Secondary battery and electronic device

Abstract

The application provides a secondary battery and an electronic device. The secondary battery comprises a wound electrode assembly, the electrode assembly comprises a first electrode sheet, each coil of the first electrode sheet comprises two flat areas, and the width of the flat areas is L mm along the width direction of the electrode assembly. A plurality of through holes are arranged on the first area and the second area of at least one coil of the first electrode sheet, and the plurality of through holes on the second area are symmetrical to the plurality of through holes on the first area along a center line. A first through hole is arranged close to a first edge, N through holes are arranged on the first area along the direction from the first edge to the center, 5≤N≤20 and N is a positive integer, the diameter of the maximum circumscribed circle of the outer contour of the first through hole is D1 mm, D1=A×L, 1.5%≤A≤6%, the diameter of the maximum circumscribed circle of the outer contour of the nth through hole is Dn mm, Dn=B×D1, 2≤n≤N, 0.6≤B≤0.9. The above arrangement improves the cycle performance of the secondary battery. n mm, D n =B n‑1 ×D1, 2≤n≤N, 0.6≤B≤0.9. The above arrangement improves the cycle performance of the secondary battery.

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 have advantages such as good rate performance, light weight, long cycle life, no memory effect and good stability, and are widely used energy storage and power products under current technological conditions.

[0003] With the increasing demand for high-capacity applications, the size of secondary batteries is gradually increasing, and the length and width of the electrodes in secondary batteries are also increasing. This makes the electrodes prone to black spots due to insufficient electrolyte wetting, which reduces the cycle performance of secondary batteries. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and electronic device to improve the wetting of the electrode sheet, especially the middle part of the electrode sheet, by the electrolyte, thereby improving the cycle performance of the secondary battery while taking into account the strength of the electrode sheet.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] The first aspect of this application provides a secondary battery including a wound electrode assembly. The electrode assembly includes a first electrode sheet. Each turn of the first electrode sheet includes two straight regions and two bent regions connected to the two straight regions. The two bent regions are arranged opposite to each other along the width direction of the electrode assembly. Along the width direction of the electrode assembly, each straight region has a first edge and a second edge. The width of a single straight region is L mm. The center of the straight region is located at a distance of L / 2 from the first edge or the second edge. A straight line passing through the center and perpendicular to the width direction of the electrode assembly is the center line of the straight region. The area from the first edge to the center line is the first region of the straight region, and the area from the center line to the second edge is the second region of the straight region. At least one turn of the first electrode sheet has multiple through holes in both the first region and the second region. The multiple through holes in the second region are symmetrical about the multiple through holes in the first region along the center line. A first through hole is provided near the first edge. Along the direction from the first edge to the center line, N through holes are sequentially provided in the first region, where 5 ≤ N ≤ 20 and N is a positive integer. The diameter of the maximum circumscribed circle of the outer contour of the first through-hole on the surface of the first electrode is D1 mm, where D1 = A × L, 1.5% ≤ A ≤ 6%, or optionally, 1.8% ≤ A ≤ 3.75%. The diameter of the maximum circumscribed circle of the outer contour of the nth through-hole on the surface of the first electrode is D... n mm, D n =B n-1×D1, 2≤n≤N, 0.6≤B≤0.9. By setting the through holes and adjusting the values ​​of N, A, and B within the above ranges, while taking into account the electrode strength of the secondary battery, it is beneficial to shorten the flow path of the electrolyte in the width direction of the first electrode in the wound state, improve the penetration efficiency of the electrolyte in the width direction of the first electrode in the wound state, and the through holes set on the first electrode absorb and store the electrolyte, forming an electrolyte potential difference in the middle of the electrode assembly where the electrolyte is easily depleted, improving the electrolyte replenishment efficiency during the cycle of the secondary battery, strengthening the wetting effect of the electrolyte on the electrode assembly, and thus improving the cycle performance of the secondary battery.

[0007] In one or more embodiments, the first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector. Based on the surface area of ​​the flat region, the percentage of the sum of the areas of the outer contours of the through holes on the first material layer in any flat region is S, where 0.5% ≤ S ≤ 18%. By adjusting the percentage of the sum of the areas of the outer contours of the multiple through holes within the above range, while taking into account the strength of the first electrode, it is beneficial to shorten the flow path of the electrolyte in the width direction of the first electrode in the wound state, improve the penetration efficiency of the electrolyte in the width direction of the first electrode in the wound state, and reduce the risk of black spots or lithium plating in the middle of the electrode assembly due to insufficient electrolyte wetting in the middle of the wound electrode assembly in the later stage of the secondary battery cycle due to insufficient electrolyte. Shortening the flow path of the electrolyte in the width direction of the first electrode in the wound state improves the cycle performance of the secondary battery while taking into account the safety performance of the secondary battery.

[0008] In one or more embodiments, the spacing between two adjacent through holes in the first region along the width direction of the electrode assembly is 5 mm to 22 mm. By adjusting the spacing between two adjacent through holes in the first region within the above range, the distance between the two adjacent through holes is moderate, which is beneficial to improving the wetting effect of the electrolyte on the electrode sheet, especially the middle part of the electrode sheet. At the same time, it reduces the actual production and processing difficulty and the risk of local collapse of the first electrode sheet during processing, thereby improving the wetting efficiency and performance of the electrolyte on the electrode assembly, and thus improving the cycle performance of the secondary battery.

[0009] In one or more embodiments, the thickness of the electrode assembly is T mm, and the distance between the first through-hole and the first edge along the width direction of the electrode assembly is L1 mm, where T / 2 ≤ L1 ≤ L / 4, and 20 ≤ T ≤ 70. By adjusting the values ​​of L1 and T within the above ranges, it is beneficial to reduce the risk of insufficient wetting of the electrode by the electrolyte, and at the same time, it is beneficial to reduce the risk of local collapse of the flat area of ​​the first electrode by the through-hole, thereby improving the wetting efficiency and performance of the electrode by the electrolyte, improving the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery, while also taking into account the safety performance of the secondary battery.

[0010] In one or more embodiments, the first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector. Along the length of the electrode assembly, the first material layer in the straight region has opposing third and fourth edges. The shortest distance between a single through-hole and the third or fourth edge is L2 mm, where 5 ≤ L2 ≤ 10. By adjusting the value of L2 within the above range, the risk of bending of the first electrode edge or powder shedding of the material layer due to the through-hole being too close to the edge of the material layer is reduced. This also helps reduce the risk of insufficient wetting of the electrode by the electrolyte, while reducing the impact of the through-hole on the strength of the first electrode. This improves the wetting efficiency and performance of the electrode, enhances the wetting effect of the electrolyte on the electrode, improves the cycle performance of the secondary battery, and simultaneously ensures the safety performance of the secondary battery.

[0011] In one or more embodiments, 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 thickness of the first material layer on one side of the first current collector is H1 μm, where 120 ≤ H1 ≤ 600. By controlling the thickness H1 of the first material layer within the above range, the safety risk caused by poor electrode strength due to an excessively thin material layer is reduced. This helps to reduce the actual processing difficulty, improve the diffusion efficiency of the electrolyte, improve the wetting effect of the electrolyte on the electrode, and improve the cycle performance of the secondary battery.

