Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device. The secondary battery comprises a winding type electrode assembly, and through holes are formed in a first straight area and a second straight area of at least one circle of first pole piece of the electrode assembly; n through holes are formed in the first area of the first straight area in the direction from the first edge to the center line, the diameter of the maximum circumcircle of the first through hole is D11mm, D11 = A * L, 1.5% < = A < = 6%, the diameter of the maximum circumcircle of the nth through hole is D1n mm, D1n = B2n-2 * D11, 2 < = n < = N, 0.4 < = B < = 0.9; m through holes are formed in the first area of the second straight area, the diameter of the maximum circumcircle of the first through hole is D21mm, D21 = B * D11, the diameter of the maximum circumcircle of the mth through hole is D2m mm, D2m = B2m-1 * D11, and m is larger than or equal to 2 and smaller than or equal to M. Through the arrangement, the cycle performance of the secondary battery is improved.

Description

Technical Field

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

[0002] Secondary batteries have the advantages of good rate performance, light weight, long cycle life, no memory effect and good stability. They are widely used energy storage and power products under current technical conditions.

[0003] With the demand for high-capacity applications, the volume of secondary batteries has gradually increased, and the length and width of the pole pieces in the secondary batteries have also increased accordingly, making the pole pieces susceptible to black spots due to insufficient electrolyte infiltration, thereby reducing the cycle performance of the secondary batteries. Summary of the invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device to improve the wetting of the electrolyte on the pole piece, especially the middle part of the pole piece, thereby improving the cycle performance of the secondary battery while taking into account the strength of the pole piece.

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

[0006] The first aspect of the present application provides a secondary battery, comprising a wound electrode assembly, the electrode assembly comprising a first electrode sheet, each circle of the first electrode sheet comprising two straight areas and two bending areas connected to the two straight areas, and the two bending areas are arranged oppositely along the width direction of the electrode assembly; along the width direction of the electrode assembly, any straight area has a first edge and a second edge opposite to each other, the length of a single straight area is L mm, the position at a distance of L / 2 from the first edge or the second edge is the center of the straight area, the straight line passing through the center and perpendicular to the width direction of the electrode assembly is the center line of the straight area, the area from the first edge to the center line is the first area of ​​the straight area, and the area from the center line to the second edge is the second area of ​​the straight area. The two straight areas include a first straight area and a second straight area arranged along the thickness direction of the electrode assembly, and a plurality of through holes are arranged on the first area and the second area of ​​the first straight area and the second area of ​​at least one circle of the first electrode sheet, and the plurality of through holes in the second area are symmetrical with the plurality of through holes arranged on the first area along the center line. A first through hole of the first straight area is provided near the first edge of the first straight area, and N through holes are provided in sequence on the first area of ​​the first straight area along the direction from the first edge to the center line, where N is a positive integer; wherein the diameter of the maximum circumscribed circle of the outer contour of the first through hole on the first area of ​​the first straight area on the surface of the first pole piece is D 11 mm, D 11= A × L, 1.5% ≤ A ≤ 6%, optionally, 1.8% ≤ A ≤ 3.75%; the diameter of the largest circumscribed circle of the outer contour of the nth through hole on the first region of the first flat region on the surface of the first electrode tab is D 1n mm, D 1n = B 2n-2 × D 11 , 2 ≤ n ≤ N, 0.6 ≤ B ≤ 0.9. The first through hole of the second flat region is provided near the first edge of the second flat region. Along the direction from the first edge to the center line, M through holes are sequentially arranged on the first region of the second flat region, and M is a positive integer; among them, the diameter of the largest circumscribed circle of the outer contour of the first through hole on the first region of the second flat region on the surface of the first electrode tab is D 21 mm, D 21 = B × D 11 , the diameter of the largest circumscribed circle of the outer contour of the mth through hole on the first region of the second flat region on the surface of the first electrode tab is D 2m mm, D 2m = B 2m-1 × D 11 , 2 ≤ m ≤ M. By setting and regulating the values of A and B within the above ranges, while taking into account the strength of the electrode tab of the secondary battery, it is beneficial to shorten the flow path of the electrolyte in the width direction of the first electrode tab in the wound state, improve the penetration efficiency of the electrolyte in the width direction of the first electrode tab in the wound state, and moreover, the through holes provided on the first electrode tab absorb and store the electrolyte, forming an electrolyte potential difference at the position where the electrolyte is easily consumed in the middle of the electrode assembly, improving the replenishment efficiency of the electrolyte during the cycling of the secondary battery, strengthening the wetting effect of the electrolyte on the electrode assembly, and thus improving the cycling performance of the secondary battery.

[0007] In one or more embodiments, 3 ≤ N ≤ 11, 2 ≤ M ≤ 9 and M < N. By regulating the values of N and M within the above ranges, while taking into account the strength of the electrode tab of the secondary battery, it is beneficial to shorten the flow path of the electrolyte in the width direction of the first electrode tab in the wound state, improve the penetration efficiency of the electrolyte in the width direction of the first electrode tab in the wound state, strengthen the wetting effect of the electrolyte on the electrode assembly, and thus improve the cycling performance of the secondary battery, while reducing the processing difficulty.

[0008] In one or more embodiments, a plurality of through holes are provided in the plurality of first straight areas of the electrode assembly, and 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 straight areas; and / or, a plurality of through holes are provided in the plurality of second straight areas of the electrode assembly, and 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 straight areas. Through the above arrangement, along the thickness direction of the electrode assembly, the flow path of the electrolyte is shortened and increased. When the electrode assembly is injected, the electrolyte flows through the flow path formed by the plurality of through holes corresponding to each other in the plurality of first straight areas and / or the plurality of second straight areas, shortening the electrolyte infiltration path, increasing the infiltration speed, and thereby improving the cycle performance of the electrode assembly.

[0009] In one or more embodiments, along the thickness direction of the electrode assembly, the centers of the maximum circumscribed circles of the outer contours of the plurality of through holes in the first straight region and the plurality of through holes in the corresponding second straight region are separated. Through the above arrangement, the strength of the electrode sheet of the electrode assembly is improved, while taking into account the wetting efficiency and wetting performance of the electrolyte to the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0010] In one or more embodiments, along the thickness direction of the electrode assembly, the projections of the plurality of through holes in the first straight region are separated from the projections of the plurality of through holes in the corresponding second straight region. Through the above arrangement, the strength of the electrode sheet of the electrode assembly is improved, while taking into account the wetting efficiency and wetting performance of the electrolyte to the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0011] In one or more embodiments, 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, and based on the surface area of ​​the first straight region of the first electrode sheet, the sum of the areas of the outer contours of the plurality of through holes on the first material layer in the first straight region accounts for S1, 0.5%≤S1≤10%; and / or, based on the surface area of ​​the second straight region of the first electrode sheet, the sum of the areas of the outer contours of the plurality of through holes on the first material layer in the second straight region accounts for S2, 0.2%≤S2≤6%. By regulating the values ​​of S1 and S2 within the above range, while taking into account the strength of the first electrode sheet, it is beneficial to shorten the flow path of the electrolyte in the width direction of the first electrode sheet in the wound state, improve the penetration efficiency of the electrolyte in the width direction of the first electrode sheet in the wound state, and reduce the insufficient infiltration of the electrolyte into the middle of the wound electrode assembly, thereby improving the cycle performance of the secondary battery, while taking into account the safety performance of the secondary battery.

[0012] In one or more embodiments, along the width direction of the electrode assembly, the spacing between two adjacent through holes located in the first area of ​​the first straight area is 6mm to 45mm; and / or, the spacing between two adjacent through holes located in the first area of ​​the second straight area is 8mm to 80mm. The above arrangement is conducive to improving the infiltration effect of the electrolyte on the electrode sheet, especially the middle part of the electrode sheet, while reducing the actual production and processing difficulty, reducing the risk of local collapse of the first electrode sheet during the processing, and improving the infiltration efficiency and infiltration performance of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0013] In one or more embodiments, along the width direction of the electrode assembly, the thickness of the electrode assembly is T mm, the distance between the first through hole of the first straight area and the first edge of the first straight area is L1 mm, T / 2≤L1≤L / 4, 20≤T≤70; the distance between the first through hole of the second straight area and the first edge of the second straight area is L2 mm, 10+D 11 +(D 11 +D 21 ) / 3≤L2≤40+D 11 +(D 11 +D 21 ) / 3. By adjusting the values ​​of L1 and L2 within the above range, it is helpful to reduce the risk of insufficient infiltration of the electrolyte into the electrode sheet, and at the same time, it is helpful to reduce the risk of local collapse of the straight area of ​​the through hole to the first electrode sheet, thereby improving the infiltration efficiency and infiltration performance of the electrolyte into the electrode sheet, thereby improving the cycle performance of the secondary battery, while taking into account the safety performance of the secondary battery.

[0014] In one or more embodiments, the first pole piece 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 any straight area has a third edge and a fourth edge relative to each other, and the shortest distance between a single through hole and the third edge or the fourth edge is L3 mm, 5≤L3≤10. By regulating the value of L3 within the above range, the risk of bending the edge of the first pole piece or powdering the material layer due to the through hole being set too close to the edge of the material layer is reduced, and it is helpful to reduce the risk of insufficient infiltration of the electrolyte into the pole piece, improve the infiltration effect of the electrolyte on the pole piece, improve the cycle performance of the secondary battery, and take into account the safety performance of the secondary battery.

