cylindrical secondary batteries and electronic devices

Abstract

This application provides a cylindrical secondary battery and an electronic device. The cylindrical secondary battery includes an electrode assembly with a central hole radius of b mm and an electrode assembly radius of a mm. The electrode assembly includes a first electrode sheet, which includes a first current collector and a first material layer. Along the winding direction of the electrode assembly, the first material layer sequentially includes a first region and a second region. Along the radial direction of the electrode assembly, the distance between the first region and the winding center of the electrode assembly is c1 mm, where 1.5b ≤ c1 ≤ 5.5b. Multiple first recesses are provided on the surface of the first region. The distance between the second region and the winding center of the electrode assembly is c2 mm, where 0.8a ≤ c2 ≤ a. Multiple second recesses are provided on the surface of the second region. This design helps reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode sheet and excessive tensile stress causing breakage of the outer electrode sheet and the generation of burrs.

Description

Technical Field

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

[0002] Cylindrical secondary batteries, such as cylindrical lithium-ion batteries, are used in a variety of fields. They have the characteristics of high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the consumer electronics field.

[0003] However, in the later stages of lithium-ion battery cycling, the electrodes expand and the current collector stretches, resulting in excessive tensile stress on the outer electrodes, which can easily cause them to break, and excessive compressive stress on the inner electrodes, which can easily cause them to collapse, thus reducing the safety and cycle performance of the secondary battery. Summary of the Invention

[0004] The purpose of this application is to provide a cylindrical secondary battery and electronic device that helps reduce the tensile and compressive stresses generated by electrode expansion during cycling, thereby improving the safety and cycle performance of the cylindrical secondary battery. The specific technical solution is as follows:

[0005] The first aspect of this application provides a cylindrical secondary battery, including a wound electrode assembly. The electrode assembly includes a central hole with a radius of b mm, and the electrode assembly has a radius of a mm. The electrode assembly includes a first electrode sheet, which includes a first current collector and a first material layer on one surface of the first current collector. Along the winding direction of the electrode assembly, the first material layer sequentially includes a first region and a second region. Specifically, along the radial direction of the electrode assembly, the distance between the first region and the winding center of the electrode assembly is c1 mm, where 1.5b ≤ c1 ≤ 5.5b, optionally 1.5b ≤ c1 ≤ 4b; further optionally, 2.9b ≤ c1 ≤ 3.5b; a plurality of first recesses are provided on the surface of the first region. Along the radial direction, the distance between the second region and the winding center of the electrode assembly is c2 mm, where 0.8a ≤ c2 ≤ a, optionally 0.9a ≤ c2 ≤ 1a; further optionally, 0.96a ≤ c2 ≤ 0.98a; a plurality of second recesses are provided on the surface of the second region. This application reduces the compressive stress caused by the expansion of the inner electrode and the tensile stress caused by the expansion of the outer electrode during the later stages of cycling by creating recesses in different regions at varying distances from the winding center on the surface of the first material layer. This effectively reduces the safety risks of short circuits caused by excessive compressive stress leading to collapse of the inner electrode and excessive tensile stress leading to breakage and burr formation of the outer electrode. Simultaneously, it improves the wetting effect of the electrolyte on the electrode, reducing the risk of lithium plating in the secondary battery, thereby improving the cycle performance of the secondary battery. Therefore, the cylindrical secondary battery of this application exhibits excellent safety and cycle performance.

[0006] In one or more embodiments, based on the surface area of ​​the first material layer, the ratio of the sum of the areas of the first region and the second region is S, where 2% ≤ S ≤ 55%; optionally, 10% ≤ S ≤ 20%; and further optionally, 12% ≤ S ≤ 18%. By adjusting the value of S within the above range, the cylindrical secondary battery exhibits good safety and cycle performance while taking into account actual production requirements.

[0007] In one or more embodiments, along the thickness direction of the first electrode, the thickness of the first electrode is T μm, 60 ≤ T ≤ 450; the average depth of the plurality of first recesses is H1 μm, 1.5% ≤ H1 / T × 100% ≤ 35%; optionally, 3% ≤ H1 / T × 100% ≤ 15%; further optionally, 5% ≤ H1 / T × 100% ≤ 10%; and / or, the average depth of the plurality of second recesses is H2 μm, 1.5% ≤ H2 / T × 100% ≤ 35%; optionally, 3% ≤ H2 / T × 100% ≤ 15%; further optionally, 5% ≤ H2 / T × 100% ≤ 10%. With the above configuration, while taking into account actual production requirements, the cylindrical secondary battery has good safety and cycle performance.

[0008] In one or more embodiments, 0.1 ≤ H1 / H2 ≤ 5; optionally, 0.2 ≤ H1 / H2 ≤ 3; further optionally, 0.3 ≤ H1 / H2 ≤ 1.5. By adjusting the value of H1 / H2 within the above range, the cylindrical secondary battery exhibits good safety and cycle performance while taking into account actual production requirements.

[0009] In one or more embodiments, along the thickness direction of the first electrode, a single first recess has a first projection on the surface of the first material layer. Along the length direction of the unfolded first electrode, the shortest distance between the outer contours of two adjacent first projections is d1 mm, where 0.1 ≤ d1 ≤ 15; optionally, 0.5 ≤ d1 ≤ 8; further optionally, 1 ≤ d1 ≤ 5; and / or, along the thickness direction of the first electrode, a single second recess has a second projection on the surface of the first material layer. Along the length direction of the unfolded first electrode, the shortest distance between the outer contours of two adjacent second projections is d2 mm, where 0.1 ≤ d2 ≤ 10; optionally, 0.3 ≤ d2 ≤ 5; further optionally, 0.5 ≤ d2 ≤ 2. With the above configuration, while considering actual production requirements, the cylindrical secondary battery exhibits good safety and cycle performance.

[0010] In one or more embodiments, the secondary battery satisfies at least one of the following characteristics: a plurality of first recesses or a plurality of second recesses are distributed in a dotted pattern on the surface of the first material layer; along the thickness direction of the first electrode, the shape of the first projection of a single first recess on the surface of the first material layer is circular, elliptical, or a regular polygon; the diameter of the largest circumscribed circle of the outer contour of the single first projection is D1 mm, 0.2≤D1≤5; optionally, 0.5≤D1≤4.5; further optionally, 1≤D1≤4; and / or, along the thickness direction of the first electrode, the shape of the second projection of a single second recess on the surface of the first material layer is circular, elliptical, or a regular polygon; the diameter of the largest circumscribed circle of the outer contour of the single second projection is D2 mm, 0.1≤D2≤6; optionally, 0.2≤D2≤5.5; further optionally, 0.5≤D2≤5. Through the above configuration, while considering the production cost and capacity of the secondary battery, the cylindrical secondary battery has good safety performance and cycle performance.

[0011] In one or more embodiments, along the thickness direction of the first electrode, the shape of the first projection of a single first recess on the surface of the first material layer is strip-shaped. Along the length direction of the unfolded first electrode, the average width of the plurality of first projections is W1 mm, where 0.2 ≤ W1 ≤ 5; optionally, 0.6 ≤ W1 ≤ 2; further optionally, 1 ≤ W1 ≤ 1.5; and / or, along the thickness direction of the first electrode, the shape of the second projection of a single second recess on the surface of the first material layer is strip-shaped. Along the length direction of the unfolded first electrode, the average width of the plurality of second projections is W2 mm, where 0.1 ≤ W2 ≤ 6; optionally, 0.1 ≤ W2 ≤ 3; further optionally, 0.2 ≤ W2 ≤ 1. Through the above configuration, while considering the production cost and capacity of the secondary battery, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0012] In one or more embodiments, a plurality of first recesses extend along the width direction of the unfolded first electrode and are spaced apart along the length direction of the unfolded first electrode. Based on the width of the unfolded first electrode, the length ratio of a single second projection is L1, where 5% ≤ L1 ≤ 95%; and / or, a plurality of second recesses extend along the width direction of the unfolded first electrode and are spaced apart along the length direction of the unfolded first electrode. Based on the width of the unfolded first electrode, the length ratio of a single second projection is L2, where 10% ≤ L2 ≤ 95%. Through the above configuration, while considering both practical production and energy density, the cylindrical secondary battery of this application exhibits good safety and cycle performance.

[0013] In one or more embodiments, along the width direction after the first electrode is unfolded, the length of a single first projection is L3 mm, where 9 ≤ L3 ≤ 150 mm; optionally, 15 ≤ L3 ≤ 80 mm; further optionally, 20 ≤ L3 ≤ 55 mm; and / or, along the width direction after the first electrode is unfolded, the length of a single second projection is L4 mm, where 18 ≤ L4 ≤ 180 mm; optionally, 30 ≤ L4 ≤ 100 mm; further optionally, 50 ≤ L4 ≤ 80 mm. With the above settings, while considering both practical production and energy density, the cylindrical secondary battery of this application has good safety and cycle performance.

[0014] In one or more embodiments, a first material layer is located on the surface of the first current collector facing the winding center of the electrode assembly. In one or more embodiments, the first electrode further includes a second material layer located on the surface of the first current collector away from the winding center of the electrode assembly; the surface of the region of the second material layer opposite to the first region is provided with a plurality of first protrusions, at least some of the first protrusions being disposed opposite to some of the first recesses; and / or, the surface of the region of the second material layer opposite to the second region is provided with a plurality of second protrusions, at least some of the second protrusions being disposed opposite to some of the second recesses. In one or more embodiments, the region of the first current collector opposite to the first region is provided with a plurality of third protrusions in the direction of the second material layer; and / or, the region of the first current collector opposite to the second region is provided with a plurality of fourth protrusions in the direction of the second material layer. In one or more embodiments, at least some of the third protrusions correspond to some of the first recesses; and / or, at least some of the fourth protrusions correspond to some of the second recesses. Through the above configuration, the safety performance and cycle performance of the cylindrical secondary battery are improved while satisfying mass production manufacturability.

[0015] In one or more embodiments, the first electrode is a positive electrode.

[0016] A second aspect of this application provides an electronic device comprising the cylindrical secondary battery of any of the above embodiments. Thus, the electronic device of this application has excellent performance.

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

[0018] This application embodiment, by providing recesses in different regions at varying distances from the winding center on the surface of the first material layer, reduces the compressive stress generated by the expansion of the inner electrode sheet during the later stages of cycling and the tensile stress generated by the expansion of the outer electrode sheet. This effectively reduces the safety risks of short circuits caused by excessive compressive stress leading to collapse of the inner electrode sheet and excessive tensile stress leading to breakage and burr formation of the outer electrode sheet. Simultaneously, it improves the wetting effect of the electrolyte on the electrode sheet, reducing the risk of lithium plating in the secondary battery, thereby improving the cycle performance of the secondary battery. Therefore, the cylindrical secondary battery of this application exhibits excellent safety and cycle performance.