[0012] In one or more embodiments, the thickness of the first current collector is H2 μm, where 5 ≤ H2 ≤ 20. By adjusting the thickness H2 of the first current collector within the above range, it is beneficial to reduce the processing difficulty of the first electrode, while taking into account the cycle performance of the secondary battery and improving the strength of the first electrode.

[0013] In one or more embodiments, 80 ≤ L ≤ 600. By adjusting the width L of a single flat region within the above range, it is beneficial to reduce the processing difficulty while taking into account both the strength and cycle performance of the first electrode.

[0014] In one or more embodiments, the first electrode is a positive electrode and / or a negative electrode. By providing through holes in the flat areas of the positive and / or negative electrode, it is beneficial to improve the wetting efficiency and performance of the electrolyte on the electrode, especially the middle part of the electrode, thereby improving the wetting effect of the electrolyte on the electrode and thus improving the cycle performance of the secondary battery while taking into account the electrode strength.

[0015] In one or more embodiments, the shape of the outer contour of a single through-hole includes one of a circle, an ellipse, or a polygon. By adjusting the shape of the outer contour of the through-hole within the above range, the actual processing difficulty is reduced, the wetting performance of the electrode assembly is taken into account, and production efficiency is improved.

[0016] In one or more embodiments, the secondary battery is a pouch secondary battery or a prismatic secondary battery.

[0017] 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.

[0018] The beneficial effects of the embodiments of this application are as follows:

[0019] This application provides a secondary battery and an electronic device. By setting through holes of different sizes in each ring of the first electrode along the width direction of the electrode assembly, it is beneficial to improve the wetting of the electrode by the electrolyte, shorten the transport path of the electrolyte on the electrode, and at the same time take into account the strength of the electrode. This makes the secondary battery safe and have good cycle performance.

[0020] 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

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0022] Figure 1 This is a schematic diagram of the winding structure formed by the electrode assembly in one embodiment of this application;

[0023] Figure 2 for Figure 1 A schematic diagram of the first straight region of one turn of the first electrode in the wound structure formed by the electrode assembly;

[0024] Figure 3 for Figure 1A schematic diagram of the first straight region of the first electrode sheet in one loop of the wound structure formed by the electrode assembly along the width and length directions of the electrode assembly.

[0025] Figure 4 This is a partial structural diagram of the first electrode sheet located in the first flat region along the thickness direction of the electrode assembly in one embodiment of this application;

[0026] Figure 5 This is a schematic diagram of the winding structure formed by the electrode assembly in another embodiment of this application;

[0027] Figure 6 This is a schematic diagram showing the diffusion of electrolyte on a portion of the first electrode during the wettability test of the first electrode.

[0028] Reference numerals: Electrode assembly 001; First electrode 10; Flat region 101; First flat region 1011; Bending region 102; Through hole 20; First through hole 21; First edge 31; Second edge 32; Center of flat region 33; Center line 34; Third edge 35; Fourth edge 36; First current collector 41; First material layer 42. Detailed Implementation

[0029] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and 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.

[0030] As the volume of secondary batteries increases, the length and width of the electrodes also increase, which can easily lead to insufficient electrolyte wetting in the center of the electrodes. In the later stages of battery cycling, black spots or lithium plating are prone to occur on the electrodes, especially in the center, resulting in a decline in the cycle performance of the secondary battery. Based on this, this application provides a secondary battery that, by shortening the electrolyte transport path on the electrodes, achieves good electrode wetting and provides excellent cycle performance.

[0031] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0032] The first aspect of this application provides a secondary battery, including a wound electrode assembly. The electrode assembly includes a first electrode sheet. Each turn of the first electrode sheet includes two straight regions and two bent regions connected to the two straight regions. The two bent regions are arranged opposite to each other along the width direction of the wound electrode assembly. Along the width direction of the electrode assembly, each straight region has a first edge and a second edge. The width of a single straight region is L mm. The center of the straight region is located at a distance L / 2 from the first edge or the second edge. A straight line passing through the center and perpendicular to the width direction of the electrode assembly is the center line of the straight region. The area from the first edge to the center line is the first region of the straight region, and the area from the center line to the second edge is the second region of the straight region. At least one turn of the first electrode sheet has multiple through holes in both the first region and the second region. The multiple through holes in the second region are symmetrical about the multiple through holes in the first region along the center line. A first through hole is provided near the first edge. Along the direction from the first edge to the center line, N through holes are sequentially provided in the first region, where 5 ≤ N ≤ 20, and N is a positive integer. For example, the value of N can be any one of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. The diameter of the largest circumscribed circle of the outer contour of the first through-hole on the surface of the first electrode is D1 mm, where D1 = A × L, 1.5% ≤ A ≤ 6%, and optionally, 1.8% ≤ A ≤ 3.75%. For example, the value of A can be any one of 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.2%, 2.5%, 2.8%, 3%, 3.25%, 3.5%, 3.75%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5.0%, 5.2%, 5.5%, 5.8%, or 6%. The diameter of the largest circumscribed circle of the outer contour of the nth through-hole on the surface of the first electrode is D. n mm, D n =B n-1 ×D1, 2≤n≤N, 0.6≤B≤0.9, for example, when N is 20, 2≤n≤20, and the value of n can be any one of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20; the value of B can be any one of 0.6, 0.64, 0.68, 0.71, 0.75, 0.79, 0.83, 0.87, 0.9. In this application, it is understood that "multiple" refers to two or more, and "through hole" refers to a hole that penetrates the material layer and the current collector of the first electrode plate. The thickness of the through hole is the sum of the thicknesses of the first current collector and the first material layer in the first electrode plate.

[0033] In this application, the first electrode can be a positive electrode and / or a negative electrode. For ease of understanding, the width direction of the electrode assembly in its wound state is defined as the X direction, the thickness direction as the Y direction, and the length direction as the Z direction. It is understood that the positive electrode, positive electrode material layer, positive electrode current collector, negative electrode, negative electrode material layer, negative electrode current collector, and separator in their wound state have the same length, width, and thickness directions as the electrode assembly. For example, as shown... Figures 1 to 2 As shown, the electrode assembly 001 is formed by stacking and winding a separator, a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on two surfaces of the positive current collector. The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on two surfaces of the negative current collector. The first electrode sheet 10 is the negative electrode sheet. In the wound state, the electrode assembly 001 includes multiple turns of the first electrode sheet 10. Each turn of the first electrode sheet 10 includes two straight regions 101 and two bent regions 102 disposed opposite to each other along the width direction (X direction) of the electrode assembly 001. Along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction of the first electrode sheet 10 after unfolding), any straight region 101 has an opposing first edge 31 and a second edge 32. The first flat region 1011 includes a first edge 31 and a second edge 32. A straight line passing through the center 33 of the first flat region 1011 and perpendicular to the width direction (X direction) (i.e. the length direction after the first electrode 10 is unfolded) of the electrode assembly 001 is the center line 34 of the first flat region 1011. The area from the first edge 31 to the center line 34 of the first flat region 1011 is the first region of the first flat region 1011. The area from the center line 34 of the first flat region 1011 to the second edge 32 is the second region of the first flat region 1011. The first region and the second region are symmetrical about the center line 34.

[0034] Along the width direction (X direction) of the electrode assembly (i.e., the length direction after the first electrode 10 is unfolded), through holes 20 are provided in both the first and second regions of the first straight region 1011. The through holes 20 in the second region are symmetrical about the center line 34 with the through holes 20 in the first region, and thus the through holes 20 in the first region and the through holes 20 in the second region are symmetrical about the center line 34. A first through hole 21 is provided near the first edge 31, and five through holes are sequentially provided in the first region along the direction from the first edge 31 to the center line 34. It should be noted that the number, size, and spacing of the through holes in the figure are for illustrative purposes only.

