Secondary battery, preparation method thereof and electronic device

Abstract

The invention discloses a secondary battery, a preparation method thereof and an electronic device. A secondary battery includes an electrode assembly. The electrode assembly comprises a plurality of positive pole pieces and a plurality of positive pole lugs, wherein each positive pole piece comprises a positive current collector and a positive active material layer which are arranged in a stacked manner; the positive pole piece comprises a first positive pole edge; the positive pole lug is formed by extending the positive pole current collector from the first positive pole edge; the positive pole piece comprises a positive empty foil area, and the surface of a positive current collector of the positive empty foil area is not provided with a positive active material layer. The extension direction of the positive tab is the positive direction, and the positive empty foil area extends to the first positive edge along the positive direction. And the positive empty foil region and the positive tab are at least partially overlapped when being observed along the positive direction.

Description

Technical Field

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

[0002] Lithium-ion batteries have been widely used in mobile and portable electrical appliances due to their advantages such as high energy density, high average open circuit voltage and long cycle life. As electronic products develop towards miniaturization and multifunctionality, the energy density and safety performance requirements of lithium-ion batteries are becoming increasingly higher. Lithium-ion batteries include electrode assemblies, and the width and length of the positive electrode sheets of the electrode assemblies are usually shorter than those of the negative electrode sheets to reduce the risk of lithium deposition at the edges of the negative electrode sheets. During the manufacturing process of the electrode assembly, the edges of the negative electrode sheets and the positive electrode sheets may be misaligned. For example, due to the existence of tolerances, the edges of the active material layers coated on the front and back sides of the current collector are misaligned, thereby causing the edges of the negative electrode sheets and the positive electrode sheets to be misaligned, or when the multiple tabs formed by die-cutting are bent and welded to the electrode terminals, the tabs pull the tabs to cause the edges of the negative electrode sheets and the positive electrode sheets to be misaligned. In this case, it is usually necessary to increase the edge area of ​​the negative electrode sheet that extends beyond the positive electrode sheet (also called the overhang area) to reduce the risk of lithium plating due to insufficient negative electrode surplus caused by misalignment of the edge of the negative electrode sheet, but this will cause a large loss of energy density. Summary of the invention

[0003] One object of the present application is to provide a secondary battery and a preparation method and an electronic device thereof that can reduce the risk of lithium deposition at the edge of a negative electrode plate and at the same time help to improve the energy density.

[0004] In a first aspect, the present application provides a secondary battery, comprising an electrode assembly. The electrode assembly comprises a plurality of positive electrode sheets and a plurality of positive electrode tabs, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer stacked. The positive electrode sheet comprises a first positive electrode edge, and the positive electrode tab is formed by the positive electrode current collector extending from the first positive electrode edge. The positive electrode sheet comprises a positive electrode empty foil area, and the surface of the positive electrode current collector in the positive electrode empty foil area is not provided with a positive electrode active material layer. The extension direction of the positive electrode tab is a first direction, and the positive electrode empty foil area extends along the first direction to the first positive electrode edge. When viewed along the first direction, the positive electrode empty foil area at least partially overlaps with the positive electrode tab.

[0005] In the present application, the positive electrode sheet is provided with a positive electrode empty foil area, and the positive electrode empty foil area partially overlaps with the positive electrode ear along the first direction, so that the positive electrode empty foil area can directly lead the current generated by the positive electrode sheet to the positive electrode ear, and the positive electrode empty foil area plays the role of the positive electrode ear. The provision of the positive electrode empty foil area can increase the CB value at this position, thereby reducing the risk of lithium precipitation due to insufficient negative electrode margin at the edge of the negative electrode sheet located on the side where the positive electrode empty foil area is located. And even if multiple positive electrode ears are bent and connected to the electrode terminal, resulting in the misalignment of the edge of the positive electrode sheet and the edge of the negative electrode sheet, due to the presence of the positive electrode empty foil area, the edge of the negative electrode sheet is not easy to produce lithium precipitation, so there is no need to increase the length of the negative electrode sheet exceeding the positive electrode sheet along the first direction, which is conducive to improving the energy density.

