Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and an electronic device, the secondary battery comprises an electrode assembly, and the electrode assembly comprises a first pole piece, a second pole piece and an isolating membrane. The first pole piece comprises a first current collector and a first active material layer. The first current collector includes a first surface and a second surface facing away from a center of the electrode assembly in the first direction. In the first direction, the first pole piece comprises a first part, and a first active material layer is arranged on the first surface of the first part. The first part comprises a first part, and the first part is a part of the outermost pole piece of the electrode assembly in the first direction. The first active material layer at the first part is provided with a first groove, and the first active material layer at the first part is divided into a plurality of sub-regions by the first groove, so that the expansion rate of the secondary battery is improved, and the circulation capacity is improved.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] With the widespread adoption of consumer electronics such as laptops, mobile phones, handheld game consoles, tablets, power banks, and drones, the requirements for the safety performance and cycle life of rechargeable batteries are becoming increasingly stringent. Rechargeable batteries include electrode components. In related technologies, due to factors such as energy density and safety, the edges of the outermost electrode layer of the electrode component are prone to warping and lithium deposition during cycling, reducing the safety and cycle life of the rechargeable battery. Summary of the Invention

[0003] The inventors of this application have discovered that during the cycling process of a secondary battery, the negative electrode extends and acts on the positive electrode, causing strong stress concentration at the edge of the outermost positive electrode in the thickness direction of the electrode assembly. This leads to the edge of the positive electrode lifting, further resulting in localized unevenness at the bonding interface between the separator and the positive electrode, forming annular wrinkles. As cycling continues, due to electrolyte consumption, electrolyte bridging occurs on the outermost positive electrode in the thickness direction of the electrode assembly, forming black spots and lithium plating, thereby affecting the cycle capacity retention rate and expansion rate of the secondary battery.

[0004] In view of this, it is necessary to provide a secondary battery and electronic device to improve the performance of the secondary battery.

[0005] This application provides a secondary battery including an electrode assembly. The electrode assembly includes a first electrode, a second electrode, and a separator, which are sequentially stacked. The first electrode includes a first current collector and a first active material layer disposed on at least a portion of the first current collector. The first current collector includes a first surface and a second surface disposed opposite to each other along the thickness direction of the first current collector. The second surface is away from the center of the electrode assembly in a first direction, which is the thickness direction of the electrode assembly. Along the first direction, the first electrode includes a first portion, and the first surface of the first current collector in the first portion is provided with the first active material layer. The first portion includes a first part, which is the outermost electrode of the electrode assembly in the first direction. The first active material layer in the first part is provided with a first groove, which divides the first active material layer in the first part into multiple sub-regions. By dividing the first active material layer in the first part into multiple sub-regions through the first groove, the force exerted by the extension of the second electrode on the first electrode is dispersed, the strong stress concentration formed at the edge of the first part in the first direction is reduced, the uneven adhesion between the first part and the separator is improved, thereby improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate.

[0006] In one or more of the above optional embodiments, the first groove includes a plurality of spaced-apart first sub-grooves and a plurality of spaced-apart second sub-grooves, with at least one first sub-groove intersecting with at least one second sub-groove, dividing the first active material layer of the first part into multiple sub-regions. By intersecting at least one first sub-groove and at least one second sub-groove in the first part, the number of divided sub-regions is increased, further dispersing the force exerted by the extension of the second electrode on the first electrode, reducing the strong stress concentration formed at the edge of the first part in the first direction, further improving the uneven adhesion between the first part and the separator, and thus further improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate.

[0007] In one or more of the above optional embodiments, along the direction perpendicular to the extension of the first sub-groove, the width of the first sub-groove on the surface of the first active material layer is W1, where 5μm≤W1≤100μm. By ensuring W1≥5μm, the width of the first sub-groove is guaranteed, reducing stress concentration in the first part, which is beneficial to improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate; by controlling W1≤100μm, the width of the first sub-groove is controlled, reducing the amount of the first active material layer that is removed, thus reducing the impact on the energy density of the secondary battery.

[0008] In one or more of the above optional embodiments, 10μm≤W1≤60μm. By having W1≥10μm, the width of the first sub-groove is increased, further reducing the stress concentration in the first part, which is more conducive to improving the expansion rate of the secondary battery and improving the cycle capacity retention rate; by having W1≤60μm, the width of the first sub-groove is further controlled, further reducing the amount of the first active material layer that is removed, and reducing the impact on the energy density of the secondary battery.

[0009] In one or more of the above optional embodiments, along the thickness direction of the first active material layer, the thickness of the first active material layer located in the first part is H1, and the depth of the first sub-groove is H2, where 10%≤H2 / H1≤80%, 25μm≤H1≤65μm, and 25μm≤H1≤65μm. By ensuring H2 / H1≥1% and 25μm≤H1≤65μm, the depth of the first sub-groove is guaranteed, which helps reduce stress concentration in the first part, improves the expansion rate of the secondary battery, and enhances the cycle capacity retention rate. By controlling the depth of the first sub-groove by H2 / H1≤80%, the amount of the first active material layer removed is reduced, decreasing the impact on the energy density of the secondary battery and reducing the risk of the first current collector being broken down.

[0010] In one or more of the above optional embodiments, 20% ≤ H2 / H1 ≤ 60%. By having H2 / H1 ≥ 20%, the depth of the first sub-groove is increased, which further helps to reduce stress concentration in the first part, further helps to improve the expansion rate of the secondary battery, and improves the cycle capacity retention rate. By having H2 / H1 ≤ 60%, the depth of the first sub-groove is further controlled, further reducing the amount of the first active material layer that is removed, and further reducing the impact on the energy density of the secondary battery.

[0011] In one or more of the above optional embodiments, the width of the first sub-groove is gradually reduced from the surface of the first active material layer toward the first current collector along the thickness direction of the first active material layer. This is beneficial to reduce the amount of the first active material layer that is removed and reduce the impact on the energy density of the secondary battery.

[0012] In one or more of the above optional embodiments, the width at the middle depth position of the first sub-groove along the thickness direction of the first active material layer is W2, where 1 / 3 ≤ W2 / W1 ≤ 2 / 3. By ensuring W2 / W1 ≥ 1 / 3, it is beneficial to reduce stress concentration in the first part in the first direction, improve the expansion rate of the secondary battery, and increase cycle capacity. By ensuring W2 / W1 ≤ 2 / 3, controlling the width at the middle depth position of the first sub-groove is beneficial to reduce the amount of the first active material layer removed, thus reducing the impact on the energy density of the secondary battery.

[0013] In one or more of the above alternative embodiments, the same location of the first sub-groove intersects with a second sub-groove. This reduces the problem of excessive removal of the first active material layer at the same location due to the intersection of the first sub-groove with multiple second sub-grooves, and also reduces the risk of current collector puncture at the intersection location.

[0014] In one or more of the above optional embodiments, on the surface of the first active material layer of the first part, the minimum distance between adjacent first sub-grooves is D1, 1mm≤D1≤10mm. By having D1≥1mm, reducing the number of first sub-grooves while keeping the area of ​​the first part constant helps to reduce the amount of first active material layer removed, thus reducing the impact on the energy density of the secondary battery. By having D1≤10mm, ensuring the number of first sub-grooves while keeping the area of ​​the first part constant helps to reduce stress concentration in the first direction, thus improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate. Alternatively, the minimum distance between adjacent second sub-grooves is D2, 1mm≤D2≤10mm. By having D2≥1mm, reducing the number of second sub-grooves while keeping the area of ​​the first part constant helps to reduce the amount of first active material layer removed, thus reducing the impact on the energy density of the secondary battery. By having D2≤10mm, ensuring the number of second sub-grooves while keeping the area of ​​the first part constant helps to reduce stress concentration in the first direction, thus improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate.

[0015] In one or more of the above optional embodiments, the first electrode, the separator, and the second electrode are stacked in sequence and arranged in a wound structure.

[0016] In one or more of the above optional embodiments, the second surface of the first current collector located in the first part is not provided with an active material layer, which is beneficial to improving the energy density of the secondary battery.

