Secondary battery and electronic device

Abstract

The application provides a secondary battery and an electronic device. An electrode assembly in the secondary battery is formed by winding a first electrode sheet, a separator and a second electrode sheet after stacking. The total number of turns of the first electrode sheet is N turns, 2≤N≤60. The first electrode sheet comprises a first current collector and a first material layer. The areal density of the first material layer is Q1 mg / cm 2 , 15≤Q1≤80. The first material layer is provided with a plurality of first stripes extending along the width direction of the first electrode sheet after being unwound, and the plurality of first stripes are arranged at intervals along the length direction of the first electrode sheet after being unwound. Each turn of the first electrode sheet comprises a first flat area and a first bending area. In the nth turn of the first electrode sheet, the number of first stripes in the first bending area is L1, L1 is an integer, the number of first stripes in the first flat area is K1, and the following conditions are met: 2≤n≤0.25N, 1≤K1 / L1≤2, L1=Q1 / 4; 0.25N The secondary battery has good cycle performance.

Description

Technical Field

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

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

[0003] Currently, a high coating weight (positive electrode material layer coating weight greater than 15 mg / cm³) is adopted. 2 Lithium-ion batteries are used in multiple systems, which helps to meet the requirements of high energy density and long battery life of lithium-ion batteries. However, they bring about the problem of poor wetting ability of electrolyte in the positive electrode material layer, which makes it difficult for electrolyte to diffuse in the positive electrode sheet, thus affecting the performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device to improve the cycle performance of the secondary battery. The specific technical solution is as follows:

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

[0006] The first aspect of this application provides a secondary battery, which includes a flat electrode assembly formed by stacking and winding a first electrode, a separator, and a second electrode. The first electrode has a total of N turns, where 8 ≤ N ≤ 60 and N is a positive integer. The first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector. The coating surface density of the first material layer is Q1 mg / cm³. 215≤Q1≤80. The first material layer is provided with multiple first stripes, which extend along the width direction after the first electrode sheet is unfolded, and are spaced apart along the length direction after the first electrode sheet is unfolded. Each ring of the first electrode sheet includes a first straight region and a first bent region connected to the first straight region. In the nth ring of the first electrode sheet, the number of first stripes located in the first bent region is L1, where L1 is an integer rounded down, and the number of first stripes located in the first straight region is K1. n, N, L1, K1, and Q1 satisfy: 2≤n≤0.25N, 1≤K1 / L1≤2, L1=Q1 / 4; 0.25N<n≤0.7N, 3≤K1 / L1≤4, L1=Q1 / 3; 0.7N<n≤N, 2≤K1 / L1≤3.5, L1=Q1 / 3.5. This application improves the wetting performance of the electrolyte on the first electrode by setting different numbers of stripes in the straight and bent regions of the first electrode in different rings. This increases the penetration efficiency of the electrolyte in the first electrode while maintaining a high energy density in the secondary battery. At the same time, the different number of stripes in the first bent region and the first straight region of each ring of the first electrode improves the uniformity of electrolyte distribution in the first electrode and enhances the cycle performance of the secondary battery.

[0007] In one embodiment of this application, 20 ≤ N ≤ 40; and / or, 35 ≤ Q1 ≤ 50. When the total number of turns N of the first electrode and the coating density Q1 of the first material layer are within the range of this application, the secondary battery has a high energy density.

[0008] In one embodiment of this application, the cross-sectional area of ​​a single first stripe is S1μm. 2 The following conditions must be met for n, N, and S1: 2 ≤ n ≤ 0.25 N, 25 ≤ S1 ≤ 300; 0.25 N < n ≤ 0.7 N, 1000 ≤ S1 ≤ 5000; 0.7 N < n ≤ N, 250 ≤ S1 ≤ 3000. By setting first stripes of different cross-sectional areas on the first electrode with different numbers of turns, the uniformity of electrolyte distribution in the first electrode can be improved, thus enhancing both the energy density and cycle performance of the secondary battery.

[0009] In one embodiment of this application, the width of the first electrode is W1 mm ​​along the width direction after the first electrode is unfolded, and the length of a single first stripe is F1 mm. n, N, F1, and W1 satisfy the following conditions: 2 ≤ n ≤ 0.25 N, 0.5 ≤ F1 / W1 ≤ 0.8; 0.25 N < n ≤ 0.7 N, 0.4 ≤ F1 / W1 ≤ 0.6; 0.7 N < n ≤ N, 0.2 ≤ F1 / W1 ≤ 0.4. By setting first stripes of different lengths on first electrodes with different numbers of turns, it is beneficial to improve the uniformity of electrolyte distribution in the first electrode, thereby improving the cycle performance of the secondary battery while maintaining high energy density.

[0010] In one embodiment of this application, 40 ≤ W1 ≤ 200. When the width of the first electrode is within the above range, it is beneficial to control the length of the first stripe, thus taking into account the energy density of the secondary battery.

[0011] In one embodiment of this application, a plurality of first stripes located in a first straight region are distributed at equal intervals; and / or, a plurality of first stripes located in a first bent region are distributed at equal intervals. This arrangement improves the operability of setting first stripes in the first material layer, and enhances the cycle performance of the secondary battery while satisfying mass production manufacturability.

[0012] In one embodiment of this application, the total number of turns of the second electrode is M, where 8 ≤ M ≤ 60 and M is a positive integer. The second electrode includes a second current collector and a second material layer located on at least one surface of the second current collector, the coating surface density of the second material layer being Q2 mg / cm³. 2 6≤Q2≤80. The second material layer is provided with multiple second stripes, which extend along the width direction after the second electrode sheet is unfolded, and are spaced apart along the length direction after the second electrode sheet is unfolded. Each ring of the second electrode sheet includes a second straight region and a second bent region connected to the second straight region. In the m-th ring of the second electrode sheet, the number of second stripes located in the second bent region is L2, and the number of second stripes located in the second straight region is K2. m, M, L2, K2, and Q2 satisfy: 2≤m≤0.25M, 1≤K2 / L2≤2, L2=Q2 / 4; 0.25M<m≤0.7M, 3≤K2 / L2≤4, L2=Q2 / 3; 0.7M<m≤M, 2≤K2 / L2≤3.5, L2=Q2 / 3.5. This application improves the wetting performance of the electrolyte on the second electrode by setting different numbers of stripes in the straight and bent regions of different rings of the second electrode. This increases the electrolyte penetration efficiency on the second electrode. At the same time, the different number of stripes in the second bent region and the second straight region of each ring of the second electrode improves the uniformity of electrolyte distribution in the second electrode. While the electrolyte has good wetting performance on the first electrode, the cycle performance of the secondary battery is further improved.

[0013] In one embodiment of this application, the cross-sectional area of ​​a single second stripe is S²μm. 2 The following conditions must be met for m, M, and S2: 2 ≤ m ≤ 0.25M, 25 ≤ S2 ≤ 300; 0.25M < m ≤ 0.7M, 1000 ≤ S2 ≤ 5000; 0.7M < m ≤ M, 250 ≤ S2 ≤ 3000. By setting second stripes of different cross-sectional areas on second electrodes with different numbers of turns, the uniformity of electrolyte distribution in the second electrodes can be improved, thus enhancing both the energy density and cycle performance of the secondary battery.

[0014] In one embodiment of this application, the width of the second electrode is W2 mm along its unfolded width direction, and the length of a single first stripe is F2 mm. m, M, F2, and W2 satisfy the following conditions: 2 ≤ m ≤ 0.25 M, 0.5 ≤ F2 / W2 ≤ 0.8; 0.25 M < m ≤ 0.7 M, 0.4 ≤ F2 / W2 ≤ 0.6; 0.7 M < m ≤ M, 0.2 ≤ F2 / W2 ≤ 0.4. By setting second stripes of different lengths on second electrodes with different numbers of turns, it is beneficial to improve the uniformity of electrolyte distribution in the second electrode, thereby improving the cycle performance of the secondary battery while maintaining high energy density.

[0015] In one embodiment of this application, 45 ≤ W2 ≤ 210. The width of the second electrode is within the above range, which is beneficial for controlling the length of the second stripe and taking into account the energy density of the secondary battery.

[0016] A second aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. The secondary battery of this application exhibits excellent cycle performance; therefore, the electronic device of this application has a long service life.