[0006] According to some embodiments of the present application, along the first direction, the positive electrode empty foil area includes a first edge opposite to the edge of the first positive electrode, and the distance between the first positive electrode edge and the first edge is L1, 0<L1≤2 mm. When L1 is within the above range, it is beneficial to keep the CB value at the edge of the first positive electrode greater than 1 when the length of the negative electrode sheet on the side where the first positive electrode edge is located is not long enough due to misalignment, thereby reducing the risk of lithium deposition at the edge of the negative electrode sheet; and the reduction of the positive electrode active material layer in the first direction caused by the setting of the positive electrode empty foil area is limited, that is, the capacity loss is limited, and the impact on the energy density is small. According to some embodiments of the present application, along the width direction perpendicular to the first direction, the positive electrode tab includes a second edge and a third edge that are arranged opposite to each other, 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 exceeds the second edge by a distance of W1 mm, the fifth edge exceeds the third edge by a distance of W2 mm, the distance between the second edge and the third edge is W mm, 0≤W1≤W / 2, 0≤W2≤W / 2. When W1 and W2 are within the above ranges, the area of ​​the positive electrode empty foil area that exceeds the positive electrode tab in the width direction can share the impact force on the positive electrode tab when the secondary battery falls, reduce the risk of stress concentration points in the positive electrode tab causing tearing, and improve the drop performance; and the reduction in the width direction of the positive electrode active material layer caused by the setting of the positive electrode empty foil area is limited, and the impact on the energy density is small.

[0007] According to some embodiments of the present 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, 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 exceeds the first positive electrode edge by a distance of L2; along a direction opposite to the first direction, the second negative electrode edge exceeds the second positive electrode edge by a distance of L3, 1≤L2 / L3≤10. When L2 / L3 is within the above range, the risk of edge lithium deposition caused by the misalignment of the edges of the positive electrode sheet and the negative electrode sheet located on one side of the pole ear can be reduced, and L2 can be controlled not to be too large, thereby reducing the impact of L2 on energy density.

[0008] According to some embodiments of the present application, 0.1 mm≤L2≤1 mm, 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 deposition at the edge of the first negative electrode and to improve the energy density.

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

[0010] According to some embodiments of the present application, along the first direction, the length of the first insulating member 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 sheet, and the first insulating member has little effect on energy density.

[0011] According to some embodiments of the present application, the first insulating member is an insulating coating, and the insulating coating includes at least one of boehmite, aluminum oxide, silicon oxide, and zirconium oxide.

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

[0013] According to some embodiments of the present application, the second insulating member 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 perpendicular to the first direction. When the width of the first region is within the above range, along the width direction, the second insulating member can effectively isolate the positive electrode empty foil area and the negative electrode plate to reduce the risk of short circuit, and the second insulating member has little effect on energy density.

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

[0015] The second aspect of the present application provides a method for preparing a secondary battery, comprising: arranging 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, 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 the positive electrode active material layer; baking the positive electrode current collector after the gap coating; removing the adhesive; and die-cutting the blank area to form a positive electrode sheet and a positive electrode ear, the positive electrode sheet comprising a first positive electrode edge, the positive electrode ear protruding from the first positive electrode edge along a first direction, the positive electrode sheet comprising a positive electrode empty foil area not provided with a positive electrode active material layer, and when observed along the first direction, the positive electrode empty foil area at least partially overlaps with the positive electrode ear.

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

[0017] A third aspect of the present application provides an electronic device, comprising any one of the above-mentioned secondary batteries, or comprising a secondary battery manufactured by any one of the above-mentioned secondary battery manufacturing methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of a positive electrode plate in one embodiment.

[0019] Figure 2 Schematic diagram of a cross-section of a positive electrode sheet in one embodiment.

[0020] Figure 3 Schematic diagram of a positive electrode sheet and a negative electrode sheet in one embodiment.

[0021] Figure 4Schematic diagram of gap coating on the surface of the positive electrode current collector in one embodiment.

[0022] Figure 5 This is a schematic diagram of an embodiment in which an insulating member is provided in the blank area.

[0023] Description of main component symbols: The following specific embodiments will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

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

[0025] When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be a component in between. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be a component in between.

[0026] Unless otherwise defined, when the term "plurality" is used to describe the number of components, it specifically means that the components are two or more.

