Cylindrical secondary battery and electronic device

Abstract

This application provides a cylindrical secondary battery and an electronic device, including an electrode assembly. The electrode assembly includes a negative electrode sheet, which includes a negative current collector. A first negative electrode material layer is disposed on the surface of the negative current collector opposite to the winding center of the electrode assembly. Along the length direction of the unfolded negative electrode sheet and along the winding direction of the electrode assembly, the first negative electrode material layer includes a first segment and a second segment connected in sequence. Based on the length of the first negative electrode material layer, the length of the first segment accounts for 9% to 75%, and the length of the second segment accounts for 25% to 91%. Multiple first stripes are disposed on the first segment, and multiple second stripes are disposed on the second segment. Along the thickness direction of the negative electrode sheet, the average depth of the multiple first stripes is H1 μm, the average depth of the multiple second stripes is H2 μm, and the thickness of the first negative electrode material layer is H0 μm, where 50 ≤ H0 ≤ 100, 0.15 ≤ H2 / H0 ≤ 0.7, and 0.45 ≤ H1 / H2 ≤ 0.95. This configuration is beneficial for improving the lithium plating performance and cycle performance of the cylindrical secondary battery.

Description

Technical Field

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

[0002] Cylindrical secondary batteries, such as cylindrical lithium-ion batteries, are used in various high-rate discharge systems (such as 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 consumer electronics field.

[0003] Currently, high-power cylindrical lithium-ion batteries are typically designed with a full-tab design, where the positive and negative tabs extend from opposite directions and are fabricated using full-tab flattening or rolling techniques. However, in the later stages of cycling, insufficient electrode wetting and CB loss in full-tab cylindrical lithium-ion batteries reduce the kinetic performance of the battery, accelerating lithium plating and cycle degradation. Summary of the Invention

[0004] The purpose of this application is to provide a cylindrical secondary battery and electronic device to improve the wetting performance of the electrolyte on the negative electrode sheet, while reducing CB loss, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of cylindrical secondary batteries to explain the invention, the cylindrical secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] The first aspect of this application provides a cylindrical secondary battery, which includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector, and a first negative electrode material layer is disposed on the surface of the negative current collector away from the winding center of the electrode assembly. Along the length direction of the unfolded negative electrode and along the winding direction of the electrode assembly, the first negative electrode material layer includes a first segment and a second segment connected in sequence. Based on the length of the first negative electrode material layer, the length ratio of the first segment is 9% to 75%, and the length ratio of the second segment is 25% to 91%. Optionally, based on the length of the first negative electrode material layer, the length ratio of the first segment is 17% to 60%, and the length ratio of the second segment is 40% to 83%. The first segment is provided with a plurality of first stripes, which extend along the width direction of the unfolded negative electrode and are spaced apart along the length direction of the unfolded negative electrode. The second segment is provided with a plurality of second stripes, which extend along the width direction of the unfolded negative electrode and are spaced apart along the length direction of the unfolded negative electrode. Along the thickness direction of the negative electrode sheet, the average depth of the multiple first stripes in the first segment is H1 μm, the average depth of the multiple second stripes in the second segment is H2 μm, and the thickness of the first negative electrode material layer is H0 μm. The values ​​are: 50 ≤ H0 ≤ 100, 0.15 ≤ H2 / H0 ≤ 0.7, 0.45 ≤ H1 / H2 ≤ 0.95; optionally, 0.3 ≤ H2 / H0 ≤ 0.6, 0.7 ≤ H1 / H2 ≤ 0.85. By optimizing the stripe arrangement on the negative electrode sheet, setting first and second stripes of varying depths effectively reduces the risk of lithium plating and cycle performance degradation caused by insufficient CB value due to stripes placed at the lower CB value point (the initial winding segment) in the inner ring of the negative electrode sheet. Simultaneously, it ensures good wettability of the electrolyte to the negative electrode sheet, resulting in good lithium plating and cycle performance for the cylindrical secondary battery.

