Secondary battery, method of manufacturing the same, and electronic device

Abstract

The application discloses a secondary battery, a preparation method thereof and an electronic device. The secondary battery comprises an electrode assembly. The electrode assembly comprises a plurality of positive electrode sheets and a plurality of positive electrode tabs. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged in a stack. The positive electrode sheet comprises a first positive electrode edge. The positive electrode tab is formed by extending the positive electrode current collector from the first positive electrode edge. The positive electrode sheet comprises a positive electrode empty foil area. The surface of the positive electrode current collector of the positive electrode empty foil area is not provided with the positive electrode active material layer. The extension direction of the positive electrode tab is a positive electrode direction. The positive electrode empty foil area extends to the first positive electrode edge along the positive electrode direction. The positive electrode empty foil area and the positive electrode tab at least partially overlap along the positive electrode direction.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery, its preparation method, and an electronic device thereof. Background Technology

[0002] Lithium-ion batteries are widely used in mobile and portable electronic devices due to their high energy density, high average open-circuit voltage, and long cycle life. As electronic products become increasingly miniaturized and multifunctional, the requirements for the energy density and safety performance of lithium-ion batteries are also rising. Lithium-ion batteries consist of electrode components. The width and length of the positive electrode are typically shorter than the negative electrode to reduce the risk of lithium plating at the edges of the negative electrode. During the manufacturing process of the electrode components, misalignment may occur between the edges of the negative and positive electrodes. For example, tolerances can cause misalignment at the edges of the active material layers coated on both sides of the current collector, leading to misalignment between the negative and positive electrodes. Alternatively, when multiple die-cut tabs are bent and welded to the electrode terminals, the tabs can pull on the electrodes, causing misalignment between the edges of the negative and positive electrodes. In this case, it is usually necessary to increase the edge region of the negative electrode that extends beyond the positive electrode (also known as the overhang region) to reduce the risk of lithium plating due to insufficient negative electrode margin caused by the misalignment of the negative electrode edge. However, this will result in a significant loss of energy density. Summary of the Invention

[0003] One objective of this application is to provide a secondary battery, a method for its preparation, and an electronic device thereof that can reduce the risk of lithium plating at the edge of the negative electrode and improve energy density.

[0004] This application provides a secondary battery, including an electrode assembly. The electrode assembly includes a plurality of positive electrode sheets and a plurality of positive electrode tabs. The positive electrode sheets include a positive current collector and a positive active material layer stacked together. The positive electrode sheet includes a first positive electrode edge, and the positive electrode tabs are formed by the positive current collector extending from the first positive electrode edge. The positive electrode sheet includes a positive electrode empty foil region, and the surface of the positive current collector in the positive electrode empty foil region is not provided with a positive active material layer. The extension direction of the positive electrode tabs is a first direction, and the positive electrode empty foil region extends to the first positive electrode edge along the first direction. Viewed along the first direction, the positive electrode empty foil region and the positive electrode tabs at least partially overlap.

[0005] In this application, the positive electrode sheet is configured with a positive electrode empty foil region, and the positive electrode empty foil region partially overlaps with the positive electrode tab along the first direction. This allows the positive electrode empty foil region to directly draw the current generated by the positive electrode sheet to the positive electrode tab, thus functioning as the positive electrode tab. The presence of the positive electrode empty foil region increases the CB value at that location, thereby reducing the risk of lithium plating at the edge of the negative electrode sheet located on the side with the positive electrode empty foil region due to insufficient negative electrode margin. Even if multiple positive electrode tabs are bent and connected to the electrode terminals, causing misalignment between the edges of the positive and negative electrode sheets, the presence of the positive electrode empty foil region makes it less likely for lithium plating to occur at the edge of the negative electrode sheet. This eliminates the need to increase the length of the negative electrode sheet extending beyond the positive electrode sheet along the first direction, thereby improving energy density.

[0006] According to some embodiments of this application, along the first direction, the positive electrode empty foil region includes a first edge opposite to the first positive electrode edge, and the distance between the first positive electrode edge and the first edge is L1, where 0 < L1 ≤ 2 mm. When L1 is within the above range, it is beneficial to keep the CB value at the first positive electrode edge greater than 1 when the negative electrode sheet does not extend sufficiently beyond the positive electrode sheet on the side where the first positive electrode edge is located due to misalignment, thereby reducing the risk of lithium plating at the edge of the negative electrode sheet; and the reduction in the positive electrode active material layer in the first direction due to the setting of the positive electrode empty foil region is limited, that is, the capacity loss is limited, and the impact on energy density is small. According to some embodiments of this application, along the width direction perpendicular to the first direction, the positive electrode tab includes a second edge and a third edge disposed opposite to each other, and the positive electrode empty foil region includes a fourth edge located on one side of the second edge and a fifth edge located on one side of the third edge. The fourth edge extends beyond the second edge by a distance of W1 mm, the fifth edge extends beyond the third edge by a distance of W2 mm, and the distance between the second edge and the third edge is W mm, where 0 ≤ W1 ≤ W / 2 and 0 ≤ W2 ≤ W / 2. When W1 and W2 are within the above ranges, the area of ​​the positive electrode empty foil region extending beyond the positive electrode tab in the width direction can distribute the impact force on the positive electrode tab when the secondary battery is dropped, reducing the risk of stress concentration points and tearing of the positive electrode tab, and improving drop performance; and the reduction in the positive electrode active material layer in the width direction due to the setting of the positive electrode empty foil region is limited, and the impact on energy density is small.

