Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment, a first negative electrode material layer is provided with a first groove, and a part of a negative electrode tab is electrically connected with a negative electrode current collector in the first groove. A second groove is formed in the surface, facing the first groove, of the first positive electrode material layer, and a thinning area is formed in the part, located between the positive electrode current collector and the second groove, of the first positive electrode material layer. The thinning area comprises a first section and a second section, and the second section and the first section are sequentially arranged in the second direction. In the first direction, the average thickness of the first section is T1 [mu] m, and the average thickness of the second section is T2 [mu] m, T1lt; t2. The first insulating layer is arranged in the second groove; in the first direction, within the projection range of the first positive electrode section, the orthogonal projection of the first groove is located within the orthogonal projection range of the first insulating layer. The risk of lithium precipitation of the second negative electrode material layer can be reduced, and the risk of lithium precipitation near the first groove can be reduced.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a secondary battery and an electronic device. Background Art

[0002] Lithium-ion secondary batteries are widely used in products such as mobile phones, laptop computers, and electric vehicles due to their advantages of high energy density and low pollution. With the rapid development of industries such as consumer electronics and new energy vehicles, the market's requirements for the cycling performance of lithium-ion secondary batteries are increasing day by day. However, the problem of lithium deposition on the negative electrode tab restricts the cycling performance of lithium-ion secondary batteries. Summary of the Invention

[0003] This application aims to provide a secondary battery and an electronic device to reduce the risk of lithium deposition in the secondary battery.

[0004] In a first aspect, this application provides a secondary battery, which includes a negative electrode tab and a positive electrode tab, an isolation film, and a negative electrode tab that are stacked and wound. The positive electrode tab includes a first positive electrode segment, and the negative electrode tab includes a first negative electrode segment and a second negative electrode segment. The first negative electrode segment and the second negative electrode segment are respectively located on both sides of the first positive electrode segment in the thickness direction. The positive electrode tab includes a positive electrode current collector and a first positive electrode material layer provided on the surface of the positive electrode current collector. The negative electrode tab includes a negative electrode current collector and a first negative electrode material layer, and the first negative electrode material layer is provided on the surface of the negative electrode current collector facing the first positive electrode material layer. In the first negative electrode segment, the first negative electrode material layer is provided with a first groove, and the first groove exposes the negative electrode current collector. A part of the negative electrode tab is electrically connected to the negative electrode current collector in the first groove, and another part of the negative electrode tab extends out of the negative electrode tab. In the first positive electrode segment, the surface of the first positive electrode material layer facing the first groove is provided with a second groove. The first positive electrode material layer includes a thinning region. Along a first direction, the part of the first positive electrode material layer located between the positive electrode current collector and the second groove forms the thinning region. The first direction is the thickness direction of the first positive electrode segment at the second groove. The thinning region includes a first section and a second section, and along a second direction, the second section and the first section are arranged in sequence. Along the first direction, the average thickness of the first section is T1 μm, and the average thickness of the second section is T2 μm, where T1 < T2; the second direction is the direction in which the negative electrode tab extends out of the negative electrode tab. The secondary battery further includes a first insulating layer, and the first insulating layer is provided in the second groove; along the first direction, within the projection range of the first positive electrode segment, the orthogonal projection of the first groove is located within the orthogonal projection range of the first insulating layer.

[0005] In the above technical solution, the thinning region adopts a thickness gradient design. A larger thickness T2 is set in the second section far from the first edge, which helps retain sufficient positive electrode material and effectively improves the energy density of the secondary battery. Simultaneously, a smaller thickness T1 is used in the first section near the first edge, reducing the amount of lithium ions extracted near the first edge and mitigating the phenomenon of lithium ions migrating across the positive electrode current collector to the second negative electrode material layer and accumulating at its edge, thereby reducing the risk of lithium plating in the second negative electrode material layer. Simultaneously, within the projection range of the first positive electrode section, the orthogonal projection of the first groove falls within the orthogonal projection range of the first insulating layer, which can reduce the amount of lithium ions extracted from the first positive electrode material layer to the first groove region, thereby reducing the risk of lithium plating near the first groove. Furthermore, placing the first insulating layer within the second groove reduces the space occupied by the first insulating layer in the thickness of the first positive electrode section, further improving the energy density of the secondary battery.

[0006] In some embodiments, the thickness of the thinned region gradually decreases to form a sloping structure. The sloping structure is more conducive to matching the smooth change in lithium-ion extraction from far to near the first edge, enabling continuous adjustment of lithium-ion extraction, reducing local fluctuations in lithium-ion extraction caused by abrupt thickness changes, and thus more efficiently mitigating the migration and enrichment of lithium ions into the second anode material layer, further reducing the risk of lithium plating at the edge of the second anode material layer. Furthermore, the sloping structure adheres more tightly to the first insulating layer, reducing interface gaps and further reducing the risk of the first insulating layer detaching due to uneven stress, swelling, or cyclic expansion of the electrode, thereby improving structural stability.

[0007] In some embodiments, along a second direction, the first positive electrode material layer includes a first edge, and a thinning region extends to the first edge; at the first edge, the thickness of the thinning region is T. a μm, 0.5≤T a ≤5. By using T a Controlling the value within the range of 0.5 to 5 allows for the retention of an appropriate amount of positive electrode material in the first edge region. This reduces the risk of pulverization and detachment in this region, maintains the structural stability of the thinned area, and keeps the amount of lithium removed from this region at a reasonably low level, mitigating the migration of lithium ions to the second negative electrode material layer and reducing the risk of lithium plating at the edge of the second negative electrode material layer. Furthermore, it ensures stable coverage of the positive electrode current collector by the thinned region, reduces the exposure of the positive electrode current collector, and improves the safety performance of the secondary battery. Further, 1≤T a A value of ≤4 can achieve a better balance between reducing edge pulverization and shedding in the thinned area, maintaining safety performance, and reducing the risk of lithium plating in the second anode material, thereby further improving the overall performance of the secondary battery.

[0008] In some embodiments, the secondary battery further includes a second insulating layer, which is at least partially disposed on the first negative electrode material layer. Along a first direction, the second insulating layer covers the first groove. Along a second direction, at the end away from the first edge, the first insulating layer extends beyond the second insulating layer by a length W. a mm, 2≤W a ≤5. By using W a By controlling the value within the range of 2 to 5, on the one hand, the migration of lithium ions from the first positive electrode segment to the negative electrode tab region can be reduced, thereby reducing the risk of lithium plating in the first negative electrode segment; on the other hand, the waste of positive electrode material and space occupation caused by excessive extension of the first insulating layer can be reduced, thereby improving the energy density of the secondary battery while improving insulation reliability.

[0009] In some embodiments, along the opposite direction of the third direction, on one side of the first insulating layer, the length of the first insulating layer extending beyond the second insulating layer is L1 mm, where 2 ≤ L1 ≤ 5. By controlling L1 within the range of 2 to 5, on the one hand, it is beneficial for the first insulating layer to fully cover the second insulating layer in the third direction, forming continuous insulation protection in the lateral connection area between the first positive electrode segment and the negative electrode tab, further reducing the risk of short circuit due to misalignment during winding; on the other hand, it can reduce the waste of positive electrode material and space occupation caused by excessive extension of the first insulating layer, thereby improving insulation reliability and increasing the energy density of the secondary battery. Based on the same inventive concept, along the third direction, on the other side of the first insulating layer, the length of the first insulating layer extending beyond the second insulating layer is L2 mm, where 2 ≤ L2 ≤ 5.

[0010] In some embodiments, along the second direction, the second groove includes a second edge disposed opposite to the first edge; along the second direction, the distance between the first insulating layer and the second edge is W1 mm, where 0.5 ≤ W1 ≤ 1. By controlling W1 within the range of 0.5 to 1, on the one hand, a reasonable gap can be reserved between the second groove and the first insulating layer in the second direction to accommodate the precision deviation of the adhesive bonding process, reduce the high point of the first insulating layer attached to the edge of the second groove, and thus improve the adhesion stability of the first insulating layer; on the other hand, this gap reduces the amount of lithium stripping by partially removing the positive electrode material, thereby reducing the lithium plating phenomenon at the negative electrode tab; at the same time, the retained portion of the positive electrode material can also take into account the energy density of the secondary battery, achieving a triple optimization of adhesive bonding reliability, lithium plating protection, and energy density gain.

[0011] In some embodiments, along a third direction, the second groove includes a third edge and a fourth edge disposed opposite to each other. Along this third direction, the distance between the first insulating layer and the third edge is L3 mm, where 0.5 ≤ L3 ≤ 1.5. By controlling L3 within the range of 0.5 to 1, on the one hand, a reasonable gap can be reserved between the second groove and the first insulating layer in the third direction to accommodate the precision deviation of the adhesive bonding process, further reducing the high point of the first insulating layer adhering to the third edge, thereby improving the adhesion strength and stability of the first insulating layer; on the other hand, this gap reduces the amount of lithium stripping by partially removing the positive electrode material, reducing lithium plating at the negative electrode tab; simultaneously, the retained portion of the positive electrode material can also maintain the energy density of the secondary battery, further achieving a triple optimization of adhesive bonding reliability, lithium plating protection, and energy density gain. Based on the same inventive concept, along a third direction, the distance between the first insulating layer and the fourth edge is L4 mm, where 0.5 ≤ L4 ≤ 1.5.

[0012] In some embodiments, the first insulating layer further includes a first extension extending from the first edge of the positive electrode sheet, the first extension extending from the first edge by a length L. a mm, 0.5≤L a ≤1.5. By using L a By controlling the length within the range of 0.5 to 1.5, on the one hand, the first extension can block the amount of lithium stripping at the first edge, reducing the lithium plating phenomenon in the second negative electrode section caused by lithium ions migrating across the positive electrode current collector; on the other hand, this length range can reduce the first extension from entering the top sealing area and interfering with the packaging process, ensuring the reliability of the shell packaging, and achieving dual optimization of lithium plating prevention and control at the edge of the second negative electrode section and shell packaging reliability.

[0013] In some embodiments, the thickness of the first positive electrode material layer is H μm along the first direction. At one end in the opposite direction of the second direction, the first insulating layer includes a fifth edge, and along the first direction, the thinning region includes a first position that overlaps with the orthogonal projection of the fifth edge. Along the first direction, the thinning region includes a first region covered by the first insulating layer, and the first position is located at the maximum thickness of the first region; the thickness of the thinning region at the first position is H1 μm, and 0.25 ≤ H1 / H ≤ 0.75. By controlling the ratio of H1 / H within the range of 0.25 to 0.75, on the one hand, the thickness of the first insulating layer can be adapted to fully accommodate the first insulating layer, while reducing the highest point of the first insulating layer after bonding from exceeding the surface of the first positive electrode material layer, effectively reducing the overall excessive thickness of the first positive electrode segment, thereby improving the energy density of the secondary battery; on the other hand, the portion of the positive electrode material layer not covered by the first insulating layer in the thinning region can be fully utilized, further improving the energy density of the secondary battery.

[0014] In some embodiments, the first positive electrode material layer includes a first surface facing the first negative electrode material layer, and the first insulating layer does not protrude from the first surface, which can reduce the additional space occupied by the first insulating layer in the secondary battery and help improve the energy density of the secondary battery; at the same time, it can reduce the risk of wrinkles or warping of the electrode due to the protrusion of the first insulating layer during the electrode winding process, thereby enhancing the structural stability of the secondary battery.

[0015] In some embodiments, the surface roughness of the thinned region is R μm, where 2 ≤ R ≤ 15. By controlling R within the range of 2 to 15, on the one hand, a moderate surface roughness can be used to create a mechanical anchoring effect between the thinned region and the first insulating layer, thereby improving the adhesion strength between them and reducing the risk of the first insulating layer slipping, lifting, or falling off; on the other hand, it can reduce the penetration of electrolyte into the rough surface, thereby inhibiting the swelling of the first insulating layer, the dissolution of cobalt ions, and the formation of hard by-products, and enhancing the interfacial stability of the first positive electrode material layer.

