Cylindrical secondary battery and electronic device

Abstract

The invention provides a cylindrical secondary battery and an electronic device, a second pole piece comprises a first section and a second section connected with the first section along a winding direction of an electrode assembly, and the second section is a part of the second pole piece exceeding a first winding starting end surface along a direction opposite to the winding direction; the second section is provided with a first position connected with the first section on the surface facing the winding center of the electrode assembly, and the volume of the second section is Acm3; the volume of a first cylinder formed by rotating 360 degrees from the first position by taking the winding center as the center of the cylinder in the opposite direction of the winding direction is B cm < 3 >, 40% < = A / B < = 90%, and 0.45 < = B < = 7.8. Through the arrangement, the energy density of the cylindrical secondary battery is considered, and meanwhile, the mechanical safety performance of the cylindrical secondary battery after circulation is improved.

Description

Technical Field

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

[0002] Cylindrical secondary batteries, such as cylindrical lithium-ion batteries, have the characteristics of high specific energy, high operating voltage, low self-discharge rate, small size, and light weight. After cycling, the electrode assembly of the cylindrical secondary battery will expand. After the electrode assembly contacts the battery casing, the electrode assembly continues to expand, squeezing the battery casing. Conversely, the electrode assembly will also receive a reaction force from the battery casing, squeezing and deforming the stress concentration points of the electrode assembly. This can cause the inner ring of the electrode assembly to collapse, posing a safety risk to the cylindrical secondary battery.

[0003] In the prior art, by reducing the diameter of the electrode assembly, the speed at which the electrode assembly expands and contacts the battery case is slowed down, thereby reducing the reaction force received by the electrode assembly after contact with the battery case. However, reducing the diameter of the electrode assembly will lead to a decrease in the energy density of the cylindrical secondary battery. Summary of the Invention

[0004] The purpose of this application is to provide a cylindrical secondary battery and an electronic device that improves the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the cylindrical secondary battery. The specific technical solution is as follows:

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

[0006] The first aspect of the present application provides a cylindrical secondary battery, comprising an electrode assembly of a wound structure, wherein the electrode assembly comprises a first electrode sheet, a second electrode sheet, and a diaphragm, wherein the diaphragm is disposed between the first electrode sheet and the second electrode sheet, and wherein the first electrode sheet has a first winding starting end face. Along the winding direction of the electrode assembly, the second electrode sheet comprises a first section and a second section connected to the first section, and along the opposite direction of the winding direction, the second section is a portion of the second electrode sheet extending beyond the winding starting end face, and the second section has a first position connected to the first section on a surface facing the winding center of the electrode assembly, and the volume of the second section is Acm 3 Along the radial direction of the electrode assembly, the first position is closer to the winding center than the first winding starting end face. In the opposite direction of the winding direction, the volume of the first cylinder formed by rotating 360° from the first position with the winding center as the center of the cylinder is B cm 3 , 40%≤A / B≤90%, 0.45≤B≤7.8, preferably, 0.5≤B≤1.2.

[0007] This application regulates the volume of the second-segment support structure by adjusting the A / B range, thereby increasing the support strength of the second-segment support structure on the winding center of the electrode assembly, reducing the degree of deformation caused by compression at the stress concentration point of the electrode assembly, and improving the mechanical safety performance of the cylindrical secondary battery after cycling. Furthermore, regulating the range of the ratio of the volume of the second segment to the volume of the aforementioned column can reduce the risk of reduced energy density due to an excessively large volume share of the support structure in the electrode assembly. In this way, the mechanical safety performance of the cylindrical secondary battery after cycling can be improved while taking into account the energy density of the secondary battery.

[0008] In one or more embodiments of the present application, the diameter of the first cylinder is D1 mm, the second section has a second winding starting end face, and the diameter of the second cylinder formed by winding one circle starting from the second winding starting end face along the winding direction is D2 mm, 1.5≤D2≤10, preferably, 1.5≤D2≤3; 0.5≤D2 / D1≤0.94, preferably, 0.72≤D2 / D1≤0.84. By adjusting D2 and D2 / D1 within the above ranges, it is beneficial to adjust the diameter of the second cylinder formed by winding one circle starting from the second winding starting end face of the second section, and adjust the ratio of the diameter of the second cylinder to the diameter of the cylinder formed by winding one circle along the winding direction of the electrode assembly from the winding starting end face of the electrode assembly, thereby adjusting the diameter of the support structure formed by the second section, reducing the risk of insufficient support of the electrode assembly due to a too small diameter of the support structure, and reducing the risk of a low energy density of the secondary battery due to an excessively large diameter of the support structure. While taking into account the energy density of the secondary battery, the mechanical safety performance of the cylindrical secondary battery after cycling is improved.

[0009] In one or more embodiments of the present application, the number of windings of the second section is N, 1≤N≤10, preferably, 3≤N≤6. By regulating the value of N within the above range, the number of windings of the second section is moderate, reducing the risk of insufficient support for the electrode assembly due to too few windings of the second section, and reducing the risk of too many windings of the second section leading to a lower energy density of the secondary battery. While taking into account the energy density of the secondary battery, the mechanical safety performance of the cylindrical secondary battery after cycling is improved.

[0010] In one or more embodiments of the present application, the second section includes a first hollow foil region. Along the winding direction of the electrode assembly, the length of the first hollow foil region is L1 mm, the length of the material layer in the second section is L2 mm, and 20% ≤ L1 / (L1 + L2) ≤ 70%. By regulating the ratio of the length of the hollow foil region in the second section to the length of the material layer in the second section, the support strength of the second section for the electrode assembly is increased, thereby improving the mechanical safety performance of the cylindrical secondary battery after cycling.

[0011] In one or more embodiments of the present application, the starting section of the first pole piece includes a second empty foil area. Along the winding direction of the electrode assembly, the length of the second empty foil area is L3 mm. From the first winding starting end face, the length of the first pole piece wound one circle along the winding direction of the electrode assembly is L4 mm, and 20% ≤ L3 / L4 ≤ 30%. By regulating the ratio of the length of the empty foil area of ​​the first pole piece to the length of the first pole piece wound one circle along the winding direction of the electrode assembly, the support structure formed by the empty foil area of ​​the first pole piece can also support the electrode assembly, thereby improving the supporting strength of the empty foil area of ​​the first pole piece to the electrode assembly. In addition, by regulating the length of the empty foil area of ​​the first pole piece, the risk of causing the secondary battery energy density to be too low is reduced. While taking into account the energy density of the secondary battery, the mechanical safety performance of the cylindrical secondary battery after cycling is improved.