[0007] According to some embodiments of this application, the electrode assembly includes a negative electrode sheet. Along a first direction, the positive electrode sheet includes a second positive electrode edge opposite to the first positive electrode edge, and the negative electrode sheet includes a first negative electrode edge located on one side of the first positive electrode edge and a second negative electrode edge opposite to the first negative electrode edge. The distance by which the first negative electrode edge extends beyond the first positive electrode edge is L2. Along the opposite direction from the first direction, the distance by which the second negative electrode edge extends beyond the second positive electrode edge is L3, where 1 ≤ L2 / L3 ≤ 10. When L2 / L3 is within the above range, the risk of edge lithium plating due to misalignment of the edges of the positive and negative electrode sheets on one side of the tab can be reduced, and L2 can be controlled to avoid being too large, thus reducing the impact of L2 on energy density.

[0008] According to some embodiments of this application, 0.1 mm ≤ L2 ≤ 1 mm, and 0.1 mm ≤ L3 ≤ 0.50 mm. When L2 and L3 are within the above ranges, it is beneficial to reduce the risk of lithium plating at the edge of the first negative electrode and to improve the energy density.

[0009] According to some embodiments of this application, the secondary battery includes a first insulating member disposed on the surface of the positive electrode tab. The first insulating member includes an edge, which, when viewed along a thickness direction perpendicular to a first direction, partially overlaps with the edge of the first positive electrode. By configuring the first insulating member, the risk of short circuit due to contact between the positive electrode tab and the negative electrode can be reduced.

[0010] According to some embodiments of this application, the length of the first insulating member along the first direction is 0.2 mm to 2 mm. When the length of the first insulating member is within the above range, the first insulating member can effectively reduce the risk of short circuit between the positive electrode tab and the negative electrode plate, and the first insulating member has little impact on the energy density.

[0011] According to some embodiments of this application, the first insulating element is an insulating coating, which includes at least one of boehmite, alumina, silicon dioxide, and zirconium oxide.

[0012] According to some embodiments of this application, the secondary battery includes a second insulating member disposed on at least one side of the positive electrode plate and covering at least a portion of the positive electrode empty foil area. The second insulating member is used to isolate the positive electrode empty foil area and the negative electrode plate, reducing the risk of short circuit due to contact between the positive electrode empty foil area and the negative electrode plate.

[0013] According to some embodiments of this application, the second insulating member includes a first region covering the positive electrode active material layer. The width of the first region is 0.05 mm to 2 mm along a width direction perpendicular to the first direction. When the width of the first region is within the above range, the second insulating member can effectively isolate the positive electrode empty foil area and the negative electrode sheet along the width direction to reduce the risk of short circuits, and the second insulating member has a relatively small impact on energy density.

[0014] According to some embodiments of this application, the second insulating member includes a second region covering the first insulating member, and the length of the second region along the first direction is 0.05 mm to 2 mm. When the length of the second region is within the above range, the second insulating member can effectively isolate the positive electrode empty foil area and the negative electrode sheet along the first direction to reduce the risk of short circuit, and the second insulating member has little impact on energy density.

[0015] A second aspect of this application provides a method for preparing a secondary battery, comprising: setting an adhesive on the surface of a positive electrode current collector; performing gap coating on the surface of the positive electrode current collector and the surface of the adhesive to form a coated area and a blank area, wherein the surface of the positive electrode current collector in the coated area is coated with a positive electrode active material layer, and the surface of the positive electrode current collector in the blank area is not coated with a positive electrode active material layer; baking the positive electrode current collector after gap coating; removing the adhesive; and die-cutting the blank area to form a positive electrode sheet and a positive electrode tab, wherein the positive electrode sheet includes a first positive electrode edge, the positive electrode tab protrudes from the first positive electrode edge along a first direction, and the positive electrode sheet includes a positive electrode empty foil area without a positive electrode active material layer, wherein when viewed along the first direction, the positive electrode empty foil area and the positive electrode tab at least partially overlap.

[0016] According to some embodiments of this application, before the step of die-cutting the blank area, the method further includes: providing an insulating element in the blank area, wherein the insulating element is adjacent to the edge of the positive electrode active material layer of the coating area.

[0017] A third aspect of this application provides an electronic device comprising any of the aforementioned secondary batteries, or comprising a secondary battery prepared using any of the aforementioned secondary battery preparation methods. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the positive electrode sheet in one embodiment.

[0019] Figure 2 This is a cross-sectional schematic diagram of the positive electrode sheet in one embodiment.

[0020] Figure 3 This is a schematic diagram of the positive and negative electrode plates in one embodiment.

[0021] Figure 4This is a schematic diagram of the gap coating applied to the surface of the positive electrode current collector in one embodiment.

[0022] Figure 5 This is a schematic diagram of an embodiment where an insulating element is installed in the blank area.