[0017] In one or more of the above optional embodiments, the first electrode further includes a second part, with the first part and the second part arranged sequentially. Neither the first surface nor the second surface of the first current collector located in the second part has an active material layer. Along the winding direction of the electrode assembly, the first part connects to the second part, and the second part includes the winding tail end of the first electrode. Providing a second part at the winding tail end of the first electrode, where neither the first nor the second surface has an active material layer, helps to provide extension space for the first part of the first electrode, further disperses the force exerted by the extension of the second electrode on the first electrode, reduces the strong stress concentration formed at the edge of the first part in the first direction, improves the uneven adhesion between the first part and the separator, and thus improves the expansion rate of the secondary battery and enhances the cycle capacity retention rate.

[0018] In one or more of the above optional embodiments, in the unfolded state of the first electrode, along the length direction of the first electrode, the first electrode includes a starting edge located at the starting end of the winding of the electrode assembly and a finishing edge located at the ending end of the winding of the electrode assembly. The first part includes a fifth edge and a sixth edge along the length direction of the first electrode. Along the length direction of the first electrode, the starting edge, the fifth edge, the sixth edge, and the finishing edge are arranged sequentially. Along the length direction of the first electrode, the distance between the starting edge and the fifth edge is A1, and the distance between the sixth edge and the finishing edge is A2, where 0 ≤ A2 / A1 ≤ 0.5, and 0 mm ≤ A2 ≤ 100 mm. In the wound structure electrode assembly, the stress generated by the expansion and extension of the second electrode will accumulate at the winding ending section of the electrode assembly; therefore, the distance between the area where the first groove is provided and the winding ending end should not be too large. By setting 0≤A2 / A1≤0.5 and 0mm≤A2≤100mm, the stress accumulated at the end of the first electrode can be reduced by the first groove, reducing the risk of wrinkling of the first electrode, thereby improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate.

[0019] In one or more of the above optional embodiments, the first electrode is a positive electrode. During the cycling process of the secondary battery, the negative electrode active material layer expands, and the negative electrode extends and acts on the positive electrode, causing strong stress concentration at the edge of the outermost positive electrode in the thickness direction of the electrode assembly. This leads to the edge of the positive electrode lifting, further causing local unevenness at the bonding interface between the separator and the positive electrode, forming annular wrinkles, which in turn affects the expansion rate and cycle capacity retention of the secondary battery. Dividing the outermost first active material layer of the positive electrode into multiple sub-regions can disperse the force exerted by the extension of the negative electrode on the positive electrode, reduce the strong stress concentration at the edge of the first part in the first direction, improve the uneven bonding between the first part and the separator, thereby improving the expansion rate of the secondary battery and enhancing the cycle capacity retention rate.

[0020] In one or more of the above optional embodiments, the second electrode is a negative electrode, and the second electrode includes a second active material layer. The material of the second active material layer includes silicon, and based on the total mass of the second active material layer, the mass percentage of silicon element is W%, 3≤W≤40. W≥3 is beneficial to improving the energy density of the secondary battery; W≤40 is beneficial to reducing the risk of excessive cycle expansion rate due to excessive expansion of the negative electrode or the appearance of annular wrinkles at the tail of the positive electrode.

[0021] In one or more of the above optional embodiments, 15≤W≤30. W≥15 is beneficial to further improve the energy density of the secondary battery; W≤30 is beneficial to further reduce the risk of excessive cycle expansion rate or annular wrinkles at the tail of the positive electrode due to excessive expansion of the negative electrode.

[0022] In one or more of the above optional embodiments, the first sub-groove and / or the second sub-groove are inclined along the length direction of the first electrode. The angle between the extension direction of the first sub-groove and the extension direction of the second sub-groove and the length direction of the first electrode is α, where 30°≤α≤75°. By setting the first sub-groove and / or the second sub-groove to be inclined, it is beneficial to increase the length of a single first sub-groove and / or a single second sub-groove in the extension direction, which is more beneficial to improving the stress concentration of the first electrode. By setting α≥30°, it is beneficial to increase the length of a single first sub-groove and / or a single second sub-groove in the extension direction, which is more beneficial to improving the stress concentration of the first electrode, further improving the expansion rate of the secondary battery, and improving the cycle capacity retention rate; by setting α≤75°, it is beneficial to match the process capability of the grooving equipment, reducing the possibility that the grooving equipment cannot complete the etching in one go due to the excessive length of a single first sub-groove and / or a single second sub-groove, thus affecting manufacturing efficiency.

[0023] In one or more of the above optional embodiments, 40°≤α≤60° is beneficial to further improve the effect of the first sub-groove and / or the second sub-groove on improving the stress concentration of the first electrode, further improve the expansion rate of the secondary battery, and improve the cycle capacity retention rate; and is also beneficial to further improve manufacturing efficiency.

[0024] In one or more of the above optional embodiments, along the width direction of the first electrode, the first electrode includes a third edge and a fourth edge disposed opposite to each other. The minimum distance between the first sub-groove and / or the second sub-groove and the third edge is L1, and the minimum distance between the first sub-groove and / or the second sub-groove and the fourth edge is L2, where 0.5mm≤L1≤5mm and / or 0.5mm≤L2≤5mm. By setting L1≥0.5mm and / or L2≥0.5mm, the risk of the first electrode tearing from the third or fourth edge due to the first sub-groove and / or the second sub-groove being too close to the third and / or fourth edge can be reduced, thereby improving the manufacturing yield of the secondary battery. By setting L1≤5mm and / or L2≤5mm, the area ratio of the first sub-groove and / or the second sub-groove in the first electrode can be increased, thereby improving the effect of the first sub-groove and / or the second sub-groove in improving the stress concentration of the first electrode, further improving the expansion rate of the secondary battery, and improving the cycle capacity retention rate.

[0025] In one or more of the above optional embodiments, 1mm ≤ L1 ≤ 3mm, and / or 1mm ≤ L2 ≤ 3mm. This is beneficial for further improving manufacturing yield and further improving the expansion rate of the secondary battery, thereby improving the cycle capacity retention rate.

[0026] In one or more of the above optional embodiments, the first part includes a second part, which is the outermost electrode of the electrode assembly in the first direction. The first part and the second part are disposed opposite to each other in the first direction. The first active material layer located in the second part is provided with a first groove. The edge of the second part is still subjected to stress concentration in the first direction, causing the edge of the second part to lift up, dividing the first active material layer of the second part into multiple sub-regions, dispersing the force of the negative electrode sheet extension on the positive electrode sheet, reducing the strong stress concentration formed at the edge of the second part in the first direction, improving the uneven adhesion between the second part and the separator, thereby improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate.

[0027] In one or more of the above optional embodiments, the ratio S of the area of ​​the first groove in the second part to the area of ​​the first groove in the first part is 0.3 ≤ S ≤ 1. S ≥ 0.3 ensures that the area of ​​the first groove in the second part is sufficient, which helps reduce the strong stress concentration formed at the edge of the second part in the first direction, improves the uneven adhesion between the second part and the separator, and thus improves the expansion rate of the secondary battery and enhances the cycle capacity retention rate. S ≤ 1 helps reduce the amount of the first active material layer removed from the second part, reducing the impact on the energy density of the secondary battery.

[0028] In one or more of the above optional embodiments, the secondary battery further includes a housing containing electrode components and an electrolyte, the electrolyte comprising at least one of propylene carbonate, ethylene carbonate, or diethyl carbonate. The electrolyte comprising the above components can improve lithium-ion transport efficiency, increase the effective capacity of the secondary battery, and reduce energy density loss caused by the grooving of the first electrode.

[0029] Embodiments of this application provide an electronic device including the secondary battery in any of the above embodiments.

[0030] The aforementioned secondary battery separates the first active material layer of the first part into multiple sub-regions by using the first groove to disperse the force exerted by the negative electrode on the positive electrode, reduce the strong stress concentration formed at the edge of the first part in the first direction, improve the uneven adhesion between the first part and the separator, thereby improving the expansion rate of the secondary battery, increasing the cycle capacity retention rate, and extending the service life of electronic devices using the secondary battery. Attached Figure Description

[0031] Figure 1 A cross-sectional schematic diagram of a secondary battery in some embodiments is shown.

[0032] Figure 2 A schematic diagram of the first electrode sheet after unfolding is shown in some embodiments.

[0033] Figure 3A schematic diagram of the first electrode after unfolding is shown in some other embodiments.