[0027] Some embodiments of the present application will be described below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0028] An embodiment of the present application provides a secondary battery, including a shell, an electrode assembly contained in the shell, and an electrode terminal connected to the electrode assembly and extending out of the shell. The electrode terminal is used to electrically connect to an external element, and the electrode terminal includes a positive terminal and a negative terminal. The electrode assembly includes a plurality of positive pole sheets, a plurality of negative pole sheets, a plurality of separators, a plurality of positive pole ears, and a plurality of negative pole ears, each separator is arranged between adjacent positive pole sheets and negative pole sheets, a plurality of positive pole ears are electrically connected to a plurality of positive pole sheets, respectively, a plurality of negative pole ears are electrically connected to a plurality of negative pole sheets, respectively, and the electrode assembly is formed by stacking a plurality of positive pole sheets, a plurality of separators, and a plurality of negative pole sheets alternately in sequence. The plurality of positive pole ears are electrically connected to the positive terminal after being bent, and the plurality of negative pole ears are electrically connected to the negative terminal after being bent. Optionally, the shell is a metal shell or a packaging bag formed by packaging such as an aluminum-plastic film. Optionally, the material of the separator can be polypropylene or polyethylene, etc.

[0029] See also Figure 1 and Figure 2 , the positive electrode sheet 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 which are stacked. The positive electrode active material layer 12 may be disposed on one surface or two opposite surfaces of the positive electrode current collector 11. The positive electrode sheet 10 includes a first positive electrode edge 10A, and the positive electrode tab 20 is formed by the positive electrode current collector 11 extending from the first positive electrode edge 10A, and the positive electrode tab 20 is integrally arranged with the positive electrode current collector 11. The positive electrode sheet 10 includes a positive electrode empty foil area 101, and the surface of the positive electrode current collector 11 of the positive electrode empty foil area 101 is not provided with a positive electrode active material layer 12. Optionally, one surface or two opposite surfaces of the positive electrode current collector 11 of the positive electrode empty foil area 101 is not provided with a positive electrode active material layer 12. In some embodiments, the positive electrode active material layer 12 covers the entire surface of the positive electrode current collector 11 in the positive electrode sheet 10 except the positive electrode empty foil area 101. The extension direction of the positive electrode tab 20 is the first direction X. The positive electrode empty foil area 101 extends along the first direction to the first positive electrode edge 10A. Observed along the first direction X, the positive electrode empty foil area 101 at least partially overlaps with the positive electrode tab 20. The overlapping portion between the positive electrode empty foil area 101 and the positive electrode tab 20 is directly connected. The current generated by the positive electrode plate 10 can be led to the positive electrode tab 20 through the positive electrode empty foil area 101, that is, the positive electrode empty foil area 101 can play the role of a tab. The setting of the positive electrode empty foil area 101 can increase the CB value at this position, thereby reducing the risk of lithium precipitation due to insufficient negative electrode residue at the edge of the negative electrode plate located on the side where the positive electrode empty foil area 101 is located. In this application, the CB value refers to the ratio between the capacity of the negative electrode plate per unit area and the capacity of the positive electrode plate per unit area under the same conditions, for example, at an ambient temperature of 25°C and a discharge rate of 0.1C. Moreover, even if the multiple positive electrode tabs 20 are bent and electrically connected to the positive terminal, causing the edge of the positive electrode sheet 10 and the edge of the negative electrode sheet to be misaligned, due to the existence of the positive electrode empty foil area 101, the edge of the negative electrode sheet located on the side where the positive electrode empty foil area 101 is located is not easy to produce lithium deposition due to insufficient negative electrode residue. In this way, there is no need to increase the length of the negative electrode sheet exceeding the positive electrode sheet 10 along the first direction X, which is beneficial to improve the energy density.

[0030] Along the first direction X, the positive electrode empty foil area 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 the present 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 distances between the first positive electrode edge 10A and the first edge 101A at various positions are equal or unequal. In some embodiments, 0<L1≤2 mm. Optionally, L1 is 0.2 mm, 0.5 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm or a range consisting of any two of the values. When L1 is within the above range, in the case that the length of the negative electrode sheet on the side where the first positive electrode edge 10A is located is not long enough, 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 deposition at the edge of the negative electrode sheet; and the reduction of the positive electrode active material layer 12 in the first direction X caused by the setting of the positive electrode empty foil area 101 is limited, that is, the capacity loss is limited, and the impact on the 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 cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium rich manganese-based material, lithium nickel cobalt aluminum oxide and combinations thereof.

