Cylindrical secondary battery and electronic device

Abstract

A cylindrical secondary battery and an electronic device. The cylindrical secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer. The first negative electrode material layer is located between the negative electrode current collector and the second negative electrode material layer, the first negative electrode material layer and the second negative electrode material layer each comprise a silicon-based material, and based on the mass of the negative electrode material layer, the mass percentage content of the element Si in the first negative electrode material layer is greater than the mass percentage content of the element Si in the second negative electrode material layer. The second negative electrode material layer is provided with a plurality of stripes, the plurality of stripes extend in the width direction of the negative electrode sheet when the negative electrode sheet is unfolded, and the plurality of stripes are arranged at intervals in the length direction of the negative electrode sheet when the negative electrode sheet is unfolded. By means of the described configuration, an electrolyte has good wetting performance on the negative electrode sheet, and the cylindrical secondary battery has good lithium precipitation performance and cycle performance.

Description

Cylindrical secondary battery and electronic device 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, are used in a variety of high-rate discharge systems (e.g., discharge rates greater than 3C). 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 field of consumer electronics.

[0003] Currently, high-power cylindrical lithium-ion batteries typically utilize a full-tab design, with the positive and negative tabs extending from opposite sides. These batteries are manufactured using a full-tab cutting, stacking, or flattening technique. However, this flattened structure can lead to electrode wetting issues, particularly in the center of the electrode, which can negatively impact lithium-ion battery performance. While electrode perforation can be used to improve electrode wetting, this can result in a loss of active material mass and lead to lithium plating.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a cylindrical secondary battery and electronic device to improve the lithium deposition performance and cycle performance of the secondary battery. The specific technical solution is as follows:

[0006] 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.

[0007] The first aspect of the present application provides a cylindrical secondary battery, comprising a negative electrode plate, the negative electrode plate comprising 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 comprising a first negative electrode material layer and a second negative electrode material layer. The first negative electrode material layer is located between the negative electrode current collector and the second negative electrode material layer, and both the first negative electrode material layer and the second negative electrode material layer comprise a silicon-based material. Based on the mass of the negative electrode material layers, the mass percentage of Si in the first negative electrode material layer is greater than the mass percentage of Si in the second negative electrode material layer. The second negative electrode material layer is provided with a plurality of stripes, the plurality of stripes extending along the width of the unfolded negative electrode plate, and the plurality of stripes being spaced apart along the length of the unfolded negative electrode plate. By providing stripes on the second negative electrode material layer, the electrolyte's wettability to the negative electrode sheet can be improved. The relatively low Si content in the second negative electrode material layer helps reduce the volume expansion of the negative electrode material layer during cycling. Simultaneously, providing stripes on the second negative electrode material layer reduces the capacity loss of the negative electrode sheet. Furthermore, the relatively high Si content in the first negative electrode material layer helps increase the capacity of the negative electrode sheet, effectively reducing the risk of lithium plating caused by insufficient CB value due to the provision of stripes on the second negative electrode material layer, thereby improving the cycling performance of the cylindrical secondary battery. While the electrolyte has good wettability to the negative electrode sheet, the cylindrical secondary battery has good lithium plating and cycling performance.

[0008] In one or more embodiments of the present application, the thickness of the second negative electrode material layer along the thickness direction of the negative electrode sheet is D μm, and the depth of a single stripe is d μm. Based on the mass of the second negative electrode material layer, the mass percentage of Si element in the second negative electrode material layer is W, and the gram capacity of the silicon-based material is C. Si mAh / g, 1.01≤W×C Si ×d / D≤15.87, preferably 3.20≤W×C Si ×d / D≤4.76; 10≤D≤55, preferably 12≤D≤45; 0.6%≤W≤5%, preferably 1%≤W≤2%; 1300≤C Si ≤1800, preferably 1400≤C Si ≤1600. By adjusting W×C Si ×d / D, W, C SiThe values ​​of and D are within the scope of this application, so that the total amount of Si in the second negative electrode material layer is within an appropriate range. When stripes are set on the second negative electrode material layer, the wetting performance of the electrolyte on the negative electrode plate can be improved. At the same time, the capacity loss of the negative electrode plate is small, and the volume expansion of the negative electrode material layer is more uniform during the cycle, so that the flow rate of the electrolyte in the negative electrode plate is increased, thereby effectively reducing the risk of lithium plating caused by insufficient CB value due to the setting of stripes in the second negative electrode material layer, thereby improving the cycle performance of the cylindrical secondary battery.

[0009] In one or more embodiments of the present application, along the length direction of the unfolded negative electrode sheet, the second negative electrode material layer includes a first section, a second section, and a third section connected in sequence. Based on the length of the second negative electrode material layer, the length of the first section accounts for 10% to 30%, the length of the second section accounts for 40% to 80%, and the length of the third section accounts for 10% to 30%. The stripes on the first section have a first density, the stripes on the second section have a second density, and the stripes on the third section have a third density, the second density is greater than the first density, and the third density is less than or equal to the second density. By regulating the size relationship between the first density, the second density, and the third density, the distribution of the electrolyte in the negative electrode sheet is more consistent, reducing the risk of lithium plating caused by inconsistent wetting effect of the electrolyte on the negative electrode sheet during the winding process of the cylindrical secondary battery, improving the wetting performance of the electrolyte on the negative electrode sheet, and improving the cycle performance of the cylindrical secondary battery.

[0010] In one or more embodiments of the present application, the number of stripes on the second negative electrode material layer per 2 cm in the first section is 1 to 3, the number of stripes on the second negative electrode material layer per 2 cm in the second section is 4 to 6, and the number of stripes on the second negative electrode material layer per 2 cm in the third section is 2 to 4. By regulating the number of stripes on the second negative electrode material layer per 2 cm in each section, i.e., the values ​​of a1, a2, and a3, within the above range, the distribution of the electrolyte in the negative electrode sheet is made more uniform, reducing the risk of lithium plating caused by inconsistent electrolyte wetting of the negative electrode sheet during the winding process of preparing a cylindrical secondary battery, improving the electrolyte wetting performance of the negative electrode sheet, and improving the cycle performance of the cylindrical secondary battery.

[0011] In one or more embodiments of the present application, the width of a single stripe along the length direction of the unfolded negative electrode sheet is n μm, with 45 ≤ n ≤ 85. By regulating the width n of the single stripe within the above range, it is beneficial to improve the wetting performance of the electrolyte on the negative electrode sheet, and improve the penetration efficiency of the electrolyte into the negative electrode sheet. At the same time, the capacity loss of the negative electrode sheet is small, which is beneficial to reduce the risk of lithium deposition caused by insufficient CB value due to the provision of stripes in the second negative electrode material layer. Therefore, while the electrolyte has good wetting performance on the negative electrode sheet, the cylindrical secondary battery has good lithium deposition performance and cycle performance.

[0012] In one or more embodiments of the present application, the depth of a single stripe along the thickness direction of the negative electrode sheet is d μm, 1≤d≤30. By regulating the depth d of a single stripe within the above range, it is beneficial to improve the wetting performance of the electrolyte on the negative electrode sheet, improve the penetration efficiency of the electrolyte into the negative electrode sheet, and at the same time help reduce the risk of the second negative electrode material layer being penetrated by the stripes when the stripes are set. The capacity loss of the negative electrode sheet is small, thereby reducing the risk of lithium deposition caused by insufficient CB value due to the setting of stripes in the second negative electrode material layer. Therefore, while the electrolyte has good wetting performance on the negative electrode sheet, the cylindrical secondary battery has good lithium deposition performance and cycle performance.

[0013] In one or more embodiments of the present application, based on the thickness of the negative electrode material layer, the thickness percentage of the second negative electrode material layer is T, 40%≤T≤80%, preferably 50%≤T≤75%. By regulating the thickness percentage T of the second negative electrode material layer within the above range, when stripes are provided on the second negative electrode material layer, the risk of the second negative electrode material layer being pierced by the stripes is reduced and the capacity loss of the negative electrode plate is small, thereby reducing the risk of lithium plating caused by insufficient CB value due to the provision of stripes on the second negative electrode material layer. In addition, while taking into account the capacity of the negative electrode plate, it is beneficial to suppress the volume expansion of the first negative electrode material layer during the cycle. The volume expansion of the second negative electrode material layer with stripes is more uniform, thereby improving the cycle performance of the secondary battery.

