting directions of the first notch 211, the first opening 215, the second notch 221 and the second opening 225 are changed from the third direction Z to the second direction Y. Under this design, because the lateral length of the pole piece is smaller than the vertical length, the area of ​​the notch is reduced, and the loss of energy density is relatively low, about 0.7%. However, because the direction with a longer length is also the farthest place of the electrolyte transmission path in the cycle process, it is the shortest board for improvement. Under the lateral notch design of this embodiment, the circulation level and the hot box are still significantly improved compared with Example 1, which can meet customer requirements, but it is slightly lower than Example 1.

[0160] In Comparative Example 5, the notch area is reduced compared to Example 1, and a first opening 215 is only set in the middle position of the first pole piece 210, and a second opening 225 is set in the middle position of the second pole piece 220, and it does not extend to the head and tail positions of the pole pieces. Similarly, its improvement effect is slightly worse than that of Example 1, but the loss of energy density will be further reduced.

[0161] In comparative example 1, at the late stage of the cycle, the shape of the failed middle part of the anode electrode is similar to a "dog bone". In comparative example 6, the notch morphology is designed to be similar to the purple spot lithium precipitation failure morphology. Under this design, the energy density can be improved by about 0.3% compared with embodiment 1, and the cycle level is close to the improvement level of the hot box.

[0162] In Example 4, compared with Example 1, the ratio of the effective connection length of the first connection portion 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is reduced from 5% to 1.5%. Under this design, the energy density of the secondary battery 001 is further lost by about 0.16% due to the active material at the first notch 211, the first opening 215, the second notch 221 and the second opening 225, and the average maximum tolerance temperature is basically the same. However, since the effective connection length of the first connection portion 212 along the third direction Z is too small, the physical support force is insufficient, and the average expansion rate is increased, the pole piece expansion during the cycle will cause the connection points in the middle of some layers to break, so that the part loses electronic contact and can no longer be deintercalated and deintercalated lithium, resulting in deterioration of the cycle performance.

[0163] In Example 5, compared with Example 1, the ratio of the effective connection length of the first connection portion 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is increased from 5% to 20.0%. Under this design, the energy density of the secondary battery 001 is greater than that of the secondary battery 001 in Example 1. The transmission path of the electrolyte is reduced, resulting in insufficient electrolyte transmission capacity and heat dissipation capacity of the electrode assembly, an increase in the average expansion rate, and deterioration of the cycle and high temperature environment tolerance.

[0164] In comparative example 7, compared with example 1, the ratio of the effective connection length of the first connection portion 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is reduced from 5% to 0.8%. Under this design, the energy density of the secondary battery 001 is reduced by about 0.23% due to the reduction of active material loss at the positions of the first notch 211, the first opening 215, the second notch 221 and the second opening 225, and the average maximum tolerance temperature is basically the same. Compared with example 5, since the effective connection length of the first connection portion 212 along the third direction Z is further reduced, the physical support force is insufficient, and the average expansion rate is increased, the pole piece expansion during the cycle will cause the connection points in the middle of some layers to break, so that the part loses electronic contact and can no longer be deintercalated and deintercalated lithium, resulting in further deterioration of the cycle performance.

[0165] In comparative example 8, compared with example 1, the ratio of the effective connection length of the first connection portion 212 along the third direction Z to the length of the second pole piece 220 along the third direction Z is increased from 5% to 55%. Under this design, the energy density of the secondary battery 001 increases by about 0.32% due to the increase of active materials at the positions of the first notch 211, the first opening 215, the second notch 221 and the second opening 225. Compared with example 5, the transmission path of the electrolyte is further reduced, resulting in insufficient electrolyte transmission capacity and heat dissipation capacity of the electrode assembly, an increase in the average expansion rate, and further deterioration of the cycle and high temperature environment tolerance.

[0166] 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 separator and a second electrode sheet stacked in layers, characterized in that: The first pole piece is provided with at least one first notch, the first notch penetrates the first pole piece along a first direction, and the first notch extends to the edge of the first pole piece; the first pole piece also includes a first connecting portion, the first notch and the first connecting portion are arranged in sequence along a third direction; along the third direction, the projection of the first connecting portion falls within the projection range of the first notch; the length of the first pole piece along the third direction is S1, and the effective connection length of the first connecting portion along the third direction is S2, 1%≤(S2 / S1)×100%≤50%; the first direction is the thickness direction of the first pole piece, and the first direction, the second direction and the third direction are perpendicular to each other.

2. The secondary battery according to claim 1, wherein: 2%≤(S2 / S1)×100%≤10%.

3. The secondary battery according to claim 1, wherein: The second pole piece is provided with at least one second notch, and the second notch penetrates the second pole piece along the first direction; along the first direction, a projection of the first notch and a projection of the second notch at least partially overlap.

4. The secondary battery according to claim 3, characterized in that: The second notch extends to the edge of the second pole piece, and the second pole piece also includes a second connecting portion. The second notch and the second connecting portion are arranged in sequence along the third direction; along the third direction, the projection of the second connecting portion falls within the projection range of the second notch.

5. The secondary battery according to claim 4, characterized in that: The first pole piece is a cathode pole piece, and the second pole piece is an anode pole piece; the first notch and the second notch are arranged correspondingly, and along the first direction, the projection of the second notch is located within the projection of the first notch.

6. The secondary battery according to claim 1, wherein: The first pole piece is provided with at least one first opening, and the first opening penetrates the first pole piece along the first direction; along the third direction, the distances between the center of the first opening and the two edges of the first pole piece are L1 and L2 respectively, and |L1-L2|≤5mm.

7. The secondary battery according to claim 4, characterized in that: The first pole piece is provided with at least one first opening, and the first opening penetrates the first pole piece along the first direction; the second pole piece is provided with at least one second opening, and the second opening penetrates the second pole piece along the first direction; Along the third direction, the distances from the center of the first opening to the two edges of the first pole piece are L1 and L2 respectively, and the distances from the second opening to the two edges of the second pole piece are L3 and L4 respectively, |L1-L2|≤5mm, |L3-L4|≤5mm.

8. The secondary battery according to claim 7, characterized in that The number of the second openings is the same as the number of the first openings, and the second openings are arranged corresponding to the first openings.

9. The secondary battery according to claim 8, characterized in that The first pole piece is a cathode pole piece, and the second pole piece is an anode pole piece; along the first direction, the projection of the second opening is located within the projection of the first opening.

10. The secondary battery according to claim 6, wherein: The first connecting portion is also provided with a first flare, which penetrates the first connecting portion along the first direction; the first flare is provided at at least one end of the first opening along the third direction, and the first flare is connected to the first opening; along the third direction, the projection of the first opening is located within the projection of the first flare.

11. The secondary battery according to claim 6, wherein: The first notch and / or the first opening may have an arc-shaped corner.

12. An electrical equipment, characterized in that: Comprising the secondary battery according to any one of claims 1 to 11.

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