[0016] In some embodiments, the first negative electrode material layer includes a first portion; along the second direction, the first negative electrode material layer includes a sixth edge, and the portion of the first negative electrode material layer located between the sixth edge and the first groove forms the first portion. Along the first direction, the negative electrode tab covers at least part of the first portion, which can enhance the structural strength of the negative electrode edge, effectively reduce the risk of the negative electrode tearing due to the negative electrode tab pulling, and at the same time facilitate compatibility with the precision errors of the slitting process, simplifying the control difficulty of the cutting process.

[0017] In some embodiments, the secondary battery further includes a positive electrode tab and a third insulating layer. A first positive electrode material layer has a third groove, which exposes the positive current collector. A portion of the positive electrode tab is electrically connected to the positive current collector within the third groove, and another portion of the positive electrode tab extends beyond the positive electrode sheet. The third insulating layer is disposed on the first positive electrode material layer, covering the third groove along a first direction. The first positive electrode material layer also includes a first covering area covered by the third insulating layer, with the thickness of the first covering area decreasing sequentially along a second direction. By designing the thickness of the first covering area as a gradient decreasing structure along the second direction, the lithium-ion insertion / extraction rate within the first covering area decreases synchronously with the thickness reduction, effectively reducing the migration of lithium ions to the second negative electrode segment, thereby reducing the risk of lithium plating caused by lithium-ion accumulation in the second negative electrode segment.

[0018] In some embodiments, the secondary battery further includes a first adhesive layer disposed between the negative electrode tab and the negative electrode current collector. The first negative electrode segment further includes a second negative electrode material layer disposed on the surface of the negative electrode current collector facing away from the first negative electrode material layer. The second negative electrode material layer includes a second portion; along a first direction, the orthogonal projection of the second portion overlaps with the orthogonal projection of the first groove. The retention of the second portion increases the thickness of the negative electrode sheet in the negative electrode tab bonding area, which precisely matches the thinning area within the second groove on the positive electrode side. Simultaneously, the thickness T of the thinning area near the first edge... a The thickness is controlled within the range of 0.5μm to 5μm (preferably 1μm to 4μm), which matches the size of the negative electrode sheet in the negative electrode tab bonding area. This provides a suitable accommodating space for the thickened part of the negative electrode sheet, effectively filling the thickness allowance of the first positive electrode section (second groove). This is beneficial to achieve the complementary thickness and size matching of the positive and negative electrode sheets in the negative electrode tab connection area, making the thickness of the overall stacked / wound structure of the positive and negative electrode sheets more uniform and reducing the problem of increased interface gap caused by inconsistent thickness of the positive and negative electrode sheets.

[0019] In some embodiments, the secondary battery further includes an electrolyte comprising a first component selected from at least one of 2,2-difluoroethyl acetate, ethyl difluoroacetate, and fluoroacetic acid-2-fluoroethyl ester. Based on the total mass of the electrolyte, the mass percentage of the first component is A%, 10 ≤ A ≤ 60. By controlling A within the range of 10 to 60, on the one hand, the first component has a sufficient content, which preferentially forms a continuous and dense protective layer on the surface of the broken positive electrode material particles, effectively suppressing side reactions in the slotted region, reducing electrolyte consumption, and improving the cycle stability of the secondary battery; on the other hand, it can reduce the accumulation of fluorinated products at the bonding interface between the first insulating layer and the thinned region, thereby maintaining good bonding strength between them, reducing the generation of interfacial gaps, and thus reducing the phenomenon of lithium ions escaping from the gaps, which is beneficial to reducing the risk of lithium plating at the negative electrode tab.

[0020] In some embodiments, the electrolyte further includes a second component selected from at least one of ethylene carbonate and propylene carbonate. Based on the total mass of the electrolyte, the mass percentage of the first component is B%, and 0.5 ≤ A / B ≤ 5. By controlling A / B within the range of 0.5 to 5, on the one hand, sufficient first component can react on the surface of the broken positive electrode particles in the slotted region, forming a continuous and dense protective layer, thereby enhancing the suppression of side reactions in the slotted region; on the other hand, it helps the second component to fully participate in the solvation structure of lithium ions, achieving regulation of the distribution of the first component, reducing excessive reaction of the first component, and regulating the content of fluorinated byproducts between the first insulating layer and the thinned region; simultaneously, it helps maintain a suitable viscosity of the electrolyte to improve its fluidity, ensuring lithium ion transport efficiency, and thus achieving synergistic enhancement of side reaction suppression, adhesion performance, and kinetic performance.

[0021] In some embodiments, the electrolyte further includes a third component selected from at least one of the following compounds;

[0022] .

[0023] Based on the total mass of the electrolyte, the mass percentage of the third component is C%, 0.5 ≤ C ≤ 5. By controlling C within the range of 0.5 to 5, on the one hand, the third component has a sufficient content to fully utilize its preferential film-forming characteristics, so as to form a uniform and dense CEI film in the thinned region, reducing the problems of excessive film thickness and increased impedance caused by electrolyte enrichment, thereby improving the lithium-ion insertion / extraction efficiency; on the other hand, it is beneficial to effectively suppress the dissolution of transition metals caused by the exposure of the active surface due to the sag treatment through the coordination of sulfonyl functional groups with transition metals, reduce the occurrence of side reactions, and further improve the cycle stability of the secondary battery.

[0024] In some embodiments, the charging cutoff voltage of the secondary battery is GV, where 4.55 ≤ G ≤ 4.65. By controlling G within the range of 4.55 to 4.65 V, on the one hand, it helps to fully utilize the advantages of high voltage, enabling the positive electrode material layer to achieve a greater amount of lithium removal at a higher potential, thereby improving the energy density of the secondary battery; on the other hand, with the structural design of the first insulating layer, the second groove, and the thinning region of this application, the problem of excessive lithium ion removal from the positive electrode and migration to the negative electrode under high voltage can be effectively alleviated, and lithium plating on the surface of the negative electrode can be suppressed, thereby improving the stability of the secondary battery during high-voltage charging.

[0025] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0026] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0027] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.

[0028] Figure 1 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application; Figure 2 This is a schematic diagram showing the stacking of the positive electrode, separator, and negative electrode in some embodiments of this application; Figure 3 This is a schematic diagram of the stacked structure of the first positive electrode segment, the first negative electrode segment, and the second negative electrode segment in the related technology; Figure 4 This is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application; Figure 5 This is a schematic diagram of the stacked structure of the first positive electrode segment, the first negative electrode segment, and the second negative electrode segment in some embodiments of this application; Figure 6 This is a schematic diagram of a partial stacked structure of the first positive electrode segment and the first negative electrode segment in some embodiments of this application; Figure 7 This is a top view of the positive and negative electrode plates of some embodiments of this application; Figure 8 This is a schematic diagram of a partial stacked structure of the first positive electrode segment and the first negative electrode segment in some embodiments of this application; Figure 9 This is a schematic diagram of a partial stacked structure of the first positive electrode segment and the first negative electrode segment in some embodiments of this application; Figure 10 This is a partial structural schematic diagram of the positive electrode sheet in some embodiments of this application; Figure 11 This is a top view of the positive electrode sheet of some embodiments of this application.

[0029] Explanation of reference numerals in the attached figures: 1000, secondary battery; 100. Shell; 200. Electrode assembly; 10. Positive electrode sheet; 13. Positive current collector; 11. First positive electrode material layer; 12. Second positive electrode material layer; 14. Thinning region; 141. First section; 142. Second section; 143. First position; 144. First coverage area; 145. First surface; 10a, First positive electrode section; 10a2, Second groove; 10a3, Third groove; 101. First edge; 102. Second edge; 103. Third edge; 104. Fourth edge; 105. Fifth edge; 106. Sixth edge; 20. Negative electrode sheet; 23. Negative electrode current collector; 21. First negative electrode material layer; 22. Second negative electrode material layer; 24. First part; 25. Second part; 20a, First negative electrode section; 20a1, First groove; 20b, second negative electrode segment; 20b1, edge region; 30. Separating membrane; 40. First adhesive layer; 50. First insulating layer; 51. First extension; 60. Second insulating layer; 70. Third insulating layer; 300, positive electrode tab; 400, negative electrode tab; X, first direction; Y, second direction; Z, third direction. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0031] In this application, the term "embodiment" means that a particular feature, structure, or characteristic commonly described with respect to that embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0032] In the explanation of the embodiments of this application, technical terms such as "first" and "second" are used to distinguish different objects and should not be construed as indicating or implying relative importance, nor do they mean that the specified technical features have a specific meaning in terms of quantity, specific order, or primary and secondary relationship. In the explanation of the embodiments of this application, "multiple" refers to two or more, unless otherwise explicitly and specifically defined.

[0033] In the description of the embodiments of this application, the term "and / or" is used to describe the relationship between related objects, which can reflect three types of relationships. For example, A and / or B can present the following three situations: only A exists, A and B exist simultaneously, and only B exists. In addition, the character " / " in this document usually means that the related objects before and after are in an "or" relationship; " / " can also represent a proportional relationship; when " / " appears in a table, it can also indicate that the corresponding substance and parameter do not exist, and its specific meaning needs to be determined according to the actual scenario.

[0034] The technical features described in the different embodiments of this application below can be combined with each other as long as they do not conflict with each other.

[0035] Firstly, this application proposes a secondary battery 1000. Please refer to... Figure 1 The secondary battery 1000 includes a housing 100, an electrode assembly 200, an electrolyte (not shown in the figure), a positive electrode tab 300, and a negative electrode tab 400. The housing 100 houses the electrode assembly 200 and the electrolyte, which permeates the electrode assembly 200 within the housing 100. One end of the positive electrode tab 300 is electrically connected to the electrode assembly 200 within the housing 100, and the other end extends outside the housing 100 to allow the positive electrode to be drawn out. One end of the negative electrode tab 400 is electrically connected to the electrode assembly 200 within the housing 100, and the other end extends outside the housing 100 to allow the negative electrode to be drawn out.

[0036] For electrode assembly 200, please refer to Figure 1 and Figure 2 The electrode assembly 200 is disposed within the housing 100, and includes a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10, the separator 30, and the negative electrode 20 are stacked and wound together. Figure 2 The diagram illustrates a stacked structure of a positive electrode 10, a negative electrode 20, and a separator 30, for example, stacked along the thickness direction of the positive electrode 10 and wound along its length direction to form a wound electrode assembly 200. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20 for insulating separation between them.

[0037] For positive electrode plate 10, please refer to... Figure 2 The positive electrode 10 includes a positive current collector 13, a first positive electrode material layer 11, and a second positive electrode material layer 12. The positive current collector 13 can be made of flat aluminum foil, which has high conductivity, helping to improve the maximum charge / discharge rate of the secondary battery 1000. In other embodiments, the positive current collector 13 can also be made of titanium foil or other foil materials that can adapt to the positive electrode potential. The first positive electrode material layer 11 and the second positive electrode material layer 12 are respectively disposed on two surfaces in the thickness direction of the positive current collector 13. The positive electrode material layers (first positive electrode material layer 11 and second positive electrode material layer 12) include a positive electrode material, a conductive agent, and a binder, etc. These material components are mixed and stirred evenly, then coated onto the surface of the positive current collector 13 to obtain the positive electrode material layer. The positive electrode material includes at least one of lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium manganese iron phosphate.

[0038] For negative electrode plate 20, please refer to... Figure 2The negative electrode 20 includes a negative electrode current collector 23, a first negative electrode material layer 21, and a second negative electrode material layer 22. The negative electrode current collector 23 can be a flat copper foil, which has high conductivity, helping to improve the maximum charge / discharge rate of the secondary battery 1000. In other embodiments, the negative electrode current collector 23 can also be made of titanium foil, nickel foil, stainless steel foil, or other foil materials suitable for the negative electrode potential. The first negative electrode material layer 21 and the second negative electrode material layer 22 can be disposed on two surfaces in the thickness direction of the negative electrode current collector 23. The negative electrode material layers (first negative electrode material layer 21 and second negative electrode material layer 22) include a negative electrode material, a conductive agent, and a binder. These materials are mixed and stirred evenly, then coated onto the surface of the negative electrode current collector 23 to obtain the negative electrode material layer. The negative electrode material includes at least one of elemental silicon, silicon-carbon composite materials, silicon oxide compounds, and silicon alloys, and may also include at least one of graphite, soft carbon, and hard carbon.