[0012] In one or more embodiments of the present application, the second section does not have a first empty foil area. Providing the second section including a material layer is beneficial for improving the supporting strength of the support structure formed by the second section for the electrode assembly while taking into account the energy density of the secondary battery.

[0013] In one or more embodiments of the present application, the second pole piece includes a second material layer, the second material layer includes a second active material, the second active material includes silicon, and based on the second material layer, the percentage of silicon is W, 0.5%≤W≤10%, preferably, 2%≤W≤10%. By regulating the silicon content in the second material layer, it is beneficial to regulate the degree of expansion of the electrode assembly of the cylindrical secondary battery in the later stage of the cycle of the cylindrical secondary battery, reduce the shell pressure applied to the electrode assembly after expansion, and thereby reduce the degree of indentation of the inner ring of the electrode assembly, thereby improving the mechanical safety performance of the cylindrical secondary battery in the later stage of the cycle. In addition, regulating the silicon content of the second material layer to a moderate level can improve the mechanical safety performance of the cylindrical secondary battery after the cycle while taking into account the energy density of the secondary battery.

[0014] In one or more embodiments of the present application, the second pole piece includes a second current collector, and the yield strength of the second current collector is σMPa, 200≤σ≤700, preferably, 300≤σ≤500. By regulating the yield strength of the second current collector, the risk of current collector fracture due to excessively high yield strength and low plasticity is reduced, and the risk of insufficient support strength due to excessively low yield strength is reduced. This is conducive to improving the support strength of the support structure formed by the second section for the electrode assembly, and is conducive to improving the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the secondary battery.

[0015] In one or more embodiments of the present application, the first electrode sheet is a positive electrode sheet, and the second electrode sheet is a negative electrode sheet. By regulating the range of the ratio of the volume of the support structure of the second section on the negative electrode sheet to the volume of the column formed by winding one circle from the winding starting end face of the electrode assembly along the winding direction of the electrode assembly, the support strength of the negative electrode current collector to the winding center of the electrode assembly is improved, the degree of deformation caused by compression at the stress concentration point of the electrode assembly is reduced, and the mechanical safety performance of the cylindrical secondary battery after cycling is improved. In addition, regulating the range of the ratio of the volume of the second section to the volume of the above-mentioned column is conducive to reducing the risk of reduced energy density due to excessive volume share of the support structure in the electrode assembly, and is conducive to improving the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the secondary battery.

[0016] A second aspect of the present application provides an electronic device comprising the cylindrical secondary battery of any of the aforementioned embodiments. The cylindrical secondary battery of the present application not only takes into account the secondary battery energy density but also has good mechanical safety performance after cycling of the cylindrical secondary battery. Therefore, the electronic device of the present application has a long service life.

[0017] Beneficial effects of the embodiments of the present application:

[0018] The embodiments of the present application regulate the volume of the second-segment support structure by adjusting the range of A / B, thereby increasing the support strength of the second-segment support structure on the winding center of the electrode assembly, reducing the degree of deformation caused by compression at the stress concentration point of the electrode assembly, and improving the mechanical safety performance of the cylindrical secondary battery after cycling. Furthermore, regulating the range of the ratio of the volume of the second segment to the volume of the aforementioned column can reduce the risk of reduced energy density due to an excessively large volume share of the support structure in the electrode assembly, thereby improving the mechanical safety performance of the cylindrical secondary battery after cycling while maintaining the energy density of the secondary battery.

[0019] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 A schematic diagram of a wound structure formed by an electrode assembly in one embodiment of the present application;

[0022] Figure 2A schematic diagram of a wound structure formed by an electrode assembly in another embodiment of the present application;

[0023] Figure 3 This is a computed tomography (CT) image of the inner ring electrode of a cylindrical lithium-ion battery in the late stage of cycling in the prior art.

[0024] Reference numerals: electrode assembly 100 ; diaphragm 30 ; first pole piece 10 ; first current collector 11 ; first material layer 12 ; second pole piece 20 ; second current collector 21 ; second material layer 22 . DETAILED DESCRIPTION

[0025] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0027] After the cylindrical secondary battery is cycled, the electrode assembly of the cylindrical secondary battery will expand. After the electrode assembly contacts the secondary battery shell, the battery assembly will be squeezed by the secondary battery shell, that is, the electrode assembly will be subjected to the reaction force of the secondary battery shell, and the stress concentration point of the electrode assembly will be squeezed and deformed. The squeezing force is transmitted inward to the innermost circle through the electrode piece. The innermost circle electrode piece releases stress by indentation, but the indented electrode piece causes a safety risk to the cylindrical secondary battery. If the diameter of the electrode assembly is reduced, although the speed at which the electrode assembly contacts the secondary battery shell after expansion can be slowed down, and the reaction force received by the electrode assembly after contacting the secondary battery shell can be reduced, reducing the diameter of the electrode assembly will lead to a decrease in the energy density of the cylindrical secondary battery. Therefore, the present application provides a cylindrical secondary battery that can improve the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the cylindrical secondary battery. The specific technical solution is as follows:

[0028] The first aspect of the present application provides a cylindrical secondary battery, comprising an electrode assembly of a wound structure, wherein the electrode assembly comprises a first electrode sheet, a second electrode sheet, and a diaphragm, wherein the diaphragm is disposed between the first electrode sheet and the second electrode sheet, and wherein the first electrode sheet has a first winding starting end face. Along the winding direction of the electrode assembly, the second electrode sheet comprises a first section and a second section connected to the first section, and along the opposite direction of the winding direction, the second section is a portion of the second electrode sheet extending beyond the winding starting end face, and the second section has a first position connected to the first section on a surface facing the winding center of the electrode assembly, and the volume of the second section is Acm 3Along the radial direction of the electrode assembly, the first position is closer to the winding center than the first winding starting end face. Along the winding direction, the volume of the first cylinder formed by rotating 360° from the first position with the winding center as the center of the cylinder is B cm 3 , 40%≤A / B≤90%, 0.45≤B≤7.8, preferably, 0.5≤B≤1.2. For example, the value of B can be 0.45, 0.47, 0.5, 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.2, 7.5, 7.6, 7.7, 7.8, or a range consisting of any two of these values. The value of A / B can be 40%, 43%, 46%, 50%, 53%, 56%, 60%, 63%, 66%, 70%, 73%, 76%, 80%, 83%, 86%, 90%, or a range consisting of any two of these values.

