Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the length of an electrode assembly is a mm, the width of the electrode assembly is b mm, and 2 < = a / b < = 14. The total number of turns of the electrode assembly is M, and M is larger than or equal to 10 and smaller than or equal to 60. The Dv50 of the positive electrode active material is V1 [mu] m, 10 < = V1 < = 30. The positive current collector is provided with a plurality of first stripes. The width of a single first stripe is W1 [mu] m, and 3 < = W1 < = V1. Dv50 of the negative electrode active material is V2 [mu] m, and V2 is greater than or equal to 10 and less than or equal to 30. The negative current collector is provided with a plurality of second stripes. The width of a single second stripe is W2 [mu] m, and 3 < = W2 < = V2. In the mth circle of electrode assembly, the number of the first stripes is N1, and N1 is larger than or equal to 3 and smaller than or equal to 30. The following conditions are satisfied: (1) m is greater than or equal to 2 and less than or equal to 0.25 M, and N2 / N1 is greater than or equal to 2 and less than or equal to 5; (2) 0.25 M < m < = 0.7 M, and 2 < = N2 / N1 < = 4; and (3) 0.7 M < m < = M, and 3 < = N1 < = 30. Through the arrangement, the secondary battery has good cycle performance while having mechanical performance.

Description

Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, boast high specific energy, high operating voltage, low self-discharge, compact size, and light weight, making them widely used in consumer electronics. With the widespread adoption of lithium-ion batteries, the market is placing increasingly higher demands on their energy density and battery life.

[0003] Currently, narrow and long lithium-ion batteries are used in multiple systems, but the narrow and long structure will bring about the wetting problem in the middle of the electrode assembly, especially the poor wetting in the middle of the electrode sheet. Lithium deposition occurs in the late cycle, causing the performance of the lithium-ion battery to deteriorate. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device that can improve the cycle performance of the secondary battery while taking into account the mechanical properties of the secondary battery. The specific technical solution is as follows:

[0005] It should be noted that, in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries.

[0006] A first aspect of the present application provides a secondary battery comprising an electrode assembly formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet. The electrode assembly has a length of a mm and a width of b mm, with 2 ≤ a / b ≤ 14. The total number of turns of the electrode assembly is M, with 10 ≤ M ≤ 60, preferably 20 ≤ M ≤ 35, and M being a positive integer. The positive electrode sheet comprises a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer comprises a positive electrode active material, and the Dv50 of the positive electrode active material is V1 μm, with 10 ≤ V1 ≤ 30. The positive current collector has a plurality of first stripes disposed within the region where the positive electrode material layer is disposed. The plurality of first stripes extend along the width of the unfolded electrode assembly and are spaced apart along the length of the unfolded electrode assembly. Along the unfolded length of the electrode assembly, the width of a single first stripe is W1 μm, with 3 ≤ W1 ≤ V1. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material having a Dv50 of V2μm, with 10≤V2≤30. The negative electrode current collector is provided with a plurality of second stripes within the region where the negative electrode material layer is provided. The plurality of second stripes extend along the width of the unfolded electrode assembly and are spaced apart along the length of the unfolded electrode assembly. Along the length of the unfolded electrode assembly, the width of a single second stripe is W2μm, with 3≤W2≤V2. In the mth cycle of the electrode assembly, the number of first stripes is N1, with 3≤N1≤30, and preferably, 5≤N1≤20. The number of second stripes is N2, where N2 is an integer rounded down, and m, M, N1, and N2 satisfy the following: (1) 2≤m≤0.25M, 2≤N2 / N1≤5; (2) 0.25M<m≤0.7M, 2≤N2 / N1≤4; (3) 0.7M<m≤M, 3≤N1≤30. The present application regulates the values ​​of a / b, M, V1, W1, V2, W2, and N1 within the above ranges, and sets different numbers of first stripes and second stripes in electrode assemblies located in different circles. While taking into account the mechanical properties of the secondary battery, the application can improve the wetting performance of the electrolyte on the positive and negative electrode sheets, improve the penetration efficiency of the electrolyte on the positive and negative electrode sheets, and further improve the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0007] In one or more embodiments of the present application, when m, M, N1 and N2 satisfy 0.7M<m≤M, 3≤N1≤30, N2=0. When 0.7M<m≤M, 3≤N1≤30, by not setting the second stripe on each circle within the corresponding number of circles of the electrode assembly, the wetting effect of the electrolyte on the electrode assembly can be improved while taking into account the mechanical properties of the secondary battery, thereby improving the cycle performance of the secondary battery.

[0008] In one or more embodiments of the present application, along the thickness direction of the electrode assembly, the depth of a single first stripe is D1μm, and the depth of a single second stripe is D2μm. When m, M, N1, and N2 satisfy 2≤m≤0.25M, 2≤N2 / N1≤5, in the electrode assembly of the mth circle, 1≤W2 / W1≤4, 1≤D2 / D1≤2. When 2≤m≤0.25M, 2≤N2 / N1≤5, by regulating the values ​​of W2 / W1 and D2 / D1 within the above range, the risk of excessive local accumulation of electrolyte can be reduced, while taking into account the mechanical properties and thermal stability of the secondary battery, it is beneficial to improve the wetting performance of the electrolyte on the positive and negative electrode sheets, further improving the wetting effect of the electrolyte on the interior of the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0009] In one or more embodiments of the present application, when m, M, N1 and N2 satisfy 0.25M<m≤0.7M, 2≤N2 / N1≤4, in the electrode assembly of the mth circle, 1≤W2 / W1≤2, 1≤D2 / D1≤2. When 0.25M<m≤0.7M, 2≤N2 / N1≤4, by regulating the value of W2 / W1 and the value of D2 / D1 within the above range, the risk of excessive local accumulation of the electrolyte can be reduced, while taking into account the mechanical properties and thermal stability of the secondary battery, it is beneficial to improve the wetting performance of the electrolyte on the positive electrode sheet and the negative electrode sheet, thereby improving the wetting effect of the electrolyte on the entire electrode assembly, thereby improving the cycle performance of the secondary battery.

[0010] In one or more embodiments of the present application, the thickness of the positive electrode current collector is T1 μm, 8 ≤ T1 ≤ 30, 2 ≤ D1 ≤ 0.5 T1; and / or the thickness of the negative electrode current collector is T2 μm, 4 ≤ T2 ≤ 30, 2 ≤ D2 ≤ 0.5 T2. By regulating the values ​​of T1, D1, T2, and D2 within the above ranges, it is beneficial to improve the wettability of the electrolyte on the positive and negative electrode sheets, thereby improving the wettability of the electrolyte on the electrode assembly, while taking into account the mechanical properties of the secondary battery and improving the cycle performance of the secondary battery.

[0011] In one or more embodiments of the present application, 2≤D1≤12; and / or, 2≤D2≤12. By regulating the values ​​of D1 and D2 within the above ranges, the wettability of the electrolyte to the positive and negative electrode sheets is improved, thereby improving the wettability of the electrolyte to the electrode assembly, thereby improving the cycle performance of the secondary battery while taking into account the mechanical properties.

[0012] In one or more embodiments of the present application, 2≤m≤0.7M, 12≤N2≤25. When 2≤m≤0.7M, by setting a second stripe within the above range on each circle within the corresponding number of circles of the electrode assembly, while taking into account the mechanical properties of the secondary battery, it is beneficial to improve the wetting performance of the electrolyte on the negative electrode sheet, thereby improving the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0013] In one or more embodiments of the present application, along the thickness direction of the electrode assembly after expansion, each first stripe has a first projection on the separator, and each second stripe has a second projection on the same separator. The spacing between any first projection and an adjacent second projection is A mm, 0.2 ≤ A ≤ 5, preferably, 0.8 ≤ A ≤ 2. By regulating the value of A within the above range, the first stripes and the second stripes are arranged in combination, which is beneficial for the secondary battery to improve the electrolyte infiltration performance of the electrode assembly while taking into account the mechanical properties, thereby improving the cycle performance of the secondary battery.