[0017] The beneficial effects of the embodiments of this application are as follows:

[0018] This application embodiment improves the wetting performance of the electrolyte on the first electrode by setting different numbers of stripes in the straight and bent regions of the first electrode in different rings. This increases the penetration efficiency of the electrolyte in the first electrode while maintaining a high energy density in the secondary battery. At the same time, the different number of stripes in the first bent region and the first straight region of each ring of the first electrode improves the consistency of electrolyte distribution in the first electrode and enhances the cycle performance of the secondary battery.

[0019] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

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

[0022] Figure 2 This is a partial structural schematic diagram of the first electrode sheet according to one embodiment of this application;

[0023] Figure 3 This is a partial structural schematic diagram of the first electrode sheet according to another embodiment of this application;

[0024] Figure 4 This is a partial structural schematic diagram of the first electrode sheet in another embodiment of this application;

[0025] Figure 5 This is a partial structural schematic diagram of the second electrode sheet according to one embodiment of this application;

[0026] Figure 6 This is a schematic diagram of the diffusion of electrolyte on the first electrode during the electrode wettability test of this application.

[0027] Reference numerals: Electrode assembly 001; First electrode 10; First material layer 11; First current collector 12; Second electrode 20; Second material layer 21; Second current collector 22; Diaphragm 30; First stripe 101; First straight region 102; First bending region 103; Second stripe 201; Second straight region 202; Second bending region 203. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0029] It should be noted that the invention description in this application uses lithium-ion batteries as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0030] Currently, to address the problem of poor electrolyte wetting ability in the positive and / or negative electrode material layers of high-coating-quality lithium-ion batteries, the main methods include: increasing the settling time after electrolyte injection during lithium-ion battery manufacturing to improve electrolyte diffusion, but this increases production costs and reduces the initial efficiency of the lithium-ion battery; optimizing the electrolyte composition, such as adding dimethyl carbonate or carboxylic acid esters to improve electrolyte conductivity, but side reactions can occur between the electrolyte and the positive and / or negative electrode active materials during lithium-ion battery cycling, generating excess gas and potentially causing safety issues; controlling the porosity of the positive and / or negative electrode sheets, making the edge porosity greater than the center porosity, improves edge wetting, but reduces the wetting effect in the middle part of the positive and / or negative electrode sheets, easily leading to electrolyte breakage in the middle. Therefore, this application provides a secondary battery that can improve the electrode wetting performance of the electrolyte and improve the cycle performance of the secondary battery.

[0031] The first aspect of this application provides a secondary battery, which includes a flat electrode assembly. The electrode assembly is formed by stacking and winding a first electrode, a separator, a second electrode, and another separator, or by stacking and winding a separator, a first electrode, another separator, and a second electrode. The first electrode has a total of N turns, where 8 ≤ N ≤ 60 and N is a positive integer, preferably 20 ≤ N ≤ 40. For example, N is 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or a range of any two of these values. The first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector. The coating surface density of the first material layer is Q1 mg / cm³. 2The first material layer has multiple first stripes, which extend along the width direction of the first electrode sheet after it has been unfolded, and are spaced apart along the length direction of the first electrode sheet after it has been unfolded. The first material layer has multiple first stripes, which extend along the width direction of the first electrode sheet after it has been unfolded, and are spaced apart along the length direction of the first electrode sheet after it has been unfolded. Each ring of the first electrode includes a first flat region and a first bent region connected to the first flat region. In the first electrode of the nth ring, the number of first stripes located in the first bent region is L1, where L1 is an integer rounded down. The number of first stripes located in the first flat region is K1. n, N, L1, K1, and Q1 satisfy: 2≤n≤0.25N, 1≤K1 / L1≤2, L1=Q1 / 4; 0.25N<n≤0.7N, 3≤K1 / L1≤4, L1=Q1 / 3; 0.7N<n≤N, 2≤K1 / L1≤3.5, L1=Q1 / 3.5. In some embodiments, when 2≤n≤0.25N, L1=Q1 / 4, K1 / L1 is 1, 1.2, 1.4, 1.6, 1.8, 2 or any two of these values; when 0.25N<n≤0.7N, L1=Q1 / 3, K1 / L1 is 3, 3.2, 3.4, 3.6, 3.8, 4 or any two of these values; when 0.7N<n≤N, L1=Q1 / 3.5, K1 / L1 is 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.5 or any two of these values. Where n, L1, and K1 are integers rounded down. For example, taking N = 20 and Q1 = 20 as examples, when 2 ≤ n ≤ 5 (i.e., 0.25 × 20), L1 = 20 / 4 = 5, and 5 ≤ K1 ≤ 10; when 5 < n ≤ 14 (i.e., 0.7 × 20), L1 = 20 / 3 ≈ 6.7, and L1 is rounded down to 6, so 18 ≤ K1 ≤ 24; when 14 < n ≤ 20, L1 = 20 / 3.5 ≈ 5.7, and L1 is rounded down to 5, so 10 ≤ K1 ≤ 17. It can be understood that each turn of the first electrode refers to starting from one end of the first electrode and ending at the end of one revolution along the winding direction of the electrode assembly, with the starting and ending points aligned in the thickness direction of the electrode assembly. In this application, the starting point of the first turn of the first electrode is the starting end of the first material layer of the first electrode, and so on. The definition above can also be used for the second electrode in each revolution as described below.

[0032] In this application, for ease of understanding, the positive electrode sheet in its unfolded state is defined with its length direction as the X direction and its width direction as the Y direction. It can be understood that the negative electrode sheet and the separator in their unfolded state have the same length and width directions as the positive electrode sheet, and the winding direction of the electrode assembly is the W direction. For example... Figure 1 and Figure 2 As shown, the first electrode 10 is a positive electrode, and the second electrode 20 is a negative electrode. The flat electrode assembly 001 is formed by stacking and winding the first electrode 10, the separator 30, the second electrode 20, and the separator 30. The flat electrode assembly 001 includes a flat region and two bent regions connected to the flat region. The first electrode 10 includes a first current collector 12 and a first material layer 11 located on the two surfaces of the first current collector 12. The first material layer 11 is provided with a plurality of first stripes 101, which are spaced apart along the X direction. Along the X direction, the first electrode 10 includes a first flat region 102 and a first bent region 103 connected to the first flat region 102. It should be noted that the first flat region of the first electrode is the same as the flat region of the electrode assembly, and the first bent region of the first electrode is the same as the bent region of the electrode assembly. Figure 1 The total number of turns of the first electrode in the middle, Figure 2 The number, size, length, and spacing of the first stripe in the first straight area and the first curved area are merely illustrative examples and are not intended to limit the scope of this application. In this application, "multiple" refers to two or more, and the specific number of the first stripe can be calculated according to the formula of this application.

[0033] When the coating surface density of the first material layer is less than the range of this application, there is no significant problem with the wetting of the secondary battery, but the energy density is low, making it unsuitable for large-scale production and industrial applications. When the coating surface density of the first material layer is greater than the range of this application, the thickness of the first material layer in the secondary battery is large, making it difficult to achieve high energy density while simultaneously ensuring the wetting performance of the electrolyte on the first electrode. Existing electrolyte system theoretical designs can no longer meet the performance requirements of secondary batteries. In addition, when the first electrode is a positive electrode, due to the large coating surface density, the adhesion between the positive electrode material layer and the positive electrode current collector is reduced, making it easy for cracks to appear on the surface of the positive electrode material layer. During cycling, the positive electrode active material falls off, leading to rapid capacity decay of the secondary battery. When the first electrode is a negative electrode, cracks on the surface of the negative electrode material layer will cause uneven current density of the negative electrode during cycling, resulting in lithium plating during charging, further aggravating the capacity decay of the secondary battery and significantly reducing cycle performance. This application improves the wetting performance of the electrolyte on the first electrode by adjusting the coating density of the first material layer within the aforementioned range and setting stripes on the first material layer. This achieves high energy density in the secondary battery while simultaneously enhancing the wetting performance of the electrolyte on the first electrode, thus increasing the electrolyte penetration efficiency on the first electrode. Due to the compression between the electrode and the separator during winding, when the same number of first stripes are set in the first straight region and the first bent region of the first electrode, electrolyte diffusion in the first bent region is difficult, resulting in less improvement in the wetting effect of the electrolyte on the first electrode and a higher likelihood of lithium plating, thereby reducing the cycle performance of the secondary battery. When the same number of first stripes are set in each turn of the first electrode, the different wetting effects of the electrolyte on the first electrode located at different turns can easily lead to electrolyte breakage, further reducing the cycle performance of the secondary battery. This application improves the wetting performance of the electrolyte on the first electrode by setting different numbers of stripes in the straight and bent regions of different coils of the first electrode. This increases the electrolyte penetration efficiency of the first electrode. Furthermore, the different numbers of stripes in the first bent and straight regions of different coils of the first electrode improve the uniformity of electrolyte distribution within the first electrode, thus enhancing the cycle performance of the secondary battery. In this application, when 2≤n≤0.25N, 3≤L1≤20, 3≤K1≤40; when 0.25N<n≤0.7N, 5≤L1≤26, 15≤K1≤104; when 0.7N<n≤N, 4≤L1≤22, 8≤K1≤77.For example, when 2 ≤ n ≤ 0.25N, L1 can be 3, 5, 7, 10, 12, 15, 17, 20, or a range of any two of these values, and K1 can be 3, 5, 7, 10, 12, 15, 17, 20, 22, 25, 27, 30, 32, 35, 37, 40, or a range of any two of these values; when 0.25N < n ≤ 0.7N, L1 can be 5, 7, 10, 12, 15, 17, 20, 22, 25, 26, or a range of any two of these values, and K1 can be 15, 17, 20, 23, 27, 30, 33, 37, 40, 4 3, 47, 50, 53, 57, 60, 63, 67, 70, 73, 77, 80, 83, 87, 90, 93, 97, 100, 102, 104, or any two of these values; when 0.7N < n ≤ N, L1 can be 4, 5, 7, 10, 12, 15, 17, 20, 22, or any two of these values, and K1 can be 8, 10, 13, 17, 20, 23, 27, 30, 33, 37, 40, 43, 47, 50, 53, 57, 60, 63, 67, 70, 73, 77, or any two of these values.