[0014] In one or more embodiments of the present application, based on the mass of the Si element in the negative electrode material layer, the mass percentage of the Si element in the second negative electrode material layer is X, 5%≤X≤20%, preferably 8%≤X≤15%. Based on the mass of the Si element in the negative electrode material layer, by regulating the mass percentage X of the Si element in the second negative electrode material layer within the above range, the content of the Si element in the second negative electrode material layer is relatively low, and the volume expansion of the second negative electrode material layer with stripes is relatively uniform, so that the electrolyte is more evenly distributed in the negative electrode sheet, which increases the flow rate of the electrolyte in the negative electrode sheet, thereby improving the cycle performance of the secondary battery; at the same time, when stripes are set on the second negative electrode material layer, the capacity loss of the negative electrode sheet is relatively small, thereby reducing the risk of lithium plating caused by insufficient CB value due to the setting of stripes in the second negative electrode material layer. Therefore, while the electrolyte has good wetting performance on the negative electrode sheet, the cylindrical secondary battery has good lithium plating performance and cycle performance.

[0015] The 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 provided in the present application has good lithium deposition performance and cycle performance, and therefore, the electronic device of the present application has a long service life.

[0016] Beneficial effects of this application:

[0017] The embodiment of the present application can improve the electrolyte's wetting performance on the negative electrode plate by providing stripes on the second negative electrode material layer. The mass percentage of the Si element in the first negative electrode material layer is greater than the mass percentage of the Si element in the second negative electrode material layer. The content of the Si element in the second negative electrode material layer is relatively low, which is beneficial to reducing the volume expansion of the negative electrode material layer during the cycle. At the same time, by providing stripes on the second negative electrode material layer, the capacity loss of the negative electrode plate is small. Furthermore, the content of the Si element in the first negative electrode material layer is relatively high, which is beneficial to improving the capacity of the negative electrode plate, thereby effectively reducing the risk of lithium plating caused by insufficient CB value due to providing stripes on the second negative electrode material layer, thereby improving the cycle performance of the cylindrical secondary battery. While the electrolyte has good wetting performance on the negative electrode plate, the cylindrical secondary battery has good lithium plating performance and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0019] FIG1 is a front view of a negative electrode sheet in one embodiment of the present application;

[0020] FIG2 is a cross-sectional view of the negative electrode sheet in FIG1 along the AA direction;

[0021] FIG3 is a schematic structural diagram of a negative electrode sheet in one embodiment of the present application;

[0022] FIG4 is a front view of a negative electrode sheet in another embodiment of the present application.

[0023] Reference numerals: negative electrode sheet 100 ; negative electrode current collector 10 ; negative electrode material layer 20 ; first negative electrode material layer 21 ; second negative electrode material layer 22 ; first segment 221 ; second segment 222 ; third segment 223 ; stripe 30 . DETAILED DESCRIPTION

[0024] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0025] 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.

[0026] In order to solve the problem of electrode wetting caused by the flattened structure of the full tab in cylindrical lithium-ion batteries, especially the poor wetting in the middle of the electrode, which in turn affects the performance of the lithium-ion battery, the following methods are currently mainly used to improve it: increasing the standing time after the electrolyte is injected during the preparation process of the lithium-ion battery to improve the diffusion of the electrolyte, but while the production cost increases, the initial efficiency of the lithium-ion battery is reduced. Alternatively, the electrolyte components are optimized, such as adding dimethyl carbonate or carboxylic acid ester to the electrolyte to improve the conductivity of the electrolyte, but during the cycle of the lithium-ion battery, side reactions will occur between the electrolyte and the positive active material and / or the negative active material, generating excess gas, which can easily cause safety problems. Furthermore, the porosity of the positive electrode and / or the negative electrode is controlled so that the edge porosity of the positive electrode and / or the negative electrode is greater than the middle porosity. Although the edge wetting is improved, the wetting effect of the middle part of the positive electrode and / or the negative electrode is reduced, which can easily lead to electrolyte bridge failure in the middle part. The inventors have discovered that providing stripes on the negative electrode plate can effectively improve the problem of electrolyte wetting of the negative electrode plate. However, this also reduces the capacity of the negative electrode plate, resulting in insufficient local CB value and lithium deposition on the negative electrode plate. This problem is particularly prominent on negative electrode plates containing Si, which in turn reduces the cycling performance of lithium-ion batteries. Therefore, the present application provides a secondary battery that can improve the electrolyte wetting performance of the negative electrode plate when the negative electrode plate contains Si, thereby improving the cycling performance of the secondary battery.

[0027] The first aspect of the present application provides a cylindrical secondary battery, comprising a negative electrode plate, the negative electrode plate comprising 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 comprising a first negative electrode material layer and a second negative electrode material layer. The first negative electrode material layer is located between the negative electrode current collector and the second negative electrode material layer, and both the first negative electrode material layer and the second negative electrode material layer comprise a silicon-based material. Based on the mass of the negative electrode material layers, the mass percentage of Si element in the first negative electrode material layer is greater than the mass percentage of Si element in the second negative electrode material layer. The second negative electrode material layer is provided with a plurality of stripes, the plurality of stripes extending along the width direction of the unfolded negative electrode plate, and the plurality of stripes are spaced apart along the length direction of the unfolded negative electrode plate. By providing stripes on the second negative electrode material layer, the wetting performance of the electrolyte on the negative electrode plate can be improved, thereby increasing the penetration efficiency of the electrolyte on the negative electrode plate. The negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer, and the mass percentage of the Si element in the first negative electrode material layer is greater than the mass percentage of the Si element in the second negative electrode material layer. The content of the Si element in the second negative electrode material layer is relatively low, which is beneficial to reducing the volume expansion of the negative electrode material layer during the cycle. At the same time, the stripes are only provided on the second negative electrode material layer, and the capacity loss of the negative electrode plate is small. Furthermore, the content of the Si element in the first negative electrode material layer is relatively high, which is beneficial to improving the capacity of the negative electrode plate, thereby effectively reducing the risk of lithium plating caused by insufficient CB value due to the provision of stripes in the second negative electrode material layer, thereby improving the cycle performance of the cylindrical secondary battery. As a result, while the electrolyte has good wetting performance on the negative electrode plate, the cylindrical secondary battery has good lithium plating performance and cycle performance.

[0028] In this application, the CB value refers to the ratio between the capacity of the negative electrode sheet and the capacity of the positive electrode sheet per unit area under the same conditions. CB = (gram capacity of negative electrode active material × mass of negative electrode active material per unit area of ​​negative electrode sheet × mass percentage of negative electrode active material in negative electrode material layer) / (gram capacity of positive electrode active material × mass of positive electrode active material per unit area of ​​positive electrode sheet × mass percentage of positive electrode active material in positive electrode material layer). The above unit area refers to 1mm 2. The present application has no special restrictions on the particle size of the silicon-based material. The silicon-based material can be selected from micron-scale silicon-based materials or nano-scale silicon-based materials, as long as the purpose of the present application can be met. For example, the average particle size of the micron-scale silicon-based material can be 3μm to 20μm, and the average particle size of the nano-scale silicon-based material can be 1nm to 100nm. The present application has no special restrictions on the type of silicon-based material, as long as the purpose of the present application can be achieved. For example, the micron-scale silicon-based material includes but is not limited to at least one of micron-scale silicon material, micron-scale silicon-carbon material or micron-scale silicon-oxygen material, micron-scale silicon material includes micron-scale silicon element, micron-scale silicon-carbon material includes at least one of micron-scale α-SiC (hexagonal crystal structure) or micron-scale β-SiC (cubic crystal structure), and micron-scale silicon-oxygen material includes at least one of micron-scale SiO or micron-scale SiO2. Nanoscale silicon-based materials include but are not limited to at least one of nanoscale silicon materials, nanoscale silicon-carbon materials or nanoscale silicon-oxygen materials, nanoscale silicon materials include nanoscale silicon element, nanoscale silicon-carbon materials include at least one of nanoscale α-SiC (hexagonal crystal structure) or nanoscale β-SiC (cubic crystal structure), and nanoscale silicon-oxygen materials include at least one of nanoscale SiO or nanoscale SiO2.

[0029] In one embodiment of the present application, along the thickness direction of the negative electrode sheet, the thickness of the second negative electrode material layer is D μm, and the depth of a single stripe is d μm. Based on the mass of the second negative electrode material layer, the mass percentage of Si element in the second negative electrode material layer is W, and the gram capacity of the silicon-based material is C. Si mAh / g, 1.01≤W×C Si ×d / D≤15.87. In some embodiments, 3.20≤W×C Si ×d / D≤4.76. For example, W×C SiThe value of ×d / D can be 1.01, 1.05, 1.1, 1.5, 2, 2.5, 3, 3.2, 3.5, 4, 4.5, 4.76, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 15.87, or a range consisting of any two thereof. In some embodiments, 10≤D≤55, and in other embodiments, 12≤D≤45. For example, the value of D can be 10, 12, 15, 17, 20, 22, 25, 27, 30, 32, 35, 37, 40, 42, 45, 47, 50, 52, 55, or a range consisting of any two thereof. In some embodiments, 0.6%≤W≤5%, in other embodiments, 1%≤W≤2%. For example, the value of W can be 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.2%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%, or a range consisting of any two of these values. In some embodiments, 1300≤C Si ≤1800, in some other embodiments, 1400≤C Si ≤1600, for example, C Si The value of can be 1300, 1320, 1350, 1370, 1400, 1420, 1450, 1470, 1500, 1520, 1550, 1570, 1600, 1620, 1650, 1670, 1700, 1720, 1750, 1770, 1800 or a range consisting of any two of these values.