[0034] Figure 4 A schematic diagram of the first electrode sheet after unfolding is shown in some other embodiments.

[0035] Figure 5 It shows Figure 4 A schematic diagram of the structure of the first pole piece after unfolding from another perspective.

[0036] Figure 6 A schematic diagram of the first electrode after unfolding is shown in some other embodiments.

[0037] Figure 7 A schematic diagram of the structure of the first electrode sheet from another perspective is shown in some embodiments.

[0038] Figure 8 A cross-sectional schematic diagram of the secondary battery in some other embodiments is shown.

[0039] Figure 9 Schematic diagrams of the electronic devices in some embodiments are shown.

[0040] Explanation of key component symbols: Secondary battery 100 Electrode assembly 10 First Straight Zone 10A First Corner Area 10B Second Straight Zone 10C Second corner area 10D First Polar Film 11 Third Edge 113 Fourth Edge 114 Part 11A Part 2, 11B Subregion 11C Part 1, Chapter 110 First current collector 111 First active material layer 112 First surface 111A Second surface 111B Second pole piece 12 Second current collector 121 Second active material layer 122 Separator 13 First Pole Ear 20 Second pole ear 30 40 housing Part 2, Episode 120 First groove 101 First sub-groove 101A Second sub-groove 101B First edge 1011 Second edge 1012 Electronic devices 200 First direction X Second direction Y Third direction Z The following specific embodiments will further illustrate this application in conjunction with the above-described accompanying drawings. Detailed Implementation

[0041] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0042] When a component is considered to be "located" on another component, it can be directly on the other component or may also be interspersed with other components. When a component is considered to be "connected" to another component, it can be directly connected to the other component or may also be interspersed with other components.

[0043] 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 herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] It is understandable that the term "perpendicular" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately perpendicular or equal to each other. For example, combined with numerical description, perpendicularity can refer to the angle between two straight lines within the range of 90° ± 10°, the dihedral angle between two planes within the range of 90° ± 10°, or the angle between a straight line and a plane within the range of 90° ± 10°. The two components described as "perpendicular" do not have to be absolutely straight lines or planes; they can be approximately straight lines or planes. From a macroscopic perspective, if the overall direction of extension is a straight line or plane, the component can be considered a "straight line" or "plane".

[0045] Unless otherwise defined, the term "multiple" in this document, when used to describe the number of components, specifically means that the component is two or more.

[0046] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0047] Please see Figures 1 to 3 One embodiment of this application provides a secondary battery 100, including an electrode assembly 10. The electrode assembly 10 includes a first electrode 11, a second electrode 12, and a separator 13 disposed between the first electrode 11 and the second electrode 12. The first electrode 11, the separator 13, and the second electrode 12 are stacked sequentially.

[0048] The first electrode 11 includes a first current collector 111 and a first active material layer 112 disposed on at least a portion of the first current collector 111. Along the thickness direction of the first electrode 11, the first current collector 111 includes a first surface 111A and a second surface 111B disposed opposite to each other. The first surface 111A faces the center of the electrode assembly 10 in a first direction X, and the second surface 111B faces away from the center of the electrode assembly 10 in the first direction X, where the first direction X is the thickness direction of the electrode assembly 10.

[0049] The second electrode 12 includes a second current collector 121 and a second active material layer 122 disposed on at least a portion of the second current collector 121.

[0050] In some embodiments, the first electrode 11 is a positive electrode, and the second electrode 12 is a negative electrode. Correspondingly, the first current collector 111 is a positive current collector, and the first active material layer 112 includes a first active material, which is a positive active material; the second current collector 121 is a negative current collector, and the second active material layer 122 includes a second active material, which is a negative active material. During cycling, the negative active material layer of the secondary battery 100 expands, and the negative electrode extends and acts on the positive electrode, causing a strong stress concentration at the edge of the outermost positive electrode in the thickness direction of the electrode assembly. This leads to the edge of the positive electrode lifting, further causing local unevenness at the bonding interface between the separator and the positive electrode, forming annular wrinkles, which in turn affects the expansion rate and cycle capacity retention of the secondary battery. Dividing the outermost active material layer of the positive electrode into multiple sub-regions can disperse the force exerted by the extension of the negative electrode on the positive electrode, reduce the strong stress concentration formed at the edge of the first part in the first direction, improve the uneven adhesion between the first part and the separator, thereby improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate.

[0051] In other embodiments, the first electrode 11 may be configured as the negative electrode and the second electrode 12 as the positive electrode.

[0052] The positive electrode current collector can be made of aluminum foil or nickel foil, and the negative electrode current collector can be made of at least one of copper foil, nickel foil or carbon-based current collector.

[0053] The separator 13 comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene comprises at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.

[0054] In some embodiments, the secondary battery 100 includes a first tab 20 and a second tab 30. The first tab 20 is electrically connected to a first current collector 111, and the second tab 30 is electrically connected to a second current collector 121. The first tab 20 and the second tab 30 can be connected to external components (not shown).

[0055] In some embodiments, along the first direction X, the first electrode 11 includes a first portion 11A. The first surface 111A of the first current collector 111 located in the first portion 11A is provided with a first active material layer 112.

[0056] The first part 11A includes a first portion 110, which is the outermost electrode of the electrode assembly 10 in the first direction X.

[0057] The first active material layer 112 located in the first part 110 is provided with a first groove 101, which divides the first active material layer 112 of the first part 110 into multiple sub-regions 11C.

[0058] During cycling, the negative electrode of the secondary battery 100 extends and acts on the positive electrode, causing strong stress concentration at the edge of the outermost positive electrode in the thickness direction of the electrode assembly 10. This leads to the edge of the positive electrode lifting, which further causes local unevenness at the bonding interface between the separator 13 and the positive electrode, forming annular wrinkles. As cycling continues, electrolyte consumption causes electrolyte bridging on the outermost positive electrode in the thickness direction of the electrode assembly 10, resulting in black spots and lithium deposition. This affects the cycle capacity retention and expansion rate of the secondary battery 100.

[0059] This application divides the first active material layer 112 of the first part 110 into multiple sub-regions 11C by the first groove 101, disperses the force of the negative electrode sheet extension on the positive electrode sheet, reduces the strong stress concentration formed at the edge of the first part 110 in the first direction X, improves the uneven adhesion between the first part 110 and the separator 13, and thus improves the expansion rate of the secondary battery 100 and improves the cycle capacity retention rate.

[0060] In some embodiments, the second surface 111B of the first current collector 111 located in the first portion 11A is not provided with an active material layer, that is, the first portion 11A is a single-sided coating area, which is beneficial to improve the cycle capacity retention rate.

[0061] like Figure 1As shown, in some embodiments, the first electrode 11, the separator 13, and the second electrode 12 are stacked in sequence and arranged in a wound structure, that is, the electrode assembly 10 is a wound structure.

[0062] like Figure 3 As shown, in some embodiments, the first electrode 11 includes a second portion 11B. The first portion 11A and the second portion 11B are arranged sequentially. Neither the first surface 111A nor the second surface 11B of the first current collector 111 located in the second portion 11B has an active material layer. Along the winding direction of the electrode assembly 10, the first portion 110 connects to the second portion 11B, and the second portion 11B includes the winding tail end of the first electrode 11. That is, the second portion 11B is an empty foil area. The second portion 11B provides extension space for the first portion 11A, reducing the probability or degree of wrinkling in the first portion 11A.

[0063] like Figure 1 As shown, in some embodiments, the electrode assembly 10 may be divided into a first straight region 10A, a first corner region 10B, a second straight region 10C, and a second corner region 10D connected sequentially in the winding direction. The first straight region 10A and the second straight region 10C are arranged opposite to each other in a first direction X, and the first corner region 202 and the second corner region 204 are arranged opposite to each other. The first corner region 10B connects the first straight region 10A and the second straight region 10C, and the second corner region 10D connects the first straight region 10A and the second straight region 10C. The first part 110 is located in either the first straight region 10A or the second straight region 10C.

[0064] The corner area is the bent part of the electrode assembly 10. The corner area is a concept opposite to the straight area. When viewed along the direction in which the first tab 20 or the second tab 30 protrudes from the electrode assembly 10, the first corner area 10B and the second corner area 10D can be arranged in an arc shape.