[0014] In one or more embodiments of the present application, along the length direction of the electrode assembly after unfolding, the spacing between two adjacent first stripes is B1 mm, and m, M, and B1 satisfy the following conditions: 2≤m≤0.7M, 1≤B1≤35; 0.7M<m≤M, 3≤B1≤35. Preferably, 2≤m≤0.7M, 3≤B1≤10; 0.7M<m≤M, 5≤B1≤20. By regulating the value of B1 within the above range, the secondary battery is beneficial to improving the wetting performance of the electrolyte on the positive electrode sheet while taking into account both mechanical properties and processing properties, thereby improving the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0015] In one or more embodiments of the present application, the spacing between two adjacent second stripes along the length of the unfolded electrode assembly is B2 mm, where m, M, and B2 satisfy the following conditions: 2 ≤ m ≤ 0.7 M, 1 ≤ B2 ≤ 12, and preferably, 5 ≤ B2 ≤ 7. By regulating the value of B2 within the above range, the secondary battery can improve the electrolyte wetting performance of the negative electrode sheet while taking into account both mechanical and processing properties, thereby improving the electrolyte wetting effect on the electrode assembly and thus improving the cycle performance of the secondary battery.

[0016] A second aspect of the present application provides an electronic device comprising the secondary battery of any of the aforementioned embodiments. The secondary battery of the present application can have good cycle performance while taking into account mechanical properties. Therefore, the electronic device of the present application has a long service life.

[0017] Beneficial effects of this application:

[0018] The embodiment of the present application regulates the values ​​of a / b, M, V1, W1, V2, W2, and N1 within the above-mentioned ranges, and sets different numbers of first stripes and second stripes in electrode assemblies located in different circles. While taking into account the mechanical properties of the secondary battery, it is possible to improve the wetting performance of the electrolyte on the positive electrode sheet and the negative electrode sheet, thereby improving the penetration efficiency of the electrolyte on the positive electrode sheet and the negative electrode sheet, and further improving the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0019] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 This is a schematic structural diagram of an electrode assembly according to an embodiment of the present application;

[0022] Figure 2 for Figure 1 Schematic diagram of a winding structure formed by an electrode assembly;

[0023] Figure 3 for Figure 2 A schematic diagram of the local structure of the electrode assembly after expansion;

[0024] Figure 4 This is a schematic diagram of the partial structure of the electrode assembly after unfolding in another embodiment of the present application;

[0025] Figure 5 Schematic diagram of a test of the distance A between a first projection and an adjacent second projection.

[0026] Reference numerals: electrode assembly 001 ; positive electrode sheet 10 ; positive electrode current collector 11 ; positive electrode material layer 12 ; first stripe 13 ; negative electrode sheet 20 ; negative electrode current collector 21 ; negative electrode material layer 22 ; second stripe 23 ; separator 30 . DETAILED DESCRIPTION

[0027] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0029] The length of the electrode assembly is a mm, and the width of the electrode assembly is b mm. Figure 1 As shown, the length of electrode assembly 001 is a, and the width of electrode assembly 001 is b. When 2≤a / b≤14, the length of the electrode assembly is greater than the width of the electrode assembly, resulting in insufficient electrolyte infiltration into the interior of the electrode assembly. In the later stages of the secondary battery cycle, the electrode assembly is prone to lithium deposition, resulting in a decrease in the cycle performance of the secondary battery. Based on this, the present application provides a secondary battery that can effectively improve the electrolyte infiltration effect on the electrode assembly, while taking into account the mechanical properties of the secondary battery and improving the cycle performance of the secondary battery.

[0030] The first aspect of the present application provides a secondary battery, the secondary battery comprising an electrode assembly, the electrode assembly being formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet, the length of the electrode assembly being a mm, the width of the electrode assembly being b mm, and 2≤a / b≤14. For example, the value of a / b can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or a range consisting of any two of the values. The total number of turns of the electrode assembly is M turns, 10≤M≤60, preferably, 20≤M≤35, and M is a positive integer. For example, the value of M can be 10, 13, 15, 17, 20, 23, 25, 27, 30, 33, 35, 37, 40, 43, 45, 47, 50, 53, 55, 57, 60, or a range consisting of any two of the values. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material. The Dv50 of the positive electrode active material is V1μm, and 10≤V1≤30. For example, the value of V1 can be 10, 13, 15, 17, 20, 23, 25, 27, 30, or a range consisting of any two of these values. The positive electrode current collector is provided with a plurality of first stripes in the region where the positive electrode material layer is provided. The plurality of first stripes extend along the width direction of the electrode assembly after unfolding and are spaced apart along the length direction of the electrode assembly after unfolding. Along the length direction of the electrode assembly after unfolding, the width of a single first stripe is W1μm, and 3≤W1≤V1. For example, when the value of V1 is 10, 3≤W1≤10, and the value of W1 can be 3, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two of these values; when the value of V1 is 20, 3≤W1≤20, and the value of W1 can be 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 15, 17, 20, or a range consisting of any two of these values; when the value of V1 is 30, 3≤W1≤30, and the value of W1 can be 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 15, 17, 20, 23, 25, 27, 30, or a range consisting of any two of these values. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer including a negative electrode active material, the Dv50 of the negative electrode active material being V2μm, and 10≤V2≤30. For example, the value of V1 can be 10, 13, 15, 17, 20, 23, 25, 27, 30, or a range consisting of any two of these values. The negative electrode current collector is provided with a plurality of second stripes within the region where the negative electrode material layer is provided. The plurality of second stripes extend along the width of the unfolded electrode assembly and are spaced apart along the length of the unfolded electrode assembly. Along the length of the unfolded electrode assembly, the width of a single second stripe is W2 μm, with 3 ≤ W2 ≤ V2.For example, when the value of V2 is 10, 3≤W2≤10, and the value of W2 can be 3, 3.3, 3.5, 3.7, 4, 4.3, 4.5, 4.7, 5, 5.3, 5.5, 5.7, 6, 6.3, 6.5, 6.7, 7, 7.3, 7.5, 7.7, 8, 8.3, 8.5, 8.7, 9, 9.3, 9.5, 9.7, 10 or a range consisting of any two of them; when the value of V2 is 20, 3≤W2≤20, and the value of W2 can be 3, 4, 5 , 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range consisting of any two of these values; when the value of V2 is 30, 3≤W2≤30, and the value of W2 can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, or a range consisting of any two of these values. In the electrode assembly of the mth circle, the number of first stripes is N1, 3≤N1≤30, preferably, 5≤N1≤20. For example, the value of N1 can be 3, 5, 10, 13, 15, 17, 20, 23, 25, 27, 30, or a range consisting of any two of these values. The number of second stripes is N2, where N2 is an integer rounded down, and m, M, N1, and N2 satisfy the following: (1) 2≤m≤0.25M, 2≤N2 / N1≤5; (2) 0.25M<m≤0.7M, 2≤N2 / N1≤4; (3) 0.7M<m≤M, 3≤N1≤30. For example, when 2≤m≤0.25M, the value of N2 / N1 can be 2, 2.3, 2.5, 2.7, 3, 3.3, 3.5, 3.7, 4, 4.3, 4.5, 4.7, 5, or a range consisting of any two of these values. When 0.25M<m≤0.7M, the value of N2 / N1 can be 2, 2.3, 2.5, 2.7, 3, 3.3, 3.5, 3.7, 4, or a range consisting of any two of these values. In this application, the starting point of the first circle of the electrode assembly is the starting end of the electrode assembly, wherein the starting point of the first circle of the electrode assembly is the position where the area with the positive electrode material layer on the positive electrode current collector and the area with the negative electrode material layer on the separator and the negative electrode current collector begin to overlap along the thickness direction of the electrode assembly. It can be understood that the first circle of the electrode assembly refers to the electrode assembly starting from the end face where the starting point of the electrode assembly is located, winding one circle along the winding direction of the electrode assembly, and ending at the other end face of the electrode assembly. At this time, the other end face of the electrode assembly is the ending point, and the starting point and the ending point are flush in the thickness direction of the electrode assembly. The same applies to the electrode assemblies of other circles.