[0023] Explanation of key component symbols: The following specific embodiments will further illustrate this application in conjunction with the above-described accompanying drawings. Detailed Implementation

[0024] The following specific embodiments are exemplary and not limiting, and are intended to provide a basic understanding of this application, and are not intended to identify key or decisive elements of this application or limit the scope of protection. As long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner.

[0025] When a component is considered "set on" another component, it can be directly set on the other component or may also be interspersed with other components. When a component is considered "connected to" another component, it can be directly connected to the other component or may also be interspersed with other components.

[0026] Unless otherwise defined, the term "multiple" in this document, when used to describe the number of components, specifically means that the component is two or more.

[0027] Some embodiments of this application will now be described with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0028] One embodiment of this application provides a secondary battery, including a casing, an electrode assembly housed within the casing, and electrode terminals connected to the electrode assembly and extending out of the casing. The electrode terminals are used for electrical connection to external components and include positive and negative terminals. The electrode assembly includes multiple positive electrode plates, multiple negative electrode plates, multiple separators, multiple positive electrode tabs, and multiple negative electrode tabs. Each separator is disposed between adjacent positive and negative electrode plates. The multiple positive electrode tabs are electrically connected to the multiple positive electrode plates, and the multiple negative electrode tabs are electrically connected to the multiple negative electrode plates. The electrode assembly is formed by alternately stacking multiple positive electrode plates, multiple separators, and multiple negative electrode plates. The multiple positive electrode tabs are bent and electrically connected to the positive terminal, and the multiple negative electrode tabs are bent and electrically connected to the negative terminal. Optionally, the casing is a metal casing or a packaging bag formed by encapsulation with an aluminum-plastic film, etc. Optionally, the separator material can be polypropylene or polyethylene, etc.

[0029] Please see Figure 1 and Figure 2 The positive electrode 10 includes a positive current collector 11 and a positive active material layer 12 stacked together. The positive active material layer 12 may be disposed on one surface or two opposite surfaces of the positive current collector 11. The positive electrode 10 includes a first positive edge 10A, and a positive electrode tab 20 is formed by extending the positive current collector 11 from the first positive edge 10A, and the positive electrode tab 20 is integrally disposed with the positive current collector 11. The positive electrode 10 includes a positive empty foil region 101, and the surface of the positive current collector 11 in the positive empty foil region 101 is not provided with the positive active material layer 12. Optionally, one surface or two opposite surfaces of the positive current collector 11 in the positive empty foil region 101 are not provided with the positive active material layer 12. In some embodiments, the positive active material layer 12 covers the entire surface of the positive current collector 11 in the positive electrode 10 except for the positive empty foil region 101. The extension direction of the positive electrode tab 20 is a first direction X. The positive electrode empty foil region 101 extends along a first direction to the first positive electrode edge 10A. Viewed along the first direction X, the positive electrode empty foil region 101 at least partially overlaps with the positive electrode tab 20. The overlapping portion between the positive electrode empty foil region 101 and the positive electrode tab 20 is directly connected. The current generated by the positive electrode sheet 10 can be led out through the positive electrode empty foil region 101 to the positive electrode tab 20; that is, the positive electrode empty foil region 101 can function as a tab. The provision of the positive electrode empty foil region 101 can increase the CB value at that location, thereby reducing the risk of lithium deposition due to insufficient negative electrode margin at the edge of the negative electrode sheet located on the side where the positive electrode empty foil region 101 is located. In this application, the CB value refers to the ratio between the capacity of a unit area of ​​the negative electrode sheet and the capacity of a unit area of ​​the positive electrode sheet under the same conditions, for example, at an ambient temperature of 25°C and a discharge rate of 0.1C. Furthermore, even if multiple positive electrode tabs 20 are bent and electrically connected to the positive terminal, causing misalignment between the edges of the positive electrode sheet 10 and the negative electrode sheet, due to the presence of the positive electrode empty foil region 101, the edge of the negative electrode sheet located on the side of the positive electrode empty foil region 101 is less likely to produce lithium plating due to insufficient negative electrode margin. Thus, it is not necessary to increase the length of the negative electrode sheet extending beyond the positive electrode sheet 10 along the first direction X, which is beneficial to improving energy density.

[0030] Along the first direction X, the positive electrode empty foil region 101 includes a first edge 101A opposite to the first positive electrode edge 10A, and the distance between the first positive electrode edge 10A and the first edge 101A is L1. In this application, L1 is the longest distance between the first positive electrode edge 10A and the first edge 101A. Optionally, along the first direction X, the distance between the first positive electrode edge 10A and the first edge 101A at various locations may be equal or unequal. In some embodiments, 0 < L1 ≤ 2 mm. Optionally, L1 is a range of 0.2 mm, 0.5 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, or any two of these values. When L1 is within the above range, if the negative electrode sheet is not long enough beyond the positive electrode sheet 10 on the side where the first positive electrode edge 10A is located due to misalignment, it is beneficial to keep the CB value at the edge of the negative electrode sheet greater than 1, thereby reducing the risk of lithium plating at the edge of the negative electrode sheet; and the reduction of the positive electrode active material layer 12 in the first direction X due to the setting of the positive electrode empty foil region 101 is limited, that is, the capacity loss is limited and the impact on energy density is small.