[0007] In one or more embodiments, along the length direction of the unfolded negative electrode sheet, the spacing between two adjacent first stripes is A1 mm, and the spacing between two adjacent second stripes is A2 mm, where 0.2 ≤ A1 / A2 ≤ 3, and 2 ≤ A2 ≤ 10; optionally, 0.5 ≤ A1 / A2 ≤ 1.5. By adjusting the values ​​of A1 / A2 and A2 within the above ranges, the wetting efficiency and performance of the electrolyte on the negative electrode sheet are improved, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0008] In one or more embodiments, along the length direction of the unfolded negative electrode sheet, the width of a single first stripe is W1 μm, the width of a single second stripe is W2 μm, 0.1 ≤ W1 / W2 ≤ 1.5, and 70 ≤ W2 ≤ 120; optionally, 0.6 ≤ W1 / W2 ≤ 1.2. By adjusting the values ​​of W1 / W2 and W2 within the above ranges, the risk of insufficient wetting of the negative electrode sheet by the electrolyte is reduced, and the lithium plating performance and cycle performance of the cylindrical secondary battery are improved while maintaining energy density.

[0009] In one or more embodiments, along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single first stripe to the width of the first negative electrode material layer is P1, where 0.2 ≤ P1 ≤ 1; or, the ratio of the length of a single second stripe to the width of the first negative electrode material layer is P2, where 0.2 ≤ P2 ≤ 1; optionally, 0.3 ≤ P1 ≤ 0.8; 0.3 ≤ P2 ≤ 0.8. By adjusting the values ​​of P1 and P2 within the above ranges, it is beneficial for the flow of electrolyte on the first negative electrode material layer, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0010] In one or more embodiments, along the width direction of the unfolded negative electrode sheet, the negative electrode current collector includes an empty foil region connected to the first negative electrode material layer. The empty foil region is provided with multiple third stripes, which extend along the width direction of the unfolded negative electrode sheet and are spaced apart along the length direction of the unfolded negative electrode sheet. By providing third stripes in the empty foil region, it is beneficial to provide more electrolyte flow channels for the empty foil region, especially the flattened portion within the empty foil region, thereby improving the internal resistance consistency of the secondary battery layers and thus improving the cycle performance and lithium plating performance of the cylindrical secondary battery.

[0011] In one or more embodiments, along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single third stripe to the width of the empty foil area is P3, where 0.1 ≤ P3 ≤ 0.7; optionally, 0.2 ≤ P3 ≤ 0.5. By adjusting P3 within the above range, it is beneficial for the flow of electrolyte in the empty foil area, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery while taking into account mechanical safety performance.

[0012] In one or more embodiments, along the thickness direction of the negative electrode sheet, the thickness of the negative electrode current collector is T0 μm, the average depth of the plurality of third stripes in the empty foil area opposite to the first segment is T1 μm, and the average depth of the plurality of third stripes in the empty foil area opposite to the second segment is T2 μm, where 3 ≤ T0 ≤ 20, 0.15 ≤ T2 / T0 ≤ 0.7, and 0.45 ≤ T1 / T2 ≤ 0.95. By adjusting the values ​​of T1 / T0, T2 / T0, and T0 within the above ranges, it is beneficial to set third stripes of different depths in the empty foil area, thereby improving the cycle performance of the cylindrical secondary battery while taking into account mechanical safety performance.

[0013] A second aspect of this application provides an electronic device comprising the cylindrical secondary battery of any of the foregoing embodiments. The cylindrical secondary battery of this application exhibits good cycle performance and lithium plating performance; therefore, the electronic device of this application has a long service life.

[0014] The beneficial effects of the embodiments of this application are as follows:

[0015] This application embodiment optimizes the stripe setting on the negative electrode sheet by setting first and second stripes of different depths. This effectively reduces the risk of lithium plating and cycle performance degradation caused by insufficient CB value due to setting stripes in the inner circle of the negative electrode sheet where the CB value is low. At the same time, it ensures that the electrolyte has good wettability to the negative electrode sheet, so that the cylindrical secondary battery has good lithium plating performance and cycle performance.

[0016] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0018] Figure 1 This is a schematic diagram of the winding structure formed by the electrode assembly in one embodiment of this application;

[0019] Figure 2 for Figure 1 A partial front view of the negative electrode sheet after the electrode assembly is unfolded;

[0020] Figure 3 for Figure 2 A cross-sectional view of the negative electrode sheet along the PP direction;

[0021] Figure 4 This is a cross-sectional view of the negative electrode sheet along the PP direction in another embodiment of this application;

[0022] Figure 5 This is a partial front view of the negative electrode sheet in another embodiment of this application;

[0023] Figure 6 This is a partial front view of the negative electrode sheet in another embodiment of this application;

[0024] Figure 7 This is a partial front view of the negative electrode sheet in another embodiment of this application;

[0025] Figure 8 for Figure 7 A cross-sectional view of the negative electrode plate along the QQ direction;

[0026] Reference numerals: Electrode assembly 001; Positive electrode 10; Positive current collector 11; Positive electrode material layer 12; Negative electrode 20; Negative current collector 21; First negative electrode material layer 22; Second negative electrode material layer 23; Separator 30; First stripe 221; First stripe 222; Empty foil area 210; Third stripe 211; Fourth stripe 231. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of cylindrical secondary batteries to explain this application, but the cylindrical secondary batteries in this application are not limited to lithium-ion batteries.