[0030] In this application, for ease of understanding, the negative electrode sheet is defined as having its own length direction as the X direction, its own width direction as the Y direction, and its own thickness direction as the Z direction in the unfolded state, and a three-dimensional coordinate system is established along the X direction, the Y direction, and the Z direction. As shown in Figures 1 and 2, the negative electrode sheet 100 in Figure 1 is sectioned along AA to obtain Figure 2. Along the thickness direction (Z direction) of the negative electrode sheet 100, the thickness of the second negative electrode material layer 22 is Dμm, and the depth of a single stripe 30 is dμm. By regulating W×C SiThe value of ×d / D is within the scope of this application, so that the total amount of Si in the second negative electrode material layer is within a suitable range. When stripes are set on the second negative electrode material layer, the wetting performance of the electrolyte on the negative electrode plate can be improved. At the same time, the capacity loss of the negative electrode plate is small. The volume expansion of the negative electrode material layer during the cycle is more uniform, so that the flow rate of the electrolyte in the negative electrode plate is improved, thereby effectively reducing the risk of lithium plating caused by insufficient CB value due to the setting of stripes in the second negative electrode material layer, thereby improving the cycle performance of the cylindrical secondary battery. Regulating the thickness D of the second negative electrode material layer within the above range is conducive to reducing the risk of the second negative electrode material layer being penetrated by the stripes when the stripes are set, and at the same time can reduce the risk of lithium plating caused by insufficient CB value due to the setting of stripes in the second negative electrode material layer. Regulating the gram capacity C of the silicon-based material Si Within the above range, when stripes are set on the second negative electrode material layer, the capacity loss of the negative electrode plate is small, which is beneficial to reducing the risk of lithium plating caused by insufficient CB value due to setting stripes on the second negative electrode material layer. Regulating the mass percentage W of the Si element in the second negative electrode material layer within the above range, when stripes are set on the second negative electrode material layer, the capacity loss of the negative electrode plate is small, which is beneficial to reducing the risk of lithium plating caused by insufficient CB value due to setting stripes on the second negative electrode material layer. At the same time, the volume expansion of the negative electrode material layer during the cycle is relatively uniform, so that the flow rate of the electrolyte in the negative electrode plate is improved. Therefore, while the electrolyte has good wetting properties for the negative electrode plate, the cylindrical secondary battery has good lithium plating performance and cycle performance. The present application does not have any special restrictions on the method of regulating the gram capacity of the silicon-based material, as long as the purpose of the present application can be achieved, for example, different types of commercially available silicon-based materials can be selected or the average particle size of the same silicon-based material can be adjusted to adjust the gram capacity of the silicon-based material, and combined with the "C Si The test method of "test" is used to determine the gram capacity of silicon-based materials and select the silicon-based materials with the required gram capacity. 。 The present application does not impose any particular restrictions on the method for regulating the average particle size of silicon-based materials, as long as the purpose of the present application can be achieved. For example, this can be achieved by mechanically crushing and ball-milling the particles of the silicon-based material. Generally, for the same silicon-based material, extending the ball-milling time will reduce the average particle size and increase the gram capacity of the silicon-based material; shortening the ball-milling time will increase the average particle size and decrease the gram capacity of the silicon-based material. In the present application, the average particle size can be understood as an equivalent diameter, which generally refers to the diameter of a sphere with the same volume as an object of irregular shape. In the present application, the area of ​​the silicon-based material particles to be measured on the cross-section of the negative electrode piece is measured by obtaining the negative electrode piece, and then the diameter of the circle with the same area is used as the equivalent diameter of the silicon-based material particles to be measured.

[0031] In one embodiment of the present application, as shown in FIG3 , along the length direction (X direction) of the unfolded negative electrode sheet 100, it can be understood that the length direction (X direction) of the unfolded negative electrode sheet 100 is the same as the winding direction W direction of the negative electrode sheet 100 when preparing a cylindrical secondary battery. The second negative electrode material layer 22 includes a first segment 221, a second segment 222, and a third segment 223 connected in sequence. It can be understood that when preparing a cylindrical secondary battery, when the electrode assembly is wound, the negative electrode sheet is wound from the position where the first segment is located. After winding, the first segment is located near the winding center of the electrode assembly, and the third segment is located away from the winding center of the electrode assembly. Based on the length of the second negative electrode material layer 22, the length of the first segment 221 accounts for 10% to 30%, the length of the second segment 222 accounts for 40% to 80%, and the length of the third segment 223 accounts for 10% to 30%. For example, the length of the first segment 221 may be 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, or a range consisting of any two of these values, the length of the second segment 222 may be 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, or a range consisting of any two of these values, and the length of the third segment 223 may be 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, or a range consisting of any two of these values. The stripes 30 on the first segment 221 have a first density, the stripes 30 on the second segment 222 have a second density, and the stripes 30 on the third segment 223 have a third density, where the second density is greater than the first density and the third density is less than or equal to the second density. By regulating the relationship between the first density, the second density, and the third density, the distribution of the electrolyte in the negative electrode sheet is made more uniform, reducing the risk of lithium precipitation caused by inconsistent wetting of the electrolyte on the negative electrode sheet during the winding process of the cylindrical secondary battery, improving the wetting performance of the electrolyte on the negative electrode sheet, improving the wetting efficiency of the electrolyte on the negative electrode sheet, and improving the cycle performance of the cylindrical secondary battery. Therefore, while the electrolyte has good wetting performance on the negative electrode sheet, the cylindrical secondary battery has good cycle performance. In this application, the first density refers to the number of stripes on the second negative electrode material layer per unit length in the first section, the second density refers to the number of stripes on the second negative electrode material layer per unit length in the second section, and the third density refers to the number of stripes on the third negative electrode material layer per unit length in the third section, where every 2 cm is a unit length.

[0032] In one embodiment of the present application, the number a1 of stripes on the second negative electrode material layer per 2 cm in the first section is 1 to 3, the number a2 of stripes on the second negative electrode material layer per 2 cm in the second section is 4 to 6, and the number a3 of stripes on the second negative electrode material layer per 2 cm in the third section is 2 to 4. For example, the number a1 of stripes on the second negative electrode material layer per 2 cm in the first section may be 1, 2, or 3, the number a2 of stripes on the second negative electrode material layer per 2 cm in the second section is 4, 5, or 6, and the number a3 of stripes on the second negative electrode material layer per 2 cm in the third section may be 2, 3, or 4. By regulating the number of stripes on the second negative electrode material layer per 2 cm in each section, i.e., the values ​​of a1, a2, and a3, within the above range, the distribution of the electrolyte in the negative electrode sheet is more uniform, reducing the risk of lithium precipitation caused by inconsistent electrolyte wetting of the negative electrode sheet during the winding process of preparing a cylindrical secondary battery, improving the wetting performance of the electrolyte on the negative electrode sheet, improving the wetting efficiency of the electrolyte on the negative electrode sheet, and improving the cycle performance of the cylindrical secondary battery. Therefore, while the electrolyte has good wetting performance on the negative electrode sheet, the cylindrical secondary battery has good cycle performance. In this application, the values ​​of a1, a2, and a3, i.e., the number of stripes on the second negative electrode material layer per 2 cm in each section, are all integers.