[0065] like Figure 8 As shown, in some embodiments, the first electrode 11, the separator 13, and the second electrode 12 are stacked sequentially, that is, the electrode assembly 10 is arranged in a stacked configuration. In this case, along the first direction X, the outermost first electrode 11 is the negative electrode, and the second electrode 12 is the positive electrode.

[0066] Please see Figure 2 In some embodiments, the length direction of the unfolded first electrode 11 is taken as the second direction Y, and the width direction of the unfolded first electrode 11 is taken as the third direction Z. The first direction X, the second direction Y, and the third direction Z are perpendicular to each other.

[0067] The first active material layer 112 located in the first part 110 is provided with a plurality of first grooves 101 extending along the third direction Z and spaced apart along the second direction Y, which increases the number of sub-regions 11C of the first active material layer 112 of the first part 110, which is beneficial to improve the expansion rate of the secondary battery 100 and improve the cycle capacity retention rate.

[0068] In some embodiments, the first active material layer 112 located in the first part 110 is provided with a plurality of first grooves 101 extending along the second direction Y and spaced along the third direction Z, which increases the number of sub-regions 11C of the first active material layer 112 of the first part 110, which is beneficial to improve the expansion rate of the secondary battery 100 and improve the cycle capacity retention rate.

[0069] Please see Figure 3 In some embodiments, the first active material layer 112 located in the first part 110 is provided with a plurality of first grooves 101, some of the first grooves 101 extend along the second direction Y and are spaced apart along the third direction Z, and some of the first grooves 101 extend along the third direction Z and are spaced apart along the second direction Y.

[0070] Please see Figure 4 and Figure 6 In some embodiments, the first groove 101 includes a plurality of spaced-apart first sub-grooves 101A and a plurality of spaced-apart second sub-grooves 101B, with at least one first sub-groove 101A and at least one second sub-groove 101B intersecting each other, dividing the first active material layer 112 of the first part 110 into a plurality of sub-regions 11C. This facilitates dividing the first active material layer 112 of the first part 110 into a greater number of sub-regions 11C, further reducing stress concentration in the first part 110 in the first direction X, improving the expansion rate of the secondary battery 100, and enhancing the cycle capacity retention rate.

[0071] like Figure 6 As shown, in some embodiments, one of the first sub-groove 101A and the second sub-groove 101B extends along the second direction Y, and the other extends along the third direction Z.

[0072] like Figure 4 As shown, in some other embodiments, the length extension direction of the first sub-groove 101A is inclined relative to the second direction Y and the third direction Z, and the length extension direction of the second sub-groove 101B is inclined relative to the second direction Y and the third direction Z.

[0073] In some embodiments, the angle between the extension direction of the first sub-groove 101A and / or the extension direction of the second sub-groove 101B and the second direction Y is α, where 30°≤α≤75°. By setting α≥30°, it is beneficial to increase the length of a single first sub-groove 101A and / or a single second sub-groove 101B in the extension direction, which is more conducive to improving the stress concentration of the first electrode by the first sub-groove 101A and / or the second sub-groove 101B, further improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate. By setting α≤75°, it is beneficial to match the process capability of the grooving equipment, reducing the possibility that the grooving equipment cannot complete the etching in one go due to the excessive length of a single first sub-groove 101A and / or a single second sub-groove 101B, thus affecting manufacturing efficiency.

[0074] Optionally, α can be any one or any combination of 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, and 75°.

[0075] In some embodiments, 40°≤α≤60°. This is beneficial for further improving the effect of the first sub-groove 101A and / or the second sub-groove 101B in reducing stress concentration in the first electrode 11, further improving the expansion rate of the secondary battery 100, and increasing the cycle capacity retention rate; and it is also beneficial for further improving manufacturing efficiency.

[0076] In other embodiments, the first sub-groove 101A extends in an arc along its length, and the second sub-groove 101B extends in an arc along its length.

[0077] In other embodiments, one of the first sub-groove 101A and the second sub-groove 101B extends in an arc direction, while the other extends in a second direction Y, or extends in a third direction Z, or is inclined relative to the second direction Y and the third direction Z.

[0078] In some embodiments, the first sub-groove 101A and the second sub-groove 101B are formed by laser etching.

[0079] In some embodiments, the same position of the first sub-groove 101A intersects with a second sub-groove 101B, reducing the number of times the intersection point of the first sub-groove 101A and the second sub-groove 101B is repeatedly etched by the laser, reducing the risk of the first current collector 111 being broken down, and improving the manufacturing yield of the secondary battery 100.

[0080] Please see Figure 7In some embodiments, the first sub-groove 101A includes a first edge 1011 and a second edge 1012 located on the surface of the first active material layer 112. Along a direction perpendicular to the first edge 1011 and the second edge 1012, the width of the first sub-groove 101A is W1, where 5μm ≤ W1 ≤ 100μm. By ensuring W1 ≥ 5μm, the width of the first sub-groove 101A is maintained, reducing stress concentration on the first portion 110 in the first direction X, which is beneficial for improving the expansion rate of the secondary battery 100 and increasing the cycle capacity retention rate. By controlling W1 ≤ 100μm, the width of the first sub-groove 101A is reduced, decreasing the amount of the first active material layer 112 removed and reducing the impact on the energy density of the secondary battery 100.

[0081] Optionally, W1 can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 2 9μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 41μm m, 42μm, 43μm, 44μm, 45μm, 46μm, 47μm, 48μm, 49μm, 50μm, 51μm, 52μm, 53μm, 5 The range consisting of any one or any two of the following: 4μm, 55μm, 56μm, 57μm, 58μm, 59μm, 60μm, 61μm, 62μm, 63μm, 64μm, 65μm, 66μm, 67μm, 68μm, 69μm, 70μm, 71μm, 72μm, 73μm, 74μm, 75μm, 76μm, 77μm, 78μm, 79μm, 80μm, 81μm, 82μm, 83μm, 84μm, 85μm, 86μm, 87μm, 88μm, 89μm, 90μm, 91μm, 92μm, 93μm, 94μm, 95μm, 96μm, 97μm, 98μm, 99μm, and 100μm.

[0082] In some embodiments, 10μm≤W1≤60μm, by W1≥10μm, increases the width of the first sub-groove 101A, further reduces the stress concentration of the first part 110 in the first direction X, further improves the expansion rate of the secondary battery 100 and increases the cycle capacity; by W1≤60μm, the width of the first sub-groove 101A is further controlled, further reduces the first active material layer 112 that is removed, and reduces the impact on the energy density of the secondary battery 100.

[0083] In some embodiments, the width range of the second sub-groove 101B is the same as the width range of the first sub-groove 101A.

[0084] Please see Figure 7 In some embodiments, along the thickness direction of the first active material layer 112, the thickness of the first active material layer 112 located in the first part 110 is H1, and the depth of the first sub-groove 101A is H2, where 10%≤H2 / H1≤80%, and 25μm≤H1≤65μm. Maintaining the depth of the first sub-groove 101A by ensuring H2 / H1≥10% helps reduce stress concentration in the first part 110 in the first direction X, which is beneficial for improving the expansion rate of the secondary battery 100 and increasing the cycle capacity retention rate. Controlling the depth of the first sub-groove 101A by H2 / H1≤80% reduces the amount of the first active material layer 112 that is removed, reducing the impact on the energy density of the secondary battery 100, and also reducing the risk of the first current collector 111 being broken down, thus improving the manufacturing yield of the secondary battery 100.

[0085] Optionally, the value of H2 / H1 can be a range of any one or any two of the following: 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, and 80%.

[0086] H1 can be any one or any combination of two of the following: 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 41μm, 42μm, 43μm, 44μm, 45μm, 46μm, 47μm, 48μm, 49μm, 50μm, 51μm, 52μm, 53μm, 54μm, 55μm, 56μm, 57μm, 58μm, 59μm, 60μm, 61μm, 62μm, 63μm, 64μm, and 65μm.

[0087] In some embodiments, 20% ≤ H2 / H1 ≤ 60%, with H2 / H1 ≥ 20%, increases the depth of the first sub-groove 101A, which further helps to reduce the stress concentration on the first part 110 in the first direction X, further helps to improve the expansion rate of the secondary battery 100, and increases the cycle capacity. With H2 / H1 ≤ 60%, the depth of the first sub-groove 101A is further controlled, further reducing the amount of the first active material layer 112 that is removed, and further reducing the impact on the energy density of the secondary battery 100.