[0029] For example, Figure 1 As shown, the first electrode sheet 10 is a positive electrode sheet, the second electrode sheet 20 is a negative electrode sheet, and the electrode assembly 100 is formed by stacking and winding a separator 30, a negative electrode sheet, a separator 30, and a positive electrode sheet. The first electrode sheet 10 includes a first current collector 11 and a first material layer 12 disposed on both surfaces of the first current collector 11. The second electrode sheet 20 includes a second current collector 21 and a second material layer 22 disposed on both surfaces of the second current collector 21. Figure 1 The first electrode sheet 10 of the electrode assembly 100 shown in FIG is a positive electrode sheet, the second electrode sheet 20 is a negative electrode sheet, point G is the first position, point H is the position of the first winding starting end face, and Figure 1 In the case shown, the first position is closer to the winding center than the first winding starting end face. Then, along the winding direction, starting from the first position and rotating 360° to the cross section of the cylinder surrounded by the first winding starting end face is as follows: Figure 1 In addition, Figure 2 A schematic diagram of the winding structure of an electrode assembly is shown, in which the first electrode sheet 10 is a negative electrode sheet and the second electrode sheet 20 is a positive electrode sheet.

[0030] When the value of B is too small, for example, less than the lower limit of this application, the support strength at the winding center of the electrode assembly is low, resulting in low mechanical safety performance of the cylindrical secondary battery after cycling. When the value of B is too large, for example, greater than the upper limit of this application, the uniformity of the support structure formed by the second segment may be reduced. When the electrode assembly is impacted by external force, stress will be concentrated in a specific area, for example, the stress will be concentrated in the first position, which may easily cause the second electrode sheet to break or wrinkle, resulting in low mechanical safety performance of the cylindrical secondary battery after cycling. In addition, when the value of B is greater than the upper limit of this application, the effective portion of the electrode assembly accounts for too small a proportion, resulting in low energy density of the secondary battery. When the value of A / B is too small, for example, less than the lower limit of this application, the volume of the second segment of the second electrode sheet at the winding center of the electrode assembly used to support the electrode assembly accounts for a small proportion, and the support strength provided by the second segment is low, resulting in low mechanical safety performance of the cylindrical secondary battery after cycling. When the value of A / B is too large, for example, greater than the upper limit of this application, the volume of the second segment accounts for a large proportion, resulting in low energy density of the secondary battery.

[0031] The present application adjusts the volume of the support structure of the second section by adjusting the range of A / B, thereby increasing the support strength of the support structure of the second section to the winding center of the electrode assembly, reducing the degree of deformation caused by compression at the stress concentration point of the electrode assembly, and improving the mechanical safety performance of the cylindrical secondary battery after cycling. In addition, adjusting the range of the ratio of the volume of the second section to the volume of the above-mentioned column can reduce the risk of a reduction in energy density due to an excessively large volume share of the support structure in the electrode assembly, and can improve the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the secondary battery. In the present application, the second section refers to the portion of the second electrode sheet that extends beyond the starting end face of the first winding, such as Figure 1 In the figure, the second section is the portion of the negative electrode sheet from point G in the opposite direction of the winding direction to the starting end face of the negative electrode sheet. The second section may include only the portion of the empty foil area in the second electrode sheet, the second section may include the portion of the material layer in the second electrode sheet and the portion of the empty foil area, or the second section may include the portion of the material layer in the second electrode sheet, that is, no empty foil area is provided in the second section.

[0032] In one or more embodiments of the present application, the diameter of the first cylinder is D1 mm, the second section has a second winding starting end face, and the diameter of the second cylinder formed by winding one circle from the second winding starting end face along the winding direction is D2 mm, 1.5≤D2≤10, preferably, 1.5≤D2≤3, for example, the value of D2 can be 1.5, 1.8, 2, 2.3, 2.6, 3, 3.3, 3.6, 4, 4.3, 4.6, 5, 5.3, 5.6, 6, 6.3, 6.6, 7, 7.3, 7.6, 8, 8.3, 8.6, 9, 9.3, 9.6, 10 or a range consisting of any two values ​​thereof; 0.5≤D2 / D1≤0.94, preferably, 0.72≤D2 / D1≤0.84, for example, the value of D2 / D1 can be 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94 or a range consisting of any two values ​​thereof. By regulating D2 and D2 / D1 within the above range, it is beneficial to regulate the size of the diameter of the second column formed by winding one circle from the second winding starting end face of the second section, and to regulate the ratio of the diameter of the second column to the diameter of the column formed by winding one circle from the winding starting end face of the electrode assembly along the winding direction of the electrode assembly, thereby regulating the diameter of the support structure formed by the second section, reducing the risk of insufficient support for the electrode assembly due to the small diameter of the support structure, and reducing the risk of low energy density of the secondary battery due to excessive diameter of the support structure, thereby improving the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the secondary battery.

[0033] In one or more embodiments of the present application, the number of winding turns of the second segment is N, 1≤N≤10, preferably, 3≤N≤6, for example, the value of N can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two values ​​therein. Wherein, the second segment of each circle refers to one end of the second segment as the starting point, and one end wound in the opposite direction of the winding direction of the electrode assembly is the end point, and the starting point and the end point are flush in the thickness direction of the electrode assembly. In the present application, the starting point of the second segment of the first circle is the first position, and so on. The second segment of each circle hereinafter can also refer to the above definition. By regulating the value of N within the above range, the number of winding turns of the second segment is moderate, avoiding the risk of insufficient support for the electrode assembly due to too few winding turns of the second segment, and at the same time reducing the risk of too many winding turns of the second segment leading to a lower energy density of the secondary battery, while taking into account the energy density of the secondary battery, the mechanical safety performance of the cylindrical secondary battery after cycling is improved.

[0034] In one or more embodiments of the present application, the second section includes a first hollow foil area, and along the winding direction of the electrode assembly, the length of the first hollow foil area is L1 mm, the length of the material layer in the second section is L2 mm, and 20%≤L1 / (L1+L2)≤70%. For example, the value of L1 / (L1+L2) can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70% or a range consisting of any two values ​​therein. By regulating the ratio of the length of the hollow foil area in the second section to the length of the material layer in the second section, it is beneficial to improve the supporting strength of the second section to the electrode assembly and improve the mechanical safety performance of the cylindrical secondary battery after cycling.