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

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

[0021] Figure 1 This is a schematic diagram of the winding structure formed by the electrode assembly in one embodiment of this application;

[0022] Figure 2 This is a partial front view of the positive electrode sheet after the electrode assembly in another embodiment of this application has been unfolded.

[0023] Figure 3 This is a partial front view of the positive electrode sheet after the electrode assembly in another embodiment of this application has been unfolded.

[0024] Figure 4 for Figure 2 A cross-sectional view of the positive electrode sheet along the PP direction.

[0025] Reference numerals: Electrode assembly 001; Center hole 0010; Positive electrode (first electrode) 10; First current collector 11; First material layer 12; Second material layer 13; Negative electrode 20; Second current collector 21; Negative electrode material layer 22; Separator 30; First recess 121; First convex portion 131; Third convex portion 111; Second recess 122; Second convex portion 132; Fourth convex portion 112; Winding start end face 0011; Winding end face 0012. Detailed Implementation

[0026] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0027] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of cylindrical secondary batteries to explain this application, but the cylindrical secondary batteries in this application are not limited to lithium-ion batteries.

[0028] In existing cylindrical secondary batteries, such as cylindrical lithium-ion batteries, the electrodes expand during the later stages of cycling. This expansion and contraction is particularly pronounced when the negative electrode contains silicon-containing active materials. The inner electrode layer collapses due to inward compression, while the outer electrode layer experiences excessive tensile stress, leading to electrode breakage, especially in the current collector, and the formation of burrs. Short circuits are also more likely during charging and discharging, and lithium plating can occur at localized electrode interfaces, negatively impacting the battery's cycle performance and safety. Current solutions typically increase the foil thickness to enhance electrode strength, but this reduces the energy density of the electrode assembly for the same specifications and increases manufacturing costs. Furthermore, it doesn't significantly improve the problem of electrode breakage and collapse during the later stages of cycling. Therefore, this application provides a cylindrical secondary battery and electronic device that reduces the safety risks of outer electrode breakage due to excessive tensile stress and inner electrode collapse due to excessive compressive stress, thereby improving the safety and cycle performance of the cylindrical secondary battery.

[0029] The first aspect of this application provides a cylindrical secondary battery, including a wound electrode assembly. The electrode assembly includes a central hole with a radius of b mm, and the electrode assembly has a radius of a mm. The electrode assembly includes a first electrode sheet, which includes a first current collector and a first material layer on one surface of the first current collector. Along the winding direction of the electrode assembly, the first material layer sequentially includes a first region and a second region. The distance from the first region to the winding center of the electrode assembly along the radial direction is c1 mm, where 1.5b ≤ c1 ≤ 5.5b, optionally 1.5b ≤ c1 ≤ 4b, and further optionally 2.9b ≤ c1 ≤ 3.5b. For example, the value of c1 can be 1.5b, 2b, 3.5b, 4b, 4.5b, 5b, 5.5b, or a range consisting of any two of these values. A plurality of first recesses are provided on the surface of the first region. Along the radial direction, the distance from the second region to the winding center of the electrode assembly is c2 mm, where 0.8a ≤ c2 ≤ a, optionally 0.9a ≤ c2 ≤ 1a, and further optionally 0.96a ≤ c2 ≤ 0.98a. For example, the value of c2 can be 0.8a, 0.82a, 0.84a, 0.86a, 0.88a, 0.9a, 0.92a, 0.94a, 0.96a, 0.98a, a, or a range of any two of these values. A plurality of second recesses are provided on the surface of the second region.

[0030] In calculating the positions of the first and second regions, the distance from the first region of the first electrode plate of the electrode assembly to the center point of the central hole is denoted as c1. c1 can be the minimum distance between the center point of the central hole and the first region, or the maximum distance between the center point of the central hole and the first region, or the distance between the center point of the central hole and the midpoint of the first region; no limitation is imposed here. The distance from the second region of the first electrode plate of the electrode assembly to the center point of the central hole is denoted as c2. c2 can be the minimum distance between the center point of the central hole and the second region, or the maximum distance between the center point of the central hole and the second region, or the distance between the center point of the central hole and the midpoint of the second region; no limitation is imposed here.

[0031] In this application, the first electrode can be a positive electrode and / or a negative electrode. The electrode assembly, in its unfolded state, is defined with its length direction as the X direction, its width direction as the Y direction, and its thickness direction as the Z direction. It is understood that the negative electrode, positive electrode, and separator, in their unfolded state, have the same length, width, and thickness directions as the electrode assembly, and the winding direction of the electrode assembly is the W direction. For example, the first electrode is a positive electrode, such as... Figure 1 As shown, the electrode assembly 001 includes a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10 includes a first current collector 11 and a first material layer 12 located on one surface of the first current collector 11. Along the winding direction (W direction) of the electrode assembly 001, the electrode assembly 001 has a winding start end face 0011 and a winding end face 0012. Along the winding direction (W direction) of the electrode assembly 001, the bottom surface of the first cylinder formed by rotating 360° from the winding start end face 0011 with the winding center O of the electrode assembly 001 as the center is the center hole 0010 of the electrode assembly 001, and the radius of the center hole 0010 is a mm. Along the opposite direction of the winding direction (W direction) of the electrode assembly 001, the radius of the second cylinder formed by rotating 360° from the winding end face 0012 with the winding center O of the electrode assembly 001 as the center is b mm. mm, which means the radius of the electrode assembly 001 is b mm. Along the winding direction (W direction) of the electrode assembly 001, the first material layer 12 is wound. The first material layer 12 includes a first region and a second region in sequence. The first region is M to N, and the surface of the first region is provided with a plurality of first recesses 121. The second region is M' to N', and the surface of the second region is provided with a plurality of second recesses 122 respectively. Figure 1 The number of layers of the first material layer, the number, size, length, and spacing of the first and second recesses are merely illustrative examples and are not intended to limit the scope of this application. In this application, "multiple" refers to two or more.

[0032] When recesses are provided on all layers of the first material, the area of ​​these recesses on the electrode is too large, resulting in a large expansion space. This makes it easy for electrolyte bridging to occur between some electrode layers, leading to increased electrochemical impedance during battery cycling and greater resistance to ion conduction, thus reducing the battery's cycle performance. Simultaneously, excessive contact between the electrolyte and the electrode increases the number of side reactions and byproducts, leading to increased electrode thickness and hardness. Consequently, the battery's ability to mitigate the safety risks of inner electrode collapse due to excessive extrusion pressure and outer electrode breakage due to excessive tensile stress, resulting in burrs and short circuits, is poorly improved. Furthermore, the electrode assembly diameter is too large, resulting in a low yield rate for lithium-ion batteries with the same casing specifications in actual production, failing to meet actual production requirements. Alternatively, using a larger casing reduces the battery's capacity and energy density. Both scenarios increase production costs and reduce capacity, resulting in poor cost-effectiveness. This application features recesses on the surface of the first material layer at varying distances from the winding center. Specifically, a first recess is created in a first region near the beginning of the electrode assembly, and a second recess is created in a second region near the end. Both the inner and outer rings of the electrode assembly have expansion space, reducing the compressive stress generated by the expansion of the inner ring electrode and the tensile stress generated by the expansion of the outer ring electrode during later stages of cycling. This effectively reduces the safety risks of short circuits caused by excessive compressive stress leading to collapse of the inner ring electrode and excessive tensile stress leading to breakage and burr formation of the outer ring electrode. Simultaneously, it improves the wetting effect of the electrolyte on the electrode, reducing the risk of lithium plating in the secondary battery and thus improving the cycle performance. Furthermore, the appropriately sized expansion space keeps the distance between the positive and negative electrodes and between electrode layers within a suitable range during charging and discharging, resulting in lower electrochemical impedance of the secondary battery. These features ensure that the average diameter of the electrode assembly is within a suitable range, reducing actual production costs and increasing production capacity. Therefore, the cylindrical secondary battery of this application exhibits excellent safety and cycle performance.

[0033] It should be noted that the "surface" on which the first material layer is located can be the entire area of ​​the surface of the first current collector or a part of the surface of the first current collector. This application does not have any particular restrictions, as long as the purpose of this application can be achieved.

[0034] In one or more embodiments, 0.8a > 5.5b. Through the above configuration, the first region and the second region are located at different positions on the first material layer. At this time, recesses are provided in different regions on the surface of the first material layer at different distances from the winding center. The first region is close to the central hole, and the second region is close to the end of the electrode assembly. Both the inner and outer rings of the electrode assembly have expansion space, which can reduce the extrusion pressure generated by the expansion of the inner ring electrode and the tensile stress generated by the expansion of the outer ring electrode in the later stages of cycling. This effectively reduces the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner ring electrode and excessive tensile stress leading to breakage and burr formation of the outer ring electrode. It also reduces the risk of lithium plating in the secondary battery. Furthermore, the above configuration ensures that the average diameter of the electrode assembly is within a suitable range, reducing actual production costs and increasing production capacity. Therefore, the cylindrical secondary battery of this application has good safety and cycle performance.

[0035] In one or more embodiments, 15mm ≤ a ≤ 20mm. For example, the value of a can be 15, 16, 17, 17.5, 18, 19, 20, or a range of any two of these values. By adjusting the value of a within the above range, it is beneficial to balance the strength and cycle performance of the first electrode with actual production needs, thereby reducing processing difficulty.

[0036] In one or more embodiments, 1mm ≤ b ≤ 4mm. For example, the value of b can be 1, 1.5, 2, 2.5, 3, 3.5, 4, or a range of any two of these values. By adjusting the value of b within the above range, it is beneficial to balance the strength and cycle performance of the first electrode with actual production needs, thereby reducing processing difficulty.

[0037] In one or more embodiments, based on the surface area of ​​the first material layer, the percentage of the sum of the areas of the first region and the second region is S, where 2% ≤ S ≤ 55%; optionally, 10% ≤ S ≤ 20%; further optionally, 12% ≤ S ≤ 18%. For example, the value of S can be 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, or a range of any two of these values. By controlling the value of S within the aforementioned range, it is beneficial to reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode and excessive tensile stress leading to breakage of the outer electrode and the generation of burrs. Simultaneously, it improves the electrolyte's wetting effect on the electrode, reducing the risk of lithium plating in the secondary battery, thereby improving its cycle performance. Furthermore, at this point, the distances between the positive and negative electrodes and between electrode layers during charging and discharging are within a suitable range, resulting in lower electrochemical impedance and a more suitable average diameter of the electrode assembly, thus reducing actual production costs and increasing production capacity. Therefore, while meeting practical production requirements, cylindrical secondary batteries exhibit excellent safety and cycle performance.