[0088] In some embodiments, the ratio of the depth of the second sub-groove 101B to the thickness of the first active material layer 112 satisfies the range of the ratio H2 / H1.

[0089] In some embodiments, along the thickness direction of the first active material layer 112, the width of the first sub-groove 101A gradually decreases from the surface of the first active material layer 112 toward the first current collector 111. That is, the width formed by the first edge 1011 and the second edge 1012 of the first sub-groove 101A on the surface of the first active material layer 112 is the maximum width of the first sub-groove 101A, which helps to reduce the amount of the first active material layer 112 that is removed and reduces the impact on the energy density of the secondary battery 100.

[0090] In some embodiments, along the thickness direction of the first active material layer 112, the width at the middle depth position of the first sub-groove 101A is W2, 1 / 3≤W2 / W1≤2 / 3. By having W2 / W1≥1 / 3, it is beneficial to reduce the stress concentration of the first part 110 in the first direction X, improve the expansion rate of the secondary battery 100, and enhance the cycle capacity retention rate. By having W2 / W1≤2 / 3, controlling the width at the middle depth position of the first sub-groove 101A is beneficial to reduce the amount of the first active material layer 112 that is removed, thereby reducing the impact on the energy density of the secondary battery 100.

[0091] Optionally, the value of W2 / W1 can be any one or a range of any two of 1 / 3, 5 / 12, 1 / 2, 7 / 12, and 2 / 3.

[0092] In some embodiments, the ratio of the width at the middle depth position of the second sub-groove 101B to the depth of the second sub-groove 101B satisfies the ratio range of W2 / W1.

[0093] Please see Figure 4In some embodiments, on the surface of the first active material layer 112 of the first part 110, the minimum distance between adjacent first sub-grooves 101A is D1, where 1mm ≤ D1 ≤ 10mm. By having D1 ≥ 1mm, the number of first sub-grooves 101A is reduced while keeping the area of ​​the first part 110 constant, which helps to reduce the amount of the first active material layer 112 that is removed and reduces the impact on the energy density of the secondary battery 100. By having D1 ≤ 10mm, the number of first sub-grooves 101A is maintained while keeping the area of ​​the first part 110 constant, which helps to reduce the stress concentration on the first part 110 in the first direction X, which helps to improve the expansion rate of the secondary battery 100 and improve the cycle capacity retention rate.

[0094] In some embodiments, on the surface of the first active material layer 112 of the first part 110, the minimum distance between adjacent second sub-grooves 101B is D2, where 1mm ≤ D2 ≤ 10mm. By having D2 ≥ 1mm, while keeping the area of ​​the first part 110 constant, reducing the number of second sub-grooves 101B is beneficial to reducing the amount of the first active material layer 112 that is removed, thus reducing the impact on the energy density of the secondary battery 100. By having D2 ≤ 10mm, while keeping the area of ​​the first part 110 constant, ensuring the number of second sub-grooves 101B is beneficial to reducing the stress concentration on the first part 110 in the first direction X, thus improving the expansion rate of the secondary battery 100 and increasing the cycle capacity retention rate.

[0095] When the minimum distance between adjacent first sub-grooves 101A satisfies D1, and when the minimum distance between adjacent second sub-grooves 101B satisfies D2, under the condition that the area of ​​the first part 110 remains unchanged, it is beneficial to divide the first active material layer 112 of the first part 110 into more sub-regions 11C, which is further beneficial to reduce the stress concentration of the first part 110 in the first direction X, and to improve the expansion rate of the secondary battery 100 and improve the cycle capacity retention rate.

[0096] In some embodiments, with the first electrode 11 unfolded, along the length direction of the first electrode 11, the first electrode 11 includes a starting edge located at the starting end of the winding of the electrode assembly 10 and a finishing edge located at the ending end of the winding of the electrode assembly 10. The first portion 110 includes a fifth edge and a sixth edge along the length direction of the first electrode 11. Along the length direction of the first electrode 11, the starting edge, the fifth edge, the sixth edge, and the finishing edge are arranged sequentially. Along the length direction of the first electrode 11, the distance between the starting edge and the fifth edge is A1, and the distance between the sixth edge and the finishing edge is A2, where 0 ≤ A2 / A1 ≤ 0.5, and 0 mm ≤ A2 ≤ 100 mm. In the wound electrode assembly 10, since the stress generated by the expansion and extension of the second electrode 12 accumulates at the ending section of the winding of the electrode assembly 10, the distance between the area where the first groove 101 is provided and the ending end of the winding should not be too large. By setting 0≤A2 / A1≤0.5 and 0mm≤A2≤100mm, the first groove 101 can reduce the stress accumulated at the end of the first electrode 11, reduce the risk of wrinkling of the first electrode 11, and thus improve the expansion rate of the secondary battery 100 and improve the cycle capacity retention rate. It should be noted that the method for determining A1 and A2 is as follows: with the first electrode 11 unfolded, a first tangent is drawn along the side of the first part 110 closest to the starting edge, and a second tangent is drawn along the side of the first part 110 closest to the ending edge. The distance between the starting edge and the first tangent is measured as A1, and the distance between the ending edge and the second tangent is measured as A2.

[0097] Optionally, A2 can be 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm, 23mm, 24mm, 25mm, 26mm, 27mm, 28mm, 29mm, 30mm, 31mm, 32mm, 33mm, 34mm, 35mm, 36mm, 37mm, 38mm, 39mm, 40mm, 41mm, 42mm, 43mm, 44mm, 45mm, 46mm, 47mm, 48mm, 49mm, 50mm, 51mm, 5 The range consisting of any one or any two of the following: 2mm, 53mm, 54mm, 55mm, 56mm, 57mm, 58mm, 59mm, 60mm, 61mm, 62mm, 63mm, 64mm, 65mm, 66mm, 67mm, 68mm, 69mm, 70mm, 71mm, 72mm, 73mm, 74mm, 75mm, 76mm, 77mm, 78mm, 79mm, 80mm, 81mm, 82mm, 83mm, 84mm, 85mm, 86mm, 87mm, 88mm, 89mm, 90mm, 91mm, 92mm, 93mm, 94mm, 95mm, 96mm, 97mm, 98mm, 99mm, and 100mm.

[0098] In some embodiments, along the width direction of the first electrode 11, the first electrode 11 includes a third edge 113 and a fourth edge 114 disposed opposite to each other, the minimum distance between the first sub-groove 101A and / or the second sub-groove 101B and the third edge 113 is L1, the minimum distance between the first sub-groove 101A and / or the second sub-groove 101B and the fourth edge 114 is L2, 0.5mm≤L1≤5mm, and / or, 0.5mm≤L2≤5mm. By setting L1≥0.5mm and / or L2≥0.5mm, the risk of the first electrode 11 tearing from the third edge 113 or the fourth edge 114 due to the first sub-groove 101A and / or the second sub-groove 101B being too close to the third edge 113 and / or the fourth edge 114 can be reduced, thereby improving the manufacturing yield of the secondary battery 100. By setting L1≤5mm and / or L2≤5mm, the area ratio of the first sub-groove 101A and / or the second sub-groove 101B in the first electrode 11 can be increased, thereby improving the effect of the first sub-groove 101A and / or the second sub-groove 101B in improving the stress concentration of the first electrode 11, further improving the expansion rate of the secondary battery 100, and improving the cycle capacity retention rate.

[0099] Optionally, L1 can be any one or any two of 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, and 5mm; L2 can be any one or any two of 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, and 5mm.

[0100] In some embodiments, 1mm ≤ L1 ≤ 3mm, and / or 1mm ≤ L2 ≤ 3mm. This is beneficial for further improving manufacturing yield and the expansion rate of secondary batteries, as well as improving cycle capacity retention.

[0101] Please see Figure 1 In some embodiments, the first portion 11A includes a second portion 120, which is the outermost electrode of the electrode assembly 10 in the first direction X. The first portion 110 and the second portion 120 are disposed opposite to each other along the first direction X. A first active material layer 112 located in the second portion 120 is provided with a first groove 101. Optionally, the first portion 110 is located in a first flat region 10A, and the second portion 120 is located in a second flat region 10C.