[0033] In one embodiment of the present application, as shown in FIG2 , along the length direction (X direction) after the negative electrode sheet 100 is unfolded, the width of a single stripe 30 is n μm, 45 ≤ n ≤ 85. For example, the value of n can be 45, 47, 50, 52, 55, 57, 60, 62, 65, 67, 70, 72, 75, 77, 80, 82, 85 or a range consisting of any two values ​​therein. By regulating the width n of a single stripe within the above range, it is beneficial to improve the wetting performance of the electrolyte on the negative electrode sheet, and improve the penetration efficiency of the electrolyte on the negative electrode sheet. At the same time, the capacity loss of the negative electrode sheet is small, which is beneficial to reduce the risk of lithium precipitation caused by insufficient CB value due to the provision of stripes in the second negative electrode material layer. Therefore, while the electrolyte has good wetting performance on the negative electrode sheet, the cylindrical secondary battery has good lithium precipitation performance and cycle performance. In this application, the cross-section of a single stripe refers to the plane formed by the stripe along the length direction and the thickness direction of the electrode assembly after it is unfolded (or the cross-section obtained by cutting the stripe along the length direction and the thickness direction after the electrode assembly is unfolded). This application does not particularly limit the cross-sectional shape of a single stripe, as long as it can achieve the purpose of this application. For example, the cross-section of a single stripe can be triangular, arc-shaped (the area is smaller than the semicircle with the same radius), semicircular, rectangular, trapezoidal or square. In this application, the width of a single stripe refers to the maximum dimension of the cross-section of a single stripe along the length direction of the negative electrode sheet after it is unfolded.

[0034] In one embodiment of the present application, as shown in FIG2 , along the thickness direction (Z direction) of the negative electrode sheet 100, the depth of a single stripe 30 is d μm, 1≤d≤30. For example, the value of d can be 1, 2, 3, 5, 7, 10, 12, 15, 17, 20, 22, 25, 27, 30 or a range consisting of any two values ​​therein. By regulating the depth d of a single stripe within the above range, it is beneficial to improve the wetting performance of the electrolyte on the negative electrode sheet, improve the penetration efficiency of the electrolyte into the negative electrode sheet, and at the same time, it is beneficial to reduce the risk of the second negative electrode material layer being penetrated by the stripes when setting the stripes. The capacity loss of the negative electrode sheet is small, thereby reducing the risk of lithium precipitation caused by insufficient CB value due to setting stripes in the second negative electrode material layer. Therefore, while the electrolyte has good wetting performance on the negative electrode sheet, the cylindrical secondary battery has good lithium precipitation performance and cycle performance. Among them, along the thickness direction of the negative electrode sheet, the depth of the single stripe is less than the thickness of the second negative electrode material layer. In this application, the depth of a single stripe refers to the distance between the surface of the negative electrode sheet and the deepest point of the single stripe along the thickness direction of the negative electrode sheet.

[0035] In one embodiment of the present application, based on the thickness of the negative electrode material layer, the thickness of the second negative electrode material layer is T, 40%≤T≤80%. In some embodiments, 50%≤T≤75%. For example, the value of T can be 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80% or a range consisting of any two values ​​therein. By regulating the thickness percentage T of the second negative electrode material layer within the above range, when stripes are set on the second negative electrode material layer, the risk of the second negative electrode material layer being pierced by the stripes is reduced and the capacity loss of the negative electrode plate is small, thereby reducing the risk of lithium plating caused by insufficient CB value due to the setting of stripes on the second negative electrode material layer. In addition, while taking into account the capacity of the negative electrode plate, it is beneficial to suppress the volume expansion of the first negative electrode material layer during the cycle. The volume expansion of the second negative electrode material layer with stripes is more uniform, thereby improving the cycle performance of the secondary battery. Therefore, while the electrolyte has good wetting properties for the negative electrode sheets, the cylindrical secondary battery has good lithium plating properties and cycle performance. In the present application, the thickness percentage of the second negative electrode material layer in the negative electrode material layer can be regulated by regulating the thickness of the first negative electrode material layer and / or the thickness of the second negative electrode material layer. In the present application, the thickness of the first negative electrode material layer and the thickness of the second negative electrode material layer can be regulated by means known to those skilled in the art. For example, when the first negative electrode slurry is coated on the surface of the negative electrode current collector, on the basis of other conditions remaining unchanged and the solid content of the first negative electrode slurry being constant, the coating amount of the first negative electrode slurry is increased to increase the thickness of the first negative electrode material layer. The thickness regulation method of the second negative electrode material layer is understood in the same way. This application does not impose any special restrictions, as long as the purpose of this application can be achieved.

[0036] In one embodiment of the present application, based on the mass of Si in the negative electrode material layer, the mass percentage of Si in the second negative electrode material layer is X, and 5%≤X≤20%. In some embodiments, 8%≤X≤15%. For example, the value of X can be 5%, 7%, 8%, 10%, 12%, 15%, 17%, 20%, or a range consisting of any two values ​​therein. Based on the mass of Si in the negative electrode material layer, by regulating the mass percentage of Si in the second negative electrode material layer X within the above range, the content of Si in the second negative electrode material layer is relatively low, which is beneficial for suppressing the volume expansion of the first negative electrode material layer during cycling. The volume expansion of the second negative electrode material layer with stripes is more uniform, making the electrolyte more evenly distributed in the negative electrode sheet, increasing the flow rate of the electrolyte in the negative electrode sheet, and thus improving the cycle performance of the secondary battery. At the same time, when stripes are provided on the second negative electrode material layer, the capacity loss of the negative electrode sheet is relatively small, thereby reducing the risk of lithium plating caused by insufficient CB value due to the provision of stripes in the second negative electrode material layer. Therefore, while the electrolyte has good wetting properties for the negative electrode, the cylindrical secondary battery has good lithium deposition performance and cycle performance.

[0037] In one embodiment of the present application, the multiple stripes in the second negative electrode material layer are evenly spaced along the length of the unfolded negative electrode sheet. This arrangement facilitates the operability of disposing the multiple stripes in the second negative electrode material layer, improves the electrolyte's wettability of the negative electrode sheet, and enhances the cycle performance of the secondary battery while meeting mass production manufacturability requirements.

[0038] This application does not impose any particular restrictions on the shape and location of the stripes, as long as they meet the objectives of this application. For example, along the unfolded width of the negative electrode sheet, the second negative electrode material layer has two opposing edges. The stripes can extend from either edge along the width of the negative electrode sheet, or the stripes can be located between the two edges. The stripes can also be angled with the unfolded length of the negative electrode sheet, with the angle ranging from 30° to 150°. This arrangement helps improve the electrolyte wetting of the negative electrode sheet, thereby enhancing the cycle performance of the secondary battery while meeting mass production manufacturability. This application does not impose any particular restrictions on the length of the stripes, as long as they meet the objectives of this application. For example, along the unfolded width of the negative electrode sheet, the length of the stripes can account for 60% to 100% of the width of the second negative electrode material layer. When the length of the stripes accounts for 100% of the width of the second negative electrode material layer along the unfolded width of the negative electrode sheet, as shown in Figure 4, the length of a single stripe 30 along the unfolded width Y of the negative electrode sheet is equal to the width 22 of the second negative electrode material layer. In the present application, the features of the above embodiments can be combined arbitrarily, and the embodiments obtained by the combination are also within the protection scope of the present application.

[0039] In the present application, "the negative electrode material layer located on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector itself, or on two surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector itself. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode current collector, or it can be a partial area of ​​the surface of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this 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, foam nickel, foam copper 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.). In the present application, there is no special restriction on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4μm to 20μm. In addition to the silicon-based material, the first negative electrode material layer also includes a first negative electrode active material, and the second negative electrode material layer also includes a second negative electrode active material in addition to the silicon-based material. The present application has no particular restrictions on the types of the first negative electrode active material and the second negative electrode active material, as long as the purpose of the present application can be achieved. For example, the first negative electrode active material and the second negative electrode active material can each be independently selected from at least one of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon or soft carbon. Optionally, the first negative electrode material layer may further include a first conductive agent, a first negative electrode binder and a first dispersant, and the second negative electrode material layer may further include a second conductive agent, a second negative electrode binder and a second dispersant. The present application does not particularly limit the types of the first negative electrode binder and the second negative electrode binder, as long as the purpose of the present application can be achieved. For example, the first negative electrode binder and the second negative electrode binder may include but are not limited to at least one of 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 does not particularly limit the types of the first conductive agent and the second conductive agent, as long as the purpose of the present application can be achieved. For example, the first conductive agent and the second conductive agent may include but are 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 nanocarbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers. Specifically, the metal may include but are not limited to at least one of copper, nickel, aluminum or silver. The conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.The first dispersant and the second dispersant may include, but are not limited to, carboxymethyl cellulose or sodium carboxymethyl cellulose.