[0031] In this application, for ease of understanding, the electrode assembly is defined as having its own length direction as the X direction, its own width direction as the Y direction, and its own thickness direction as the Z direction in the unfolded state. It is understood that the positive electrode sheet, positive electrode material layer, positive electrode current collector, negative electrode sheet, negative electrode material layer, negative electrode current collector and separator have their own length direction, width direction and thickness direction as the same as the electrode assembly in the unfolded state, and the winding direction of the electrode assembly is the W direction. Figure 2 and Figure 3 As shown, the electrode assembly 001 is formed by stacking and winding a separator 30, a positive electrode sheet 10, a separator 30, and a negative electrode sheet 20. The positive electrode sheet 10 includes a positive electrode collector 11 and a positive electrode material layer 12 provided on both surfaces of the positive electrode collector 11. The negative electrode sheet 20 includes a negative electrode collector 21 and a negative electrode material layer 22 provided on both surfaces of the negative electrode collector 21. The positive electrode collector 11 is provided with a plurality of first stripes 13 in the area where the positive electrode material layer 12 is provided. The plurality of first stripes 13 extend along the width direction Y after the electrode assembly 001 is unfolded and are spaced apart along the length direction X after the electrode assembly 001 is unfolded. The negative electrode collector 21 is provided with a plurality of second stripes 23 in the area where the negative electrode material layer 22 is provided. The plurality of second stripes 23 extend along the width direction Y after the electrode assembly 001 is unfolded and are spaced apart along the length direction X after the electrode assembly 001 is unfolded. As shown Figure 4 As shown, along the length direction of the electrode assembly 001 after unfolding, the width of a single first stripe 13 is W1μm, and the width of a single second stripe 23 is W2μm. It should be noted that in this application, the above-mentioned "multiple" refers to two or more, and the number, size, and spacing of the first and second stripes in the figure are for illustrative purposes only.

[0032] When the values ​​of W1 and W2 are too small, that is, less than the lower limit of this application, the storage space of the electrolyte on the positive electrode sheet and the negative electrode sheet is insufficient. In the later stage of the cycle of the secondary battery, the electrolyte does not wet the positive electrode sheet and / or the negative electrode sheet sufficiently, which can easily lead to a decrease in the cycle performance of the secondary battery. When the values ​​of W1 and W2 are too large, that is, greater than the upper limit of this application, since the width of the first stripe is greater than the Dv50 of the positive electrode active material and the width of the second stripe is greater than the Dv50 of the negative electrode active material, in the actual production coating process, the first stripe is easily filled with the positive electrode slurry and / or the second stripe is easily filled with the negative electrode slurry, resulting in the first stripe being unable to improve the electrolyte wetting of the positive electrode sheet, and the second stripe being unable to improve the electrolyte wetting of the negative electrode sheet. At the same time, the strength of the positive and negative current collectors is reduced. Because the electrolyte preferentially diffuses along the stripes in the positive and negative electrode sheets, providing only the first stripes on the positive current collector can easily lead to poor electrolyte wetting of the negative electrode sheet. Providing only the second stripes on the negative current collector can also lead to poor electrolyte wetting of the positive electrode sheet. Providing the same number of stripes on both the positive and negative current collectors can easily lead to reduced mechanical properties, thereby affecting the safety of the secondary battery. When the value of N1 is too small, that is, less than the lower limit value of this application, the number of first stripes in each circle of the electrode assembly is small, and the corresponding number of second stripes in each circle is also small, and the electrolyte has less infiltration space for the positive electrode plate and the negative electrode plate, which can easily lead to a decrease in the cycle performance of the secondary battery; when the value of N1 is too large, that is, greater than the upper limit value of this application, the number of first stripes in each circle of the electrode assembly is large, and the corresponding number of second stripes in each circle is also large, which can easily lead to a decrease in the mechanical properties of the positive electrode collector and the negative electrode collector, thereby affecting the safety performance of the secondary battery. In the actual production process, the number of first stripes and second stripes is large, which is not conducive to the processing and large-scale production of the electrode assembly. The present application regulates the values ​​of a / b, M, V1, W1, V2, W2, and N1 within the above ranges, and sets different numbers of first stripes and second stripes in electrode assemblies located in different circles. While taking into account the mechanical properties of the secondary battery, it can improve the wetting performance of the electrolyte on the positive electrode sheet and the negative electrode sheet, improve the penetration efficiency of the electrolyte on the positive electrode sheet and the negative electrode sheet, and further improve the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0033] In one or more embodiments of the present application, when m, M, N1 and N2 satisfy 0.7M<m≤M, 3≤N1≤30, 0≤N2≤200. For example, when m, M, N1 and N2 satisfy 0.7M<m≤M, 3≤N1≤30, the value of N2 can be 0, 3, 5, 6, 8, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or a range consisting of any two of these values. When 0.7M<m≤M, 3≤N1≤30, by setting the second stripes within the above range on each circle within the corresponding number of circles of the electrode assembly, while taking into account the mechanical properties of the secondary battery, the wetting performance of the electrolyte on the negative electrode plate can be improved, the penetration efficiency of the electrolyte on the negative electrode plate is improved, and the wetting effect of the electrolyte on the electrode assembly is improved, thereby improving the cycle performance of the secondary battery.

[0034] In one or more embodiments of the present application, when m, M, N1 and N2 satisfy 0.7M<m≤M, 3≤N1≤30, N2=0. When 0.7M<m≤M, 3≤N1≤30, by not setting the second stripe on each circle within the corresponding number of circles of the electrode assembly, the wetting effect of the electrolyte on the electrode assembly can be improved while taking into account the mechanical properties of the secondary battery, thereby improving the cycle performance of the secondary battery.

[0035] In one or more embodiments of the present application, Figure 4 As shown, along the thickness direction Z of the electrode assembly 001, the depth of a single first stripe 13 is D1 μm, and the depth of a single second stripe 23 is D2 μm. When m, M, N1, and N2 satisfy 2≤m≤0.25M and 2≤N2 / N1≤5, in the mth circle of the electrode assembly, 1≤W2 / W1≤4 and 1≤D2 / D1≤2. For example, when m, M, N1, and N2 satisfy 2≤m≤0.25M and 2≤N2 / N1≤5, in the mth circle of the electrode assembly, the value of W2 / W1 can be 1, 1.3, 1.5, 1.7, 2, 2.3, 2.5, 2.7, 3, 3.3, 3.5, 3.7, 4, or a range consisting of any two of these values, and the value of D2 / D1 can be 1, 1.2, 1.5, 1.7, 2, or a range consisting of any two of these values. When 2≤m≤0.25M and 2≤N2 / N1≤5, by regulating the values ​​of W2 / W1 and D2 / D1 within the above range, the risk of excessive local accumulation of electrolyte can be reduced. While taking into account the mechanical properties and thermal stability of the secondary battery, it is beneficial to improve the wetting performance of the electrolyte on the positive electrode sheet and the negative electrode sheet, improve the penetration efficiency of the electrolyte on the positive electrode sheet and the negative electrode sheet, further improve the wetting effect of the electrolyte on the inside of the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0036] In one or more embodiments of the present application, when m, M, N1, and N2 satisfy 0.25M<m≤0.7M, 2≤N2 / N1≤4, in the electrode assembly of the mth circle, 1≤W2 / W1≤2, and 1≤D2 / D1≤2. For example, when m, M, N1, and N2 satisfy 0.25M<m≤0.7M, 2≤N2 / N1≤4, in the electrode assembly of the mth circle, the value of W2 / W1 may be 1, 1.2, 1.5, 1.7, 2, or a range consisting of any two thereof, and the value of D2 / D1 may be 1, 1.2, 1.5, 1.7, 2, or a range consisting of any two thereof. When 0.25M<m≤0.7M and 2≤N2 / N1≤4, by regulating the values ​​of W2 / W1 and D2 / D1 within the above range, the risk of excessive local accumulation of electrolyte can be reduced. While taking into account the mechanical properties and thermal stability of the secondary battery, it is beneficial to improve the wetting performance of the electrolyte on the positive electrode sheet and the negative electrode sheet, and improve the penetration efficiency of the electrolyte on the positive electrode sheet and the negative electrode sheet, thereby improving the wetting effect of the electrolyte on the entire electrode assembly, thereby improving the cycle performance of the secondary battery.

