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, the electrode assembly comprises M circles of first pole pieces, and each circle of first pole piece comprises two straight areas; in the width direction of the electrode assembly, the width of a single straight area is Lmm; from the ending ends of the first pole pieces and along the reverse direction of the winding direction of the electrode assembly, through holes are formed in the straight areas of the N circles of first pole pieces, N is larger than or equal to 15 and smaller than or equal to 70, N is a positive integer and smaller than or equal to M, and at least one through hole is formed in each straight area; the diameter of the maximum circumcircle of the through holes in the straight area of the first circle of first pole piece from the ending end of the first pole piece is D1 mm, D1 = A * L, 1.5% < = A < = 6%, the diameter of the maximum circumcircle of the through holes in the straight area of the nth circle of first pole piece is Dn mm, Dn = Bn-1 * D1, 2 < = n < = N, and 0.6 < = B < = 0.9. 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 this application is to provide a secondary battery and an electronic device to improve the infiltration of the electrolyte into 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. The specific technical solution is as follows:

[0005] The first aspect of the present application provides a secondary battery, including a wound electrode assembly, the electrode assembly including M circles of first pole pieces, each circle of the first pole piece including 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, the width of a single straight area is L mm; from the tail end of the first pole piece and in the opposite direction of the winding direction of the electrode assembly, through holes are arranged on the straight areas of the N circles of the first pole piece, 15≤N≤70, N is a positive integer and N≤M, and at least one through hole is arranged on each straight area. Starting from the tail end of the first pole piece and in the opposite direction of the winding direction of the electrode assembly, the diameter of the maximum circumscribed circle of the outer contour of the through hole on the straight area of ​​the first pole piece of the first circle on the surface of the first pole piece is D1 mm, D1 = A × L, 1.5% ≤ A ≤ 6%, optionally, 1.8% ≤ A ≤ 3.75%, the diameter of the maximum circumscribed circle of the outer contour of the through hole on the straight area of ​​the first pole piece of the nth circle on the surface of the first pole piece is D n mm, D n =B n-1×D1, 2≤n≤N, 0.6≤B≤0.9. Through the setting of through holes and regulating the values ​​of N, A and B within the above range, that is, step-shaped through holes are set on the straight area of ​​the multi-circle first electrode sheet, and a step-shaped flow channel for the electrolyte is formed in the thickness direction of the electrode assembly, so that when the electrolyte flows to the center of the electrode assembly through the step-shaped flow channel, the through holes set on each circle of the straight area absorb and store the electrolyte, and an electrolyte potential difference is formed at the position of the middle part of the electrode assembly where the electrolyte is easily consumed, which increases the infiltration rate of the electrolyte from the outer circle to the inner circle, thereby improving the electrolyte replenishment efficiency during the cycle of the secondary battery, strengthening the infiltration effect of the electrolyte on the electrode assembly, and further improving the cycle performance of the secondary battery. In addition, since the through holes arranged on the straight area from the outer circle to the inner circle of the first pole piece gradually decrease from the tail end of the first pole piece in the opposite direction of the winding direction of the electrode assembly, it is beneficial to reduce the risk of collapse of the middle part of the electrode assembly due to too many through holes, while taking into account the safety performance of the secondary battery.

[0006] In one or more embodiments, the two straight regions include a first straight region and a second straight region arranged along the thickness direction 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 regions; and / or, 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 regions. The above arrangement shortens and increases the flow path of the electrolyte, improves the infiltration speed, improves the cycle performance of the electrode assembly, and takes into account the safety performance of the secondary battery.

[0007] In one or more embodiments, the two straight regions include a first straight region and a second straight region arranged along the thickness direction of the electrode assembly, and along the thickness direction of the electrode assembly, the projection of the through hole in the first straight region of the first pole piece of the nth circle is located within the projection of the through hole in the first straight region of the first pole piece of the n-1th circle; and / or, the projection of the through hole in the second straight region of the first pole piece of the nth circle is located within the projection of the through hole in the second straight region of the first pole piece of the n-1th circle. By providing through holes on the first straight region and / or the second straight region of the first pole piece of multiple circles, the infiltration effect of the electrolyte on the electrode assembly is enhanced, thereby improving the cycle performance of the secondary battery, while taking into account the safety performance of the secondary battery.

[0008] In one or more embodiments, the thickness of the electrode assembly is T mm, and along the width direction of the electrode assembly, any straight area has a first edge and a second edge relative to each other, and along the direction from the first edge to the second edge, the shortest distance between the through hole center of the through hole on the straight area and the first edge or the second edge is L1 mm, T / 2≤L1≤L / 4, 20≤T≤70. By regulating the values ​​of T and L1 within the above range, it is helpful to reduce the risk of insufficient electrolyte infiltration of the electrode sheet, and at the same time, it is helpful to reduce the risk of local collapse of the through hole to the straight area of ​​the first electrode sheet, thereby improving the cycle performance of the secondary battery, while taking into account the safety performance of the secondary battery.

[0009] In one or more embodiments, along the width direction of the electrode assembly, the distance between the centers of two adjacent through holes located on the straight area is L2 mm, 5≤L2≤30. By adjusting L2 within the above range, the distance between the two adjacent through holes is moderate, which is conducive 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, improving the wetting efficiency and wetting performance of the electrolyte on the electrode assembly, and improving the cycle performance of the secondary battery.