[0038] In one or more embodiments, the thickness of the first electrode is T μm along the thickness direction of the first electrode, where 60 ≤ T ≤ 450. For example, the value of T can be 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 4 The range is 30, 440, 450, or any two of these values; the average depth of the plurality of first recesses is H1 μm, 1.5% ≤ H1 / T × 100% ≤ 35%, optionally, 3% ≤ H1 / T × 100% ≤ 15%; further optionally, 5% ≤ H1 / T × 100% ≤ 10%; for example, the value of H1 / T × 100% can be 1.5%, 2%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or any two of these values. By controlling the values ​​of T and H1 / T×100% within the aforementioned range, it is beneficial to further reduce the safety risk of inner electrode collapse due to excessive extrusion pressure, and also to reduce the safety risk of outer electrode breakage and short circuits caused by excessive tensile stress. Simultaneously, it improves the electrolyte's wetting effect on the electrodes, reducing the risk of lithium plating in the secondary battery, thereby improving the cycle performance of the secondary battery. Furthermore, the appropriate gaps between the positive and negative electrodes and between electrode layers during charging and discharging result in lower electrochemical impedance of the secondary battery, further ensuring that the average diameter of the electrode assembly is within a suitable range, reducing actual production costs and increasing production capacity. Therefore, while meeting practical production requirements, cylindrical secondary batteries exhibit good safety and cycle performance.

[0039] In one or more embodiments, the thickness of the first electrode is T μm along its thickness direction, where 60 ≤ T ≤ 450. For example, the value of T can be 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430. 440, 450, or any combination thereof; the average depth of the plurality of second recesses is H2μm, 1.5%≤H2 / T×100%≤35%, optionally, 3%≤H2 / T×100%≤15%; further optionally, 5%≤H2 / T×100%≤10%, for example, the value of H2 / T×100% can be 1.5%, 2%, 3%, 5%, 6%, 7%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or any combination thereof. By controlling the values ​​of T and H2 / T×100% within the aforementioned range, it is beneficial to further reduce the safety risk of short circuits caused by the outer electrode sheet fracture and burr formation due to excessive tensile stress in the electrode assembly. It also reduces the safety risk of the inner electrode sheet collapsing due to excessive extrusion pressure. Simultaneously, it improves the electrolyte's wetting effect on the electrode sheets, reducing the risk of lithium plating in the secondary battery, thereby improving the cycle performance of the secondary battery. Furthermore, the appropriate gaps between the positive and negative electrode sheets and between electrode layers during charging and discharging result in a lower electrochemical impedance in the secondary battery, further ensuring that the average diameter of the electrode assembly is within a suitable range, reducing actual production costs and increasing production capacity. Therefore, while meeting practical production requirements, cylindrical secondary batteries exhibit excellent safety and cycle performance.

[0040] In one or more embodiments, the thickness of the first electrode is T μm along the thickness direction, where 60 ≤ T ≤ 450. For example, the value of T can be 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, etc. The range is 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, or any combination thereof; the average depth of the plurality of first recesses is H1 μm, 1.5% ≤ H1 / T × 100% ≤ 35%, optionally, 3% ≤ H1 / T × 100% ≤ 15%; further optionally, 5% ≤ H1 / T×100% ≤ 10%; for example, the value of H1 / T×100% can be 1.5%, 2%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or a range of any two of these values; and, the average depth of the plurality of second recesses is H2μm, 1.5% ≤ H2 / T×100% ≤ 35%. Optionally, 3% ≤ H2 / T × 100% ≤ 15%; further optionally, 5% ≤ H2 / T × 100% ≤ 10%, for example, the value of H2 / T × 100% can be 1.5%, 2%, 3%, 5%, 6%, 7%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or a range of any two of these values. For example, as... Figure 2 and Figure 4 As shown, Figure 2 The first electrode in the process is cut along the PP direction to obtain Figure 4 Along the thickness direction (Z direction) of the first electrode 10, the thickness of the first electrode 10 is T μm, the average depth of the plurality of first recesses 121 is H1 μm, and the average depth of the plurality of second recesses 122 is H2 μm. By adjusting the values ​​of T, H1 / T×100%, and H2 / T×100% within the above range, it is beneficial to reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode and excessive tensile stress leading to breakage of the outer electrode and the generation of burrs. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the appropriate gap between the positive and negative electrode sheets and between electrode layers during charging and discharging results in a smaller electrochemical impedance of the secondary battery, further keeping the average diameter of the electrode assembly within a suitable range, reducing actual production costs and increasing production capacity. Therefore, while taking into account actual production requirements, the cylindrical secondary battery has good safety and cycle performance.

[0041] In one or more embodiments, the thickness of the first current collector can be from 4 μm to 30 μm along the thickness direction of the first electrode.

[0042] In this application, the thickness of the first electrode can be controlled by means known to those skilled in the art. For example, when the first current collector is fixed, and the slurry is coated on the surface of the first current collector, with the solid content of the slurry fixed, the thickness of the first material layer can be increased by increasing the coating weight per unit area, and the thickness of the first electrode will increase accordingly; the thickness of the first material layer can be decreased by decreasing the coating weight per unit area, and the thickness of the first electrode will decrease accordingly; the thickness of the first material layer can also be decreased by increasing the cold pressing pressure when the first electrode is cold-pressed, and the thickness of the first material layer can decrease accordingly; the thickness of the first electrode can be increased by decreasing the cold pressing pressure, and the thickness of the first material layer can increase accordingly.

[0043] In one or more embodiments, 0.1 ≤ H1 / H2 ≤ 5; optionally, 0.2 ≤ H1 / H2 ≤ 3; further optionally, 0.3 ≤ H1 / H2 ≤ 1.5. For example, the value of H1 / H2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, or a range of any two of these values. The presence of a first and a second recess within the aforementioned depth ratio range on the inner and outer rings of the electrode assembly helps to further reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner ring electrode and excessive tensile stress leading to breakage and burr formation of the outer ring electrode. Simultaneously, it improves the electrolyte's wetting effect on the electrode, reducing the risk of lithium plating in the secondary battery and thus enhancing its cycle performance. Furthermore, the appropriate gaps between the positive and negative electrodes and between electrode layers during charging and discharging result in lower electrochemical impedance in the secondary battery. In actual production, the recesses with the aforementioned depth ratio can be set according to the actual tensile and extrusion stresses, reducing production costs and increasing capacity. Therefore, while meeting practical production requirements, the cylindrical secondary battery exhibits excellent safety and cycle performance.

[0044] In one or more embodiments, along the thickness direction of the first electrode, a single first recess has a first projection on the surface of the first material layer. Along the length direction of the first electrode after it is unfolded, the shortest distance between the outer contours of two adjacent first projections is d1 mm, 0.1≤d1≤15; optionally, 0.5≤d1≤8; further optionally, 1≤d1≤5. For example, the value of d1 can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range of any two of these values. By adjusting the value of d1 within the aforementioned range, the processing difficulty of the first electrode sheet is reduced, minimizing the risk of excessive powder shedding during processing leading to loss of active materials and consequently lower energy density of the secondary battery. This also ensures uniform pore distribution in the first electrode sheet, facilitating electrolyte flow and improving its wetting effect, thereby enhancing the cycle performance of the secondary battery. Furthermore, it helps reduce the safety risk of inner electrode sheet collapse due to excessive extrusion pressure, and also mitigates the safety risk of outer electrode sheet breakage and short circuits caused by excessive tensile stress. In addition, the appropriate gaps between the positive and negative electrodes and between electrode layers during charging and discharging reduce actual production costs and increase capacity. Therefore, while meeting practical production requirements, cylindrical secondary batteries exhibit excellent safety and cycle performance.

[0045] In one or more embodiments, along the thickness direction of the first electrode, a single second recess has a second projection on the surface of the first material layer. Along the length direction of the first electrode after it is unfolded, the shortest distance between the outer contours of two adjacent second projections is d2 mm, where 0.1 ≤ d2 ≤ 10; optionally, 0.3 ≤ d2 ≤ 5; further optionally, 0.5 ≤ d2 ≤ 2. For example, the value of d2 can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two of these values. By controlling the value of d2 within the aforementioned range, the processing difficulty of the first electrode sheet is reduced, minimizing the risk of excessive powder shedding during processing leading to loss of active materials and consequently reduced energy density of the secondary battery. This also ensures uniform pore distribution in the first electrode sheet, facilitating electrolyte flow and improving its wetting effect, thereby enhancing the cycle performance of the secondary battery. Furthermore, it helps reduce the safety risks of short circuits caused by excessive tensile stress leading to outer electrode sheet breakage and burr formation, as well as the safety risks of inner electrode sheet collapse due to excessive extrusion. In addition, the appropriate gaps between the positive and negative electrodes and between electrode layers during charging and discharging reduce actual production costs and increase capacity. Therefore, while meeting practical production requirements, cylindrical secondary batteries exhibit excellent safety and cycle performance.

[0046] In one or more embodiments, along the thickness direction of the first electrode, a single first recess has a first projection on the surface of the first material layer. Along the length direction of the unfolded first electrode, the shortest distance between the outer contours of two adjacent first projections is d1 mm, where 0.1 ≤ d1 ≤ 15; optionally, 0.5 ≤ d1 ≤ 8; further optionally, 1 ≤ d1 ≤ 5. For example, the value of d1 can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of these values; and, along the thickness direction of the first electrode, a single second recess has a second projection on the surface of the first material layer. Along the length direction of the unfolded first electrode, the shortest distance between the outer contours of two adjacent second projections is d2. mm, 0.1≤d2≤10; optionally, 0.3≤d2≤5; further optionally, 0.5≤d2≤2, for example, the value of d2 can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range of any two of these values. For example, such as... Figure 2 and Figure 3 As shown, along the thickness direction (Z direction) of the first electrode 10, a single first recess 121 has a first projection on the surface of the first material layer 12. Along the length direction (X direction) of the first electrode 10 after it is unfolded, the shortest distance between the outer contours of two adjacent first projections is d1 mm. Along the thickness direction (Z direction) of the first electrode 10, a single second recess 122 has a second projection on the surface of the first material layer 12. Along the length direction (X direction) of the first electrode 10 after it is unfolded, the shortest distance between the outer contours of two adjacent second projections is d2 mm. By controlling the values ​​of d1 and d2 within the aforementioned range, the processing difficulty of the first electrode sheet is reduced, minimizing the risk of excessive powder shedding during processing leading to loss of active materials and consequently lower energy density of the secondary battery. This also ensures uniform pore distribution in the first electrode sheet, facilitating electrolyte flow and improving its wetting effect, thereby enhancing the cycle performance of the secondary battery. Furthermore, it reduces the safety risks associated with excessive pressure causing inner electrode collapse and excessive tensile stress leading to outer electrode breakage, burr formation, and short circuits. Additionally, the moderate gaps between the positive and negative electrodes and between electrode layers during charging and discharging result in more uniform stress on the electrodes, reducing actual production costs and increasing production capacity. Therefore, while meeting practical production requirements, cylindrical secondary batteries exhibit excellent safety and cycle performance.

