Secondary battery and electric device

Abstract

The application relates to the technical field of energy storage, in particular to a secondary battery and an electric device. 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 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 further comprises a first connecting part, and the first notch and the first connecting part are sequentially arranged along a third direction. Along the third direction, the projection of the first connecting part falls within the projection range of the first notch. The length of the first pole piece along the third direction is S1, the effective connecting length of the first connecting part along the third direction is S2, and 1% <= (S2 / S1) * 100% <= 50%. By controlling the length of the first notch in the third direction to be sufficient, the distance of electrolyte transmission to the middle position of the first pole piece is effectively shortened, the electrolyte consumed in the middle of the battery cell is quickly supplemented, and the problem of cycle failure is caused.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a secondary battery and an electric device. BACKGROUND

[0002] In order to improve the charge-discharge capacity of the secondary battery and meet the demand of consumers for fast charging and fast discharging, the multi-tab structure is favored in the fast charging and fast discharging system because it can significantly reduce the ohmic impedance of the battery compared with the single-tab structure, has good ability to improve the charging speed and reduce the temperature rise, and thus is widely used in mobile phone battery products. Among them, the laminated structure has low impedance and high energy density performance of the multi-tab structure, and is widely used in mobile phone battery products. SUMMARY

[0003] For the fast charging and fast discharging battery system, the transmission speed of the electrolyte in the cycle process is high, and the electrolyte consumed in the middle of the cycle process needs to be quickly supplemented. The electrolyte supplement speed of the laminated battery in the related art, especially for the battery system with large length and width and high charge-discharge speed, is a big problem, which limits its application in the fast charging and fast discharging system. In addition, the laminated battery also needs to be fixed by hot pressing, and the hot pressing will further compress the space between the separator and the pole piece, reduce the electrolyte transmission path, and worsen the electrolyte supplement. In addition, the heat problem in the use process of the battery makes the safety performance of the battery decline.

[0004] Therefore, the present application provides a secondary battery and an electric device, which can improve the electrolyte supplement speed and improve the heat dissipation capacity of the electrode assembly and improve the safety of the electrode assembly in use.

[0005] In a first aspect, an embodiment of the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising a first pole piece, a separator and a second pole piece which are sequentially stacked. 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 further comprises 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, 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.

[0006] The first notch on the first tab penetrates the first tab along the first direction and extends to the edge of the first tab, which is conducive to the electrolyte at the edge of the first tab infiltrating to the middle position of the first tab through the first notch. The first tab further comprises a first connecting portion, and the first notch and the first connecting portion are arranged in sequence along a third direction. Along the third direction, a projection of the first connecting portion falls within a projection range of the first notch, wherein a ratio of an effective connecting length of the first connecting portion along the third direction to a length of the first tab along the third direction is greater than or equal to 1%, which is conducive to maintaining the electronic path of the first tab as a whole and making the first tab have a certain strength to reduce the occurrence of the first tab breaking. The ratio of the effective connecting length of the first connecting portion along the third direction to the length of the first tab along the third direction is less than or equal to 50%, which controls the first notch 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 tab, and is conducive to the electrolyte entering the middle position of the first tab from the first notch to quickly supply the electrolyte consumed in the middle of the battery cell, thereby improving the problem of purple stain and lithium precipitation due to ion broken bridge, thereby leading to cycle failure. In addition, the first tab is provided with the first notch, which is conducive 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 connecting length of the first connecting portion refers to the length of the first connecting portion capable of forming an electronic path in the third direction.

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

[0008] In the above embodiments, 2%≤(S2 / S1)×100%≤10%.

[0009] In one or more of the above embodiments, the second tab is provided with at least one second notch, and the second notch penetrates the second tab 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.

[0010] In the secondary battery, the second notch is arranged on the second tab and extends through the second tab along the first direction, so as to effectively shorten the distance of electrolyte transmission to the middle position of the second tab, and the projection of the first notch and the projection of the second notch at least partially overlap along the first direction, so as to widen the channel of electrolyte transmission between the first tab and the adjacent second tab in the first direction, and facilitate the electrolyte to enter the middle position between the first tab and the adjacent second tab from the first notch and the second notch, so as to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0011] In one or more of the embodiments above, the second notch extends to the edge of the second tab, and the second tab further comprises 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 secondary battery, the second notch extends to the edge of the second tab, and the second tab further comprises 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.

[0013] In one or more of the embodiments above, the first tab is a cathode tab, and the second tab is an anode tab; 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 secondary battery, the first notch and the second notch are arranged correspondingly along the first direction, and the projection of the second notch is located within the projection of the first notch, so as to facilitate the second tab to cover the first tab along the first direction, so as to improve the problem of lithium precipitation.

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

[0016] In the secondary battery, the absolute value of the distance between the center of the first opening and the two edges of the first tab is controlled within 5mm, so as to control the first opening at the position close to the middle of the first tab, and facilitate the electrolyte to enter the position close to the middle of the first tab from the first opening, 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 connecting length of the first connecting portion.