[0010] In one or more embodiments, the two straight areas include a first straight area and a second straight area arranged along the thickness direction of the electrode assembly, and along the thickness direction of the electrode assembly, there is at least a partial overlap between the projection of the through hole in the first straight area and the projection of the through hole in the corresponding second straight area. Through the above arrangement, along the thickness direction of the electrode assembly, multiple through holes corresponding to each other in multiple first straight areas and / or multiple second straight areas form a stepped circulation channel. When the electrode assembly is injected with liquid, the electrolyte flows to the center of the electrode assembly through the stepped circulation channel, thereby enhancing 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 of the secondary battery.

[0011] 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. Based on the surface area of ​​the straight area, the sum of the outer contours of the through holes on the first material layer of the straight area of ​​the first pole piece of the first circle accounts for S, 1%≤S≤35%. By adjusting S within the above range, while taking into account the strength of the first pole piece, it is beneficial to shorten the flow path of the electrolyte in the width direction of the first pole piece in the wound state, which is beneficial to reduce the insufficient infiltration of the electrolyte into the middle of the wound electrode assembly, thereby improving the cycle performance of the secondary battery and taking into account the safety performance of the secondary battery.

[0012] 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 region has a third edge and a fourth edge relative to each other, and the shortest distance between the through hole center of the through hole in the straight region and the third edge or the fourth edge is L3 mm, 5≤L3≤18. For example, by regulating the value of L3 within the above range, the risk of the first pole piece being short-circuited due to the through hole being set at the edge of the material layer is reduced, and the risk of insufficient infiltration of the electrolyte into the pole piece is reduced, the infiltration effect of the electrolyte on the pole piece is improved, and the cycle performance of the secondary battery is improved, while taking into account the safety performance of the secondary battery.

[0013] 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, 120≤H1≤600. 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 excessively thin 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.

[0014] In one or more embodiments, the thickness of the first current collector is H2 μm, 5 ≤ H2 ≤ 20. By adjusting the value of H2 within the above range, it is helpful to reduce the processing difficulty of the first pole piece, take into account the cycle performance of the secondary battery, and improve the strength of the first pole piece.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] In one or more embodiments, the secondary battery is a soft-pack secondary battery or a square secondary battery. When the secondary battery is configured as the above-mentioned type, it is beneficial to the application and production of the secondary battery of the present application.

[0019] 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.

[0020] Beneficial effects of the embodiments of the present application:

[0021] The embodiments of the present application provide a secondary battery and an electronic device. By arranging stepped through holes on the straight area of ​​the multi-turn first electrode sheet along the thickness 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.

[0022] 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

[0023] 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.

[0024] Figure 1 A schematic diagram of a winding structure formed by an electrode assembly in one embodiment of the present application;

[0025] Figure 2 for Figure 1 A schematic diagram of a first straight region of a first pole piece in the first turn of a winding structure formed by an electrode assembly;

[0026] Figure 3 for Figure 1 A partial schematic diagram of the first straight area of ​​the first pole piece of the first turn in the winding structure formed by the electrode assembly unfolding along the width direction and the length direction of the electrode assembly;

[0027] Figure 4 This is a partial structural schematic diagram of the first pole piece of the first circle along the thickness direction of the electrode assembly in one embodiment of the present application;

[0028] Figure 5 A schematic diagram of a winding structure formed by an electrode assembly in another embodiment of the present application;

[0029] 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.

[0030] Figure markings: electrode assembly 001; first electrode piece 10; first electrode piece 11 of the first circle; straight area 101; first straight area 1011; first straight area 1012; bending area 102; through hole 20; tail end 103 of the first electrode piece; first through hole 21; first edge 31; second edge 32; third edge 33; fourth edge 34; first current collector 41; first material layer 42. DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] 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:

[0034] The first aspect of the present application provides a secondary battery, including a wound electrode assembly, the electrode assembly including M circles of first pole pieces, each circle of the first pole piece including 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, the width of a single straight area is L mm; from the tail end of the first pole piece, and along the opposite direction of the winding direction of the electrode assembly, the straight areas of the N circles of the first pole piece are provided with through holes, 15≤N≤70, N is a positive integer and N≤M. For example, the value of N can be any one of 15, 17, 21, 25, 28, 31, 35, 37, 42, 45, 47, 51, 55, 58, 61, 65, 67, 70, and each straight area is provided with at least one through hole. Starting from the tail end of the first pole piece and in the opposite direction of the winding direction of the electrode assembly, the diameter of the maximum circumscribed circle of the outer contour of the through hole on the straight area of ​​the first pole piece of the first circle on the surface of the first pole piece is D1 mm, D1 = 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 through hole on the straight area of ​​the first pole piece of the nth circle on the surface of the first pole piece is D n mm, D n =B n-1 ×D1, 2≤n≤N, 0.6≤B≤0.9. For example, when N is 20, 2≤n≤20, the value of n can be any one of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20; the value of B can be any one of 0.6, 0.64, 0.68, 0.71, 0.75, 0.79, 0.83, 0.87, 0.9. In the present application, it can be understood that "multiple" means two or more, and "through hole" means a hole that passes through 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.

[0035] 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 As shown, the electrode assembly 001 is formed by stacking and winding a separator, a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet includes a positive electrode collector and a positive electrode material layer disposed on both surfaces of the positive electrode collector. The negative electrode sheet includes a negative electrode collector and a negative electrode material layer disposed 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 disposed opposite to each other along the width direction (X direction) of the electrode assembly 001. The two straight areas of each circle of the first pole piece 10 include a first straight area 1011 and a second straight area 1012 arranged along the thickness direction (Y direction) of the electrode assembly 001. Starting from the tail end 103 of the first pole piece 10 and in the opposite direction of the winding direction (W direction) of the electrode assembly, six through holes 20 are respectively arranged on the first straight area 1011 and the second straight area 1012 of the first circle of the first pole piece 11 and other multiple circles of the first pole piece. It should be noted that the number, size and spacing of the through holes in the figure are only for exemplary description.