[0047] In one or more embodiments, a plurality of first recesses or a plurality of second recesses are distributed in a dotted pattern on the surface of the first material layer. Along the thickness direction of the first electrode, the shape of the first projection of a single first recess on the surface of the first material layer is a circle, an ellipse, or a regular polygon. The diameter of the largest circumscribed circle of the outer contour of a single first projection is D1 mm, 0.2≤D1≤5; optionally, 0.5≤D1≤4.5; further optionally, 1≤D1≤4. For example, the value of D1 can be 0.2, 0.4, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, or a range of any two of these values. By adjusting the value of D1 within the aforementioned range, it is beneficial to further reduce the safety risk of inner electrode collapse due to excessive extrusion pressure, and also to reduce the safety risk of outer electrode breakage and short circuit caused by excessive tensile stress. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first concave part on the surface of the first electrode is moderate, reducing the risk of increased electrochemical impedance due to increased local accumulation of electrolyte side reactions. Therefore, while taking into account the production cost and capacity of the secondary battery, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0048] In one or more embodiments, a plurality of first recesses or a plurality of second recesses are distributed in a dotted pattern on the surface of the first material layer. Along the thickness direction of the first electrode, the shape of the second projection of a single second recess on the surface of the first material layer is a circle, an ellipse, or a regular polygon. The diameter of the largest circumscribed circle of the outer contour of a single second projection is D2 mm, 0.1≤D2≤6; optionally, 0.2≤D2≤5.5; further optionally, 0.5≤D2≤5. For example, the value of D2 can be 0.1, 0.2, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, or a range of any two of these values. By adjusting the value of D2 within the aforementioned range, it is beneficial to further reduce the safety risk of short circuits caused by the outer electrode sheet breaking and generating burrs due to excessive tensile stress in the electrode assembly. It also reduces the safety risk of the inner electrode sheet collapsing due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the electrode sheet, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the second concave part on the surface of the first electrode sheet is moderate, reducing the risk of increased electrochemical impedance due to increased local aggregation of electrolyte side reactions. Therefore, while taking into account the production cost and capacity of the secondary battery, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0049] In one or more embodiments, a plurality of first recesses or a plurality of second recesses are distributed in a dotted pattern on the surface of the first material layer. Along the thickness direction of the first electrode, the shape of the first projection of a single first recess on the surface of the first material layer is circular, elliptical, or a regular polygon. The diameter of the largest circumscribed circle of the outer contour of a single first projection is D1 mm, 0.2≤D1≤5; optionally, 0.5≤D1≤4.5; further optionally, 1≤D1≤4. For example, the value of D1 can be 0.2, 0.4, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, or a range consisting of any two of these values; and, along the thickness direction of the first electrode, the shape of the second projection of a single second recess on the surface of the first material layer is circular, elliptical, or a regular polygon. The diameter of the largest circumscribed circle of the outer contour of a single second projection is D2. mm, 0.1≤D2≤6; optionally, 0.2≤D2≤5.5; further optionally, 0.5≤D2≤5, for example, the value of D2 can be 0.1, 0.2, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6 or a range of any two of these values. For example, as... Figure 2 As shown, along the thickness direction (Z direction) of the first electrode 10, the first projection of a single first recess 121 on the surface of the first material layer 12 is circular, and the diameter of the largest circumscribed circle of the outer contour of the single first projection is D1 mm. The second projection of a single second recess 122 on the surface of the first material layer 12 is circular, and the diameter of the largest circumscribed circle of the outer contour of the single second projection is D2 mm. By adjusting the values ​​of D1 and D2 within the above range, it is beneficial to reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode and excessive tensile stress leading to breakage of the outer electrode and the generation of burrs. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first and second recesses on the surface of the first electrode is moderate, reducing the risk of increased electrochemical impedance due to increased local aggregation of electrolyte and side reactions. Therefore, while taking into account the production cost and capacity of the secondary battery, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0050] In one or more embodiments, along the thickness direction of the first electrode, the shape of the first projection of a single first recess on the surface of the first material layer is strip-shaped, and along the length direction after the first electrode is unfolded, the average width of multiple first projections is W1 mm, 0.2≤W1≤5; optionally, 0.6≤W1≤2; further optionally, 1≤W1≤1.5. For example, the value of W1 can be 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5 or a range of any two of these values. By adjusting the value of W1 within the aforementioned range, it is beneficial to further reduce the safety risk of inner electrode collapse due to excessive extrusion pressure, and also to reduce the safety risk of outer electrode breakage and short circuit due to excessive tensile stress. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first concave part on the surface of the first electrode is moderate, reducing the risk of increased electrochemical impedance due to increased local accumulation of electrolyte side reactions. Therefore, while taking into account the production cost and capacity of the secondary battery, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0051] In one or more embodiments, along the thickness direction of the first electrode, the shape of the second projection of a single second recess on the surface of the first material layer is strip-shaped, and along the length direction after the first electrode is unfolded, the average width of multiple second projections is W2 mm, 0.1≤W2≤6; optionally, 0.1≤W2≤3; further optionally, 0.2≤W2≤1. For example, the value of W2 can be 0.1, 0.15, 0.2, 0.4, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, or a range consisting of any two of these values. By adjusting the value of W2 within the aforementioned range, it is beneficial to further reduce the safety risk of short circuits caused by the outer electrode sheet breaking and generating burrs due to excessive tensile stress in the electrode assembly. It also reduces the safety risk of the inner electrode sheet collapsing due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the electrode sheet, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the second concave part on the surface of the first electrode sheet is moderate, reducing the risk of increased electrochemical impedance due to increased local accumulation of electrolyte side reactions. Therefore, while taking into account the production cost and capacity of the secondary battery, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0052] In one or more embodiments, along the thickness direction of the first electrode, the shape of the first projection of a single first recess on the surface of the first material layer is strip-shaped, and along the length direction of the first electrode after it is unfolded, the average width of the plurality of first projections is W1 mm, 0.2≤W1≤5; optionally, 0.6≤W1≤2; further optionally, 1≤W1≤1.5, for example, the value of W1 can be 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5 or a range consisting of any two of these values; and, along the thickness direction of the first electrode, the shape of the second projection of a single second recess on the surface of the first material layer is strip-shaped, and along the length direction of the first electrode after it is unfolded, the average width of the plurality of second projections is W2. mm, 0.1≤W2≤6; optionally, 0.1≤W2≤3; further optionally, 0.2≤W2≤1, for example, the value of W2 can be 0.1, 0.15, 0.2, 0.4, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6 or a range of any two of these values. For example, such as... Figure 3 As shown, along the thickness direction (Z direction) of the first electrode 10, the first projection of a single first recess 121 on the surface of the first material layer 10 is strip-shaped. Along the length direction (X direction) of the first electrode 10 after it is unfolded, the average width of the multiple first projections is W1 mm. Similarly, along the thickness direction (Z direction) of the first electrode 10, the second projection of a single second recess 122 on the surface of the first material layer 12 is strip-shaped. Along the length direction (X direction) of the first electrode 10 after it is unfolded, the average width of the multiple second projections is W2 mm. By adjusting the values ​​of W1 and W2 within the aforementioned range, it is beneficial to reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode and excessive tensile stress leading to breakage of the outer electrode and the generation of burrs. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first and second recesses on the surface of the first electrode is moderate, reducing the risk of increased electrochemical impedance due to increased local aggregation of electrolyte side reactions. Therefore, while taking into account the production cost and capacity of the secondary battery, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0053] In one or more embodiments, a plurality of first recesses extend along the width direction of the first electrode after it is unfolded and are spaced apart along the length direction of the first electrode after it is unfolded. Based on the width of the first electrode after it is unfolded, the length ratio of a single first projection is L1, where 5% ≤ L1 ≤ 95%. For example, the value of L1 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range of any two of these values. By adjusting the value of L1 within the aforementioned range, it is beneficial to further reduce the safety risk of inner electrode collapse due to excessive extrusion pressure, and also to reduce the safety risk of outer electrode breakage and short circuit caused by excessive tensile stress. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first concave part on the surface of the first electrode is moderate, reducing the risk of increased electrochemical impedance due to increased local accumulation of electrolyte side reactions, and also reducing the risk of loss of active material and reduced energy density of the secondary battery due to excessive powder shedding during the processing of the first electrode. Therefore, while taking into account both actual production and energy density, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0054] In one or more embodiments, a plurality of second recesses extend along the width direction of the first electrode after it is unfolded and are spaced apart along the length direction of the first electrode after it is unfolded. Based on the width of the first electrode after it is unfolded, the length ratio of a single second projection is L2, where 10% ≤ L2 ≤ 95%. For example, the value of L2 can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range of any two of these values. By adjusting the value of L2 within the aforementioned range, it is beneficial to further reduce the safety risk of short circuits caused by the outer electrode sheet fracture and burr formation due to excessive tensile stress in the electrode assembly. It also reduces the safety risk of the inner electrode sheet collapsing due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the electrode sheet, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the second concave part on the surface of the first electrode sheet is moderate, reducing the risk of increased electrochemical impedance due to increased local aggregation of electrolyte side reactions. It also reduces the risk of loss of active material due to excessive powder shedding during the processing of the first electrode sheet, which leads to a decrease in the energy density of the secondary battery. Therefore, while taking into account both actual production and energy density, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0055] In one or more embodiments, a plurality of first recesses extend along the width direction of the first electrode sheet after it has been unfolded and are spaced apart along the length direction of the first electrode sheet after it has been unfolded. Based on the width of the first electrode sheet after it has been unfolded, the length ratio of a single first projection is L1, where 5% ≤ L1 ≤ 95%. For example, the value of L1 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any two of these values. The range of the composition; and, multiple second recesses extend along the width direction after the first electrode is unfolded and are spaced apart along the length direction after the first electrode is unfolded, based on the width after the first electrode is unfolded, the length ratio of a single second projection is L2, 10%≤L2≤95%, for example, the value of L2 can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a range of any two of these values. By adjusting the values ​​of L1 and L2 within the aforementioned range, it is beneficial to reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode and excessive tensile stress leading to breakage of the outer electrode and the generation of burrs. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the appropriate size of the first and second recesses on the surface of the first electrode reduces the risk of increased electrochemical impedance due to increased local aggregation of electrolyte and side reactions. It also reduces the risk of loss of active materials due to excessive powder shedding during the processing of the first electrode, which in turn reduces the energy density of the secondary battery. Therefore, while taking into account both actual production and energy density, the cylindrical secondary battery of this application has good safety and cycle performance.