[0039] The separator 30 is disposed between the positive electrode 10 and the negative electrode 20, serving to insulate and separate the positive and negative electrodes. The separator 30 can adopt a porous structure, which allows lithium ions to freely shuttle between the positive and negative electrodes, thereby realizing the charging and discharging process of the secondary battery 1000.

[0040] For the negative electrode tab 400, please refer to... Figure 3 The positive electrode 10 includes a first positive electrode segment 10a, and the negative electrode 20 includes a first negative electrode segment 20a and a second negative electrode segment 20b. The first negative electrode segment 20a and the second negative electrode segment 20b are located on both sides of the thickness direction (first direction X) of the first positive electrode segment 10a.

[0041] The first positive electrode material layer 11 of the first positive electrode segment 10a faces the first negative electrode segment 20a, and the first negative electrode material layer 21 of the first negative electrode segment 20a faces the first positive electrode material layer 11. The second positive electrode material layer 12 of the first positive electrode segment 10a faces the second negative electrode segment 20b, and the second negative electrode material layer 22 of the second negative electrode segment 20b faces the second positive electrode layer 12.

[0042] In the first negative electrode section 20a, the first negative electrode material layer 21 is provided with a first groove 20a1. The first groove 20a1 can be formed on the first negative electrode material layer 21 by means of laser cleaning or mechanical punching, so that the negative electrode current collector 23 is exposed. A part of the negative electrode tab 400 is disposed in the first groove 20a1, and the negative electrode tab 400 is electrically connected to the negative electrode current collector 23. The connection method includes, but is not limited to, welding or bonding with conductive adhesive. The other part of the negative electrode tab 400 extends out of the negative electrode plate 20. The current of the negative electrode plate 20 can be gathered and transmitted through the negative electrode tab 400, thereby leading out the negative electrode of the secondary battery 1000.

[0043] In the embodiments of this application, the secondary battery 1000 can be a cylindrical battery or a flat battery.

[0044] When the secondary battery 1000 is a cylindrical battery, the positive electrode 10 is wound into several turns. The first positive electrode segment 10a is any segment of the positive electrode 10 after winding, which can be a complete turn, 1 / 2 turn, or 1 / 3 turn, etc. For the negative electrode 20, the negative electrode 20 is wound into several turns. The first negative electrode segment 20a and the second negative electrode segment 20b are located on different winding turns. Along the winding direction, the lengths of the two negative electrode segments are approximately equal to the length of the first positive electrode segment 10a. Among them, along the winding direction of the negative electrode 20, the first groove 20a1 is approximately located in the middle of the first negative electrode segment 20a.

[0045] When the secondary battery 1000 is a flat battery, please refer to... Figure 4 The positive electrode 10 includes several straight sections, one of which is the first positive electrode section 10a. The first negative electrode section 20a and the second negative electrode section 20b are located on two different straight sections of the negative electrode 20, respectively, and are located on opposite sides of the thickness direction of the first positive electrode section 10a. The section with the first groove 20a1 is the first negative electrode section 20a, and the other is the second negative electrode section 20b. Along the winding direction, the lengths of the first negative electrode section 20a and the second negative electrode section 20b are approximately equal to those of the first positive electrode section 10a. It is understood that when the secondary battery 1000 is a flat battery, the definition of the first positive electrode section 10a, the first negative electrode section 20a, and the second negative electrode section 20b can also refer to the definition method of the cylindrical battery described above.

[0046] The inventors of this application have discovered that creating a first groove 20a1 on the first negative electrode material layer 21 to connect the negative electrode tab 400 reduces the amount of material remaining in the first negative electrode material layer 21. For the first positive electrode material layer 11 on the first positive electrode segment 10a, lithium ions will still be released from the area corresponding to the first groove 20a1. Due to the presence of the first groove 20a1, the first negative electrode material layer 21 in this area lacks sufficient material to embed the lithium ions released from the positive electrode, easily leading to lithium plating near the first groove 20a1.

[0047] To reduce lithium ion extraction from the first positive electrode material layer 11 in the region corresponding to the first groove 20a1, please refer to... Figure 3The secondary battery 1000 includes a first insulating layer 50. The first insulating layer 50 is disposed on the surface of the first positive electrode material layer 11 facing the first groove 20a1. The first insulating layer 50 and the first groove 20a1 correspond to each other in the thickness direction of the first positive electrode segment 10a, and the width dimension (third direction Z) of the first insulating layer 50 is slightly larger than the width dimension of the first groove 20a1, and its length dimension (second direction Y) is larger than the length dimension of the first groove 20a1. For example, along the first direction X, within the projection range of the first positive electrode segment 10a, the orthogonal projection of the first groove 20a1 lies within the orthogonal projection range of the first insulating layer 50. The first insulating layer 50 covers a portion of the first positive electrode material layer 11 (the region corresponding to the first groove 20a1) to suppress the extraction of lithium ions from this portion of the region into the first negative electrode material layer 21, thereby reducing the risk of lithium plating in the first negative electrode material layer 21.

[0048] However, further research by the inventors of this application revealed that, due to the presence of the first insulating layer 50, lithium ions that should migrate toward the first negative electrode material layer 21 are blocked by the first insulating layer 50. Near the edge of the first positive electrode segment 10a (the edge in the second direction Y, i.e., the first edge 101), lithium ions released from the first positive electrode material layer 11 are blocked by the first insulating layer 50 and cannot diffuse toward the first negative electrode segment 20a. Instead, they cross the positive electrode current collector 13 and migrate toward the second negative electrode material layer 22 in the second negative electrode segment 20b. This leads to lithium ion accumulation at the edge of the second negative electrode material layer 22 (the edge in the second direction Y, i.e., the edge region 20b1), easily causing lithium plating in the second negative electrode material layer 22.

[0049] By removing the material layer of the first positive electrode material layer 11 corresponding to the position of the first groove 20a1, the positive electrode current collector 13 is exposed. Then, the area of ​​the exposed positive electrode current collector 13 is covered with the first insulating layer 50. Although this can reduce lithium ion release, the size of the first insulating layer 50 needs to be larger than the part where the material layer was removed in order to fully cover the exposed positive electrode current collector 13. Otherwise, due to the thermal effect of the electrode and the swelling effect of the first insulating layer 50, the first insulating layer 50 may shrink and warp, thereby misaligning with the positive electrode current collector 13. The exposed positive electrode current collector 13 is prone to short circuit when it comes into contact with the negative electrode 20. In order to fully cover the exposed positive electrode current collector 13 and reduce the risk of the positive electrode current collector 13 being exposed, the first insulating layer 50 needs to appropriately cover part of the first positive electrode material layer 11. This part of the first positive electrode material layer 11 covered by the first insulating layer 50 will also experience the above-mentioned lithium ion migration to the second negative electrode material layer 22 due to the obstruction of the first insulating layer 50, thereby aggravating the lithium plating problem of the second negative electrode material layer 22. In addition, the part of the first positive electrode material layer 11 covered by the first insulating layer 50 may still exert some capacity. Completely removing the first positive electrode material layer 11 in this area will cause a large loss of positive electrode material in this area, resulting in a significant decrease in the energy density of the secondary battery 1000.

[0050] To reduce the above-mentioned problems, please refer to the embodiments of this application. Figure 5 and Figure 6 In the first positive electrode section 10a, a second groove 10a2 is formed on the surface of the first positive electrode material layer 11 facing the first groove 20a1. The first positive electrode material layer 11 includes a thinned region 14. Along the first direction X, the portion of the first positive electrode material layer 11 located between the positive current collector 13 and the second groove 10a2 forms the thinned region 14. The second groove 10a2 can be formed on the first positive electrode material layer 11 by means of laser cleaning or mechanical punching, but the second groove 10a2 will not expose the positive current collector 13. A portion of the first positive electrode material layer 11 still exists between the second groove 10a2 and the positive current collector 13, which can reduce the direct contact between the positive current collector 13 and the negative electrode sheet 20, further reducing the risk of short circuit. Simultaneously, along the first direction X, the second groove 10a2 is positioned opposite to the first groove 20a1. When the negative electrode tab 400 protrudes from the first groove 20a1 along the first direction X, the second groove 10a2 can accommodate and avoid the negative electrode tab 400, reducing the thickness space occupied by the negative electrode tab 400 in the first negative electrode section 20a, thereby improving the energy density of the secondary battery 1000. Optionally, the first direction X is the thickness direction of the first positive electrode section 10a located at the second groove 10a2.

[0051] Regarding the thinning region 14, please refer to the embodiments of this application. Figure 6, the thinning region 14 includes a first section 141 and a second section 142. Along the second direction Y, the second section 142 and the first section 141 are arranged in sequence; along the first direction X, the average thickness of the first section 141 is T1 μm, and the average thickness of the second section 142 is T2 μm, and T1 < T2. Wherein, the second direction Y is the direction in which the negative electrode tab 400 extends out of the negative electrode plate 20. The first insulating layer 50 is disposed in the second groove 10a2. Along the first direction X, within the projection range of the first positive electrode segment 10a, the orthogonal projection of the first groove 20a1 is within the orthogonal projection range of the first insulating layer 50.

[0052] In the embodiment of the present application, the thinning region 14 adopts a thickness gradient design. A larger thickness T2 is set in the second section 142 away from the first edge 101, which is beneficial to retaining sufficient positive electrode material and effectively improving the energy density of the secondary battery 1000; and a smaller thickness T1 can be adopted in the first section 141 close to the first edge 101, reducing the amount of lithium ions escaping from the region near the first edge 101, alleviating the phenomenon that lithium ions cross the positive electrode current collector 13 and migrate to the second negative electrode material layer 22 and accumulate at its edge, thereby reducing the risk of lithium deposition in the second negative electrode material layer 22. At the same time, along the first direction X, within the projection range of the first positive electrode segment 10a, the orthogonal projection of the first groove 20a1 is within the orthogonal projection range of the first insulating layer 50, which can reduce the number of lithium ions escaping from the first positive electrode material layer 11 to the region of the first groove 20a1, and can also reduce the risk of lithium deposition near the first groove 20a1. In addition, disposing the first insulating layer 50 in the second groove 10a2 can reduce the occupation of the thickness space of the first positive electrode segment 10a by the first insulating layer 50, and further improve the energy density of the secondary battery 1000.

[0053] Therefore, in the embodiment of the present application, by opening the second groove 10a2 that does not expose the positive electrode current collector 13 in the first positive electrode material layer 11, and setting the thinning region 14 with a T1 < T2 gradient between the second groove 10a2 and the positive electrode current collector 13; at the same time, embedding the first insulating layer 50 into the second groove 10a2 and making the orthogonal projection of the first groove 20a1 fall within the orthogonal projection range of the first insulating layer 50, it is possible to improve the energy density of the secondary battery 1000 while reducing the risks of short circuit and lithium deposition in the secondary battery 1000.

[0054] It is understood that regarding the definition of the first segment 141 and the second segment 142, along the second direction Y, the widths of the first segment 141 and the second segment 142 can be set to be equal. For example, the thinning region 14 can be divided into two segments of equal width along the second direction Y. In some other embodiments, the widths of the first segment 141 and the second segment 142 can also be unequal. For example, the width of the first segment 141 is 0.7 to 1.3 times the width of the second segment 142. The width ratio can be adjusted according to the secondary battery model 1000. This application does not impose further limitations, as long as the thinning region 14 is divided into two segments and the design requirement that the average thickness T1 of the first segment 141 is less than the average thickness T2 of the second segment 142 is met.

[0055] Regarding the shape of the thinning region 14, in some embodiments, the thinning region 14 can be a two-level or multi-level stepped structure, with each level of the step arranged sequentially along the second direction Y, and the thickness along the first direction X decreasing gradually from the side away from the first edge 101 to the side closer to the first edge 101. By adopting a two-level or multi-level stepped structure, the thickness segments can be flexibly divided according to the lithium removal requirements at different locations in actual application scenarios. This allows for the retention of sufficient positive electrode material in the area away from the first edge 101 to ensure a secondary battery energy density of 1000, while also controlling the amount of lithium ions removed from the area close to the first edge 101 through the step-by-step thinning design, reducing the migration and enrichment of lithium ions across the positive electrode current collector 13 to the second negative electrode material layer 22.