[0029] For high-power cylindrical secondary batteries, typically all-tab cylindrical lithium-ion batteries, in the later stages of cycling, the electrolyte wetting effect is poor on the surface of the negative electrode sheet away from the center of the electrode assembly winding, especially near the center. This poor wetting of the negative electrode sheet leads to a decrease in the cycle performance of the lithium-ion battery. Existing technologies use grooving to improve electrode wetting, but because the initial CB value on the inner ring of the negative electrode sheet away from the center of the electrode assembly is lower than other locations, insufficient CB at this point leads to lithium plating during the overall capacity decay of the negative electrode sheet in the later stages of cycling, thus affecting the kinetics and cycle performance of the cylindrical lithium-ion battery. Therefore, this application provides a cylindrical secondary battery with a negative electrode sheet exhibiting good wetting effect, and the secondary battery itself exhibiting good lithium plating performance and cycle performance. The specific technical solution is as follows:

[0030] The first aspect of this application provides a cylindrical secondary battery, which includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector, and a first negative electrode material layer is disposed on the surface of the negative current collector away from the winding center of the electrode assembly. Along the length direction of the unfolded negative electrode and along the winding direction of the electrode assembly, the first negative electrode material layer includes a first segment and a second segment connected in sequence. Based on the length of the first negative electrode material layer, the length ratio K1 of the first segment is 9% to 75%, and the length ratio K2 of the second segment is 25% to 91%. Optionally, based on the length of the first negative electrode material layer, the length ratio K1 of the first segment is 17% to 60%, and the length ratio K2 of the second segment is 40% to 83%. For example, the length percentage K1 of the first segment can be 9%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, or a range of any two of these values. The length percentage K2 of the second segment can be 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 91%, or a range of any two of these values. The first segment has multiple first stripes that extend along the width direction of the unfolded negative electrode sheet and are spaced apart along the length direction of the unfolded negative electrode sheet. The second segment has multiple second stripes that extend along the width direction of the unfolded negative electrode sheet and are spaced apart along the length direction of the unfolded negative electrode sheet. Along the thickness direction of the negative electrode sheet, the average depth of the multiple first stripes in the first segment is H1 μm, the average depth of the multiple second stripes in the second segment is H2 μm, and the thickness of the first negative electrode material layer is H0 μm, 50≤H0≤100, 0.15≤H2 / H0≤0.7, 0.45≤H1 / H2≤0.95; optionally, 0.3≤H2 / H0≤0.6, 0.7≤H1 / H2≤0.85.For example, the value of H0 can be 50, 52, 55, 58, 60, 62, 65, 68, 70, 72, 75, 78, 80, 82, 85, 88, 90, 92, 95, 98, 100, or a range of any two of these values; the value of H2 / H0 can be 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5, 0.52. The values ​​of H1 / H2 can be 0.45, 0.48, 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, or any two of these values; the values ​​of H1 / H2 can be 0.45, 0.48, 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, or any two of these values.

[0031] In this application, the length direction of the electrode assembly in its unfolded state is defined as the X direction, the width direction as the Y direction, and the thickness direction as the Z direction. It can be understood that the negative electrode, positive electrode, and separator in their unfolded state have the same length, width, and thickness directions as the electrode assembly, and the winding direction of the electrode assembly is the W direction. Figures 1 to 3 As shown, the electrode assembly 001 includes a positive electrode 10, a negative electrode 20, and a separator 30. The negative electrode 20 includes a negative current collector 21, and a first negative electrode material layer 22 is disposed on the surface of the negative current collector 21 away from the winding center of the electrode assembly 001. Along the length direction (X direction) of the unfolded negative electrode 20 and along the winding direction (W direction) of the electrode assembly 001, the first negative electrode material layer 22 includes a first segment (not shown in the figure) and a second segment (not shown in the figure) connected in sequence. The first segment is provided with a plurality of first stripes 221, which extend along the width direction (Y direction) of the unfolded negative electrode 20 and are spaced apart along the length direction (X direction) of the unfolded negative electrode 20. The second segment is provided with a plurality of second stripes 222, which extend along the width direction (Y direction) of the unfolded negative electrode 20 and are spaced apart along the length direction (X direction) of the unfolded negative electrode 20. The average depth of the multiple first stripes 221 located in the first segment is H1μm, the average depth of the multiple second stripes 222 located in the second segment is H2μm, the average depth of the multiple first stripes 221 located in the third segment is H3μm, and the thickness of the first negative electrode material layer 22 is H0μm.