[0035] When the values ​​of N, A, and / or B are too small, i.e., less than the lower limit of this application, the number of through holes provided on the first region of the first flat area of ​​the first electrode is insufficient, and / or each through hole is too small. This results in fewer flow paths for the electrolyte in the width direction (i.e., the length direction after the first electrode is unfolded) of the first electrode in its wound state, and insufficient wetting of the electrolyte in the thickness direction of the electrode assembly. This leads to insufficient wetting of the middle part of the wound electrode assembly. In the later stages of the secondary battery cycle, the middle part of the electrode assembly is prone to black spots or lithium plating due to insufficient electrolyte, thus failing to effectively improve the cycle performance of the secondary battery. When the values ​​of N, A, and / or B are too large, i.e., greater than the upper limit of this application, the excessive number of through holes provided on the first electrode, and / or each through hole being too large, leads to a decrease in the strength of the flat area of ​​the first electrode, consequently reducing the strength of the first electrode and affecting the safety performance of the secondary battery. Furthermore, in actual production, a large number of through holes is detrimental to the processing and large-scale production of the electrode assembly. This application, by setting through holes and adjusting the values ​​of N, A, and B within the aforementioned ranges, while ensuring the safety performance of the secondary battery, helps to shorten the flow path of the electrolyte in the width direction (i.e., the length direction after the first electrode sheet is unfolded) of the electrode assembly in the wound state, thereby improving the penetration efficiency of the electrolyte in the width direction (i.e., the length direction after the first electrode sheet is unfolded) of the electrode assembly in the wound state. Furthermore, the through holes set on the first electrode sheet absorb and store the electrolyte, forming an electrolyte potential difference in the middle of the electrode assembly where the electrolyte is easily depleted, improving the electrolyte replenishment efficiency during the cycle of the secondary battery, enhancing the wetting effect of the electrolyte on the electrode assembly, and thus improving the cycle performance of the secondary battery. In this application, the aforementioned "at least one turn of the first electrode sheet has multiple through holes in both the first and second regions" means that multiple through holes are set in the first and second regions of one turn of the first electrode sheet, or that multiple through holes are set in the first and second regions of multiple turns of the first electrode sheet.

[0036] In one or more embodiments, 80 ≤ L ≤ 600. For example, the value of L can be any one of 80, 140, 180, 220, 260, 290, 320, 340, 380, 420, 460, 500, 550, and 600. By adjusting the value of L within the above range, it is beneficial to shorten the flow path of the electrolyte in the width direction (i.e., the length direction after the first electrode sheet is unfolded) of the electrode assembly in the wound state, and the effect of improving the penetration efficiency of the electrolyte in the width direction (i.e., the length direction after the first electrode sheet is unfolded) of the electrode assembly in the wound state is more obvious. While taking into account the safety performance of the secondary battery, it further improves the cycle performance of the secondary battery, while also taking into account the actual production needs and reducing the processing difficulty.

[0037] In one or more embodiments, the first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector. Based on the surface area of ​​the flat region, the percentage of the sum of the areas of the outer contours of the through holes on the first material layer in any flat region is S, where 0.5% ≤ S ≤ 18%. For example, the value of S can be any one of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, and 18%. By adjusting the value of S within the aforementioned range, while maintaining the strength of the first electrode, it is beneficial to shorten the flow path of the electrolyte in the width direction (i.e., the length direction after the first electrode is unfolded) of the electrode assembly in the wound state. This improves the penetration efficiency of the electrolyte in the width direction (i.e., the length direction after the first electrode is unfolded) of the electrode assembly in the wound state. It also helps to reduce the risk of black spots or lithium plating in the middle of the electrode assembly due to insufficient electrolyte wetting in the wound electrode assembly during the later stages of the secondary battery cycle. By shortening the flow path of the electrolyte in the width direction (i.e., the length direction after the first electrode is unfolded) of the electrode assembly in the wound state, the cycle performance of the secondary battery is improved, while also taking into account the safety performance of the secondary battery.

[0038] In one or more embodiments, the spacing L3 between two adjacent through-holes located in the first region along the width direction of the electrode assembly is 5 mm to 22 mm. For example, the value of L3 can be any one of 5, 6, 8, 10, 12, 14, 15, 18, 20, and 22. Figure 2 As shown, along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction after the first electrode sheet is unfolded), the distance between two adjacent through holes 20 in the first region is L3 mm. In this application, the distance between two adjacent through holes refers to the shortest distance between the edge of any through hole and the edge of the adjacent through hole along the width direction of the electrode assembly (i.e., the length direction after the first electrode sheet is unfolded). By adjusting the value of L3 within the above range, the distance between two adjacent through holes is made moderate, which is beneficial to improving the wetting effect of the electrolyte on the electrode sheet, especially the middle part of the electrode sheet, while reducing the actual production and processing difficulty and the risk of local collapse of the first electrode sheet during processing. This improves the wetting efficiency and performance of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0039] In one or more embodiments, the thickness of the electrode assembly is T mm, and the distance between the first through-hole and the first edge along the width direction of the electrode assembly is L1 mm, where T / 2 ≤ L1 ≤ L / 4, and 20 ≤ T ≤ 70. For example, the value of T can be any one of 20, 25, 30, 40, 45, 50, 55, 60, 65, and 70. Figure 2As shown, along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction after the first electrode sheet is unfolded), the distance between the first through hole 21 and the first edge 31 is L1 mm. In this application, along the width direction of the electrode assembly, the distance between the first through hole and the first edge refers to the shortest distance between the edge of the first through hole and the first edge along the width direction of the electrode assembly (i.e., the length direction after the first electrode sheet is unfolded). Furthermore, the first through hole is the through hole closest to the first edge, and the distances between other through holes and the first edge are not less than the distance between the first through hole and the first edge. By adjusting the values ​​of L1 and T within the above range, it is beneficial to reduce the risk of insufficient wetting of the electrode sheet by the electrolyte, and at the same time, it is beneficial to reduce the risk of local collapse of the flat area of ​​the first electrode sheet by the through hole, improve the wetting efficiency and performance of the electrode sheet by the electrolyte, improve the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery, while taking into account the safety performance and processing performance of the secondary battery.

[0040] In one or more embodiments, 10 ≤ L1 ≤ 150. For example, the value of L1 can be any one of 10, 25, 45, 65, 80, 90, 100, 110, 130, and 150. By adjusting the value of L1 within the above range, it is beneficial to reduce the risk of insufficient wetting of the electrode by the electrolyte, and at the same time, it is beneficial to reduce the risk of local collapse of the flat area of ​​the first electrode by the through hole, improve the wetting efficiency and performance of the electrode by the electrolyte, improve the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery, while taking into account the safety performance and processing performance of the secondary battery.

[0041] In one or more embodiments, 10 ≤ L1 ≤ 40. For example, the value of L1 can be any one of 10, 15, 20, 25, 27, 30, 34, 38, and 40. By adjusting the value of L1 within the above range, it is beneficial to reduce the risk of insufficient wetting of the electrode by the electrolyte, and at the same time, it is beneficial to reduce the risk of local collapse of the flat area of ​​the first electrode by the through hole, improve the wetting efficiency and performance of the electrode by the electrolyte, improve the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery, while taking into account the safety performance and processing performance of the secondary battery.