[0015] In one or more embodiments, the first pole piece includes a first current collector and a first material layer located on at least one surface of the first current collector, and the thickness of the first material layer on a single side of the first current collector is H1 μm, 120≤H1≤600. By regulating the thickness H1 of the first material layer within the above range, the safety risk caused by the poor strength of the pole piece due to the excessive thinness of the material layer is reduced, which is conducive to reducing the actual processing difficulty, improving the diffusion efficiency of the electrolyte, improving the infiltration effect of the electrolyte on the pole piece, and improving the cycle performance of the secondary battery.

[0016] In one or more embodiments, the thickness of the first current collector is H2 μm, 5 ≤ H2 ≤ 20. By adjusting H2 within the above range, it is helpful to reduce the processing difficulty of the first pole piece, while taking into account the cycle performance of the secondary battery, and improving the strength of the first pole piece.

[0017] In one or more embodiments, 80≤L≤600. By adjusting the width L of a single straight region within the above range, it is beneficial to reduce the processing difficulty while taking into account the strength and cycle performance of the first pole piece.

[0018] In one or more embodiments, the first electrode sheet is a positive electrode sheet and / or a negative electrode sheet. By providing a through hole on the flat area of ​​the positive electrode sheet and / or the negative electrode sheet, it is beneficial to improve the wetting efficiency and wetting performance of the electrolyte on the electrode sheet, especially the middle part of the electrode sheet, and improve the wetting effect of the electrolyte on the electrode sheet, thereby improving the cycle performance of the secondary battery while taking into account the strength of the electrode sheet.

[0019] 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 the production efficiency is improved.

[0020] In one or more embodiments, the secondary battery is a soft pack secondary battery or a square secondary battery.

[0021] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. The secondary battery of the present application has good cycle performance, so the electronic device of the present application has a long service life.

[0022] Beneficial effects of the embodiments of the present application:

[0023] The embodiments of the present application provide a secondary battery and an electronic device. By respectively providing through holes of different numbers and sizes in the first straight area and the second straight area of ​​at least one circle of the first electrode sheet along the width direction of the electrode assembly, it is beneficial to improve the infiltration of the electrolyte into the electrode sheet, shorten the transmission path of the electrolyte on the electrode sheet, and take into account the strength of the electrode sheet, so that the secondary battery has both safety performance and good cycle performance.

[0024] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and a person skilled in the art can also obtain other embodiments based on these drawings.

[0026] Figure 1 A schematic diagram of a winding structure formed by an electrode assembly in one embodiment of the present application;

[0027] Figure 2 for Figure 1 A schematic diagram of a first straight region and a second straight region of one circle of a first electrode sheet in a winding structure formed by an electrode assembly;

[0028] Figure 3 for Figure 1 A partial schematic diagram of a first straight region of a first electrode sheet in a winding structure formed by an electrode assembly being unfolded along the width direction and the length direction of the electrode assembly;

[0029] Figure 4 This is a partial structural schematic diagram of a first electrode sheet located in a first straight region along the thickness direction of an electrode assembly in one embodiment of the present application;

[0030] Figure 5 A schematic diagram of a winding structure formed by an electrode assembly in another embodiment of the present application;

[0031] Figure 6 Schematic diagram of the diffusion of electrolyte on part of the first pole piece during the wettability test of the first pole piece.

[0032] Figure markings: electrode assembly 001; first electrode piece 10; straight area 101; first straight area 1011; second straight area 1012; bending area 102; through hole 20; first through hole 211 on the first straight area; first through hole 221 on the second straight area; first edge 31; second edge 32; center 33 of the straight area; center line 34; third edge 35; fourth edge 36; first current collector 41; first material layer 42. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0034] As the volume of the secondary battery increases, the length and width of the pole piece in the secondary battery also increase, which easily leads to the problem of insufficient electrolyte infiltration in the middle of the pole piece. In the later stage of the secondary battery cycle, the pole piece, especially the middle of the pole piece, is prone to black spots or lithium precipitation, resulting in a decrease in the cycle performance of the secondary battery. Based on this, the present application provides a secondary battery, which has a good infiltration effect on the pole piece due to the shortened transmission path of the electrolyte on the pole piece, and the secondary battery has good cycle performance while taking into account safety performance.

[0035] It should be noted that in the specific implementation of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0036] The first aspect of the present application provides a secondary battery, comprising a wound electrode assembly, the electrode assembly comprising a first pole piece, each circle of the first pole piece comprising two straight areas and two bending areas connected to the two straight areas, and the two bending areas are arranged oppositely along the width direction of the wound electrode assembly; along the width direction of the electrode assembly, any straight area has a first edge and a second edge opposite to each other, the length of a single straight area is L mm, the position at a distance of L / 2 from the first edge or the second edge is the center of the straight area, the straight line passing through the center and perpendicular to the width direction of the electrode assembly is the center line of the straight area, the area from the first edge to the center line is the first area of ​​the straight area, and the area from the center line to the second edge is the second area of ​​the straight area. The two straight areas include a first straight area and a second straight area arranged along the thickness direction of the electrode assembly, and a plurality of through holes are arranged on the first area and the second area of ​​the first straight area and the second area of ​​at least one circle of the first pole piece, and the plurality of through holes in the second area are symmetrical with the plurality of through holes arranged on the first area along the center line. The first through hole of the first straight area is arranged near the first edge of the first straight area, and N through holes are arranged in sequence on the first area of ​​the first straight area from the first edge to the center line, where N is a positive integer. The diameter of the maximum circumscribed circle of the outer contour of the first through hole on the first area of ​​the first straight area on the surface of the first pole piece is D 11 mm, D 11=A×L, 1.5%≤A≤6%, optionally, 1.8%≤A≤3.75%. For example, the value of A can be any one of 1.5%, 1.6%, 1.7%, 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%, 6%. The diameter of the maximum circumscribed circle of the outer contour of the nth through hole in the first area of ​​the first straight region on the surface of the first pole piece is D 1n mm, D 1n =B 2n-2 ×D 11 , 2≤n≤N, 0.6≤B≤0.9. For example, 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, and 0.9. The first through hole of the second straight area is arranged near the first edge of the second straight area, and M through holes are arranged in sequence on the first area of ​​the second straight area along the direction from the first edge to the center line, where M is a positive integer. Among them, the diameter of the maximum circumscribed circle of the outer contour of the first through hole in the first area of ​​the second straight area on the surface of the first pole piece is D 21 mm, D 21 =B×D 11 The diameter of the maximum circumscribed circle of the outer contour of the mth through hole in the first region of the second straight region on the surface of the first pole piece is D 2m mm, D 2m =B 2m-1 ×D 11 , 2≤m≤M. In the present application, it is understood that "multiple" means two or more, and "through hole" means a hole that penetrates the material layer and the current collector of the first pole piece, and the thickness of the through hole is the sum of the thickness of the first current collector and the first material layer in the first pole piece.

[0037] In the present application, the first electrode sheet can be a positive electrode sheet and / or a negative electrode sheet. For ease of understanding, the electrode assembly is defined as having its own width direction as the X direction, its own thickness direction as the Y direction, its own length direction as the Z direction, and its own winding direction as the W direction in a wound state. It can be understood that the positive electrode sheet, the positive electrode material layer, the positive electrode collector, the negative electrode sheet, the negative electrode material layer, the negative electrode collector, and the separator are in the same length direction, width direction, and thickness direction as the electrode assembly in a wound state. For example, Figure 1 to Figure 2As 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 electrode collector and a positive electrode material layer arranged on both surfaces of the positive electrode collector. The negative electrode sheet includes a negative electrode collector and a negative electrode material layer arranged on both surfaces of the negative electrode collector. The first electrode sheet 10 is a 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 areas 101 and two bending areas 102 arranged oppositely along the width direction (X direction) of the electrode assembly 001. The two straight areas 101 include a first straight area 1011 and a second straight area 1012 arranged along the thickness direction of the electrode assembly. Along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction after the first electrode sheet 10 is unfolded), any straight area 101 has a first edge 31 and a second edge 32 opposite to each other. Among them, the center line 34 of the first straight area 1011 passes through the center 33 of the first straight area 1011 and is perpendicular to the width direction (X direction) of the electrode assembly 001 (i.e., the length direction of the first electrode piece 10 after unfolding). The first straight area 1011 has a first edge 31 and a second edge 32 opposite to each other. The area from the first edge 31 to the center line 34 of the first straight area 1011 is the first area of ​​the first straight area 1011, and the area from the center line 34 of the first straight area 1011 to the second edge 32 is the second area of ​​the first straight area 1011. The first area of ​​the first straight area 1011 and the second area of ​​the first straight area 1011 are symmetrical about the center line 34. The center line 34 of the second straight area 1012 passes through the center 33 of the second straight area 1012 and is perpendicular to the width direction (X direction) of the electrode assembly 001 (i.e., the length direction of the first electrode piece 10 after unfolding). The second straight area 1012 includes a first edge 31 and a second edge 32. The area from the first edge 31 to the center line 34 of the second straight area 1012 is the first area of ​​the second straight area 1012. The area from the center line 34 of the second straight area 1012 to the second edge 32 is the second area of ​​the second straight area 1012. The first area of ​​the second straight area 1012 is symmetrical to the second area of ​​the second straight area 1012 about the center line 34.