[0056] In other embodiments, the thickness of the thinning region 14 gradually decreases along the second direction Y, thus forming a sloped structure. The sloped structure is more conducive to matching the smooth change in lithium-ion extraction from far to near the first edge 101, enabling continuous adjustment of lithium-ion extraction and reducing local fluctuations in lithium-ion extraction caused by abrupt thickness changes. This more efficiently alleviates the migration and enrichment of lithium ions into the second negative electrode material layer 22, further reducing the risk of lithium plating at the edge of the second negative electrode material layer 22. Furthermore, the sloped structure adheres more tightly to the first insulating layer 50, reducing interface gaps and further lowering the risk of the first insulating layer 50 detaching due to uneven stress, swelling, or cyclic expansion of the electrode, thus improving structural stability. In addition, the sloped structure is easier to process and can be formed in one step using standardized processes such as laser cleaning or mechanical punching, simplifying the processing flow, reducing process difficulty, and thus improving production yield.

[0057] In some embodiments, please refer to Figure 6 Along the second direction Y, the first positive electrode material layer 11 includes a first edge 101, and a thinning region 14 extends to the first edge 101; at the first edge 101, the thickness of the thinning region 14 is T. a μm, 0.5≤T a ≤5. Ta You can choose any value from 0.5 to 5, or any range between two values, such as 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any range from 1 to 4.5, 1.5 to 4, 2 to 3.5, etc. T a The size can reflect the amount of delithiation at the first edge 101 of the thinned region 14, T a The smaller the value, the less positive electrode material remains at the first edge 101, and the lower the amount of lithium ions that can be extracted in that region; T a The larger the area, the greater the amount of delithiation in that region.

[0058] By T a By controlling the thickness within the range of 0.5 to 5, on the one hand, an appropriate amount of positive electrode material can be retained in the first edge 101 region, which can reduce the risk of pulverization and shedding in this region, maintain the structural stability of the thinned region 14, and control the amount of lithium delithiation in this region at a reasonably low level, thereby mitigating the migration of lithium ions to the second negative electrode material layer 22 and reducing the risk of lithium plating at the edge of the second negative electrode material layer 22. On the other hand, it can ensure the stable coverage of the positive electrode current collector 13 by the thinned region 14, reduce the exposure of the positive electrode current collector 13, and improve the safety performance of the secondary battery 1000. At the same time, it can adapt to the installation space of the negative electrode tab 400, reduce the occupation of the negative electrode tab 400 on the thickness space of the first negative electrode section 20a (so that the second groove 10a2 can accommodate part of the negative electrode tab 400), and further improve the energy density of the secondary battery 1000. Furthermore, 1≤T a ≤4 can achieve a better balance between reducing edge pulverization and shedding in the thinned region 14, maintaining safety performance, and reducing the risk of lithium plating in the second anode material, thereby further improving the overall performance of the secondary battery 1000.

[0059] In some embodiments, please refer to Figure 5 and Figure 6 The first insulating layer 50 also includes a first extension 51 extending from the first edge 101 to the positive electrode 10, the first extension 51 extending from the first edge 101 by a length L. a mm, 0.5≤L a ≤1.5. L a You can select any value from 0.5 to 1.5, or any range between two values, such as 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or any range from 0.6 to 1.4, 0.8 to 1.2, 0.9 to 1.1, etc. By using L... aBy controlling the length within the range of 0.5 to 1.5, on the one hand, the first extension 51 can block the amount of lithium stripping at the first edge 101, reducing the lithium plating phenomenon in the second negative electrode section 20b caused by lithium ions migrating across the positive electrode current collector 13; simultaneously, the first insulating layer 50 itself has a certain strength, and its adherence to the inclined surface of the second groove 10a2 allows the first extension 51 to naturally tilt towards the second negative electrode section 20b, further covering the first edge 101, thereby reducing the migration of active lithium ions to the second negative electrode section 20b and further enhancing the lithium plating suppression effect on the second negative electrode section 20b. On the other hand, this length range can reduce the first extension 51 from entering the top sealing area and interfering with the packaging process, ensuring the reliability of the housing 100 packaging, and achieving dual optimization of lithium plating prevention at the edge of the second negative electrode section 20b and the reliability of the housing 100 packaging.

[0060] In some embodiments, please refer to Figure 6 Along the first direction X, the thickness of the first positive electrode material layer 11 is H μm. At one end in the opposite direction of the second direction Y, the first insulating layer 50 includes a fifth edge 105. Along the first direction X, the thinning region 14 includes a first position 143 that overlaps with the orthogonal projection of the fifth edge 105. Along the first direction X, the thinning region 14 includes a first region (not shown in the figure) covered by the first insulating layer 50, for example, the orthogonal projection of the first insulating layer 50 on the thinning region 14 overlaps with the first region, and the first position 143 is the location of the maximum thickness of the first region. The thickness of the thinning region 14 at the first position 143 is H1 μm, 0.25 ≤ H1 / H ≤ 0.75. The ratio H1 / H can be any value from 0.25 to 0.75, or any range between two values, such as 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, etc., or any range from 0.3 to 0.7, 0.4 to 0.6, 0.45 to 0.55, etc.

[0061] The H1 / H ratio reflects the maximum relative height of the first insulating layer 50 at the bonding position in the thinning region 14, directly affecting the overall thickness of the first positive electrode section 10a and its fit with the negative electrode tab 400. By controlling the H1 / H ratio within the range of 0.25 to 0.75, on the one hand, the thickness of the first insulating layer 50 can be adapted to fully accommodate it, while reducing the highest point of the first insulating layer 50 after bonding from exceeding the surface of the first positive electrode material layer 11, effectively reducing the overall excessive thickness of the first positive electrode section 10a, thereby improving the energy density of the secondary battery 1000; on the other hand, it allows full utilization of the portion of the positive electrode material layer in the thinning region 14 not covered by the first insulating layer 50, further improving the energy density of the secondary battery 1000.

[0062] It is understandable that, for the area covered by the first insulating layer 50, although the first position 143 is the thickest point in that area, its impact on the overall thickness of the first positive electrode segment 10a is relatively small. This is because the fifth edge 105 of the first insulating layer 50 extends beyond the lower edge of the second insulating layer 60 in the opposite direction of the second direction Y. The lower edge of the second insulating layer 60 is located in the first negative electrode material layer 21, and this lower edge is not the thickest part of the negative electrode sheet 20 (typically, the thickness of the negative electrode tab 400 is greater than the thickness of the first negative electrode material layer 21). The thickest part of the negative electrode sheet 20 is usually located at the overlap between the negative electrode tab 400 and the second insulating layer 60. Meanwhile, the thinner portion (T) of the thinning region 14... a The structure is positioned opposite to the thicker part of the first negative electrode section 20a, which allows for good structural avoidance.

[0063] In some embodiments, the first insulating layer 50 includes a substrate layer and an adhesive layer, the adhesive layer being disposed on the surface of the substrate layer. The substrate layer includes at least one of polyimide, polyethylene terephthalate, polyurethane, etc. The adhesive layer includes at least one of polyimide, polyurethane, thermoplastic polyurethane, epoxy resin, polyacrylate, etc. The various materials of the above-mentioned substrate layer and adhesive layer possess excellent insulation and chemical stability, enabling the first insulating layer 50 to have strong mechanical support and insulation properties, reducing the deformation of the first insulating layer 50 during the charging and discharging process of the secondary battery 1000, and helping to maintain stable performance in the electrochemical environment inside the secondary battery 100.

[0064] In the embodiments of this application, the thickness of the first insulating layer 50 is T μm, where 5 ≤ T ≤ 20. T can be any value from 5 to 20, or any range between two values, such as any value of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or any range between 6 and 19, 8 and 17, 10 and 15. By controlling T within the range of 5 to 20, on the one hand, the first insulating layer 50 can be guaranteed to have sufficient mechanical strength and insulation performance, effectively supporting its bonding shape in the thinning region 14, and reducing the deformation of the first insulating layer 50 caused by the expansion and contraction of the electrode during the charging and discharging of the secondary battery 1000; on the other hand, it can reduce the overall thickness space occupied by the first insulating layer 50 in the first positive electrode section 10a, thereby balancing the structural stability and high energy density of the secondary battery 1000.

[0065] In some embodiments, please refer to Figure 5 and Figure 6The first positive electrode material layer 11 includes a first surface 145 facing the first negative electrode material layer 21. The first insulating layer 50 does not protrude from the first surface 145, which can reduce the additional space occupied by the first insulating layer 50 in the internal space of the secondary battery 1000 and help improve the energy density of the secondary battery 1000. At the same time, it can reduce the risk of wrinkles or warping of the electrode due to the protrusion of the first insulating layer 50 during the electrode winding process, thereby enhancing the structural stability of the secondary battery 1000.

[0066] In the embodiments of this application, the second groove 10a2 can be formed on the first positive electrode material layer 11 by means of laser cleaning or mechanical punching, which will give the surface of the thinned region 14 a certain roughness. For example, the surface roughness of the thinned region 14 is R μm, where 2≤R≤15. R can be any value from 2 to 15, or any range between two values, such as any value of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or any range from 3 to 14, 5 to 12, 7 to 10. The magnitude of the roughness R affects the bonding strength between the first insulating layer 50 and the thinned region 14. By controlling R within the range of 2 to 15, on the one hand, a moderate surface roughness can be used to create a mechanical anchoring effect between the thinned region 14 and the first insulating layer 50, thereby increasing the bonding strength between them and reducing the risk of the first insulating layer 50 slipping, lifting, or falling off; on the other hand, it can reduce the penetration of electrolyte into the rough surface, thereby inhibiting the formation of hard byproducts caused by the swelling of the first insulating layer 50, the dissolution of cobalt ions, and the reaction of the adhesive layer, and enhancing the interfacial stability of the first positive electrode material layer 11.

[0067] In some embodiments, please refer to Figure 6 The secondary battery 1000 also includes a second insulating layer 60, which is at least partially disposed on the first negative electrode material layer 21. Along the first direction X, the second insulating layer 60 covers the first groove 20a1 and part of the negative electrode tab 400. The provision of the second insulating layer 60 can reduce the exposure of the negative electrode current collector 23, thereby reducing the risk of short circuit between the negative electrode current collector 23 and the negative electrode tab 400 and the first positive electrode segment 10a. At the same time, the second insulating layer 60 can cover some burrs (such as welding burrs or cutting burrs) on the negative electrode tab 400, thereby reducing the possibility of short circuit due to contact between burrs and the first positive electrode segment 10a.

[0068] Please refer to Figure 6 and Figure 7 Along the opposite direction of the second direction Y, at the end furthest from the first edge 101, the first insulating layer 50 extends beyond the second insulating layer 60 by a length W. a mm, 2≤W a ≤5. W aYou can choose any value from 2 to 5, or a range between any two values, such as any value from 2 to 5, or any range from 2.5 to 4.5, or 3 to 4. By using W... a Controlling the value within the range of 2 to 5 can, on the one hand, facilitate the full coverage of the second groove 10a2 by the first insulating layer 50, forming continuous insulation protection between the first positive electrode section 10a and the negative electrode tab 400, further reducing the risk of short circuit between the two; and can reduce the migration of lithium ions from the first positive electrode section 10a to the negative electrode tab 400 region, thereby reducing the risk of lithium plating in the first negative electrode section 20a; on the other hand, it can reduce the waste of positive electrode material and space occupation caused by the excessive extension of the first insulating layer 50, effectively improving the energy density of the secondary battery 1000 while improving insulation reliability.