[0037] In one or more embodiments of the present application, Figure 4As shown, the thickness of the positive electrode current collector 11 is T1 μm, 8≤T1≤30, and 2≤D1≤0.5T1. For example, the value of T1 can be 8, 10, 12, 15, 17, 20, 22, 25, 27, 30, or a range consisting of any two values ​​therein. When the value of T1 is 8, 2≤D1≤4, and the value of D1 can be 2, 2.2, 2.5, 2.7, 3, 3.2, 3.5, 3.7, 4, or a range consisting of any two values ​​therein; when the value of T1 is 30, 2≤D1≤15, and the value of D1 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two values ​​therein; and / or, the thickness of the negative electrode current collector 21 is T2 μm, 4≤T2≤30, and 2≤D2≤0.5T2. For example, the value of T2 can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 20, 22, 25, 28, 30, or a range consisting of any two of these values. When the value of T2 is 4, the value of D2 can be 2; when the value of T2 is 30, the value of D2 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of these values. By regulating the values ​​of T1, D1, T2, and D2 within the above range, it is beneficial to improve the wetting performance of the electrolyte on the positive electrode sheet and the negative electrode sheet, improve the penetration efficiency of the electrolyte on the positive electrode sheet and the negative electrode sheet, and thus improve the wetting performance of the electrolyte on the electrode assembly. At the same time, it is beneficial to reduce the risk of the positive electrode collector being penetrated by the first stripe and / or the negative electrode collector being penetrated by the second stripe when setting the first stripe and the second stripe, while taking into account the mechanical properties of the secondary battery, the cycle performance of the secondary battery is improved.

[0038] In one or more embodiments of the present application, 2≤D1≤12, for example, the value of D1 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or a range consisting of any two of these values; and / or, 2≤D2≤12, for example, the value of D2 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or a range consisting of any two of these values. By regulating the values ​​of D1 and D2 within the above ranges, it is beneficial to improve the wetting performance of the electrolyte on the positive electrode sheet and the negative electrode sheet, improve the penetration efficiency of the electrolyte on the positive electrode sheet and the negative electrode sheet, and thus improve the wetting performance of the electrolyte on the electrode assembly. At the same time, it is beneficial to reduce the risk of the positive electrode current collector being penetrated by the first stripe and / or the negative electrode current collector being penetrated by the second stripe when the first stripe and the second stripe are set, thereby improving the cycle performance of the secondary battery while taking into account the mechanical properties.

[0039] In one or more embodiments of the present application, 2≤m≤0.7M, 12≤N2≤25. For example, when 2≤m≤0.7M, the value of N2 can be 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, or a range consisting of any two of these values. When 2≤m≤0.7M, by providing a second stripe within the above range on each circle within the corresponding number of circles of the electrode assembly, while taking into account the mechanical properties of the secondary battery, it is beneficial to improve the wetting performance of the electrolyte on the negative electrode sheet, improve the penetration efficiency of the electrolyte on the negative electrode sheet, and further improve the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0040] In one or more embodiments of the present application, Figure 4 As shown, along the thickness direction Z direction after the electrode assembly 001 is unfolded, each first stripe 13 has a first projection on the separator 30, and each second stripe 23 has a second projection on the same separator. The spacing between any first projection and the adjacent second projection is Amm, 0.2≤A≤5, preferably, 0.8≤A≤2. For example, the value of A can be 0.2, 0.4, 0.5, 0.8, 1, 1.2, 1.4, 1.5, 1.8, 2, 2.2, 2.4, 2.5, 2.8, 3, 3.2, 3.4, 3.5, 3.8, 4, 4.2, 4.4, 4.5, 4.8, 5 or a range consisting of any two values ​​therein. By regulating the value of A within the above range, the first stripes and the second stripes are arranged in combination, which is beneficial for the secondary battery to improve the electrolyte infiltration performance of the electrode assembly while taking into account the mechanical properties, thereby improving the cycle performance of the secondary battery.

[0041] In one or more embodiments of the present application, Figure 4As shown, along the length X direction of the electrode assembly 001 after unfolding, the spacing between two adjacent first stripes 13 is B1 mm, and m, M, and B1 satisfy the following: 2≤m≤0.7M, 1≤B1≤35; 0.7M<m≤M, 3≤B1≤35. Preferably, 2≤m≤0.7M, 3≤B1≤10; 0.7M<m≤M, 5≤B1≤20. For example, when 2≤m≤0.7M, the value of B1 can be 1, 3, 5, 7, 10, 13, 15, 17, 20, 23, 25, 27, 30, 32, 35, or a range consisting of any two of these values; when 0.7M<m≤M, the value of B1 can be 3, 5, 7, 10, 13, 15, 17, 20, 23, 25, 27, 30, 33, 35, or a range consisting of any two of these values. By regulating the value of B1 within the above range, the secondary battery can improve the wetting performance of the electrolyte on the positive electrode sheet while taking into account the mechanical properties and processing performance, thereby improving the penetration efficiency of the electrolyte on the positive electrode sheet, and further improving the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0042] In one or more embodiments of the present application, Figure 4 As shown, along the length direction X after the electrode assembly 001 is unfolded, the spacing between two adjacent second stripes 23 is B2 mm, and m, M and B2 satisfy: 2≤m≤0.7M, 1≤B2≤12, preferably, 5≤B2≤7. For example, when 2≤m≤0.7M, the value of B2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or a range consisting of any two values ​​therein. By regulating the value of B2 within the above range, the secondary battery is beneficial to improving the wetting performance of the electrolyte on the negative electrode sheet while taking into account the mechanical properties and processing properties, thereby improving the penetration efficiency of the electrolyte on the negative electrode sheet, and further improving the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0043] In this application, the cross-section of a single stripe refers to a plane formed along the length and thickness of the stripe after the electrode assembly is unfolded (or a cross-section of the stripe along the length and thickness of the electrode assembly after the electrode assembly is unfolded). This application does not particularly limit the cross-sectional shape of a single first stripe or a single second stripe, as long as it can achieve the purpose of this application. For example, the cross-section of a single first stripe or a single second stripe can each independently be selected from at least one of a triangle, an arc (with an area smaller than a semicircle with the same radius), a semicircle, a rectangle, a trapezoid, or a square.