[0034] In one embodiment of this application, the cross-sectional area of ​​a single first stripe is S1μm. 2n, N, and S1 satisfy the following conditions: 2≤n≤0.25N, 25≤S1≤300; 0.25N<n≤0.7N, 1000≤S1≤5000; 0.7N<n≤N, 250≤S1≤3000. For example, when 2 ≤ n ≤ 0.25 N, S1 can be 25, 50, 100, 150, 200, 250, 300, or any two of these values; when 0.25 N < n ≤ 0.7 N, S1 can be 1000, 1250, 1500, 2000, 2500, 4000, 5000, or any two of these values; when 0.7 N < n ≤ N, S1 can be 250, 500, 750, 1000, 1250, 1500, 2000, 2500, 3000, or any two of these values. By setting first stripes of different cross-sectional areas on the first electrode with different numbers of turns, it is beneficial to improve the uniformity of electrolyte distribution in the first electrode. While the secondary battery has a high energy density, it is also beneficial to improve the wetting performance of the electrolyte on the first electrode, increasing the electrolyte penetration efficiency on the first electrode, thus giving the secondary battery good cycle performance. In this application, the cross-section of a single first fringe refers to the plane formed by the first fringe along its length direction and its own thickness direction after being unfolded along the first electrode sheet (or the cross-section obtained by taking a section view of the first fringe along its length direction and thickness direction after being unfolded along the first electrode sheet). Wherein, along the thickness direction of the first electrode sheet, the depth of the first fringe is less than the thickness of the first material layer. This application does not impose any particular limitation on the cross-sectional shape of the first fringe, as long as it achieves the purpose of this application. For example, the cross-section of the first fringe can be triangular, arc-shaped (with an area smaller than a semicircle with the same radius), semicircular, rectangular, trapezoidal, or square. Preferably, the cross-section of the first fringe is rectangular. When the cross-section of the first fringe is rectangular, the width of the cross-section of the first fringe along its length direction after being unfolded along the first electrode sheet is 1.25 μm to 250 μm. For example, the cross-sectional width of the first fringe is 1.25μm, 2μm, 5μm, 10μm, 20μm, 40μm, 60μm, 80μm, 100μm, 120μm, 140μm, 170μm, 200μm, 220μm, 250μm, or a range of any two of these values.

[0035] In one embodiment of this application, along the width direction after the first electrode is unfolded, the width of the first electrode is W1 mm, the length of a single first stripe is F1 mm, and n, N, F1 and W1 satisfy: 2≤n≤0.25N, 0.5≤F1 / W1≤0.8; 0.25N<n≤0.7N, 0.4≤F1 / W1≤0.6; 0.7N<n≤N, 0.2≤F1 / W1≤0.4. For example, when 2 ≤ n ≤ 0.25 N, F1 / W1 is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or a range of any two of these values; when 0.25 N < n ≤ 0.7 N, F1 / W1 is 0.4, 0.45, 0.5, 0.55, 0.6, or a range of any two of these values; when 0.7 N < n ≤ N, F1 / W1 is 0.2, 0.25, 0.3, 0.35, 0.4, or a range of any two of these values. By setting first stripes of different lengths on the first electrode with different numbers of turns, it is beneficial to improve the uniformity of electrolyte distribution in the first electrode. While achieving high energy density in the secondary battery, it is also beneficial to improve the wetting performance of the electrolyte on the first electrode, increasing the electrolyte penetration efficiency in the first electrode, and improving the cycle performance of the secondary battery while meeting the requirements for mass production manufacturability.

[0036] In one embodiment of this application, 40 ≤ W1 ≤ 200. For example, W1 is 40, 60, 80, 100, 120, 140, 160, 180, 200, or a range of any two of these values. When the width of the first electrode is within the above range, it is beneficial to control the length of the first stripe, thus balancing the energy density of the secondary battery. In this application, when 2 ≤ n ≤ 0.25 N, 20 ≤ F1 ≤ 160; when 0.25 N < n ≤ 0.7 N, 16 ≤ F1 ≤ 120; when 0.7 N < n ≤ N, 8 ≤ F1 ≤ 80. When 2 ≤ n ≤ 0.25N, F1 can be 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160 or any two of these values; when 0.25N < n ≤ 0.7N, F1 can be 16, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 or any two of these values; when 0.7N < n ≤ N, F1 can be 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80 or any two of these values.

[0037] In one embodiment of this application, a plurality of first stripes located in a first flat region are distributed at equal intervals; and / or, a plurality of first stripes located in a first bent region are distributed at equal intervals. This arrangement improves the operability of setting the first stripes in the first material layer, enhances the wetting performance of the electrolyte on the first electrode, and improves the cycle performance of the secondary battery while meeting mass production manufacturability requirements.

[0038] This application does not impose any particular limitation on the shape and position of the first stripe, as long as it meets the purpose of this application. For example, along the width direction of the first electrode sheet after it has been unfolded, the first material layer has two opposing edges, and the first stripe can extend from either edge along the width direction of the first electrode sheet, or the first stripe can be located between the two edges. There can also be an angle between the first stripe and the length direction of the first electrode sheet after it has been unfolded, with the angle being 30° to 150°. Figure 2 As shown, the first stripe 101 extends along the Y direction from one edge of the first material layer 11 and is evenly distributed in the first straight region and the first bent region; as Figure 3 As shown, the first stripe 101 is located between the two edges of the first material layer 11 and is evenly distributed in the first straight area and the first bent area; as Figure 4 As shown, the first stripe 101 has an angle α with the X direction. This arrangement improves the uniformity of electrolyte distribution in the first electrode, enhancing the high energy density of the secondary battery while also improving the electrolyte's wetting performance on the first electrode and increasing its penetration efficiency. This satisfies both mass production manufacturability and the cycle performance of the secondary battery. It should be noted that... Figures 2 to 4 The number, size, length, spacing, position, and shape of the first stripe in the first straight area and the first curved area are merely illustrative examples and are not intended to limit this application.