[0038] Along the width direction (X direction) of the electrode assembly (i.e., the length direction of the first electrode sheet 10 after unfolding), through holes 20 are provided on the first area and the second area of ​​the first straight area 1011, and the through holes 20 provided on the second area are symmetrical with the through holes 20 provided on the first area along the center line 34, that is, the first area of ​​the first straight area 1011 with through holes 20 and the second area of ​​the first straight area 1012 are symmetrical along the center line 34; through holes 20 are provided on the first area and the second area of ​​the second straight area 1012, and the through holes 20 provided on the second area are symmetrical with the through holes 20 provided on the first area along the center line 34, that is, the first area of ​​the second straight area 1012 with through holes 20 and the second area of ​​the second straight area 1012 are symmetrical along the center line 34. The first through hole 211 is provided on the first straight area 1011 near the first edge 31, and three through holes 20 are provided in sequence on the first area along the direction from the first edge 31 to the center line 34. The second straight area 1012 is provided with a first through hole 221 near the first edge 31, and two through holes 20 are sequentially provided on the first area 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 only for exemplary description.

[0039] When the value of A and / or B is too small, that is, less than the lower limit of the present application, the through holes set on the first straight area and the second straight area of ​​the first pole piece are too small, the electrolyte has few flow paths in the width direction of the first pole piece in the wound state (that is, the length direction after the first pole piece is unfolded), and the electrolyte does not wet the electrode assembly in the thickness direction, that is, it does not wet the middle part of the wound electrode assembly. In the late cycle of the secondary battery, the middle part of the electrode assembly is prone to produce black spots or lithium precipitation due to insufficient electrolyte, thereby failing to effectively improve the cycle performance of the secondary battery. When the value of A and / or B is too large, that is, greater than the upper limit of the present application, the through hole set on the first pole piece is too large, resulting in a decrease in the strength of the straight area of ​​the first pole piece, and the strength of the first pole piece is reduced accordingly, thereby affecting the safety performance of the secondary battery. At the same time, the loss of active materials is too much, resulting in a decrease in the energy density of the secondary battery. Moreover, in the actual production process, a large number of through holes is not conducive to the processing and large-scale production of electrode assemblies. The present application provides through holes of different sizes in the first straight area and the second straight area, and adjusts the values ​​of A and B within the above range, which is beneficial to shorten the flow path of the electrolyte in the width direction of the first electrode sheet in the wound state (i.e., the length direction of the first electrode sheet after unfolding) while taking into account the safety performance of the secondary battery, and improves the penetration efficiency of the electrolyte in the width direction of the first electrode sheet in the wound state (i.e., the length direction of the first electrode sheet after unfolding), and the through holes provided on the first electrode sheet absorb and store the electrolyte, and form an electrolyte potential difference at the position of the middle part of the electrode assembly where the electrolyte is easily consumed, thereby improving the replenishment efficiency of the electrolyte during the circulation of the secondary battery, enhancing the infiltration effect of the electrolyte on the electrode assembly, and thus improving the circulation performance of the secondary battery. In the present application, the above-mentioned "a plurality of through holes are provided on the first straight area and the second straight area of ​​at least one circle of the first electrode sheet" means that a plurality of through holes are provided on the first straight area and the second straight area of ​​a circle of the first electrode sheet, or a plurality of through holes are provided on the first straight area and the second straight area of ​​multiple circles of the first electrode sheet.

[0040] In one or more embodiments, 3 ≤ N ≤ 11, 2 ≤ M ≤ 9 and M < N. For example, the value of N can be any one of 3, 4, 5, 6, 7, 8, 9, 10, 11; when N is 11, 2 ≤ n ≤ 11, and the value of n can be any one of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. The value of M can be any one of 2, 3, 4, 5, 6, 7, 8, 9; when M is 9, 2 ≤ m ≤ 9, and the value of m can be any one of 2, 3, 4, 5, 6, 7, 8, 9. By adjusting the values of N and M within the above ranges, while taking into account the safety performance of the secondary battery, it is beneficial to shorten the flow path of the electrolyte in the width direction of the first electrode sheet in the wound state (i.e., the length direction after the first electrode sheet is unfolded), improve the penetration efficiency of the electrolyte in the width direction of the first electrode sheet in the wound state (i.e., the length direction after the first electrode sheet is unfolded), and the through holes provided on the first electrode sheet absorb and store the electrolyte, forming an electrolyte potential difference at the position where the electrolyte is easily consumed in the middle of the electrode assembly, improving the replenishment efficiency of the electrolyte during the cycling of the secondary battery, strengthening the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycling performance of the secondary battery, and at the same time reducing the processing difficulty.

[0041] In one or more embodiments, 80 mm ≤ L ≤ 600 mm. For example, the value of L can be any one of 80, 100, 140, 180, 220, 260, 290, 300, 320, 340, 380, 420, 460, 500, 520, 550, 580, 600. By adjusting the value of L within the above range, it is more obvious to shorten the flow path of the electrolyte in the width direction of the electrode assembly in the wound state (i.e., the length direction after the first electrode sheet is unfolded) and improve the penetration efficiency of the electrolyte in the width direction of the electrode assembly in the wound state (i.e., the length direction after the first electrode sheet is unfolded). While taking into account the safety performance of the secondary battery, the cycling performance of the secondary battery is further improved, while taking into account the actual production requirements and reducing the actual processing difficulty.

[0042] In one or more embodiments, a plurality of through holes are provided in a plurality of first flat regions in the electrode assembly, and along the thickness direction of the electrode assembly, at least a partial overlapping region exists between the projections of the plurality of through holes corresponding to each other in the plurality of first flat regions.

[0043] In one or more embodiments, a plurality of through holes are provided in a plurality of second flat regions in the electrode assembly, and along the thickness direction of the electrode assembly, at least a partial overlapping region exists between the projections of the plurality of through holes corresponding to each other in the plurality of second flat regions.

[0044] In one or more embodiments, multiple first straight areas in the electrode assembly are provided with multiple through holes, and along the thickness direction of the electrode assembly, there is at least a partial overlap between the projections of the multiple through holes corresponding to each other in the multiple first straight areas, and, multiple second straight areas in the electrode assembly are provided with multiple through holes, and along the thickness direction of the electrode assembly, there is at least a partial overlap between the projections of the multiple through holes corresponding to each other in the multiple second straight areas.

[0045] In the present application, through holes are provided on the first straight areas and the second straight areas of multiple circles of first pole pieces, and there is at least a partial overlapping area between the projections of the multiple through holes corresponding to each other in the multiple first straight areas and / or the multiple second straight areas along the thickness direction of the electrode assembly. Along the thickness direction of the electrode assembly, the multiple through holes corresponding to each other in the multiple first straight areas and / or the multiple second straight areas shorten and increase the flow path of the electrolyte. When the electrode assembly is injected with liquid, the electrolyte flows through the flow path formed by the multiple through holes corresponding to each other in the multiple first straight areas and / or the multiple second straight areas, and infiltrates into each circle of the first pole piece where the through holes are located, thereby shortening the infiltration path of the electrolyte, increasing the infiltration speed, and thereby improving the cycle performance of the electrode assembly.

[0046] In one or more embodiments, along the thickness direction of the electrode assembly, the centers of the maximum circumscribed circles of the outer contours of the multiple through holes in the first straight area and the multiple through holes in the corresponding second straight area are separated. The through hole on the second straight area corresponding to the through hole on the first straight area means that, along the thickness direction of the electrode assembly, the projection of any through hole on the first straight area on the second straight area, along the width direction of the electrode assembly, the through hole with the shortest distance from the projection edge of the projection of the through hole on the first straight area on the second straight area is the through hole on the second straight area corresponding to the through hole on the first straight area; the centers of the circles being separated means that the two centers of the circles are not on the same straight line perpendicular to the width direction of the electrode assembly. Figure 2 As shown, the first through hole 211 on the first straight area 1011 corresponds to the first through hole 221 on the second straight area 1012, and the centers of the maximum circumscribed circles of the outer contours of the through hole 211 and the through hole 221 are separated. By setting the centers of the maximum circumscribed circles of the outer contours of the plurality of through holes in the first straight area and the plurality of through holes in the second straight area corresponding thereto to be separated, the centers of the through holes on the odd-numbered straight areas of the electrode assembly and the through holes on the even-numbered straight areas are separated along the winding direction, thereby improving the pole piece strength of the electrode assembly, while taking into account the infiltration efficiency and infiltration performance of the electrolyte to the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0047] In one or more embodiments, along the thickness direction of the electrode assembly, the projections of the plurality of through holes in the first straight region are separated from the projections of the plurality of through holes in the corresponding second straight region. By setting the projections of the plurality of through holes in the first straight region to be separated from the projections of the plurality of through holes in the corresponding second straight region, the strength of the electrode sheet of the electrode assembly is improved, while taking into account the wetting efficiency and wetting performance of the electrolyte to the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0048] In one or more embodiments, the first pole piece includes a first current collector and a first material layer located on at least one surface of the first current collector, and based on the surface area of ​​the first straight region of the first pole piece, the sum of the areas of the outer contours of the plurality of through holes on the first material layer of the first straight region accounts for S1, 0.5%≤S1≤10%. For example, the value of S1 may be any one of 0.5%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.3%, 3.8%, 4%, 6%, 6.5%, 7%, 8%, 9%, and 10%.

[0049] In one or more embodiments, the first pole piece includes a first current collector and a first material layer located on at least one surface of the first current collector, and based on the surface area of ​​the second straight region of the first pole piece, the sum of the areas of the outer contours of the plurality of through holes on the first material layer in the second straight region accounts for S2, 0.2%≤S2≤6%. For example, the value of S2 can be any one of 0.2%, 0.8%, 1.5%, 2%, 2.5%, 3%, 3.3%, 3.8%, 4%, 4.5%, 4.8%, 5%, 5.3%, 5.8%, and 6%.