[0035] In one or more embodiments of the present application, the starting section of the first electrode sheet includes a second empty foil area. Along the winding direction of the electrode assembly, the length of the second empty foil area is L3 mm. Starting from the first winding starting end face, the length of the first electrode sheet wound one circle along the winding direction of the electrode assembly is L4 mm. 20%≤L3 / L4≤30%. For example, the value of L3 / L4 can be 20%, 23%, 25%, 26%, 28%, 30%, or a range consisting of any two values ​​therein. By regulating the ratio of the length of the empty foil area of ​​the first electrode sheet to the length of the first electrode sheet wound one circle along the winding direction of the electrode assembly, the support structure formed by the empty foil area of ​​the first electrode sheet also supports the electrode assembly, thereby improving the supporting strength of the empty foil area of ​​the first electrode sheet to the electrode assembly. In addition, regulating the length of the empty foil area of ​​the first electrode sheet is beneficial to reducing the risk of too low energy density of the secondary battery, while taking into account the energy density of the secondary battery, and improving the mechanical safety performance of the cylindrical secondary battery after cycling.

[0036] In one or more embodiments of the present application, the second section does not have a first empty foil area. Providing the second section including a material layer is beneficial for improving the supporting strength of the support structure formed by the second section for the electrode assembly while taking into account the energy density of the secondary battery.

[0037] In one or more embodiments of the present application, the second electrode includes a second material layer, the second material layer includes a second active material, the second active material includes silicon, and based on the second material layer, the percentage of silicon is W, 0.5%≤W≤10%, preferably, 2%≤W≤10%, for example, the value of W can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two values ​​therein. By regulating the silicon content in the second material layer, it is beneficial to regulate the degree of expansion of the electrode assembly of the cylindrical secondary battery in the later stage of the cycle of the cylindrical secondary battery, reduce the shell pressure applied to the electrode assembly after expansion, and thereby reduce the degree of indentation of the inner ring of the electrode assembly, thereby improving the mechanical safety performance of the cylindrical secondary battery after cycling. In addition, regulating the silicon content of the second material layer to a moderate level can improve the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the secondary battery.

[0038] In one or more embodiments of the present application, the second active material includes a silicon-based material, which includes at least one of a silicon-carbon composite material, a silicon-oxygen composite material, or pure silicon. By selecting such a second active material, the post-cycling expansion of the cylindrical secondary battery can be reduced, thereby improving the structural stability of the electrode assembly and enhancing the mechanical safety of the cylindrical secondary battery after cycling.

[0039] The present application has no particular restrictions on the silicon-carbon composite material, as long as the purpose of the present application can be achieved. Based on the mass of the silicon-carbon composite material, the mass percentage of the silicon element is 30% to 70%, and the mass percentage of the carbon element is 30% to 70%. For example, the silicon-carbon composite material can be a composite material obtained by deposition. Exemplarily, the silicon-carbon composite material can be a silicon material deposited on a carbon skeleton, or a carbon material deposited on a silicon skeleton. The silicon-oxygen composite material includes SiOx, wherein 0<x<2. Exemplarily, the silicon-oxygen composite material can include silicon monoxide (SiO, the molar ratio of silicon and oxygen is 1:1).

[0040] In one or more embodiments of the present application, the second active material further comprises at least one of artificial graphite or natural graphite. By selecting such a second active material, the post-cycling expansion of the cylindrical secondary battery can be reduced, thereby improving the structural stability of the electrode assembly and enhancing the mechanical safety of the cylindrical secondary battery after cycling.

[0041] In the present application, the mass percentage of silicon element can be controlled by adjusting the proportion of silicon-based material in the second material layer.

[0042] In one or more embodiments of the present application, the second pole piece includes a second current collector, and the yield strength of the second current collector is σMPa, 200≤σ≤700, preferably, 300≤σ≤500, for example, the value of σ can be 200, 220, 250, 280, 300, 320, 350, 380, 400, 420, 450, 480, 500, 520, 550, 580, 600, 620, 650, 680, 700 or a range consisting of any two values ​​therein. By regulating the yield strength of the second current collector, the risk of current collector fracture due to excessively high current collector yield strength and low plasticity is reduced, and the risk of insufficient support strength due to too low current collector yield strength is reduced, which is conducive to improving the support strength of the support structure formed by the second section to the electrode assembly, thereby improving the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the secondary battery.

[0043] This application does not specifically limit the method for controlling the yield strength, as long as it can achieve the objectives of this application. For example, second current collectors with different yield strengths can be selected and combined with the "σ test" method in this application to determine the yield strength of the second current collector, and then select the second current collector with the desired yield strength.

[0044] In one or more embodiments of the present application, the first electrode sheet is a positive electrode sheet, and the second electrode sheet is a negative electrode sheet. By controlling the range of the ratio of the volume of the support structure of the second section on the negative electrode sheet to the volume of the column formed by winding one circle from the winding starting end face of the electrode assembly along the winding direction of the electrode assembly, the support strength of the negative electrode current collector to the winding center of the electrode assembly is improved, the degree of deformation caused by compression at the stress concentration point of the electrode assembly is reduced, and the mechanical safety performance of the cylindrical secondary battery after cycling is improved. In addition, regulating the range of the ratio of the volume of the second section to the volume of the above-mentioned column is conducive to reducing the risk of reduced energy density due to excessive volume of the support structure in the electrode assembly, thereby improving the mechanical safety performance of the cylindrical secondary battery after cycling while taking into account the energy density of the secondary battery.

[0045] In one or more embodiments of the present application, the thickness of the second current collector is C μm, 4 ≤ C ≤ 15, preferably 6 ≤ C ≤ 10. For example, the value of C can be 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two of these values. By regulating the thickness of the second current collector within the above range, the support strength of the second segment of the second pole piece can be increased, thereby improving the mechanical safety performance of the cylindrical secondary battery after cycling.