[0032] When the length ratio K1 of the first segment is too small, for example, less than the lower limit of this application, that is, when the length ratio K2 of the second segment is too large, the area where the second stripe is set on the first negative electrode material layer is too large, and there is too much electrolyte on the negative electrode sheet, which is prone to side reactions with the negative electrode active material, increases the negative electrode interface impedance, and easily leads to lithium plating at the negative electrode interface. At the same time, the loss of negative electrode active material is too great. While reducing the energy density of the secondary battery, the surface of the negative electrode sheet, especially the area near the winding center of the electrode assembly (inner ring or winding start section of the negative electrode sheet), is prone to insufficient CB, which further increases the risk of lithium plating at the negative electrode interface, thereby affecting the lithium plating performance and cycle performance of the secondary battery. When the length ratio K1 of the first segment is too large, for example, greater than the upper limit of this application, i.e., the length ratio K2 of the second segment is too small, the area where the second stripe is set on the first negative electrode material layer is too small. This is not conducive to the flow of electrolyte on the negative electrode sheet, the wetting effect of electrolyte on the negative electrode sheet is poor, the kinetics of the negative electrode sheet deteriorates and lithium plating easily occurs, and the cycle performance and lithium plating performance of the secondary battery cannot be significantly improved. When the value of H2 / H0 is too small, for example, less than the lower limit of this application, the depth of the second stripe on the first negative electrode material layer is too small. This is not conducive to the flow of electrolyte on the negative electrode sheet, the wetting effect of electrolyte on the negative electrode sheet is poor, the electrochemical impedance of the negative electrode sheet is large, the kinetics of the negative electrode sheet deteriorates and lithium plating easily occurs, and the cycle performance and lithium plating performance of the secondary battery cannot be significantly improved. When the H2 / H0 value is too large, for example, greater than the upper limit of this application, the depth of the second stripe on the first negative electrode material layer is too large, resulting in excessive loss of negative electrode active material. This can further increase the risk of lithium plating at the negative electrode interface due to insufficient CB (concentration bond), thus affecting the lithium plating performance and cycle performance of the secondary battery. When the H1 / H2 value is too small, i.e., less than the lower limit of this application, it is not conducive to the flow of electrolyte on the negative electrode sheet. In the later stages of cycling, insufficient electrolyte wetting can increase the negative electrode interface resistance, thereby affecting the cycle performance of the secondary battery. When the H1 / H2 value is too large, i.e., greater than the upper limit of this application, the negative electrode sheet near the center of the electrode assembly winding (i.e., the inner ring of the negative electrode sheet) experiences excessive loss of negative electrode active material. This can further increase the risk of lithium plating at the negative electrode interface due to insufficient CB, reducing the safety performance of the secondary battery and thus affecting its lithium plating performance and cycle performance.This application sets a first stripe on the first segment and a second stripe on the second segment, and adjusts the length ratios K1 and K2 of the first segment, H0, H2 / H0, and H1 / H2 within the aforementioned ranges. The first and second stripes are set in combination, achieving a synergistic effect. This accelerates the flow of electrolyte on the negative electrode, effectively improving the wetting efficiency and performance of the electrolyte on the negative electrode layer. While ensuring the effective wetting of the negative electrode, it reduces the risk of lithium plating and cycle performance degradation due to insufficient CB value in the negative electrode, especially in areas with low CB values ​​(near the electrode assembly winding center or the winding start section), caused by the stripes. This improves the lithium plating and cycle performance of the secondary battery. Through this arrangement, the cylindrical secondary battery achieves good lithium plating and cycle performance while ensuring good electrolyte wetting of the negative electrode. In this application, the "surface" in "a first negative electrode material layer is disposed on the surface of the negative electrode current collector away from the winding center of the electrode assembly" can be the entire surface of the negative electrode current collector or a part of the surface of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved. In this application, the thickness H0 of the first negative electrode material layer can be controlled by means known to those skilled in the art. For example, when coating the negative electrode slurry onto the surface of the negative electrode current collector, given a certain solid content in the negative electrode slurry, the thickness H0 of the first negative electrode material layer can be increased by increasing the coating weight, and decreased by decreasing the coating weight; alternatively, when cold-pressing the negative electrode sheet, the thickness H0 of the first negative electrode material layer can be decreased by increasing the cold-pressing pressure, and increased by decreasing the cold-pressing pressure.