[0032] See also Figure 1In some embodiments, along the first direction X, the positive electrode tab 20 is located within the positive electrode empty foil area 101, that is, along the width direction Y perpendicular to the first direction X, the width of the positive electrode empty foil area 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 that are arranged opposite to each other, and the positive electrode empty foil area 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 exceeds the second edge 20B by a distance of W1 mm, the fifth edge 101C exceeds the third edge 20C by a distance of W2 mm, and 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 is 0.1W, 0.2W, 0.3W, 0.4W, 0.5W or a range consisting of any two of them. Optionally, W2 is 0.1W, 0.2W, 0.3W, 0.4W, 0.5W or a range consisting of any two of them. When W1 and W2 are within the above range, the area of ​​the positive electrode empty foil area 101 that exceeds the positive electrode tab 20 in the width direction Y can share the impact force on the positive electrode tab 20 when the secondary battery falls, reduce the risk of stress concentration points in the positive electrode tab 20 causing tearing, and improve the 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 area 101 is limited, and the impact on the energy density is small.

[0033] See also 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 that are stacked. The negative electrode active material layer 32 can 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 sheet 10 includes a second positive electrode edge 10B opposite to the first positive electrode edge 10A, and the negative electrode sheet 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 that the first negative electrode edge 30A exceeds the first positive electrode edge 10A is L2, and L2>0. Along the direction opposite to the first direction X, the distance that the second negative electrode edge 30B exceeds the second positive electrode edge 10B is L3, and L3>0. By configuring L2 and L3, the CB value at the first negative electrode edge 30A and the CB value at the second negative electrode edge 30B can be maintained greater than 1, reducing the risk of lithium deposition at the first negative electrode edge 30A and the second negative electrode edge 30B.

[0035] Since the multiple tabs will pull the pole pieces when they are bent and connected to the electrode terminals, the misalignment amplitude of the edges of the positive pole piece 10 and the negative pole piece 30 on one side of the pole piece may be greater than the misalignment amplitude of the edges of the positive pole piece 10 and the negative pole piece 30 on the opposite side of the pole piece, thereby making the edge of the negative pole piece 30 on one side of the pole piece more prone to lithium deposition. To this end, in some embodiments, 1≤L2 / L3≤10. Optionally, L2 / L3 is 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 a range consisting of any two of these values. When L2 / L3 is within the above range, the risk of lithium deposition caused by the misalignment of the edges of the positive pole piece 10 and the negative pole piece 30 on one side of the pole piece can be reduced, and L2 can be controlled not to be too large, reducing the impact of L2 on energy density. Preferably, 1≤L2 / L3≤4, which is beneficial to reducing the risk of lithium deposition at the edge 30A of the first negative electrode and has little impact on the energy density.

[0036] In some embodiments, 0.1 mm ≤ L2 ≤ 1 mm, 0.1 mm ≤ L3 ≤ 0.5 mm. Optionally, L2 is 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 a range consisting of any two of them. Optionally, L3 is 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or a range consisting of any two of them. When L2 and L3 are within the above range, it is beneficial to reduce the risk of lithium deposition at the edge 30A of the first negative electrode, and the impact on energy density is 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 soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbon composite, lithium titanate, and one or more metals that can form an alloy with lithium.

[0038] See also Figure 3 In some embodiments, the secondary battery includes a first insulating member 50, which is disposed on the surface of the positive electrode tab 20. The first insulating member 50 includes an insulating member edge 50A. When viewed along the thickness direction Z perpendicular to the first direction, the insulating member 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 contact short circuit between the positive electrode tab 20 and the negative electrode sheet 30 can be reduced.

[0039] In some embodiments, the first insulating member 50 is an insulating coating, and the insulating coating includes ceramic particles and an adhesive. Optionally, the ceramic particles include at least one of boehmite, aluminum oxide, silicon oxide and zirconium oxide. The above-mentioned ceramic particles can increase the strength of the first insulating member 50 and reduce the risk of contact short circuit caused by puncture of the first insulating member 50. Optionally, the adhesive includes at least one of epoxy resin, acrylate, styrene-butadiene rubber, polytetrafluoroethylene and polyvinylidene fluoride. The above-mentioned adhesive has strong viscosity, so that the first insulating member 50 has good adhesion to the positive electrode tab 20, reducing the risk of the first insulating member 50 falling off.

[0040] In some embodiments, the length of the first insulating member 50 is 0.2 mm to 2 mm along the first direction X. 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 contact short circuit between the positive electrode tab 20 and the negative electrode tab 30, and the first insulating member 50 has little effect on the energy density.