[0042] In one or more embodiments, the first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector. Along the length of the electrode assembly, the first material layer in the straight region has opposing third and fourth edges. The shortest distance between a single through-hole and the third or fourth edge is L2 mm, where 5 ≤ L2 ≤ 10. For example, the value of L2 can be any one of 5, 6, 7, 7.5, 8, 9, or 10. Figure 3As shown, along the length direction (Z direction) of the electrode assembly 001 (i.e., the width direction after the first electrode sheet is unfolded), the first material layer of the flat region 101 has opposing third edges 35 and fourth edges 36. The first through hole 21 is close to the third edge 35, and the shortest distance between the first through hole 21 and the third edge 35 is L2 mm. In this application, along the length direction of the electrode assembly, the shortest distance between the through hole and the third or fourth edge refers to the closest distance between the edge of any through hole and the third or fourth edge along the length direction of the electrode assembly (i.e., the width direction after the first electrode sheet is unfolded). Furthermore, along the length direction of the electrode assembly (i.e., the width direction after the first electrode sheet is unfolded), the distance between any through hole and the third or fourth edge is not less than the aforementioned shortest distance. By adjusting the value of L2 within the above range, the risk of bending of the first electrode edge or powder shedding of the material layer due to the through hole being too close to the edge of the material layer is reduced. It also helps to reduce the risk of insufficient wetting of the electrode by the electrolyte. At the same time, it helps to reduce the impact of the through hole on the safety performance of the first electrode, improves the wetting efficiency and performance of the electrode by the electrolyte, improves the wetting effect of the electrode by the electrolyte, improves the cycle performance of the secondary battery, and takes into account the safety performance of the secondary battery.

[0043] In one or more embodiments, 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 thickness of the first material layer on one side of the first current collector is H1 μm, and 120 ≤ H1 ≤ 600. For example, the value of H1 can be any one of 120, 160, 200, 260, 320, 360, 420, 480, 520, 580, and 600. Figure 4 As shown, the first electrode 10 includes a first current collector 41 and a first material layer 42 located on both surfaces of the first current collector 41. The thickness of the first material layer 42 on one side of the first current collector is H1 μm. By adjusting the value of H1 within the above range, the safety risk caused by poor electrode strength due to an excessively thin material layer is reduced. This helps to reduce the actual processing difficulty, improve the diffusion efficiency of the electrolyte, improve the wetting effect of the electrolyte on the electrode, and improve the cycle performance of the secondary battery. In this application, the thickness H1 of the first material layer can be adjusted by means known to those skilled in the art. For example, when coating the surface of the first current collector with slurry, under the premise that other conditions remain unchanged and the solid content of the slurry is constant, the amount of coating per unit area can be increased to increase the thickness of the first material layer. This application does not impose any particular limitation, as long as the purpose of this application can be achieved.

[0044] In one or more embodiments, the thickness of the first current collector is H2 μm, where 5 ≤ H2 ≤ 20. For example, the value of H2 can be any one of 5, 6, 8, 10, 12.5, 15, 17, or 20. Figure 4As shown, the thickness of the first current collector 41 of the first electrode 10 is H2 μm. By adjusting the value of H2 within the above range, it is beneficial to reduce the processing difficulty of the first electrode, while taking into account the cycle performance of the secondary battery and improving the strength of the first electrode. This application does not impose any particular restrictions on the method of adjusting the thickness H2 of the first current collector, as long as it can achieve the purpose of this application. For example, commercially available current collectors with different thicknesses can be selected, and the thickness of the current collector of the first electrode can be determined by combining the test method of "N, A, B, S, L1, L2, L3, H1, H2 test" in this application, and then the current collector of the first electrode with the required thickness can be selected.

[0045] In one or more embodiments, each ring of the first electrode includes a first flat region and a second flat region, and along the thickness direction of the electrode assembly, there is at least partial overlap between the projections of the multiple through holes corresponding to each other in the multiple first flat regions.

[0046] In one or more embodiments, each ring of the first electrode includes a first flat region and a second flat region, and along the thickness direction of the electrode assembly, there is at least partial overlap between the projections of the multiple corresponding through holes in the multiple second flat regions.

[0047] In one or more embodiments, each first electrode includes a first flat region and a second flat region. The electrode assembly has a plurality of through holes in the plurality of first flat regions. Along the thickness direction of the electrode assembly, there is at least a partial overlap between the projections of the plurality of through holes corresponding to each other in the plurality of first flat regions. The electrode assembly also has a plurality of through holes in the plurality of second flat regions. Along the thickness direction of the electrode assembly, there is at least a partial overlap between the projections of the plurality of through holes corresponding to each other in the plurality of second flat regions.

[0048] In this application, by providing through holes in the first and / or second straight regions of the multiple first electrode plates, and by providing at least partial overlap between the projections of the multiple through holes corresponding to each other in the multiple first and / or multiple second straight regions along the thickness direction of the electrode assembly, the multiple through holes corresponding to each other in the multiple first and / or multiple second straight regions shorten and increase the flow path of the electrolyte. When the electrode assembly is injected with electrolyte, the electrolyte flows through the flow path formed by the multiple through holes corresponding to each other in the multiple first and / or multiple second straight regions, wetting each first electrode plate where the through holes are located. This shortens the wetting path of the electrolyte, increases the wetting speed, and thus improves the cycle performance of the electrode assembly.

[0049] In one or more embodiments, through holes are arranged in a matrix along the length direction of the electrode assembly (i.e., the width direction after the first electrode sheet is unfolded). In this application, multiple rows of through holes are provided in any flat area along the width direction after the first electrode sheet is unfolded, and the spacing between corresponding through holes in each row is equal. This application does not impose a particular limitation on the number of rows of through holes. Those skilled in the art can set the number of rows according to the actual specifications of the first electrode sheet, as long as the purpose of this application can be achieved. For example, the number of rows of through holes in the first flat area of ​​the first electrode sheet can be from 1 to 20.

[0050] In one or more embodiments, the shape of the outer contour of a single through-hole includes a circle, an ellipse, or a polygon. In this application, there is no particular limitation on the shape of the polygon, as long as it achieves the purpose of this application. For example, the shape of the outer contour of a single through-hole can be independently selected from a triangle, rectangle, trapezoid, square, pentagon, or hexagon. By adjusting the shape of the outer contour of the through-hole, the actual processing difficulty is reduced, and the actual production efficiency is improved.

[0051] In one or more embodiments, the first electrode is a negative electrode. By providing multiple through holes in the straight area of ​​at least one ring of the negative electrode, it is beneficial to further improve the wetting efficiency and performance of the electrolyte on the negative electrode, especially the middle part of the negative electrode, thereby better improving the wetting effect of the electrolyte on the negative electrode and improving the cycle performance of the secondary battery.

[0052] In one or more embodiments, the first electrode is a positive electrode. By providing multiple through holes in the straight area of ​​at least one ring of the positive electrode, it is beneficial to further improve the wetting efficiency and performance of the electrolyte on the positive electrode, especially the middle part of the positive electrode, thereby better improving the wetting effect of the electrolyte on the positive electrode and improving the cycle performance of the secondary battery.