[0031] In some embodiments, the positive electrode current collector 11 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof. The positive electrode active material layer 12 includes a positive electrode active material, which may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium-rich manganese-based materials, lithium nickel cobalt aluminum oxide, and combinations thereof.

[0032] Please see Figure 1In some embodiments, along the first direction X, the orthographic projection of the positive electrode tab 20 lies within the orthographic projection of the positive electrode empty foil region 101, that is, along the width direction Y perpendicular to the first direction X, the width of the positive electrode empty foil region 101 is greater than or equal to the width of the positive electrode tab 20. Along the width direction Y, the positive electrode tab 20 includes a second edge 20B and a third edge 20C disposed opposite to each other. The positive electrode empty foil region 101 includes a fourth edge 101B located on one side of the second edge 20B and a fifth edge 101C located on one side of the third edge 20C. The fourth edge 101B extends beyond the second edge 20B by a distance of W1 mm, and the fifth edge 101C extends beyond the third edge 20C by a distance of W2 mm. The distance between the second edge 20B and the third edge 20C is W mm. In some embodiments, 0 ≤ W1 ≤ W / 2, 0 ≤ W2 ≤ W / 2. Optionally, W1 can be a range of 0.1W, 0.2W, 0.3W, 0.4W, 0.5W, or any two of these values. Optionally, W2 can be a range of 0.1W, 0.2W, 0.3W, 0.4W, 0.5W, or any two of these values. When W1 and W2 are within the above ranges, the area of ​​the positive electrode empty foil region 101 that extends beyond the positive electrode tab 20 in the width direction Y can distribute the impact force on the positive electrode tab 20 when the secondary battery is dropped, reducing the risk of stress concentration points and tearing of the positive electrode tab 20, thus improving drop performance; and the reduction in the positive electrode active material layer 12 in the width direction Y caused by the setting of the positive electrode empty foil region 101 is limited, and the impact on energy density is small.

[0033] Please see Figure 3 In some embodiments, the negative electrode sheet 30 includes a negative electrode current collector 31 and a negative electrode active material layer 32 stacked together. The negative electrode active material layer 32 may be disposed on one surface or two opposite surfaces of the negative electrode current collector 31. Along the first direction X, the negative electrode sheet 30 includes a first negative electrode edge 30A located on one side of the first positive electrode edge 10A. The negative electrode tab 40 is formed by the negative electrode current collector 31 extending from the first negative electrode edge 30A along the first direction X.

[0034] Along the first direction X, the positive electrode 10 includes a second positive electrode edge 10B opposite to the first positive electrode edge 10A, and the negative electrode 30 includes a second negative electrode edge 30B opposite to the first negative electrode edge 30A and located on one side of the second positive electrode edge 10B. Along the first direction X, the distance by which the first negative electrode edge 30A extends beyond the first positive electrode edge 10A is L2, where L2 > 0. Along the direction opposite to the first direction X, the distance by which the second negative electrode edge 30B extends beyond the second positive electrode edge 10B is L3, where L3 > 0. By configuring L2 and L3, the CB value at the first negative electrode edge 30A and the second negative electrode edge 30B can be maintained greater than 1, reducing the risk of lithium plating at both the first negative electrode edge 30A and the second negative electrode edge 30B.

[0035] Because the bending of multiple tabs and their connection to the electrode terminals pulls on the electrode sheets, the misalignment of the edges of the positive electrode 10 and the negative electrode 30 on one side of the tab may be greater than the misalignment of the edges of the positive electrode 10 and the negative electrode 30 on the opposite side of the tab. This makes the edge of the negative electrode 30 on the tab side more prone to lithium plating. Therefore, in some embodiments, 1 ≤ L2 / L3 ≤ 10. Optionally, L2 / L3 is a range of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or any two of these values. When L2 / L3 is within the above range, the risk of lithium plating due to the misalignment of the edges of the positive electrode 10 and the negative electrode 30 on one side of the tab can be reduced, and L2 can be controlled to avoid being too large, thus reducing the impact of L2 on energy density. Preferably, 1≤L2 / L3≤4, which helps reduce the risk of lithium plating at the edge 30A of the first negative electrode and has a smaller impact on energy density.

[0036] In some embodiments, 0.1 mm ≤ L2 ≤ 1 mm, and 0.1 mm ≤ L3 ≤ 0.5 mm. Optionally, L2 is a range of 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or any two of these values. Optionally, L3 is a range of 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or any two of these values. When L2 and L3 are within the above ranges, it is beneficial to reduce the risk of lithium plating at the edge 30A of the first negative electrode, and the impact on energy density is relatively small.

[0037] In some embodiments, the negative electrode current collector 31 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof. The negative electrode active material layer 32 includes a negative electrode active material, which may include one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxides, silicon-carbon composites, lithium titanate, and metals capable of forming alloys with lithium.

[0038] Please see Figure 3 In some embodiments, the secondary battery includes a first insulating member 50 disposed on the surface of the positive electrode tab 20. The first insulating member 50 includes an insulating edge 50A. Viewed along the thickness direction Z perpendicular to the first direction, the insulating edge 50A partially overlaps with the first positive electrode edge 10A. Optionally, the first insulating member 50 covers the surface of the positive electrode tab 20 by coating. By configuring the first insulating member 50, the risk of short circuit due to contact between the positive electrode tab 20 and the negative electrode 30 can be reduced.