[0041] See also 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 sheet 10 and covers at least a portion of the positive electrode empty foil area 101. Optionally, the second insulating member 60 is bonded to the surface of the positive electrode collector 11 of the positive electrode empty foil area 101. Optionally, the second insulating member 60 is bonded to the surface of the positive electrode active material layer 12 away from the positive electrode collector 11. Optionally, the second insulating member 60 covers the entire positive electrode empty foil area 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 area 101 and the negative electrode sheet 30, reducing the risk of contact short circuit between the positive electrode empty foil area 101 and the negative electrode sheet 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 ~ 2 mm. In this embodiment, the first region 61 is located on two opposite sides of the positive electrode empty foil area 101 in the width direction Y. In another embodiment, the first region 61 is only located on one side of the positive electrode empty foil area 101 in the width direction Y. Optionally, W3 is 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 a range consisting of 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 area 101 and the negative electrode plate 30 to reduce the risk of short circuit, and the second insulating member 60 has little effect on the energy density. It should be noted that, Figure 3 , the width of the positive electrode empty foil area 101 in the width direction Y is shown as W4 - W3 , which is used to indirectly show the width W3 of the first area 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. Along the first direction X, the length L4 of the second region 62 is 0.05 mm to 2 mm. Optionally, L4 is 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 a range consisting of any two of the 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 area 101 and the negative electrode plate 30 to reduce the risk of short circuit, and the second insulating member 60 has little effect on energy density.

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

[0045] Step S1, see Figure 4 , an adhesive 70 is provided on the surface of the positive electrode current collector 11. The portion of the positive electrode current collector 11 covered by the adhesive 70 is used to form a positive electrode empty foil area and a positive electrode tab. In some embodiments, the number of adhesives 70 is multiple, and the multiple adhesives 70 are arranged at intervals along the coating direction of the active material slurry. In some embodiments, the adhesive 70 has the property of shrinking upon heating to facilitate the subsequent removal of the adhesive 70. In some embodiments, the adhesive 70 is a foaming glue.

[0046] Step S2, see Figure 4, gap coating is performed on the surface of the positive current collector 11 and the surface of the adhesive 70 to form a coating area 110 and a blank area 120. Specifically, the positive active material slurry is coated on the surface of the positive current collector 11 and the surface of the adhesive 70 by gap coating. The surface of the positive current collector 11 in the coating area 110 is coated with a positive active material layer formed by the positive active material slurry, and the surface of the positive current collector 11 in the blank area 120 is not coated with a positive active material layer.

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

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

[0049] Step S4, removing the adhesive member 70. After the adhesive member 70 is removed, the positive electrode current collector 11 used to form the positive electrode hollow foil area is exposed outside the positive electrode active material layer.

[0050] Step S5, die-cutting the blank area 120 to form a positive electrode sheet and a positive electrode ear. The positive electrode sheet includes a first positive electrode edge, the positive electrode ear 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, and when viewed along the first direction, the positive electrode empty foil area and the positive electrode ear at least partially overlap. Among them, the coating area edge 110A is the first positive electrode edge.

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

[0052] One embodiment of the present application also provides an electronic device, including any of the above secondary batteries or the secondary batteries prepared by the above preparation method. The electronic device of the present application can be, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini CD, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0053] The performance of the secondary battery provided in the present application is described below through specific examples and comparative examples.

[0054] Example 1 Preparation of positive electrode sheet: The positive electrode active material (lithium cobalt oxide), conductive agent (conductive carbon black and carbon nanotubes), and binder (polyvinylidene fluoride) are dissolved in N-methylpyrrolidone solution in 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 collector, and the adhesive is bonded to the surface of the positive electrode collector. The positive electrode slurry is applied to the surface of the positive electrode collector and the surface of the adhesive by gap coating to obtain a positive electrode active material layer. The adhesive is removed and the positive electrode sheet and positive electrode ear are formed by die cutting. The structure of the positive electrode sheet is as follows Figure 1 shown.

[0055] Preparation of negative electrode sheet: negative electrode active material (graphite), conductive agent (conductive carbon black), thickener (sodium carboxymethyl cellulose), binder (styrene-butadiene rubber) are mixed in a mass ratio of 97.5:1:0.5:1, and then deionized water is added as a solvent, and 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 negative electrode current collector to obtain a negative electrode active material layer. Then, after cold pressing and cutting, a negative electrode sheet is obtained.

[0056] Preparation of isolation film: Polyethylene film is selected as the isolation film.