[0044] This application imposes no particular restrictions on the shape and position of the first and second stripes, as long as they meet the objectives of this application. For example, along the unfolded width of the electrode assembly, the positive electrode current collector has two opposing edges. The first stripe can originate from either edge and extend along the unfolded width of the electrode assembly, or the first stripe can be located between the two edges. The first stripe can also be at an angle of 30° to 150° with the unfolded length of the electrode assembly. Along the unfolded width of the electrode assembly, the negative electrode current collector has two opposing edges. The second stripe can originate from either edge and extend along the unfolded width of the electrode assembly, or the second stripe can be located between the two edges. The second stripe can also be at an angle of 30° to 150° with the unfolded length of the electrode assembly. This arrangement helps improve the wettability of the electrolyte to the positive and negative electrode sheets, thereby improving the electrolyte wettability of the electrode assembly, while ensuring mass production manufacturability and enhancing the cycle performance of the secondary battery. This application imposes no particular restrictions on the length of the first and second stripes, as long as it meets the objectives of this application. For example, along the unfolded width of the electrode assembly, the length of the first stripe may account for 60% to 100% of the width of the region on the positive electrode current collector where the positive electrode material layer is disposed. When the length of the first stripe accounts for 100% of the width of the region on the positive electrode current collector where the positive electrode material layer is disposed, along the unfolded width of the electrode assembly, the length of a single first stripe is equal to the width of the region on the positive electrode current collector where the positive electrode material layer is disposed. Along the unfolded width of the electrode assembly, the length of the second stripe may account for 60% to 100% of the width of the region on the negative electrode current collector where the negative electrode material layer is disposed. When the length of the second stripe accounts for 100% of the width of the region on the negative electrode current collector where the negative electrode material layer is disposed, along the unfolded width of the electrode assembly, the length of a single second stripe is equal to the width of the region on the negative electrode current collector where the negative electrode material layer is disposed.

[0045] In the present application, the features of the above embodiments can be combined arbitrarily, and the embodiments obtained by the combination are also within the protection scope of the present application.

[0046] The present application does not particularly limit the type of positive electrode current collector, as long as it can achieve the purpose of the present application. For example, the positive electrode current collector can include aluminum foil, aluminum alloy foil, or a composite current collector (such as an aluminum-carbon composite current collector).

[0047] In the present application, “a positive electrode material layer provided on at least one surface of the positive electrode current collector” means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the “surface” here can be the entire area of ​​the surface of the positive electrode current collector, or a partial area of ​​the surface of the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the type of positive electrode active material, as long as the purpose of this application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, for example, non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 30μm to 120μm. In the present application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. The present application has no particular restrictions on the type of positive electrode binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The conductive polymer may include, but is not limited to, at least one of a polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art may select the ratio based on actual needs, as long as the objectives of the present application are achieved.

[0048] In one embodiment of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on one surface of the positive electrode current collector, and the positive electrode current collector is provided with a first stripe in the surface area where the positive electrode material layer is provided. In another embodiment of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on both surfaces of the positive electrode current collector, and the positive electrode current collector is provided with a first stripe in any one of the surface areas where the positive electrode material layer is provided. Through the above arrangement, while taking into account the mechanical properties, the positive electrode current collector has good processing performance. In addition, it is conducive to improving the wetting performance of the electrolyte on the positive electrode plate, improving the penetration efficiency of the electrolyte on the positive electrode plate, and then improving the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0049] The present application does not impose any particular restrictions on the method for preparing the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the positive electrode sheet includes but is not limited to the following steps: (1) selecting a positive electrode current collector, and setting a first stripe within the scope of the present application in the area where the positive electrode material layer is set on the positive electrode current collector along the length direction after the positive electrode current collector is unfolded; (2) coating the positive electrode slurry on the surface where the first stripe is set, and forming a positive electrode material layer after drying; (3) coating the positive electrode slurry on the other surface of the positive electrode current collector where the first stripe is not set, and after drying, cold pressing and cutting to obtain a positive electrode sheet with a positive electrode material layer set on both sides. In another embodiment, the method for preparing the positive electrode sheet includes but is not limited to the following steps:

[0050] (1) Select a positive electrode current collector, and set the first stripe within the scope of this application in the area where the positive electrode material layer is set on the positive electrode current collector along the length direction after the positive electrode current collector is unfolded; (2) Coat the surface of the positive electrode current collector where the first stripe is set, and after drying, cold press and cut to obtain a positive electrode sheet with a positive electrode material layer set on one side. This application does not specifically limit the solid content of the above-mentioned positive electrode slurry. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not specifically limit the process parameters of the above-mentioned drying, cold pressing and cutting. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not specifically limit the preparation method of the first stripe. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the stripes can be set by pulsed laser etching. The depth D1 of a single first stripe and the width W1 of a single first stripe can be adjusted by the power and defocus of the pulsed laser emitter, and the spacing B1 between adjacent first stripes can be adjusted by adjusting the spacing between the pulsed laser emitters.

[0051] There is no particular limitation on the type of the negative electrode current collector in this application, as long as the object of this application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.).

[0052] In this application, the "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer may be disposed on one surface of the negative electrode current collector along its own thickness direction, or may be disposed on both surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of the surface of the negative electrode current collector, or may be a partial area of the surface of the negative electrode current collector. There is no particular limitation in this application, as long as the object of this application can be achieved. There is no particular limitation on the type of the negative electrode active material in this application, as long as the object of this application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O with a spinel structure 12 , Li-Al alloy, or at least one of metallic lithium. In this application, there is no particular limitation on the thickness of the negative electrode material layer, as long as the object of this application can be achieved. For example, the thickness of a single-layer negative electrode material layer is 30 μm to 110 μm. Optionally, the negative electrode material layer may further include a negative electrode binder and a conductive agent. There is no particular limitation on the type of the negative electrode binder in the negative electrode material layer in this application, as long as the object of this application can be achieved. For example, the negative electrode binder may be of the same type as the positive electrode binder in the above positive electrode material layer. There is no particular limitation on the type of the conductive agent in the negative electrode material layer in this application, as long as the object of this application can be achieved. For example, the conductive agent may be of the same type as the conductive agent in the above positive electrode material layer. There is no particular limitation on the mass ratio of the negative electrode active material, the conductive agent, and the negative electrode binder in the negative electrode material layer in this application, as long as the object of this application can be achieved.

[0053] In one or more embodiments of the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on one surface of the negative electrode current collector, and the negative electrode current collector is provided with a second stripe in the surface area where the negative electrode material layer is provided. In another embodiment of the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on both surfaces of the negative electrode current collector, and the negative electrode current collector is provided with a second stripe in any one of the surface areas where the negative electrode material layer is provided. Through the above arrangement, while taking into account the mechanical properties, the negative electrode current collector has good processing performance. In addition, it is conducive to improving the wetting performance of the electrolyte on the negative electrode plate, improving the penetration efficiency of the electrolyte on the negative electrode plate, and then improving the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0054] The present application does not impose any particular restrictions on the method for preparing the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the negative electrode sheet includes but is not limited to the following steps: (1) selecting a negative electrode current collector, and setting a second stripe within the scope of the present application in the area where the negative electrode material layer is set on the negative electrode current collector along the length direction after the negative electrode current collector is unfolded; (2) coating the surface of the negative electrode current collector where the second stripe is set with a negative electrode slurry, and forming a negative electrode material layer after drying; (3) coating the other surface of the negative electrode current collector where the second stripe is not set with a negative electrode slurry, and after drying, cold pressing and cutting to obtain a negative electrode sheet with a negative electrode material layer set on both sides. In another embodiment, the method for preparing the negative electrode sheet includes but is not limited to the following steps:

[0055] (1) Select a negative electrode current collector, and set a second stripe within the scope of this application in the area where the negative electrode material layer is set on the negative electrode current collector along the length direction after the negative electrode current collector is unfolded; (2) Coat the surface of the negative electrode current collector where the second stripe is set, and after drying, cold press and cut to obtain a negative electrode sheet with a negative electrode material layer set on one side. This application does not specifically limit the solid content of the above-mentioned negative electrode slurry. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not specifically limit the process parameters of the above-mentioned drying, cold pressing and cutting. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not specifically limit the preparation method of the second stripe. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the stripes can be set by pulsed laser etching. The depth D2 and the width W2 of a single second stripe can be controlled by the power and defocus of the pulsed laser emitter, and the spacing B2 between adjacent second stripes can be controlled by adjusting the spacing between the pulsed laser emitters.