[0039] In some embodiments, the first insulating element 50 is an insulating coating comprising ceramic particles and an adhesive. Optionally, the ceramic particles include at least one selected from boehmite, alumina, silicon dioxide, and zirconium oxide. These ceramic particles can increase the strength of the first insulating element 50 and reduce the risk of short circuits due to punctures. Optionally, the adhesive includes at least one selected from epoxy resin, acrylate, styrene-butadiene rubber, polytetrafluoroethylene, and polyvinylidene fluoride. These adhesives have strong adhesion, ensuring good adhesion between the first insulating element 50 and the positive electrode tab 20, reducing the risk of the first insulating element 50 detaching.

[0040] In some embodiments, the length of the first insulating member 50 along the first direction X is 0.2 mm to 2 mm. When the length of the first insulating member 50 is within the above range, the first insulating member 50 can effectively reduce the risk of short circuit between the positive electrode tab 20 and the negative electrode plate 30, and the first insulating member 50 has little impact on the energy density.

[0041] Please see Figure 3 In some embodiments, the secondary battery includes a second insulating member 60, which is disposed on at least one side of the positive electrode 10 and covers at least a portion of the positive electrode empty foil region 101. Optionally, the second insulating member 60 is bonded to the surface of the positive electrode current collector 11 in the positive electrode empty foil region 101. Optionally, the second insulating member 60 is bonded to the surface of the positive electrode active material layer 12 opposite to the surface of the positive electrode current collector 11. Optionally, the second insulating member 60 covers the entire positive electrode empty foil region 101. The second insulating member 60 includes an insulating material, which may be selected from at least one of polyethylene, polypropylene, phenolic resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, or polyurethane. The second insulating member 60 is used to isolate the positive electrode empty foil region 101 and the negative electrode 30, reducing the risk of short circuit between the positive electrode empty foil region 101 and the negative electrode 30.

[0042] In some embodiments, the second insulating member 60 includes a first region 61 covering the positive electrode active material layer 12. Along the width direction Y, the width of the first region 61 is W3, and the width of the second insulating member 60 is W4. In some embodiments, W3 is 0.05 mm to 2 mm. In this embodiment, the first region 61 is located on opposite sides of the positive electrode empty foil region 101 in the width direction Y. In another embodiment, the first region 61 is located only on one side of the positive electrode empty foil region 101 in the width direction Y. Optionally, W3 is a range of 0.05 mm, 0.2 mm, 0.5 mm, 0.8 mm, 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, or any two of these values. When W3 is within the above range, along the width direction Y, the second insulating member 60 can effectively isolate the positive electrode empty foil region 101 and the negative electrode sheet 30 to reduce the risk of short circuit, and the second insulating member 60 has a relatively small impact on energy density. It should be noted that... Figure 3 The diagram shows the width of the positive electrode empty foil region 101 in the width direction Y as W4-W3, which is used to indirectly show the width W3 of the first region 61 and the width W4 of the second insulating member 60.

[0043] In some embodiments, the second insulating member 60 includes a second region 62 covering the first insulating member 50. The length L4 of the second region 62 along the first direction X is 0.05 mm to 2 mm. Optionally, L4 is a range of 0.05 mm, 0.2 mm, 0.5 mm, 0.8 mm, 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, or any two of these values. When L4 is within the above range, along the first direction X, the second insulating member 60 can effectively isolate the positive electrode empty foil region 101 and the negative electrode sheet 30 to reduce the risk of short circuits, and the second insulating member 60 has a relatively small impact on energy density.

[0044] One embodiment of this application provides a method for preparing a secondary battery, comprising the following steps.

[0045] Step S1, please refer to Figure 4 An adhesive element 70 is disposed on the surface of the positive electrode current collector 11. The portion of the positive electrode current collector 11 covered by the adhesive element 70 is used to form the positive electrode empty foil region and the positive electrode tab. In some embodiments, there are multiple adhesive elements 70, which are spaced apart along the coating direction of the active material slurry. In some embodiments, the adhesive element 70 has heat-shrinking properties to facilitate subsequent removal of the adhesive element 70. In some embodiments, the adhesive element 70 is a foam adhesive.

[0046] For step S2, please refer to [link / reference]. Figure 4A gap coating is performed on the surfaces of the positive electrode current collector 11 and the adhesive 70 to form a coating area 110 and a blank area 120. Specifically, a positive electrode active material slurry is coated onto the surfaces of the positive electrode current collector 11 and the adhesive 70 through a gap coating method. The surface of the positive electrode current collector 11 in the coating area 110 is coated with a positive electrode active material layer formed by the positive electrode active material slurry, while the surface of the positive electrode current collector 11 in the blank area 120 is not coated with a positive electrode active material layer.