[0036] When the value of N, A, and / or; B is too small, that is, less than the lower limit of this application, the number of turns of the first pole piece with through holes is insufficient, and / or; the through holes set on the straight area of ​​each turn of the first pole piece are too small, the electrolyte does not wet the electrode assembly in the thickness direction, that is, the middle part of the wound electrode assembly is not wet enough, 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 in the late cycle of the secondary battery, the middle part of the electrode assembly is prone to 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 N, A, and / or; B is too large, that is, greater than the upper limit of this application, due to the excessive number of turns of the first pole piece with through holes, and / or; the through holes set on the straight area of ​​each turn of the first pole piece are too large, resulting in a decrease in the safety performance 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, excessive loss of active materials leads to 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. By setting through holes and regulating the values ​​of N, A and B within the above range, that is, setting stepped through holes on the straight area of ​​the multi-circle first pole piece, a stepped flow channel for the electrolyte is formed in the thickness direction of the electrode assembly, so that when the electrolyte flows to the center of the electrode assembly through the stepped flow channel, the through holes set on each circle of the straight area absorb and store the electrolyte, and an electrolyte potential difference is formed at the position of the middle part of the electrode assembly where the electrolyte is easily consumed, which increases the infiltration rate of the electrolyte from the outer circle to the inner circle, thereby improving the replenishment efficiency of the electrolyte during the cycle of the secondary battery, strengthening the infiltration effect of the electrolyte on the electrode assembly, and thus improving the cycle performance of the secondary battery. In addition, since the through holes arranged on the straight area from the outer circle to the inner circle of the first pole piece gradually decrease from the tail end of the first pole piece in the opposite direction of the winding direction of the electrode assembly, it is beneficial to reduce the risk of collapse of the middle part of the electrode assembly due to too many through holes, while taking into account the safety performance of the secondary battery.

[0037] In one or more embodiments, 80≤L≤600. For example, the value of L can be any one of 80, 120, 160, 200, 220, 260, 290, 300, 320, 340, 380, 420, 460, 500, 540, 570, and 600. By adjusting the value of L within the above range, it is beneficial to shorten the flow path of the electrolyte in the width direction of the electrode assembly in the wound state (i.e., the length direction after the first pole piece is unfolded), and the effect of improving 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 pole piece is unfolded) is more obvious. While taking into account the safety performance of the secondary battery, the cycle performance of the secondary battery is further improved, while taking into account the actual production needs and reducing the actual processing difficulty.

[0038] In one or more embodiments, 15≤M≤75. For example, the value of M may be any one of 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, and 75. By adjusting the value of M within the above range, it is beneficial to reduce the actual processing difficulty while taking into account the safety performance and cycle performance of the first pole piece.

[0039] In one or more embodiments, along the width direction of the electrode assembly, the first straight area of ​​each circle of the first electrode sheet; and / or the second straight area are provided with Y through holes, 4≤Y≤25. For example, the value of Y can be any one of 4, 7, 9, 11, 14, 15, 18, 21, and 25. By adjusting the value of Y within the above range, it is beneficial to reduce the actual processing difficulty while taking into account the safety performance and cycle performance of the first electrode sheet.

[0040] In one or more embodiments, the two straight regions include a first straight region and a second straight region arranged along the thickness direction 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 multiple through holes corresponding to each other in the multiple first straight regions. In one or more embodiments, the two straight regions include a first straight region and a second straight region arranged along the thickness direction 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 multiple through holes corresponding to each other in the multiple second straight regions. In one or more embodiments, the two straight regions include a first straight region and a second straight region arranged along the thickness direction 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 multiple through holes corresponding to each other in the multiple first straight regions, and, there is at least a partial overlap between the projections of the multiple through holes corresponding to each other in the multiple second straight regions. Through holes are provided on the first straight area and the second straight area of ​​the multi-turn first pole piece, and along the thickness direction of the electrode assembly, there is at least a partial overlap 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, the multiple through holes corresponding to each other in the multiple first straight areas and / or the multiple second straight areas form a stepped flow path, shortening and increasing the flow path of the electrolyte. When the electrode assembly is injected with liquid, the electrolyte flows through the stepped 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, which increases the infiltration rate of the electrolyte, shortens the infiltration path of the electrolyte, and increases the infiltration speed, thereby improving the cycle performance of the electrode assembly.

[0041] In one or more embodiments, the two straight regions include a first straight region and a second straight region arranged along the thickness direction of the electrode assembly, and along the thickness direction of the electrode assembly, the projection of the through hole in the first straight region of the first pole piece of the nth circle is located within the projection of the through hole in the first straight region of the first pole piece of the n-1th circle. In one or more embodiments, along the thickness direction of the electrode assembly, the projection of the through hole in the second straight region of the first pole piece of the nth circle is located within the projection of the through hole in the second straight region of the first pole piece of the n-1th circle. In one or more embodiments, along the thickness direction of the electrode assembly, the projection of the through hole in the first straight region of the first pole piece of the nth circle is located within the projection of the through hole in the first straight region of the first pole piece of the n-1th circle, and, the projection of the through hole in the second straight region of the first pole piece of the nth circle is located within the projection of the through hole in the second straight region of the first pole piece of the n-1th circle.