[0069] Please refer to Figure 7 On the side of the first insulating layer 50 along the third direction Z, the length of the first insulating layer 50 extending beyond the second insulating layer 60 is L1 mm, where 2 ≤ L1 ≤ 5. L1 can be any value from 2 to 5, or any range between two values, such as any value of 2, 2.5, 3, 3.5, 4, 4.5, or 5, or any range between 2.5 and 4.5, 3 and 4. By controlling L1 within the range of 2 to 5, on the one hand, it is beneficial for the first insulating layer 50 to fully cover the second insulating layer 60 in the third direction Z, further reducing the risk of short circuits due to misalignment during winding; on the other hand, it can reduce the waste of positive electrode material and space occupation caused by the excessive extension of the first insulating layer 50, thereby improving insulation reliability and increasing the energy density of the secondary battery 1000. Based on the same inventive concept, on the other side of the first insulating layer 50 along the third direction Z, the length of the first insulating layer 50 extending beyond the second insulating layer 60 is L2 mm, where 2 ≤ L2 ≤ 5; L2 can be set similarly to L1 as described above, and will not be elaborated in detail in this application. Among them, the first direction X, the second direction Y, and the third direction Z are all perpendicular to each other.

[0070] In some embodiments, please refer to Figure 7Along the second direction Y, the second groove 10a2 includes a second edge 102 disposed opposite to the first edge 101; along the second direction Y, the distance between the first insulating layer 50 and the second edge 102 is W1 mm, 0.5 ≤ W1 ≤ 1. W1 can be any value from 0.5 to 1, or any range between two values, such as any value of 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc., or any range between 0.6 and 0.9, 0.7 and 0.8, etc. By controlling W1 within the range of 0.5 to 1, on the one hand, a reasonable gap can be reserved between the second groove 10a2 and the first insulating layer 50 in the second direction Y to accommodate the precision deviation of the adhesive bonding process, reduce the high point of the first insulating layer 50 attached to the edge of the second groove 10a2, and thus improve the bonding stability of the first insulating layer 50; on the other hand, this gap reduces the amount of lithium stripping by partially removing the positive electrode material, thereby reducing the lithium plating phenomenon at the negative electrode tab 400; at the same time, the retained positive electrode material can also take into account the energy density of the secondary battery 1000, achieving a triple optimization of adhesive bonding reliability, lithium plating protection, and energy density gain.

[0071] In some embodiments, please refer to Figure 7 Along the third direction Z, the second groove 10a2 includes a third edge 103 and a fourth edge 104 disposed opposite to each other. Along the third direction Z, the distance between the first insulating layer 50 and the third edge 103 is L3mm. L3 can be any value from 0.5 to 1, or any range between two values, such as any value of 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any range between 0.6 and 0.9, 0.7 and 0.8. By controlling L3 within the range of 0.5 to 1, on the one hand, a reasonable gap can be reserved between the second groove 10a2 and the first insulating layer 50 in the third direction Z to accommodate the precision deviation of the adhesive process, further reducing the high point of the first insulating layer 50 adhering to the third edge 103, thereby improving the adhesion strength and stability of the first insulating layer 50; on the other hand, this gap reduces the amount of lithium stripping by partially removing the positive electrode material, reducing the lithium plating phenomenon at the negative electrode tab 400; at the same time, the retained positive electrode material can also take into account the energy density of the secondary battery 1000, further achieving a triple optimization of adhesive reliability, lithium plating protection, and energy density gain. Based on the same inventive concept, along the third direction Z, the distance between the first insulating layer 50 and the fourth edge 104 is L4mm, 0.5≤L4≤1.5; L4 can be set similarly to L3 as described above, and will not be elaborated in this application.

[0072] In some embodiments, please refer to Figure 8The first negative electrode material layer 21 includes a first portion 24. Along the second direction Y, the first negative electrode material layer 21 includes a sixth edge 106, and the portion of the first negative electrode material layer 21 located between the sixth edge 106 and the first groove 20a1 forms the first portion 24. Along the first direction X, the negative electrode tab 400 covers at least a portion of the first portion 24. In this embodiment, by retaining the first portion 24, the negative electrode material layer in this region can effectively support the negative electrode tab 400. On the one hand, it can enhance the structural strength of the edge of the negative electrode sheet 20, effectively reducing the risk of the negative electrode sheet 20 being torn due to the pulling of the negative electrode tab 400, while also facilitating the compatibility with the precision error of the slitting process and simplifying the control difficulty of the cutting process; on the other hand, although the negative electrode material layer retained in this area will increase the local thickness of the negative electrode sheet 20, the corresponding positive electrode sheet 10 is provided with an inclined second groove 10a2. The second groove 10a2 presents the thinnest thickness gradient feature near the edge, which can just accommodate the thickened part of the negative electrode sheet 20, achieving a precise match between the thickness of the positive and negative electrode sheets 20, thereby reducing problems such as lithium plating or stress concentration leading to tearing caused by uneven local thickness.

[0073] In some embodiments, please refer to Figure 9 The secondary battery 1000 also includes a first adhesive layer 40, which is disposed between the negative electrode tab 400 and the negative electrode current collector 23. The first adhesive layer 40 may be made of conductive adhesive to achieve electrical connection between the negative electrode tab 400 and the negative electrode current collector 23; or a protruding structure may be provided on the negative electrode tab 400, which contacts the negative electrode current collector 23 to achieve electrical connection between the two.

[0074] The first negative electrode segment 20a also includes a second negative electrode material layer 22. It can be understood that the second negative electrode material layer 22 extends from the second negative electrode segment 20b to the first negative electrode segment 20a, such that the first negative electrode segment 20a also includes the second negative electrode material layer 22. The second negative electrode material layer 22 is disposed on the surface of the negative electrode current collector 23 opposite to the first negative electrode material layer 21, and the second negative electrode material layer 22 includes a second portion 25. Along the first direction X, the orthogonal projection of the second portion 25 overlaps with the orthogonal projection of the first groove 20a1. The first adhesive layer 40 achieves bonding between the negative electrode tab 400 and the negative electrode current collector 23, eliminating the need for welding heads and welding bases in traditional welding processes. This avoids the generation of welding burrs, reducing the risk of short circuits caused by burrs contacting the positive electrode sheet 10. Furthermore, since no support space is needed for the welding base, the second portion 25 of the second negative electrode material layer 22 corresponding to the first groove 20a1 can be completely preserved, fully utilizing the internal space of the secondary battery 1000 and effectively improving its energy density. The preservation of the second portion 25 also increases the thickness of the negative electrode sheet 20 in the bonding area of ​​the negative electrode tab 400 to a certain extent, perfectly matching the thinning region 14 within the second groove 10a2 on the positive electrode side. This thinning region 14 is a smoothly transitioning inclined structure, with its thickness decreasing from far from the first edge 101 to near the first edge 101, and its thickness T near the first edge 101... a The thickness is controlled within the range of 0.5μm to 5μm (preferably 1μm to 4μm), which matches the size of the negative electrode 20 in the bonding area of ​​the negative electrode tab 400. This provides a suitable accommodating space for the thickened part of the negative electrode 20, effectively filling the thickness allowance of the first positive electrode section 10a (second groove 10a2). This is beneficial to achieve the thickness complementarity and size adaptation of the positive and negative electrode 20 in the connection area of ​​the negative electrode tab 400, making the thickness of the overall stacked / wound structure of the positive and negative electrode 20 more uniform and reducing the problem of increased interface gap caused by inconsistent thickness of the positive and negative electrode 20.

[0075] It should be noted that retaining the second part 25 increases the thickness of the first negative electrode segment 20a at the negative electrode tab 400. In the embodiments of this application, by providing the second groove 10a2, a portion of the negative electrode tab 400 can be accommodated, achieving effective adaptation with the adhesive tab structure and reducing the problem of increased local thickness caused by the superposition of the negative electrode tab 400 and the second part 25. This not only reduces the risk of short circuits but also ensures the integrity of the second negative electrode material layer 22, effectively improving the energy density of the secondary battery 1000.

[0076] In some embodiments, please refer to Figure 10 and Figure 11The secondary battery 1000 also includes a positive electrode tab 300 and a third insulating layer 70. A third groove 10a3 is provided in the first positive electrode material layer 11, exposing the positive current collector 13. A portion of the positive electrode tab 300 is electrically connected to the positive current collector 13 within the third groove 10a3, and another portion extends out of the positive electrode plate 10. The third insulating layer 70 is disposed on the first positive electrode material layer 11, covering the third groove 10a3 along the first direction X. The first positive electrode material layer 11 also includes a first covering area 144 covered by the third insulating layer 70, with the thickness of the first covering area 144 decreasing sequentially along the second direction Y.

[0077] It should be noted that the third insulating layer 70 covering the positive electrode tab 300 also covers part of the first positive electrode material layer 11. Because the positive electrode material in the covered area is blocked by the third insulating layer 70, the lithium ions that have been extracted and inserted may migrate to the second negative electrode segment 20b on the other side, easily leading to lithium plating in the second negative electrode segment 20b. To reduce this problem, in the embodiments of this application, the thickness of the first covering area 144 is designed as a gradient decreasing structure along the second direction Y. The amount of lithium ion extraction and insertion within the first covering area 144 decreases synchronously with the thinning of the thickness, which can effectively reduce the migration of lithium ions to the second negative electrode segment 20b, thereby reducing the risk of lithium plating in the second negative electrode segment 20b caused by lithium ion aggregation.

[0078] In some embodiments, the charging cutoff voltage of the secondary battery 1000 is GV, where 4.55 ≤ G ≤ 4.65. G can be any value from 4.55 to 4.65, or a range between any two values, such as any value of 4.55, 4.56, 4.57, 4.58, 4.59, 4.60, 4.61, 4.62, 4.63, 4.64, 4.65, etc., or any range from 4.56 to 4.64, 4.58 to 4.62, 4.59 to 4.61, etc. By controlling G within the range of 4.55 to 4.65 V, on the one hand, it helps to fully utilize the advantages of high voltage, enabling the positive electrode material layer to achieve a greater amount of lithium removal at a higher potential, thereby improving the energy density of the secondary battery 1000; on the other hand, with the structural design of the first insulating layer 50, the second groove 10a2, and the thinning region 14 of this application, the problem of excessive lithium ion removal from the positive electrode and migration to the negative electrode under high voltage can be effectively alleviated, and the lithium plating phenomenon on the surface of the negative electrode can be suppressed, thereby improving the stability of the secondary battery 1000 during high-voltage charging.

[0079] The inventors of this application have discovered that when the second groove 10a2 is formed in the first positive electrode material layer 11 (for example, by laser cleaning or mechanical punching), this process can damage the structural integrity of some positive electrode material particles, leading to particle breakage. The broken positive electrode material particles expose more active sites, increasing the reactivity of the first groove 20a1 region with the electrolyte, easily triggering side reactions, and thus accelerating electrolyte consumption, which is detrimental to improving the cycle capacity retention rate of the secondary battery 1000.

[0080] To mitigate the aforementioned problems, in the embodiments of this application, the electrolyte includes a first component, which comprises at least one of 2,2-difluoroethyl acetate, ethyl difluoroacetate, and fluoroacetic acid-2-fluoroethyl ester. Each of the materials in the first component possesses high stability and can undergo oxidative decomposition reactions at the active sites exposed by the broken cathode material particles. This allows for the formation of a dense protective layer rich in fluorinated products on the surface of the broken cathode material particles, suppressing side reactions caused by particle breakage and improving cycle stability. Furthermore, the presence of the first component in the electrolyte system reduces the electrolyte viscosity, improving its fluidity and promoting film formation of the first component on the cathode material layer surface. This reduces ineffective electrolyte consumption and further enhances the cycle stability of the secondary battery 1000.

[0081] Further research by the inventors of this application revealed that when the content of the first component is too high, it leads to the formation of excessive fluorinated products, which easily results in the enrichment of fluorinated products at the bonding interface between the first insulating layer 50 and the thinned region 14, thus hindering the improvement of their bonding strength. For example, it causes an interfacial gap between the first insulating layer 50 and the thinned region 14, through which some lithium ions may escape, thereby reducing the risk of lithium plating at the negative electrode tab 400.