[0033] In this application, the CB value refers to the ratio between the capacity of a negative electrode sheet per unit area and the capacity of a positive electrode sheet per unit area under the same conditions, such as an ambient temperature of 25°C and a discharge rate of 0.1C. CB = (Specific capacity of negative electrode active material × Mass of negative electrode active material per unit area of ​​negative electrode sheet) / (Specific capacity of positive electrode active material × Mass of positive electrode active material per unit area of ​​positive electrode sheet). The aforementioned unit area refers to 1 mm². 2 .

[0034] In one or more embodiments, 7.5 ≤ H2 ≤ 70; and / or, 3.375 ≤ H1 ≤ 66.5. For example, the value of H2 can be 7.5, 7.8, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, 65, 68, 70, or a range of any two of these values; the value of H1 can be 3.375, 3.4, 3.5, 3.8, 4, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, 65, 66, 66.5, or a range of any two of these values. By adjusting the values ​​of H2 and H1 within the aforementioned range, the first and second stripes are set together, achieving a synergistic effect. This accelerates the flow of electrolyte on the negative electrode, effectively improving the wetting efficiency and performance of the electrolyte on the negative electrode layer. While ensuring the wetting effect of the electrolyte on the negative electrode, it reduces the risk of lithium plating and cycle performance degradation due to insufficient CB value in the negative electrode, especially in areas with low CB values ​​in the inner ring of the negative electrode (near the winding center of the electrode assembly or the starting section of the winding), thereby improving the lithium plating performance and cycle performance of the secondary battery.

[0035] In one or more embodiments, such as Figure 3 As shown, along the length direction (X direction) of the unfolded negative electrode plate 20, the distance between two adjacent first stripes 221 is A1 mm, and the distance between two adjacent second stripes 222 is A2 mm, where 0.2 ≤ A1 / A2 ≤ 3, 2 ≤ A2 ≤ 10; optionally, 0.5 ≤ A1 / A2 ≤ 1.5. For example, the value of A1 / A2 can be 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, or a range of any two of these values; the value of A2 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two of these values. By adjusting the values ​​of A1 / A2 and A2 within the aforementioned range, it is beneficial for the electrolyte to flow on the negative electrode sheet, and the electrolyte can easily flow to the inner ring of the negative electrode sheet, improving the wetting effect of the electrolyte on the negative electrode sheet and enhancing its wetting performance. Simultaneously, it helps reduce the processing difficulty of the grooving process and the risk of local collapse of the first negative electrode material layer, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery. In this application, the spacing between two adjacent first stripes refers to the distance between the centers of the widths of two adjacent first stripes along the length direction after the negative electrode sheet is unfolded. The spacing between two adjacent second stripes refers to the distance between the centers of the widths of two adjacent second stripes along the length direction after the negative electrode sheet is unfolded.