[0053] When the first electrode is a positive or negative electrode, the electrode assembly also includes a second electrode. For example, when the first electrode is a negative electrode, the second electrode is a positive electrode; when the first electrode is a positive electrode, the second electrode is a negative electrode.

[0054] In one or more embodiments, the first electrode is both a positive electrode and a negative electrode. For example... Figure 5As shown, along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction after the first electrode 10 is unfolded), the first electrode 10 is a positive electrode and a negative electrode. Five through holes 20 are provided in the first region of each straight area of ​​each ring of the positive and negative electrode. By providing multiple through holes in the straight areas of at least one ring of the positive and at least one ring of the negative electrode, it is beneficial to improve the wetting efficiency and performance of the electrolyte on the electrode, especially the middle part of the electrode, thereby improving the wetting effect of the electrolyte on the electrode and thus improving the cycle performance of the secondary battery.

[0055] In this application, when the first electrode is a positive electrode, "the first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector" means that the positive electrode includes a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector. The aforementioned "positive electrode material layer located 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 it can be disposed on two surfaces of the positive current collector along its own thickness direction. It should be noted that "surface" here refers to the coating area in the positive current collector where the positive electrode material layer is disposed. This application does not have any particular limitation on the positive current collector, as long as it can achieve the purpose of this application. For example, the positive current collector can include aluminum foil, aluminum alloy foil, or composite current collectors (such as aluminum-carbon composite current collectors). The positive electrode material layer in this application includes a positive electrode active material. This application does not have any particular limitation on the type of positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. This application does not particularly limit the type of positive electrode binder in the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the type of conductive agent in the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation 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 it can achieve the purpose of this application.

[0056] In the present application, when the first electrode sheet is a negative electrode sheet, "the first electrode sheet includes a first current collector and a first material layer located on at least one surface of the first current collector" means that the negative electrode sheet includes a negative current collector and a negative electrode material layer located on at least one surface of the negative current collector. The above-mentioned "negative electrode material layer located on at least one surface of the negative current collector" means that the negative electrode material layer can be disposed on one surface of the negative current collector along its own thickness direction, or can be disposed on two surfaces of the negative current collector along its own thickness direction. It should be noted that the "surface" here refers to the coating area of the negative current collector where the negative electrode material layer is provided. The present application does not particularly limit the negative current collector, as long as the purpose of the present application can be achieved. For example, the negative 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 the present application contains a negative electrode active material. The present application does not particularly limit the type of the negative electrode active material, as long as the purpose of the present 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. Optionally, the negative electrode material layer may further include a conductive agent and a negative electrode binder. The present application does not particularly limit the type of the conductive agent in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent can be the same as the conductive agent in the above-mentioned positive electrode material layer. The present application does not particularly limit the type of the negative electrode binder in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the negative electrode binder can be the same as the positive electrode binder in the above-mentioned positive electrode material layer. In the present application, the negative electrode material layer further includes a thickening agent. The present application does not particularly limit the type of the thickening agent, as long as the purpose of the present application can be achieved. For example, the thickening agent can include at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, negative electrode binder and thickening agent in the negative electrode material layer, as long as the purpose of the present application can be achieved.

[0057] This application does not impose any particular limitation on the preparation method of the first electrode sheet, as long as it can achieve the purpose of this application. For example, the preparation method of the first electrode sheet includes, but is not limited to, the following steps: (1) preparing a slurry; (2) coating the slurry on one surface of the first current collector and drying it to obtain a first electrode sheet with a material layer on one side; (3) coating the slurry on the other surface of the current collector and drying it to obtain a first electrode sheet with a material layer on both sides; (4) after cold pressing and slitting, pre-winding the first electrode sheet, determining the two straight areas of each turn of the first electrode sheet and the two bent areas connected to the two straight areas, the two bent areas being arranged opposite each other along the width direction of the electrode assembly, and corresponding through holes being provided on the straight areas of the first electrode sheet, and along the direction from the edge of each straight area to the center line of the straight area, the diameter of the largest circumscribed circle of the outer contour of the through hole on the surface of the first electrode sheet gradually decreases, thus obtaining the first electrode sheet.

[0058] This application does not impose any particular limitation on the solid content of the slurry, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the drying temperature and time, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the process parameters for cold pressing and slitting, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the above-mentioned method of setting through holes, as long as it can achieve the purpose of this application. For example, through holes can be set by drilling with a circular cutter. The diameter of the largest circumcircle of the outer contour of each through hole on the surface of the first electrode is controlled by adjusting the power and cutting depth of the circular cutter. The proportion S of the sum of the areas of the outer contours of multiple through holes is controlled by adjusting the surface area of ​​the flat area, the number of through holes, the shape of the through holes, the power of the circular cutter, the cutting depth, the spacing or cutting frequency between the circular cutters. The spacing L3 between two adjacent through holes is controlled by adjusting the spacing or cutting frequency between the circular cutters. The distance L1 between the first through hole and the first edge along the width direction of the electrode assembly (i.e., the length direction after the first electrode is unfolded) is controlled by adjusting the spacing or cutting frequency between the circular cutters. The shortest distance L2 between a single through hole and the third or fourth edge along the length direction of the electrode assembly (i.e., the width direction after the first electrode is unfolded) is controlled by adjusting the spacing or cutting frequency between the circular cutters, etc.

[0059] In other implementations, through holes can also be formed by pulsed laser drilling. The diameter of the largest circumcircle of the outer contour of each through hole on the surface of the first electrode is controlled by adjusting the power and defocusing amount of the pulsed laser emitter. The proportion S of the sum of the areas of the outer contours of multiple through holes is controlled by adjusting the surface area of ​​the flat area, the number of through holes, the power of the pulsed laser emitter, the defocusing amount, the spacing between the pulsed laser emitters, or the laser emission frequency. The spacing L3 between two adjacent through holes is controlled by adjusting the spacing between the pulsed laser emitters or the laser emission frequency. The distance L1 between the first through hole and the first edge along the width direction of the electrode assembly (i.e., the length direction after the first electrode is unfolded) is controlled by adjusting the spacing between the pulsed laser emitters or the laser emission frequency. The shortest distance L2 between a single through hole and the third or fourth edge along the length direction of the electrode assembly (i.e., the width direction after the first electrode is unfolded) is controlled by adjusting the spacing between the pulsed laser emitters or the laser emission frequency, etc.

[0060] In this application, those skilled in the art will understand that when a through hole is formed on the first electrode by using a circular cutter or a pulsed laser, the thickness of the through hole is the sum of the material layer thickness of the electrode and the current collector thickness.

[0061] The secondary battery in this application includes an electrolyte, which comprises a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not limit the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. This application does not particularly limit the non-aqueous solvent, as long as it achieves the purpose of this application. For example, the non-aqueous solvent may include, but is 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 fluorocarbonate 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 vinylene carbonate. Fluorinated carbonate 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, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0062] 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 40 μm.

[0063] In one or more embodiments, the secondary battery is a pouch battery or a prismatic battery. By providing through-holes of different sizes in each ring of the first electrode along the width direction of the electrode assembly, it is beneficial to improve the wetting of the electrode by the electrolyte, shorten the electrolyte transport path on the electrode, and simultaneously maintain the electrode strength. This allows the secondary battery to achieve both safety and good cycle performance.