[0046] In the present application, when the first electrode sheet is a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector. The positive electrode material layer can be arranged on one surface of the positive electrode current collector along the thickness direction of itself, or on two surfaces of the positive electrode current collector along the thickness direction of itself. It should be noted that the "surface" here refers to the coating area of ​​the positive electrode current collector where the negative electrode material layer is provided. The present application has no special restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode material layer of the present application contains a positive electrode active material. The present application has no special restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganate, lithium iron manganese phosphate or lithium titanate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, for example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine or sulfur. In the present application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. The present application has no special restrictions on the type of positive electrode binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the mass ratio of the positive active material, conductive agent and positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0047] In the present application, when the second electrode sheet is a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. The negative electrode material layer can be provided on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here refers to the coating area of ​​the negative electrode current collector where the negative electrode material layer is provided. The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or a composite current collector (such as a lithium copper composite current collector, a carbon copper composite current collector, a nickel copper composite current collector, a titanium copper composite current collector, etc.). Optionally, the negative electrode material layer may also include a conductive agent and a negative electrode binder. The present application has no particular restrictions on the type of conductive agent in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent can be the same as the conductive agent in the above-mentioned positive electrode material layer. The present application does not particularly limit the type of negative electrode binder in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the negative electrode binder can be the same type as the positive electrode binder in the positive electrode material layer described above. The present application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, and negative electrode binder in the negative electrode material layer, as long as the purpose of the present application can be achieved.

[0048] The present application does not impose any particular restrictions on the method for preparing the first electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the electrode sheet includes but is not limited to the following steps: (1) preparing a first slurry; (2) coating the slurry on one surface of the first current collector, and drying to obtain a first electrode sheet with a first material layer on one side; (3) coating the slurry on the other surface of the first current collector, and drying to obtain a electrode sheet with a first material layer on both sides; (4) predetermining the first winding starting end face and starting section of the first electrode sheet, and determining the second empty foil area of ​​the first electrode sheet; (5) after cold pressing the sheet into strips, determining the coating area of ​​the first current collector with the first material layer and the second empty foil area along the width direction of the unfolded first electrode sheet, thereby obtaining the first electrode sheet.

[0049] In the present application, the values ​​of L3 / L4 can be controlled by regulating the length of the area where the first slurry is coated on the surface of the first current collector and the length of the starting section of the first pole piece. The present application has no particular restrictions on the solid content of the above-mentioned first slurry, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the temperature and time of the above-mentioned drying, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the process parameters of the above-mentioned cold pressing and slitting, as long as the purpose of the present application can be achieved.

[0050] The present application does not impose any particular restrictions on the method for preparing the second electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the electrode sheet includes but is not limited to the following steps: (1) preparing a second slurry; (2) coating the slurry on one surface of the second current collector, and drying to obtain a electrode sheet with a second material layer on one side; (3) coating the slurry on the other surface of the second current collector, and drying to obtain a second electrode sheet with a second material layer on both sides; (4) pre-determining the first section, the second section, and the first position of the second electrode sheet, and determining the first empty foil area in the second section and the material layer in the second section; (5) after cold-pressing the sheet into strips, determining the coating area of ​​the second current collector with the second material layer and the first empty foil area along the width direction of the unfolded second electrode sheet, thereby obtaining the second electrode sheet.

[0051] In the present application, the value of L1 / L2 can be controlled by regulating the length of the area where the second slurry is coated on the surface of the second current collector and the length of the second section of the second pole piece. The present application has no particular restrictions on the solid content of the above-mentioned second slurry, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the temperature and time of the above-mentioned drying, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the process parameters of the above-mentioned cold pressing and slitting, as long as the purpose of the present application can be achieved.

[0052] The cylindrical secondary battery in the present application includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), lithium bis(trifluoromethanesulfonylimide) (LiTFSI) or lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. Above-mentioned linear carbonate compound can include but not limited to at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate or methyl ethyl carbonate.Above-mentioned cyclic carbonate can include but not limited to at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate or vinyl ethylene carbonate.Fluorinated carbonate compound can include but not limited to at least one of fluoroethylene carbonate, 1,2-difluoro ethylene carbonate, 1,1-difluoro ethylene carbonate, 1,1,2-trifluoro ethylene carbonate, 1,1,2,2-tetrafluoro ethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate or trifluoromethyl ethylene carbonate. The carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone or caprolactone. The ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The 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-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0053] The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. The diaphragm of the present application may have a porous structure. The present application has no particular restrictions on the size of the pore size of the porous structure of the diaphragm, as long as the purpose of the present application can be achieved. For example, the size of the pore size can be 0.01 μm to 1 μm. The present application has no particular restrictions on the thickness of the diaphragm, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm can be 5 μm to 40 μm.

[0054] The cylindrical secondary battery of the present application also includes a housing for accommodating the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte, as well as other components of cylindrical secondary batteries known in the art. This application does not limit these other components. This application does not specifically limit the housing and can be any housing known in the art, as long as it can achieve the purpose of this application.

[0055] The cylindrical secondary battery of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In one or more embodiments of the present application, the cylindrical secondary battery may include, but is not limited to, a lithium-ion secondary battery (lithium-ion battery), a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0056] The present application does not impose any particular restrictions on the preparation method of a cylindrical secondary battery, and any preparation method known in the art may be selected as long as the purpose of the present application can be achieved. For example, the preparation method of a cylindrical secondary battery includes, but is not limited to, the following steps: stacking a diaphragm, a first electrode, a diaphragm, and a second electrode in sequence, ensuring that the diaphragm is located between the second electrode and the first electrode, and along the thickness direction of the electrode, aligning a predetermined first position in the second electrode with the first winding starting end face of the first electrode, winding the second section of the second electrode, and then starting to feed the first electrode for normal winding, and flattening and welding it as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting an electrolyte into the shell and sealing it to obtain a cylindrical secondary battery.

[0057] In the present application, when winding, the second section is wound first, and then the stacked diaphragm, first electrode piece, diaphragm and second electrode piece are wound. By controlling the length of the second section and the number of winding turns N of the second section, the value of A, the value of A / B, and the value of D2 can be adjusted; by controlling the diameter of the winding needle used during winding and the length of the second section, the value of B and the value of D1 can be adjusted; the length of the second section can be adjusted by the difference in length of the second electrode piece wound earlier than the first electrode piece during winding.

[0058] A second aspect of the present application provides an electronic device comprising a cylindrical secondary battery according to any of the aforementioned embodiments. The cylindrical secondary battery of the present application has good mechanical safety performance after cycling while taking into account the secondary battery energy density. Therefore, the electronic device of the present application has a long service life.