[0102] The edge of the second part 120 is still subjected to stress concentration in the first direction X, causing the edge of the second part 120 to lift up, dividing the first active material layer 112 of the second part 120 into multiple sub-regions 11C, dispersing the force of the negative electrode sheet extension on the positive electrode sheet, reducing the strong stress concentration formed on the edge of the second part 120 in the first direction X, improving the uneven adhesion between the second part 120 and the separator 13, thereby improving the expansion rate of the secondary battery 100 and increasing the cycle capacity retention rate.

[0103] In some embodiments, the edge of the second part 120 is subjected to less stress in the first direction X than the edge of the first part 110 is subjected to more stress in the first direction X.

[0104] In some embodiments, the ratio S of the area of ​​the first groove 101 located in the second part 120 to the area of ​​the first groove 101 located in the first part 110 is 0.3 ≤ S ≤ 1. Ensuring the area of ​​the first groove 101 located in the second part 120 helps to reduce the strong stress concentration formed at the edge of the second part 120 in the first direction X, improves the uneven adhesion between the second part 120 and the separator 13, and thus improves the expansion rate of the secondary battery 100 and enhances the cycle capacity retention rate.

[0105] In some embodiments, 0.3 ≤ S ≤ 0.8. By ensuring S ≥ 0.3, the area of ​​the first groove 101 in the second part 120 is guaranteed, which helps to reduce the strong stress concentration formed at the edge of the second part 120 in the first direction X, improves the uneven adhesion between the second part 120 and the separator 13, and thus improves the expansion rate of the secondary battery 100 and enhances the cycle capacity retention rate. By controlling S ≤ 0.8, the area of ​​the first groove 101 in the second part 120 is controlled, which helps to reduce the amount of the first active material layer 112 that is removed, and reduces the impact on the energy density of the secondary battery 100.

[0106] In some embodiments, the first electrode 11 is a positive electrode, and the second electrode 12 is a negative electrode. The second electrode 12 includes a second active material layer 122, the material of which is silicon. Based on the total mass of the second active material layer 122, the mass percentage of silicon is W%, 3≤W≤40%. W≥3 is beneficial for improving the energy density of the secondary battery 100; W≤40 is beneficial for reducing the risk of excessive cycle expansion due to excessive expansion of the negative electrode or the appearance of annular wrinkles at the tail of the positive electrode.

[0107] Optionally, the value of W can be any one or any combination of two of the following: 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40.

[0108] In some embodiments, 15 ≤ W ≤ 30. W ≥ 15 is beneficial to further improve the energy density of the secondary battery 100; W ≤ 30 is beneficial to further reduce the risk of excessive cycle expansion rate or annular wrinkles at the tail of the positive electrode due to excessive expansion of the negative electrode.

[0109] Please see Figure 1 In some embodiments, the secondary battery 100 includes a housing 40, and the electrode assembly 10 is disposed within the housing 40. Optionally, the secondary battery 100 is a pouch battery, and the housing 40 includes an aluminum-plastic film. Optionally, the secondary battery 100 is a hard-shell battery, and the housing 40 includes a steel shell.

[0110] In some embodiments, the housing houses the electrode assembly 10 and an electrolyte, which includes at least one of propylene carbonate, ethylene carbonate, or diethyl carbonate. The electrolyte, comprising these components, can improve lithium-ion transport efficiency, increase the effective capacity of the secondary battery 100, and reduce energy density loss caused by the grooving of the first electrode 11.

[0111] Please see Figure 9This application also provides an electronic device 200 employing the aforementioned secondary battery 100. In one embodiment, the electronic device 200 of this application may be, but is not limited to, electronic devices, drones, backup power supplies, electric vehicles, electric motorcycles, electric-assisted bicycles, power tools, large household battery modules, etc.

[0112] The present application will be described in detail below through specific embodiments and comparative examples. Specifically, a wound lithium-ion secondary battery, a first electrode as a positive electrode, and a second electrode as a negative electrode are used as examples to illustrate the present application, along with specific preparation processes and testing methods. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0113] Example 1 Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride (PVDF) are dissolved in an N-methylpyrrolidone (NMP) solution at a weight ratio of 97.5:1:1.5 to form a positive electrode slurry. Aluminum foil is used as the positive electrode current collector. The positive electrode slurry is coated onto the current collector, and after drying, cold pressing, and slitting, a first groove is etched in the first part of the positive electrode sheet to obtain the positive electrode roll.

[0114] Preparation of negative electrode sheet: The negative electrode active material artificial graphite, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 96:1.5:2.5, deionized water is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; dried, and then cold-pressed, cut, and slit to obtain a negative electrode roll.

[0115] Preparation of the isolation membrane: A polyethylene (PE) membrane with a thickness of 5 μm was selected.

[0116] Electrolyte preparation: In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of 4:2:4. Lithium salt LiPF6 was added and mixed evenly to obtain the electrolyte, wherein the mass percentage concentration of LiPF6 was 12.5%.

[0117] Electrode assembly fabrication: The positive electrode roll, separator, and negative electrode roll are wound together to obtain a bare cell, wherein the first part is located on the outermost side of the straight section of the electrode assembly.

[0118] Assembly: Place the perforated aluminum-plastic film in the assembly fixture with the perforated surface facing upwards, place the electrode assembly in the perforation, and apply external force to press it firmly. Then, cover the electrode assembly with another perforated aluminum-plastic film with the perforated surface facing downwards, and heat-seal the two aluminum-plastic films around their perimeter using a hot-pressing method to obtain the assembled electrode assembly.

[0119] Electrolyte injection encapsulation: Electrolyte is injected into the assembled electrode assembly, and after vacuum encapsulation, standing, hot pressing formation, shaping and other processes, a secondary battery is obtained.

[0120] Comparative Example 1 The difference from Example 1 is that the positive electrode does not have a first groove. It should be noted that, apart from the differences mentioned above, all other parameters of Comparative Example 1 are the same as those of Example 1.

[0121] Examples 2-47 should be noted that, apart from the differences mentioned above, all other parameters in Examples 2-46 are the same as those in Example 1.

[0122] The differences from Example 1 are as follows: the values ​​of W1, H2 / H1, H1, W2 / W1, D1, D2, α, L1, the number of grooves at the intersection of the first and second sub-grooves, and the electrolyte composition are specifically recorded in Table 1. In each embodiment, the angle between the extension direction of the first sub-groove and the length direction of the first electrode is the same as the angle between the extension direction of the second sub-groove and the length direction of the first electrode; the minimum distance L1 between the first sub-groove and the third edge, the minimum distance L1 between the second sub-groove and the third edge, the minimum distance L2 between the first sub-groove and the fourth edge, and the minimum distance L2 between the second sub-groove and the fourth edge are all equal.

[0123] Then, 20 secondary batteries from each embodiment were selected for cycle capacity retention testing, annular wrinkling testing, thickness expansion rate testing, and volumetric energy density testing. W1, H2 / H1, W2 / W1, D1, and D2 were measured using a CCD microscope.

[0124] Cyclic capacity retention test method: The lithium-ion battery was placed in a 45℃ environment and left to stand for 5 minutes. Then, it was charged and discharged according to the following steps: discharged at a constant current of 0.5C to 3V, left to stand for 5 minutes, then charged at a constant current of 1.1C to 4.25V, then charged at a constant current of 0.7C to 4.51V, then charged at a constant voltage to 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.5C to 3V. This constitutes one cycle. The initial discharge capacity C0 of the lithium-ion battery was recorded. This cycle was repeated 500 times, and the discharge capacity C1 after 500 cycles was measured. During the cycle test, the lithium-ion battery was observed for any signs of smoke, fire, or explosion. Capacity retention rate = C1 / C0 × 100%. The average capacity retention rate of the 20 samples was taken.

[0125] Circular wrinkle test method: The secondary battery was disassembled and measured using a CCD. When the annular area accounted for more than 50% of the area of ​​the first part, it was determined to be a severe annular wrinkle; when the annular area accounted for between 10% and 50% of the area of ​​the first part, it was determined to be a moderate annular wrinkle; when the annular area accounted for less than 10% of the area of ​​the first part, it was determined to be a slight annular wrinkle; and when the annular area accounted for 0% of the area of ​​the first part, it was determined to be an un-annular wrinkle.