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

[0058] Preparation of lithium-ion battery: stack the positive electrode sheet, polyethylene separator, and negative electrode sheet in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to obtain an electrode assembly; place the electrode assembly in an aluminum-plastic film packaging bag, perform hot pressing bonding at a preset pressure, and obtain a lithium-ion battery after liquid injection and formation. The length, width, and thickness of the battery are 19.255mm, 11.9mm, and 3.94mm, respectively. The width W of the positive electrode tab is 2.4mm, and the width of the negative electrode tab is 2.4mm.

[0059] The remaining embodiments and comparative examples are based on the steps of embodiment 1 with parameter changes, and the specific changed parameters are shown in the following table.

[0060] The test methods for various parameters of this application are described below.

[0061] (1) Energy density test: The lithium-ion battery was pre-treated at 25°C, and after standing at room temperature for 60 minutes, the initial voltage and capacity of the battery were measured; the lithium-ion battery was loaded into the test equipment, and the energy density test was performed according to the following steps: first, it was charged to 4.48V at a constant current of 1C at 25°C, and then charged at a constant voltage of 4.48V until the current dropped to 0.05C; then, it was discharged to 3.0V at a constant current of 1C at 25°C. The discharge capacity and the weight of the battery were recorded, and the energy density (Wh / kg) of the battery was calculated.

[0062] (2) Lithium deposition test of negative electrode: The lithium-ion batteries were placed in a high and low temperature box 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, and 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, and finally the lithium-ion batteries were fully charged and waited for disassembly.

[0063] Lithium deposition test pass criteria: Disassemble the fully charged lithium-ion battery, and if the side of the negative electrode sheet where the first negative electrode edge is located is golden yellow, there is no lithium deposition. Test 10 lithium-ion batteries, the number of batteries that fail the test is X, and the lithium deposition failure rate is X / 10.

[0064] (3) Drop test: The lithium-ion battery was pre-treated at 25°C, and after standing at room temperature for 60 minutes, the voltage of the lithium-ion battery before the drop test was tested; the lithium-ion battery was placed in a fixture and dropped freely from a position 1.5m above the ground in the following order using a drop device: head-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), and repeated 6 rounds. After the drop, it was left at room temperature for 24 hours, and the voltage of the lithium-ion battery was measured and recorded. The appearance of the lithium-ion battery was checked and photographed before and after the test.

[0065] Drop test pass criteria: no smoke, no leakage, voltage drop <50mV. Test 10 lithium-ion batteries, the number of batteries that pass the test is X, and the test pass rate is X / 10.

[0066] (4) Length or width test: Disassemble the lithium-ion battery, take out 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 ear, and the width W1 and W2 of the positive electrode empty foil area exceeding the positive electrode ear.

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

[0068] Table 1 lists the parameters and evaluation results of various embodiments and comparative examples. Wherein, W1=W2. When W1 / W is less than 0, it indicates that the edge of the positive electrode empty foil area does not exceed the edge of the positive electrode tab, and the width of the positive electrode empty foil area is less than the width of the positive electrode tab.

[0069] Table 1 As can be seen from Table 1, compared with Comparative Example 1, Examples 11-13 can reduce the lithium deposition failure rate on one side of the edge of the first negative electrode by configuring the positive electrode empty foil area, and can reduce the distance L2 of the first negative electrode edge beyond the first positive electrode edge, thereby improving the energy density. This is because the setting of the positive electrode empty foil area can increase the CB value of the first negative electrode edge, thereby reducing the risk of lithium deposition at the first negative electrode edge, and the setting of the positive electrode empty foil area can also enable the first negative electrode edge to still maintain sufficient negative electrode margin when misalignment occurs, thereby facilitating reducing the distance L2 of the first negative electrode edge beyond the first positive electrode edge.

[0070] It can be seen from Examples 1-6 that as the length L1 of the positive electrode empty foil area increases, the lithium deposition failure rate at the edge of the first negative electrode tends to decrease, and the energy density tends to increase. Example 1-5 satisfies 0<L1≤2 mm, and has a lower lithium deposition failure rate and a higher energy density. In Example 6, L1>2 mm, and the setting of the positive electrode empty foil area leads to a larger capacity loss in its length direction, resulting in a lower energy density.