[0036] In one or more embodiments, 0.4 ≤ A1 ≤ 30. For example, the value of A1 can be 0.4, 0.5, 0.8, 1, 3, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, or a range of any two of these values. By adjusting the value of A1 within the above range, it is beneficial for the flow of electrolyte on the negative electrode sheet, and the electrolyte can easily flow to the inner ring of the negative electrode sheet, improving the wetting effect of the electrolyte on the negative electrode sheet and enhancing the wetting performance of the electrolyte on the negative electrode sheet. At the same time, it helps to reduce the processing difficulty of the grooving process and the risk of local collapse of the first negative electrode material layer, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0037] In one or more embodiments, such as Figure 3 As shown, along the length direction (X direction) of the unfolded negative electrode plate 20, the width of a single first stripe 221 is W1μm, the width of a single second stripe 222 is W2μm, 0.1≤W1 / W2≤1.5, 70≤W2≤120; optionally, 0.6≤W1 / W2≤1.2. For example, the value of W1 / W2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5 or a range of any two of these values; the value of W2 can be 70, 72, 75, 78, 80, 82, 85, 88, 90, 92, 95, 98, 100, 102, 105, 108, 110, 112, 115, 118, 120 or a range of any two of these values. By adjusting the values ​​of W1 / W2 and W2 within the aforementioned range, it is beneficial for the electrolyte to flow through the negative electrode sheet, especially the inner ring of the negative electrode sheet. This reduces the risk of insufficient wetting of the negative electrode sheet by the electrolyte and improves the wetting effect of the electrolyte on the negative electrode sheet. At the same time, it helps to reduce the processing difficulty and the risk of insufficient CB due to excessive loss of negative electrode active material in the inner ring of the negative electrode sheet, which leads to lithium plating at the negative electrode interface. While taking into account the energy density, it improves the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0038] In one or more embodiments, 7 ≤ W1 ≤ 180. For example, the value of W1 can be 7, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, or a range of any two of these values. By adjusting the value of W1 within the above range, it is beneficial to the flow of electrolyte in the negative electrode sheet, especially in the inner ring of the negative electrode sheet, which reduces the risk of insufficient wetting of the negative electrode sheet by the electrolyte and improves the wetting effect of the electrolyte on the negative electrode sheet. At the same time, it helps to reduce the processing difficulty and the risk of insufficient CB due to excessive loss of negative electrode active material in the inner ring of the negative electrode sheet, which leads to lithium plating at the negative electrode interface. While taking into account the energy density, it improves the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0039] In one or more embodiments, along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single first stripe to the width of the first negative electrode material layer is P1, where 0.2 ≤ P1 ≤ 1; or, the ratio of the length of a single second stripe to the width of the first negative electrode material layer is P2, where 0.2 ≤ P2 ≤ 1; optionally, 0.3 ≤ P1 ≤ 0.8; 0.3 ≤ P2 ≤ 0.8. For example, the value of P1 can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range of any two values ​​therein; the value of P2 can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range of any two values ​​therein. By adjusting the values ​​of P1 and P2 within the aforementioned range, it is beneficial for the electrolyte to flow through the first negative electrode material layer, reducing the risk of insufficient wetting of the negative electrode sheet, especially along the width direction after the negative electrode sheet is unfolded, and the middle part of the negative electrode sheet. This effectively improves the wetting performance of the electrolyte on the negative electrode sheet, while reducing the processing difficulty in the actual production process and reducing the risk of excessive loss of negative electrode active material content in the first negative electrode material layer leading to lithium plating at the negative electrode interface. This improves the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0040] In this application, the negative electrode sheet may further include a second negative electrode material layer, such as... Figure 1As shown, the negative electrode sheet 20 also includes a second negative electrode material layer 23, which is disposed on a surface facing the winding center of the electrode assembly 001. Here, "surface" can refer to the entire surface of the negative electrode current collector or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved. In one or more embodiments, the second negative electrode material layer is provided with a plurality of fourth stripes, which extend along the width direction of the unfolded negative electrode sheet and are spaced apart along the length direction of the unfolded negative electrode sheet. In one or more embodiments, as... Figure 4 As shown, along the thickness direction of the negative electrode sheet 20, the thickness of the second negative electrode material layer is H'0 μm, and the average depth of the plurality of fourth stripes is H4 μm, 0.15≤H4 / H'0≤0.7, 50≤H'0≤100. In one or more embodiments, along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single third stripe to the width of the second negative electrode material layer is P4, 0.2≤P4≤1. In one or more embodiments, as... Figure 4 As shown, along the length direction (X direction) of the unfolded negative electrode plate 20, the width of a single fourth stripe 231 is W4 μm, where 70 ≤ W4 ≤ 120. In one or more embodiments, as... Figure 4 As shown, along the length direction (X direction) of the unfolded negative electrode sheet 20, the spacing between two adjacent fourth stripes 231 is A4 mm, where 2 ≤ A4 ≤ 10. This arrangement improves the wetting effect of the electrolyte on the second negative electrode material layer. The different stripe arrangements in the first and second negative electrode material layers result in good electrolyte wetting of the negative electrode sheet, reducing the risk of lithium plating due to insufficient CB value in the negative electrode sheet, especially in areas with low CB values ​​(near the electrode assembly winding center or the winding start section). This improves the lithium plating performance and cycle performance of the cylindrical secondary battery. In this application, the spacing between two adjacent fourth stripes refers to the distance between the centers of the widths of two adjacent fourth stripes along the length direction of the unfolded negative electrode sheet.