[0040] The present application has no particular restrictions on the preparation method of the negative electrode sheet, as long as it can achieve the purpose of the present application. For example, the preparation method of the negative electrode sheet includes but is not limited to the following steps: (1) uniformly mixing a mixture of a first negative electrode active material and a silicon-based material, a first negative electrode binder, a first conductive agent and a first dispersant to obtain a first negative electrode slurry, and uniformly mixing a mixture of a second negative electrode active material and a silicon-based material, a second negative electrode binder, a second conductive agent and a second dispersant to obtain a second negative electrode slurry; (2) coating the first negative electrode slurry on one surface of the negative electrode collector, and drying it to obtain a negative electrode sheet coated with the first negative electrode material layer, and coating the second negative electrode slurry on the surface of the first negative electrode material layer away from the negative electrode collector, and drying it to obtain a negative electrode sheet coated with the first negative electrode material layer and the second negative electrode material layer on one side; (3) repeating the above operation on the other surface of the negative electrode collector to obtain a negative electrode sheet coated with the first negative electrode material layer and the second negative electrode material layer on both sides; (4) after cold pressing and slitting, a corresponding number of stripes are sequentially arranged in the first section, the second section and the third section of the second negative electrode material layer along the length direction of the negative electrode sheet to obtain a negative electrode sheet.

[0041] The present application has no particular restrictions on the solid content of the first negative electrode slurry and the second negative electrode slurry in the above step (1), as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the time and temperature of the drying in the above step (2), 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 cold pressing in the above step (4), as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the method of setting the stripes in the above step (4), as long as the purpose of the present application can be achieved. For example, the stripes can be set by pulsed laser etching. The depth d and width n of a single stripe can be adjusted by the power and defocus of the pulsed laser emitter, and the distance between adjacent stripes can be adjusted by adjusting the spacing between the pulsed laser emitters. Among them, when the first negative electrode slurry and the second negative electrode slurry are coated on one surface of the negative electrode collector, the stripes are only set on one surface of the negative electrode sheet; when the first negative electrode slurry and the second negative electrode slurry are coated on both surfaces of the negative electrode collector, the stripes are respectively set on both surfaces of the negative electrode sheet. The present application has no particular restrictions on the adjustment of the values ​​of D and T, as long as the purpose of the present application can be achieved. For example, the values ​​of D and T can be regulated by adjusting the coating amount of the negative electrode material layer. When the coating amount of the first negative electrode material layer is constant, the coating amount of the second negative electrode material layer is increased, the value of D becomes larger, and the value of T becomes larger; when the coating amount of the second negative electrode material layer is reduced, the value of D becomes smaller, and the value of T becomes smaller. The present application has no special restrictions on regulating the values ​​of W and X, as long as the purpose of the present application can be achieved. For example, the values ​​of W and X can be regulated by adjusting the proportion of silicon-based materials in the mixture of the second negative electrode active material and the silicon-based material. When the proportion of silicon-based materials in the mixture of the first negative electrode active material and the silicon-based material is constant, the proportion of silicon-based materials in the mixture of the second negative electrode active material and the silicon-based material is increased, the value of W becomes larger, and the value of X becomes larger; when the proportion of silicon-based materials in the mixture of the second negative electrode active material and the silicon-based material is reduced, the value of W becomes smaller, and the value of X becomes smaller.

[0042] In the present application, a cylindrical secondary battery includes a positive electrode sheet. The present application has no special restrictions on the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet includes a positive electrode collector and a positive electrode material layer arranged on at least one surface of the positive electrode collector. The above-mentioned "positive electrode material layer arranged on at least one surface of the positive electrode collector" means that the positive electrode material layer can be arranged on one surface of the positive electrode collector along the thickness direction of itself, or on two surfaces of the positive electrode collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode collector, or it can be a partial area of ​​the surface of the positive electrode collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the positive electrode collector, as long as the purpose of the present application can be achieved. For example, the positive electrode collector can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode material layer of the present application includes a positive electrode active material. The present application has no special restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (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 iron manganese phosphate or lithium titanate. In the present application, the positive electrode active material may also include non-metallic elements, for example, non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm, preferably 6μm to 18μm. The thickness of the single-sided positive electrode material layer is 30μm to 120μm. In the present application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. The present application does not impose any particular 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 can be the same type as the negative electrode binder in the above-mentioned first negative electrode material layer and the second negative electrode material layer. The present application does not impose any 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 can be the same type as the conductive agent in the above-mentioned first negative electrode material layer and the second negative electrode material layer. The present application does not impose any particular restrictions on the mass ratio of the positive electrode active material, the positive electrode binder, and the conductive agent 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.

[0043] 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 50 μm.

[0044] The cylindrical secondary battery of 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(trifluoromethanesulfonyl imide) (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.

[0045] 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 known in the art for cylindrical secondary batteries. 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.

[0046] The cylindrical secondary battery of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In one embodiment 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.

[0047] This application does not particularly limit the preparation method of a cylindrical secondary battery; any preparation method known in the art may be used, as long as the objectives of this application are achieved. For example, the preparation method of a cylindrical secondary battery includes, but is not limited to, the following steps: stacking a separator, a positive electrode sheet, a separator, and a negative electrode sheet in sequence, and performing winding and folding operations as needed to obtain a wound electrode assembly; placing the electrode assembly in a housing; injecting an electrolyte into the housing and sealing the housing to obtain a cylindrical secondary battery.

[0048] The 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 provided in the present application has good lithium deposition performance and cycle performance, and therefore, the electronic device of the present application has a long service life.

[0049] 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.

[0050] Example

[0051] 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.

[0052] Test methods and equipment:

[0053] At an ambient temperature of 25°C, the lithium-ion battery was disassembled, the negative electrode sheet was taken out, and it was soaked in dimethyl carbonate (DMC) for 20 minutes. Then, the negative electrode sheet was placed in an oven and dried at 80°C for 12 hours to obtain a negative electrode sheet sample. Si The above method was used to sample the negative electrode samples in the test of D, d, T, W, X and n, the average particle size test of silicon-based material particles, and the test of D, d, T, W, X and n.

[0054] C Si The test:

[0055] The negative electrode sheet to be tested is weighed to obtain the mass M of the negative electrode sheet. A copper foil of the same area is weighed to obtain the mass m of the negative electrode current collector copper foil. The mass of the negative electrode material layer to be tested is Mm. The negative electrode sheet to be tested is used as the working electrode, the lithium sheet is used as the counter electrode, and the separator is placed between the negative electrode sheet to be tested and the lithium sheet to play an isolating role. The electrolyte is injected and assembled to obtain a button battery. The button battery is tested using a blue electric tester, and the voltage, capacity and current of the button battery during the test are recorded: (1) Standing for 3 hours; (2) 0.05C DC discharge to 0.005V, 50μA DC discharge again to 0.005V; (3) Standing for 5 minutes; (4) 0.05C constant current charge to 2V; (5) Standing for 5 minutes; (6) Steps (2) to (5) are cycled for 2 cycles (cls); End. The capacity after the second cycle is taken as the capacity C0 of the button battery. The gram capacity of the negative electrode material layer under test is calculated as C0 / (Mm). The separator and electrolyte used in the test are the same as those in Example 1-1.

[0056] As shown in Figure 1, a cross section of a negative electrode sheet 100 along AA is prepared, and the cross section of the negative electrode sheet 100 along AA is ion polished to obtain a cross section of the negative electrode sheet 100 as shown in Figure 2. The cross section of the negative electrode sheet 100 is observed using a scanning electron microscope, and the silicon-based material and graphite particles in the negative electrode material layer 20 in the cross section of the negative electrode sheet 100 are distinguished and counted using a backscattering mode to obtain the proportion a1 of graphite particles in the negative electrode material layer 20 and the proportion b1 of silicon-based materials in the negative electrode material layer 20. Among them, due to the higher atomic number and higher electron density of the silicon-based material, and the stronger interaction between the silicon-based material and the test electron beam than the interaction between the graphite particles and the test electron beam, the silicon-based material area is brighter, and similarly, the graphite particle area is darker. An elemental analysis test was performed on the negative electrode material layer 20 in the cross section of the negative electrode sheet 100 using an X-ray energy dispersive spectrometer (EDS). The C material and the Si material were distinguished using an X-ray energy dispersive spectrometer (EDS), and the proportion of graphite particles in the negative electrode material layer 20, a2, and the proportion of silicon-based materials in the negative electrode material layer 20, b2, were determined. The proportion of graphite particles in the negative electrode material layer 20 is a = (a1 + a2) / 2, and the proportion of silicon-based materials in the negative electrode material layer 20 is b = (b1 + b2) / 2. Based on the gram capacity C0 / (Mm) of the negative electrode material layer 20 being tested, the proportion of silicon-based materials in the negative electrode material layer 20, and the gram capacity of graphite particles (360 mAh / g), C Si =C0 / (Mm)-360a / b, to obtain the gram capacity C of the silicon-based material Si .