[0071] It can be seen from Examples 7-10 and Example 3 that as W1 / W increases, the energy density tends to decrease. Examples 8-9 and Example 3 satisfy 0≤W1 / W≤0.5, 0≤W2 / W≤0.5, and have a higher drop pass rate and a higher energy density. In Example 7, W1<0, W2<0, the stress during the drop is easily concentrated on the positive electrode ear and creates the risk of tearing, resulting in a lower drop pass rate. In Example 10, W1 / W>0.5, W2 / W>0.5, the setting of the positive electrode empty foil area results in a large capacity loss in the width direction, resulting in a lower energy density.

[0072] It can be seen from Examples 11-21 and Example 3 that as the distance L2 of the edge of the first negative electrode beyond the edge of the first positive electrode increases, the energy density tends to decrease. Examples 12-20 and Example 3 satisfy 0.1 mm≤L2≤1 mm, and have higher energy density and lower lithium deposition failure rate. In Example 11, L2<0.1mm, L2 is small, lithium deposition is easy to occur at the edge of the first negative electrode, and the lithium deposition failure rate is high. In Example 21, L2>1 mm, L2 is large, the impact on energy density is greater, and the energy density is low.

[0073] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application, and are not used as limitations on the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments are within the scope of the present application.

Claims

1. A secondary battery, characterized in that: The electrode assembly comprises a plurality of positive electrode sheets and a plurality of positive electrode tabs, the positive electrode sheets comprise a positive electrode current collector and a positive electrode active material layer which are stacked, the positive electrode sheets comprise a first positive electrode edge, the positive electrode tabs are formed by the positive electrode current collector extending from the first positive electrode edge, the positive electrode sheets comprise a positive electrode hollow foil area, and the positive electrode active material layer is not provided on the surface of the positive electrode current collector in the positive electrode hollow foil area; The positive electrode tab extends in a first direction, and 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 at least partially overlaps with the positive electrode tab.

2. The secondary battery according to claim 1, wherein Along the first direction, the positive electrode empty foil area 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 according to claim 1, wherein Along the width direction perpendicular to the first direction, the positive electrode ear includes a second edge and a third edge arranged opposite to each other, 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 exceeds the second edge by a distance of W1 mm, the fifth edge exceeds the third edge by a distance of W2 mm, 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 according to claim 1, wherein: 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 exceeds the first positive electrode edge by a distance L2. Along the direction opposite to the first direction, the second negative electrode edge exceeds the second positive electrode edge by a distance L3, 1≤L2 / L3≤10.

5. The secondary battery according to claim 4, characterized in that 0.1 mm≤L2≤1 mm, 0.1 mm≤L3≤0.50mm.

6. The secondary battery according to claim 1, wherein: The secondary battery includes a first insulating member, which is disposed on a surface of the positive electrode tab. The first insulating member includes an insulating member edge, and when viewed along a thickness direction perpendicular to the first direction, the insulating member edge partially overlaps with an edge of the first positive electrode.

7. The secondary battery according to claim 6, characterized in that Along the first direction, the length of the first insulating member is 0.2 mm to 2 mm.

8. The secondary battery according to claim 6, wherein: The first insulating member is an insulating coating, and the insulating coating includes at least one of boehmite, aluminum oxide, silicon oxide, and zirconium oxide.

9. The secondary battery according to claim 6, characterized in that: The secondary battery comprises a second insulating member, which is arranged on at least one side of the positive electrode plate and covers at least a portion of the positive electrode empty foil area.

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

11. The secondary battery according to claim 9, characterized in that The second insulating member includes a second region covering the first insulating member, and a length of the second region along the first direction is 0.05 mm to 2 mm.

12. A method for preparing a secondary battery, characterized in that: include: Disposing an adhesive on the surface of the 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 coating area and a blank area, wherein the surface of the positive electrode current collector in the coating 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 the positive electrode active material layer; Baking the positive electrode current collector after gap coating; removing the adhesive member; The blank area is die-cut to form a positive electrode sheet and a positive electrode ear, wherein the positive electrode sheet includes a first positive electrode edge, and the positive electrode ear protrudes from the first positive electrode edge along a first direction, and the positive electrode sheet includes a positive electrode empty foil area without the positive electrode active material layer, and when observed along the first direction, the positive electrode empty foil area at least partially overlaps with the positive electrode ear.

13. The method for preparing a secondary battery according to claim 12, characterized in that: Before the step of die-cutting the blank area, the method further comprises: An insulating member is disposed in the blank area, and the insulating member is adjacent to an edge of the positive electrode active material layer in the coating area.

14. An electronic device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 11, or a secondary battery prepared by the method for preparing a secondary battery according to any one of claims 12 to 13.

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