[0050] In one or more embodiments, the first pole piece includes a first current collector and a first material layer located on at least one surface of the first current collector, and based on the surface area of ​​the first straight region of the first pole piece, the sum of the areas of the outer contours of the plurality of through holes on the first material layer in the first straight region accounts for S1, 0.5%≤S1≤10%. For example, the value of S1 may be any one of 0.5%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.3%, 3.8%, 4%, 6%, 6.5%, 7%, 8%, 9%, 10%; and, based on the surface area of ​​the second straight region of the first pole piece, the sum of the areas of the outer contours of the plurality of through holes on the first material layer in the second straight region accounts for S2, 0.2%≤S2≤6%. For example, the value of S2 can be any one of 0.2%, 0.8%, 1.5%, 2%, 2.5%, 3%, 3.3%, 3.8%, 4%, 4.5%, 4.8%, 5%, 5.3%, 5.8%, and 6%.

[0051] In the present application, by regulating the values ​​of S1 and / or S2 within the above range, while taking into account the strength of the first electrode sheet, it is beneficial to shorten the flow path of the electrolyte in the width direction of the first electrode sheet in the wound state (i.e., the length direction after the first electrode sheet is unfolded), and improve the penetration efficiency of the electrolyte in the width direction of the first electrode sheet in the wound state (i.e., the length direction after the first electrode sheet is unfolded). It is beneficial to reduce the risk of black spots or lithium precipitation in the middle of the electrode assembly due to insufficient electrolyte infiltration into the middle part of the wound electrode assembly in the late cycle of the secondary battery, shorten the flow path of the electrolyte in the width direction of the first electrode sheet in the wound state (i.e., the length direction after the first electrode sheet is unfolded), thereby improving the cycle performance of the secondary battery and taking into account the safety performance of the secondary battery.

[0052] In one or more embodiments, along the width direction of the electrode assembly, the spacing L4 between two adjacent through holes located in the first area of ​​the first straight zone is 6 mm to 45 mm; for example, the value of L4 can be any one of 6, 8, 10, 11, 13, 15, 18, 20, 25, 30, 38, 40, and 45.

[0053] In one or more embodiments, along the width direction of the electrode assembly, the spacing L5 between two adjacent through holes located in the first region of the second straight region is 8 mm to 80 mm. For example, the value of L5 can be any one of 8, 10, 15, 20, 25, 31, 35, 40, 45, 50, 55, 60, 65, 71, 78, and 80.

[0054] In one or more embodiments, along the width direction of the electrode assembly, the spacing L4 between two adjacent through holes located in the first area of ​​the first straight zone is 6 mm to 45 mm, for example, the value of L4 can be any one of 6, 8, 10, 11, 13, 15, 18, 20, 25, 30, 38, 40, 45; and, the spacing L5 between two adjacent through holes located in the first area of ​​the second straight zone is 8 mm to 80 mm, for example, the value of L5 can be any one of 8, 10, 15, 20, 25, 31, 35, 40, 45, 50, 55, 60, 65, 71, 78, 80. Figure 2As shown, along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction of the first pole piece 10 after unfolding), the spacing between two adjacent through holes 20 located in the first area of ​​the first straight area 1011 is L4 mm, and the spacing between two adjacent through holes 20 located in the first area of ​​the second straight area 1012 is L5 mm. In this application, the spacing 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 of the first pole piece after unfolding). By adjusting the distance L4 between two adjacent through holes located in the first area of ​​the first straight zone within the above range, and / or adjusting the distance L5 between two adjacent through holes located in the first area of ​​the second straight zone within the above range, the distance between two adjacent through holes in the first straight zone and the second straight zone 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, while reducing the difficulty of actual production and processing, as well as the risk of local collapse of the first electrode sheet during the processing process, and improving the wetting efficiency and wetting performance of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery.

[0055] In one or more embodiments, the thickness of the electrode assembly is T mm, and along the width direction of the electrode assembly, the distance between the first through hole of the first straight area and the first edge of the first straight area is L1 mm, T / 2≤L1≤L / 4, 20≤T≤70, for example, the value of T can be any one of 20, 25, 30, 40, 45, 50, 55, 60, 65, 70. The distance between the first through hole of the second straight area and the first edge of the second straight area is L2 mm, 10+D 11 +(D 11 +D 21 ) / 3≤L2≤40+D 11 +(D 11 +D 21 ) / 3. Figure 2As shown, along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction of the first pole piece 10 after unfolding), the distance between the first through hole 211 of the first straight area 1011 and the first edge 31 is L1 mm, and the distance between the first through hole 221 of the second straight area 1012 and the first edge 31 is L2 mm. In the present application, along the width direction of the electrode assembly, the distance between the first through hole and the first edge refers to the closest distance between the through hole edge of the first through hole and the first edge along the width direction of the electrode assembly (i.e., the length direction of the first pole piece after unfolding). In addition, 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 T, L1 and L2 within the above range, it is helpful to reduce the risk of insufficient infiltration of the electrolyte into the electrode sheet, and at the same time it is helpful to reduce the risk of local collapse of the flat area of ​​the through hole to the first electrode sheet, thereby improving the wetting efficiency and wetting performance of the electrolyte on the electrode sheet, and improving 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 of the secondary battery.

[0056] In one or more embodiments, 10≤L1≤40. For example, the value of L can be any one of 10, 15, 20, 25, 30, 35, and 40. By adjusting the value of L1 within the above range, it is helpful to reduce the risk of insufficient infiltration of the electrode sheet by the electrolyte, and at the same time, it is helpful to reduce the risk of local collapse of the first straight area of ​​the first electrode sheet by the through hole, improve the infiltration efficiency and infiltration performance of the electrode sheet by the electrolyte, improve the infiltration 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.

[0057] In one or more embodiments, 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. Along the length direction of the electrode assembly, the first material layer in any straight region has a third edge and a fourth edge opposite to each other. The shortest distance between a single through hole and the third edge or the fourth edge is L3 mm, and 5≤L3≤10. For example, the value of L3 may be any one of 5, 6, 7, 7.5, 8, 9, and 10. Figure 3As shown, along the length direction (Z direction) of the electrode assembly 001 (i.e., the width direction after the first pole piece is unfolded), the first material layer of the first straight region 1011 has a third edge 35 and a fourth edge 36 relative to each other, the first through hole 211 is close to the third edge 35, and the shortest distance between the first through hole 211 and the third edge 35 is L3mm. In the present application, the shortest distance between the through hole and the third edge or the fourth edge along the length direction of the electrode assembly refers to the shortest distance between the through hole edge of any through hole and the third edge or the fourth edge along the length direction of the electrode assembly (i.e., the width direction after the first pole piece is unfolded). Moreover, along the length direction of the electrode assembly (i.e., the width direction after the first pole piece is unfolded), the distance between any through hole and the third edge or the fourth edge is not less than the above shortest distance. By adjusting the value of L3 within the above range, the risk of the through hole being set too close to the edge of the material layer, resulting in bending of the edge of the first electrode or powdering of the material layer, is reduced, and it is beneficial to reduce the risk of insufficient infiltration of the electrolyte into the electrode, and at the same time it is beneficial to reduce the impact of the setting of the through hole on the safety performance of the first electrode, thereby improving the wetting efficiency and wetting performance of the electrolyte on the electrode, improving the wetting effect of the electrolyte on the electrode, and improving the cycle performance of the secondary battery, while taking into account the safety performance of the secondary battery.

[0058] In one or more embodiments, the first pole piece includes a first current collector and a first material layer located on at least one surface of the first current collector, and 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 pole piece 10 includes a first current collector 41 and a first material layer 42 located on both surfaces of the first current collector 41, and the thickness of the first material layer 42 on one side of the first current collector is H1μm. By adjusting the value of H1 within the above range, the safety risk caused by the poor strength of the pole piece due to the thin material layer is reduced, which is conducive to reducing the actual processing difficulty, improving the diffusion efficiency of the electrolyte, improving the wetting effect of the electrolyte on the pole piece, and improving the cycle performance of the secondary battery. In the present application, the thickness H1 of the first material layer can be regulated by means known to those skilled in the art. For example, when the slurry is coated on the surface of the first current collector, on the basis of other conditions unchanged and a certain solid content of the slurry, the amount of coating per unit area is increased to increase the thickness of the first material layer. This application does not impose any special restrictions, as long as the purpose of this application can be achieved.

[0059] In one or more embodiments, the thickness of the first current collector is H2 μm, 5≤H2≤20. For example, the value of H2 can be any one of 5, 6, 8, 10, 12.5, 15, 17, and 20. Figure 4As shown, the thickness of the first current collector 41 of the first pole piece 10 is H2μm. By adjusting the value of H2 within the above range, it is helpful to reduce the processing difficulty of the first pole piece, while taking into account the cycle performance of the secondary battery, and improving the strength of the first pole piece. The present application has no special restrictions on the regulation method of the first current collector thickness H2, as long as the purpose of the present application can be achieved. For example, commercially available current collectors with different thicknesses can be selected, and combined with the "N, M, A, D" in the present application. 11 , B, D 21 The thickness of the current collector of the first pole piece is determined by the test method of "test of S1, S2, L1, L2, L3, L4, L5, H1, H2", and then the current collector of the first pole piece of the required thickness is selected.