[0057] Average particle size test of silicon-based materials:

[0058] The average particle size of the silicon-based material was tested using a scanning electron microscope (SEM). As shown in Figure 1, a cross-section of the negative electrode sheet 100 along AA was prepared, and the cross-section of the negative electrode sheet 100 along AA was ion polished to obtain a cross-section of the negative electrode sheet 100 as shown in Figure 2. The cross-section of the negative electrode sheet 100 was observed using a scanning electron microscope, and the silicon-based material and graphite particles of the negative electrode material layer 20 in the cross-section of the negative electrode sheet 100 were distinguished by backscattering mode. The equivalent diameters of 32 silicon-based material particles were randomly selected and measured, and the average value was the average particle size of the measured silicon-based material. In this application, the average particle size can be understood as an equivalent diameter, which generally refers to the diameter of a sphere with the same volume as an object of irregular shape. The area of ​​the particles of the silicon-based material to be measured in the cross-section of the negative electrode sheet is measured, and then the diameter of a circle with the same area as the area is used as the equivalent diameter of the particles of the silicon-based material to be measured.

[0059] Tests for D, d, T, W, X, and n:

[0060] A cross-section of a negative electrode sheet 100 along the AA line was prepared as shown in Figure 1 , and the cross-section of the negative electrode sheet 100 along the AA line was ion polished to obtain the cross-section of the negative electrode sheet 100 shown in Figure 2 . The cross-section of the negative electrode sheet 100 was observed using a scanning electron microscope, revealing the clear boundary line between the two-layer coating, the boundary line between the first negative electrode material layer 21 and the negative electrode current collector 10, and the cross-sectional shape of the stripes 30. The maximum length between the cross-sections of a single stripe 30 along the length of the unfolded negative electrode sheet 100 was measured, which was the width n of a single stripe 30. The positions of the first negative electrode material layer 21, the second negative electrode material layer 22 and the negative electrode current collector 10 are determined by two dividing lines. Along the thickness direction of the negative electrode sheet 100 (Z direction), the distance from the surface of the negative electrode sheet 100 to the double-layer coating dividing line is measured, which is the thickness D of the second negative electrode material layer 22. The distance between the surface of the negative electrode sheet 100 and the deepest point of the single stripe 30 is the depth d of the single stripe 30. The distance between the surface of the negative electrode sheet 100 and the dividing line between the negative electrode material layer 20 and the negative electrode current collector 10 is the thickness of the negative electrode material layer 20. The thickness D of the second negative electrode material layer 22 divided by the thickness of the negative electrode material layer 20 is the thickness ratio T of the second negative electrode material layer 22.

[0061] An X-ray energy dispersive spectrometer (EDS) is used to perform elemental analysis tests on the negative electrode material layer 20, the first negative electrode material layer 21, and the second negative electrode material layer 22 in the cross section of the negative electrode sheet 100, respectively, to calculate the mass percentage W of the Si element in the second negative electrode material layer 22 based on the mass of the second negative electrode material layer 22, and the mass percentage X of the Si element in the second negative electrode material layer 22 based on the mass of the Si element in the negative electrode material layer 20.

[0062] Lithium deposition performance test:

[0063] The lithium-ion batteries in the examples and comparative examples were placed in a constant temperature box at 10°C for 60 minutes, then charged at a constant current of 2C to 4.2V, then charged at a constant voltage of 4.2V to a current of 0.05C. After standing for 5 minutes, they were discharged at a constant current of 0.5C to 2.5V. This constituted one cycle. After 10 cycles of the above charge and discharge process, the batteries were charged at a constant current of 2C to 4.2V. The lithium-ion batteries were disassembled and the lithium deposition state on the surface of the negative electrode was observed. The non-lithium deposited area of ​​the negative electrode surface was golden yellow, while the lithium deposited area was off-white.

[0064] The criteria for judging the degree of lithium deposition in lithium-ion batteries are as follows: a lithium deposition area of ​​0% indicates no lithium deposition, a lithium deposition area greater than 0 and less than or equal to 2% indicates mild lithium deposition, a lithium deposition area greater than 2% and less than or equal to 20% indicates moderate lithium deposition, and a lithium deposition area greater than 20% and less than or equal to 100% indicates severe lithium deposition, where the percentage of the lithium deposition area is calculated based on the total area of ​​the negative electrode material layer.

[0065] Cyclic performance test:

[0066] The lithium-ion batteries in the examples and comparative examples were subjected to charge and discharge cycle tests in a 25°C constant temperature box. The lithium-ion batteries were charged to 4.2V at a constant current of 2C, charged to 0.05V at a constant voltage of 4.2V, and allowed to stand for 5 minutes before being discharged to 2.5V at a constant current of 6C. This was the first cycle, and the first cycle discharge capacity C1 was recorded. After 600 cycles according to the above cycle process, the lithium-ion battery discharge capacity C 600 The 600th cycle capacity retention rate is calculated as an indicator for evaluating the wetting effect of the negative electrode sheet and the cycling performance of the lithium-ion battery, as shown in formula (I). A lower 600-cycle (cls) capacity retention rate indicates poorer wetting effect of the negative electrode sheet in the lithium-ion battery and poorer cycling performance of the lithium-ion battery. A higher 600-cls capacity retention rate indicates better wetting effect of the negative electrode sheet in the lithium-ion battery and better cycling performance of the lithium-ion battery.

[0067] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0068] Example 1-1

[0069] <Preparation of negative electrode sheet>

[0070] A mixture of natural graphite, a first negative electrode active material, and nano-SiO2, a silicon-based material, sodium carboxymethyl cellulose, a first dispersant, and styrene-butadiene rubber, a first negative electrode binder, were mixed in a mass ratio of 97.3:1.7:1.0, deionized water was added as a solvent, and the mixture was stirred and mixed uniformly to obtain a first negative electrode slurry with a solid content of 50 wt%. A mixture of natural graphite, a second negative electrode active material, and nano-SiO2, a second dispersant, sodium carboxymethyl cellulose, and styrene-butadiene rubber, a second negative electrode binder, were mixed in a mass ratio of 97.3:1.7:1.0, deionized water was added as a solvent, and the mixture was stirred and mixed uniformly to obtain a second negative electrode slurry with a solid content of 50 wt%. The first negative electrode slurry was evenly coated on one surface of the negative electrode current collector copper foil and dried at 105°C. The second negative electrode slurry was evenly coated on the surface of the first negative electrode material layer away from the negative electrode current collector copper foil and dried at 105°C to obtain a negative electrode sheet coated on one side with the first and second negative electrode material layers. 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 the first and second negative electrode material layers. After cold pressing and slitting, the end of the second negative electrode material layer is determined for the production of cylindrical lithium-ion batteries.

[0071] Starting from the end of the second negative electrode material layer, along the length of the negative electrode sheet, the first, second, and third sections of the second negative electrode material layer are determined. Based on the length of the second negative electrode material layer, the first section accounts for 30%, the second section accounts for 40%, and the third section accounts for 30%. The number of stripes per 2 cm of the second negative electrode material layer in the first section, a1, is 2; the number of stripes per 2 cm of the second negative electrode material layer in the second section, a2, is 5; and the number of stripes per 2 cm of the second negative electrode material layer in the third section, a3, is 3.

[0072] As shown in FIG2 , after unfolding the negative electrode sheet 100, a cross-sectional observation is conducted along the length direction (X direction) and the thickness direction (Z direction). The cross-sectional shape of a single stripe 30 is arc-shaped, the depth d of a single stripe 30 is 5.33 μm, and the width n of a single stripe 30 is 65 μm. Based on the above data, laser etching stripes are formed on the first, second, and third sections of the surface of the two second negative electrode material layers of the negative electrode sheet, resulting in a negative electrode sheet with a specification of 62 mm × 1464 mm. The mass percentage of Si element based on the mass of the first negative electrode material layer is 5.8%; the mass percentage of Si element W based on the mass of the second negative electrode material layer is 0.8%; the mass percentage of Si element X based on the mass of Si element in the negative electrode material layer is 12%, and the gram capacity C of the silicon-based material nano-scale SiO is 0.8%. Si The capacity is 1500 mAh / g, the average particle size of the silicon-based material nano-scale SiO is 75 nm, the ball milling time is 6 h, the thickness D of the second negative electrode material layer is 20 μm, and based on the thickness of the negative electrode material layer, the thickness of the second negative electrode material layer accounts for T of 60%.

[0073] <Preparation of positive electrode sheet>

[0074] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and are fully stirred and mixed to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 105°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. Thereafter, the above steps are repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 105°C for 4h to obtain a positive electrode sheet with a specification of 60.3mm×1400mm for standby use. Among them, the coating weight of the positive electrode material layer is 12mg / cm 2 The compaction density of the positive electrode material layer is 3.4g / cm3 .