[0056] In one or more embodiments, along the width direction after the first pole piece is unfolded, the length of a single first projection is L3 mm, 9≤L3≤150; optionally, 15≤L3≤80; further optionally, 20≤L3≤55. For example, the value of L3 can be 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150 or a range of any two of these values. By adjusting the value of L3 within the aforementioned range, it is beneficial to further reduce the safety risk of inner electrode collapse due to excessive extrusion pressure, and also to reduce the safety risk of outer electrode breakage and short circuit caused by excessive tensile stress. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first concave part on the surface of the first electrode is moderate, reducing the risk of increased electrochemical impedance due to increased local accumulation of electrolyte side reactions, and also reducing the risk of loss of active material and reduced energy density of the secondary battery due to excessive powder shedding during the processing of the first electrode. Therefore, while taking into account both actual production and energy density, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0057] In one or more embodiments, along the width direction after the first pole piece is unfolded, the length of a single second projection is L4 mm, 18≤L4≤180; optionally, 30≤L4≤100; further optionally, 50≤L4≤80. For example, the value of L4 can be 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, or a range of any two of these values. By adjusting the value of L4 within the aforementioned range, it is beneficial to further reduce the safety risk of short circuits caused by the outer electrode sheet fracture and burr formation due to excessive tensile stress in the electrode assembly. It also reduces the safety risk of the inner electrode sheet collapsing due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the electrode sheet, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the second concave part on the surface of the first electrode sheet is moderate, reducing the risk of increased electrochemical impedance due to increased local aggregation of electrolyte side reactions. It also reduces the risk of loss of active material due to excessive powder shedding during the processing of the first electrode sheet, which leads to a decrease in the energy density of the secondary battery. Therefore, while taking into account both actual production and energy density, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0058] In one or more embodiments, along the width direction after the first electrode sheet is unfolded, the length of a single first projection is L3 mm, where 9 ≤ L3 ≤ 150; optionally, 15 ≤ L3 ≤ 80; further optionally, 20 ≤ L3 ≤ 55. For example, the value of L3 can be 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, or a range consisting of any two of these values; and, along the width direction after the first electrode sheet is unfolded, the length of a single second projection is L4 mm. mm, 18≤L4≤180; optionally, 30≤L4≤100; further optionally, 50≤L4≤80, for example, the value of L4 can be 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180 or a range of any two of these values. For example, such as... Figure 3 As shown, along the width direction (Y direction) of the first electrode 10 after unfolding, the length of a single first projection is L3 mm, and the length of a single second projection is L4 mm. By adjusting the values ​​of L3 and L4 within the above range, it is beneficial to reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode and excessive tensile stress leading to breakage of the outer electrode and the generation of burrs. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first and second recesses on the surface of the first electrode is moderate, reducing the risk of increased electrochemical impedance due to increased local aggregation of electrolyte and side reactions. It also reduces the risk of loss of active material due to excessive powder shedding during the processing of the first electrode, which leads to a decrease in the energy density of the secondary battery. Therefore, while taking into account both actual production and energy density, the cylindrical secondary battery of this application has good safety performance and cycle performance.

[0059] In one or more embodiments, along the thickness direction of the first electrode, the first projection of a single first recess on the surface of the first material layer is strip-shaped. Along the width direction of the first electrode after it has been unfolded, the first material layer has two opposing edges, and the first recess extends from either of these edges along the width direction of the first electrode after it has been unfolded; or, the first recess is located between the two edges. In one or more embodiments, along the thickness direction of the first electrode, the second projection of a single second recess on the surface of the first material layer is strip-shaped. Along the width direction of the first electrode after it has been unfolded, the first material layer has two opposing edges, and the second recess extends from either of these edges along the width direction of the first electrode after it has been unfolded; or, the second recess is located between the two edges. In one or more embodiments, along the thickness direction of the first electrode, the first projection of a single first recess on the surface of the first material layer is strip-shaped, and there is an angle between the first recess and the unfolded length direction of the first electrode, the angle being 15° to 90°; and / or, along the thickness direction of the first electrode, the second projection of a single second recess on the surface of the first material layer is strip-shaped, and there is an angle between the second recess and the unfolded length direction of the first electrode, the angle being 15° to 90°. This configuration improves the uniformity of electrolyte distribution in the first electrode, resulting in high energy density in the secondary battery. It also improves the wetting performance of the electrolyte on the first electrode, increasing the electrolyte penetration efficiency. Furthermore, it reduces the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. Therefore, while meeting mass production manufacturability requirements, it improves the cycle performance and safety performance of the secondary battery.

[0060] In one or more embodiments, the first material layer is located on the surface of the first current collector facing the center of the electrode assembly winding. Exemplarily, such as... Figure 1 As shown, the first material layer 12 is located on the surface of the first current collector 11 facing the winding center of the electrode assembly 001. This configuration reduces the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode and excessive tensile stress causing breakage of the outer electrode and the generation of burrs, thus improving the cycle performance of the secondary battery while also considering the energy density and processing performance of the secondary battery.

[0061] In one or more embodiments, the first electrode further includes a second material layer located on the surface of the first current collector away from the winding center of the electrode assembly; the surface of the region of the second material layer opposite to the first region is provided with a plurality of first protrusions, at least some of the first protrusions being disposed opposite to some of the first recesses. This arrangement improves the operability of providing the first recesses and first protrusions on the first electrode, enhances the wetting performance of the electrolyte on the electrode, further reduces the safety risk of the inner electrode collapsing due to excessive extrusion pressure, and improves the safety and cycle performance of the cylindrical secondary battery while meeting mass production manufacturability requirements.

[0062] In one or more embodiments, the first electrode further includes a second material layer located on the surface of the first current collector away from the winding center of the electrode assembly; the surface of the region of the second material layer opposite to the second region is provided with a plurality of second protrusions, at least some of the second protrusions being disposed opposite to some of the second recesses. This arrangement improves the operability of providing the second recesses and second protrusions on the first electrode, enhances the wetting performance of the electrolyte on the electrode, and further reduces the safety risk of short circuits caused by excessive tensile stress leading to breakage of the outer electrode ring and the generation of burrs. While meeting the requirements for mass production manufacturability, it also improves the safety and cycle performance of the cylindrical secondary battery.

[0063] In one or more embodiments, the first electrode further includes a second material layer located on the surface of the first current collector away from the winding center of the electrode assembly; the surface of the region of the second material layer opposite to the first region is provided with a plurality of first protrusions, at least some of the first protrusions being disposed opposite to some of the first recesses; and the surface of the region of the second material layer opposite to the second region is provided with a plurality of second protrusions, at least some of the second protrusions being disposed opposite to some of the second recesses. Exemplarily, as... Figure 1 and Figure 4 As shown, the first electrode 10 also includes a second material layer 13, which is located on the surface of the first current collector 11 away from the winding center of the electrode assembly 001. The surface of the area of ​​the second material layer 13 opposite to the first region is provided with multiple first protrusions 131, which are opposite to the first recesses 121. The surface of the area of ​​the second material layer 13 opposite to the second region is provided with multiple second protrusions 132, which are opposite to the second recesses 122. This arrangement improves the operability of setting the first recesses, first protrusions, second recesses, and second protrusions on the first electrode, which is beneficial for improving the wetting performance of the electrolyte on the electrode. It also helps reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode and excessive tensile stress leading to breakage of the outer electrode and the generation of burrs. This improves the safety and cycle performance of the cylindrical secondary battery while meeting mass production manufacturability requirements.

[0064] In one or more embodiments, the region of the first current collector opposite the first region is provided with a plurality of third protrusions in the direction of the second material layer. This arrangement improves the operability of providing the first recess and third protrusions on the first electrode, enhances the wetting performance of the electrolyte on the electrode, and further reduces the safety risk of the inner electrode collapsing due to excessive extrusion pressure. While meeting the requirements for mass production manufacturability, it also improves the safety and cycle performance of the cylindrical secondary battery.

[0065] In one or more embodiments, the region of the first current collector opposite the second region is provided with a plurality of fourth protrusions in the direction of the second material layer. This arrangement improves the operability of providing the second recess and fourth protrusions on the first electrode, enhances the wetting performance of the electrolyte on the electrode, and further reduces the safety risk of short circuits caused by excessive tensile stress leading to breakage of the outer electrode ring and the generation of burrs. While meeting the requirements for mass production manufacturability, it also improves the safety and cycle performance of the cylindrical secondary battery.

[0066] In one or more embodiments, the region of the first current collector opposite to the first region is provided with a plurality of third protrusions in the direction toward the second material layer; and, the region of the first current collector opposite to the second region is provided with a plurality of fourth protrusions in the direction toward the second material layer. For example, as... Figure 1 and Figure 4 As shown, the area of ​​the first current collector 11 opposite to the first region is provided with a plurality of third protrusions 111 in the direction of the second material layer 13; and the area of ​​the first current collector 11 opposite to the second region is provided with a plurality of fourth protrusions 112 in the direction of the second material layer 13. Through the above arrangement, the operability of providing the first recess, third protrusion, second recess, and fourth protrusion on the first electrode sheet is improved, which is beneficial to improving the wetting performance of the electrolyte on the electrode sheet. It is also beneficial to further reduce the safety risks of short circuits caused by excessive extrusion pressure leading to collapse of the inner electrode sheet and excessive tensile stress leading to breakage of the outer electrode sheet and the generation of burrs. While meeting the requirements for mass production manufacturability, it improves the safety performance and cycle performance of the cylindrical secondary battery.

[0067] In one or more embodiments, at least a portion of the third protrusion corresponds to a portion of the first recess. This arrangement improves the operability of providing the first recess and the third protrusion on the first electrode, enhances the wetting performance of the electrolyte on the electrode, and further reduces the safety risk of the inner electrode collapsing due to excessive extrusion pressure. While meeting the requirements for mass production manufacturability, it also improves the safety and cycle performance of the cylindrical secondary battery.

[0068] In one or more embodiments, at least a portion of the fourth protrusion corresponds to a portion of the second recess. This arrangement improves the operability of providing the second recess and the fourth protrusion on the first electrode, enhances the wetting performance of the electrolyte on the electrode, and further reduces the safety risk of short circuits caused by excessive tensile stress leading to breakage of the outer electrode ring and the generation of burrs. While meeting the requirements for mass production manufacturability, it also improves the safety and cycle performance of the cylindrical secondary battery.

[0069] In one or more embodiments, at least a portion of the third protrusion corresponds to a portion of the first recess; and at least a portion of the fourth protrusion corresponds to a portion of the second recess. This arrangement improves the operability of providing the first recess, third protrusion, second recess, and fourth protrusion on the first electrode, enhances the wetting performance of the electrolyte on the electrode, and further reduces the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. While meeting mass production manufacturability requirements, it also improves the safety and cycle performance of the cylindrical secondary battery.