[0060] In one or more embodiments, along the length direction of the electrode assembly (i.e., the width direction of the first pole piece after it is unfolded), the through holes arranged on any straight area of ​​the first pole piece are distributed in a matrix. In the present application, along the width direction of the first pole piece after it is unfolded, multiple rows of through holes are arranged in any straight area, and the spacing between the corresponding through holes in each row is equal. The present application has no special restrictions on the number of rows of through holes, and those skilled in the art can set them according to the actual specifications of the first pole piece, as long as the purpose of the present application can be achieved. For example, the number of rows of through holes arranged on the first straight area of ​​the first pole piece can be H3 rows, 2≤H3≤40; the number of rows of through holes arranged on the second straight area of ​​the first pole piece can be H4 rows, 2≤H4≤40.

[0061] 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. In the present application, there is no particular limitation on the shape of the polygon, as long as the purpose of the present application can be achieved. For example, the shape of the outer contour of a single through hole can be independently selected from one of a triangle, a rectangle, a trapezoid, a square, a pentagon or a 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.

[0062] In one or more embodiments, the first electrode sheet is a negative electrode sheet. By respectively providing a plurality of through holes on the first straight area and the second straight area of ​​at least one circle of the negative electrode sheet, it is beneficial to further improve the wetting efficiency and wetting performance of the electrolyte on the negative electrode sheet, especially the middle part of the negative electrode sheet, better improve the wetting effect of the electrolyte on the negative electrode sheet, and improve the cycle performance of the secondary battery.

[0063] In one or more embodiments, the first electrode sheet is a positive electrode sheet. By respectively providing a plurality of through holes on the first straight area and the second straight area of ​​at least one circle of the positive electrode sheet, it is beneficial to further improve the wetting efficiency and wetting performance of the electrolyte on the positive electrode sheet, especially the middle part of the positive electrode sheet, better improve the wetting effect of the electrolyte on the positive electrode sheet, and improve the cycle performance of the secondary battery.

[0064] When the first electrode sheet is a positive electrode sheet or a negative electrode sheet, the electrode assembly further includes a second electrode sheet. For example, when the first electrode sheet is a negative electrode sheet, the second electrode sheet is a positive electrode sheet; when the first electrode sheet is a positive electrode sheet, the second electrode sheet is a negative electrode sheet.

[0065] In one or more embodiments, the first electrode sheet is a positive electrode sheet and a negative electrode sheet. Figure 5 As shown, along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction after the first electrode sheet 10 is unfolded), the first electrode sheet 10 is a positive electrode sheet and a negative electrode sheet, and three through holes 20 are provided on the first area and the second area of ​​the first straight area 1011 of each circle of the positive electrode sheet and the negative electrode sheet, and two through holes 20 are provided on the first area and the second area of ​​the second straight area 1012 of each circle of the positive electrode sheet and the negative electrode sheet. By providing a plurality of through holes on the first and second straight areas of at least one circle of the positive electrode sheet and at least one circle of the negative electrode sheet, it is beneficial to improve the infiltration efficiency and infiltration performance of the electrolyte on the electrode sheet, especially the middle part of the electrode sheet, and improve the infiltration effect of the electrolyte on the electrode sheet, thereby improving the cycle performance of the secondary battery.

[0066] In the present application, when the first electrode sheet is a positive 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 positive electrode sheet includes a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector. The above-mentioned “positive electrode material layer located on at least one surface of the positive electrode current collector” means that the positive electrode material layer can be arranged on one surface of the positive electrode current collector along its own thickness direction, or can be arranged on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the “surface” here refers to the coating area where the positive electrode material layer is arranged in the positive electrode current collector. The present application has no special restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode material layer of the present application includes a positive electrode active material. The present application has no special restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganate, lithium iron manganese phosphate or lithium titanate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, for example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. The present application does not particularly limit the type of positive electrode binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal 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 above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the mass ratio of the positive active material, the conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0067] In the present application, when the first electrode sheet is a negative electrode sheet, the statement "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 thickness direction, or can be disposed on both surfaces of the negative current collector along its 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 places no particular restrictions on 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 places no particular restrictions on 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, or at least one of them. Optionally, the negative electrode material layer may further include a conductive agent and a negative electrode binder. The present application places no particular restrictions on 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 of the same type as the conductive agent in the above-mentioned positive electrode material layer. The present application places no particular restrictions on 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 of the same type 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 places no particular restrictions on 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, but is not limited to, at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose. The present application places no particular restrictions on 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.

[0068] The present application has no particular restrictions on the preparation method of the first pole piece, as long as the purpose of the present application can be achieved. For example, the preparation method of the first pole piece includes but is not limited to the following steps: (1) preparing slurry; (2) coating the slurry on one surface of the first current collector, and drying to obtain the first pole piece with a material layer on one side; (3) coating the slurry on the other surface of the current collector, and drying to obtain the first pole piece with a material layer on both sides; (4) after cold pressing and stripping, pre-winding the first pole piece, determining two straight areas of each circle of the first pole piece and two bending areas connected to the two straight areas, the two bending areas are arranged oppositely along the width direction of the electrode assembly, and different numbers and sizes of through holes are arranged on the first straight area and the second straight area of ​​the first pole piece, and along the direction from the edge of each straight area to the center line of the straight area, the diameter of the maximum circumscribed circle of the outer contour of the through hole arranged on the surface of the first pole piece gradually decreases, so as to obtain the first pole piece.

[0069] The present application has no special restrictions on the solid content of the above-mentioned slurry, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the temperature and time of the above-mentioned drying, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the process parameters of the above-mentioned cold pressing and slitting, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the above-mentioned way of setting the through holes, as long as the purpose of the present application can be achieved. For example, the through holes can be set by punching with a circular cutter, and the diameter of the maximum circumscribed circle of the outer contour of each through hole on the surface of the first pole piece is regulated by adjusting the power and cutting depth of the circular cutter; the proportion S1 of the sum of the areas of the outer contours of the multiple through holes on the first straight zone and the proportion S2 of the sum of the areas of the outer contours of the multiple through holes on the second straight zone are adjusted by adjusting the surface area of ​​the corresponding straight zone, the number of through holes, the shape of the through holes, the power of the circular cutter, the cutting depth, and the distance between the circular cutters. The spacing or cutting frequency of two adjacent through holes on adjacent straight areas is regulated by adjusting the spacing or cutting frequency between the circular cutters; along the width direction of the electrode assembly (i.e. the length direction of the first pole piece after unfolding), the distance L1 or L2 between the first through hole and the first edge is regulated by adjusting the spacing or cutting frequency between the circular cutters; along the length direction of the electrode assembly (i.e. the width direction of the first pole piece after unfolding), the shortest distance L3 between a single through hole and the third edge or the fourth edge is regulated by adjusting the spacing or cutting frequency between the cutting frequencies, etc.

[0070] In other embodiments, through holes can be set by pulsed laser drilling, and the diameter of the maximum circumscribed circle of the outer contour of each through hole on the surface of the first pole piece is regulated by adjusting the power and defocus of the pulsed laser emitter; the proportion S1 of the sum of the areas of the outer contours of multiple through holes on the first material layer of the first straight zone and the proportion S2 of the sum of the areas of the outer contours of multiple through holes on the first material layer of the second straight zone are regulated by adjusting the surface area of ​​the corresponding straight zone, the number of through holes, the power of the pulsed laser emitter, the defocus, the spacing between the pulsed laser emitters or the laser emission frequency; the distance between adjacent straight zones is regulated by adjusting the surface area of ​​the corresponding straight zone, the number of through holes, the power of the pulsed laser emitter, the defocus, the spacing between the pulsed laser emitters or the laser emission frequency; The distance L4 or L5 between two adjacent through holes in the region is regulated by adjusting the distance between the pulse laser emitters or the laser emission frequency; along the width direction of the electrode assembly (i.e. the length direction after the first pole piece is unfolded), the distance L1 or L2 between the first through hole and the first edge is regulated by adjusting the distance between the pulse laser emitters or the laser emission frequency; along the length direction of the electrode assembly (i.e. the width direction after the first pole piece is unfolded), the shortest distance L3 between a single through hole and the third edge or the fourth edge is regulated by adjusting the distance between the pulse laser emitters or the laser emission frequency.

[0071] In the present application, it can be understood by those skilled in the art that when a through hole is provided on the first pole piece by pulse laser drilling, the thickness of the through hole is the sum of the thickness of the pole piece material layer and the thickness of the current collector.

[0072] The secondary battery in the present application includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalate borate) (LiBOB), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) or lithium difluoroborate. The present application does not limit the content of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no special restrictions on non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or ethyl methyl carbonate. The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate or vinyl ethylene 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-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 above-mentioned carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0073] The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or at least one of aramid. The type of diaphragm may include at least one of woven membranes, non-woven membranes, microporous membranes, composite membranes, rolled membranes or spun membranes. The diaphragm of the present application may have a porous structure, and the present application has no particular restrictions on the size of the pore size of the porous structure of the diaphragm, as long as the purpose of the present application can be achieved. For example, the size of the pore size can be 0.01 μm to 1 μm. The present application has no particular restrictions on the thickness of the diaphragm, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm can be 5 μm to 40 μm.

[0074] In one or more embodiments, the secondary battery is a soft-pack secondary battery or a square secondary battery. Along the width direction of the electrode assembly, by providing a plurality of through holes of different numbers and sizes in the first straight area and the second straight area of ​​at least one circle of the first pole piece, it is beneficial to improve the infiltration of the electrolyte into the pole piece, shorten the transmission path of the electrolyte on the pole piece, and take into account the strength of the pole piece, so that the secondary battery has good cycle performance while taking into account safety performance.