[0082] To mitigate the aforementioned problems, in the embodiments of this application, the mass percentage of the first component is A%, based on the total mass of the electrolyte, with 10 ≤ A ≤ 60. A can be any value from 10 to 60, or any range between two values, such as any value of 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or any range from 15 to 55, 20 to 50, 25 to 45, 30 to 40, etc. By controlling A within the range of 10 to 60, on the one hand, the first component has a sufficient content, which can form a continuous and dense protective layer on the surface of the broken positive electrode material particles, effectively suppressing the side reactions in the slotted area, reducing electrolyte consumption, and improving the cycle stability of the secondary battery 1000; on the other hand, it can reduce the accumulation of fluoride products at the bonding interface between the first insulating layer 50 and the thinned area 14, thereby maintaining good bonding strength between the two, reducing the generation of interface gaps, and thus reducing the phenomenon of lithium ions escaping from the gaps, which is beneficial to reducing the risk of lithium plating at the negative electrode tab 400.

[0083] In some embodiments, the electrolyte further includes a second component, which includes at least one of ethylene carbonate and propylene carbonate. The second component has strong polarity and, compared to the first component, can preferentially participate in the solvation structure of lithium ions, reducing the proportion of the first component in the solvation structure. This helps to increase the amount of free first component in the electrolyte, reducing the increase in electrolyte viscosity caused by the introduction of the second component and improving ion transport. On the other hand, after the second component participates in the lithium-ion solvation structure, when solvated lithium-ion clusters migrate to the bonding interface between the first insulating layer 50 and the thinned region 14 and undergo side reactions, the presence of the second component allows both the first and second components to undergo side reactions simultaneously. This can suppress the aggregation of fluorinated products at the interface caused by excessive decomposition of the first component, thereby improving the problem of interface adhesion deterioration caused by the increased content of the first component.

[0084] The inventors discovered that increasing the amount of the second component increases the viscosity of the electrolyte, which is detrimental to improving electrolyte wetting efficiency and has a poor effect on improving kinetics. To mitigate this problem, in the embodiments of this application, the mass percentage of the second component is B% based on the total mass of the electrolyte, with a value of 15 ≤ B ≤ 40. B can be any value from 15 to 40, or any range between two values, such as 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, or any range from 18 to 38, 20 to 35, 22 to 32, 25 to 30. By controlling B within the range of 15 to 40, the second component has a sufficient content, fully utilizing its strong polarity to preferentially participate in the solvation structure of lithium ions, reducing the proportion of the first component in the solvation structure. This facilitates the formation of a suitable protective layer of fluorine-containing material on the surface of the broken positive electrode particles in the slotted area, improving interfacial adhesion performance. On the other hand, it can reduce the problem of increased electrolyte viscosity caused by excessive content of the second component, maintain good wetting fluidity of the electrolyte, ensure the kinetic performance of the secondary battery 1000, and achieve dual optimization of interface adhesion stability and kinetic performance.

[0085] In some embodiments, 0.5 ≤ A / B ≤ 5. A / B can be any value from 0.5 to 5, or any range between two values, such as 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any range from 1 to 4, 1.5 to 3.5, 2 to 3, etc. The essence of A / B is a control parameter between suppressing side reactions in the grooved area and maintaining interfacial adhesion performance. By controlling the A / B ratio within the range of 0.5 to 5, on the one hand, sufficient first component can react on the surface of the broken positive electrode particles in the slotted area to form a continuous and dense protective layer, thereby enhancing the suppression effect on side reactions in the slotted area; on the other hand, it helps the second component to fully participate in the solvation structure of lithium ions, thereby controlling the distribution of the first component, reducing the excessive reaction of the first component, and controlling the content of fluorinated byproducts at the bonding interface between the first insulating layer 50 and the thinned region 14, which helps to improve the bonding strength between the first insulating layer 50 and the thinned region 14; at the same time, it is beneficial to maintain a suitable viscosity of the electrolyte to improve its fluidity, ensure the lithium ion transport efficiency, and thus achieve synergistic enhancement of side reaction suppression, bonding performance, and kinetic performance.

[0086] The inventors of this application have discovered that electrolyte accumulation is prone to occur on both sides of the first positive electrode segment 10a along the width direction (second direction Y) of the positive electrode sheet 10. The side of the thinned region 14 closest to the first positive electrode segment 10a along the width direction experiences electrolyte accumulation, which easily leads to a larger CEI film thickness, increased impedance, and is detrimental to lithium-ion insertion / extraction. Furthermore, before bonding the first insulating layer 50 to the thinned region 14, processes such as laser cleaning or mechanical punching can easily damage the coating layer on the surface of the positive electrode material, leading to exposure of the active surface and exacerbating the dissolution of transition metals (such as cobalt), which is detrimental to improving the cycle stability of the secondary battery 1000.

[0087] In some embodiments of this application, the electrolyte further includes a third component, which includes at least one of the following compounds;

[0088] .

[0089] The inventors discovered that when the adhesive layer of the positive electrode material is thinned, the surface coating of the positive electrode active particles is damaged. Transition metal ions, such as Co... 3+ Easier dissolution is detrimental to improving cycle performance. By adding a third component to the electrolyte, the lone pair electrons in the sulfonyl functional group specifically bind to cobalt atoms or other transition metal atoms on the lithium-containing transition metal composite oxide, preferentially forming a film in the thinning region 14. During the formation of the secondary battery 100, a highly stable inorganic protective thin layer containing fluoride and sulfonic acid / sulfate is formed, significantly improving the uniformity of film formation at the bonding position of the first insulating layer 50, reducing the problem of inconsistent film impedance caused by uneven electrolyte distribution, thereby effectively suppressing excessive CEI film thickening, reducing interfacial impedance, and ensuring lithium ion insertion / extraction efficiency. On the other hand, the electron-rich sulfonyl functional groups in the third component can coordinate with transition metals with empty orbitals, suppressing the problem of transition metal dissolution caused by the destruction of the coating layer, reducing the side reaction problem caused by the crosstalk of transition metal ions to the negative electrode, and thus improving the cycle stability of the secondary battery 1000.

[0090] Based on the total mass of the electrolyte, the mass percentage of the third component is C%, 0.5 ≤ C ≤ 5. C can be any value from 0.5 to 5, or any range between two values, such as 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any range from 1 to 4, 1.5 to 3.5, 2 to 3. By controlling C within the range of 0.5 to 5, on the one hand, the third component has a sufficient content to fully utilize its preferential film-forming characteristics, facilitating the formation of a uniform and dense CEI film in the thinning region 14. This reduces the problems of excessive film thickness and increased impedance caused by electrolyte enrichment, thereby improving the lithium-ion insertion / extraction efficiency. On the other hand, it facilitates the coordination of sulfonyl functional groups with transition metals, effectively suppressing the dissolution of transition metals caused by the exposure of the active surface during the grooving process, reducing side reactions, and further improving the cycle stability of the secondary battery 1000.

[0091] Secondly, this application also proposes an electronic device, including a secondary battery 1000 as described in any embodiment of the first aspect above. The electronic device involved in the embodiments of this application is not particularly limited and can be any electronic device known in the prior art. For example, electronic devices include, but are not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys encompass fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0092] The following examples and comparative examples illustrate the implementation of this application in more detail. Various tests and evaluations are performed as examples according to the methods described below; other test methods known in the art may also be used. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0093] Example 1-1: <Preparation of the positive electrode> Lithium cobalt oxide, carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97.3:1.2:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%, which was then stirred evenly. A 10 μm thick aluminum foil was used as the positive electrode current collector. The above positive electrode slurry was coated onto one surface of the current collector in the thickness direction and dried to obtain a first positive electrode material layer. This process was repeated on the other surface to obtain a second positive electrode material layer, resulting in a positive electrode sheet with double-sided coatings. The sheet was then cold-pressed. The positive electrode sheet had a length of 1024 mm, a width of 88 mm, and a single-sided positive electrode material layer thickness H of 40 μm.

[0094] <Preparation of Negative Electrode Sheets> Artificial graphite (negative electrode material), conductive carbon black (Super P) (conductive agent), and styrene-acrylic rubber (binder) were mixed at a mass ratio of 97.5:1:1.5. Deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 70 wt%, and the mixture was stirred evenly. A copper foil with a thickness of 6 μm was selected as the negative electrode current collector. The above negative electrode slurry was coated on the surface of the negative electrode current collector and dried to obtain a first negative electrode material layer. The above steps were then repeated on the other surface to obtain a second negative electrode material layer, thus obtaining a negative electrode sheet with negative electrode material layers coated on both sides. The sheet was then cold-pressed. The length of the negative electrode sheet was 1075 mm, the width was 90.2 mm, and the thickness of the negative electrode material layer on one side was 51 μm.

[0095] <Preparation of the separating membrane> A porous polyethylene membrane is used as the substrate layer, and a ceramic layer containing alumina ceramic and polyacrylic acid adhesive is coated on one side of the substrate layer to form a release membrane (mass ratio of 7:3).

[0096] <Electrolyte Preparation> In a dry argon atmosphere, dimethyl carbonate and diethyl carbonate are mixed at a mass ratio of 1:1 to obtain an organic solvent. Lithium hexafluorophosphate is then added to the organic solvent, dissolved, and mixed thoroughly to obtain an electrolyte with a lithium salt concentration of 1.0 mol / L. The electrolyte contains a first component (ethyl difluorophosphate) and a second component (ethylene carbonate). Based on the total mass of the electrolyte, the mass percentage of the first component (A%) is 50%, the mass percentage of the second component (B%) is 20%, and the remainder is the organic solvent.

[0097] <Preparation of Lithium-ion Batteries> A first groove is created on the first negative electrode material layer using laser cleaning technology to expose the negative electrode current collector. An 80 μm thick nickel sheet is used as the negative electrode tab, which is welded to the negative electrode current collector within the first groove. A second groove is created on the first positive electrode material layer using laser cleaning technology, with a thinning region reserved within the second groove. The surface roughness of the thinning region is R μm, where R=8. Along the width direction of the positive electrode sheet (second direction), the positive electrode current collector includes a first edge, and the thinning region extends to the first edge, with the thickness of the thinning region gradually decreasing. (Refer to...) Figure 5 At the first edge, the thickness of the thinned region is T. a μm, T a =2.5. Along the width direction (second direction) of the positive electrode sheet, the thinning region is divided into a first segment and a second segment of equal width. The average thickness of the first segment is T1 μm, T1 = 6.5; the average thickness of the second segment is T2 μm, T2 = 15; T1 <T2。

[0098] A first insulating layer made of polyimide, with a thickness of 15 μm, is bonded to the first positive electrode material layer, and a portion of the first insulating layer is located within the second groove. A second insulating layer made of polyimide, with a thickness of 15 μm, is bonded to the first negative electrode material layer, and the second insulating layer covers the first groove. The first insulating layer includes a first extension extending from the first edge of the positive electrode sheet, the first extension extending beyond the first edge by a length L. a mm, L a =1; The thinning region includes a first region covered by the first insulating layer, the maximum thickness of the first region includes a first position, and the thickness of the thinning region at the first position is H1μm, H1=20.

[0099] A flat electrode assembly is obtained by stacking and winding a separator, a negative electrode sheet, a separator, and a positive electrode sheet. On one side of the negative electrode sheet in the width direction (second direction), the negative electrode sheet includes an overhang extending beyond the positive electrode sheet, with a width of 1 mm. The negative electrode tab is located on a straight section of the negative electrode sheet, which is the first negative electrode section. A straight section of the positive electrode sheet is positioned opposite the first negative electrode section, and this straight section is the first positive electrode section. On the other side of the first positive electrode section, a straight section of the negative electrode sheet is the second negative electrode section. (See reference...) Figure 5 .

[0100] Specifically, along the thickness direction of the positive electrode sheet (first direction), within the projection range of the first positive electrode segment, the orthogonal projection of the first groove lies within the orthogonal projection range of the first insulating layer. (See reference...) Figure 7 At the end furthest from the first edge, the first insulating layer extends beyond the second insulating layer by a length of W. a mm, W a =3; Along the third direction, on one side of the first insulating layer, the length of the first insulating layer extending beyond the second insulating layer is L1mm, L1=3; Along the third direction, on the other side of the first insulating layer, the length of the first insulating layer extending beyond the second insulating layer is L2mm, L2=3; Along the second direction, the second groove includes a second edge disposed opposite to the first edge; Along the second direction, the distance between the first insulating layer and the second edge is W1mm, W1=0.8; Along the third direction, the second groove includes a third edge and a fourth edge disposed opposite to each other; Along the third direction, the distance between the first insulating layer and the third edge is L3mm, L3=1; The distance between the first insulating layer and the fourth edge is L4mm; L4=1; After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, capacity testing, degassing, and edge trimming, a lithium-ion battery is obtained.