[0042] Through holes are set on the first straight area and the second straight area of ​​multiple turns of first electrode sheets, and along the thickness direction of the electrode assembly, the projection of the through hole in the first straight area of ​​the nth turn of the first electrode sheet is located within the projection of the through hole in the first straight area of ​​the n-1th turn of the first electrode sheet and / or the projection of the through hole in the second straight area of ​​the nth turn of the first electrode sheet is located within the projection of the through hole in the second straight area of ​​the n-1th turn of the first electrode sheet. Along the thickness direction of the electrode assembly, multiple through holes corresponding to each other in multiple first straight areas and / or multiple second straight areas form a stepped flow channel. When the electrode assembly is injected with liquid, the electrolyte flows to the center of the electrode assembly through the stepped flow channel, thereby enhancing the wetting effect of the electrolyte on the electrode assembly, thereby improving the cycle performance of the secondary battery. In addition, since the through holes set on the straight area from the outer circle to the inner circle of the first pole piece gradually decrease from the tail end of the first pole piece in the opposite direction of the winding direction of the electrode assembly, it is beneficial to reduce the risk of collapse of the middle part of the electrode assembly due to the setting of the through holes, while taking into account the safety performance of the secondary battery.

[0043] In one or more embodiments, the thickness of the electrode assembly is T mm, along the width direction of the electrode assembly, any straight region has a first edge and a second edge opposite to each other, along the direction from the first edge to the second edge, the shortest distance between the through hole center of the through hole on the straight region and the first edge or the second edge 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. 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), any straight area 101 has a first edge 31 and a second edge 32 relative to each other. Along the direction (X direction) from the first edge 31 to the second edge 32, the shortest distance between the through hole center of the through hole 20 on any straight area 101 and the first edge 31 is L1 mm. In the present application, along the direction from the first edge to the second edge, the shortest distance between the through hole center of the through hole and the first edge or the second edge refers to the minimum value of the distance between the through hole center closest to the first edge and the first edge and the distance between the through hole center closest to the second edge and the second edge along the width direction of the electrode assembly (i.e., the length direction after unfolding the first pole piece). In addition, since the through hole center of each through hole closest to the first edge or the second edge has the shortest distance to the first edge or the second edge is L1 mm, the distance between the through hole center of other through holes and the first edge or the second edge is not less than L1 mm. By regulating the values ​​of T and L1 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.

[0044] In one or more embodiments, 10≤L1≤40, and the value of L1 can be any one of 10, 14, 18, 22, 25, 28, 32, 36, 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 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.

[0045] In one or more embodiments, along the width direction of the electrode assembly, the distance between the centers of two adjacent through holes located on the straight area is L2 mm, 5≤L2≤30. For example, the value of L2 can be any one of 5, 6, 8, 10, 12, 14, 15, 16, 18, 19, 20, 21, 23, 25, and 30. 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 the through-hole centers of two adjacent through holes 20 located on the straight area 101 is L2mm. In the present application, the spacing between the through-hole centers of two adjacent through holes refers to the closest distance between the through-hole center of any through hole and the through-hole center 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 value of L2 within the above range, the distance between the two adjacent through holes is moderate, which is conducive to improving the wetting effect of the electrolyte on the pole piece, especially the middle part of the pole piece, while reducing the actual production and processing difficulty, as well as the risk of local collapse of the first pole piece 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.

[0046] In one or more embodiments, the two straight regions include a first straight region and a second straight region arranged along the thickness direction of the electrode assembly, and along the thickness direction of the electrode assembly, there is at least a partial overlap between the projection of the through hole in the first straight region and the projection of the through hole in the corresponding second straight region. By providing through holes on the first straight region and the second straight region of the multi-turn first pole piece, and providing that along the thickness direction of the electrode assembly, there is at least a partial overlap between the projection of the through hole in the first straight region and the projection of the through hole in the corresponding second straight region, the infiltration rate of the electrolyte is increased, the infiltration path of the electrolyte is shortened, the cycle performance of the electrode assembly is improved, and the processing difficulty is reduced.

[0047] 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. Based on the surface area of ​​the straight area, the sum of the areas of the outer contours of the through holes on the first material layer of the straight area of ​​the first pole piece of the first circle accounts for S, 1%≤S≤35%. For example, the value of S can be any one of 1%, 3%, 5%, 8%, 11%, 14%, 17%, 19%, 21%, 23%, 25%, 27%, 30%, 32%, and 35%. Since the diameter of the maximum circumscribed circle of the outer contour of the through hole of the first pole piece of the first circle on the surface of the first pole piece is the largest from the end of the first pole piece and in the opposite direction of the winding direction of the electrode assembly, by adjusting the value of S within the above range, the sum of the areas of the outer contours of the multiple through holes of each circle of the first pole piece accounts for 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 help reduce the risk of black spots or lithium precipitation in the middle of the electrode assembly due to insufficient electrolyte infiltration into the middle of the wound electrode assembly in the late cycle of the secondary battery. The flow path of the electrolyte in the width direction of the first electrode sheet in the wound state is shortened, thereby improving the cycle performance of the secondary battery while taking into account the safety performance of the secondary battery.

[0048] 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 the through hole center and the third edge or the fourth edge in the straight region is L3 mm, and 5≤L3≤18. For example, the value of L3 can be any one of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, and 18. 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 area has a third edge 33 and a fourth edge 34 relative to each other, the first through hole 21 is close to the third edge 33, and the shortest distance between the through hole center of the first through hole 21 and the third edge 33 is L3 mm. In the present application, along the length direction of the electrode assembly, the shortest distance between the through hole center of the through hole and the third edge or the fourth edge refers to the shortest distance between the through hole center 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). In addition, along the length direction of the electrode assembly (i.e., the width direction after the first pole piece is unfolded), the distance between the through hole center of 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.

[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, the thickness of the first material layer is H1 μm, 120≤H1≤600. For example, the value of H1 can be any one of 120, 160, 200, 260, 320, 360, 420, 480, 520, 580, 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.