[0017] In one or more of the embodiments above, the first tab is provided with at least one first opening, the first opening penetrating the first tab along the first direction; the second tab is provided with at least one second opening, the second opening penetrating the second tab along the first direction; along the third direction, the distance between the center of the first opening and the two edges of the first tab is L1 and L2 respectively, the distance between the center of the second opening and the two edges of the second tab is 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 connecting part.

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

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

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

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

[0022] In the secondary battery described above, the projection of the second opening is located within the projection of the first opening, which is conducive to the second tab covering the first tab along the first direction to improve the problem of lithium precipitation.

[0023] In one or more of the embodiments above, the first connecting part is further provided with a first flared portion, the first flared portion penetrating the first connecting part along the first direction; the first flared portion is arranged at at least one end of the first opening along the third direction, and the first flared portion communicates with the first opening; along the third direction, the projection of the first opening is located within the projection of the first flared portion.

[0024] The secondary battery has the first flared portion penetrating the first connecting portion along the first direction and communicating with the first opening, and a projection of the first opening is located within a projection of the first flared portion along the third direction, so as to widen at least one end of the first opening along the third direction, and improve the flow efficiency of the electrolyte to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0025] In one or more of the embodiments above, the corner of the first notch is arranged in an arc shape.

[0026] In the secondary battery above, the corner of the first notch is arranged in an arc shape, so that the corner of the first notch is kept smooth, thereby improving the problem of the corner of the first notch breaking due to stress concentration.

[0027] In one or more of the embodiments above, the corner of the first opening is arranged in an arc shape.

[0028] In the secondary battery above, the corner of the first opening is arranged in an arc shape, so that the corner of the first opening is kept smooth, thereby improving the problem of the corner of the first opening breaking due to stress concentration.

[0029] In the secondary battery above, by arranging the 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, and the first pole piece further comprises a first connecting portion, and along the third direction, a 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 keep the electronic path of the whole first pole piece and beneficial to make the first pole piece have a certain strength to reduce the occurrence of first pole piece breakage; 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%, which controls the first notch to have sufficient length in the third direction, thereby effectively shortening the distance of the electrolyte transmission to the middle position of the first pole piece, and is beneficial 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, and improves the problem of purple stain lithium precipitation due to ion broken bridge, thereby causing cycle failure.

[0030] In a second aspect, the embodiments of the present application provide a kind of electric equipment, including the secondary battery in one or more of the embodiments above. BRIEF DESCRIPTION OF DRAWINGS

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

[0032] Figure 2 For Figure 1 The exploded schematic diagram of the secondary battery.

[0033] Figure 3 This is a schematic diagram of the structure of the first electrode in one embodiment of this application.

[0034] Figure 4 This is a schematic diagram of the structure of the first electrode in another embodiment of this application.

[0035] Figure 5 This is a schematic diagram of the structure of the first electrode in another embodiment of this application.

[0036] Figure 6 This is a schematic diagram of the structure of the first electrode in another embodiment of this application.

[0037] Figure 7 This is a schematic diagram of the structure of the first electrode in another embodiment of this application.

[0038] Figure 8 This is a schematic diagram of the structure of the second electrode and the first electrode in one embodiment of this application.

[0039] Figure 9 This is a schematic diagram of the structure of the second electrode and the first electrode in another embodiment of this application.

[0040] Figure 10 This is a schematic diagram of the structure of the second electrode and the first electrode in another embodiment of this application.

[0041] Figure 11 This is a schematic diagram of the structure of an electrical device in one embodiment of this application.

[0042] Explanation of main component symbols

[0043] 001 Secondary Battery

[0044] 100 housing

[0045] 110 cavity

[0046] 200 electrode assembly

[0047] 210 First Polar Film

[0048] 211 First Gap

[0049] 212 First connecting part

[0050] 215 First Opening

[0051] 216 First flare

[0052] 220 Second Electrode

[0053] 221 Second Gap

[0054] 222 Second connecting part

[0055] 225 second opening

[0056] 226 second flared portion

[0057] 230 diaphragm

[0058] 300 first tab

[0059] 400 second tab

[0060] 002 electrical device

[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 with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application.

[0065] It should be noted that unless specifically stated and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be broadly understood, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected. When a component is considered to be "connected" to another component, it can be directly connected to another component or there can be a middle component. When a component is considered to be "provided" on another component, it can be directly provided on another component or there can be a middle component.

[0066] Unless otherwise specified, the term "a plurality of" used herein refers to two or more.

[0067] The terms "first", "second", and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implying the number, specific order or primary and secondary relationship of the indicated technical features.

[0068] It should be noted that when a certain parameter is greater than, equal to or less than a certain endpoint value, it should be understood that the endpoint value allows a tolerance of ±5%.

[0069] It should be noted that the size of each structure shown in the drawings is given for better understanding and more convenient description, and the present application is not limited to the size shown in the drawings. In order to make the present application clear, the elements irrelevant to the description are omitted from the details of the specification.