[0059] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0060] Example

[0061] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0062] Test methods and equipment:

[0063] Tests for A, N, B, D1, and D2:

[0064] At an ambient temperature of 25°C, industrial computed tomography (industrial CT, Zeiss Xradia620Versa) was used to perform a CT scan of the electrode assembly in the wound structure along the width direction of the electrode assembly after it was unfolded. The image obtained by the computed tomography scan can be used to observe the radial cross-section of the electrode assembly in the lithium-ion battery. The average thickness of the second section is multiplied by the width after unfolding to obtain the volume A of the second section. The number of windings N of the second section is measured. In the radial direction of the electrode assembly, when the first position is closer to the winding center than the starting end face of the first winding, the diameter of the first cylinder formed by rotating 360° from the first position with the winding center as the center of the cylinder is repeatedly measured 5 times, and the average value is taken to obtain the diameter D1 of the first cylinder. Calculate π×(D1 / 2) 2 × q to obtain the volume B of the first cylinder, where q is the width of the electrode assembly after unfolding. Measure the diameter of the second cylinder formed by winding one turn along the winding direction starting from the starting end of the second winding. Repeat this measurement five times. The average of the five measurements is the diameter of the second cylinder, which is D2.

[0065] L1, L2, L3, L4 testing:

[0066] Determine the second section of the second pole piece that exceeds the first winding starting end face, and measure the length of the first empty foil area in the unfolded second section from the second winding starting end face of the second section along the winding direction of the electrode assembly, which is L1, and measure the length of the material layer in the second section of the unfolded second pole piece, which is L2.

[0067] The length of the second empty foil area of ​​the unfolded first electrode sheet, measured from the first winding starting end face of the first electrode sheet along the winding direction of the electrode assembly, is L3. The length of the first electrode sheet wound one turn along the winding direction of the electrode assembly from the first winding starting end face is L4.

[0068] W's test:

[0069] The lithium-ion battery was discharged at 0.5C to 2.5V, and the lithium-ion battery was disassembled. The center position of the second pole piece along the length direction and the width direction after the second pole piece was unfolded was determined. A length of 60 mm along the length direction and a length of 50 mm along the width direction after the second pole piece was unfolded were measured. A rectangle centered on the above center position was determined. Twelve sample discs with a radius of 7 mm were taken from the above rectangle. The silicon percentage was measured using an inductively coupled plasma (ICP) device. The average silicon percentage of the 12 sample discs was calculated as W.

[0070] σ test:

[0071] The lithium-ion battery was disassembled, and the second electrode in the lithium-ion battery was removed. The second material layer on the second electrode was scrubbed with deionized water to obtain a second current collector. The yield strength of the second current collector was tested according to "YB / T 4334-2013 Metal Foil Tensile Test Method at Room Temperature" and "GB / T 228-2010 Metallic Materials Tensile Test Part 1: Room Temperature Test Method" to obtain the yield strength of the second current collector, which is σ.

[0072] Pole piece indentation distance test:

[0073] The lithium-ion battery was subjected to a charge and discharge cycle test at an ambient temperature of 25°C. The charge and discharge voltage range was 2.5V to 4.2V. The battery was charged to 4.2V at a constant current of 2C, then charged to 0.05C at a constant voltage of 4.2V and left to stand for 5 minutes. The battery was then discharged to 2.5V at a constant current of 6C. The above charge and discharge process was repeated 600 times. After the lithium-ion battery was fully charged, industrial computed tomography (industrial CT, Zeiss Xradia 620Versa) was used to perform a CT scan of the electrode assembly of the wound structure along the radial direction of the electrode assembly. The distance from the position where the electrode assembly is sunken to the position where the innermost electrode sheet has the largest sunken distance is the sunken distance. Figure 3 As shown, the distance between point E and point F is the pole piece indentation distance.

[0074] Impact test:

[0075] After charging the lithium-ion battery at a constant current of 2C to 4.2V, charge it at a constant voltage of 0.05C to reach full charge. Place the fully charged lithium-ion battery on the test bench. Place a round rod with a diameter of 15.8mm and a length of at least 6cm at the center of the wide face of the lithium-ion battery. Wait until the longitudinal axis of the lithium-ion battery is parallel to the test bench surface and perpendicular to the longitudinal axis of the round rod. Use a 9.1kg weight to drop the battery vertically from a height of 610mm onto the intersection of the round rod and the lithium-ion battery.

[0076] Test pass criteria: pass if there is no fire or explosion.

[0077] Twenty lithium-ion batteries were tested in each example or comparative example, and the impact pass rate of the lithium-ion battery = the number of batteries that passed / 20. A higher impact pass rate, i.e., a higher number of batteries that passed, indicates better mechanical properties of the lithium-ion battery.

[0078] Energy density test:

[0079] First, the mass of the lithium-ion battery is measured to obtain the mass M of the lithium-ion battery.

[0080] Then charge the lithium-ion battery according to the following operating procedures, and then discharge it to obtain the discharge capacity E of the lithium-ion battery:

[0081] Charging: Charge at 3C constant current to 4.2V, then charge at 4.2V constant voltage to 0.05C;

[0082] Discharge: Discharge at a constant current of 0.2C to 2.5V, and obtain the discharge energy E.

[0083] The energy density (ED) of a lithium-ion battery can be calculated using the following formula: ED (Wh / kg) = E / M.

[0084] Example 1

[0085] <Preparation of positive electrode sheet>

[0086] The first electrode is the positive electrode, which is made of lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and are fully stirred and mixed to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 105°C to obtain a positive electrode sheet coated with a single-sided positive electrode material layer. The above steps are then repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with a double-sided positive electrode material layer. The first winding starting end face and starting section of the positive electrode sheet are predetermined, and the second empty foil area of ​​the positive electrode sheet is determined. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 105°C for 4h to obtain a positive electrode sheet with a size of 66.5mm×1422mm, wherein the coating weight of the positive electrode material layer is 206mg / 1540.25mm 2 The thickness of the positive electrode sheet after cold pressing is 120μm.