[0056] The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. The diaphragm of the present application may have a porous structure. The present application has no particular restrictions on the size of the pore size of the porous structure of the diaphragm, as long as the purpose of the present application can be achieved. For example, the size of the pore size can be 0.01 μm to 1 μm. The present application has no particular restrictions on the thickness of the diaphragm, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm can be 5 μm to 50 μm.

[0057] The secondary battery of the present application includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) or lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. Above-mentioned linear carbonate compound can include but not limited to at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate or methyl ethyl carbonate.Above-mentioned cyclic carbonate can include but not limited to at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate or vinyl ethylene carbonate.Fluorinated carbonate compound can include but not limited to at least one of fluoroethylene carbonate, 1,2-difluoro ethylene carbonate, 1,1-difluoro ethylene carbonate, 1,1,2-trifluoro ethylene carbonate, 1,1,2,2-tetrafluoro ethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate or trifluoromethyl ethylene carbonate. The carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone or caprolactone. The ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0058] The secondary battery of the present application also includes a housing for accommodating the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the housing and can be any housing known in the art, as long as it can achieve the purpose of this application.

[0059] The present application does not particularly limit the secondary battery, which may include any device that generates an electrochemical reaction. In one embodiment of the present application, the secondary battery may include but is not limited to: a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery or a lithium ion polymer secondary battery, etc.

[0060] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking a positive electrode sheet, a separator, a negative electrode sheet, and another separator in sequence, and winding, folding, etc. as needed to obtain an electrode assembly, placing the electrode assembly in a casing, injecting an electrolyte into the casing, and sealing it to obtain a secondary battery. Alternatively, stacking a separator, a positive electrode sheet, another separator, and a negative electrode sheet in sequence, and winding, folding, etc. as needed to obtain an electrode assembly, placing the electrode assembly in a casing, injecting an electrolyte into the casing, and sealing it to obtain a secondary battery.

[0061] A second aspect of the present application provides an electronic device comprising the secondary battery of any of the aforementioned embodiments. The secondary battery of the present application can have good cycle performance while taking into account mechanical properties. Therefore, the electronic device of the present application has a long service life.

[0062] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0063] Example

[0064] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0065] Test methods and equipment:

[0066] Dv50 test:

[0067] At an ambient temperature of 25°C, the lithium-ion battery was disassembled, and the positive and negative electrode sheets were removed. They were washed with dimethyl carbonate (DMC) for 30 minutes and then air-dried for 2 hours to obtain positive electrode sheet samples and negative electrode sheet samples. The positive electrode material layer on the positive electrode sheet and the negative electrode material layer on the negative electrode sheet were scraped off with a scraper, and the scraped powders were heat-treated at 500°C in a tube furnace under argon protection for 4 hours to obtain positive electrode active material samples and negative electrode active material samples.

[0068] Weigh 0.05g of the positive electrode active material sample to be tested into a 50mL clean beaker. Add 20mL of ethanol to completely disperse the positive electrode active material sample in the ethanol. Ultrasonicate the sample in a 120W ultrasonic cleaner for 30 minutes. Determine the particle size distribution of the positive electrode active material using a laser particle size analyzer. In the volume-based particle size distribution of the positive electrode active material, the particle size at which 50% of the cumulative volume is measured, starting from the smallest particle size, is the Dv50 (V1) of the positive electrode active material.

[0069] Weigh 0.05g of the negative electrode active material sample to be tested into a clean 50mL beaker. Add 20mL of ethanol to completely disperse the negative electrode active material sample in the ethanol. Ultrasonicate the sample in a 120W ultrasonic cleaner for 30 minutes. Determine the particle size distribution of the negative electrode active material using a laser particle size analyzer. In the volume-based particle size distribution of the negative electrode active material, the particle size at which 50% of the cumulative volume is measured, starting from the smallest particle size, is the Dv50 (V2) of the negative electrode active material.

[0070] Tests for M, a, b, W1, W2, N1, N2, D1, D2, T1, T2, B1, B2:

[0071] At an ambient temperature of 25°C, the lithium-ion battery was disassembled to confirm the total number of turns M of the electrode assembly. The length a and width b of the electrode assembly were measured with a soft ruler. The positive and negative electrode sheets were removed and soaked in dimethyl carbonate (DMC) for 20 minutes. The positive and negative electrode sheets were then placed in an oven and dried at 80°C for 12 hours to obtain positive and negative electrode sheet samples. The positive electrode material layer on the surface of the positive electrode sheet was scrubbed with N-methylpyrrolidone (NMP), and the negative electrode material layer on the surface of the negative electrode sheet was scrubbed with deionized water to obtain the positive and negative electrode current collectors.

[0072] Along the length of the unfolded electrode assembly, use a soft ruler to measure the length of the positive electrode current collector and identify different regions of the positive electrode current collector. Count the number of first stripes N1 within each circle of each region of the positive electrode current collector. Select different regions of the positive electrode current collector along the length and thickness of the unfolded electrode assembly and prepare longitudinal cross-sections of the positive electrode current collector with a length of 2 mm. These longitudinal cross-sections in different regions of the positive electrode current collector are measured using a scanning electron microscope. Along the length of the unfolded electrode assembly, measure the maximum length between the cross-sections of individual first stripes, which is the width W1 of each first stripe. Measure the spacing B1 between two adjacent first stripes. Measure the thickness T1 of the positive electrode current collector along the thickness of the electrode assembly. Measure the distance from the surface of the positive electrode current collector to the deepest point of each first stripe, which is the depth D1 of each first stripe.

[0073] Along the length of the unfolded electrode assembly, use a soft ruler to measure the length of the negative electrode current collector and identify different regions of the negative electrode collector. Count the number of second stripes N2 within each circle of each region of the negative electrode collector. Select different regions of the negative electrode current collector along the length and thickness of the unfolded electrode assembly and prepare longitudinal cross-sections of the negative electrode current collector with a length of 2 mm. These longitudinal cross-sections in different regions of the negative electrode current collector are measured using a scanning electron microscope. Along the length of the unfolded electrode assembly, measure the maximum length between the cross-sections of individual second stripes, which is the width W2 of each second stripe. Measure the spacing B2 between two adjacent second stripes. Measure the thickness T2 of the negative electrode current collector along the thickness of the electrode assembly. Measure the distance from the surface of the negative electrode current collector to the deepest point of each second stripe, which is the depth D2 of each second stripe.

[0074] A's test:

[0075] At an ambient temperature of 25°C, the lithium-ion battery was disassembled, the electrode assembly was taken out and unfolded, and the starting ends of the positive electrode current collector and the negative electrode current collector were determined so that the distance between the first projection of the first first stripe on the diaphragm and the second projection of the first second stripe on the diaphragm was 1 mm. The maximum number of second stripes contained between two adjacent first stripes in different regions of the electrode assembly was observed at this time, and the corresponding number of second stripes were placed between two adjacent first stripes. The projections of the middle positions of the corresponding number of second stripes on the diaphragm along the thickness direction of the electrode assembly and along the length direction of the unfolded electrode assembly coincided with the center lines of the two adjacent first stripes, as shown in FIG. Figure 5 As shown, the spacings A1 mm and A2 mm between the first projection and the adjacent second projection on both sides are measured along the length direction X of the electrode assembly after unfolding, and the spacing A between the first projection and the adjacent second projection is A=(A1+A2) / 2.