[0070] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0071] An embodiment of the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising a first electrode sheet, a separator and a second electrode sheet which are sequentially stacked. The first electrode sheet is provided with at least one first notch, the first notch penetrating the first electrode sheet along a first direction and extending to an edge of the first electrode sheet; the first electrode sheet further comprises a first connecting portion, the first notch and the first connecting portion being sequentially arranged along a third direction; along the third direction, a projection of the first connecting portion falls within a projection range of the first notch; a length of the first electrode sheet along the third direction is S1, an effective connecting length of the first connecting portion along the third direction is S2, 1%≤(S2 / S1)*100%≤50%; the first direction is a thickness direction of the first electrode sheet, the first direction, the second direction and the third direction are perpendicular to each other.

[0072] The first notch on the first electrode sheet penetrates the first electrode sheet along the first direction and extends to the edge of the first electrode sheet, which is conducive to the electrolyte at the edge of the first electrode sheet infiltrating to the middle position of the first electrode sheet through the first notch. The first electrode sheet further comprises a first connecting portion, the first notch and the first connecting portion being sequentially arranged along the third direction, along the third direction, a projection of the first connecting portion falls within a projection range of the first notch, wherein the ratio of the effective connecting length of the first connecting portion along the third direction to the length of the first electrode sheet along the third direction is greater than or equal to 1%, which is conducive to maintaining the electronic path of the first electrode sheet as a whole and making the first electrode sheet have a certain strength to reduce the occurrence of first electrode sheet breakage; the ratio of the effective connecting length of the first connecting portion along the third direction to the length of the first electrode sheet along the third direction is less than or equal to 50%, which controls the length of the first notch in the third direction to be sufficient, thereby effectively shortening the distance of the electrolyte transmission to the middle position of the first electrode sheet, which is conducive to the electrolyte entering the middle position of the first electrode sheet from the first notch to quickly replenish the electrolyte consumed in the middle of the battery cell, and improving the problem of purple stain and lithium precipitation caused by ion broken bridge, thereby leading to cycle failure. It should be noted that the effective connecting length of the first connecting portion refers to the length of the first connecting portion in the third direction which can form an electronic path.

[0073] Some embodiments of the present application will be described in detail with reference to the drawings. The features of the following embodiments and examples can be combined with each other without conflict.

[0074] Please refer to Figure 1 and Figure 2The embodiment of the present application provides a secondary battery 001, which comprises an electrode assembly 200 and a first tab 300 connected with the electrode assembly 200. The secondary battery 001 further comprises a second tab 400 connected with the electrode assembly 200, and the first tab 300 and the second tab 400 have different polarities.

[0075] In some embodiments, the secondary battery 001 further comprises a shell 100 having a cavity 110, and the electrode assembly 200 is arranged in the cavity 110 in the shell 100. Part of the first tab 300 extends out of the shell 100 and is used for electrical connection with an external structure. Part of the second tab 400 extends out of the shell 100 and is used for electrical connection with the external structure.

[0076] In other embodiments, the first tab 300 is connected with a conductive first adapter (not shown) which partially extends out of the shell 100 and is used for electrical connection with the external structure. The second tab 400 is connected with a conductive second adapter (not shown) which partially extends out of the shell 100 and is used for electrical connection with the external structure.

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

[0078] Please refer to Figure 2 and Figure 3 In some embodiments, the electrode assembly 200 comprises a first electrode plate 210, a second electrode plate 220 and a separator 230 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 separator 230 are sequentially stacked to form a stacked structure.

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

[0080] The first direction X is a thickness direction of the first electrode plate 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 electrode plate 210 is provided with one first notch 211.

[0082] In some embodiments, the first pole piece 210 further comprises a first connecting portion 212, the first notch 211 and the first connecting portion 212 are arranged in sequence along the third direction Z, and a projection of the first connecting portion 212 falls within a projection range of the first notch 211 along the third direction Z. Since the edge of the first pole piece 210 in the length direction is farther away 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 of the electrolyte from the first notch 211 to the middle position of the first pole piece 210, and facilitates the electrolyte to infiltrate from the first notch 211 to the middle position of the first pole piece 210.

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

[0084] Referring to Figure 5 In some embodiments, the first pole piece 210 is provided with two first notches 211, one of the first notches 211 extends to an 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, a projection of one of the first notches 211 only partially overlaps with a projection of the other first notch 211. At this time, the first connecting portion 212 is a portion connecting the two first notches 211 along the third direction Z.

[0085] Referring to Figure 6 In some embodiments, the first pole piece 210 is provided with two first notches 211, one of the first notches 211 extends to an 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, a projection of one of the first notches 211 does not overlap with a projection of the other first notch 211. At this time, there are two first connecting portions 212, which are arranged in sequence along the third direction Z with the two first notches 211 respectively.

[0086] In some embodiments, the third direction Z can also be the width direction of the electrode assembly 200, 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 an edge of the first pole piece 210 in the width direction.

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

[0088] In some embodiments, the sizes of the two or more first notches 211 are the same.

[0089] In some embodiments, the sizes of the two or more first notches 211 are different.