[0050] 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 beneficial to reduce the processing difficulty of the first pole piece, take into account the cycle performance of the secondary battery, and improve 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 of different thicknesses can be selected, and the thickness of the current collector of the first pole piece can be determined by combining the test method of "N, A, D1, B, S, L1, L2, L3, H1, H2 test" in this application, and then the current collector of the first pole piece of the required thickness is selected.

[0051] In one or more embodiments, the through holes provided on any straight area of ​​the first pole piece are distributed in a matrix along the length direction of the electrode assembly (i.e., the width direction after the first pole piece is unfolded). In the present application, multiple rows of through holes are provided in any straight area along the width direction after the first pole piece is unfolded, and the spacing between the corresponding through holes in each row is equal. The present application does not have any special restrictions on the number of rows of through holes. 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 provided in each straight area can be 3 to 20 rows.

[0052] 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.

[0053] In one or more embodiments, the first electrode sheet is a negative electrode sheet. By providing a plurality of through holes on the 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.

[0054] In one or more embodiments, the first electrode sheet is a positive electrode sheet. By providing a plurality of through holes on the 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.

[0055] 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.

[0056] In one or more embodiments, the first electrode sheet is a positive electrode sheet and a negative electrode sheet. Figure 5 As shown, the first electrode sheet 10 is a positive electrode sheet and a negative electrode sheet, and along the width direction (X direction) of the electrode assembly 001 (i.e., the length direction of the first electrode sheet 10 after unfolding), 6 through holes 20 are provided on each straight area 101 of each circle of positive electrode sheets and negative electrode sheets. By providing a plurality of through holes of different sizes on the straight areas of multiple circles of positive electrode sheets and multiple circles of negative electrode sheets, a stepped flow path of the electrolyte is constructed, which is conducive to improving the wetting efficiency and wetting performance of the electrolyte on the electrode sheets, especially the middle part of the electrode sheets, and improving the wetting effect of the electrolyte on the electrode sheets, thereby improving the cycle performance of the secondary battery.

[0057] 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.

[0058] 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 own thickness direction, or can be disposed on two surfaces of the negative current collector along its own thickness direction. It should be noted that the "surface" here refers to the coating area of the negative current collector where the negative electrode material layer is provided. The present application 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 at least one of metallic lithium. 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 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.

[0059] 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, setting a through hole of corresponding size on the straight area of ​​each circle of the first pole piece, and, starting from the tail end of the first pole piece and in the opposite direction of the winding direction of the electrode assembly, the diameter of the maximum circumscribed circle of the outer contour of the through hole set on each straight area of ​​each circle of the first pole piece on the surface of the first pole piece gradually decreases, so as to obtain the first pole piece.

[0060] 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 adjusted by adjusting the power and cutting depth of the circular cutter; the proportion S of the sum of the areas of the outer contours of the multiple through holes is adjusted by adjusting the surface area of ​​the straight area of ​​the first circle of the first pole piece, the number of through holes, the shape of the through holes, the power of the circular cutter, the cutting depth, the spacing between the circular cutters or the cutting frequency; along the width direction of the electrode assembly (that is, the length of the first pole piece after unfolding) Along the width direction of the electrode assembly (i.e., the length direction of the first pole piece after unfolding), the shortest distance L1 between the through-hole center of the through-hole on the straight area and the first or second edge is regulated by adjusting the spacing between the circular cutters or the cutting frequency; along the length direction of the electrode assembly (i.e., the width direction of the first pole piece after unfolding), the shortest distance L2 between the through-hole center of the through-hole on the straight area and the third edge or the fourth edge is regulated by adjusting the spacing between the circular cutters or the cutting frequency.

[0061] In other embodiments, through holes can also be set by pulse 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 pulse laser emitter; the proportion S of the sum of the areas of the outer contours of the plurality of through holes is regulated by adjusting the surface area of ​​the straight area of ​​the first pole piece of the first circle, the number of through holes, the shape of the through holes, the power of the pulse laser emitter, the defocus, the spacing 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 spacing L between the through hole centers of two adjacent through holes is 2 is regulated by adjusting the spacing 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 shortest distance L1 between the through hole center of the through hole on the straight area and the first edge or the second edge is regulated by adjusting the spacing 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 L2 between the through hole center of the through hole on the straight area and the third edge or the fourth edge is regulated by adjusting the spacing between the pulse laser emitters or the laser emission frequency.

[0062] 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 circular cutting knife punching or pulsed laser punching, 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.

[0063] 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.

[0064] 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.

[0065] 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 stepped through hole in the 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.

[0066] 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.

[0067] The present application does not particularly limit the preparation method of the secondary battery, and a preparation method known in the art can 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 order, and winding, folding, etc. as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly in a shell, injecting an electrolyte into the shell and sealing it to obtain a secondary battery. In one or more embodiments, the diaphragm, the first pole piece, the diaphragm and the first pole piece are stacked in order, and winding, folding, etc. as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly in a shell, injecting an electrolyte into the shell and sealing it to obtain a secondary battery.

[0068] 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.

[0069] 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.

[0070] Example

[0071] 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.

[0072] Test methods and equipment:

[0073] Tests for N, A, D1, B, S, L1, L2, L3, H1, H2:

[0074] At an ambient temperature of 25°C, the lithium-ion battery was disassembled to obtain an electrode assembly, which was observed using an electron scanning microscope to obtain the number of turns N of the first pole piece with through holes, and the number of through holes in the first straight area of ​​each turn of the first pole piece with through holes. Then, the pole piece with through holes was taken out, i.e., the first pole piece, and soaked in dimethyl carbonate (DMC) for 20 minutes. 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.