[0126] Test methods for manufacturing yield of secondary batteries: Breakdown refers to the breakdown of the first current collector during laser etching of the first groove. Each comparative and example group tested 20 secondary batteries. After fabricating the first groove, the state of the first current collector was observed for defects such as holes or tears. The number of secondary batteries without holes or tears in the first current collector was recorded as X1, and the manufacturing yield was recorded as X1 / 20.

[0127] Thickness expansion rate test method: Place the lithium-ion battery in a 45°C environment and let it stand for 5 minutes. Then, perform a charge-discharge cycle as follows: discharge at a constant current of 0.5C to 3V, let it stand for 5 minutes, then charge at a constant current of 1.1C to 4.25V, then charge at a constant current of 0.7C to 4.51V, then charge at a constant voltage to 0.05C, let it stand for 5 minutes, and then discharge at a constant current of 0.5C to 3V. This completes one cycle. Repeat this cycle 500 times. Record the initial thickness H0 of the lithium-ion battery. After 500 cycles, measure the thickness H3 of the secondary battery. The expansion rate is calculated as (H3 - H0) / H0 × 100%.

[0128] Volumetric energy density testing method: Under ambient conditions of 25°C, the secondary battery was allowed to stand for 10 minutes, then charged at a constant current of 0.2C to the charging limit voltage, and then charged at a constant voltage to 0.02C, and allowed to stand for 5 minutes. Next, it was discharged at a constant current of 0.2C to the discharge cutoff voltage, and allowed to stand for 5 minutes. The discharge capacity C0 was recorded. The volumetric energy density was calculated using the following formula: Volumetric energy density = Plateau voltage × C0 / Volume of secondary battery. The relative volumetric energy density was converted based on Example 1.

[0129] Table 1 In Table 1, "\" indicates that this data is not available.

[0130] As can be seen from Comparative Example 1 and Examples 1-47, dividing the first active material layer of the first part into multiple sub-regions can disperse the force exerted by the negative electrode sheet on the positive electrode sheet, reduce the strong stress concentration formed at the edge of the first part in the first direction, improve the uneven adhesion between the first part and the separator, thereby improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate.

[0131] As can be seen from Examples 1 and 2, the number of grooves at the intersection of the first sub-groove and the second sub-groove is 0, meaning that the first groove does not intersect with any other first groove. Figure 2 and Figure 3 The illustrated embodiment. By intersecting the first and second sub-grooves, the first active material layer of the first part is divided into more sub-regions, which further helps to reduce the stress concentration in the first part in the first direction, improves the expansion rate of the secondary battery, and enhances the cycle capacity retention rate.

[0132] As can be seen from Examples 2-8, the width of the first sub-groove is W1, where 5μm ≤ W1 ≤ 100μm. Ensuring the width of the first sub-groove reduces stress concentration in the first part in the first direction, which is beneficial for improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate. Controlling the width of the first sub-groove reduces the amount of the first active material layer removed, thus reducing its impact on the energy density of the secondary battery. When W1 < 5μm, the width of the first sub-groove is too small, the wrinkling degree of the first part increases, the cycle capacity retention rate of the secondary battery decreases, and the expansion rate increases. When W1 > 100μm, the width of the first sub-groove is too large, the amount of the first active material layer removed increases, and the energy density of the secondary battery decreases.

[0133] From Examples 9-14, it can be seen that along the thickness direction of the first active material layer, the thickness of the first active material layer in the first part is H1, and the depth of the first sub-groove is H2, with 10% ≤ H2 / H1 ≤ 80%. Ensuring the depth of the first sub-groove helps reduce stress concentration in the first part in the first direction, improves the expansion rate of the secondary battery, and enhances the cycle capacity retention rate. By controlling the depth of the first sub-groove, the amount of the removed first active material layer is reduced, decreasing the impact on the energy density of the secondary battery and reducing the risk of the first current collector being broken down. As the depth of the first sub-groove increases, it affects the energy density of the secondary battery. When H2 / H1 < 1%, the depth of the first sub-groove is too small, the wrinkling degree of the first part increases, the cycle capacity retention rate of the secondary battery decreases, and the expansion rate increases. When H2 / H1 > 80%, the depth of the first sub-groove is too large, and the positive electrode current collector is broken down.

[0134] As can be seen from Examples 1, 32 and 33, when 25μm≤H1≤65μm, the energy density of the secondary battery can be guaranteed not to be too low, while the cycle capacity retention rate is maintained within a certain range.

[0135] As can be seen from Examples 15-22, on the surface of the first active material layer in the first part, the minimum distance between adjacent first sub-grooves is D1, where 1mm ≤ D1 ≤ 10mm. With the area of ​​the first part remaining constant, reducing the number of first sub-grooves helps to reduce the amount of first active material layer removed, thus reducing the impact on the energy density of the secondary battery. Maintaining the number of first sub-grooves helps to reduce stress concentration in the first direction, thus improving the expansion rate of the secondary battery and increasing the cycle capacity retention rate. When D1 < 1mm, the minimum distance between adjacent first sub-grooves is too small. With the area of ​​the first part remaining constant, increasing the number of first sub-grooves increases the amount of first active material layer removed, reducing the energy density of the secondary battery. When D1 > 10mm, the minimum distance between adjacent first sub-grooves is too large. With the area of ​​the first part remaining constant, fewer first sub-grooves result in a smaller cycle capacity retention rate and a larger expansion rate of the secondary battery.

[0136] On the surface of the first active material layer in the first part, the minimum distance between adjacent second sub-grooves is D2, where 1mm ≤ D2 ≤ 10mm. With the area of ​​the first part remaining constant, reducing the number of second sub-grooves helps to reduce the amount of first active material layer removed, thus reducing the impact on the energy density of the secondary battery. Maintaining a sufficient number of second sub-grooves helps to reduce stress concentration in the first direction, thus improving the expansion rate of the secondary battery and increasing cycle capacity retention. When D2 < 1mm, the minimum distance between adjacent second sub-grooves is too small. With the area of ​​the first part remaining constant, increasing the number of second sub-grooves increases the amount of first active material layer removed, reducing the energy density of the secondary battery. When D2 > 10mm, the minimum distance between adjacent second sub-grooves is too large. With the area of ​​the first part remaining constant, fewer second sub-grooves result in a smaller cycle capacity retention and a larger expansion rate.

[0137] As can be seen from Examples 23-26, the ratio S of the area of ​​the first groove in the second part to the area of ​​the first groove in the first part is 0.3 ≤ S ≤ 1. Maintaining the area of ​​the first groove in the second part improves the degree of annular wrinkling in the second part, thereby improving the expansion rate of the secondary battery 100 and increasing the cycle capacity retention rate. When S < 0.3, the area of ​​the first groove in the second part decreases, which is detrimental to improving the degree of annular wrinkling in the second part.

[0138] As can be seen from Examples 27-30, along the thickness direction of the first active material layer, the width W2 at the middle depth position of the first sub-groove, where 1 / 3 ≤ W2 / W1 ≤ 2 / 3, is beneficial for reducing stress concentration in the first part in the first direction, improving the expansion rate of the secondary battery, and increasing the cycle capacity retention rate. Controlling the width at the middle depth position of the first sub-groove is beneficial for reducing the amount of the first active material layer removed, thus reducing the impact on the energy density of the secondary battery. When W2 / W1 > 2 / 3, the amount of the first active material layer removed increases, reducing the energy density of the secondary battery.

[0139] As can be seen from Examples 12 and 31, when the ratio of H2 / H1 is large and the number of grooves at the intersection of the first sub-groove and the second sub-groove is greater than 2, the positive current collector is easily broken down by the laser, and the manufacturing yield of the secondary battery is reduced.

[0140] As can be seen from Examples 2 and 32, when the electrolyte contains at least one of EC, PC or DEC, it is beneficial to improve the energy density.

[0141] As can be seen from Examples 2, 35 to 41, when 30°≤α≤75°, a high cycle capacity retention rate, a low expansion rate, and a high energy density can be achieved. When α<30°, the improvement in cycle capacity retention rate and expansion rate compared to when α≥30° is not significant, but it will affect manufacturing efficiency. Therefore, 30°≤α≤75° is selected. Further, 40°≤α≤60° is preferred.