[0090] In some embodiments, the length of the first tab 210 along the third direction Z is S1, the effective connection length of the first connecting part 212 along the third direction Z is S2, and 1%≤(S2 / S1)×100%≤50%. The ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the first tab 210 along the third direction Z is greater than or equal to 1%, which is beneficial to maintaining the electronic path of the first tab 210 as a whole. The ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the first tab 210 along the third direction Z is less than or equal to 50%, which controls the length of the first notch 211 in the third direction Z to be sufficient, thereby effectively shortening the distance of the electrolyte transmission to the middle position of the first tab 210, and facilitating the electrolyte to enter the middle position of the first tab 210 from the first notch 211 to quickly replenish the electrolyte consumed in the middle of the battery cell, thereby improving the problem of purple stain lithium precipitation due to ion broken bridge, thereby causing cycle failure.

[0091] It is worth noting that the effective connection length of the first connecting part 212 along the third direction Z refers to the length of the first connecting part 212 in the third direction Z that can form an electronic path along the second direction Y.

[0092] In some embodiments, 2%≤(S2 / S1)×100%≤10%. The ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the first tab 210 along the third direction Z is greater than or equal to 2%, which is beneficial to further maintaining the electronic path of the first tab 210 as a whole, and making the first tab 210 have a certain strength to reduce the occurrence of first tab 210 broken belt. The ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the first tab 210 along the third direction Z is less than or equal to 10%, which further controls the length of the first notch 211 in the third direction Z to be sufficient, thereby effectively shortening the distance of the electrolyte transmission to the middle position of the first tab 210, and facilitating the electrolyte to enter the middle position of the first tab 210 from the first notch 211 to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0093] Please refer toFigure 7 In some embodiments, the first tab 210 is provided with at least one first opening 215, which penetrates the first tab 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 connecting part 212.

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

[0096] In some embodiments, the first tab 210 is provided with one first opening 215, and along the third direction Z, the center of the first opening 215 is respectively L1 and L2 away from the two edges of the first tab 210, and |L1-L2|≤5mm. The absolute value of the distance between the center of the first opening 215 and the two edges of the first tab 210 is controlled within 5mm, which is beneficial to control the first opening 215 at a position close to the middle of the first tab 210, and is beneficial to the electrolyte entering the first opening 215 to the position close to the middle of the first tab 210 to quickly replenish the electrolyte consumed in the middle of the battery cell.

[0097] In other embodiments, the first tab 210 is provided with a plurality of first openings 215, and along the third direction Z, at least one of the plurality of first openings 215 has a center that is respectively L1 and L2 away from the two edges of the first tab 210, and |L1-L2|≤5mm.

[0098] In some embodiments, |L1-L2| is any one of 0mm, 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, or any value between any two of them.

[0099] Please refer to Figure 8 In some embodiments, the second tab 220 is provided with at least one second notch 221, which penetrates the second tab 220 along the first direction X.

[0100] In some embodiments, the second tab 220 is provided with one second notch 221. In other embodiments, the second tab 220 is provided with two second notches 221, which are arranged in sequence along the third direction Z. In other embodiments, the second tab 220 is provided with three, four, five, or the like second notches 221.

[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 through which the electrolyte is transported between the first tab 210 and the adjacent second tab 220 in the first direction X, and facilitating the electrolyte to enter the middle position between the first tab 210 and the adjacent second tab 220 from the first notch 211 and the second notch 221 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 tab 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 tab 220. The second tab 220 further comprises a second connecting portion 222, and the second notch 221 and the second connecting portion 222 are arranged in sequence 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 tab 210 is a cathode tab, and the second tab 220 is an anode tab.

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

[0106] Please refer to Figure 9 In some embodiments, the second connecting portion 222 is provided with at least one second opening 225, and the second opening 225 penetrates the second connecting portion 222 along the first direction X.

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

[0108] In some embodiments, the second connecting portion 222 is provided with a second opening 225, and along the third direction Z, the distance between the center of the second opening 225 and the two edges of the second pole piece 220 is L3 and L4 respectively, and |L3-L4|≤5mm. 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 beneficial to control the second opening 225 at the position close to the middle of the second pole piece 220, and beneficial to the electrolyte entering the position close to the middle of the second pole piece 220 from the second opening 225 to quickly supplement 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, and along the third direction Z, the center of at least one of the plurality of second openings 225 is located at a distance of L3 and L4 from the two edges of the second pole piece 220 respectively, and |L3-L4|≤5mm.

[0110] In some embodiments, |L3-L4| is any one of 0mm, 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, or any value between two of them.

[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 correspondingly arranged with the first openings 215, which is beneficial to the rapid flow of electrolyte between the first openings 215 and the second openings 225 to quickly supplement 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 to the second pole piece 220 covering the first pole piece 210 along the first direction X to improve the problem of lithium precipitation.

[0113] Please refer to Figure 10 In some embodiments, the first connecting portion 212 is further provided with a first flared portion 216, and the first flared portion 216 penetrates the first connecting 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 flared portion 216, thereby widening the first opening 215 and improving the flow efficiency of the electrolyte to quickly supplement the electrolyte consumed in the middle of the battery cell.

[0114] In some embodiments, the first flared portion 216 is arranged at at least one end of the first opening 215 along the third direction Z, and the first flared portion 216 is in communication with the first opening 215. In other embodiments, the first flared portion 216 is arranged at both ends of the first opening 215 along the third direction Z.