[0075] The secondary battery of the present application is not particularly limited, and may include any device that generates an electrochemical reaction. In one or more embodiments of the present application, the secondary battery may include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0076] The present application has no particular restrictions on the preparation method of the secondary battery, and any preparation method known in the art may be selected as long as the purpose of the present application can be achieved. For example, the preparation method of the secondary battery includes but is not limited to the following steps: stacking the diaphragm, the first pole piece, the diaphragm and the second pole piece in sequence, and winding and folding them as needed to obtain an electrode assembly with a winding structure, placing the electrode assembly in a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery.

[0077] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. The secondary battery of the present application has good cycle performance, so the electronic device of the present application has a long service life.

[0078] The electronic device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. For example, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0079] Example

[0080] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0081] Test methods and equipment:

[0082] N, M, A, D 11 , B, D 21 , S1, S2, L1, L2, L3, L4, L5, H1, H2 tests:

[0083] At an ambient temperature of 25°C, the lithium-ion battery was disassembled to obtain an electrode assembly, and an electron scanning microscope was used to observe along the width direction of the electrode assembly to obtain the number of through holes in the first area on the first straight area of ​​the first pole piece provided with through holes, which is the number of through holes N, and the number of through holes in the first area on the second straight area, which is the number of through holes M. Then, the pole piece provided with through holes was taken out, i.e., the first pole piece, and soaked in dimethyl carbonate (DMC) for 20 minutes, and then the first pole piece was placed in an oven and dried at 80°C for 12 hours to obtain a test sample of the first pole piece.

[0084] The first pole piece is pre-wound, and an electron scanning microscope is used to measure the length L of the straight region of the first pole piece and the diameter D of the maximum circumscribed circle of the outer contour of the first through hole on the first straight region on the surface of the first pole piece. 11 , and calculate the diameter D 11 The ratio of the length L is A; at the same time, the diameter D of the maximum circumscribed circle of the outer contour of the first through hole on the second straight area on the surface of the first pole piece is measured by an electron scanning microscope. 21 , and bring it into D 21 =B×D 11Calculate the value B. Then, the length and width of the first straight area and the area of ​​the outer contour of the through hole are measured on the first pole piece by using an electron scanning microscope, and the ratio of the sum of the areas of the outer contours of the multiple through holes to the area of ​​the first straight area is calculated, which is the proportion S1 of the sum of the areas of the outer contours of the multiple through holes. The area of ​​the outer contour of the through hole in the second straight area is measured on the first pole piece by using an electron scanning microscope, and the ratio of the sum of the areas of the outer contours of the multiple through holes to the area of ​​the second straight area is calculated, which is the proportion S2 of the sum of the areas of the outer contours of the multiple through holes.

[0085] An electron scanning microscope is used to measure the distance L4 between two adjacent through holes on the first straight area of ​​the first pole piece and the distance L5 between two adjacent through holes on the second straight area along the width direction of the electrode assembly; an electron scanning microscope is used to measure the distance L1 between the first through hole on the first straight area of ​​the first pole piece and the first edge, and the distance L2 between the first through hole on the second straight area and the first edge; and an electron scanning microscope is used to measure the shortest distance L3 between a single through hole on the first pole piece and the third edge or the fourth edge along the length direction of the electrode assembly.

[0086] Cycle performance test:

[0087] The lithium-ion batteries in the embodiments and comparative examples were subjected to a charge-discharge cycle test in a 25°C constant temperature box. The lithium-ion batteries were charged to 4.2V at a constant current of 2C, and then charged to 0.05V at a constant voltage of 4.2V. After standing for 5 minutes, they were discharged to 2.5V at a constant current of 6C. This was the first cycle, and the first cycle discharge capacity C1 was recorded. After 600 cycles according to the above cycle process, the lithium-ion battery discharge capacity C 600 , the cycle capacity retention rate of the 600th cycle is calculated as an index for evaluating the wetting effect of the electrolyte on the first pole piece and the cycle performance of the lithium-ion battery, and the formula is shown in formula (I). When the 600-cycle (cls) capacity retention rate is lower, it indicates that the wetting effect of the electrolyte on the first pole piece in the lithium-ion battery is worse, and the cycle performance of the lithium-ion battery is worse; when the 600cls capacity retention rate is higher, it indicates that the wetting effect of the electrolyte on the first pole piece in the lithium-ion battery is better, and the cycle performance of the lithium-ion battery is better.

[0088] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0089] Pole wettability test:

[0090] The diffusion distance of the electrolyte on the surface of the first electrode piece is used to characterize the wettability of the electrolyte on the first electrode piece. The specific operation steps are as follows:

[0091] At an ambient temperature of 25°C, the lithium-ion battery was discharged at 0.5C to 2.5V and then disassembled, the first electrode piece with a through hole was taken out, and the electrolyte and the side reaction products on the surface were removed by dimethyl carbonate (DMC) cleaning for 10 minutes, and then placed in a 25°C environment for 2 hours to obtain a dry first electrode piece; a 5mL medical syringe was used to inhale the electrolyte, and the air at the head of the medical syringe was discharged; the unfolded dry first electrode piece was placed on a horizontal table, the medical syringe was located directly above the first electrode piece and perpendicular to the first electrode piece, and the vertical distance between the needle head of the medical syringe and the first electrode piece was 3cm, 1mL of electrolyte was dripped vertically and fell on the first electrode piece, and the diffusion distance of the electrolyte was measured after 1 minute; a soft ruler with an accuracy of 0.5mm was used to measure the distance between the two points where the electrolyte diffused the farthest on the first electrode piece, such as Figure 6 As shown, Figure 6 The value of d in the figure is measured 5 times and the average value is taken to obtain the diffusion distance d of the electrolyte in the first electrode 10. The electrolyte is the same as the electrolyte in Example 1. Figure 6 It is only a schematic diagram of the structure of a portion of the first pole piece in the middle position along the length direction (X direction) after the first pole piece is unfolded, which is only for exemplary description.

[0092] When the first electrode sheet is a positive electrode sheet and a negative electrode sheet, the diffusion distance of the electrolyte in the negative electrode sheet obtained by measuring 5 times and the diffusion distance of the electrolyte in the positive electrode sheet obtained by measuring 5 times are averaged to obtain the diffusion distance d of the electrolyte in the first electrode sheet.

[0093] Shock Test:

[0094] After charging the lithium-ion battery to 4.2V at a constant current of 2C, charge it to 0.05C at a constant voltage to reach a fully charged state. Place the fully charged lithium-ion battery on the test bench, and place a round bar with a diameter of 15.8mm and a length of at least 6cm at the center of the wide surface of the lithium-ion battery. Wait for the longitudinal axis of the lithium-ion battery to be parallel to the surface of the test bench and perpendicular to the longitudinal axis of the round bar. Use a 9.1kg heavy hammer to drop it vertically from a height of 610mm and let it fall at the intersection of the round bar and the lithium-ion battery.

[0095] Test pass criteria: pass if no fire or explosion occurs.

[0096] 100 lithium-ion batteries are tested in each embodiment or comparative example, and the impact passing rate of the lithium-ion battery = the number of passed batteries / 100. The greater the impact passing rate of the lithium-ion battery, that is, the greater the number of passed batteries, the better the safety performance of the lithium-ion battery.

[0097] Example 1

[0098] <Preparation of negative electrode sheet>

[0099] The first electrode sheet is a negative electrode sheet. The negative electrode active materials artificial graphite, sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97.3:1.7:1.0, and then deionized water is added as a solvent, stirred and mixed evenly, and a negative electrode slurry with a solid content of 50wt% is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness H2 of 12.5μm, and dried at 105°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. After that, the above steps are repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. Then, after cold pressing and stripping, the coating area and empty foil area of ​​the negative electrode current collector provided with a negative electrode material layer are determined along the length direction of the unfolded negative electrode sheet, and the coating weight of the negative electrode material layer is 14.6mg / cm 2 After cold pressing, the thickness H1 of the negative electrode material layer on one side of the negative electrode current collector is 360 μm.

[0100] The negative electrode sheet is pre-wound, and one surface of the negative electrode sheet is selected to determine the first straight area, the second straight area, and the two bending areas connected to the two straight areas of each circle of the first electrode sheet, wherein the width of the straight area is set to 240 mm and the length of the straight area is set to 334 mm. The first edge, the second edge, and the center line of each straight area are determined. In the first area from the first edge to the center line of the first straight area and the second area from the second edge to the center line of the first straight area, along the width direction of the unfolded negative electrode sheet, 15 rows of through holes are set in the first area of ​​the first straight area of ​​each circle, and 6 through holes are set in each row. Along the direction from the first edge to the center line, the maximum circumscribed circle of the outer contour of the through holes set in the first area on the surface of the electrode sheet gradually decreases, and the multiple through holes set in the second area are symmetrical with the multiple through holes set in the first area along the center line of the straight area. In the first area along the first edge of the second straight area to the center line and in the second area along the second edge of the second straight area to the center line, 15 rows of through holes are arranged in the first area of ​​each circle of the second straight area along the width direction of the electrode assembly, and 5 through holes are arranged in each row. Along the direction from the first edge to the center line, the maximum circumscribed circle of the outer contour of the through holes arranged in the first area on the surface of the electrode piece gradually decreases, and the multiple through holes arranged in the second area are symmetrical with the multiple through holes arranged in the first area along the center line of the straight area.