[0039] In one embodiment of this application, the total number of turns of the second electrode is M, where 8 ≤ M ≤ 60 and M is a positive integer. For example, M is 8, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or a range of any two of these values. The second electrode includes a second current collector and a second material layer located on at least one surface of the second current collector. The coating surface density of the second material layer is Q2 mg / cm³. 2The criterion is 6 ≤ Q2 ≤ 80, preferably 12 ≤ Q2 ≤ 40. For example, Q2 can be 6, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or a range of any two of these values. The second material layer is provided with a plurality of second stripes, which extend along the width direction of the unfolded second electrode sheet and are spaced apart along the length direction of the unfolded second electrode sheet. Each ring of the second electrode plate includes a second straight region and a second bent region connected to the second straight region. In the m-th ring of the second electrode plate, the number of second stripes located in the second bent region is L2, where L2 is an integer rounded down. The number of second stripes located in the second straight region is K2. m, M, L2, K2, and Q2 satisfy: 2≤m≤0.25M, 1≤K2 / L2≤2, L2=Q2 / 4; 0.25M<m≤0.7M, 3≤K2 / L2≤4, L2=Q2 / 3; 0.7M<m≤M, 2≤K2 / L2≤3.5, L2=Q2 / 3.5. In some embodiments, when 2≤m≤0.25M, L2=Q2 / 4, K2 / L2 is 1, 1.2, 1.4, 1.6, 1.8, 2 or a range of any two of these values; when 0.25M<m≤0.7M, L2=Q2 / 3, K2 / L2 is 3, 3.2, 3.4, 3.6, 3.8, 4 or a range of any two of these values; when 0.7M<m≤M, L2=Q2 / 3.5, K2 / L2 is 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.5 or a range of any two of these values. Where m, L2, and K2 are integers rounded down. For example, taking M = 20 and Q2 = 20 as examples, when 2 ≤ m ≤ 5 (i.e., 0.25 × 20), L2 = 20 / 4 = 5, and 5 ≤ K2 ≤ 10; when 5 < m ≤ 14 (i.e., 0.7 × 20), L2 = 20 / 3 ≈ 6.7, and rounding L2 down gives a value of 6, so 18 ≤ K2 ≤ 24; when 14 < m ≤ 20, L2 = 20 / 3.5 ≈ 5.7, and rounding L2 down gives a value of 5, so 10 ≤ K2 ≤ 17. Figure 1 and Figure 5 As shown, the second electrode 20 includes a second current collector 22 and a second material layer 21 located on both surfaces of the second current collector 22. The second material layer 21 is provided with a plurality of second stripes 201, which are spaced apart along the X direction. Along the X direction, the second electrode 20 includes a second straight region 202 and a second bent region 203 connected to the second straight region 202. It should be noted that the second straight region of the second electrode is the same as the straight region of the electrode assembly, and the second bent region of the second electrode is the same as the bent region of the electrode assembly. Figure 1 The total number of turns of the second electrode in the middle Figure 5The number, size, length, and spacing of the second stripes in the second straight region and the second bent region are merely illustrative examples and are not intended to limit the scope of this application. In this application, "multiple" refers to two or more, and the specific number of the second stripes can be calculated according to the formula in this application. By setting different numbers of stripes in the straight and bent regions of different rings of the second electrode, this application can improve the wetting performance of the electrolyte on the second electrode while achieving high energy density in the secondary battery, thereby increasing the electrolyte penetration efficiency in the second electrode. Furthermore, the different number of stripes in the second bent region and the second straight region of each ring of the second electrode can improve the consistency of electrolyte distribution in the second electrode. While ensuring good wetting performance of the electrolyte on the first electrode, this further improves the cycle performance of the secondary battery. In this application, when 2≤m≤0.25M, 1≤L2≤20, 1≤K2≤40; when 0.25M<m≤0.7M, 2≤L2≤26, 6≤K2≤104; when 0.7M<m≤M, 1≤L2≤22, 2≤K2≤77. When 2 ≤ m ≤ 0.25M, L2 can be 1, 3, 5, 7, 10, 12, 15, 17, 20, or any range of two of these values, and K2 can be 1, 3, 5, 7, 10, 13, 15, 17, 20, 23, 25, 27, 30, 33, 35, 37, 40, or any range of two of these values. When 0.25M < m ≤ 0.7M, L2 can be 2, 5, 7, 10, 12, 15, 17, 20, 22, 25, 26, or any range of two of these values, and K2 can be 6, 10, 12, 15, 17, 20, 23, 27, 30, 33, 37, 40, or any range of two of these values. 0, 43, 47, 50, 53, 57, 60, 63, 67, 70, 73, 77, 80, 83, 87, 90, 93, 97, 100, 102, 104, or any two of these values; when 0.7M < m ≤ M, L2 can be 1, 3, 5, 7, 10, 12, 15, 17, 20, 22, or any two of these values, and K2 can be 2, 5, 8, 10, 13, 17, 20, 23, 27, 30, 33, 37, 40, 43, 47, 50, 53, 57, 60, 63, 67, 70, 73, 77, or any two of these values.

[0040] In one embodiment of this application, the cross-sectional area of ​​a single second stripe is S²μm. 2, m, M and S2 satisfy: 2≤m≤0.25M, 25≤S2≤300; 0.25M<m≤0.7M, 1000≤S2≤5000; 0.7M<m≤M, 250≤S2≤3000. For example, when 2 ≤ m ≤ 0.25M, S2 is 25, 50, 100, 150, 200, 250, 300, or a range of any two of these values; when 0.25M < m ≤ 0.7M, S2 is 1000, 1250, 1500, 2000, 2500, 4000, 5000, or a range of any two of these values; when 0.7M < m ≤ M, S2 is 250, 500, 750, 1000, 1250, 1500, 2000, 2500, 3000, or a range of any two of these values. By setting second stripes with different cross-sectional areas on second electrodes with different numbers of turns, it is beneficial to improve the uniformity of electrolyte distribution in the second electrodes. This not only improves the wetting performance of the electrolyte on the second electrodes while maintaining high energy density in the secondary battery, but also increases the electrolyte penetration efficiency. Furthermore, while ensuring good wetting performance of the electrolyte on the first electrode, it further enhances the cycle performance of the secondary battery. In this application, the cross-section of a single second stripe refers to the plane formed by the second stripe along its length and thickness direction after unfolding the second electrode (or the cross-section obtained by cross-sectionally viewing the second stripe along its length and thickness direction after unfolding the second electrode). The depth of the second stripe along the thickness direction of the second electrode is less than the thickness of the second material layer. This application does not impose any particular limitation on the cross-sectional shape of the second stripe, as long as it achieves the purpose of this application. For example, the cross-section of the second stripe can be triangular, arc-shaped (with an area smaller than a semicircle with the same radius), semicircular, rectangular, trapezoidal, or square. Preferably, the cross-section of the second stripe is rectangular. When the cross-section of the second fringe is rectangular, the width of the cross-section of the second fringe along the length direction after the second electrode is unfolded is from 1.25 μm to 250 μm. For example, the width of the cross-section of the second fringe can be 1.25 μm, 2 μm, 5 μm, 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 170 μm, 200 μm, 220 μm, 250 μm, or a range of any two of these values.

[0041] In one embodiment of this application, along the width direction after the second electrode is unfolded, the width of the second electrode is W2 mm, the length of a single second stripe is F2 mm, and m, M, F2 and W2 satisfy: 2≤m≤0.25M, 0.5≤F2 / W2≤0.8; 0.25M<m≤0.7M, 0.4≤F2 / W2≤0.6; 0.7M<m≤M, 0.2≤F2 / W2≤0.4. For example, when 2 ≤ m ≤ 0.25 M, F2 / W2 is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or any two of these values; when 0.25 M < m ≤ 0.7 M, F2 / W2 is 0.4, 0.45, 0.5, 0.55, 0.6, or any two of these values; when 0.7 M < m ≤ M, F2 / W2 is 0.2, 0.25, 0.3, 0.35, 0.4, or any two of these values. By setting second stripes of different lengths on the second electrode with different numbers of turns, it is beneficial to improve the uniformity of electrolyte distribution in the second electrode. While achieving high energy density in the secondary battery, it is also beneficial to improve the wetting performance of the electrolyte on the second electrode, increasing the electrolyte penetration efficiency in the second electrode. While meeting the requirements for mass production manufacturability and ensuring good wetting performance of the electrolyte on the first electrode, it further improves the cycle performance of the secondary battery.

[0042] In one embodiment of this application, 45 ≤ W2 ≤ 210. For example, W2 is 45, 60, 80, 100, 120, 140, 160, 180, 200, 210, or a range of any two of these values. When the width of the second electrode is within the above range, it is beneficial to control the length of the second stripe, ensuring good wetting performance of the electrolyte on the first electrode while also considering the energy density of the secondary battery. In this application, when 2 ≤ m ≤ 0.25 M, 22 ≤ F2 ≤ 168; when 0.25 M < m ≤ 0.7 M, 18 ≤ F2 ≤ 126; when 0.7 M < m ≤ M, 9 ≤ F2 ≤ 84. When 2 ≤ m ≤ 0.25M, F2 can be 22, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 165, 168 or any two of these values; when 0.25M < m ≤ 0.7M, F2 can be 18, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 126 or any two of these values; when 0.7M < m ≤ M, F2 can be 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 84 or any two of these values.