[0076] Cyclic performance test:

[0077] The lithium-ion batteries in the examples and comparative examples were subjected to charge and discharge cycle tests in a 25°C constant temperature box. The lithium-ion batteries were charged to 4.2V at a constant current of 2C, charged to 0.05V at a constant voltage of 4.2V, and allowed to stand for 5 minutes before being discharged to 2.5V at a constant current of 6C. This was the first cycle, and the first cycle discharge capacity C1 was recorded. After 600 cycles according to the above cycle process, the lithium-ion battery discharge capacity C 600 The 600th cycle capacity retention rate is calculated as an indicator for evaluating the electrolyte's wetting effect on the positive and negative electrode sheets, as well as the cycling performance of the lithium-ion battery, as shown in Formula (I). A lower 600cls capacity retention rate indicates poorer wetting effect of the electrolyte on the positive and negative electrode sheets in the lithium-ion battery, and poorer cycling performance of the lithium-ion battery. A higher 600cls capacity retention rate indicates better wetting effect of the electrolyte on the positive and negative electrode sheets in the lithium-ion battery, and better cycling performance of the lithium-ion battery.

[0078] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0079] Mechanical properties test:

[0080] The lithium-ion batteries in each embodiment and comparative example were charged at a constant current of 2C to 4.2V, and then at a constant voltage of 4.2V to 0.05C to reach a full charge. The fully charged lithium-ion batteries were placed on a test bench. A round rod with a diameter of φ15.8mm and a length of 6cm was placed at the center of the wide face of the lithium-ion battery, with the longitudinal axes of the lithium-ion battery and the round rod parallel to the surface of the test bench, and perpendicular to the longitudinal axes of the lithium-ion battery and the round rod (forming a cross). A 9.1kg weight was dropped vertically and freely from a height of 610mm above the test bench, landing on the intersection of the round rod and the lithium-ion battery.

[0081] Judgment standard: Pass if there is no fire or explosion.

[0082] Twenty lithium-ion batteries were tested in each example or comparative example, and the impact pass rate of the lithium-ion battery = the number of batteries that passed / 20. A higher impact pass rate, i.e., a higher number of batteries that passed, indicates better mechanical properties of the lithium-ion battery.

[0083] Example 1

[0084] <Preparation of positive electrode sheet>

[0085] An aluminum foil with a thickness T1 of 16 μm is selected as the positive electrode current collector. Along the length direction of the unfolded positive electrode current collector, the area where the positive electrode material layer is set on the positive electrode current collector is determined, and the first stripe is laser etched in this area. When 2≤m≤7, N1=10, W1=4μm, D1=2μm, B1=9.996mm; when 7<m≤21, N1=10, W1=4μm, D1=2μm, B1=9.996mm; when 21<m≤30, N1=10, W1=4μm, D1=2μm, B1=9.996mm.

[0086] The positive electrode active material lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and are fully stirred and mixed to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on the surface of the positive electrode collector where the first stripe is laser-etched, and dried at 105°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. Thereafter, the above steps are repeated on the other surface of the positive electrode collector to obtain a positive electrode sheet with a double-sided positive electrode material layer. Then, after cold pressing, cutting, and striping, it is dried under vacuum conditions at 105°C for 4 hours to obtain a positive electrode sheet with a specification of 196mm×1990mm for standby use. Among them, the coating weight of the positive electrode material layer is 15mg / cm 2 The compaction density of the positive electrode material layer is 3.4g / cm 3 .

[0087] <Preparation of negative electrode sheet>

[0088] A copper foil with a thickness T2 of 10 μm was selected as the negative electrode current collector. Along the length direction of the unfolded negative electrode current collector, the area where the negative electrode material layer was set was determined on the negative electrode current collector, and the second stripe was laser etched in this area. When 2≤m≤7, N2=40, W2=10 μm, D2=4 μm, and B2=2.49 mm; when 7<m≤21, N2=30, W2=6 μm, D2=4 μm, and B2=3.327 mm; when 21<m≤30, N1=0.

[0089] The negative electrode active materials artificial graphite, sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97.3:1.7:1.0, and then deionized water is added as a solvent, stirred and mixed evenly to obtain a negative electrode slurry with a solid content of 50wt%. The negative electrode slurry is evenly coated on the surface of the above-mentioned negative electrode collector where the second stripe is laser-etched, and dried at 105°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. Thereafter, the above steps are repeated on the other surface of the negative electrode collector to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 105°C for 4 hours to obtain a negative electrode sheet with a specification of 200mm×2000mm for standby use. Among them, the coating weight of the negative electrode material layer is 8.6mg / cm 2 The compaction density of the negative electrode material layer is 1.6g / cm 3 .

[0090] <Diaphragm>

[0091] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0092] <Preparation of Electrolyte>

[0093] In a dry argon atmosphere glove box, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 to create a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent and thoroughly mixed to create an electrolyte. The mass percentage of LiPF6 in the electrolyte was 12.5%, with the remainder being the base solvent.

[0094] <Preparation of lithium-ion batteries>

[0095] The prepared diaphragm, positive electrode sheet, diaphragm, and negative electrode sheet are stacked in order, with the diaphragm acting as an insulator between the positive and negative electrodes, where A = 1.243 mm. After winding, flattening, current collector welding, shell insertion, inkjet printing, vacuum drying, electrolyte injection, sealing, and high-temperature stabilization, the battery is formed into a capacity to obtain a lithium-ion battery. During the winding process, the starting positions determined by the laser etching of the first and second stripes are followed. The upper limit voltage for the formation is 3.6 V, the formation temperature is 45°C, and the formation stabilization time is 2 hours.

[0096] Example 2 to Example 20

[0097] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0098] Comparative Example 1 to Comparative Example 2

[0099] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0100] Comparative Example 3

[0101] Except that the second stripe is not provided in the step of <Preparation of Negative Electrode Sheet>, the rest is the same as that of Example 1.

[0102] Comparative Example 4

[0103] Except that the first stripe is not provided in the <Preparation of Positive Electrode Sheet>, the rest is the same as Example 1.

[0104] Comparative Example 5

[0105] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Example 1.

[0106] Comparative Example 6

[0107] Except that the first stripe is not provided in the <Preparation of the Positive Electrode Sheet> and the second stripe is not provided in the <Preparation of the Negative Electrode Sheet>, the rest is the same as that of Example 1.

[0108] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0109] Table 1

[0110]

[0111]

[0112] Note: “ / ” in Table 1 indicates no relevant preparation parameters.

[0113] It can be seen from Examples 1 to 20 and Comparative Examples 1 to 6 that by regulating the values ​​of a / b, M, V1, W1, V2, W2, and N1 within the scope of the present application, and setting different numbers of first stripes and second stripes in electrode assemblies located in different circles, the impact pass rate and capacity retention rate of the lithium-ion battery are improved, indicating that the electrolyte has a good infiltration effect on the electrode assembly, and the lithium-ion battery has good cycle performance while taking into account mechanical properties. In comparative example 1, the number of first stripes and second stripes in each circle of the electrode assembly is equal; in the electrode assembly of comparative example 2, along the width direction of the electrode assembly after unfolding, the width of the first stripe is greater than the Dv50 of the positive electrode active material, and the width of the second stripe is greater than the Dv50 of the negative electrode active material; in the electrode assembly of comparative example 3, only the positive electrode current collector is provided with the first stripe in the area where the positive electrode material layer is provided; in the electrode assembly of comparative example 4, only the negative electrode current collector is provided with the second stripe in the area where the negative electrode material layer is provided; the various parameters of the first stripe in the electrode assembly of comparative example 5 are the same as the various parameters of the second stripe in the electrode assembly of embodiment 1, and the various parameters of the second stripe in the electrode assembly of comparative example 5 are the same as the various parameters of the first stripe in the electrode assembly of embodiment 1; in the electrode assembly of comparative example 6, no stripes are provided on the positive electrode current collector and the negative electrode current collector. The impact pass rate and capacity retention rate of the lithium-ion batteries in Comparative Examples 1 to 6 are low, while the impact pass rate and capacity retention rate of the lithium-ion batteries in Examples 1 to 20 are higher, indicating that the electrolyte has a better wetting effect on the electrode assembly, and the lithium-ion batteries have better cycle performance while taking into account mechanical properties.