[0075] <Preparation of Separator>

[0076] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0077] <Preparation of Electrolyte>

[0078] 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. Then, lithium hexafluorophosphate (LiPF6) was added to the organic solvents and mixed thoroughly to obtain an electrolyte solution. The mass percentage of LiPF6 in the electrolyte solution was 12.5%.

[0079] <Preparation of lithium-ion batteries>

[0080] The diaphragm, positive electrode sheet, diaphragm, and negative electrode sheet prepared above are stacked in order, so that the diaphragm is located between the positive and negative electrodes to play a role of isolation. After winding, flattening, current collecting plate welding, shelling, coding, vacuum drying, electrolyte injection, sealing, high-temperature standing, and then forming capacity, a cylindrical lithium-ion battery can be obtained. Wherein, when winding, winding is carried out from the position where the first section is located. After winding is completed, the first section is located near the winding center of the electrode assembly, and the third section is located away from the winding center of the electrode assembly. The upper limit voltage of formation is 3.6V, the formation temperature is 45°C, and the formation standing time is 2h.

[0081] Examples 1-2 to 1-28

[0082] The preparation parameters were the same as those in Example 1-1, except that they were adjusted according to Table 1. When D and W changed, the coating amount of the first negative electrode material layer, the coating amount of the second negative electrode material layer, the proportion of the silicon-based material in the mixture of the first negative electrode active material and the silicon-based material, and the proportion of the silicon-based material in the mixture of the second negative electrode active material and the silicon-based material were adjusted to achieve the values ​​of D and W as shown in Table 1.

[0083] Example 1-29 to Example 1-34

[0084] The preparation parameters were the same as those in Example 1-14 except that they were adjusted according to Table 1. When the average particle size of the silicon-based material particles changed, the ball milling time was adjusted to adjust the average particle size of the silicon-based material particles to the value shown in Table 1.

[0085] Examples 1-35

[0086] The process is the same as that of Example 1-14, except that the nano-sized SiO2 silicon-based material is replaced with micro-sized SiO2 and the preparation parameters are adjusted according to Table 1. The average particle size of the micro-sized SiO2 is 12 μm, i.e., 12,000 nm.

[0087] Examples 1-36

[0088] Except that the silicon-based material nano-scale SiO is replaced by nano-scale Si and the relevant parameters are adjusted according to Table 1, the rest is the same as Example 1-34.

[0089] Example 1-37 to Example 1-53

[0090] The preparation parameters were the same as those in Example 1-1, except that they were adjusted according to Table 1. When T and X changed, the coating amount of the first negative electrode material layer, the coating amount of the second negative electrode material layer, the proportion of the silicon-based material in the mixture of the first negative electrode active material and the silicon-based material, and the proportion of the silicon-based material in the mixture of the second negative electrode active material and the silicon-based material were adjusted to achieve the values ​​of T and X as shown in Table 1. When the average particle size of the silicon-based material particles changed, the ball milling time was adjusted to achieve the average particle size of the silicon-based material particles as shown in Table 1.

[0091] Example 2-1 to Example 2-8

[0092] Except for adjusting the preparation parameters according to Table 2, the rest is the same as Example 1-1.

[0093] Comparative Example 1

[0094] Except that no stripes are provided on the second negative electrode material layer, the rest is the same as Example 1-1.

[0095] Comparative Example 2

[0096] Except for using the following steps to prepare the negative electrode sheet, the rest is the same as Example 1-1.

[0097] <Preparation of negative electrode sheet>

[0098] A mixture of natural graphite (a negative electrode active material) and nano-SiO (a silicon-based material), sodium carboxymethyl cellulose (a dispersant), and styrene-butadiene rubber (a negative electrode binder) were mixed in a mass ratio of 97.3:1.7:1.0. Deionized water was then added as a solvent and the mixture was stirred to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was evenly coated on one surface of a 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 were 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. After cold pressing and slitting, stripes were laser-etched along the length of both negative electrode material layers of the negative electrode sheet, with two stripes per 2 cm of negative electrode material layer. The resulting negative electrode sheet measured 62 mm x 1464 mm. Among them, the cross-sectional shape of a single stripe is an arc. Along the thickness direction of the negative electrode sheet, the depth d of a single stripe is 5.33 μm. Along the length direction of the unfolded negative electrode sheet, the width n of a single stripe is 65 μm. Based on the mass of the negative electrode material layer, the mass percentage of Si element is 5.8%. The gram capacity C of the silicon-based material nano-scale SiO is Si The capacity is 1500 mAh / g, the average particle size of the silicon-based material nano-scale SiO is 75 nm, and the thickness of the negative electrode material layer is 33.3 μm.

[0099] Comparative Example 3

[0100] Except for using the following steps to prepare the negative electrode sheet, the rest is the same as Example 1-1.

[0101] <Preparation of negative electrode sheet>

[0102] A mixture of natural graphite (a negative electrode active material) and nano-SiO (a silicon-based material), sodium carboxymethyl cellulose (a dispersant), and styrene-butadiene rubber (a negative electrode binder) were mixed in a mass ratio of 97.3:1.7:1.0. Deionized water was then added as a solvent and the mixture was stirred to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was evenly coated on one surface of a 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 were 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. After cold pressing and slitting, stripes were laser-etched along the length of both negative electrode material layers of the negative electrode sheet, with two stripes per 2 cm of negative electrode material layer. The resulting negative electrode sheet measured 62 mm x 1464 mm. Among them, the cross-sectional shape of a single stripe is an arc. Along the thickness direction of the negative electrode sheet, the depth d of a single stripe is 5.33 μm. Along the length direction of the unfolded negative electrode sheet, the width n of a single stripe is 65 μm. Based on the mass of the negative electrode material layer, the mass percentage of Si element is 0.8%. The gram capacity C of the silicon-based material nano-scale SiO isSi The capacity is 1500 mAh / g, the average particle size of the silicon-based material nano-scale SiO is 75 nm, and the thickness of the negative electrode material layer is 33.3 μm.

[0103] Comparative Example 4

[0104] Except for using the following steps to prepare the negative electrode sheet, the rest is the same as Example 1-1.

[0105] <Preparation of negative electrode sheet>

[0106] A mixture of natural graphite, a negative electrode active material, and nano-SiO2, a silicon-based material, a dispersant sodium carboxymethyl cellulose, and a negative electrode binder styrene-butadiene rubber are mixed in a mass ratio of 97.3:1.7:1.0, and then deionized water is added as a solvent and stirred to obtain a negative electrode slurry with a solid content of 50wt%. The negative electrode slurry is evenly coated on one surface of the negative electrode current collector copper foil and dried at 105°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. 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 with a negative electrode material layer on both sides. After cold pressing and slitting, a negative electrode sheet with a specification of 62mm×1464mm is obtained. Among them, based on the mass of the negative electrode material layer, the mass percentage of Si element is 5.8%, and the gram capacity C of the silicon-based material nano-SiO2 is 0.1%. Si The capacity is 1500 mAh / g, the average particle size of the silicon-based material nano-scale SiO is 75 nm, and the thickness of the negative electrode material layer is 33.3 μm.

[0107] Comparative Example 5

[0108] Except for swapping the positions of the first negative electrode material layer and the second negative electrode material layer, the rest is the same as Example 1-1.

[0109] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0110] Table 1

[0111] Note: “ / ” in Table 1 indicates no relevant preparation parameters.

[0112] As can be seen from Examples 1-1 to 1-53 and Comparative Examples 1 to 5, by regulating the mass percentage of Si in the first negative electrode material layer to be greater than the mass percentage of Si in the second negative electrode material layer and providing stripes on the second negative electrode material layer, the lithium ion battery exhibits less lithium deposition and improves the 600cls capacity retention rate of the lithium ion battery, indicating that the electrolyte has good wetting effect on the negative electrode sheet of the present application, and the lithium ion battery has good lithium deposition performance and cycle performance. The lithium ion battery in Comparative Example 1 does not have stripes on the second negative electrode material layer. The lithium ion batteries in Comparative Examples 2 and 3 have only one negative electrode material layer on each side of the negative electrode current collector. The lithium ion battery in Comparative Example 4 has only one negative electrode material layer on each side of the negative electrode current collector, and no stripes are provided on the negative electrode material layer. In the lithium ion battery in Comparative Example 5, the mass percentage of Si in the first negative electrode material layer is less than the mass percentage of Si in the second negative electrode material layer. The lithium-ion batteries in Comparative Examples 1 to 5 had more severe lithium deposition and lower 600cls capacity retention rates. In contrast, the lithium-ion batteries in Examples 1-1 to 1-53 had less lithium deposition and higher 600cls capacity retention rates, indicating that the electrolyte had better wetting effect on the negative electrode sheet, and the lithium-ion batteries had better lithium deposition performance and cycle performance.