[0043] This application does not impose any particular restrictions on the shape and position of the second stripe, as long as it meets the purpose of this application. For example, along the width direction of the unfolded second electrode, the second material layer has two opposing edges, and the second stripe can extend from either edge along the width direction of the second electrode, or the second stripe can be located between the two edges. There can also be an angle between the second stripe and the length direction of the unfolded second electrode, with the angle being 30° to 150°. This configuration helps improve the uniformity of electrolyte distribution in the second electrode, resulting in high energy density in the secondary battery while improving the wetting performance of the electrolyte on the second electrode, increasing the electrolyte penetration efficiency in the second electrode, and improving the cycle performance of the secondary battery while meeting mass production manufacturability requirements.

[0044] This application does not impose any particular restrictions on the first and second electrodes, as long as they achieve the purpose of this application. In one embodiment of this application, the first electrode is a positive electrode, and the second electrode is a negative electrode. When stripes are set only on the positive electrode, by setting different numbers of stripes in the straight and bent regions of different coils of the positive electrode, the secondary battery can achieve high energy density while improving the wetting performance of the electrolyte on the positive electrode and increasing the penetration efficiency of the electrolyte. Furthermore, the different numbers of stripes in the first bent and first straight regions of different coils of the positive electrode improve the uniformity of electrolyte distribution within the positive electrode, thus enhancing the cycle performance of the secondary battery. Similarly, when stripes are set on both the positive and negative electrodes, by setting different numbers of stripes in the straight and bent regions of different coils of the positive and negative electrodes, the secondary battery can achieve high energy density while improving the wetting performance of the electrolyte on the positive electrode and increasing the penetration efficiency of the electrolyte. Furthermore, the different numbers of stripes in the first bent and first straight regions of different coils of the positive electrode improve the uniformity of electrolyte distribution within the positive electrode, thus enhancing the cycle performance of the secondary battery.

[0045] In another embodiment of this application, the first electrode is a negative electrode and the second electrode is a positive electrode. When stripes are set only on the negative electrode, by setting different numbers of stripes in the straight and bent regions of different coils of the negative electrode, the secondary battery can achieve high energy density while improving the wetting performance of the electrolyte on the negative electrode and increasing the penetration efficiency of the electrolyte in the negative electrode. Simultaneously, the different numbers of stripes in the first bent and first straight regions of different coils of the negative electrode improve the uniformity of electrolyte distribution in the negative electrode, thus improving the cycle performance of the secondary battery. Similarly, when stripes are set on both the negative and positive electrodes, by setting different numbers of stripes in the straight and bent regions of different coils of the negative and positive electrodes, the secondary battery can achieve high energy density while improving the wetting performance of the electrolyte on the positive electrode and increasing the penetration efficiency of the electrolyte in the positive electrode. Furthermore, the different numbers of stripes in the first bent and first straight regions of different coils of the positive electrode improve the uniformity of electrolyte distribution in the positive electrode, thus improving the cycle performance of the secondary battery.

[0046] This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The aforementioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its own thickness direction, or on two surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or only a part of the surface area of ​​the positive current collector; this application does not impose any particular limitation, as long as it achieves the purpose of this application. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector can include aluminum foil, aluminum alloy foil, or composite current collectors (e.g., aluminum-carbon composite current collectors). The positive electrode material layer of this application includes a positive electrode active material; this application does not impose any particular limitation on the type of positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (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 manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also include non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application is achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode material layer is 50 μm to 260 μm. In this application, the positive electrode material layer may also include a conductive agent and a positive electrode binder. In this application, there are no particular limitations on the type of conductive agent in the positive electrode material layer, as long as the purpose of this application is achieved. For example, the conductive agent can be the same type as the conductive agent in the aforementioned negative electrode material layer. This application does not impose any particular restriction on the type of positive electrode binder in the positive electrode material layer, as long as it achieves the purpose of this application. For example, the positive electrode binder can be the same type as the positive electrode binder in the aforementioned positive electrode material layer. This application does not impose any particular restriction on 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 can select according to actual needs, as long as the purpose of this application is achieved.

[0047] This application places no particular restrictions on the negative electrode sheet, as long as the objectives of this application can be achieved. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The above "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along its thickness direction, or can be provided on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. This application places no particular restrictions, as long as the objectives of this application can be achieved. This application places no particular restrictions on the negative electrode current collector, as long as the objectives of this application can be achieved. For example, the negative electrode current collector can 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.). The negative electrode material layer of this application includes a negative electrode active material. This application places no particular restrictions on the type of the negative electrode active material, as long as the objectives of this application can be achieved. For example, the negative electrode active material can 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, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy or metallic lithium. In this application, there are no particular restrictions on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 20 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 260 μm. Optionally, the negative electrode material layer can further include a conductive agent and a negative electrode binder. This application places no particular restrictions on the type of the conductive agent in the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the conductive agent can be of the same type as the conductive agent in the above positive electrode material layer. This application places no particular restrictions on the type of the negative electrode binder in the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the negative electrode binder can be of the same type as the positive electrode binder in the above positive electrode material layer. This application places no particular restrictions on the mass ratio of the negative electrode active material, the conductive agent and the negative electrode binder in the negative electrode material layer, as long as the objectives of this application can be achieved.

[0048] This application does not impose any particular restrictions on the preparation method of the first electrode sheet, as long as the purpose of this application can be achieved. For example, the preparation method of the first electrode sheet includes, but is not limited to, the following steps: (1) preparing a first slurry; (2) coating the first slurry onto the surface of the first current collector, drying it, and forming a first material layer on the surface of the first current collector; (3) after cold pressing, calculating the number of first stripes in each first straight area and first bent area according to the formula, and then setting the first stripes at equal intervals in the first straight area and first bent area along the length direction of the first electrode sheet to obtain the first electrode sheet. This application does not impose any particular restrictions on the solid content of the first slurry in step (1) above, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the drying time and temperature in step (2) above, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the process parameters of cold pressing in step (3) above, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the method of setting the first stripe in step (3) above, as long as the purpose of this application can be achieved. For example, the first stripe can be set by pulsed laser etching. The cross-sectional area of ​​the first stripe can be adjusted by the power and defocusing amount of the pulsed laser emitter, and the spacing of the first stripe can be adjusted by adjusting the spacing between the pulsed laser emitters. Specifically, when the first slurry is coated on one surface of the first current collector, the first stripe is only set on one surface of the first electrode; when the first slurry is coated on one surface of the first current collector, the first stripe is set on both surfaces of the first electrode.

[0049] This application does not impose any particular restrictions on the preparation method of the second electrode, as long as the purpose of this application can be achieved. For example, the preparation method of the second electrode includes, but is not limited to, the following steps: (1) preparing a second slurry; (2) coating the second slurry onto the surface of the second current collector, drying it, and forming a second material layer on the surface of the second current collector; (3) calculating the number of second stripes in each second straight area and second bending area according to the formula after cold pressing, and then setting the second stripes at equal intervals in the second straight area and second bending area along the length direction of the second electrode to obtain the second electrode. This application does not impose any particular restrictions on the solid content of the second slurry in step (1) above, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the drying time and temperature in step (2) above, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the process parameters of cold pressing in step (3) above, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the method of setting the second stripe in step (3) above, as long as the purpose of this application can be achieved. For example, the first stripe can be set by pulsed laser etching. The cross-sectional area of ​​the first stripe can be adjusted by the power and defocusing amount of the pulsed laser emitter, and the spacing of the first stripe can be adjusted by adjusting the spacing between the pulsed laser emitters. Wherein, when the second slurry is coated on one surface of the second current collector, the second stripe is only set on one surface of the second electrode; when the second slurry is coated on one surface of the first current collector, the first stripe is set on both surfaces of the first electrode. The secondary battery in this application includes an electrolyte, which includes lithium salt and 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(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not limit the content of lithium salt in the electrolyte, as long as the purpose of this application is achieved. This application does not have particular limitations on non-aqueous solvents, as long as the purpose of this application is achieved. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate, or vinyl ethylene carbonate.Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are 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, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are 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 aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0050] This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane. The diaphragm of this application may have a porous structure, and this application does not impose any particular limitation on the size of the pores in the porous structure of the diaphragm, as long as it achieves the purpose of this application. For example, the pore size may be from 0.01 μm to 1 μm. This application does not impose any particular limitation on the thickness of the diaphragm, as long as it achieves the purpose of this application. For example, the thickness of the diaphragm may be from 5 μm to 500 μm.