[0142] As can be seen from Examples 2, 42 to 47, when 0.5mm≤L1≤5mm and 0.5mm≤L2≤5mm, a high cycle capacity retention rate, a low expansion rate, a high energy density, and a high manufacturing yield can be achieved. Further, it is preferable that 1mm≤L1≤3mm and / or 1mm≤L2≤3mm.

[0143] Examples 48 to 53 are the same as those in Example 1, except for the parameters listed in Table 2.

[0144] Table 2 As shown in Examples 1 and 48 of Table 2, when A2=0, A2 / A1=0, resulting in a higher cycle capacity retention rate and a lower expansion rate. This is because the closer the first part is to the end edge, the better its effect on improving the expansion of the first electrode's end, leading to a corresponding decrease in expansion rate and an increase in cycle capacity retention rate. As shown in Examples 1, 49, and 50, when the ratio of A2 / A1 remains unchanged, the larger A2 is, the lower the cycle capacity retention rate and the larger the expansion rate. This is because when A2 is larger and A2 / A1 remains unchanged, A1 is also larger, meaning the length of the first electrode in the entire electrode assembly is longer, and the length of the corresponding second electrode is also longer. The expansion of the second electrode is more severe, resulting in a greater expansion rate of the secondary battery. At the same time, the stress concentration at the end of the first electrode caused by the expansion of the second electrode is more severe, leading to a decrease in cycle capacity retention rate. As can be seen from Examples 1 and 51 to 53, when the value of A2 remains constant, the larger the ratio of A2 to A1, the smaller the expansion rate and the higher the cycle capacity retention rate. This is because when A2 remains constant, the larger the ratio of A2 to A1, the smaller A1 becomes, resulting in a shorter length of the first electrode and a shorter length of the second electrode. The stress concentration at the end of the first electrode caused by the expansion of the second electrode is reduced, thus lowering the expansion rate and improving the cycle capacity retention rate. However, when A2 / A1 > 0.5, the energy density of the secondary battery is relatively low. In summary, by setting 0 ≤ A2 / A1 ≤ 0.5 and 0 mm ≤ A2 ≤ 100 mm, a higher cycle capacity retention rate, a lower expansion rate, and a higher energy density can be achieved. Those skilled in the art should recognize that the above embodiments are merely illustrative of this application and not intended to limit it. Any appropriate changes and variations made to the above embodiments within the scope of the essential spirit of this application fall within the scope of this application.

Claims

1. A secondary battery, comprising an electrode assembly, the electrode assembly including a first electrode, a second electrode, and a separator, wherein the first electrode, the separator, and the second electrode are sequentially stacked; wherein, The first electrode includes a first current collector and a first active material layer disposed on at least a portion of the first current collector; the first current collector includes a first surface and a second surface disposed opposite to each other along the thickness direction of the first current collector, the second surface being away from the center of the electrode assembly in a first direction, the first direction being the thickness direction of the electrode assembly; Along the first direction, the first electrode includes a first portion, and the first surface of the first current collector located in the first portion is provided with the first active material layer; The first part includes a first portion, which is the outermost electrode of the electrode assembly in the first direction; The first active material layer located in the first part is provided with a first groove.

2. The secondary battery as described in claim 1, wherein, The first groove includes a plurality of spaced-apart first sub-grooves and a plurality of spaced-apart second sub-grooves, wherein at least one first sub-groove and at least one second sub-groove are intersected.

3. The secondary battery as described in claim 2, wherein, Along the direction perpendicular to the extension of the first sub-groove, the width of the first sub-groove on the surface of the first active material layer is W1, where 5μm≤W1≤100μm.

4. The secondary battery as described in claim 3, wherein, 10μm≤W1≤60μm.

5. The secondary battery as described in claim 2, wherein, Along the thickness direction of the first active material layer, the thickness of the first active material layer located in the first part is H1, the depth of the first sub-groove is H2, 10%≤H2 / H1≤80%, 25μm≤H1≤65μm.

6. The secondary battery as described in claim 5, wherein, 20%≤H2 / H1≤60%.

7. The secondary battery as described in claim 3, wherein, Along the thickness direction of the first active material layer, the width of the first sub-groove gradually decreases from the surface of the first active material layer toward the first current collector.

8. The secondary battery as described in claim 7, wherein, Along the thickness direction of the first active material layer, the width at the middle depth position of the first sub-groove is W2, 1 / 3≤W2 / W1≤2 / 3.

9. The secondary battery as described in claim 2, wherein, The same position of the first sub-groove intersects with a second sub-groove.

10. The secondary battery as described in claim 2, wherein, On the surface of the first active material layer in the first part, the minimum distance between adjacent first sub-grooves is D1, 1mm≤D1≤10mm; and / or, the minimum distance between adjacent second sub-grooves is D2, 1mm≤D2≤10mm.

11. The secondary battery as claimed in claim 1, wherein, The first electrode, the separator, and the second electrode are stacked sequentially and arranged in a wound structure.

12. The secondary battery as claimed in claim 11, wherein, The second surface of the first current collector located in the first part is not provided with an active material layer.

13. The secondary battery as described in claim 12, wherein, The first electrode also includes a second part, and the first part and the second part are arranged sequentially. Neither the first surface nor the second surface of the first current collector located in the second part is provided with an active material layer. Along the winding direction of the electrode assembly, the first part is connected to the second part, and the second part includes the winding tail end of the first electrode sheet.

14. The secondary battery as claimed in claim 11, wherein, With the first electrode sheet in its unfolded state, along the length direction of the first electrode sheet, the first electrode sheet includes a starting edge located at the starting end of the winding of the electrode assembly and a finishing edge located at the ending end of the winding of the electrode assembly; the first part includes a fifth edge and a sixth edge in the length direction of the first electrode sheet; along the length direction of the first electrode sheet, the starting edge, the fifth edge, the sixth edge and the finishing edge are arranged sequentially; Along the length direction of the first electrode, the distance between the starting edge and the fifth edge is A1, and the distance between the sixth edge and the ending edge is A2, 0≤A2 / A1≤0.5, 0mm≤A2≤100mm.

15. The secondary battery as claimed in claim 1, wherein, The first electrode is a positive electrode.

16. The secondary battery as claimed in claim 15, wherein, The second electrode is a negative electrode. The second electrode includes a second active material layer. The material of the second active material layer includes silicon. Based on the total mass of the second active material layer, the mass percentage of silicon element is W%, 3≤W≤40.

17. The secondary battery as claimed in claim 16, wherein, 15≤W≤30。 18. The secondary battery as described in claim 2, wherein, Along the length of the first electrode, the first sub-groove and / or the second sub-groove are inclined; the angle between the extension direction of the first sub-groove and / or the extension direction of the second sub-groove and the length direction of the first electrode is α, 30°≤α≤75°.

19. The secondary battery as claimed in claim 18, wherein, 40°≤α≤60°。 20. The secondary battery as described in claim 2, wherein, Along the width direction of the first electrode, the first electrode includes a third edge and a fourth edge disposed opposite to each other, the minimum distance between the first sub-groove and / or the second sub-groove and the third edge is L1, the minimum distance between the first sub-groove and / or the second sub-groove and the fourth edge is L2, 0.5mm≤L1≤5mm, and / or 0.5mm≤L2≤5mm.

21. The secondary battery as claimed in claim 20, wherein, 1mm≤L1≤3mm, and / or, 1mm≤L2≤3mm.

22. The secondary battery as claimed in claim 1, wherein, The first part includes a second part, which is the outermost electrode of the electrode assembly in the first direction. The first part and the second part are disposed opposite to each other along the first direction. The first active material layer located in the second part is provided with the first groove.

23. The secondary battery as claimed in claim 22, wherein, The ratio S of the area of ​​the first groove located in the second part to the area of ​​the first groove located in the first part is 0.3≤S≤1.

24. The secondary battery as claimed in claim 1, wherein, The secondary battery also includes a housing containing the electrode assembly and an electrolyte, wherein the electrolyte includes at least one of propylene carbonate, ethylene carbonate, or diethyl carbonate.

25. An electronic device, wherein, The electronic device includes a secondary battery as claimed in any one of claims 1 to 24.

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