[0041] In one or more embodiments, along the width direction of the unfolded negative electrode sheet, the negative electrode current collector includes an empty foil region connected to the first negative electrode material layer. The empty foil region is provided with a plurality of third stripes, which extend along the width direction of the unfolded negative electrode sheet and are spaced apart along the length direction of the unfolded negative electrode sheet. Figure 5 and Figure 6As shown, along the width direction (Y direction) of the unfolded negative electrode sheet 20, the negative electrode current collector 21 includes an empty foil region 210 connected to the first negative electrode material layer 22. The empty foil region 210 is provided with multiple third stripes 211, which extend along the width direction (Y direction) of the unfolded negative electrode sheet and are spaced apart along the length direction (X direction) of the unfolded negative electrode sheet 20. By providing third stripes in the empty foil region, it is beneficial to provide more electrolyte flow channels for the empty foil region, especially the flattened part in the empty foil region, and improve the diffusion efficiency of the electrolyte in the empty foil region. In addition, the third stripe in the empty foil region has little impact on the capacity of the secondary battery and can effectively reduce the electrochemical impedance. By combining the first stripe, the second stripe and the third stripe, the first stripe, the second stripe and the third stripe achieve synergistic effect, which effectively improves the wetting efficiency and wetting performance of the electrolyte to the negative electrode sheet layer, thereby improving the internal resistance consistency of the secondary battery layer, and thus improving the cycle performance and lithium plating performance of the cylindrical secondary battery.

[0042] In one or more embodiments, along the length direction after the negative electrode sheet is unfolded, the center line of the third stripe does not coincide with the center line of the first stripe or the center line of the second stripe.

[0043] In one or more embodiments, along the length of the unfolded negative electrode sheet, only a portion of the center line of the third fringe coincides with the center lines of multiple first fringe patterns. In one or more embodiments, along the length of the unfolded negative electrode sheet, only a portion of the center line of the third fringe coincides with the center lines of multiple second fringe patterns. For example... Figure 5 and Figure 6 As shown, along the length direction (X direction) of the unfolded negative electrode sheet 20, the center line of a portion of the third stripe 211 coincides with the center lines of a plurality of second stripes 222. In one or more embodiments, along the length direction of the unfolded negative electrode sheet, the center line of a portion of the third stripe coincides with the center lines of a plurality of first stripes, and simultaneously, the center line of a portion of the third stripe coincides with the center lines of a plurality of second stripes. Figure 7 As shown, along the length direction (X direction) of the unfolded negative electrode 20, the center line of a portion of the third stripe 211 coincides with the center line of multiple first stripes 221, and simultaneously, the center line of a portion of the third stripe 211 coincides with the center line of multiple second stripes 222. This arrangement accelerates the flow of electrolyte on the negative electrode, thereby further improving the wetting effect of the electrolyte on the negative electrode, resulting in better cycle performance and lithium plating performance of the cylindrical secondary battery.

[0044] In one or more embodiments, along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single third stripe to the width of the empty foil area is P3, where 0.1 ≤ P3 ≤ 0.7; optionally, 0.2 ≤ P3 ≤ 0.5. For example, the value of P3 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or a range consisting of any two of these values. By adjusting P3 within the above range, it is beneficial for the flow of electrolyte in the empty foil area, improving the wetting effect of the electrolyte on the negative electrode sheet, effectively improving the wetting performance of the electrolyte on the negative electrode sheet, and reducing the safety risk of reduced mechanical performance of the secondary battery due to the decrease in the strength of the empty foil area during the secondary battery preparation process. While taking into account mechanical safety performance, it improves the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0045] In one or more embodiments, such as Figure 8As shown, along the thickness direction (Z direction) of the negative electrode sheet 20, the thickness of the negative electrode current collector 21 is T0 μm, the average depth of the plurality of third stripes 211 set in the empty foil area 210 opposite to the first section is T1 μm, the average depth of the plurality of third stripes 211 set in the empty foil area 210 opposite to the second section is T2 μm, 3≤T0≤20, 0.15≤T2 / T0≤0.7, 0.45≤T1 / T2≤0.95. For example, the value of T0 can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range of any two of these values; the value of T2 / T0 can be 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5, 0.52, 0.55, 0. The values ​​T1 / T2 can be 0.45, 0.48, 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, or any two of these values. By adjusting the values ​​of T1 / T0, T2 / T0, and T0 within the aforementioned range, it is beneficial to set third stripes of different depths on the empty foil area, thereby improving the diffusion efficiency of the electrolyte to the empty foil area of ​​the negative electrode current collector and enhancing the wetting effect of the electrolyte on the negative electrode sheet. Simultaneously, it helps reduce the risk of the empty foil area being punctured by the third stripe when it is set in the empty foil area, thus improving the cycle performance of the cylindrical secondary battery while maintaining mechanical safety. This application does not impose any particular restrictions on the method of adjusting the thickness T0 of the negative electrode current collector, as long as it achieves the purpose of this application. For example, commercially available negative electrode current collectors of different thicknesses can be selected, and the thickness of the negative electrode current collector can be determined by combining the test methods described in this application for "testing T1, T2, H1, H2, T0, H0, H4, H'0, P1, P2, P3, P4, W1, W2, A1, A2, A4," thereby selecting a negative electrode current collector of the desired thickness.