[0047] In some embodiments, the coating area 110 extends along the coating direction of the positive electrode active material slurry, and the positive electrode current collector 11 between two adjacent coating areas 110 constitutes a blank area 120. A portion of each adhesive member 70 is located within the coating area 110, and another portion of each adhesive member 70 is located within the blank area 120 adjacent to the coating area 110. The surface of the adhesive member 70 located within the coating area 110 may be coated with a positive electrode active material layer or may not be coated with an active material layer; this application is not limited to this. In a direction perpendicular to the coating direction of the positive electrode active material slurry, the coating area 110 includes a coating area edge 110A adjacent to the blank area 120, and the adhesive member 70 includes an adhesive member edge 70A, which is concave relative to the coating area edge 110A. The portion of the positive electrode current collector 11 covered by the adhesive member 70, located between the adhesive member edge 70A and the coating area edge 110A, is used to constitute a positive electrode empty foil area.

[0048] Step S3: Bake the positive electrode current collector 11 after gap coating to solidify the positive electrode active material layer.

[0049] Step S4, remove the adhesive 70. After the adhesive 70 is removed, the positive current collector 11 used to form the positive electrode empty foil region is exposed outside the positive electrode active material layer.

[0050] Step S5: Die-cut the blank area 120 to form a positive electrode sheet and a positive electrode tab. The positive electrode sheet includes a first positive electrode edge, and the positive electrode tab protrudes from the first positive electrode edge along a first direction. The positive electrode sheet includes a positive electrode empty foil area without a positive electrode active material layer. When viewed along the first direction, the positive electrode empty foil area and the positive electrode tab at least partially overlap. The coating area edge 110A is the first positive electrode edge.

[0051] Please see Figure 5In some embodiments, prior to step S5, the secondary battery fabrication method further includes: providing an insulating element 80 in the blank area 120. The insulating element 80 is adjacent to the edge 110A of the coating area. In other words, the insulating element 80 is adjacent to the edge of the positive electrode active material layer of the coating area 110. In some embodiments, the insulating element 80 is formed in the blank area 120 by coating, and the insulating element 80 extends along the coating direction of the positive electrode active material slurry. The insulating element 80 covers the portion of the positive electrode current collector 11 exposed after the removal of the adhesive 70, serving to insulate the positive electrode tab and reduce the risk of short circuit between the positive electrode tab and the negative electrode sheet.

[0052] This application also provides an electronic device, including any of the rechargeable batteries described above or a rechargeable battery prepared by the above-described method. The electronic device of this application may be, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CD-ROMs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0053] The performance of the secondary battery provided in this application will be described below through specific embodiments and comparative examples.

[0054] Example 1 Preparation of the positive electrode sheet: Positive active material (lithium cobalt oxide), conductive agent (conductive carbon black and carbon nanotubes), and binder (polyvinylidene fluoride) are dissolved in an N-methylpyrrolidone solution at a weight ratio of 97.5:1:1.5 to form a positive electrode slurry with a solid content of 75%. Aluminum foil is used as the positive electrode current collector, and an adhesive is bonded to the surface of the current collector. The positive electrode slurry is then coated onto the surfaces of the current collector and the adhesive using a gap coating method to obtain the positive active material layer. The adhesive is removed, and the material is die-cut to form the positive electrode sheet and positive electrode tab. The structure of the positive electrode sheet is as follows: Figure 1 As shown.

[0055] Preparation of the negative electrode sheet: The negative electrode active material (graphite), conductive agent (conductive carbon black), thickener (sodium carboxymethyl cellulose), and binder (styrene-butadiene rubber) are mixed in a mass ratio of 97.5:1:0.5:1. Then, deionized water is added as a solvent, and the mixture is stirred evenly to obtain a negative electrode slurry with a solid content of 50wt%. Copper foil is used as a current collector, and the negative electrode slurry is coated on the surface of the current collector to obtain a negative electrode active material layer. Subsequently, the negative electrode sheet is obtained through cold pressing and cutting.

[0056] Preparation of the separator membrane: Polyethylene film was selected as the separator membrane.

[0057] Preparation of electrolyte: Ethyl carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propylene propionate (PP), and vinylene carbonate (VC) were mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 and the organic solvent were mixed in a weight ratio of 8:92 to obtain the electrolyte.

[0058] The lithium-ion battery is fabricated as follows: The positive electrode, polyethylene separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes, to obtain the electrode assembly. The electrode assembly is then placed in an aluminum-plastic film packaging bag and heat-pressed under a preset pressure. After electrolyte injection and formation, a lithium-ion battery is obtained. The battery's dimensions are 19.255 mm (length), 11.9 mm (width), and 3.94 mm (thickness), with a positive electrode tab width (W) of 2.4 mm and a negative electrode tab width of 2.4 mm.

[0059] The remaining embodiments and comparative examples are based on the steps of Embodiment 1 with parameter changes. The specific parameters that have been changed are shown in the table below.

[0060] The test methods for each parameter of this application are described below.

[0061] (1) Energy density test: The lithium-ion battery was pretreated at 25°C and left to stand at room temperature for 60 minutes. The initial voltage and capacity of the cell were then measured. The lithium-ion battery was then installed in the testing equipment, and the energy density was tested according to the following steps: First, it was charged at a constant current of 1C to 4.48V at 25°C, then charged at a constant voltage of 4.48V until the current dropped to 0.05C; next, it was discharged at a constant current of 1C to 3.0V at 25°C. The discharge capacity and battery weight were recorded, and the cell's energy density (Wh / kg) was calculated.