[0051] The secondary battery of this application also includes a packaging bag for containing the positive electrode, negative electrode, separator, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0052] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion secondary batteries (sodium-ion batteries), lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.

[0053] The preparation process of the secondary battery in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking a first electrode, a separator, a second electrode, and another separator in sequence, and performing operations such as winding and folding as needed to obtain a flat electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. Alternatively, stacking a separator, a first electrode, another separator, and a second electrode in sequence, and performing operations such as winding and folding as needed to obtain a flat electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery.

[0054] A second aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. The secondary battery of this application exhibits excellent cycle performance; therefore, the electronic device of this application has a long service life.

[0055] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0056] Example

[0057] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0058] Test methods and equipment:

[0059] Electrode wettability test:

[0060] The wettability of the electrolyte on the first and second electrodes is characterized by the diffusion distance of the electrolyte across the surfaces of the first and second electrodes. The specific operating steps are as follows:

[0061] Disassemble the lithium-ion battery in the examples or comparative examples, remove the first electrode, and clean it with dimethyl carbonate (DMC) for 10 minutes to remove the electrolyte and surface by-reaction products. Then place it in a 25°C environment for 2 hours to obtain a dry first electrode. Use a 5mL medical syringe to draw up the electrolyte, expelling air from the syringe tip. Place the unfolded, dry first electrode on a horizontal table, with the medical syringe directly above and perpendicular to the first electrode, the needle tip 30cm vertically dispensing 1mL of electrolyte onto the first electrode. After 1 minute, measure the diffusion distance of the electrolyte. Use a 0.5mm precision ruler to measure the distance between the two points on the first electrode where the electrolyte has diffused the furthest. Figure 6 As shown, this is Figure 6 The value of d is measured five times, and the average value d1 is taken as the diffusion distance of the electrolyte at the first electrode. The electrolyte used is the same as that in Example 1-1. Figure 6 This is only a schematic diagram of the structure of the first electrode at the very center along the length of the first electrode, and is for illustrative purposes only.

[0062] By replacing the first electrode with the second electrode, the diffusion distance d2 of the electrolyte on the second electrode can be obtained.

[0063] Cyclic performance test:

[0064] The lithium-ion batteries in the examples and comparative examples were left to stand at 25°C for 5 minutes. They were then charged at a constant current of 0.5C to 4.2V, and then charged at a constant voltage of 4.2V to a current of 0.05C. After standing for 5 minutes, they were discharged at a constant current of 0.5C to 2.8V. This was the first cycle, and the discharge capacity of the first cycle was recorded. After standing for 10 minutes, the cycle was repeated for 100 cycles, and the discharge capacity of the lithium-ion battery was recorded. The capacity retention rate after 100 cycles was calculated as an indicator of the wetting effect of the first and second electrodes in the lithium-ion battery, denoted as the 100cls capacity retention rate. A lower 100cls capacity retention rate indicates a worse wetting effect of the electrodes in the lithium-ion battery, while a higher 100cls capacity retention rate indicates a better wetting effect of the electrodes in the lithium-ion battery.

[0065] 100cls capacity retention rate = (discharge capacity after 100cls / discharge capacity in the first cycle) × 100%.

[0066] Example 1-1

[0067] <Preparation of the first electrode>

[0068] Using the first electrode as the positive electrode, lithium manganese oxide (LiMn2O4), polyvinylidene fluoride (PVDF) binder, and conductive carbon black were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94.8:2.8:2.4 and thoroughly mixed to obtain a first slurry with a solid content of 72 wt%. The first slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil current collector and dried at 105 °C to obtain a first electrode with a single-sided coating of the first material layer. The above steps were then repeated on the other surface of the same aluminum foil to obtain a first electrode with a double-sided coating of the first material layer. After cold pressing, the total number of turns N of the first electrode was confirmed to be 30, and each turn contained a first straight region and a first bent region. The surface density Q1 of the first material layer was 40 mg / cm³. 2 The width W1 of the first electrode is 120 mm, and the cross-section of the first fringe is rectangular. When 2 ≤ n ≤ 7, the number of first fringes L1 located in the first bending region is 10, the number of first fringes K1 located in the first straight region is 15, and the cross-sectional area S1 of the first fringe is 100 μm. 2 The length F1 of the first fringe is 72 mm, and the cross-sectional width of the first fringe along the length direction after the first electrode is unfolded is 5 μm; when 7 < n ≤ 21, L1 is 13, K1 is 45, and S1 is 2500 μm. 2 F1 is 60 mm, and the cross-sectional width of the first fringe is 125 μm along the length direction after the first electrode is unfolded; when 21 < n ≤ 30, L1 is 11, K1 is 33, and S1 is 1250 μm. 2 F1 is 36mm. Along the length direction of the first electrode after unfolding, the cross-sectional width of the first stripe is 62.5μm. According to the above data, the first stripe is laser-etched at equal intervals on the two first material layers of the first electrode in the first straight area and the first bending area along the length direction of the first electrode. After slitting, a first electrode with a specification of 120mm×810mm is obtained for use. The depth of the first stripe along the thickness direction of the first electrode is 20μm.

[0069] <Preparation of the Second Electrode>

[0070] The second electrode sheet was used as the negative electrode sheet. Artificial graphite, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 97.3:1.7:1.0. Deionized water was added as a solvent, and the mixture was stirred until homogeneous, yielding a second slurry with a solid content of 50 wt%. This second slurry was uniformly coated onto one surface of an 8 μm thick copper foil used as a second current collector, and dried at 105 °C to obtain a second electrode sheet with a single-sided coating of the second material layer. The above steps were then repeated on the other surface of the copper foil to obtain a second electrode sheet with a double-sided coating of the second material layer. After cold pressing, cutting, and slitting, the second electrode sheet was dried under vacuum at 105 °C for 4 hours to obtain a second electrode sheet with dimensions of 126 mm × 866 mm for later use. The surface density Q2 of the second material layer was 30 mg / cm³. 2 .

[0071] <Preparation of the diaphragm>

[0072] A 14μm thick polypropylene (PP) film was used as the separator.

[0073] <Preparation of Electrolyte>

[0074] In a dry argon-atmospheric glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20. Then, lithium hexafluorophosphate (LiPF6) was added to the organic solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 12.5%.

[0075] <Preparation of Lithium-ion Batteries>

[0076] The separator, first electrode, separator, and second electrode prepared above are stacked in sequence so that the separator is positioned between the positive and negative electrodes to provide isolation. After being wound, a flat electrode assembly is obtained. The electrode assembly is then sealed from the top and side, inkjet-printed, vacuum dried, injected with electrolyte, and allowed to stand at high temperature for capacity formation before being trimmed to obtain a lithium-ion battery.

[0077] Examples 1-2 to 1-22

[0078] Except for adjusting the relevant preparation parameters according to Tables 1 and 2, the rest is the same as in Example 1-1. When the cross-sectional area S1 of the first stripe changes, the depth of the first stripe in the first material layer does not change, but the cross-sectional width of the first stripe changes accordingly.

[0079] Examples 1-23

[0080] Except for the preparation of the first electrode, which follows the steps below and the relevant preparation parameters are adjusted according to Tables 1 and 2, the rest is the same as in Example 1-1.

[0081] <Preparation of the first electrode>

[0082] Using the first electrode as the negative electrode, artificial graphite, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 97.3:1.7:1.0. Deionized water was then added as a solvent, and the mixture was stirred until homogeneous, yielding a first slurry with a solid content of 40 wt%. This first slurry was uniformly coated onto one surface of a first current collector copper foil with a thickness of 8 μm and dried at 105 °C to obtain a first electrode with a single-sided coating of the first material layer. The above steps were then repeated on the other surface of the same copper foil to obtain a first electrode with a double-sided coating of the first material layer. After cold pressing, the total number of turns N of the first electrode was confirmed to be 32, and each turn contained a first straight region and a first bent region. The surface density Q1 of the first material layer was 30 mg / cm³. 2 The width W1 of the first electrode is 126 mm. When 2 ≤ n ≤ 8, the number L1 of the first fringe located in the first bending region is 7, the number K1 of the first fringe located in the first straight region is 10, and the cross-sectional area S1 of the first fringe is 100 μm. 2 The length F1 of the first fringe is 75 mm, and the cross-sectional width of the first fringe along the length direction after the first electrode is unfolded is 5 μm; when 8 < n ≤ 22, L1 is 10, K1 is 35, and S1 is 2500 μm. 2 F1 is 63 mm, and the cross-sectional width of the first fringe along the length of the first electrode after unfolding is 125 μm; when 22 < n ≤ 32, L1 is 8, K1 is 24, and S1 is 1250 μm. 2 F1 is 37mm. Along the length direction of the first electrode after unfolding, the cross-sectional width of the first stripe is 62.5μm. According to the above data, the first stripe is laser-etched at equal intervals on the two first material layers of the first electrode in the first straight area and the first bending area along the length direction of the first electrode. After slitting, a first electrode with a specification of 126mm×866mm is obtained for use. The depth of the first stripe along the thickness direction of the first electrode is 20μm.