[0101] A is determined to be 3.75%, B is determined to be 0.75, and the diameter D of the maximum circumscribed circle of the outer contour of the first through hole near the first edge on the first straight area on the surface of the negative electrode sheet is set along the length direction of the unfolded negative electrode sheet. 11 mm, D1 = A × L, the diameter of the maximum circumscribed circle of the outer contour of the nth through hole on the surface of the negative electrode is D 1n mm, D 1n =B2n-2 ×D 11 , the sum of the areas of the outer contours of the multiple through holes accounts for S1 of 3.479%, along the length direction of the unfolded negative electrode sheet, the distance L1 between the first through hole and the first edge is 20 mm, and the spacing L4 between two adjacent through holes is 16 mm; along the length direction of the unfolded negative electrode sheet, the diameter D of the maximum circumscribed circle of the outer contour of the first through hole close to the first edge on the second straight area on the surface of the negative electrode sheet 21 mm, D 21 =B×D 11 The diameter of the maximum circumscribed circle of the outer contour of the mth through hole on the surface of the negative electrode is D 2m mm, D 2m =B 2m-1 ×D 11 , the sum of the areas of the outer contours of the multiple through holes accounts for S2 of 1.952%. Along the length direction of the unfolded negative electrode sheet, the distance L2 between the first through hole and the first edge is 30 mm, and the spacing L5 between two adjacent through holes is 18.87 mm. Along the width direction of the unfolded negative electrode sheet, the shortest distance L3 between a single through hole and the third edge or the fourth edge of the straight area is 8 mm. According to the above parameters, laser drilling is performed on the straight area of ​​the negative electrode sheet to obtain a negative electrode sheet with a specification of 334 mm × 12288 mm.

[0102] <Preparation of positive electrode sheet>

[0103] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and are fully stirred and mixed to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12.5μm, and dried at 105°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. After that, the above steps are repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 105°C for 4h to obtain a positive electrode sheet with a specification of 330.1mm×11730mm for standby use. Among them, the coating weight of the positive electrode material layer is 16mg / cm 2 After cold pressing, the thickness of the positive electrode material layer on one side of the positive electrode collector is 400 μm.

[0104] <Diaphragm>

[0105] A polypropylene (PP) film with a thickness of 12 μm was used as the separator.

[0106] <Preparation of Electrolyte>

[0107] In a dry argon atmosphere glove box, organic solvents 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, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the base solvent, and the electrolyte was obtained after being fully mixed. Based on the mass of the electrolyte, the mass percentage of LiPF6 is 12.5%, and the balance is the base solvent.

[0108] <Preparation of lithium-ion batteries>

[0109] The prepared diaphragm, positive electrode sheet, diaphragm, and negative electrode sheet are stacked in order, so that the diaphragm is between the positive electrode and the negative electrode to play an isolating role. After winding, flattening, current collector welding, shelling, coding, vacuum drying, electrolyte injection, sealing, high-temperature standing, and forming capacity, a lithium-ion battery can be obtained. Among them, the upper limit voltage of the formation is 3.6V, the formation temperature is 45°C, and the formation standing time is 2h.

[0110] Example 2

[0111] Except that 3 through holes are arranged in each row on the first area of ​​the first straight area of ​​the negative electrode plate, 2 through holes are arranged in each row on the first area of ​​the second straight area, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1.

[0112] Example 3

[0113] Except that 11 through holes are arranged in each row on the first area of ​​the first straight area of ​​the negative electrode plate, 9 through holes are arranged in each row on the first area of ​​the second straight area, and relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1.

[0114] Example 4 to Example 12

[0115] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0116] Example 13

[0117] Except for preparing the positive electrode sheet and the negative electrode sheet according to the following steps, the rest is the same as Example 1.

[0118] <Preparation of positive electrode sheet>

[0119] The first electrode is the positive electrode. 0.8 Co 0.1 Mn 0.1O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and the mixture is fully stirred to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on one surface of the positive electrode collector aluminum foil with a thickness H2 of 12.5μm, and dried at 105°C to obtain a positive electrode sheet coated with a positive electrode material layer on one side. After that, the above steps are repeated on the other surface of the positive electrode collector aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. Then, after cold pressing and stripping, the coating area and empty foil area of ​​the positive electrode collector with a positive electrode material layer are determined along the length direction of the unfolded positive electrode sheet, and the coating weight of the positive electrode material layer is 16mg / cm 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.

[0120] The positive electrode sheet is pre-wound, and one surface of the positive electrode sheet is selected to determine the first straight area, the second straight area, and the two bending areas connected to the two straight areas of each circle of the positive electrode sheet, wherein the width of the straight area is set to 240 mm, and the length of the straight area is set to 330.1 mm. The first edge, the second edge, and the center line of each straight area are determined. In the first area from the first edge to the center line of the first straight area and the second area from the second edge to the center line of the first straight area, along the width direction of the unfolded positive electrode sheet, 15 rows of through holes are set in the first area of ​​the first straight area of ​​each circle, and 6 through holes are set in each row. Along the direction from the first edge to the center line, the maximum circumscribed circle of the outer contour of the through holes set in the first area on the surface of the electrode sheet gradually decreases, and the multiple through holes set in the second area are symmetrical with the multiple through holes set in the first area along the center line of the straight area. In the first area along the first edge of the second straight area to the center line and in the second area along the second edge of the second straight area to the center line, 15 rows of through holes are arranged in the first area of ​​each circle of the second straight area along the width direction of the electrode assembly, and 5 through holes are arranged in each row. Along the direction from the first edge to the center line, the maximum circumscribed circle of the outer contour of the through holes arranged in the first area on the surface of the electrode piece gradually decreases, and the multiple through holes arranged in the second area are symmetrical with the multiple through holes arranged in the first area along the center line of the straight area.

[0121] A is determined to be 3.75%, B is determined to be 0.75, and the diameter D of the maximum circumscribed circle of the outer contour of the first through hole near the first edge on the first straight area on the surface of the positive electrode sheet is set along the length direction of the unfolded positive electrode sheet. 11 mm, D1 = A × L, the diameter of the maximum circumscribed circle of the outer contour of the nth through hole on the surface of the positive electrode is D 1n mm, D 1n =B 2n-2 ×D11 , the sum of the areas of the outer contours of the multiple through holes accounts for S1 of 3.52%, along the length direction of the positive electrode sheet after it is unfolded, the distance L1 between the first through hole and the first edge is 20 mm, and the spacing L5 between two adjacent through holes is 16 mm; along the length direction of the positive electrode sheet after it is unfolded, the diameter D of the maximum circumscribed circle of the outer contour of the first through hole close to the first edge on the second straight area on the surface of the positive electrode sheet 21 mm, D 21 =B×D 11 The diameter of the maximum circumscribed circle of the outer contour of the mth through hole on the surface of the positive electrode is D 2m mm, D 2m =B 2m-1 ×D 11 , the sum of the areas of the outer contours of the multiple through holes accounts for S2 of 1.975%. Along the length direction of the unfolded positive electrode sheet, the distance L2 between the first through hole and the first edge is 30mm, and the spacing L5 between two adjacent through holes is 18.87mm. Along the width direction of the unfolded positive electrode sheet, the shortest distance L3 between a single through hole and the third edge or the fourth edge of the straight area is 8mm. According to the above parameters, laser drilling is performed on the straight area of ​​the positive electrode sheet to obtain a positive electrode sheet with a specification of 330.1mm×11730mm.

[0122] <Preparation of negative electrode sheet>

[0123] The negative electrode active materials artificial graphite, sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97.3:1.7:1.0, and then deionized water is added as a solvent, stirred and mixed evenly, and a negative electrode slurry with a solid content of 50wt% is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm, and dried at 105°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. After that, the above steps are repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. Then, after cold pressing and stripping, it is dried under vacuum conditions at 105°C for 4h to obtain a negative electrode sheet with a specification of 334mm×12288mm for standby use. Among them, the coating weight of the negative electrode material layer is 14.6mg / cm 2 After cold pressing, the thickness H1 of the negative electrode material layer on one side of the negative electrode current collector is 360 μm.

[0124] Embodiment 14

[0125] Except that <Preparation of positive electrode sheet> is the same as Example 13, the rest is the same as Example 1.

[0126] Comparative Example 1

[0127] Except for providing a blind hole in <Preparation of Negative Electrode Sheet>, the rest is the same as Example 1.

[0128] Comparative Example 2

[0129] Except that 2 through holes are set in each row on the first area of ​​the first straight area in <Preparation of Negative Electrode Plate>, 1 through hole is set in each row on the first area of ​​the second straight area, the value of A is 1, the value of B is 0.5, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1.

[0130] Comparative Example 3

[0131] Except that 3 through holes are set in each row on the first area of ​​the first straight area in <Preparation of Negative Electrode Plate>, 2 through holes are set in each row on the first area of ​​the second straight area, the value of A is 7, the value of B is 1, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1.

[0132] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0133]

[0134] Note: “ / ” in Table 1 indicates no relevant preparation parameters.

[0135] It can be seen from Examples 1 to 14 and Comparative Examples 1 to 3 that by setting through holes on the two straight areas of the first pole piece and adjusting A and D 11The values ​​of A and B are within the scope of this application, and the diffusion distance of the electrolyte in the first pole piece is large, which improves the 600cls capacity retention rate of the lithium-ion battery, indicating that the electrolyte has a good infiltration effect on the first pole piece, and the lithium-ion battery has good cycle performance, and the lithium-ion battery has good safety performance. No through holes are set on the straight areas of the positive pole piece and the negative pole piece in Comparative Example 1; the values ​​of A and B in Comparative Example 2 are lower than the lower limit of this application; the values ​​of A and B in Comparative Example 3 are higher than the upper limit of this application. The diffusion distance of the electrolyte in Comparative Examples 1 to Comparative Examples 2 is small, and the 600cls capacity retention rate of the obtained lithium-ion battery is low, indicating that the cycle performance of the lithium-ion battery is poor; the through hole diameter in Comparative Example 3 is large, and the impact test pass rate is low, which affects the safety performance of the lithium-ion battery, and the electrolyte contacts the pole piece too much, resulting in a relatively increased side reaction of the lithium-ion battery, and the 600cls capacity retention rate of the obtained lithium-ion battery is low, which reduces the cycle performance of the lithium-ion battery. The diffusion distance of the electrolyte in Examples 1 to 14 in the first electrode is larger, the electrolyte has a better wetting effect on the electrode, the obtained lithium-ion battery has a higher 600cls capacity retention rate, the lithium-ion battery has better cycle performance, and at the same time, the impact test pass rate is higher, taking into account the safety performance and actual production requirements of the lithium-ion battery.