[0070] In one or more embodiments, the first electrode is a positive electrode. When the first electrode is a positive electrode, it helps to reduce the processing difficulty of the first electrode during the manufacturing process, reduces the risk of excessive powder shedding during the processing of the first electrode leading to loss of active materials and thus a decrease in the energy density of the secondary battery, and also helps to reduce the safety risks of the inner electrode collapsing due to excessive extrusion pressure and the outer electrode breaking due to excessive tensile stress, resulting in burrs and short circuits. At the same time, it improves the wetting effect of the electrolyte on the electrode, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the appropriate gap between the positive and negative electrodes and between the electrode layers during charging and discharging results in a smaller electrochemical impedance of the secondary battery, thereby further improving the safety and cycle performance of the secondary battery.

[0071] In this application, the first electrode can be a positive electrode, and in this case, the first current collector is a positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector can include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). In this case, both the first material layer and the second material layer are positive material layers. The positive material layer in this application includes a positive active material. This application does not impose any particular limitation on the type of positive active material, as long as it achieves the purpose of this application. For example, the positive active material can include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. This application does not particularly limit the type of positive electrode binder in the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the type of conductive agent in the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and positive electrode binder in the positive electrode material layer; those skilled in the art can select according to actual needs, as long as it can achieve the purpose of this application.

[0072] In this application, the first electrode can be a negative electrode, and in this case, the first current collector is a negative current collector. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. 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 composite current collectors (e.g., lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). In this case, both the first material layer and the second material layer are negative electrode material layers, and the negative electrode material layer in this application includes a negative electrode active material. This application does not impose any particular limitation on the type of negative electrode active material, as long as it achieves the purpose of this application. For example, the negative electrode active material can include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO₂, etc. x(0 < x < 2), at least one of Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O with spinel structure 12 , Li-Al alloy or metallic lithium. Optionally, the negative electrode material layer may further include a conductive agent and a negative electrode binder. There is no particular limitation on the type of the conductive agent in the negative electrode material layer in this application, as long as the object of this application can be achieved. For example, the conductive agent may be of the same type as the conductive agent in the above positive electrode material layer. There is no particular limitation on the type of the negative electrode binder in the negative electrode material layer in this application, as long as the object of this application can be achieved. For example, the negative electrode binder may be of the same type as the positive electrode binder in the above positive electrode material layer. There is no particular limitation on the mass ratio of the negative electrode active material, the conductive agent and the negative electrode binder in the negative electrode material layer in this application, as long as the object of this application can be achieved.

[0073] There is no particular limitation on the preparation method of the first electrode sheet in this application, as long as the object of this application can be achieved. For example, the preparation method of the first electrode sheet includes but is not limited to the following steps: (1) preparing a slurry; (2) coating the slurry on one surface of the first current collector and drying it to form an electrode sheet including the first material layer; (3) coating the slurry on the other surface of the first current collector and drying it to obtain the first electrode sheet including the first material layer and the second material layer; (4) cutting and slitting, etc., to obtain the first electrode sheet without the first recess and the second recess; (5) pre-winding the first electrode sheet, the prepared second electrode sheet and the separator in step (4), determining the radius of the central hole of the electrode assembly and the radius of the electrode assembly, and then along the radial direction of the pre-wound electrode assembly, according to the distance between the first region and the winding center of the electrode assembly and the distance between the second region and the winding center of the electrode assembly, confirming the first region and the second region of the first material layer, and setting the first recess on the surface of the first region and the second recess on the surface of the second region, thus obtaining the first electrode sheet.

[0074] This application does not impose any particular limitation on the solid content of the above-mentioned slurry. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the above-mentioned drying, cutting, and slitting process parameters. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved. In one or more embodiments, in step (5), when the first protrusion is provided on the first region, the surface of the region of the second material layer opposite to the first region is provided with the first protrusion in the direction of the first material layer. In one or more embodiments, in step (5), when the first recess is provided on the first region, the region of the first current collector opposite to the first region is provided with the third recess in the direction of the first material layer. In one or more embodiments, in step (5), when the second protrusion is provided on the second region, the surface of the region of the second material layer opposite to the second region is provided with the second protrusion in the direction of the first material layer. In one or more embodiments, in step (5), when the second recess is provided on the second region, the region of the first current collector opposite to the second region is provided with the fourth recess in the direction of the first material layer.

[0075] This application does not impose any particular restrictions on the method of setting the first concave portion, the second concave portion, the first convex portion, the second convex portion, the third convex portion, and the fourth convex portion. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the first electrode sheet can be cold-pressed by an embossing roller to set the first concave portion, the second concave portion, the first convex portion, the second convex portion, the third convex portion, and the fourth convex portion. The shape of the projection of a single first recess and a single second recess on the first material layer can be adjusted by the shape of the protrusion on the embossing roller; the average height H1 of multiple first recesses and the average height H2 of multiple second recesses can be adjusted by the cold pressing pressure value set on the embossing roller or the height specification of the protrusion on the embossing roller; the shortest distance d1 between the outer contours of two adjacent first projections and the shortest distance d2 between the outer contours of two adjacent second projections can be adjusted by the spacing of adjacent protrusions on the embossing roller; the diameter D1 of the maximum circumscribed circle of the outer contour of a single first projection and the diameter D1 of the maximum circumscribed circle of the outer contour of a single second projection can be adjusted by the specification of the protrusion on the embossing roller; the average width W1 of multiple first projections, the average width W2 of multiple second projections, the length ratio L1 of a single first projection, the length ratio L2 of a single second projection, the length L3 of a single first projection, and the length L4 of a single second projection can be adjusted by the specification of the protrusion on the embossing roller.

[0076] In one or more embodiments, the first current collector includes a coated region having a first material layer and an empty foil region connected to the coated region, with at least a portion of the empty foil region forming a flattened portion. This arrangement facilitates the placement of the tabs and the processing of the secondary battery, promotes high-rate charging and discharging of the secondary battery, reduces internal resistance and heat generation, and thereby improves the safety and cycle performance of the cylindrical secondary battery.

[0077] In this application, the different features of the first electrode sheet, including the provision of the first recess and the second recess, can be combined, and the implementation methods or embodiments covered by the above combinations are all within the protection scope of this application.

[0078] The cylindrical secondary battery of this application includes an electrolyte comprising a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not limit the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. This application does not particularly limit the non-aqueous solvent, as long as it achieves the purpose of this application. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate, or vinylene carbonate. Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1,2-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0079] This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane. The diaphragm of this application may have a porous structure, and this application does not impose any particular limitation on the size of the pores in the porous structure of the diaphragm, as long as it achieves the purpose of this application. For example, the pore size may be from 0.01 μm to 1 μm. This application does not impose any particular limitation on the thickness of the diaphragm, as long as it achieves the purpose of this application. For example, the thickness of the diaphragm may be from 5 μm to 40 μm.

[0080] The cylindrical secondary battery of this application also includes a casing for housing the positive electrode, negative electrode, separator, and electrolyte, as well as other components known in the art for cylindrical secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it can achieve the purpose of this application.

[0081] The cylindrical secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one or more embodiments, the cylindrical secondary battery may include, but is not limited to, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0082] This application does not impose any particular limitation on the preparation method of the cylindrical secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the cylindrical secondary battery includes, but is not limited to, the following steps: stacking the separator, negative electrode, separator and positive electrode in sequence, and winding and folding them as needed to obtain a wound electrode assembly; placing the electrode assembly into the housing; welding the current collector and assembling the insulating sheet; and then injecting the electrolyte into the housing and sealing it to obtain the cylindrical secondary battery.

[0083] A second aspect of this application provides an electronic device comprising the cylindrical secondary battery of any of the above embodiments. Thus, the electronic device of this application has excellent performance.

[0084] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0085] Example

[0086] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0087] Test methods and equipment:

[0088] Tests for c1, c2, H1, H2, T, D1, D2, d1, d2, W1, W2, L1, L2, L3, and L4:

[0089] At an ambient temperature of 25°C, the lithium-ion batteries of each embodiment and comparative example were discharged at 1C to 2.8V and then disassembled to obtain electrode assemblies. Observations were made along the planes formed in the width and thickness directions of the electrode assembly to identify two regions on the first material layer where concave and convex portions are formed. The distances between these two regions and the center point of the central hole of the electrode assembly were measured, along with the radius b of the central hole and the radius a of the electrode assembly. Positive and negative electrode sheets were removed from the electrode assembly and soaked in dimethyl carbonate (DMC) for 20 minutes. Then, the positive and negative electrode sheets were placed in an oven and dried at 80°C for 12 hours to obtain test samples of the positive and negative electrode sheets. By visual observation, the electrode sheet with a concave surface was identified as the target electrode sheet, and the material layer with the concave portion was identified as the first material layer. The first and second regions of the first material layer were determined based on the winding marks and the starting and ending points of the electrode sheet.

[0090] The surface of the electrode was observed using a scanning electron microscope (SEM). Specifically, the plane formed by the length and width directions of the unfolded electrode was measured along the thickness direction of the electrode. Due to the height difference between the depth of the recess and the surface of the material layer, a relatively obvious color difference can be seen on the surface of the electrode. The recess has a projection aperture on the surface of the electrode, which can be used to distinguish the recess from the first material layer.

[0091] When the projected apertures on the first region are distributed in a dotted pattern on the first material layer, select any 5 apertures and measure the maximum circumcircle diameter of the outer contour of each aperture. Take the average value, which is the diameter D1 of the maximum circumcircle of the outer contour of a single first projection. Along the length direction after the electrode is unfolded, select any 1 aperture and measure the shortest distance between the center of the maximum circumcircle of the outer contour of the single aperture and the outer contour of the adjacent aperture. Take 5 measurements and take the average value, which is the shortest distance d1 between the outer contours of two adjacent first projections.

[0092] When the shape of the projected aperture on the first region is strip-shaped, five apertures are randomly selected, and the width of each aperture is measured along the length direction after the electrode is unfolded. The average value is the average width W1 of the multiple first projections. Specifically, the width measurement of a single aperture includes dividing the aperture into 10 equal segments along the width direction after the electrode is unfolded, measuring the values ​​at both ends of each segment along the length direction after the electrode is unfolded, for a total of 11 values. The average value is the width of a single aperture. Along the width direction after the electrode is unfolded, five apertures are randomly selected, and the length of the first projection is measured. The average value is the length L3 of a single first projection. Simultaneously, the width of the unfolded first material layer is measured and compared with L3 to obtain the length ratio L1 of a single first projection based on the unfolded length of the first electrode.

[0093] The electrode with protrusions was ion polished along its length and thickness after being unfolded to obtain a cross-section of the electrode. The cross-section of the electrode was then measured using a scanning electron microscope (SEM).

[0094] Select any 5 first recesses in the first region, measure the maximum depth from the surface of the first material layer to the single first recess along the thickness direction of the electrode, and take the average value, which is the average depth H1 of the multiple first recesses.