[0083] <Preparation of the Second Electrode>

[0084] Using the second electrode as the positive electrode, lithium manganese oxide (LiMn2O4), polyvinylidene fluoride (PVDF) binder, and conductive carbon black were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94.8:2.8:2.4 and thoroughly mixed to obtain a second slurry with a solid content of 72 wt%. This second slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a second current collector and dried at 105 °C to obtain a second electrode with a single-sided coating of the second material layer. The above steps were then repeated on the other surface of the aluminum foil to obtain a second electrode with a double-sided coating of the second material layer. After cold pressing, cutting, and slitting, the second electrode was dried under vacuum at 105 °C for 4 hours to obtain a second electrode with dimensions of 120 mm × 810 mm for later use. The surface density Q2 of the second material layer was 40 mg / cm³. 2 .

[0085] Example 2-1

[0086] Except for the preparation of the second electrode, which follows the steps below and the relevant preparation parameters are adjusted according to Tables 3 and 4, the rest is the same as in Example 1-1.

[0087] <Preparation of the Second Electrode>

[0088] Using the second electrode as the negative electrode, artificial graphite, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 97.3:1.7:1.0. Deionized water was then added as a solvent, and the mixture was stirred until homogeneous, yielding a second slurry with a solid content of 40 wt%. This second slurry was uniformly coated onto one surface of an 8 μm thick copper current collector foil and dried at 105 °C to obtain a second electrode with a single-sided coating of the second material layer. The above steps were then repeated on the other surface of the copper current collector foil to obtain a second electrode with a double-sided coating of the second material layer. After cold pressing, the total number of turns M of the second electrode was confirmed to be 32, with each turn containing a second straight section and a second bending section. The surface density Q2 of the second material layer was 30 mg / cm³. 2 The width W2 of the second electrode is 126 mm. When 2 ≤ m ≤ 8, the number L2 of the second fringe located in the second bending region is 7, the number K2 of the second fringe located in the second straight region is 10, and the cross-sectional area S2 of the second fringe is 100 μm. 2 The length F2 of the second fringe is 75 mm, and the cross-sectional width of the second fringe along the length direction after the second electrode is unfolded is 5 μm; when 8 < m ≤ 22, L2 is 10, K2 is 35, and S2 is 2500 μm. 2F2 is 63 mm, and the cross-sectional width of the second fringe along the length of the second electrode after unfolding is 125 μm; when 22 < m ≤ 32, L2 is 8, K2 is 24, and S2 is 1250 μm. 2 F2 is 37mm. Along the length direction of the second electrode after unfolding, the cross-sectional width of the second stripe is 62.5μm. Along the length direction of the second electrode, in the second straight area and the second bending area, according to the above data, the second stripe is laser-etched at equal intervals on the two second material layers of the second electrode. After slitting, a second electrode with a specification of 126mm×866mm is obtained for use. The depth of the second stripe along the thickness direction of the second electrode is 20μm.

[0089] Examples 2-2 to 2-22

[0090] Except for adjusting the relevant preparation parameters according to Tables 3 and 4, the rest is the same as in Example 2-1. When the cross-sectional area S2 of the second stripe changes, the depth of the second stripe in the second material layer does not change, but the cross-sectional width of the second stripe changes accordingly.

[0091] Comparative Example 1

[0092] Except that no stripes are etched on the first and second electrodes, and the relevant preparation parameters are adjusted according to Tables 1 and 2, the rest is the same as in Example 1-1.

[0093] Comparative Examples 2 to 6

[0094] Except for adjusting the relevant preparation parameters according to Tables 1 and 2, the rest is the same as in Example 1-1.

[0095] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0096] Table 1

[0097]

[0098]

[0099] Note: " / " in Table 1 indicates that there are no relevant preparation parameters.

[0100] Table 2

[0101]

[0102]

[0103] As can be seen from Examples 1-1 to 1-23 and Comparative Examples 1 to 6, by adjusting the total number of turns of the first electrode and the coating density of the first material layer within the scope of this application, and by setting different numbers of first stripes in the first straight area and the first bent area of ​​the first electrode in different turns, the electrolyte diffusion distance on the first electrode is greater, resulting in a higher 100cls capacity retention rate of the lithium-ion battery. This indicates that the electrolyte has better wetting performance on the first electrode, and the lithium-ion battery has better cycle performance. In Comparative Example 1, no stripes are set on the first and second electrodes of the lithium-ion battery. In Comparative Example 2, the number of first stripes in the first straight area of ​​each turn of the lithium-ion battery is the same, and the number of first stripes in the first bent area of ​​each turn is the same. In Comparative Example 3, the number of first stripes in the first straight area and the first bent area of ​​each turn of the lithium-ion battery is the same. The electrolyte diffusion distance on the first electrode is smaller, and the 100cls capacity retention rate of the lithium-ion battery is lower. This indicates that the electrolyte has a poor wetting effect on the first electrode in Comparative Examples 1 to 3, and the lithium-ion battery has poor cycle performance. In Comparative Example 4, the total number of turns of the first electrode in the lithium-ion battery is outside the scope of this application. When the total number of turns of the first electrode is too large, the diffusion of the electrolyte in the middle of the lithium-ion battery is hindered, which may cause a partial break in the electrolyte in the middle area of ​​the electrode assembly. This increases the cycle impedance of the lithium-ion battery, leading to a rapid decrease in the capacity retention rate. In Comparative Examples 5 and 6, the coating density of the first material layer in the lithium-ion battery is outside the scope of this application. When the coating density of the first material layer is too low, the energy density of the lithium-ion battery obtained in Comparative Example 5 is low, which is not suitable for large-scale production and industrial application. When the coating density of the first material layer is too high, the adhesion between the first material layer and the first current collector in the lithium-ion battery obtained in Comparative Example 6 is reduced, making it easy for cracks to appear on the surface of the first electrode. During cycling, the first active material falls off, causing the lithium-ion battery capacity to decay rapidly. Compared with Examples 1-1 to 1-23, Comparative Examples 1 to 6 show that the electrolyte in the examples has a greater diffusion distance on the first electrode and a higher 100cls capacity retention rate of the lithium-ion battery. This indicates that the electrolyte in the examples of this application has a better wetting effect on the first electrode and better cycle performance of the lithium-ion battery.

[0104] The cross-sectional area of ​​a single first stripe typically affects the cycle performance of a lithium-ion battery. As can be seen from Examples 1-1, 1-12 to 1-14, when the cross-sectional area of ​​a single first stripe is within the range of this application, the electrolyte diffusion distance on the first electrode is larger, and the 100cls capacity retention rate of the lithium-ion battery is higher. This indicates that the electrolyte in the embodiments of this application has a better wetting effect on the first electrode, resulting in better cycle performance of the lithium-ion battery. However, in Examples 1-14, the cross-sectional area and width of a single first stripe are larger, making it easier for the electrolyte to accumulate in the first stripe during flow, leading to a smaller diffusion distance of the electrolyte on the first electrode.

[0105] The length of a single first stripe typically affects the cycle performance of a lithium-ion battery. As seen in Examples 1-1, 1-15 to 1-18, when the length of a single first stripe is within the range specified in this application, the electrolyte diffusion distance on the first electrode is greater, resulting in a higher 100cls capacity retention rate for the lithium-ion battery. This indicates that the electrolyte in these examples has a better wetting effect on the first electrode, leading to better cycle performance of the lithium-ion battery. In Examples 1-18, the length of a single first stripe is relatively large, resulting in a greater diffusion distance of the electrolyte on the first electrode. However, in actual production, when the length of a single first stripe is too large, the difficulty of fine processing increases, the content of the first active material in the first material layer decreases, the energy density of the lithium-ion battery decreases, and lithium plating is more likely to occur, leading to a decrease in the 100cls capacity retention rate of the lithium-ion battery.