[0136] The number of through holes set on the first area of ​​each flat area usually affects the cycle performance and safety performance of the lithium-ion battery. It can be seen from Examples 1 to 3 that when the number of through holes set on the first area of ​​each flat area is within the scope of the present application, the diffusion distance of the electrolyte in the first pole piece is large, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are high, indicating that while taking into account the safety performance, the electrolyte in the lithium-ion battery of the present application has a good infiltration effect on the pole piece, and the lithium-ion battery has good cycle performance.

[0137] The value of A usually affects the cycle performance and safety performance of lithium-ion batteries. It can be seen from Examples 1, 4 to 6 that when the value of A is within the range of this application, the diffusion distance of the electrolyte in the first pole piece is large, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are high, indicating that while taking into account the safety performance, the electrolyte in the lithium-ion battery of this application has a good infiltration effect on the pole piece, and the lithium-ion battery has good cycle performance.

[0138] The value of B usually affects the cycle performance and safety performance of lithium-ion batteries. It can be seen from Examples 1, 7 and 8 that when the value of B is within the range of this application, the diffusion distance of the electrolyte in the first pole piece is large, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are high, indicating that while taking into account the safety performance, the electrolyte in the lithium-ion battery of this application has a good infiltration effect on the pole piece, and the lithium-ion battery has good cycle performance.

[0139] The proportions S1 and S2 of the sum of the areas of the outer contours of the through holes usually affect the cycle performance and safety performance of the lithium-ion battery. It can be seen from Examples 1 to 14 that when the sum of the areas of the outer contours of the through holes accounts for within the scope of this application, the diffusion distance of the electrolyte in the first pole piece is large, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are high, indicating that while taking into account the safety performance, the electrolyte in the lithium-ion battery of this application has a good infiltration effect on the pole piece, and the lithium-ion battery has good cycle performance.

[0140] Along the length direction of the electrode assembly, the shortest distance L3 between a single through hole and the third edge or the fourth edge usually affects the cycle performance and safety performance of the lithium-ion battery. It can be seen from Example 1, Example 9 to Example 10 that when the shortest distance between a single through hole and the third edge or the fourth edge is within the scope of this application, the diffusion distance of the electrolyte in the first pole piece is large, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are high, indicating that while taking into account the safety performance, the electrolyte in the lithium-ion battery of this application has a good infiltration effect on the pole piece, and the lithium-ion battery has good cycle performance.

[0141] The thickness H2 of the first current collector and the thickness H1 of the first material layer located on at least one surface of the first current collector usually affect the cycle performance and safety performance of the lithium-ion battery. It can be seen from Example 1, Example 11 to Example 12 that when the values ​​of H1 and H2 are within the range of this application, the diffusion distance of the electrolyte in the first pole piece is large, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are high, indicating that while taking into account the safety performance, the electrolyte in the lithium-ion battery of this application has a good infiltration effect on the pole piece, and the lithium-ion battery has good cycle performance.

[0142] Whether the first pole piece is a positive pole piece and / or a negative pole piece usually affects the cycle performance and safety performance of the lithium-ion battery. It can be seen from Example 1, Example 13 to Example 14 that when the first pole piece is a positive pole piece and / or a negative pole piece, and the parameters of the through hole are set within the scope of this application, the diffusion distance of the electrolyte in the first pole piece is large, and the 600cls capacity retention rate and impact test pass rate of the lithium-ion battery are high, indicating that while taking into account the safety performance, the electrolyte in the lithium-ion battery of this application has a good infiltration effect on the pole piece, and the lithium-ion battery has good cycle performance.

[0143] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method or article.

[0144] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0145] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, comprising a wound electrode assembly, the electrode assembly comprising a first electrode sheet, each circle of the first electrode sheet comprising two straight areas and two bending areas connected to the two straight areas, and the two bending areas are arranged opposite to each other along the width direction of the electrode assembly; Along the width direction of the electrode assembly, any of the straight regions has a first edge and a second edge opposite to each other, the width of a single straight region is L mm, the area from the first edge to the center line of the straight region is the first area of ​​the straight region, and the area from the center line to the second edge is the second area of ​​the straight region; The two straight regions include a first straight region and a second straight region arranged along the thickness direction of the electrode assembly, the first region and the second region of the first straight region and the second straight region of at least one circle of the first electrode sheet are both provided with a plurality of through holes, and the plurality of through holes in the second region are symmetrical with the plurality of through holes provided in the first region along the center line; The first through hole of the first straight area is arranged near the first edge of the first straight area, and N through holes are arranged in sequence on the first area of ​​the first straight area from the first edge to the center line, where N is a positive integer; wherein, The diameter of the maximum circumscribed circle of the first through hole in the first region of the first straight zone is D 11 mm, D 11 =A×L, 1.5%≤A≤6%, the diameter of the maximum circumscribed circle of the nth through hole in the first region of the first flat area is D 1n mm, D 1n =B 2n-2 ×D 11 , 2≤n≤N, 0.6≤B≤0.9; The first through hole of the second straight zone is arranged near the first edge of the second straight zone, and M through holes are arranged in sequence on the first area of ​​the second straight zone along the direction from the first edge to the center line, where M is a positive integer; wherein the diameter of the maximum circumscribed circle of the first through hole on the first area of ​​the second straight zone is D 21 mm, D 21 =B×D 11 , the diameter of the maximum circumscribed circle of the mth through hole in the first region of the second straight region is D 2m mm, D 2m =B 2m-1 ×D 11 , 2≤m≤M.

2. The secondary battery according to claim 1, wherein 3≤N≤11, 2≤M≤9 and M <N。 3. The secondary battery according to claim 1 or 2, wherein: 1.8％≤A≤3.75％。 4. The secondary battery according to any one of claims 1 to 3, wherein Multiple through holes are provided in multiple first straight areas in the electrode assembly, and along the thickness direction of the electrode assembly, there is at least a partial overlap between the projections of the multiple through holes corresponding to each other in the multiple first straight areas; and / or, multiple through holes are provided in multiple second straight areas in the electrode assembly, and along the thickness direction of the electrode assembly, there is at least a partial overlap between the projections of the multiple through holes corresponding to each other in the multiple second straight areas.

5. The secondary battery according to claim 4, wherein Along the thickness direction of the electrode assembly, the centers of the largest circumscribed circles of the outer contours of the plurality of through holes in the first straight region and the corresponding plurality of through holes in the second straight region are separated.

6. The secondary battery according to any one of claims 1 to 3, wherein Along the thickness direction of the electrode assembly, projections of the plurality of through holes in the first straight region are separated from projections of the plurality of through holes in the second straight region corresponding thereto.

7. The secondary battery according to any one of claims 1 to 6, wherein The first pole piece 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 first straight region of the first pole piece, the sum of the outer contour areas of multiple through holes on the first material layer in the first straight region accounts for S1, 0.5%≤S1≤10%; and / or, based on the surface area of ​​the second straight region of the first pole piece, the sum of the outer contour areas of multiple through holes on the first material layer in the second straight region accounts for S2, 0.2%≤S2≤6%.

8. The secondary battery according to any one of claims 1 to 7, wherein Along the width direction of the electrode assembly, the distance between two adjacent through holes located in the first area of ​​the first straight zone is 6mm to 45mm; and / or the distance between two adjacent through holes located in the first area of ​​the second straight zone is 8mm to 80mm.

9. The secondary battery according to any one of claims 1 to 8, wherein The thickness of the electrode assembly is T mm. Along the width direction of the electrode assembly, the distance between the first through hole of the first straight area and the first edge of the first straight area is L1 mm, T / 2≤L1≤L / 4, 20≤T≤70; the distance between the first through hole of the second straight area and the first edge of the second straight area is L2 mm, 10+D 11 +(D 11 +D 21 ) / 3≤L2≤40+D 11 +(D 11 +D 21 ) / 3.

10. The secondary battery according to any one of claims 1 to 9, wherein The first pole piece 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 any straight area has a relative third edge and a fourth edge. The shortest distance between a single through hole and the third edge or the fourth edge is L3 mm, 5≤L3≤10.

11. The secondary battery according to any one of claims 1 to 10, wherein The first pole piece 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 is H1 μm, and 120≤H1≤600.

12. The secondary battery according to claim 11, wherein The thickness of the first current collector is H2 μm, 5≤H2≤20.

13. The secondary battery according to any one of claims 1 to 12, wherein: 80≤L≤600。 14. The secondary battery according to any one of claims 1 to 13, wherein The first pole piece is a positive pole piece and / or a negative pole piece.

15. The secondary battery according to any one of claims 1 to 14, wherein The outer contour of a single through hole may be in the shape of a circle, an ellipse or a polygon.

16. The secondary battery according to any one of claims 1 to 15, wherein The secondary battery is a soft-pack secondary battery or a square secondary battery. 17 . An electronic device comprising the secondary battery according to claim 1 .

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