[0075] The first pole piece is pre-wound, and the length L of the straight area of ​​the first pole piece and the diameter D1 of the maximum circumscribed circle of the outer contour of the through hole in the straight area of ​​the first pole piece in the first circle on the surface of the first pole piece are measured by an electron scanning microscope, and the ratio of the diameter D1 to the length L is calculated, which is A; at the same time, the diameter D2 of the maximum circumscribed circle of the outer contour of the through hole in the straight area of ​​the first pole piece in the second circle on the surface of the first pole piece is measured by an electron scanning microscope, and D is substituted into n =B n-1 ×D1 calculates the B value. Then, an electron scanning microscope is used to measure the length and width of the straight area of ​​the first pole piece of the first circle and the area of ​​the outer contour of the through hole, and the ratio of the sum of the areas of the outer contours of multiple through holes to the area of ​​the straight area is calculated, which is the ratio S of the sum of the areas of the outer contours of multiple through holes.

[0076] An electron scanning microscope is used to measure the shortest distance L1 between the center of a through hole in any straight area and the first edge or the second edge; an electron scanning microscope is used to measure the spacing L2 between the centers of two adjacent through holes in any straight area along the length direction after the first pole piece is unfolded; and an electron scanning microscope is used to measure the shortest distance L3 between the center of a through hole in any straight area and the third edge or the fourth edge along the width direction after the first pole piece is unfolded.

[0077] Cycle performance test:

[0078] 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.

[0079] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0080] Pole wettability test:

[0081] 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:

[0082] 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 6As 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.

[0083] 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.

[0084] Shock Test:

[0085] 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.

[0086] Test pass criteria: pass if no fire or explosion occurs.

[0087] 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.

[0088] Example 1

[0089] <Preparation of negative electrode sheet>

[0090] 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 2After cold pressing, the thickness H1 of the negative electrode material layer on one side of the negative electrode current collector is 360 μm.

[0091] The negative electrode sheet is pre-wound, and the number of winding turns M of the negative electrode sheet is determined to be 42 turns. One surface of the negative electrode sheet is selected, and two straight areas of each turn of the negative electrode sheet and two bending areas connected to the two straight areas are determined, wherein the width of the straight area is set to 380 mm, and the length of the straight area is set to 440 mm. The first edge and the second edge of each straight area are determined, and the straight areas of 42 turns of the negative electrode sheet are selected and determined from the tail end of the negative electrode sheet and in the opposite direction of the pre-winding direction; along the width direction of the unfolded negative electrode sheet, 13 rows of through holes are respectively set on the two straight areas of each turn of the negative electrode sheet, and along the length direction of the unfolded negative electrode sheet, 10 through holes are set in each row on the two straight areas of each turn of the negative electrode sheet. Starting from the tail end of the negative electrode sheet and in the opposite direction of the pre-winding direction, the maximum circumscribed circle of the outer contour of the through hole arranged on the straight area of ​​the 1st circle negative electrode sheet to the 42nd circle negative electrode sheet close to the winding center gradually decreases.

[0092] Determine A to be 3.75%, B to be 0.75, and determine the maximum circumscribed circle diameter D1 of the outer contour of the through hole on the straight area of ​​the first circle of negative electrode sheet on the surface of the negative electrode sheet to be mm, D1 = A × L, and the maximum circumscribed circle diameter of the outer contour of the through hole on the straight area of ​​the nth circle of negative electrode sheet on the surface of the negative electrode sheet to be D n mm, D n =B n-1 ×D1. The sum of the outer contour areas of the through holes on the straight area of ​​the first circle of negative pole pieces accounts for 12.4% S. Along the length direction of the unfolded negative pole piece, the shortest distance L1 between the center of the through hole on the straight area and the first edge or the second edge is 40mm, and the distance L2 between the centers of two adjacent through holes is 17.5mm. Along the width direction of the unfolded negative pole piece, the shortest distance L3 between the center of the through hole in the straight area and the third edge or the fourth edge of the straight area is 10mm. According to the above parameters, laser drilling is performed on the straight area of ​​the negative pole piece to obtain a negative pole piece with a specification of 440mm×35219mm.

[0093] <Preparation of positive electrode sheet>

[0094] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 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 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 436.1mm×34381mm 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.

[0095] <Diaphragm>

[0096] A polypropylene (PP) film with a thickness of 12 μm was used as the separator.

[0097] <Preparation of Electrolyte>

[0098] 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.

[0099] <Preparation of lithium-ion batteries>

[0100] 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.

[0101] Example 2

[0102] Except that a through hole is provided on the straight area of ​​the negative electrode sheet of 15 turns in the opposite direction of the pre-winding direction from the tail end of the negative electrode sheet, the rest is the same as that of Example 1. The negative electrode sheet is pre-wound, and the number of turns M of the negative electrode sheet is determined to be 15 turns, the specification of the negative electrode sheet is 440 mm×12579 mm, and the specification of the positive electrode sheet is 436.1 mm×11740 mm.

[0103] Example 3

[0104] Except that a through hole is provided on the straight area of ​​the negative electrode sheet of 70 turns in the opposite direction of the pre-winding direction from the tail end of the negative electrode sheet, the rest is the same as that of Example 1. The negative electrode sheet is pre-wound, and the number of turns M of the negative electrode sheet is determined to be 70 turns, the specification of the negative electrode sheet is 440 mm×58698 mm, and the specification of the positive electrode sheet is 436.1 mm×57860 mm.

[0105] Example 4 to Example 12

[0106] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0107] Embodiment 13

[0108] 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.