[0115] In some embodiments, in the second tab 220, the second connecting portion 222 is further provided with a second flared portion 226, which penetrates the second connecting 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 portion 226, thereby widening the second opening 225 and improving the flow 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 flared portion 226 is arranged at at least one end of the second opening 225 along the third direction Z, and the second flared portion 226 is in communication with the second opening 225. In other embodiments, the second flared portion 226 is arranged at both ends of the second opening 225 along the third direction Z.

[0117] In some embodiments, the first flared portion 216 and the second flared portion 226 are correspondingly arranged, and along the first direction X, the projection of the second flared portion 226 is located within the projection of the first flared portion 216, which is conducive to the second tab 220 covering the first tab 210 along the first direction X, so as to improve the problem of lithium precipitation.

[0118] In some embodiments, the corner of the first notch 211 is arranged in an arc shape. In some embodiments, the corner of the second notch 221 is arranged in an arc shape. In some embodiments, the corner of the first opening 215 is arranged in an arc shape. In some embodiments, the corner of the second opening 225 is arranged in an arc shape. In some embodiments, the corner of the first flared portion 216 is arranged in an arc shape. In some embodiments, the corner of the second flared portion 226 is arranged in an arc shape.

[0119] It is worth noting that the corners of the first notch 211, the second notch 221, the first opening 215, the second opening 225, the first flared portion 216, and the second flared portion 226 are the end portions of the first notch 211, the second notch 221, the first opening 215, the second opening 225, the first flared portion 216, and the second flared portion 226 close to the first connecting portion 212, and the corners are kept smooth, which is conducive to improving the problem of corner fracture due to stress concentration.

[0120] For reference Figure 11 An embodiment of the present application also provides a use electric device 002 comprising the secondary battery 001 in one or more embodiments described above.

[0121] In order to verify the influence of the notch / opening arranged on the tab on the electrolyte replenishment efficiency in the middle position of the secondary battery 001, the following test is performed:

[0122] (1) Cycle test: 10 secondary batteries 001 in each group of comparative examples and each group of examples were tested. Each secondary battery 001 was placed in a 25℃ environment for 30 minutes, and then charged and discharged according to the following steps. Constant current charging at 5C to 4.2V, then constant current charging at 4C to 4.3V, then constant current charging at 3C to 4.45V, then constant voltage charging at 4.45V to 0.05C, standing for 5 minutes, constant current discharging at 1C to 3V, standing for 5 minutes, which was one cycle. According to the above cycle steps, 1000 cycles were cycled. The capacity retention rate of a single secondary battery 001 was calculated after the cycle test. The capacity retention rate was the ratio of the discharge capacity after 1000 cycles to the discharge capacity of the first cycle. The capacity retention rate of 10 secondary batteries 001 in each group of comparative examples and each group of examples after 1000 cycles was recorded, and the average value was calculated.

[0123] (2) 80℃ storage test: 10 secondary batteries 001 in each group of comparative examples and each group of examples were tested. Each secondary battery 001 was placed in a 25℃ environment for 30 minutes, and then charged and stored according to the following steps: the thickness of the secondary battery 001 at the initial voltage was measured using a micrometer, then the secondary battery 001 was fully charged, i.e. constant current charging at 0.7C to 4.45V, then constant voltage charging at 4.45V to 0.02C, then the secondary battery 001 was placed in an 80℃ constant temperature oven 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: [(thickness of the secondary battery 001 after high temperature storage - thickness of the secondary battery 001 at the initial voltage) / thickness of the secondary battery 001 at the initial voltage] x 100%. The average value of the expansion rate of 10 secondary batteries 001 in each group of comparative examples and each group of examples was calculated.

[0124] (3) Hot box test: 10 secondary batteries 001 in each group of comparative examples and each group of examples were tested. Each secondary battery 001 was placed in a 25℃ environment for 30 minutes, and then tested according to the following steps: the secondary battery 001 was fully charged, i.e. constant current charging at 0.7C to 4.45V, then constant voltage charging at 4.45V to 0.02C, in a 25℃ environment. Then the secondary battery 001 was placed in a high temperature box and heated to (130+n)±2℃ at a heating rate of 5±2℃ / min and kept for 60 minutes; (n is 0, 1, 2… and -1, -2… etc. integer), and whether the secondary battery 001 exploded, caught fire, etc. was observed. The temperature at which each secondary battery 001 began to smoke was recorded as its highest tolerance temperature. The average highest tolerance temperature of 10 secondary batteries 001 in each group of comparative examples and each group of examples was calculated.