[0113] W×C Si The value of W×d / D usually affects the lithium deposition performance and cycle performance of lithium-ion batteries. Si When the value of ×d / D is within the range of this application, the degree of lithium plating of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high, indicating that the electrolyte in the embodiment of this application has a good wetting effect on the negative electrode sheet, and the lithium plating performance and cycle performance of the lithium-ion battery are good.

[0114] The thickness D of the second negative electrode material layer generally affects the lithium deposition performance and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-11, and 1-20, when the thickness D of the second negative electrode material layer is within the range of this application, the lithium deposition degree of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high. This indicates that the electrolyte has a good wetting effect on the negative electrode sheet in the examples of this application, and the lithium deposition performance and cycling performance of the lithium-ion battery are good.

[0115] The mass percentage W of the Si element in the second negative electrode material layer generally affects the lithium deposition performance and cycle performance of the lithium-ion battery. As can be seen from Examples 1-14, 1-21, and 1-28, when the mass percentage W of the Si element in the second negative electrode material layer is within the range of this application, the lithium deposition degree of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high, indicating that the electrolyte has a good wetting effect on the negative electrode sheet in the examples of this application, and the lithium deposition performance and cycle performance of the lithium-ion battery are good.

[0116] Gram capacity C of silicon-based materials Si It usually affects the lithium deposition performance and cycle performance of lithium-ion batteries. From Examples 1-14, 1-29 to 1-36, it can be seen that when the gram capacity C of the silicon-based material is Si Within the scope of this application, the degree of lithium plating of the lithium-ion battery is relatively light, and the 600cls capacity retention rate is relatively high, indicating that the electrolyte in the embodiment of this application has a good wetting effect on the negative electrode plate, and the lithium plating performance and cycle performance of the lithium-ion battery are good.

[0117] The thickness ratio T of the second negative electrode material layer generally affects the lithium deposition performance and cycle performance of the lithium-ion battery. As can be seen from Examples 1-1, 1-37, and 1-44, when the thickness ratio T of the second negative electrode material layer is within the range of this application, the lithium deposition degree of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high, indicating that the electrolyte in the examples of this application has a good wetting effect on the negative electrode sheet, and the lithium deposition performance and cycle performance of the lithium-ion battery are good.

[0118] The mass percentage X of the Si element in the second negative electrode material layer relative to the Si element in the negative electrode material layer generally affects the lithium deposition performance and cycle performance of the lithium-ion battery. As can be seen from Examples 1-45 to 1-53, when the mass percentage X of the Si element in the second negative electrode material layer relative to the Si element in the negative electrode material layer is within the range of this application, the lithium deposition degree of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high, indicating that the electrolyte has a good wetting effect on the negative electrode plate in the examples of this application, and the lithium deposition performance and cycle performance of the lithium-ion battery are good.

[0119] The depth d of a single stripe typically affects the lithium deposition and cycling performance of a lithium-ion battery. Examples 1-1 to 1-53 show that when the depth d of a single stripe falls within the range of this application, the lithium-ion battery exhibits less lithium deposition and a higher 600cls capacity retention rate. This indicates that the electrolyte in the examples of this application effectively wets the negative electrode sheet, leading to better lithium deposition and cycling performance in the lithium-ion battery.

[0120] Table 2

[0121] The width n of a single stripe typically affects the lithium deposition and cycling performance of a lithium-ion battery. Examples 1-1, 2-1, and 2-4 show that when the width n of a single stripe falls within the range of this application, the lithium-ion battery exhibits less lithium deposition and a higher 600 cls capacity retention rate. This indicates that the electrolyte in the examples of this application effectively wets the negative electrode sheet, resulting in better lithium deposition and cycling performance for the lithium-ion battery.

[0122] The number of stripes per 2 cm of the second negative electrode material layer in each section, i.e., the values ​​of a1, a2, and a3, generally affects the lithium deposition performance and cycling performance of the lithium-ion battery. As can be seen from Examples 1-1, 2-5, and 2-6, when the number of stripes per 2 cm of the second negative electrode material layer in each section, i.e., the values ​​of a1, a2, and a3, are within the range of this application, the lithium deposition of the lithium-ion battery is relatively mild, and the 600 cls capacity retention rate is relatively high, indicating that the electrolyte has a good wetting effect on the negative electrode sheet in the examples of this application, and the lithium deposition performance and cycling performance of the lithium-ion battery are good.

[0123] The length ratio of the first, second, and third segments generally affects the lithium deposition performance and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-7, and 2-8, when the length ratio of the first, second, and third segments is within the range of this application, the lithium deposition degree of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high, indicating that the electrolyte has a good wetting effect on the negative electrode sheet in the examples of this application, and the lithium deposition performance and cycling performance of the lithium-ion battery are good.

[0124] 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.

[0125] 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.

[0126] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A cylindrical secondary battery, which comprises a negative electrode tab, the negative electrode tab includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer; The first negative electrode material layer is located between the negative electrode current collector and the second negative electrode material layer, and both the first negative electrode material layer and the second negative electrode material layer include a silicon-based material. Based on the mass of the negative electrode material layer, the mass percentage of Si element in the first negative electrode material layer is greater than that in the second negative electrode material layer; The second negative electrode material layer is provided with a plurality of stripes, the plurality of stripes extend along the width direction after the negative electrode tab is unfolded, and the plurality of stripes are spaced along the length direction after the negative electrode tab is unfolded.

2. The cylindrical secondary battery according to claim 1, wherein, Along the thickness direction of the negative electrode tab, the thickness of the second negative electrode material layer is D μm, and the depth of a single stripe is d μm; Based on the mass of the second negative electrode material layer, the mass percentage content of Si element in the second negative electrode material layer is W, and the specific capacity of the silicon-based material is C Si mAh / g, 1.01 ≤ W × C Si × d / D ≤ 15.87, 10 ≤ D ≤ 55, 0.6% ≤ W ≤ 5%, 1300 ≤ C Si ≤ 1800.

3. The cylindrical secondary battery according to claim 2, wherein, 3.20 ≤ W × C Si × d / D ≤ 4.76 4. The cylindrical secondary battery according to any one of claims 1 to 3, wherein, Along the length direction after the negative electrode tab is unfolded, the second negative electrode material layer includes a first section, a second section and a third section connected in sequence; Based on the length of the second negative electrode material layer, the length proportion of the first section is 10% to 30%, the length proportion of the second section is 40% to 80%, and the length proportion of the third section is 10% to 30%; The stripes on the first section have a first density, the stripes on the second section have a second density, and the stripes on the third section have a third density. The second density is greater than the first density, and the third density is less than or equal to the second density.

5. The cylindrical secondary battery according to claim 4, wherein, The number of stripes on the second negative electrode material layer per 2 cm in the first section is 1 to 3, the number of stripes on the second negative electrode material layer per 2 cm in the second section is 4 to 6, and the number of stripes on the second negative electrode material layer per 2 cm in the third section is 2 to 4.

6. The cylindrical secondary battery according to any one of claims 1 to 5, wherein, Along the length direction after the negative electrode tab is unfolded, the width of a single stripe is n μm, and 45 ≤ n ≤ 85.

7. The cylindrical secondary battery according to any one of claims 1 to 6, wherein, Along the thickness direction of the negative electrode tab, the depth of a single stripe is d μm, and 1 ≤ d ≤ 30.

8. The cylindrical secondary battery according to any one of claims 1 to 7, wherein, Along the thickness direction of the negative electrode tab, the thickness of the second negative electrode material layer is D μm, and 12 ≤ D ≤ 45.

9. The cylindrical secondary battery according to any one of claims 1 to 8, wherein, Based on the mass of the second negative electrode material layer, the mass percentage of Si element in the second negative electrode material layer is W, and 1% ≤ W ≤ 2%.

10. The cylindrical secondary battery according to any one of claims 1 to 9, wherein, The specific capacity of the silicon-based material is C Si mAh / g, and 1400 ≤ C Si ≤ 1600.

11. The cylindrical secondary battery according to any one of claims 1 to 10, wherein, Based on the thickness of the negative electrode material layer, the thickness proportion of the second negative electrode material layer is T, and 40% ≤ T ≤ 80%.

12. The cylindrical secondary battery according to claim 11, wherein, 50％≤T≤75％。 13. The cylindrical secondary battery according to any one of claims 1 to 12, wherein, Based on the mass of Si element in the negative electrode material layer, the mass percentage of Si element in the second negative electrode material layer is X, and 5% ≤ X ≤ 20%.

14. The cylindrical secondary battery according to claim 13, wherein, 8％≤X≤15％。 15. An electronic device, which comprises the cylindrical secondary battery according to any one of claims 1 to 14.

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