[0106] The width of the first electrode typically affects the cycle performance of lithium-ion batteries. As seen in Examples 1-1, 1-19 to 1-22, when the width of the first electrode is within the range specified in this application, the electrolyte diffusion distance on the first electrode is greater, resulting in a higher 100cls capacity retention rate for the lithium-ion battery. This indicates that the electrolyte in these examples has a better wetting effect on the first electrode, leading to better cycle performance of the lithium-ion battery. In Examples 1-22, the width of the first electrode is larger, and the length of a single first stripe also increases accordingly, resulting in a greater diffusion distance of the electrolyte on the first electrode. However, in actual production, when the length of a single first stripe is too large, the difficulty of fine processing increases, the content of the first active material in the first material layer decreases, the energy density of the lithium-ion battery decreases, and lithium plating is more likely to occur, leading to a decrease in the 100cls capacity retention rate of the lithium-ion battery.

[0107] Table 3

[0108]

[0109]

[0110] Note: " / " in Table 3 indicates that no relevant preparation parameters are available.

[0111] Table 4

[0112]

[0113]

[0114] The total number of turns of the second electrode, the coating density of the second material layer, and the different numbers of second stripes in the second straight and second bent regions of different turns of the second electrode generally affect the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-11, when the total number of turns of the second electrode and the coating density of the second material layer are within the range of this application, and when different numbers of second stripes are set in the second straight and second bent regions of different turns of the second electrode, the diffusion distance of the electrolyte between the first and second electrodes is larger, and the 100cls capacity retention rate of the lithium-ion battery is higher. This indicates that the electrolyte in the embodiments of this application has a better wetting effect on the first and second electrodes, and the cycle performance of the lithium-ion battery is better.

[0115] The cross-sectional area of ​​a single second stripe typically affects the cycle performance of a lithium-ion battery. As can be seen from Examples 2-1, 2-12 to 2-14, when the cross-sectional area of ​​a single second stripe is within the range of this application, the diffusion distance of the electrolyte between the first and second electrodes is larger, and the 100cls capacity retention rate of the lithium-ion battery is higher. This indicates that the electrolyte in the embodiments of this application has a better wetting effect on the first and second electrodes, resulting in better cycle performance of the lithium-ion battery. However, in Examples 2-14, the cross-sectional area of ​​a single first and second stripe is larger, making it easier for the electrolyte to accumulate in the first and second stripes during flow, leading to a smaller diffusion distance between the electrolyte and the first and second electrodes.

[0116] The length of a single second stripe typically affects the cycle performance of a lithium-ion battery. As seen in Examples 2-1, 2-15 to 2-18, when the length of a single second stripe is within the range specified in this application, the electrolyte diffusion distance between the first and second electrodes is greater, resulting in a higher 100cls capacity retention rate for the lithium-ion battery. This indicates that the electrolyte in these examples has a better wetting effect on the first and second electrodes, leading to better cycle performance of the lithium-ion battery. In Example 2-18, the length of a single first and second stripe is relatively large, resulting in a greater diffusion distance of the electrolyte between the first and second electrodes. However, in actual production, when the length of a single first and second stripe is too large, the difficulty of fine processing increases, leading to a decrease in the content of the first active material in the first material layer and the content of the second active material in the second material layer. This reduces the energy density of the lithium-ion battery, making it more prone to lithium plating and consequently decreasing the 100cls capacity retention rate.

[0117] The width of the second electrode typically affects the cycle performance of lithium-ion batteries. As seen in Examples 2-1, 2-19 to 2-22, when the width of the second electrode is within the range specified in this application, the electrolyte diffusion distance between the first and second electrodes is greater, resulting in a higher 100cls capacity retention rate for the lithium-ion battery. This indicates that the electrolyte in these examples has a better wetting effect on the first and second electrodes, leading to better cycle performance of the lithium-ion battery. In Example 2-22, the width of the first and second electrodes is larger, and the length of individual first and second stripes also increases accordingly. While this results in a greater diffusion distance of the electrolyte between the first and second electrodes, in actual production, when the length of individual first and second stripes is too large, the difficulty of fine processing increases, leading to a decrease in the content of the first active material in the first material layer and the content of the second active material in the second material layer. This reduces the energy density of the lithium-ion battery, making it more prone to lithium plating and consequently decreasing the 100cls capacity retention rate.

[0118] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0119] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0120] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery, comprising a flat electrode assembly, the electrode assembly being formed by stacking and winding a first electrode, a separator, and a second electrode, wherein the first electrode has a total of N turns, 8≤N≤60 and N is a positive integer; The first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector, wherein the coating areal density of the first material layer is Q1 mg / cm³. 2 , 15≤Q1≤80; The first material layer is provided with a plurality of first stripes, which extend along the width direction of the first electrode after it is unfolded, and the plurality of first stripes are spaced apart along the length direction of the first electrode after it is unfolded. Each ring of the first electrode includes a first flat region and a first bent region connected to the first flat region. In the nth ring of the first electrode, the number of first stripes located in the first bent region is L1, where L1 is an integer rounded down, and the number of first stripes located in the first flat region is K1. n, N, L1, K1, and Q1 satisfy: 2≤n≤0.25N, 1≤K1 / L1≤2, L1=Q1 / 4; 0.25N<n≤0.7N, 3≤K1 / L1≤4, L1=Q1 / 3; 0.7N<n≤N, 2≤K1 / L1≤3.5, L1=Q1 / 3.

5.

2. The secondary battery according to claim 1, wherein, 20≤N≤40; and / or, 35≤Q1≤50.

3. The secondary battery according to claim 1, wherein, The cross-sectional area of ​​a single first stripe is S1μm 2 n, N, and S1 satisfy: 2≤n≤0.25N, 25≤S1≤300; 0.25N<n≤0.7N, 1000≤S1≤5000; 0.7N<n≤N, 250≤S1≤3000.

4. The secondary battery according to claim 1, wherein, Along the width direction of the first electrode after it has been unfolded, the width of the first electrode is W1 mm, the length of a single first stripe is F1 mm, and n, N, F1, and W1 satisfy: 2≤n≤0.25N, 0.5≤F1 / W1≤0.8; 0.25N<n≤0.7N, 0.4≤F1 / W1≤0.6; 0.7N<n≤N, 0.2≤F1 / W1≤0.

4.

5. The secondary battery according to claim 4, wherein, 40≤W1≤200。 6. The secondary battery according to claim 1, wherein, The plurality of first stripes located within the first straight region are distributed at equal intervals; And / or, The plurality of first stripes located within the first bending area are distributed at equal intervals.

7. The secondary battery according to any one of claims 1 to 6, wherein, The total number of turns of the second electrode is M, where 8 ≤ M ≤ 60 and M is a positive integer; The second electrode includes a second current collector and a second material layer located on at least one surface of the second current collector, wherein the coating surface density of the second material layer is Q2 mg / cm³. 2 , 6≤Q2≤80; The second material layer is provided with a plurality of second stripes, which extend along the width direction of the second electrode after it is unfolded, and are spaced apart along the length direction of the second electrode after it is unfolded. Each ring of the second electrode includes a second straight region and a second bent region connected to the second straight region. In the m-th ring of the second electrode, the number of second stripes located in the second bent region is L2, where L2 is an integer rounded down. The number of second stripes located in the second straight region is K2. m, M, L2, K2, and Q2 satisfy: 2≤m≤0.25M, 1≤K2 / L2≤2, L2=Q2 / 4; 0.25M<m≤0.7M, 3≤K2 / L2≤4, L2=Q2 / 3; 0.7M<m≤M, 2≤K2 / L2≤3.5, L2=Q2 / 3.

5.

8. The secondary battery according to claim 7, wherein, The cross-sectional area of ​​a single second stripe is S²μm. 2 m, M, and S2 satisfy: 2≤m≤0.25M, 25≤S2≤300; 0.25M<m≤0.7M, 1000≤S2≤5000; 0.7M<m≤M, 250≤S2≤3000.

9. The secondary battery according to claim 7, wherein, Along the width direction after the second electrode is unfolded, the width of the second electrode is W2 mm, and the length of a single first stripe is F2 mm. m, M, F2, and W2 satisfy the following: 2≤m≤0.25M, 0.5≤F2 / W2≤0.8; 0.25M<m≤0.7M, 0.4≤F2 / W2≤0.6; 0.7M<m≤M, 0.2≤F2 / W2≤0.

4.

10. The secondary battery according to claim 9, wherein, 45≤W2≤210。 11. An electronic device comprising a secondary battery as described in any one of claims 1 to 10.

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