[0095] Along the thickness direction of the electrode, select any 5 flat areas, measure the thickness of the electrode, and take the average value, which is the thickness T of the first electrode.

[0096] By measuring the second concave portion in the second region using the above testing method, we can obtain the average depth H2 of multiple second concave portions, the shortest distance d2 between the outer contours of two adjacent second projections, the diameter D2 of the largest circumcircle of the outer contour of a single second projection, or the average width W2 of multiple second projections, the length L4 of a single second projection, and the length ratio L2 of a single second projection based on the unfolded length of the first pole piece.

[0097] Cyclic performance test:

[0098] The lithium-ion batteries in the examples and comparative examples were subjected to charge-discharge cycle tests at 25°C. The lithium-ion batteries were charged at a constant current of 0.5C to 4.3V, then charged at a constant voltage of 4.3V to 0.05C. After resting for 10 minutes, they were discharged at a constant current of 1C to 2.8V. This was the first cycle, and the discharge capacity C1 of the first cycle was recorded. After 400 cycles following the above process, the discharge capacity C of the lithium-ion battery was recorded. 400 The capacity retention rate at 400 cycles is used as an indicator to evaluate the cycle performance of lithium-ion batteries, as shown in Equation (I). A lower capacity retention rate at 400 cycles (cls) indicates poorer cycle performance of the lithium-ion battery; a higher capacity retention rate at 400cls indicates better cycle performance of the lithium-ion battery.

[0099] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0100] Computed tomography (CT) scan and electrode indentation distance test:

[0101] Using industrial computed tomography (industrial CT, Zeiss Xradia 620 Versa), CT scans were performed on the lithium-ion batteries in the above-mentioned embodiments and comparative examples after the "cycle performance test" along the width direction (or the axis of the electrode assembly) after the electrode assembly was unfolded, to observe the number of electrode collapse cycles and the number of electrode breakage cycles of each electrode assembly in the lithium-ion battery.

[0102] Example 1-1

[0103] <Preparation of Negative Electrode Sheets>

[0104] Artificial graphite, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 97.7:1.3:1. Deionized water was then added as a solvent, and the mixture was stirred until homogeneous, yielding a negative electrode slurry with a solid content of 50 wt%. This slurry was uniformly coated onto one surface of a 10 μm thick copper foil current collector and dried at 105 °C to obtain a negative electrode sheet with a single-sided coating of the negative electrode material. The same steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode material. After cold pressing, cutting, laser cleaning, and tab welding, a negative electrode sheet with dimensions of 210.5 mm × 2700 mm was obtained for later use. The coating weight of the negative electrode material layer was 340 mg / 1540.25 mm. 2 The dimensions of the negative electrode material layer are 194.5mm×2700mm, and the thickness of the negative electrode sheet after cold pressing is 140μm.

[0105] <Preparation of the diaphragm>

[0106] 8μm thick polyethylene (PE) was selected as the diaphragm substrate, and ceramic particles of alumina (Al2O3) and styrene-butadiene rubber (Mw = 7 × 10⁻⁶) were used as the binder. 6 The ceramic coating slurry was prepared by mixing deionized water and solvent in a mass ratio of 35:10:55. Polyvinylidene fluoride (PVDF, Mw = 8.5 × 10⁻⁶) was then added as the binder. 6 ) and thickener sodium carboxymethyl cellulose (Mw = 8 × 10) 5 The following materials were mixed at a mass ratio of 98.5:1.5, with deionized water added as a solvent. After stirring evenly, a bonding layer slurry with a solid content of 75 wt% was formed. A ceramic coating slurry was applied to one surface of the substrate and dried at 60°C, forming a ceramic coating on that surface. The bonding layer slurry was then applied to the surface of the substrate away from the ceramic coating and dried at 60°C, resulting in a diaphragm with a single-sided ceramic coating and bonding layer. The above steps were then repeated on the other surface of the substrate to obtain the diaphragm. The thickness of the single-sided ceramic coating was 2 μm, and the coating weight of the single-sided bonding layer was 2.5 mg / 5000 m³. 2 .

[0107] <Preparation of the positive electrode>

[0108] The first electrode is the positive electrode, which combines the positive electrode active material (LiMn2O4) and lithium nickel cobalt manganese oxide (LiNi). 0.91 Co 0.05 Mn 0.04 O2, conductive carbon black, and polyvinylidene fluoride (PVDF) binder are dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 58:38:2:2 and thoroughly mixed to obtain a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry is uniformly coated onto one surface of a 15 μm thick aluminum foil current collector and dried at 105 °C to obtain a positive electrode sheet coated with the first material layer. The above steps are then repeated on the other surface of the same aluminum foil to obtain a positive electrode sheet coated with both the first and second material layers. Alumina and PVDF are dissolved in N-methylpyrrolidone (NMP) solution at a weight ratio of 90:10 to obtain a ceramic slurry with a solid content of 60 wt%. A layer of ceramic slurry is coated along the edge near the positive electrode material layer on the empty foil area of ​​the positive electrode current collector to obtain a protective coating. After drying, cold pressing, and cutting, the positive electrode sheet is obtained. Among them, the positive current collector that is close to the cutting point and coated with a protective coating is retained, while the positive current collector that is not coated with a protective coating serves as the tab.

[0109] The positive electrode, separator, prepared negative electrode, and another separator are stacked and wound together. After winding, the radius b of the center hole of the electrode assembly is determined to be 3.17 mm, and the radius a of the electrode assembly is determined to be 16.29 mm. Then, along the radial direction of the electrode assembly, a first region and a second region of the first material layer are determined. The first region is located in the first material layer at a distance of 2.9b ≤ c1 ≤ 3.5b from the winding center of the electrode assembly, and the second region is located in the first material layer at a distance of 0.96a ≤ c2 ≤ 0.98a from the winding center of the electrode assembly. Configuration: Multiple first recesses are provided in the first region, and multiple second recesses are provided in the second region. Based on the surface area of ​​the first material layer, the ratio S of the sum of the areas of the first region and the second region is 13.68%. The average depth H1 of the multiple first recesses is 11.2 μm, and the average depth H2 of the multiple second recesses is 11.2 μm. Along the thickness direction of the first electrode, each first recess has a first projection on the surface of the first material layer, and the first projection is circular. Each second recess has a second projection on the surface of the first material layer, and the second projection is circular. The diameter D1 of the maximum circumscribed circle of the outer contour of each first projection is 3 mm, the diameter D2 of the maximum circumscribed circle of the outer contour of each second projection is 3 mm, the shortest distance d1 between the outer contours of two adjacent first projections is 3 mm, and the shortest distance d2 between the outer contours of two adjacent second projections is 1 mm.

[0110] The positive electrode sheet is cold-pressed using an embossing roller of appropriate specifications according to the above parameters. After cutting and slitting, a positive electrode sheet with a first concave portion, a second concave portion, a first convex portion, a second convex portion, a third convex portion, and a fourth convex portion is obtained. The coating weight of the first and second material layers is 600.5 mg / 1540.25 mm. 2 The positive electrode sheet has a size of 200.5mm × 2650mm, the first material layer has a size of 192.5mm × 2650mm, the second material layer has the same size as the first material layer, the thickness T of the first electrode sheet is 140μm, and the protective coating has a size of 2mm × 2650mm.

[0111] <Preparation of Electrolyte>

[0112] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC) and propylene carbonate (PC) were mixed at a weight ratio of 50:50 to obtain a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent and mixed thoroughly to obtain the electrolyte. The concentration of LiPF6 was 1.15 mol / L.

[0113] <Preparation of Lithium-ion Batteries>

[0114] The separator, negative electrode, and positive electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to form the electrode assembly. The tabs of the electrode assembly are flattened and then welded with current collectors. The electrode assembly is then encapsulated in a steel casing, dehydrated at 80°C, and injected with the aforementioned electrolyte. After formation and sealing pin welding, a lithium-ion battery is obtained.

[0115] Examples 1-2 to 1-29

[0116] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1. Specifically, when the thickness of the first electrode changes, the thickness of the first current collector remains unchanged, and the coating weight is adjusted so that the thickness T of the first electrode is as shown in Table 1. In Examples 1-4 and 1-5, as the value of T changes, the values ​​of a and b change accordingly. In Examples 1-4, the radius b of the central hole of the electrode assembly is 4.3 mm, and the radius a of the electrode assembly is 16.67 mm; in Examples 1-5, the radius b of the central hole of the electrode assembly is 2.9 mm, and the radius a of the electrode assembly is 16.61 mm.

[0117] Examples 2-1 to 2-7

[0118] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-1.

[0119] Comparative Example 1

[0120] Except for the fact that no recesses are provided on the surface of the first material layer in the <Preparation of Positive Electrode Sheet>, the rest is the same as in Example 1-1.

[0121] Comparative Example 2

[0122] Except for the fact that in the <Preparation of Positive Electrode Sheet> only a first recess is provided on the surface of the first material layer in a region from a distance of b to 5.14b from the winding center of the electrode assembly, the rest is the same as in Example 1-1.

[0123] Comparative Example 3

[0124] Except for the fact that in the <Preparation of Positive Electrode Sheet>, only a second recess is provided on the surface of the first material layer in the region from a distance of 0.19a to a from the winding center of the electrode assembly, the rest is the same as in Example 1-1.

[0125] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0126]

[0127]

[0128] Note: " / " in Table 1 indicates that there are no relevant preparation or result parameters.

[0129] As can be seen from Examples 1-1 to 1-29 and Comparative Examples 1 to 3, by setting the first and second recesses on the surfaces of different numbers of rings in the first material layer, the number of electrode collapse rings and electrode breakage rings is reduced, and the 400cls capacity retention rate of the lithium-ion battery is improved. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner ring electrode collapse and excessive tensile stress leading to outer ring electrode breakage and burr formation. The lithium-ion battery has good cycle performance. In Comparative Example 1, no recesses are provided on the first material layer. The lithium-ion battery in Comparative Example 1 has more electrode collapse cycles and more electrode breakage cycles, and the 400cls capacity retention rate of the lithium-ion battery is lower. In Comparative Example 2, all areas of the first material layer are provided with first recesses, and in Comparative Example 3, all areas of the first material layer are provided with second recesses. In Comparative Examples 2 and 3, by providing recesses in all areas of the first material layer, the gap between electrode layers increases, the impedance of the lithium-ion battery increases, the resistance to ion conduction during cycling is greater, the 400cls capacity retention rate is also lower, and the cycle performance of the lithium-ion battery decreases. At the same time, excessive contact between the electrolyte and the electrode leads to a relatively increase in the side reactions of the lithium-ion battery. The increase in side reaction products leads to an increase in electrode thickness and corresponding increase in electrode hardness. Consequently, the improvement effect on the safety risks of inner electrode collapse due to excessive extrusion pressure and outer electrode breakage and short circuit due to excessive tensile stress is poor. The lithium-ion batteries in Examples 1-1 to 1-29 have fewer electrode collapse cycles and fewer electrode breakage cycles, and a higher 400cls capacity retention rate. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery has good cycle performance and safety performance.