[0101] Test methods The lithium plating test method for the second negative electrode section is as follows: Under full charge conditions, disassemble a lithium-ion battery that has undergone 500 cycles and observe the second negative electrode section under a microscope. The appearance of silvery-gray to white on the surface of the transition area of ​​the second negative electrode section indicates lithium plating. Calculate the percentage of the area of ​​the transition area occupied by the lithium plating part. Less than 1% indicates no lithium plating, more than 1% to 8% indicates slight lithium plating, more than 8% to 15% indicates moderate lithium plating, and more than 15% indicates severe lithium plating.

[0102] The lithium plating test method at the first groove: Under full charge conditions, disassemble a lithium-ion battery that has undergone 500 cycles and observe the area near the second groove with a microscope. The appearance of silvery-gray white on the surface of the area 1mm away from the second groove (around the second groove) indicates lithium plating. Calculate the percentage of the area of ​​the lithium plating part in the transition area. Less than 1% indicates no lithium plating, 1% to 8% indicates slight lithium plating, more than 8% to 15% indicates moderate lithium plating, and more than 15% indicates severe lithium plating.

[0103] Energy density test method: Charge the lithium-ion battery to the cutoff voltage (4.55V for example) with a constant current of 0.5C, then charge the lithium-ion battery to 0.05C with a constant voltage of 4.55V, let it stand, and then discharge the lithium-ion battery to 3V with a constant current of 0.2C, let it stand, and record the discharge energy E; measure the length, width and thickness of the lithium-ion battery, and calculate its volume V; then the energy density W=E / V.

[0104] The lithium-ion battery used as an example in this application has a charging cut-off voltage of 4.55V and a discharging cut-off voltage of 3.0V. The charging and discharging cut-off voltages of the lithium-ion battery can be based on the printing on the outer packaging of the battery at the factory, and the charging and discharging current values ​​of the lithium-ion battery can be calculated based on the rated capacity printed on the outer packaging and the multiplier specified in this application's specification.

[0105] The drop test method is as follows: 1. Charge the lithium-ion battery to 100% SOC under ambient conditions of 25±5℃; 2. Place the lithium-ion battery into the drop tester and drop it from a height of 0.5m at a speed of 7 revolutions / min for 200 revolutions (2 drops count as 1 revolution); 3. If the lithium-ion battery does not catch fire, explode, smoke, or leak after the drop, and the voltage drop is less than 100mV, then the lithium-ion battery passes the drop test. Each group of 20 batteries is tested, and the number of batteries that pass the test is N1, with a pass rate of N1 / 20.

[0106] Cycle capacity retention test method: The cycle performance of lithium-ion batteries is evaluated by measuring the capacity retention rate at 25℃. The test procedure is as follows: The lithium-ion battery is placed in a 25℃ constant temperature chamber and allowed to stand for 30 minutes. The lithium-ion battery is then charged at a constant current of 2.1C to a voltage of 4.3V, then charged at a constant current of 1.3C to 4.45V, then at a constant current of 0.5C to 4.55V, and finally charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, it is discharged at 0.5C to 3.0V. This constitutes one charge-discharge cycle. The initial discharge capacity is recorded as C1. The charge-discharge cycle is repeated 500 times. The test is then stopped, and the discharge capacity of the 500th cycle is recorded as C2. The cycle capacity retention rate (%) of the lithium-ion battery is calculated as C2 / C1 × 100%.

[0107] The average thickness measurement method for the first and second sections (T1, T2): The cross-sections of the first and second sections of the electrode were prepared by ion beam profile grinding (CP). The thickness of the first and second sections of the electrode was measured by scanning electron microscopy (SEM, model ZEISS Sigma / X-max). Along the width direction of the positive electrode, five equal division points were taken in the first and second sections respectively, and the average thickness at the five division points was calculated to obtain T1 and T2.

[0108] Method for measuring the roughness (R) of the thinned region: The surface roughness R of the thinned region can be measured using a surface roughness measuring instrument. After removing the surface adhesive paper from the obtained positive electrode sheet, clean it with DMC to remove oil, dust, and other impurities. Use a roughness measuring instrument (e.g., Keyence VR6000) to measure the roughness of the thinned region. Place the probe perpendicular to the workpiece surface and slowly move the probe. The instrument automatically records the surface profile. The sampling length is 2 mm. Randomly select 16 points and calculate the sum of the absolute values ​​of the maximum profile peak height and the maximum profile valley depth. Average the sum to obtain the R value.

[0109] The method for testing the mass percentage of each component in the electrolyte is as follows: Pure electrolyte components are calibrated by gas chromatography (GC) as a reference. Subsequently, the sample electrolyte extracted from the battery is measured by GC. Separation is performed by utilizing the difference in solvent volatility. Quantification is performed by flame ionization detector (FID). By comparing the data with that of pure substances, the mass percentage of each substance in the electrolyte can be obtained.

[0110] Comparative Examples 1-1 to 1-3 are set according to Example 1-1, and the adjustment parameters are shown in Table 1 below.

[0111] Table 1

[0112] According to Table 1 above, in combination with Example 1-1 and Comparative Examples 1-1 to 1-2, it can be seen that by setting the second groove and forming a thinning region and defining T1 < T2, the lithium plating phenomenon of the second negative electrode segment can be effectively reduced while ensuring the high energy density of the lithium-ion battery. The thinning region adopts a gradient design of T1 < T2. On the one hand, sufficient positive electrode material is retained in the second segment far from the first edge to meet the requirements of the lithium-ion battery for high energy density; on the other hand, the thickness of the positive electrode material layer is reduced in the first segment close to the first edge, reducing the amount of lithium ions脱出 in this region and alleviating the problem of lithium ions migrating and enriching across the positive electrode current collector to the second negative electrode segment, thereby reducing the risk of lithium plating.

[0113] Examples 2-1 to 2-14 are set according to Example 1-1, and the adjusted parameters are shown in Table 2 below.

[0114] Table 2

[0115] According to Table 2 above, in combination with Examples 2-1 to 2-14 and Example 1-1, it can be seen that the thickness T a (μm) of the thinning region near the first edge, the length L a (mm) of the first insulating layer extension, and the surface roughness R (μm) of the thinning region will affect the degree of lithium plating, energy density, and passing rate of the drop test of the second negative electrode segment.

[0116] In combination with Examples 2-1 to 2-6 and Example 1-1, it can be seen that when the thickness T a of the thinning region near the first edge satisfies 0.5 ≤ T a ≤ 5 (Examples 2-2 to 2-5, 1-1), the lithium plating phenomenon of the second negative electrode segment can be effectively inhibited, while ensuring the stable energy density of the secondary battery and maintaining a high passing rate of the drop test; within this range, an appropriate amount of positive electrode material can be retained in the first edge region to maintain structural stability, and the amount of lithium ions脱出 in this region can be controlled within a reasonable range, reducing cross-collector migration and enrichment. Further, in Examples 2-3 to 2-4 and Example 1-1, the degree of lithium plating is further reduced, and the energy density and passing rate of the drop test are further improved. Therefore, further select 1 ≤ T a ≤ 4.

[0117] In combination with Examples 2-7 to 2-10 and Example 1-1, it can be seen that when the length L a of the first insulating layer extension satisfies 0.5 ≤ L aWhen the value is ≤1.5 (Examples 2-8 to 2-9, 1-1), lithium plating in the second negative electrode section can be suppressed, while ensuring a high drop test pass rate. Within this range, the extension can block lithium ions from leaving the edge area, thereby reducing the risk of lithium plating. It can also reduce interference with the casing due to excessive extension, thereby improving the drop resistance of the lithium-ion battery.

[0118] As can be seen from Examples 2-11 to 2-14 and Example 1-1, when the surface roughness R of the thinned region satisfies 2≤R≤15 (Examples 2-12 to 2-13, 1-1), the lithium plating phenomenon in the second negative electrode section can be effectively suppressed, and a high drop test pass rate can be maintained. Within this range, the thinned region and the first insulating layer can be mechanically anchored by the appropriate surface roughness, which can improve the bonding strength between the two and reduce the risk of the insulating layer falling off. At the same time, the electrolyte can be reduced from penetrating into the rough surface, thereby suppressing the swelling of the first insulating layer, the dissolution of cobalt ions and the generation of hard by-products, and enhancing the stability of the bonding interface.

[0119] Examples 3-1 to 3-4 are set with reference to Example 1-1, and the adjustment parameters are shown in Table 3 below.

[0120] Table 3

[0121] According to Table 3 above, and in conjunction with Examples 3-1 to 3-4 and Example 1-1, the ratio H1 / H of the maximum thickness H1 (μm) of the first region covered by the first insulating layer in the thinning region to the total thickness H (μm) of the first positive electrode material layer affects the lithium plating control effect and energy density performance of the lithium-ion battery. When 0.25≤H1 / H≤0.75 is satisfied (Examples 3-2 to 3-3, 1-1), it can effectively adapt to the thickness requirements of the first insulating layer and ensure that sufficient positive electrode material is retained in the thinning region: H1 / H directly determines the accommodation space of the first insulating layer in the second groove and the degree of retention of positive electrode material. Within this range, it can provide a stable bonding space for the first insulating layer, reduce its protrusion from the positive electrode material layer due to its large thickness, thereby reducing the interface gap and reducing the risk of lithium plating, and also reduce the excessive thinning of the positive electrode material layer, thereby ensuring the energy density of the lithium-ion battery.

[0122] Examples 4-1 to 4-16 are set with reference to Example 1-1, and the adjustment parameters are shown in Table 4 below.

[0123] Table 4

[0124] According to Table 4 above, and in conjunction with Examples 4-1 to 4-16 and Example 1-1, it can be seen that the length W of the first insulating layer exceeding the second insulating layer is... aThe lengths L1 (mm) and L2 (mm) of the first insulating layer extending beyond the second insulating layer on both sides along the third direction, the distance W1 (mm) between the first insulating layer and the second edge, and the distances L3 (mm) and L4 (mm) between the first insulating layer and the third and fourth edges will affect the degree of lithium plating and energy density at the first groove of the lithium-ion battery.

[0125] Combining Examples 4-1 to 4-4 with Example 1-1, it can be seen that when W a Satisfying 2≤W a When the value is ≤5 (Examples 4-2 to 4-3 and 1-1), the first insulating layer can effectively cover the second groove in the second direction. This can form a continuous insulating barrier between the first positive electrode section and the negative electrode tab, reducing the abnormal migration of lithium ions to the negative electrode tab region. It can also reduce the ineffective occupation of positive electrode material due to excessive extension, so that the insulating protection effect and energy density are maintained in a good balance. At the same time, this coverage range can also help reduce the risk of lithium plating at the first groove.

[0126] As can be seen from Examples 4-5 to 4-8 and Example 1-1, when L1 satisfies 2≤L1≤5 and L2 satisfies 2≤L2≤5 (Examples 4-6 to 4-7 and 1-1), the first insulating layer can fully cover the second insulating layer on both sides in the third direction. This not only enhances the ability to resist misalignment risks during winding and ensures stable insulation protection, but also reasonably controls space occupation, reduces ineffective loss of positive electrode material, and achieves a good balance between insulation protection and energy density. At the same time, this coverage area can also effectively reduce abnormal lithium ion accumulation at the first groove and help improve the lithium plating control effect.

[0127] As can be seen from Examples 4-9 to 4-12 and Example 1-1, when W1 satisfies 0.5≤W1≤1 (Examples 4-10 to 4-11 and 1-1), in the second direction, it is beneficial to adapt the gap between the second groove and the first insulating layer to the accuracy deviation of the adhesive application process. This can not only improve the bonding stability of the first insulating layer and reduce the impact of adhesive application deviation on the protective effect, but also reduce the amount of lithium stripping in local areas. At the same time, it can reasonably control the loss of the cathode material and achieve synergistic optimization of lithium plating protection and energy density.