[0064] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one or more embodiments of this application, the secondary battery may include, but is not limited to, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0065] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the separator, the first electrode, the separator and the second electrode in sequence, and winding and folding them as needed to obtain a wound electrode assembly; placing the electrode assembly into the housing; injecting the electrolyte into the housing and sealing it to obtain the secondary battery.

[0066] 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.

[0067] 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.

[0068] Example

[0069] 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. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0070] Test methods and equipment:

[0071] Tests for N, A, B, S, L1, L2, L3, H1, and H2:

[0072] At an ambient temperature of 25℃, the lithium-ion battery was disassembled to obtain the electrode assembly. The electrode assembly was observed along its width using an electron scanning microscope to determine the number of through holes in the first region of each straight area of ​​the first electrode sheet, which is the number of through holes, N. The electrode sheet with through holes, i.e., the first electrode sheet, was then removed and soaked in dimethyl carbonate (DMC) for 20 minutes. Afterward, the first electrode sheet was placed in an oven and dried at 80℃ for 12 hours to obtain a test sample of the first electrode sheet.

[0073] The first electrode is pre-wound. The length L of the straight section of the first electrode and the diameter D1 of the largest circumscribed circle of the outer contour of the first through-hole on the surface of the first electrode are measured using an electron scanning microscope. The ratio of diameter D1 to length L is calculated, which is A. Simultaneously, the diameter D2 of the largest circumscribed circle of the outer contour of the second through-hole on the surface of the first electrode is measured using an electron scanning microscope, and this value is then substituted into D. n =B n-1 Calculate the B value using ×D1. Next, use an electron scanning microscope to measure the length and width of the straight area of ​​the first region and the area of ​​the outer contour of the through hole on the first electrode. Calculate the ratio of the sum of the areas of the outer contours of multiple through holes to the area of ​​the straight area, which is the percentage S of the sum of the areas of the outer contours of multiple through holes.

[0074] The distance L3 between two adjacent through holes on the first electrode plate along the width direction of the electrode assembly is measured using an electron scanning microscope; the distance L1 between the first through hole and the first edge on the first electrode plate is measured using an electron scanning microscope; and the shortest distance L2 between a single through hole on the first electrode plate and the third or fourth edge along the length direction of the electrode assembly is measured using an electron scanning microscope.

[0075] Cyclic performance test:

[0076] The lithium-ion batteries in each embodiment and comparative example were subjected to charge-discharge cycle tests in a 25°C constant temperature chamber. The lithium-ion batteries were charged at a constant current of 2C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C. After resting for 5 minutes, they were discharged at a constant current of 6C to 2.5V. This was the first cycle, and the discharge capacity C1 of the first cycle was recorded. After 600 cycles following the above process, the discharge capacity C of the lithium-ion battery was recorded. 600 The capacity retention rate at 600 cycles was calculated as an indicator of the electrolyte's wetting effect on the first electrode and the cycle performance of the lithium-ion battery, as shown in Equation (I). A lower capacity retention rate at 600 cycles (cls) indicates a poorer wetting effect of the electrolyte on the first electrode and thus poorer cycle performance; conversely, a higher capacity retention rate at 600cls indicates a better wetting effect of the electrolyte on the first electrode and better cycle performance.

[0077] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0078] Electrode wettability test:

[0079] The wettability of the electrolyte on the first electrode is characterized by the diffusion distance of the electrolyte on the surface of the first electrode. The specific operating steps are as follows:

[0080] At an ambient temperature of 25℃, the lithium-ion battery was discharged to 2.5V at 0.5C and then disassembled. The first electrode with through holes was removed and cleaned with dimethyl carbonate (DMC) for 10 minutes to remove electrolyte and surface by-reaction products. It was then placed in a 25℃ environment for 2 hours to obtain a dried first electrode. Electrolyte was drawn into the first electrode using a 5mL medical syringe, and the air at the syringe tip was expelled. The dried first electrode was placed on a horizontal table, with the medical syringe directly above and perpendicular to the first electrode, with a vertical distance of 3cm between the needle tip and the first electrode. 1mL of electrolyte was dropped vertically onto the first electrode, and the diffusion distance was measured after 1 minute. A 0.5mm precision ruler was used to measure the distance between the two points on the first electrode where the electrolyte diffused the furthest. Figure 6 As shown, this is Figure 6The value of d was measured five times and the average value was taken to obtain the diffusion distance d of the electrolyte at the first electrode 10. The electrolyte used was the same as that in Example 1. Figure 6 This is only a schematic diagram of the structure of the first electrode at the very center along the length direction (X direction) after the first electrode is unfolded, and is for illustrative purposes only.

[0081] When the first electrode is both a positive and a negative electrode, the average of the five measured diffusion distances of the electrolyte on the negative electrode and the five measured diffusion distances of the electrolyte on the positive electrode is taken to obtain the diffusion distance d of the electrolyte on the first electrode.

[0082] Impact test:

[0083] The lithium-ion battery was charged at a constant current of 2C to 4.2V, then charged at a constant voltage of 0.05C to reach full charge. The fully charged lithium-ion battery was placed on a test platform, and a cylindrical rod with a diameter of 15.8mm and a length of at least 6cm was placed at the center of the wide side of the battery. The longitudinal axis of the lithium-ion battery was aligned with the surface of the test platform and perpendicular to the longitudinal axis of the cylindrical rod. A 9.1kg hammer was dropped vertically from a height of 610mm into the battery at the point where the cylindrical rod and the lithium-ion battery intersected.

[0084] The test is considered passed if the test does not ignite or explode.

[0085] Each embodiment or comparative example tests 100 lithium-ion batteries. The impact pass rate of the lithium-ion battery = number of passes / 100. A higher impact pass rate, i.e., more passes, indicates better safety performance of the lithium-ion battery.

[0086] Example 1

[0087] <Preparation of Negative Electrode Sheets>

[0088] The first electrode is the negative electrode. Artificial graphite, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97.3:1.7:1.0, and then deionized water is added as a solvent. The mixture is stirred until homogeneous, yielding a negative electrode slurry with a solid content of 50 wt%. This negative electrode slurry is uniformly coated onto one surface of a copper foil current collector with a thickness H2 of 12.5 μm, and dried at 105 °C to obtain a negative electrode with a single-sided negative electrode material layer. The above steps are then repeated on the other surface of the same copper foil current collector to obtain a negative electrode with a double-sided negative electrode material layer. After cold pressing and slitting, the coated area and uncoated area of ​​the negative electrode current collector are determined along the length of the unfolded negative electrode. The coating weight of the negative electrode material layer is 14.6 mg / cm³. 2After cold pressing, the thickness H1 of the negative electrode material layer on one side of the negative electrode current collector is 360 μm.

[0089] The negative electrode sheet is pre-wound. One surface of the negative electrode sheet is randomly selected, and two straight regions and two bent regions connecting to each turn of the negative electrode sheet are defined. The width of the straight region is set to 325 mm, and the length of the straight region is set to 418 mm. The first edge, second edge, and center line of each straight region are determined. Fifteen rows of through holes are set in the first region along the first edge to the center line and in the second region along the second edge to the center line of each straight region, with 12 through holes in each row. Along the direction from the first edge to the center line, the maximum circumcircle of the through holes in the first region gradually decreases on the electrode surface. Furthermore, the multiple through holes in the second region are symmetrical about the center line of the straight region to the multiple through holes in the first region.