[0114]

[0115]

[0116]

[0117] When 0.7M < m ≤ M, 3 ≤ N1 ≤ 30, the value of N2 generally affects the mechanical properties and cycle performance of the lithium-ion battery. As can be seen from Examples 1 and 12, when 0.7M < m ≤ M, 3 ≤ N1 ≤ 30, and the value of N2 is within the range of this application, the resulting lithium-ion battery has a high impact pass rate and capacity retention rate, indicating that the electrolyte has a good wetting effect on the electrode assembly, and the lithium-ion battery has good cycle performance while taking into account mechanical properties.

[0118] The W2 / W1 ratio in different electrode assemblies typically affects the mechanical and cycling performance of lithium-ion batteries. As can be seen from Examples 1 and 13 to 16, when the W2 / W1 ratio in different electrode assemblies is within the range of this application, the resulting lithium-ion batteries have high impact pass rates and capacity retention rates, indicating that the electrolyte has a good wetting effect on the electrode assembly, and the lithium-ion batteries have good cycling performance while maintaining good mechanical properties.

[0119] The D2 / D1 ratio in different electrode assemblies typically affects the mechanical and cycling performance of lithium-ion batteries. As can be seen from Examples 1 and 17 to 20, when the D2 / D1 ratio in different electrode assemblies is within the range of this application, the resulting lithium-ion batteries have high impact pass rates and capacity retention rates, indicating that the electrolyte has a good wetting effect on the electrode assembly, and the lithium-ion batteries have good cycling performance while maintaining good mechanical properties.

[0120] The values ​​of T1, T2, D1, and D2 generally affect the mechanical and cycling performance of lithium-ion batteries. As can be seen from Examples 1, 17, and 20, when the values ​​of T1, T2, D1, and D2 are within the ranges of this application, the resulting lithium-ion batteries exhibit high impact pass rates and capacity retention rates, indicating that the electrolyte has a good wetting effect on the electrode assembly, and the lithium-ion batteries have good cycling performance while maintaining good mechanical properties.

[0121] The value of A typically affects the mechanical and cycling performance of lithium-ion batteries. As can be seen from Examples 1 to 16, when the value of A is within the range of this application, the resulting lithium-ion batteries have high impact pass rates and capacity retention rates, indicating that the electrolyte has a good wetting effect on the electrode assembly, and the lithium-ion batteries have good cycling performance while maintaining good mechanical properties.

[0122] The values ​​of B1 and B2 generally affect the mechanical and cycling performance of lithium-ion batteries. As can be seen from Examples 1 to 16, when the values ​​of B1 and B2 are within the ranges of this application, the resulting lithium-ion batteries have high impact pass rates and capacity retention rates, indicating that the electrolyte has a good wetting effect on the electrode assembly, and the lithium-ion batteries have good cycling performance while maintaining good mechanical properties.

[0123] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0124] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0125] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising an electrode assembly, wherein the electrode assembly is formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet, wherein the electrode assembly has a length a mm, a width b mm, and 2 ≤ a / b ≤ 14; and the electrode assembly has a total number of turns M, where 10 ≤ M ≤ 60, and M is a positive integer. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode material layer including a positive electrode active material, the Dv50 of the positive electrode active material being V1 μm, 10≤V1≤30; the positive electrode current collector is provided with a plurality of first stripes in a region where the positive electrode material layer is provided, the plurality of first stripes extending along the width direction of the electrode assembly after unfolding and spaced apart along the length direction of the electrode assembly after unfolding; along the length direction of the electrode assembly after unfolding, the width of a single first stripe is W1 μm, 3≤W1≤V1; The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer including a negative electrode active material, the Dv50 of the negative electrode active material being V2 μm, 10≤V2≤30; the negative electrode current collector is provided with a plurality of second stripes in a region where the negative electrode material layer is provided, the plurality of second stripes extending along the width direction of the electrode assembly after unfolding and spaced apart along the length direction of the electrode assembly after unfolding; along the length direction of the electrode assembly after unfolding, the width of a single second stripe is W2 μm, 3≤W2≤V2; In the electrode assembly of the mth circle, the number of the first stripes is N1, 3≤N1≤30, the number of the second stripes is N2, N2 is an integer rounded down, and m, M, N1 and N2 satisfy: (1)2≤m≤0.25M, 2≤N2 / N1≤5; (2)0.25M<m≤0.7M, 2≤N2 / N1≤4; (3)0.7M<m≤M, 3≤N1≤30.

2. The secondary battery according to claim 1, wherein Along the thickness direction of the electrode assembly, the depth of a single first stripe is D1 μm, and the depth of a single second stripe is D2 μm; When m, M, N1 and N2 satisfy 2≤m≤0.25M, 2≤N2 / N1≤5, in the electrode assembly of the mth circle, 1≤W2 / W1≤4, 1≤D2 / D1≤2.

3. The secondary battery according to claim 1 or 2, wherein When m, M, N1 and N2 satisfy 0.25M<m≤0.7M, 2≤N2 / N1≤4, in the electrode assembly of the mth circle, 1≤W2 / W1≤2, 1≤D2 / D1≤2.

4. The secondary battery according to claim 2 or 3, wherein The thickness of the positive electrode current collector is T1 μm, 8≤T1≤30, 2≤D1≤0.5T1; and / or, The thickness of the negative electrode current collector is T2 μm, 4≤T2≤30, 2≤D2≤0.5T2.

5. The secondary battery according to claim 4, wherein 2≤D1≤12; and / or, 2≤D2≤12.

6. The secondary battery according to claim 1, which satisfies at least one of the following characteristics: (1)20≤M≤35； (2)5≤N1≤20； (3)2≤m≤0.7M, 12≤N2≤25; (4) When m, M, N1 and N2 satisfy 0.7M<m≤M, 3≤N1≤30, N2=0.

7. The secondary battery according to claim 1, wherein Along the thickness direction of the electrode assembly after unfolding, each first stripe has a first projection on the diaphragm, and each second stripe has a second projection on the same diaphragm. The distance between any first projection and the adjacent second projection is A mm, 0.2≤A≤5.

8. The secondary battery according to claim 7, wherein 0.8≤A≤2。 9. The secondary battery according to claim 1, wherein Along the length direction of the electrode assembly after unfolding, the distance between two adjacent first stripes is B1 mm, and m, M and B1 satisfy: 2≤m≤0.7M, 1≤B1≤35; 0.7M<m≤M,3≤B1≤35.

10. The secondary battery according to claim 9, wherein 2≤m≤0.7M,3≤B1≤10; 0.7M<m≤M,5≤B1≤20.

11. The secondary battery according to claim 1, wherein Along the length direction of the electrode assembly after unfolding, the distance between two adjacent second stripes is B2 mm, and m, M and B2 satisfy: 2≤m≤0.7M, 1≤B2≤12.

12. The secondary battery according to claim 11, wherein 5≤B2≤7。 13 . An electronic device comprising the secondary battery according to claim 1 .

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