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

[0126] Example 1:

[0127] A secondary battery 001 is assembled as follows:

[0128] (1) Preparation of anode electrode sheet: Artificial graphite, conductive carbon black (Super P), and butadiene-styrene rubber (SBR) are mixed in a weight ratio of 96:1.5:2.5, deionized water is added as a solvent, and an anode active material slurry with a weight percentage of 70wt% is prepared and stirred uniformly for standby use. A copper foil with a thickness of 10μm is used as an anode current collector, and the above-mentioned anode active material slurry is uniformly coated on one surface of the anode current collector along its thickness direction using a slot 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 the anode current collector is dried at 110°C to obtain an anode electrode sheet substrate with a single-sided anode active material layer. Then the above steps are repeated on the other surface 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 of the anode current collector in the width direction to obtain an anode electrode sheet substrate with a double-sided anode active material layer, wherein the weight of the active material layer coated per unit area is 100mg / 1540mm 2 The anode electrode sheet substrate is punched using a mold and a die cutter to obtain a single anode electrode sheet, wherein the position of the empty foil area without an anode active material layer forms an anode tab. Then, as shown in FIG. 2, along the length direction (third direction Z) of the anode electrode sheet (second electrode sheet 220), a second notch 221 is punched 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. A second opening 225 is punched 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. Wherein, along the third direction Z, the projection of the second connecting part 222 falls within the projection range of the second notch 221, and the ratio of the effective connection length of the second connecting part 222 along the third direction Z to the length of the second electrode sheet 220 along the third direction Z is 5%. Figure 7

[0129] ​(2) Preparation of the cathode electrode sheet: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5, and N-methyl pyrrolidone (NMP) was added as a solvent to prepare a cathode active material slurry with a solid content of 75 wt%, and the mixture was stirred uniformly for use. An aluminum foil with a thickness of 10 pm was used as the cathode current collector, and the above-mentioned cathode active material slurry was uniformly coated on one surface of the cathode current collector in the thickness direction thereof using a slot coater, wherein an empty foil area without a cathode active material layer was reserved at one end in the width direction of the cathode current collector, and the cathode current collector was dried at 90°C to obtain a cathode electrode sheet substrate with a single-side coated cathode active material layer. Then, the above steps were repeated on the other surface of the cathode current collector in the thickness direction thereof, and an empty foil area without a cathode active material layer was reserved at one end in the width direction of the cathode current collector to obtain a cathode electrode sheet substrate with a double-side coated cathode active material layer. The cathode electrode sheet substrate was punched using a die and a die cutter to obtain a single cathode electrode sheet, wherein the position of the empty foil area without a cathode active material layer formed a cathode tab. Along the length direction (third direction Z) of the cathode electrode sheet (first electrode sheet 210), a first notch 211 was punched at each end of the cathode electrode sheet, and the first notch 211 penetrated the first electrode sheet 210 in the first direction X. A first opening 215 was punched 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 in the third direction Z was 3 mm. Among them, along the third direction Z, the projection of the first connecting part 212 falls within the projection range of the first notch 211, and the ratio of the effective connection length of the first connecting part 212 in the third direction Z to the length of the first electrode sheet 210 in the third direction Z is 5%.

[0130] (3) Preparation of the electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC: EMC: DEC = 30:50:20 to form a base organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the base organic solvent to dissolve and mix uniformly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L, wherein the conductivity of the electrolyte is 8.0 S / m.

[0131] (4) Preparation of the separator 230: The separator 230 adopts a three-layer structure, and the thickness is 5 pm, which includes a first adhesive layer, a first substrate layer, and a second adhesive layer stacked. The first substrate layer is made of polyethylene (PE), and the first adhesive layer and the second adhesive layer both contain a first adhesive and boehmite.

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

[0133] (6) Electrode assembly 200 assembly: The punched aluminum plastic film is placed in the assembly clamp, the pit surface is upward, the electrode assembly 200 is placed in the pit, and external force is applied to compress. Then another punched aluminum plastic film is covered on the electrode assembly 200 with the pit surface downward, and the four sides of the two aluminum plastic films are heat sealed by hot pressing to obtain the assembled electrode assembly 200.

[0134] (7) Liquid injection packaging: The assembled electrode assembly 200 is injected with electrolyte, and after vacuum packaging, standing, hot pressing formation, shaping and other processes, the secondary battery 001 is obtained.

[0135] Comparative Example 1: The difference from Example 1 is that the anode and cathode electrode sheets are both set as conventional without notches / openings.

[0136] Comparative Example 2: The difference from Comparative Example 1 is that the weight of the active material layer coated per unit area on the anode current collector copper foil (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 separator 230 is set to 7 um.

[0139] Example 2: The difference from Example 1 is that the anode electrode sheet is set as conventional without notches / openings.

[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 electrode sheet 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 electrode sheet 210).

[0141] Comparative Example 5: The difference from Example 1 is that along the length direction of the anode current collector copper foil (second electrode sheet 220), only the second opening 225 is punched in the second connecting part 222, and the absolute value of the distance between the center of the second opening 225 and the two edges of the second electrode sheet 220 is controlled to be 3 mm. Among them, the ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the second electrode sheet 220 along the third direction Z is 66.66%. Along the length direction of the cathode current collector aluminum foil (first electrode sheet 210), only the first opening 215 is punched in the first connecting part 212, and the absolute value of the distance between the center of the first opening 215 and the two edges of the first electrode sheet 210 is controlled to be 3 mm. Among them, the ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the first electrode sheet 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 tab 220), a circular second flared portion 226 is punched at both ends of the second opening 225, and along the length direction of the cathode current collector aluminum foil (first tab 210), a circular first flared portion 216 is punched at both ends of the first opening 215.

[0143] Example 4: The difference from Example 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 tab 220 along the third direction Z is 1.5%.