[0087] <Preparation of negative electrode sheet>

[0088] The second electrode sheet is the negative electrode. The negative electrode active materials, artificial graphite, SiO, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR), are mixed in a mass ratio of 87:10:1.7:1.3. Deionized water is then added as a solvent and the mixture is stirred to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry is evenly coated on one surface of an 8μm-thick negative electrode current collector copper foil and dried at 105°C to obtain a negative electrode sheet coated on one side with a negative electrode material layer. The above steps are then repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. The first and second sections, as well as the first position of the negative electrode sheet are pre-determined. The first empty foil area in the second section and the material layer in the second section are also determined. The sheet is then cold pressed, cut, and slit to obtain a negative electrode sheet with dimensions of 67.45 mm x 1470 mm. Among them, the coating weight of the negative electrode material layer is 94mg / 1540.25mm 2 The thickness of the negative electrode sheet after cold pressing is 100 μm. The mass percentage W of silicon element in the negative electrode material layer of the negative electrode sheet is 6%.

[0089] <Diaphragm>

[0090] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0091] <Preparation of Electrolyte>

[0092] In a dry argon atmosphere glove box, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 to create a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent and thoroughly mixed to create an electrolyte. The mass percentage of LiPF6 in the electrolyte was 12.5%, with the remainder being the base solvent.

[0093] <Preparation of lithium-ion batteries>

[0094] The diaphragm, negative electrode sheet, diaphragm, and positive electrode sheet prepared above are stacked in order, and pre-wound first to ensure that the diaphragm is between the negative electrode and the positive electrode. Along the thickness direction of the electrode sheet, the predetermined first position in the negative electrode sheet is opposite to the first winding starting end face of the positive electrode sheet, and the second section of the negative electrode sheet is wound 5.5 times, that is, N is 5.5. Then the positive electrode sheet begins to be fed and wound normally, followed by flattening, current collecting plate welding, shell insertion, bottom penetration welding, coding, vacuum drying, electrolyte injection, cap welding, sealing, high-temperature standing, formation capacity, etc., to obtain a lithium-ion battery. Among them, the formation upper limit voltage is 3.6V, the formation temperature is 45°C, and after formation, it is left to stand at room temperature of 25°C for 24 hours.

[0095] Example 2 to Example 21

[0096] Except for adjusting the relevant preparation parameters according to Table 1 and Table 2, the rest is the same as Example 1.

[0097] Example 22 to Example 26

[0098] Except for adjusting the relevant preparation parameters according to Tables 1 and 2, the rest is the same as Example 1. Specifically, when the mass percentage W of the silicon element in the second material layer of the second electrode sheet changes, the mass percentages of sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) remain unchanged, and the mass percentages of the negative electrode active material artificial graphite and SiO material are adjusted so that the value of W is as shown in Table 1.

[0099] Example 27 to Example 30

[0100] Except for adjusting the relevant preparation parameters according to Table 1 and Table 2, the rest is the same as Example 1.

[0101] Example 31

[0102] Except for preparing the positive electrode sheet and the negative electrode sheet according to the following steps, the rest is the same as Example 1.

[0103] <Preparation of positive electrode sheet>

[0104] The second electrode is the positive electrode, which contains the positive electrode active material lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and are fully stirred and mixed to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 105°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. The above steps are then repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer. The first section, second section and first position of the positive electrode sheet are predetermined, and the first empty foil area in the second section and the material layer in the second section are determined. Then, after cold pressing, cutting and slitting, it is dried under vacuum conditions at 105°C for 4h to obtain a 66.5mm×1578.78mm positive electrode sheet. Among them, the coating weight of the positive electrode material layer is 206mg / 1540.25mm 2 , the thickness of the positive electrode sheet after cold pressing is 120μm.

[0105] <Preparation of negative electrode sheet>

[0106] The first electrode sheet is the negative electrode sheet. The negative electrode active material artificial graphite, SiO material, sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 87:10:1.7:1.3, and then deionized water is added as a solvent and stirred to mix evenly to obtain a negative electrode slurry with a solid content of 50wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm and dried at 105°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. Thereafter, the above steps are repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer.

[0107] The first winding starting end face and starting section of the negative electrode sheet are determined in advance, and the second empty foil area of ​​the negative electrode sheet is determined. Then, after cold pressing, cutting and slitting, a 67.45mm×1434.98mm negative electrode sheet is obtained, wherein the coating weight of the negative electrode material layer is 94mg / 1540.25mm 2 The thickness of the negative electrode sheet after cold pressing is 46 μm, and the mass percentage of silicon element in the negative electrode material layer of the negative electrode sheet is 6%.

[0108] Comparative Examples 1 to 3

[0109] Except for adjusting the preparation parameters according to Table 1 and Table 2, the rest is the same as Example 1.

[0110] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0111]

[0112]

[0113]

[0114] From Examples 1 to 31 and Comparative Examples 1 to 3, it can be seen that by adjusting the values ​​of A / B and B within the scope of this application, the electrode sheet indentation distance is small, the lithium-ion battery impact test pass rate is improved, the electrode assembly has good rigidity, and the battery energy density of the lithium-ion battery is high. In this way, while taking into account the energy density of the lithium-ion battery, the mechanical safety performance of the lithium-ion battery is high. The values ​​of A / B or B in Comparative Examples 1 to 3 are not within the scope of this application. In Comparative Examples 1 and 3, the rigidity of the electrode assembly is poor, the deformation of the electrode assembly is large during the impact test, and the impact test pass rate is low. In this case, the mechanical safety performance of the lithium-ion battery is poor. The energy density in Comparative Example 2 is low and does not meet actual production requirements. In Comparative Example 2, although the electrode sheet indentation distance is small, because the value of B is greater than the upper limit of this application, the uniformity of the second section support structure is reduced, and the electrode assembly is prone to stress concentration when subjected to external force impact, which in turn causes the second electrode sheet to break or wrinkle, resulting in a low impact test pass rate and low mechanical safety performance of the lithium-ion battery. In Examples 1 to 31, the lithium-ion batteries have a high energy density and a high impact test pass rate, indicating that the lithium-ion batteries of the present application have good mechanical safety performance while taking into account the energy density of the lithium-ion batteries.

[0115] The A / B ratio generally affects the energy density and mechanical safety performance of lithium-ion batteries. As can be seen from Examples 1, 12, and 13, when the A / B ratio is within the specified range, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high, indicating that the lithium-ion battery of the present application maintains a high energy density while also having good mechanical safety performance.