[0109] <Preparation of positive electrode sheet>

[0110] The first electrode is the positive electrode. 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 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.

[0111] The positive electrode sheet is pre-wound, and the number of winding turns M of the positive electrode sheet is determined to be 42 turns. One surface of the positive electrode sheet is selected at random, and two straight areas of each turn of the positive electrode sheet and two bending areas connected to the two straight areas are determined, wherein the width of the straight area is set to 380 mm, and the length of the straight area is set to 440 mm. The first edge and the second edge of each straight area are determined, and the straight areas of 42 turns of the positive electrode sheet are selected and determined from the tail end of the positive electrode sheet and in the opposite direction of the pre-winding direction; along the width direction of the unfolded positive electrode sheet, 13 rows of through holes are respectively set on the two straight areas of each turn of the positive electrode sheet, and along the length direction of the unfolded positive electrode sheet, 10 through holes are set in each row on the two straight areas of each turn of the positive electrode sheet. Starting from the tail end of the positive electrode sheet and along the opposite direction of the pre-winding direction, the maximum circumscribed circle of the outer contour of the through hole arranged on the straight area of ​​the 1st circle positive electrode sheet to the 42nd circle positive electrode sheet close to the winding center gradually decreases.

[0112] Determine A to be 3.75%, B to be 0.75, and determine the maximum circumscribed circle diameter D1 of the outer contour of the through hole on the straight area of ​​the first circle of positive electrode sheet on the surface of the positive electrode sheet as mm, D1 = A × L, and the maximum circumscribed circle diameter of the outer contour of the through hole on the straight area of ​​the nth circle of positive electrode sheet on the surface of the positive electrode sheet is D n mm, D n =B n-1 ×D1. The sum of the outer contours of the through holes on the straight area of ​​the first circle of positive pole pieces accounts for 12.4% of the total area. Along the length direction of the unfolded positive pole piece, the shortest distance L1 between the center of the through hole on the straight area and the first edge or the second edge is 40mm, and the distance L2 between the centers of two adjacent through holes is 17.5mm. Along the width direction of the unfolded positive pole piece, the shortest distance between the center of the through hole in the straight area and the third edge or the fourth edge of the straight area is 10mm. According to the above parameters, laser drilling is performed on the straight area of ​​the positive pole piece to obtain a positive pole piece with a specification of 440mm×35219mm.

[0113] <Preparation of negative electrode sheet>

[0114] 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 443.9mm×36058mm 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.

[0115] Embodiment 14

[0116] The preparation of the positive electrode sheet is the same as that of Example 13, and the negative electrode sheet is prepared according to the following steps, and the rest is the same as that of Example 1.

[0117] <Preparation of negative electrode sheet>

[0118] 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, and the mixture is stirred to obtain a negative electrode slurry with a solid content of 50wt%. The negative electrode slurry is evenly coated on one surface of the 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 the 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.

[0119] The negative electrode sheet is pre-wound, and the number of winding turns M of the negative electrode sheet is determined to be 43 turns. One surface of the negative electrode sheet is selected, and two straight areas of each turn of the negative electrode sheet and two bending areas connected to the two straight areas are determined, wherein the width of the straight area is set to 380 mm, and the length of the straight area is set to 443.9 mm. The first edge and the second edge of each straight area are determined, and the straight areas of 42 turns of the negative electrode sheet are selected and determined from the tail end of the negative electrode sheet and in the opposite direction of the pre-winding direction; along the width direction of the unfolded negative electrode sheet, 13 rows of through holes are respectively set on the two straight areas of each turn of the negative electrode sheet, and along the length direction of the unfolded negative electrode sheet, 10 through holes are set in each row on the two straight areas of each turn of the negative electrode sheet. Starting from the tail end of the negative electrode sheet and in the opposite direction of the pre-winding direction, the maximum circumscribed circle of the outer contour of the through hole arranged on the straight area of ​​the 1st circle negative electrode sheet to the 42nd circle negative electrode sheet close to the winding center gradually decreases.

[0120] Determine A to be 3.75%, B to be 0.75, and determine the maximum circumscribed circle diameter D1 of the outer contour of the through hole on the straight area of ​​the first circle of negative electrode sheet on the surface of the negative electrode sheet to be mm, D1 = A × L, and the maximum circumscribed circle diameter of the outer contour of the through hole on the straight area of ​​the nth circle of negative electrode sheet on the surface of the negative electrode sheet to be D n mm, D n =B n-1 ×D1. The sum of the outer contours of the through holes on the straight area of ​​the first circle of negative pole pieces accounts for 12.29% of the total area. Along the length direction of the unfolded negative pole piece, the shortest distance L1 between the center of the through hole on the straight area and the first edge or the second edge is 40 mm, and the distance L2 between the centers of two adjacent through holes is 17.5 mm. Along the width direction of the unfolded negative pole piece, the shortest distance L3 between the center of the through hole in the straight area and the third edge or the fourth edge of the straight area is 10 mm. According to the above parameters, laser drilling is performed on the straight area of ​​the negative pole piece to obtain a negative pole piece with a specification of 443.9 mm × 36058 mm.

[0121] Comparative Example 1

[0122] Except for providing a blind hole in <Preparation of Negative Electrode Sheet>, the rest is the same as Example 1.

[0123] Comparative Example 2

[0124] Except that in <Preparation of Negative Electrode Sheet>, through holes are provided on the straight area of ​​the negative electrode sheet for 5 turns in the opposite direction of the pre-winding direction starting from the tail end of the negative electrode sheet, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1.