[0144] Example 5: The difference from Example 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 tab 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 connection portion 212 along the third direction Z to the length of the second tab 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 connection portion 212 along the third direction Z to the length of the second tab 220 along the third direction Z is 55%.

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

[0148] Table 1

[0149]

[0150]

[0151]

[0152] Note: " / " represents no value.

[0153] In Comparative Example 1, both the cathode tab and the anode tab use a conventional overall structure, and the middle part is not provided with a notch, and a conventional coating weight and a conventional 5um-thick separator 230 substrate are matched, and the electrolyte uses a matched system charge-discharge rate design, and the conductivity is 8.0 S / m. Under this design, the speed of electrolyte transmission from the periphery to the center in the cycle process cannot match the demand of the system charge-discharge rate, and in the middle and later stages of the normal temperature cycle, the electrolyte in the middle part of the tab is insufficient, the interface purple spot lithium is precipitated, and the cycle is rapidly attenuated.

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

[0155] Comparative Example 3, on the basis of Comparative Example 1, the conductivity of the electrolyte was increased from 8.0 to 9.0, and the transmission speed of the electrolyte was accelerated by reducing the viscosity of the electrolyte. Under this design, the kinetic performance of the secondary battery 001 was significantly improved, and the room temperature cycle was significantly improved, but the activity of the electrolyte improved, which caused the high temperature stability of the entire secondary battery 001 to deteriorate significantly, and the high temperature storage level and the heat box window deteriorated significantly, which could not meet the requirements.

[0156] Comparative Example 4, on the basis of Comparative Example 1, the thickness of the separator 230 base material was increased, thereby widening the electrolyte transmission channel between the electrode sheets to improve the electrolyte transmission speed. Based on this, the room temperature cycle performance was significantly improved, basically meeting the requirement of achieving a capacity retention rate of ≥80%, and the high temperature performance was flat. However, the increase in the thickness of the separator 230 significantly deteriorated the energy density of the secondary battery 001, and the volume energy density decreased by about 3% compared to the comparative example, which could not meet the requirements.

[0157] Example 1, on the basis of Comparative Example 1, the first notch 211, the first opening 215, the second notch 221 and the second opening 225 in the third direction Z were provided on the cathode electrode sheet and the anode electrode sheet, and the first connecting part 212 and the second connecting part 222 were reserved as electronic transmission channels. Under this design, the energy density of the secondary battery 001 decreased by about 1% due to the loss of active material 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 could be used for liquid storage purposes, and the originally whole electrode sheet was basically divided into left and right two parts, the electrolyte transmission path was greatly shortened, and the cycle performance was significantly improved to meet the customer requirements. In addition, the notch can be used as an exhaust and heat dissipation channel, which is beneficial to discharging the heat and gas generated by the secondary battery 001 in a high temperature environment, and can significantly improve the heat box window of the secondary battery 001 by about 4°C.

[0158] Example 2, on the basis of Example 1, only the first notch 211 and the first opening 215 in the third direction Z are provided for the cathode electrode sheet, and the anode electrode sheet remains the gapless design of Comparative Example 1. In this design, because the active material loss of the cathode electrode sheet is the same as that of Example 1, the energy density is the same as that of Example 1, and the cycle level and heat box window are both significantly improved compared with Comparative Example 1. However, because the anode electrode sheet is designed without gaps, the liquid storage, electrolyte transmission, heat dissipation, and gas transmission channels are reduced compared with Example 1, and the improvement in cycle performance and heat box is less than that of Example 1.

[0159] Example 3, compared with Example 1, the setting direction of the first notch 211, the first opening 215, the second notch 221, and the second opening 225 is changed from the third direction Z to the second direction Y. In this design, because the length of the electrode sheet in the transverse direction is less than the length in the vertical direction, the area of the notch is reduced, and the loss of energy density is also relatively low, about 0.7%. However, because the longer direction is also the farthest place for electrolyte transmission during the cycle process, it is the shortest board for improvement. In the transverse notch design of this example, the cycle level and heat box are still significantly improved compared with Comparative Example 1, and can meet the customer's requirements, but are slightly lower than Example 1.

[0160] Comparative Example 5, compared with Example 1, the notch area is reduced, and only the first opening 215 is provided at the middle position of the first electrode sheet 210, and the second opening 225 is provided at the middle position of the second electrode sheet 220, without extending to the head and tail positions of the electrode sheet. Similarly, its improvement effect is slightly worse than that of Example 1, but the loss of energy density is further reduced.

[0161] Comparative Example 1 has a shape similar to a "dog bone" in the middle of the anode electrode sheet at the later stage of the cycle, and Comparative Example 6 designs the notch shape to be similar to the shape, matching the purple lithium precipitation failure shape. In this design, the energy density can be increased by about 0.3% compared with Example 1, and the cycle level and heat box improvement level are close.

[0162] Example 4, compared with Example 1, the ratio of the effective connection length of the first connecting part 212 in the third direction Z to the length of the second electrode sheet 220 in the third direction Z is reduced from 5% to 1.5%. In this design, the energy density of the secondary battery 001 is further lost due to the position of the first notch 211, the first opening 215, the second notch 221, and the second opening 225, and is reduced by about 0.16%, and the average maximum tolerance temperature is basically the same. However, because the effective connection length of the first connecting part 212 in the third direction Z is too small, the physical support force is insufficient, the average expansion rate increases, and during the cycle process, the connection point in some layers will be broken due to the expansion of the electrode sheet, so that this part loses electronic contact and cannot further deintercalate lithium, resulting in deterioration of the cycle performance.