[0116] The value of B typically affects the energy density and mechanical safety performance of lithium-ion batteries. As can be seen from Examples 1 to 11, Examples 14 to 16, Examples 21, and Example 31, when the value of B is within the specified range, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high, indicating that the lithium-ion battery of the present application maintains high energy density while also having good mechanical safety performance.

[0117] The value of D2 typically affects the energy density and mechanical safety performance of lithium-ion batteries. As can be seen from Examples 1, 5 to 7, 10, 11, and 14 to 16, when the value of D2 is within the specified range, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high, indicating that the lithium-ion battery of the present application maintains a high energy density while also having good mechanical safety performance.

[0118] The D2 / D1 ratio typically affects the energy density and mechanical safety of lithium-ion batteries. As can be seen from Examples 1 to 12, 14 to 16, and 21, when the D2 / D1 ratio is within the specified range, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high. This demonstrates that the lithium-ion battery of this application maintains high energy density while also exhibiting good mechanical safety.

[0119] The value of N typically affects the energy density and mechanical safety performance of lithium-ion batteries. As can be seen from Examples 1 to 12, and Examples 14 to 16, when the value of N is within the specified range, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high. This demonstrates that the lithium-ion batteries of this application maintain high energy density while also exhibiting good mechanical safety performance.

[0120] The value of L1 / (L1+L2) generally affects the energy density and mechanical safety performance of lithium-ion batteries. As can be seen from Examples 1, 17, and 18, when the value of L1 / (L1+L2) is within the application range, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high, indicating that the lithium-ion battery of the present application has good mechanical safety performance while maintaining a high energy density.

[0121] The L3 / L4 ratio generally affects the energy density and mechanical safety performance of lithium-ion batteries. As can be seen from Examples 1, 19, and 20, when the L3 / L4 ratio is within the specified range, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high. This demonstrates that the lithium-ion battery of the present application maintains high energy density while also having good mechanical safety performance.

[0122] The value of W typically affects the energy density and mechanical safety performance of lithium-ion batteries. As can be seen from Examples 6 and 22 to 26, when the value of W is within the specified range, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high, indicating that the lithium-ion battery of the present application maintains high energy density while also having good mechanical safety performance.

[0123] The value of σ generally affects the mechanical safety performance of lithium-ion batteries. As can be seen from Examples 6, 27, and 30, the pole piece indentation distance is small and the impact test pass rate is high. Moreover, as the yield strength increases, the support strength of the support structure formed by the second section increases, which can reduce the pole piece indentation distance. However, correspondingly, as the yield strength continues to increase, the current collector in the support structure formed by the second section becomes brittle and its plasticity decreases. Therefore, the impact test pass rate of Example 30 shows a downward trend relative to the impact test pass rates of Examples 27 to 29. When the value of σ is within the application range, it is beneficial to improve the mechanical safety performance of lithium-ion batteries.

[0124] The polarity of the first and second pole pieces typically affects the energy density and mechanical safety performance of lithium-ion batteries. As can be seen from Examples 1, 6, and 31, when the second pole piece is the negative pole piece, the pole piece indentation distance is small, the impact test pass rate is high, and the energy density is high, indicating that the lithium-ion battery of the present application maintains a high energy density while also having good mechanical safety performance.

[0125] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0126] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0127] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A cylindrical secondary battery, comprising a wound electrode assembly, the electrode assembly comprising a first electrode sheet, a second electrode sheet, and a separator, the separator being disposed between the first electrode sheet and the second electrode sheet, the first electrode sheet having a first winding starting end surface; Along the winding direction of the electrode assembly, the second electrode sheet includes a first section and a second section connected to the first section. Along the opposite direction of the winding direction, the second section is the portion of the second electrode sheet that exceeds the first winding starting end surface. The second section has a first position connected to the first section on the surface facing the winding center of the electrode assembly. The volume of the second section is Acm 3 ; The volume of the first cylinder formed by rotating 360° from the first position in the opposite direction of the winding direction with the winding center as the center of the cylinder is B cm 3 , 40%≤A / B≤90%, 0.45≤B≤7.

8.

2. The cylindrical secondary battery according to claim 1, wherein The diameter of the first cylinder is D1 mm, the second section has a second winding starting end face, and the diameter of the second cylinder formed by winding one circle starting from the second winding starting end face along the winding direction is D2 mm, 1.5≤D2≤10, 0.5≤D2 / D1≤0.

94.

3. The cylindrical secondary battery according to claim 2, wherein The cylindrical secondary battery satisfies at least one of the following characteristics: (1)0.5≤B≤1.2； (2)1.5≤D2≤3； (3)0.72≤D2 / D1≤0.

84.

4. The cylindrical secondary battery according to any one of claims 1 to 3, wherein The number of winding turns of the second section is N, 1≤N≤10.

5. The cylindrical secondary battery according to claim 4, wherein 3≤N≤6。 6. The cylindrical secondary battery according to any one of claims 1 to 5, wherein The second section includes a first empty foil area. Along the winding direction of the electrode assembly, the length of the first empty foil area is L1 mm. The length of the material layer in the second section is L2 mm. 20%≤L1 / (L1+L2)≤70%.

7. The cylindrical secondary battery according to any one of claims 1 to 6, wherein The starting section of the first pole piece includes a second empty foil area. Along the winding direction of the electrode assembly, the length of the second empty foil area is L3 mm. Starting from the first winding starting end face, the length of the first pole piece wound one circle along the winding direction of the electrode assembly is L4 mm, and 20%≤L3 / L4≤30%.

8. The cylindrical secondary battery according to any one of claims 1 to 5, wherein The second section is not provided with a first empty foil area.

9. The cylindrical secondary battery according to any one of claims 1 to 8, wherein The second pole piece includes a second material layer, the second material layer includes a second active material, the second active material includes silicon, and based on the second material layer, the percentage of silicon is W, 0.5%≤W≤10%.

10. The cylindrical secondary battery according to claim 9, wherein 2％≤W≤10％。 11. The cylindrical secondary battery according to any one of claims 1 to 10, wherein The second pole piece includes a second current collector, and the yield strength of the second current collector is σMPa, 200≤σ≤700.

12. The cylindrical secondary battery according to claim 11, wherein 300≤σ≤500.

13. The cylindrical secondary battery according to any one of claims 1 to 12, wherein The first pole piece is a positive pole piece, and the second pole piece is a negative pole piece. 14 . An electronic device comprising the cylindrical secondary battery according to claim 1 .

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