[0062] (2) Lithium plating test of negative electrode sheet: The lithium-ion batteries were placed in a high and low temperature chamber and pretreated at 25°C. After standing at room temperature for 60 minutes, the furnace temperature was adjusted to 0°C, 10°C, 20°C and 25°C respectively. Ten lithium-ion batteries were tested at each temperature. The lithium-ion batteries at each temperature were charged to 4.25V with a constant current of 1.5C, then charged to 4.48V with a constant current of 0.7C, then charged to 0.05C with a constant voltage until fully charged, and then discharged to 3V with 0.5C. This cycle was repeated 10 times. Finally, the lithium-ion batteries were fully charged and ready for disassembly.

[0063] The criteria for passing the lithium plating test are: when a fully charged lithium-ion battery is disassembled, if the edge of the first negative electrode in the negative electrode sheet is golden yellow, then there is no lithium plating. If 10 lithium-ion batteries are tested, and the number of batteries that fail the test is X, the lithium plating failure rate is X / 10.

[0064] (3) Drop test: The lithium-ion batteries were pretreated at 25°C and left to stand at room temperature for 60 minutes before the drop test. The batteries were then placed in a fixture and dropped freely from a height of 1.5m using a drop tester in the following sequence: head-tail-right head corner-right tail corner-left head corner-left tail corner (angle: 45±15°), repeated 6 times. After the drop test, the batteries were left to stand at room temperature for 24 hours, and the voltage was measured and recorded. The appearance of the batteries was checked and photographed before and after the test.

[0065] The criteria for passing the drop test are: no smoke, no leakage, and voltage drop <50mV. If 10 lithium-ion batteries are tested, and X batteries pass the test, the pass rate is X / 10.

[0066] (4) Length or width test: Disassemble the lithium-ion battery, remove a positive electrode sheet, and use a charge-coupled device (CCD) or a ruler to measure the length L1 of the positive electrode empty foil area, the width W of the positive electrode tab, and the widths W1 and W2 of the positive electrode empty foil area extending beyond the positive electrode tab.

[0067] The lithium-ion battery was disassembled, and a charge-coupled device was used to measure the distance between the edge of the negative electrode and the edge of the positive electrode.

[0068] Table 1 lists the parameters and evaluation results for each embodiment and comparative example. Where W1 = W2. When W1 / W is less than 0, it indicates that the edge of the positive electrode empty foil region does not extend beyond the edge of the positive electrode tab, and the width of the positive electrode empty foil region is less than the width of the positive electrode tab.

[0069] Table 1 As shown in Table 1, compared to Comparative Example 1, Examples 11-13, by configuring an empty foil region on the positive electrode, can reduce the lithium plating failure rate on one side of the first negative electrode edge and reduce the distance L2 between the first negative electrode edge and the first positive electrode edge, thereby increasing the energy density. This is because the empty foil region on the positive electrode can increase the CB value of the first negative electrode edge, thereby reducing the risk of lithium plating at the first negative electrode edge. Furthermore, the empty foil region on the positive electrode can ensure that the first negative electrode edge still maintains sufficient negative electrode margin even when misalignment occurs, which is beneficial for reducing the distance L2 between the first negative electrode edge and the first positive electrode edge.

[0070] As shown in Examples 1-6, with the increase of the length L1 of the positive electrode empty foil region, the lithium plating failure rate at the edge of the first negative electrode tends to decrease, while the energy density tends to increase. Examples 1-5 satisfy 0 < L1 ≤ 2 mm, exhibiting a lower lithium plating failure rate and a higher energy density. In Example 6, L1 > 2 mm, and the setting of the positive electrode empty foil region leads to a larger capacity loss in its length direction, resulting in a lower energy density.

[0071] As shown in Examples 7-10 and Example 3, the energy density decreases with increasing W1 / W. Examples 8-9 and Example 3 satisfy 0≤W1 / W≤0.5 and 0≤W2 / W≤0.5, exhibiting high drop pass rate and high energy density. In Example 7, W1<0 and W2<0, the stress during drop is easily concentrated on the positive electrode tab, increasing the risk of tearing and resulting in a low drop pass rate. In Example 10, W1 / W>0.5 and W2 / W>0.5, the presence of an empty foil region on the positive electrode leads to a larger capacity loss in its width direction, resulting in a lower energy density.

[0072] As shown in Examples 11-21 and Example 3, the energy density decreases as the distance L2 from the edge of the first negative electrode to the edge of the first positive electrode increases. Examples 12-20 and Example 3 satisfy 0.1 mm ≤ L2 ≤ 1 mm, exhibiting higher energy density and lower lithium plating failure rate. In Example 11, L2 < 0.1 mm, which is relatively small, making lithium plating more likely at the edge of the first negative electrode, resulting in a higher lithium plating failure rate. In Example 21, L2 > 1 mm, which is relatively large, significantly impacting the energy density, leading to a lower energy density.

[0073] Those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the spirit and essence of this application fall within the scope of this application's disclosure.