[0090] Determine A as 3.75% and B as 0.75%, and set the diameter D1mm of the maximum circumscribed circle of the first through-hole near the first edge on the surface of the negative electrode sheet along its unfolded length, where D1 = A × L. The diameter of the maximum circumscribed circle of the nth through-hole on the surface of the negative electrode sheet is D. n mm, D n =B n-1 ×D1. The sum of the areas of the outer contours of multiple through holes accounts for 5.94% of the total area. Along the length of the unfolded negative electrode sheet, the distance L1 between the first through hole and the first edge is 40mm, and the spacing L3 between two adjacent through holes is 6.85mm. Along the width of the unfolded negative electrode sheet, the shortest distance L2 between a single through hole and the third or fourth edge of the flat area is 8mm. Using the above parameters, laser drilling is performed on the flat area of ​​the negative electrode sheet to obtain a negative electrode sheet with dimensions of 16226mm × 418mm.

[0091] <Preparation of the positive electrode>

[0092] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1O2), 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 positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12.5 μm thick aluminum foil current collector and dried at 105 °C to obtain a single-sided coated positive electrode sheet. The above steps were then repeated on the other surface of the same aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 105 °C for 4 hours to obtain a positive electrode sheet with dimensions of 15437 mm × 414.1 mm for later use. The coating weight of the positive electrode material layer was 16 mg / cm³. 2 After cold pressing, the thickness of the positive electrode material layer on one side of the positive electrode current collector is 400 μm.

[0093] <Septum>

[0094] A 12μm thick polypropylene (PP) film was used as the separator.

[0095] <Preparation of Electrolyte>

[0096] 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 to obtain a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, with the remainder being the base solvent.

[0097] <Preparation of Lithium-ion Batteries>

[0098] The prepared separator, positive electrode, and negative electrode are stacked sequentially, with the separator acting as a separator between the positive and negative electrodes. The electrodes are then wound to form a wound electrode assembly, with a width of 375 mm, a length of 418 mm, and a thickness of 20 mm. After leveling, current collector welding, casing, inkjet printing, vacuum drying, electrolyte injection, sealing, and high-temperature settling, a formation capacity test is performed to obtain the lithium-ion battery. The formation upper limit voltage is 3.6V, the formation temperature is 45℃, and the formation settling time is 2 hours.

[0099] Example 2

[0100] Except for the fact that five through holes are set in each row on the first and second regions of each flat area of ​​the negative electrode material layer, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as in Example 1.

[0101] Example 3

[0102] Except for the fact that 20 through holes are set in each row in the first and second regions of each flat area of ​​the negative electrode material layer, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as in Example 1.

[0103] Examples 4 to 12

[0104] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0105] Example 13

[0106] Except for the preparation of the positive and negative electrode sheets according to the following steps, the rest is the same as in Example 1.

[0107] <Preparation of the positive electrode>

[0108] The first electrode is the positive electrode. The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1 O2), 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 positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated onto one surface of a positive electrode current collector aluminum foil with a thickness H2 of 12.5 μm and dried at 105 °C to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps were then repeated on the other surface of the same aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. After cold pressing and slitting, the coated area and uncoated area of ​​the positive electrode current collector were determined along the length of the unfolded positive electrode sheet. The coating weight of the positive electrode material layer was 16 mg / cm³. 2 After cold pressing, the thickness H1 of the positive electrode material layer on one side of the positive electrode current collector is 400 μm.

[0109] The positive electrode sheet is pre-wound. One surface of the positive electrode sheet is randomly selected, and two straight regions and two bent regions connecting to each turn of the positive electrode sheet are defined. The width of the straight region is set to 325 mm, and the length of the straight region is set to 414.1 mm. The first edge, second edge, and center line of each straight region are determined. Fifteen rows of through holes are set in the first region along the first edge to the center line and in the second region along the second edge to the center line of each straight region, with 12 through holes in each row. Along the direction from the first edge to the center line, the maximum circumcircle of the through holes in the first region gradually decreases on the electrode surface. Furthermore, the through holes in the second region are symmetrical about the center line of the straight region to the through holes in the first region.

[0110] Determine A as 3.75% and B as 0.75%, and set the diameter D1mm of the maximum circumscribed circle of the first through-hole near the first edge on the surface of the positive electrode sheet along its unfolded length, where D1 = A × L. The diameter of the maximum circumscribed circle of the nth through-hole on the surface of the positive electrode sheet is D. n mm, D n =B n-1 ×D1. The sum of the areas of the outer contours of multiple through holes accounts for 6% of the total area. Along the length of the unfolded positive electrode sheet, the distance L1 between the first through hole and the first edge is 40mm, and the spacing L3 between two adjacent through holes is 6.85mm. Along the width of the unfolded positive electrode sheet, the shortest distance L2 between a single through hole and the third or fourth edge of the flat area is 8mm. Using the above parameters, laser drilling is performed on the flat area of ​​the positive electrode sheet to obtain a positive electrode sheet with dimensions of 15437mm × 414.1mm.

[0111] <Preparation of Negative Electrode Sheets>

[0112] 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 negative electrode slurry with a solid content of 50 wt%. This slurry was uniformly coated onto one surface of a 12.5 μm thick copper foil current collector and dried at 105 °C to obtain a negative electrode sheet with a single-sided coating of the negative electrode material. The same steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode material. After cold pressing and slitting, the sheet was dried under vacuum at 105 °C for 4 hours to obtain a negative electrode sheet with dimensions of 16626 mm × 418 mm for later use. The coating weight of the negative electrode material layer was 14.6 mg / cm³. 2 After cold pressing, the thickness of the negative electrode material layer on one side of the negative electrode current collector is 360μm.

[0113] Example 14

[0114] Except for the preparation of the positive electrode sheet, which is the same as in Example 13, and the relevant parameters of the positive electrode sheet as shown in Table 1, everything else is the same as in Example 1.

[0115] Comparative Example 1

[0116] Except for the absence of a through hole in the preparation of the negative electrode sheet, the rest is the same as in Example 1.

[0117] Comparative Example 2

[0118] Except for the fact that in the <Preparation of Negative Electrode Sheet>, two through holes are set in each row, the value of A is 1, and the value of B is 0.5, the rest is the same as in Example 1.

[0119] Comparative Example 3

[0120] Except for the fact that in the <Preparation of Negative Electrode Sheet>, 5 through holes are set in each row, the value of A is 7, and the value of B is 1, the rest is the same as in Example 1.

[0121] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0122] Table 1

[0123]

[0124] Note: " / " in Table 1 indicates that there are no relevant preparation parameters.

[0125] As can be seen from Examples 1 to 14 and Comparative Examples 1 to 3, by providing through holes in the two flat regions of the first electrode and adjusting the values ​​of N, A, and B within the range of this application, the electrolyte diffusion distance of the first electrode is larger, which improves the 600cls capacity retention rate of the lithium-ion battery. This indicates that the electrolyte has a good wetting effect on the first electrode, and the lithium-ion battery has good cycle performance. At the same time, the lithium-ion battery has good safety performance. In Comparative Example 1, no through holes are provided in the flat regions of the positive and negative electrodes; in Comparative Example 2, the values ​​of N, A, and B are lower than the lower limit values ​​of this application; in Comparative Example 3, the values ​​of A and B are higher than the upper limit values ​​of this application. In Comparative Examples 1 and 2, the electrolyte diffusion distance at the first electrode was relatively small, resulting in a low 600cls capacity retention rate for the lithium-ion batteries, indicating poor cycle performance. In Comparative Example 3, the through-hole diameter was large, leading to a low impact test pass rate, which affected the safety performance of the lithium-ion batteries. Furthermore, excessive contact between the electrolyte and the electrode resulted in a relatively increased number of side reactions, further contributing to the low 600cls capacity retention rate and reduced cycle performance. In contrast, the electrolytes in Examples 1 to 14 had a longer diffusion distance at the first electrode, resulting in better electrolyte wetting of the electrode and a higher 600cls capacity retention rate. These lithium-ion batteries exhibited better cycle performance and a higher impact test pass rate, thus balancing both safety performance and practical production requirements.