[0128] Combining Examples 4-13 to 4-16 with Example 1-1, it can be seen that when L3 satisfies 0.5≤L3≤1.5 and L4 satisfies 0.5≤L4≤1.5 (Examples 4-14 to 4-15 and 1-1), in the third direction, the gap between the second groove and the first insulating layer can balance the adhesive application accuracy and material utilization. This can not only improve the bonding stability of the first insulating layer and ensure continuous insulation protection, but also reduce the ineffective waste of positive electrode materials. At the same time, it can help reduce the risk of lithium ion accumulation at the first groove, and achieve synergistic optimization of lithium plating protection and energy density.

[0129] In addition, W a The synergistic effect of L1, L2, W1, L3, and L4 can further optimize the performance of lithium-ion batteries: the reasonable range of each parameter is coordinated with each other (as in Example 1-1), which not only ensures the insulation protection effect and bonding stability of the first insulating layer, but also reduces the excessive loss of the positive electrode material, thus achieving a dual balance between lithium plating control and energy density.

[0130] Examples 5-1 to 5-16 are set up with reference to Example 1-1, and the control parameters are shown in Table 5 below. In Examples 5-1 to 5-6, the second and third components are not added. In Examples 5-7 to 5-11, the second component is added, and its mass percentage is B%, with the value of B shown in Table 5 below. In Examples 5-12 to 5-16, the second and third components are added, and the mass percentage of the third component is C%, with the value of C shown in Table 5 below.

[0131] Table 5

[0132] According to Table 5 above, and in conjunction with Examples 5-1 to 5-16 and Example 1-1, it can be seen that the content A (%) of the first component, the ratio A / B of the first component to the second component, and the content C (%) of the third component in the electrolyte will affect the degree of lithium plating at the first groove and the cycle capacity retention rate.

[0133] As can be seen from Examples 5-1 to 5-6, when the content A of the first component satisfies 10 ≤ A ≤ 60 (Examples 5-2 to 5-4, 5-6), a continuous and dense fluorine-containing protective layer can be formed on the surface of the broken positive electrode particles in the first groove region. This protective layer can effectively suppress the side reactions caused by slotting, reduce the abnormal accumulation of lithium ions in the first groove, and reduce the enrichment of fluorinated products at the bonding interface between the first insulating layer and the thinned region due to excessive content, thereby maintaining the interface bonding strength and reducing the risk of lithium ions escaping from the interface gap. This content range allows for a good balance between lithium plating control and cycle capacity retention.

[0134] As can be seen from Examples 5-7 to 5-11 and Example 1-1, when the ratio A / B of the first component to the second component satisfies 0.5 ≤ A / B ≤ 5 (Examples 5-8 to 5-9, 1-1, 5-11), the two components can form a good synergy. The second component participates in lithium-ion solvation, reducing the proportion of the first component in the solvated structure and reducing the excessive decomposition of the first component at the interface, thereby optimizing the lithium-ion transport path and reducing lithium-ion enrichment at the first groove. At the same time, this ratio range can maintain a suitable viscosity of the electrolyte, ensure lithium-ion transport efficiency, and achieve synergistic enhancement of side reaction suppression, interfacial adhesion performance, and kinetic performance.

[0135] As demonstrated in Examples 5-12 to 5-16, when the content C of the third component satisfies 0.5 ≤ C ≤ 5 (Examples 5-13 to 5-15), a uniform and dense CEI film can be formed in the thinned region, suppressing the problems of uneven film thickness and increased impedance caused by electrolyte enrichment. Its sulfonyl functional groups can also coordinate with transition metals, effectively suppressing the dissolution of transition metals initiated by the exposed active surface and reducing the occurrence of side reactions. This content range can further improve cycle capacity retention while reducing lithium plating.

[0136] Furthermore, the synergistic effect of the content of the first component A, the ratio A / B, and the content of the third component C can further optimize the performance of lithium-ion batteries. When the parameters are within a reasonable range and cooperate with each other (as in Examples 5-14), the risk of lithium plating is suppressed by the protective effect of the first component, the cycle capacity retention rate is improved by the compatibility between the components, and side reactions are reduced, thus achieving a dual balance between lithium plating control and cycle performance.

[0137] Examples 6-1 to 6-4 are set with reference to Example 1-1, and the adjustment parameters are shown in Table 6 below.

[0138] Table 6

[0139] As can be seen from Examples 6-1 to 6-4 and Example 1-1, when the charging cut-off voltage G of the secondary battery satisfies 4.55≤G≤4.65V (Examples 6-2 to 6-3, 1-1), the degree of lithium plating at the first groove can be reduced while taking into account the cycle capacity retention rate and energy density requirements of the secondary battery. Within this range, the synergistic structural design of the first insulating layer, the second groove, and the thinning region in this application can be used to alleviate the problem of excessive lithium ion extraction from the positive electrode and migration to the negative electrode under high voltage, suppress the risk of lithium plating near the first groove, and also to stimulate a greater amount of lithium removal from the positive electrode material layer through high voltage, thereby improving the energy density of the secondary battery.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A secondary battery, comprising a negative electrode tab and a positive electrode sheet, a separator, and a negative electrode sheet stacked and wound together, wherein the positive electrode sheet includes a first positive electrode segment, and the negative electrode sheet includes a first negative electrode segment and a second negative electrode segment, the first negative electrode segment and the second negative electrode segment being located on opposite sides of the thickness direction of the first positive electrode segment; the positive electrode sheet includes a positive current collector and a first positive electrode material layer disposed on the surface of the positive current collector; the negative electrode sheet includes a negative current collector and a first negative electrode material layer, the first negative electrode material layer being disposed on the surface of the negative current collector facing the first positive electrode material layer; in the first negative electrode segment, the first negative electrode material layer is provided with a first groove, the first groove exposing the negative current collector; a portion of the negative electrode tab is electrically connected to the negative current collector within the first groove, and another portion of the negative electrode tab extends out of the negative electrode sheet; characterized in that... In the first positive electrode segment, a second groove is provided on the surface of the first positive electrode material layer facing the first groove; The first positive electrode material layer includes a thinning region. Along a first direction, a portion of the first positive electrode material layer located between the positive electrode current collector and the second groove forms the thinning region; the first direction is the thickness direction of the first positive electrode segment at the second groove; The thinning region includes a first section and a second section. Along a second direction, the second section and the first section are arranged in sequence; along the first direction, the average thickness of the first section is T1 μm, and the average thickness of the second section is T2 μm, where T1 < T2; the second direction is the direction in which the negative electrode tab extends out of the negative electrode sheet; The secondary battery further includes a first insulating layer, and the first insulating layer is disposed in the second groove; along the first direction, within the projection range of the first positive electrode segment, the orthogonal projection of the first groove is within the orthogonal projection range of the first insulating layer.

2. The secondary battery according to claim 1, characterized in that, Along the second direction, the thickness of the thinning region gradually decreases.

3. The secondary battery according to claim 1, characterized in that, Along the second direction, the first positive electrode material layer includes a first edge, and the thinning region extends to the first edge; at the first edge, the thickness of the thinning region is T. a μm, 0.5≤T a ≤5.

4. The secondary battery according to claim 3, characterized in that, 1≤T a ≤4。 5. The secondary battery according to claim 3, characterized in that, The secondary battery further includes a second insulating layer, and the second insulating layer is disposed on the first negative electrode material layer. Along the first direction, the second insulating layer covers the first groove; Along the second direction, at the end furthest from the first edge, the first insulating layer extends beyond the second insulating layer by a length W. a mm, 2≤W a ≤5; Along a third direction, on one side of the first insulating layer, the length by which the first insulating layer extends beyond the second insulating layer is L1 mm, where 2 ≤ L1 ≤ 5; along the third direction, on the other side of the first insulating layer, the length by which the first insulating layer extends beyond the second insulating layer is L2 mm, where 2 ≤ L2 ≤ 5; The first direction, the second direction, and the third direction are perpendicular to each other pairwise.

6. The secondary battery according to any one of claims 3 to 5, wherein Along the second direction, the second groove includes a second edge opposite to the first edge; along the second direction, the distance between the first insulating layer and the second edge is W1 mm, where 0.5 ≤ W1 ≤ 1; Along the third direction, the second groove includes a third edge and a fourth edge that are oppositely arranged. Along the third direction, the distance between the first insulating layer and the third edge is L3 mm, and the distance between the first insulating layer and the fourth edge is L4 mm; 0.5 ≤ L3 ≤ 1.5, and / or, 0.5 ≤ L4 ≤ 1.5; The first direction, the second direction, and the third direction are perpendicular to each other pairwise.

7. The secondary battery according to claim 3, characterized in that, The first insulating layer further includes a first extension extending from the first edge of the positive electrode sheet, the first extension extending beyond the first edge by a length L. a mm, 0.5≤L a ≤1.

5.

8. The secondary battery according to claim 1, wherein Along the first direction, the thickness of the first positive electrode material layer is H μm; At one end in the opposite direction of the second direction, the first insulating layer includes a fifth edge. Along the first direction, the thinning region includes a first position whose orthogonal projection overlaps with the orthogonal projection of the fifth edge; Along the first direction, the thinning region includes a first region covered by the first insulating layer. The maximum thickness of the first region includes the first position; the thickness of the thinning region at the first position is H1 μm, where 0.25 ≤ H1 / H ≤ 0.

75.

9. The secondary battery according to claim 8, characterized in that, The first positive electrode material layer includes a first surface facing the first negative electrode material layer, and the first insulating layer does not protrude from the first surface.

10. The secondary battery according to claim 1, characterized in that, The surface roughness of the thinned region is R μm, where 2≤R≤15.

11. The secondary battery according to claim 1, characterized in that, The first negative electrode material layer includes a first portion; along the second direction, the first negative electrode material layer includes a sixth edge, and the portion of the first negative electrode material layer located between the sixth edge and the first groove forms the first portion; Along the first direction, the negative electrode tab covers at least a portion of the first portion.

12. The secondary battery according to claim 1, characterized in that, The secondary battery also includes a positive electrode tab and a third insulating layer; The first positive electrode material layer is provided with a third groove, which exposes the positive electrode current collector. A portion of the positive electrode tab is electrically connected to the positive electrode current collector within the third groove, and another portion of the positive electrode tab extends out of the positive electrode sheet. The third insulating layer is disposed on the first positive electrode material layer, and along the first direction, the first positive electrode material layer covers the third groove. The first positive electrode material layer also includes a first covering area covered by the third insulating layer, and the thickness of the first covering area decreases sequentially along the second direction.

13. The secondary battery according to claim 1, characterized in that, The secondary battery further includes a first adhesive layer, which is disposed between the negative electrode tab and the negative electrode current collector; The first negative electrode segment further includes a second negative electrode material layer, which is disposed on the surface of the negative electrode current collector that is away from the first negative electrode material layer. The second negative electrode material layer includes a second portion; along the first direction, the orthogonal projection of the second portion overlaps with the orthogonal projection of the first groove.

14. The secondary battery according to claim 1, characterized in that, The secondary battery further includes an electrolyte, which includes a first component selected from at least one of 2,2-difluoroethyl acetate, ethyl difluoroacetate, and 2-fluoroethyl fluoroacetate. Based on the total mass of the electrolyte, the mass percentage of the first component is A%, 10≤A≤60.

15. The secondary battery according to claim 14, characterized in that, The electrolyte further includes a second component, which is selected from at least one of ethylene carbonate and propylene carbonate. Based on the total mass of the electrolyte, the mass percentage of the first component is B%, and 0.5 ≤ A / B ≤ 5.

16. The secondary battery according to any one of claims 1 to 15, characterized in that, The electrolyte also includes a third component, which is selected from at least one of the following compounds of formula I-1 to I-6; Based on the total mass of the electrolyte, the mass percentage of the third component is C%, 0.5≤C≤5.

17. The secondary battery according to any one of claims 1 to 16, characterized in that, The charging cutoff voltage of the secondary battery is GV, where 4.55≤G≤4.

65.

18. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 17.

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