[0125] Comparative Example 3

[0126] The present invention is the same as Example 1 except that in <Preparation of Negative Electrode Sheet>, a through hole is provided on the straight area of ​​the negative electrode sheet for 70 turns in the opposite direction of the pre-winding direction starting from the tail end of the negative electrode sheet, the value of A is 7, the value of B is 1, and the relevant preparation parameters are adjusted according to Table 1.

[0127] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0128]

[0129] Note: “ / ” in Table 1 indicates no relevant preparation parameters.

[0130] From Examples 1 to 14 and Comparative Examples 1 to 3, it can be seen that by setting through holes on the two straight areas of the first pole piece and adjusting the values ​​of N, A, D1, and B within the scope of this application, 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 N, 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 2 is small in the first pole piece, 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 number of side reactions 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. However, the diffusion distance of the electrolyte in Examples 1 to 14 is large in the first pole piece, and the electrolyte has a better infiltration effect on the pole piece, and the 600cls capacity retention rate of the obtained lithium-ion battery is higher, and the lithium-ion battery has better cycle performance. At the same time, the impact test pass rate is high, taking into account the safety performance of the lithium-ion battery and the actual production requirements.

[0131] The number N of through holes set on each straight area of ​​each circle of the first pole piece 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 straight area of ​​each circle of the first pole piece 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.

[0132] 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.

[0133] 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.

[0134] The proportion S of the sum of the areas of the outer contours of the through holes usually affects 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 a range 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.

[0135] Along the length direction of the electrode assembly, the shortest distance L2 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 Examples 1, 5 and 6 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 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.

[0136] Along the width direction of the electrode assembly, the shortest distance L1 between a single through hole and the first edge or the second 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 first edge or the second 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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, wherein the electrode assembly comprises M turns of a first electrode sheet, each turn of the first electrode sheet comprises two straight regions and two bending regions connected to the two straight regions, the two bending regions are arranged opposite to each other along the width direction of the electrode assembly; along the width direction of the electrode assembly, the width of a single straight region is L mm; Starting from the tail end of the first pole piece and in the opposite direction of the winding direction of the electrode assembly, through holes are provided on the straight areas of N turns of the first pole piece, 15≤N≤70, N is a positive integer and N≤M, and at least one through hole is provided on each of the straight areas; From the end of the first pole piece and in the opposite direction of the winding direction of the electrode assembly, the diameter of the maximum circumscribed circle of the through hole on the straight area of ​​the first pole piece in the first circle is D1 mm, D1 = A × L, 1.5% ≤ A ≤ 6%, and the diameter of the maximum circumscribed circle of the through hole on the straight area of ​​the first pole piece in the nth circle is D n mm, D n =B n-1 ×D1, 2≤n≤N, 0.6≤B≤0.

9.

2. The secondary battery according to claim 1, wherein 1.8％≤A≤3.75％。 3. The secondary battery according to claim 1 or 2, wherein: The two straight areas include a first straight area and a second straight area arranged along the thickness direction of the electrode assembly, and along the thickness direction of the electrode assembly, 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, along the thickness direction of the electrode assembly, there is at least a partial overlapping area between the projections of the multiple through holes corresponding to each other in the multiple second straight areas.

4. The secondary battery according to claim 1, wherein The two straight areas include a first straight area and a second straight area arranged along the thickness direction of the electrode assembly. Along the thickness direction of the electrode assembly, the projection of the through hole in the first straight area of ​​the first pole piece in the nth circle is located within the projection of the through hole in the first straight area of ​​the first pole piece in the n-1th circle; and / or, the projection of the through hole in the second straight area of ​​the first pole piece in the nth circle is located within the projection of the through hole in the second straight area of ​​the first pole piece in the n-1th circle.

5. The secondary battery according to any one of claims 1 to 4, wherein The thickness of the electrode assembly is T mm. Along the width direction of the electrode assembly, any straight area has a first edge and a second edge relative to each other. Along the direction from the first edge to the second edge, the shortest distance between the center of the through hole of the straight area and the first edge or the second edge is L1 mm, T / 2≤L1≤L / 4, 20≤T≤70.

6. The secondary battery according to any one of claims 1 to 5, wherein Along the width direction of the electrode assembly, the distance between the centers of two adjacent through holes located in the straight area is L2 mm, 5≤L2≤30.

7. The secondary battery according to any one of claims 1 to 6, wherein The two straight regions include a first straight region and a second straight region arranged along the thickness direction of the electrode assembly. Along the thickness direction of the electrode assembly, there is at least a partial overlap between the projection of the through hole in the first straight region and the projection of the through hole in the corresponding second straight region.

8. The secondary battery according to any one of claims 1 to 7, 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 straight area, the sum of the outer contours of the through holes on the first material layer in the straight area of ​​the first pole piece in the first circle accounts for S, 1%≤S≤35%.

9. The secondary battery according to any one of claims 1 to 8, 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 fourth edge, and the shortest distance between the center of the through hole in the straight area and the third edge or the fourth edge is L3 mm, 5≤L3≤18.

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. The thickness of the first material layer is H1 μm, and 120≤H1≤600.

11. The secondary battery according to claim 10, wherein The thickness of the first current collector is H2 μm, 5≤H2≤20.

12. The secondary battery according to any one of claims 1 to 11, wherein 80≤L≤600。 13. The secondary battery according to any one of claims 1 to 12, wherein: The first pole piece is a positive pole piece and / or a negative pole piece.

14. The secondary battery according to any one of claims 1 to 13, wherein The outer contour of a single through hole may be in the shape of a circle, an ellipse or a polygon.

15. The secondary battery according to any one of claims 1 to 14, wherein The secondary battery is a soft-pack secondary battery or a square secondary battery. 16 . An electronic device comprising the secondary battery according to claim 1 .

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