Claims

1. A secondary battery, characterized in that, The device includes an electrode assembly comprising multiple positive electrode plates and multiple positive electrode tabs. Each positive electrode plate includes a stacked positive current collector and a positive active material layer. Each positive electrode plate includes a first positive electrode edge. Each positive electrode tab is formed by the positive current collector extending from the first positive electrode edge. Each positive electrode plate includes a positive electrode empty foil region, wherein the surface of the positive current collector in the positive electrode empty foil region is not provided with the positive active material layer. The positive electrode tab extends in a first direction. The positive electrode empty foil area extends along the first direction to the edge of the first positive electrode. When viewed along the first direction, the positive electrode empty foil area and the positive electrode tab at least partially overlap. Along the width direction perpendicular to the first direction, the positive electrode active material layer is provided on both sides of the positive electrode empty foil area. The positive electrode active material layer located on both sides of the empty foil area in the width direction extends to the edge of the first positive electrode. The electrode assembly includes a negative electrode sheet. Along the first direction, the positive electrode sheet includes a second positive electrode edge opposite to the first positive electrode edge. The negative electrode sheet includes a first negative electrode edge located on one side of the first positive electrode edge and a second negative electrode edge opposite to the first negative electrode edge. The first negative electrode edge extends beyond the first positive electrode edge by a distance L2. Along the direction opposite to the first direction, the second negative electrode edge extends beyond the second positive electrode edge by a distance L3, where 1≤L2 / L3≤10.

2. The secondary battery as described in claim 1, characterized in that, Along the first direction, the positive electrode empty foil region includes a first edge opposite to the first positive electrode edge, and the distance between the first positive electrode edge and the first edge is L1, 0 < L1 ≤ 2 mm.

3. The secondary battery as described in claim 1, characterized in that, Along the width direction, the positive electrode tab includes a second edge and a third edge disposed opposite to each other, and the positive electrode empty foil area includes a fourth edge located on one side of the second edge and a fifth edge located on one side of the third edge. The fourth edge extends beyond the second edge by a distance of W1 mm, the fifth edge extends beyond the third edge by a distance of W2 mm, and the distance between the second edge and the third edge is W mm, 0≤W1≤W / 2, 0≤W2≤W / 2.

4. The secondary battery as described in claim 1, characterized in that, 0.1 mm≤L2≤1 mm, 0.1 mm≤L3≤0.50mm.

5. The secondary battery as described in claim 1, characterized in that, The secondary battery includes a first insulating member disposed on the surface of the positive electrode tab. The first insulating member includes an edge, which, when viewed along a thickness direction perpendicular to the first direction, partially overlaps with the edge of the first positive electrode.

6. The secondary battery as described in claim 5, characterized in that, Along the first direction, the length of the first insulating element is 0.2 mm to 2 mm.

7. The secondary battery as described in claim 5, characterized in that, The first insulating element is an insulating coating, which includes at least one of boehmite, alumina, silicon dioxide, and zirconium oxide.

8. The secondary battery as described in claim 5, characterized in that, The secondary battery includes a second insulating member disposed on at least one side of the positive electrode sheet and covering at least a portion of the positive electrode empty foil area.

9. The secondary battery as described in claim 8, characterized in that, The second insulating element includes a first region covering the positive electrode active material layer, and the width of the first region is 0.05 mm to 2 mm along the width direction.

10. The secondary battery as described in claim 8, characterized in that, The second insulating element includes a second region covering the first insulating element, and the length of the second region along the first direction is 0.05 mm to 2 mm.

11. A method for preparing a secondary battery, characterized in that, include: An adhesive component is placed on the surface of the positive electrode current collector; A gap coating is applied to the surface of the positive current collector and the surface of the adhesive to form a coating area and a blank area. The surface of the positive current collector in the coating area is coated with a positive active material layer, while the surface of the positive current collector in the blank area is not coated with the positive active material layer. The positive electrode current collector after gap coating is baked; Remove the adhesive; The blank area is die-cut to form a positive electrode sheet and a positive electrode tab. The positive electrode sheet includes a first positive electrode edge, and the positive electrode tab protrudes from the first positive electrode edge along a first direction. The positive electrode sheet includes a positive electrode empty foil area without the positive electrode active material layer. When viewed along the first direction, the positive electrode empty foil area and the positive electrode tab at least partially overlap. Along the width direction perpendicular to the first direction, the positive electrode active material layer is provided on both sides of the positive electrode empty foil area. The positive electrode active material layer located on both sides of the empty foil area in the width direction extends to the first positive electrode edge. The secondary battery includes a negative electrode sheet. Along the first direction, the positive electrode sheet includes a second positive electrode edge opposite to the first positive electrode edge. The negative electrode sheet includes a first negative electrode edge located on one side of the first positive electrode edge and a second negative electrode edge opposite to the first negative electrode edge. The distance from the first negative electrode edge to the first positive electrode edge is L2. Along the direction opposite to the first direction, the distance from the second negative electrode edge to the second positive electrode edge is L3, where 1≤L2 / L3≤10.

12. The method for preparing a secondary battery as described in claim 11, characterized in that, Before the step of die-cutting the blank area, the method further includes: An insulating element is provided in the blank area, and the insulating element is adjacent to the edge of the positive electrode active material layer in the coating area.

13. An electronic device, characterized in that, It includes the secondary battery as described in any one of claims 1-10, or the secondary battery prepared by the method described in any one of claims 11-12.

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