[0126] The number N of through holes in the first region of each flat area typically affects the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1 to 3, when the number of through holes in the first region of each flat area is within the range of this application, the electrolyte diffusion distance on the first electrode is larger, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are higher. This indicates that while ensuring safety performance, the lithium-ion battery of this application has a good electrolyte wetting effect on the electrode, and the lithium-ion battery has good cycle performance.

[0127] The value of A typically affects the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1, 4 to 6, when the value of A is within the range of this application, the electrolyte has a larger diffusion distance at the first electrode, resulting in higher 600cls capacity retention and impact test pass rates for the lithium-ion battery. This indicates that while ensuring safety performance, the lithium-ion battery of this application exhibits good electrolyte wetting of the electrode, and thus good cycle performance.

[0128] The value of B typically affects the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1, 7, and 8, when the value of B is within the range specified in this application, the electrolyte has a larger diffusion distance at the first electrode, resulting in higher 600cls capacity retention and impact test pass rates for the lithium-ion battery. This indicates that while ensuring safety performance, the lithium-ion battery of this application exhibits good electrolyte wetting of the electrode, and thus good cycle performance.

[0129] The percentage S of the sum of the areas of the outer contours of the through holes typically affects the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1 to 14, when the percentage of the sum of the areas of the outer contours of the through holes falls within the range of this application, the electrolyte diffusion distance on the first electrode is larger, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are higher. This indicates that while ensuring safety performance, the lithium-ion battery of this application exhibits good electrolyte wetting effect on the electrode, resulting in excellent cycle performance.

[0130] Along the length of the electrode assembly, the shortest distance L2 between a single through-hole and the third or fourth edge typically affects the cycle performance and safety performance of a lithium-ion battery. As can be seen from Examples 1, 9, and 10, when the shortest distance between a single through-hole and the third or fourth edge is within the range of this application, the electrolyte diffusion distance on the first electrode is larger, resulting in higher 600cls capacity retention and impact test pass rates for the lithium-ion battery. This indicates that while ensuring safety performance, the lithium-ion battery of this application exhibits good electrolyte wetting of the electrode, and thus good cycle performance.

[0131] The thickness H2 of the first current collector and the thickness H1 of the first material layer on at least one surface of the first current collector typically affect the cycle performance and safety performance of a lithium-ion battery. As can be seen from Examples 1, 11, and 12, when the values ​​of H1 and H2 are within the range of this application, the electrolyte has a larger diffusion distance on the first electrode, resulting in higher 600cls capacity retention and impact test pass rates for the lithium-ion battery. This indicates that while ensuring safety performance, the lithium-ion battery of this application exhibits good electrolyte wetting of the electrode, and thus good cycle performance.

[0132] The use of a positive and / or negative first electrode typically affects the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1, 13, and 14, when the first electrode is a positive and / or negative electrode, and the parameters of the through-hole are set within the range of this application, the electrolyte diffusion distance on the first electrode is larger, resulting in higher 600cls capacity retention and impact test pass rates for the lithium-ion battery. This indicates that while ensuring safety performance, the lithium-ion battery of this application exhibits good electrolyte wetting of the electrode, and thus good cycle performance.

[0133] 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.

[0134] 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.

[0135] 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 wound electrode assembly, the electrode assembly including a first electrode sheet, each turn of the first electrode sheet including two straight sections and two bent sections connected to the two straight sections, the two bent sections being disposed opposite to each other along the width direction of the electrode assembly; Along the width direction of the electrode assembly, each of the flat regions has a first edge and a second edge, the width of a single flat region is L mm, the area from the first edge to the center line of the flat region is the first region of the flat region, and the area from the center line to the second edge is the second region of the flat region; At least one ring of the first electrode sheet has multiple through holes in both the first region and the second region, and the multiple through holes in the second region are symmetrical about the center line to the multiple through holes in the first region. A first through hole is provided near the first edge, and N through holes are sequentially provided on the first region along the direction from the first edge to the center line, where 5≤N≤20 and N is a positive integer; in, The diameter of the largest circumscribed circle of the outer contour of the first through-hole on the surface of the first electrode is D1 mm, where D1 = A × L, and 1.5% ≤ A ≤ 6%. The diameter of the largest circumscribed circle of the outer contour of the nth through-hole on the surface of the first electrode is D... n mm, D n =B n-1 ×D1, 2≤n≤N, 0.6≤B≤0.9; Each of the two flat regions of the first electrode sheet includes a first flat region and a second flat region arranged along the thickness direction of the electrode assembly. Along the thickness direction of the electrode assembly, there is at least a partial overlap between the projections of the plurality of through holes corresponding to each other in the plurality of first flat regions; and / or, there is at least a partial overlap between the projections of the plurality of through holes corresponding to each other in the plurality of second flat regions.

2. The secondary battery according to claim 1, wherein, 1.8%≤A≤3.75%。 3. The secondary battery according to claim 1, wherein, The first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector. Based on the surface area of ​​the flat region, the sum of the areas of the outer contours of the through holes on the first material layer of any flat region is S, where 0.5% ≤ S ≤ 18%.

4. The secondary battery according to claim 1, wherein, Along the width direction of the electrode assembly, the spacing between two adjacent through holes located in the first region is 5 mm to 22 mm.

5. The secondary battery according to claim 1, wherein, The thickness of the electrode assembly is T mm, and the distance between the first through hole and the first edge along the width direction of the electrode assembly is L1 mm, where T / 2≤L1≤L / 4 and 20≤T≤70.

6. The secondary battery according to claim 1, wherein, The first electrode includes a first current collector and a first material layer located on at least one surface of the first current collector. Along the length direction of the electrode assembly, the first material layer in the flat region has opposing third and fourth edges. The shortest distance between a single through-hole and the third or fourth edge is L2 mm, where 5 ≤ L2 ≤ 10.

7. The secondary battery according to claim 1, wherein, 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 thickness of the first material layer is H1 μm and 120≤H1≤600.

8. The secondary battery according to claim 7, wherein, The thickness of the first current collector is H2 μm, where 5 ≤ H2 ≤ 20.

9. The secondary battery according to claim 1, wherein, 80≤L≤600。 10. The secondary battery according to any one of claims 1 to 9, wherein, The first electrode is a positive electrode and / or a negative electrode.

11. The secondary battery according to any one of claims 1 to 9, wherein, The outer contour of a single through-hole may be circular, elliptical, or polygonal.

12. The secondary battery according to any one of claims 1 to 9, wherein, The secondary battery is a pouch battery or a square battery.

13. An electronic device comprising a secondary battery as described in any one of claims 1 to 12.

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