[0130] The value of S typically affects the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-5, when the value of S is within the range of this application, the number of electrode collapse cycles and electrode breakage cycles is low, and the 400cls capacity retention rate is high. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery exhibits good cycle performance and safety performance.

[0131] The values ​​of T, H1 / T×100%, and H2 / T×100% typically affect the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-4 to 1-11, when the values ​​of T, H1 / T×100%, and H2 / T×100% are within the range of this application, the number of electrode collapse cycles and electrode breakage cycles is low, and the 400cls capacity retention rate is high. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery exhibits good cycle performance and safety performance.

[0132] The H1 / H2 ratio typically affects the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-12 to 1-17, when the H1 / H2 ratio is within the range of this application, the number of electrode collapse cycles and electrode breakage cycles is low, and the 400cls capacity retention rate is high. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery exhibits good cycle performance and safety performance.

[0133] The values ​​of d1 and d2 typically affect the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-18 to 1-23, when the values ​​of d1 and d2 are within the range of this application, the number of electrode collapse cycles and electrode breakage cycles is low, and the 400cls capacity retention rate is high. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery exhibits good cycle performance and safety performance.

[0134] The values ​​of D1 and D2 typically affect the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-24 to 1-29, when the values ​​of D1 and D2 are within the range of this application, the number of electrode collapse cycles and electrode breakage cycles is low, and the 400cls capacity retention rate is high. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery exhibits good cycle performance and safety performance.

[0135] Table 2

[0136]

[0137] Note: “ / ” in Table 2 indicates that there are no relevant preparation or result parameters.

[0138] The values ​​of W1 and W2 typically affect the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-7, when the values ​​of W1 and W2 are within the range of this application, the number of electrode collapse cycles and electrode breakage cycles is low, and the 400cls capacity retention rate is high. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery exhibits good cycle performance and safety performance.

[0139] The values ​​of L1 and L2 typically affect the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-7, when the values ​​of L1 and L2 are within the range of this application, the number of electrode collapse cycles and electrode breakage cycles is low, and the 400cls capacity retention rate is high. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery exhibits good cycle performance and safety performance.

[0140] The values ​​of L3 and L4 typically affect the cycle performance and safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-7, when the values ​​of L3 and L4 are within the range of this application, the number of electrode collapse cycles and electrode breakage cycles is low, and the 400cls capacity retention rate is high. This indicates that the lithium-ion battery of this application can effectively reduce the safety risks of short circuits caused by excessive extrusion pressure leading to inner electrode collapse and excessive tensile stress leading to outer electrode breakage and burr formation. The lithium-ion battery exhibits good cycle performance and safety performance.

[0141] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0142] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0143] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A cylindrical secondary battery comprising an electrode assembly of a wound structure, the electrode assembly comprising a center hole with a radius of b mm, and a radius of the electrode assembly of a mm, 15 ≤ a ≤ 20; the electrode assembly comprising a first tab comprising a first current collector and a first material layer on one surface of the first current collector, the first material layer comprising, in order along a winding direction of the electrode assembly, a first region and a second region; wherein along a radial direction of the electrode assembly, the first region being located at a distance of c1 mm from a winding center of the electrode assembly, 1.5b ≤ c1 ≤ 5.5b, and a surface of the first region being provided with a plurality of first recesses; along the radial direction, the second region being located at a distance of c2 mm from the winding center of the electrode assembly, 0.8a ≤ c2 ≤ a, and a surface of the second region being provided with a plurality of second recesses, 0.8a > 5.5b, and a surface of a region located at a distance of 5.5b mm to 0.8a mm from the winding center of the electrode assembly being free of the first recesses or the second recesses; a proportion of a sum of areas of the first region and the second region based on a surface area of the first material layer being S, 2% ≤ S ≤ 55%. 2.The cylindrical secondary battery according to claim 1, satisfying at least one of the following characteristics: (1) 1.5b ≤ c1 ≤ 4b; (2) 0.9a ≤ c2 ≤ 1a. 3.The cylindrical secondary battery according to claim 1, satisfying at least one of the following characteristics: (1) 2.9b ≤ c1 ≤ 3.5b; (2) 0.96a ≤ c2 ≤ 0.98a.

4. The cylindrical secondary battery according to claim 1, wherein 10%≤S≤20%。 5. The cylindrical secondary battery according to claim 1, wherein 12%≤S≤18%。 6. The cylindrical secondary battery according to claim 1, wherein along a thickness direction of the first tab, a thickness of the first tab being T μm, 60 ≤ T ≤ 450; an average depth of the plurality of first recesses being H1 μm, 1.5% ≤ H1 / T × 100% ≤ 35%; and / or, an average depth of the plurality of second recesses being H2 μm, 1.5% ≤ H2 / T × 100% ≤ 35%. 7.The cylindrical secondary battery according to claim 6, satisfying at least one of the following characteristics: (1) 3% ≤ H1 / T × 100% ≤ 15%; (2) 3% ≤ H2 / T × 100% ≤ 15%. 8.The cylindrical secondary battery according to claim 6, satisfying at least one of the following characteristics: (1) 5% ≤ H1 / T × 100% ≤ 10%; (2) 5% ≤ H2 / T × 100% ≤ 10%.

9. The cylindrical secondary battery according to claim 6, wherein 0.1 ≤ H1 / H2 ≤ 5.

10. The cylindrical secondary battery according to claim 9, wherein 0.2 ≤ H1 / H2 ≤ 3.

11. The cylindrical secondary battery according to claim 9, wherein 0.3 ≤ H1 / H2 ≤ 1.

5.

12. The cylindrical secondary battery according to claim 1, wherein along the thickness direction of the first tab, a single one of the first recesses having a first projection on a surface of the first material layer, along a length direction of the first tab after being developed, a shortest distance between outer contours of two adjacent ones of the first projections being d1 mm, 0.1 ≤ d1 ≤ 15; and / or, In the thickness direction of the first pole piece, a single second recess has a second projection on the surface of the first material layer, and the shortest distance between the outer contours of two adjacent second projections in the length direction of the first pole piece after being developed is d2 mm, 0.1≤d2≤10.

13. The cylindrical secondary battery according to claim 12, which satisfies at least one of the following characteristics: （1）0.5≤d1≤8； （2）0.3≤d2≤5。 14. The cylindrical secondary battery according to claim 12, which satisfies at least one of the following characteristics: （1）1≤d1≤5； （2）0.5≤d2≤2。 15. The cylindrical secondary battery according to claim 1, wherein The plurality of first recesses or the plurality of second recesses are distributed in a dot shape on the surface of the first material layer, in the thickness direction of the first pole piece, a single first recess has a first projection on the surface of the first material layer in a circular, elliptical or regular polygonal shape, and the diameter of the largest circumscribed circle of the outer contour of the single first projection is D1 mm, 0.2≤D1≤5; and / or, In the thickness direction of the first pole piece, a single second recess has a second projection on the surface of the first material layer in a circular, elliptical or regular polygonal shape, and the diameter of the largest circumscribed circle of the outer contour of the single second projection is D2 mm, 0.1≤D2≤6.

16. The cylindrical secondary battery according to claim 15, which satisfies at least one of the following characteristics: （1）0.5≤D1≤4.5； （2）0.2≤D2≤5.5。 17. The cylindrical secondary battery according to claim 15, which satisfies at least one of the following characteristics: （1）1≤D1≤4； （2）0.5≤D2≤5。 18. The cylindrical secondary battery according to claim 1, wherein In the thickness direction of the first pole piece, a single first recess has a first projection on the surface of the first material layer in a strip shape, and the average width of the plurality of first projections in the length direction of the first pole piece after being developed is W1 mm, 0.2≤W1≤5; and / or, In the thickness direction of the first pole piece, a single second recess has a second projection on the surface of the first material layer in a strip shape, and the average width of the plurality of second projections in the length direction of the first pole piece after being developed is W2 mm, 0.1≤W2≤6.

19. The cylindrical secondary battery according to claim 18, which satisfies at least one of the following characteristics: （1）0.6≤W1≤2； （2）0.1≤W2≤3。 20. The cylindrical secondary battery according to claim 18, which satisfies at least one of the following characteristics: （1）1≤W1≤1.5； （2）0.2≤W2≤1。 21. The cylindrical secondary battery according to claim 18, wherein The plurality of first recesses extend in the width direction of the first pole piece after being developed and are arranged at intervals in the length direction of the first pole piece after being developed, and the length ratio of a single second projection based on the width of the first pole piece after being developed is L1, 5%≤L1≤95%; and / or, The plurality of second recesses extend in the width direction of the first pole piece after being developed and are arranged at intervals in the length direction of the first pole piece after being developed, and the length ratio of a single second projection based on the width of the first pole piece after being developed is L2, 10%≤L2≤95%.

22. The cylindrical secondary battery according to claim 21, wherein In the width direction of the first pole piece after being developed, the length of a single first projection is L3 mm, 9≤L3≤150; and / or, in the width direction of the first pole piece after being developed, the length of a single second projection is L4 mm, 18≤L4≤180.

23. The cylindrical secondary battery according to claim 22, which satisfies at least one of the following characteristics: （1）15≤L3≤80； （2）30≤L4≤100。 24. The cylindrical secondary battery according to claim 22, which satisfies at least one of the following characteristics: （1）20≤L3≤55； （2）50≤L4≤80。 25. The cylindrical secondary battery according to claim 1, wherein the first material layer is located on a surface of the first current collector facing the winding center of the electrode assembly.

26. The cylindrical secondary battery according to claim 25, wherein the first tab further comprises a second material layer located on a surface of the first current collector facing away from the winding center of the electrode assembly, a surface of a region of the second material layer opposite the first region is provided with a plurality of first protrusions, at least part of the first protrusions are arranged opposite part of the first recesses; and / or, a surface of a region of the second material layer opposite the second region is provided with a plurality of second protrusions, at least part of the second protrusions are arranged opposite part of the second recesses.

27. The cylindrical secondary battery according to claim 26, wherein the first current collector is provided with a plurality of third protrusions in a direction toward the second material layer at a region opposite the first region; and / or, the first current collector is provided with a plurality of fourth protrusions in a direction toward the second material layer at a region opposite the second region.

28. The cylindrical secondary battery according to claim 27, wherein at least part of the third protrusions correspond to part of the first recesses; and / or, at least part of the fourth protrusions correspond to part of the second recesses.

29. The cylindrical secondary battery according to any one of claims 1 to 28, wherein the first tab is a positive electrode tab.

30. An electronic device comprising the cylindrical secondary battery according to any one of claims 1 to 29.

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