[0163] Example 5, compared with Example 1, the ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the second tab 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 larger 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, the average expansion rate is increased, and the cycle and high temperature environment tolerance is deteriorated.

[0164] Comparative Example 7, compared with Example 1, the ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the second tab 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 loss of active material at the positions of the first gap 211, the first opening 215, the second gap 221 and the second opening 225, and the average maximum tolerance temperature is basically the same. Compared with Example 5, due to the further reduction of the effective connection length of the first connecting part 212 along the third direction Z, the physical support force is insufficient, the average expansion rate is increased, and during the cycle process, the connection point in some layers will be broken due to the expansion of the tab, so that this part loses electronic contact and cannot further deintercalate lithium, thereby further deteriorating the cycle performance.

[0165] Comparative Example 8, compared with Example 1, the ratio of the effective connection length of the first connecting part 212 along the third direction Z to the length of the second tab 220 along the third direction Z is increased from 5% to 55%, under this design, the energy density of the secondary battery 001 is increased by about 0.32% due to the increase of active material at the positions of the first gap 211, the first opening 215, the second gap 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, the average expansion rate is increased, and the cycle and high temperature environment tolerance is further deteriorated.

[0166] In addition, for those skilled in the art, other various corresponding changes and modifications can be made according to the technical concept of the present application, and all these changes and modifications shall belong to the protection scope of the claims of the present application.

Claims

1. A secondary battery comprising an electrode assembly, the electrode assembly comprising a first electrode sheet, a separator, and a second electrode sheet stacked, characterized in that: the first electrode sheet is provided with at least one first notch, the first notch penetrating the first electrode sheet in a first direction, and the first notch extends to an edge of the first electrode sheet; the first electrode sheet further comprises a first connecting portion, the first notch and the first connecting portion are arranged in sequence in a third direction; in the third direction, a projection of the first connecting portion falls within a projection range of the first notch; a length of the first electrode sheet in the third direction is S1, an effective connecting length of the first connecting portion in the third direction is S2, 1%≤(S2 / S1)×100%≤50%; the first direction is a thickness direction of the first electrode sheet, the first direction, a second direction, and the third direction are perpendicular to each other. 2%≤(S2 / S1)×100%≤10%.

2. The secondary battery according to claim 1, wherein The second electrode sheet is provided with at least one second notch, the second notch penetrating the second electrode sheet in the first direction; in the first direction, a projection of the first notch and a projection of the second notch at least partially overlap.

3. The secondary battery according to claim 1, wherein The second notch extends to an edge of the second electrode sheet, and the second electrode sheet further comprises a second connecting portion, the second notch and the second connecting portion are arranged in sequence in the third direction; in the third direction, a projection of the second connecting portion falls within a projection range of the second notch.

4. The secondary battery according to claim 3, wherein The first electrode sheet is a cathode electrode sheet, and the second electrode sheet is an anode electrode sheet; the first notch and the second notch are correspondingly arranged, and in the first direction, the projection of the second notch is located within the projection of the first notch.

5. The secondary battery according to claim 4, wherein The first electrode sheet is provided with at least one first opening, the first opening penetrating the first electrode sheet in the first direction; in the third direction, the center of the first opening is respectively away from the two edges of the first electrode sheet by a distance of L1 and L2, and │L1-L2│≤5mm.

6. The secondary battery according to claim 1, wherein The first electrode sheet is provided with at least one first opening, the first opening penetrating the first electrode sheet in the first direction; the second electrode sheet is provided with at least one second opening, the second opening penetrating the second electrode sheet in the first direction; 7. The secondary battery according to claim 4, wherein the positive electrode is a lithium ion secondary electrode. In the third direction, the center of the first opening is respectively away from the two edges of the first electrode sheet by a distance of L1 and L2, and the center of the second opening is respectively away from the two edges of the second electrode sheet by a distance of L3 and L4, and │L1-L2│≤5mm, │L3-L4│≤5mm. The number of the second openings is the same as that of the first openings, and the second openings are correspondingly arranged with the first openings.

8. The secondary battery according to claim 7, wherein The first electrode sheet is a cathode electrode sheet, and the second electrode sheet is an anode electrode sheet; in the first direction, the projection of the second opening is located within the projection of the first opening.

9. The secondary battery according to claim 8, wherein ​ 10. The secondary battery according to claim 6, wherein The first connecting portion is further provided with a first flared portion, which penetrates the first connecting portion along the first direction; the first flared portion is arranged at at least one end of the first opening along the third direction, and the first flared portion is in communication with the first opening; along the third direction, the projection of the first opening is located within the projection of the first flared portion.

11. The secondary battery according to claim 6, wherein The angle position of the first notch and / or the first opening is arranged in an arc shape.

12. An electrical device, characterized by A secondary battery comprising the secondary battery according to any one of claims 1 to 11.

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