[0046] This application does not impose any particular limitation on the width of a single third stripe, as long as it achieves the purpose of this application. For example, along the length direction after the negative electrode sheet is unfolded, the width of a single third stripe set in the empty foil area opposite to the first segment is W'1 μm, and the width of a single third stripe set in the empty foil area opposite to the second segment is W'2 μm, where 0.1 ≤ W'1 / W'2 ≤ 1.5, and 70 ≤ W'2 ≤ 120. By adjusting the values ​​of W'1 / W'2 and W'2 within the above range, it is beneficial to the flow of electrolyte in the empty foil area, improving the diffusion efficiency of electrolyte in the empty foil area, thereby effectively improving the wetting efficiency and wetting performance of electrolyte in the negative electrode sheet. At the same time, it reduces the processing difficulty in the actual production process and reduces the safety risk of reduced mechanical performance of the secondary battery due to the decrease in the strength of the empty foil area during the secondary battery preparation process. While taking into account mechanical safety performance, it improves the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0047] This application does not impose any particular limitation on the spacing between two adjacent third stripes, as long as the purpose of this application can be achieved. For example, along the length direction after the negative electrode sheet is unfolded, the spacing between two adjacent third stripes in the empty foil area opposite to the first segment is A'1 mm, and the spacing between two adjacent third stripes in the empty foil area opposite to the second segment is A'2 mm, where 0.2 ≤ A'1 / A'2 ≤ 3, and 2 ≤ A'2 ≤ 10. By adjusting the values ​​of A'1 / A'2 and A'2 within the above ranges, it is beneficial for the flow of electrolyte in the empty foil area, improving the electrolyte's effect on the negative electrode.

[0048] The improved wetting effect of the electrode sheet helps reduce the processing difficulty of the grooving process and the risk of local collapse in the empty foil area. While ensuring mechanical safety, it also improves the lithium plating performance and cycle performance of the cylindrical secondary battery. In this application, the spacing between two adjacent third stripes refers to the distance between the centers of the widths of two adjacent third stripes along the length direction after the negative electrode sheet is unfolded.

[0049] In this application, the cross-sections of a single first stripe, a single second stripe, a single third stripe, and a single fourth stripe refer to the planes formed by the first, second, third, and fourth stripes along their length and thickness directions after unfolding the negative electrode sheet (or the cross-sections obtained by viewing the first, second, third, and fourth stripes along their length and thickness directions after unfolding the negative electrode sheet). This application does not impose any particular limitation on the cross-sectional shape of the single first, second, third, and fourth stripes, as long as it achieves the purpose of this application. For example, the cross-sections of the single first, second, third, and fourth stripes can each be independently selected from at least one of the following: triangle, arc (with an area smaller than a semicircle with the same radius), semicircle, rectangle, trapezoid, or square.

[0050] There is no particular limitation on the cross-sectional shape obtained by cross-sectioning the first stripe, the second stripe, the third stripe, and the fourth stripe along the length direction and the width direction after being unfolded on the negative electrode tab, as long as the object of the present application can be achieved. For example, the cross-sectional shape obtained by cross-sectioning the first stripe, the second stripe, the third stripe, and the fourth stripe along the length direction and the width direction after being unfolded on the negative electrode tab can be linear, curved, or other specific shapes, etc. As Figure 2 , Figure 5 , Figure 6 and Figure 7 shown, the cross-sectional shape obtained by cross-sectioning the first stripe 221, the second stripe 222, and the third stripe 211 along the length direction (X direction) and the width direction (Y direction) after being unfolded on the negative electrode tab 20 is linear.

[0051] There is no particular limitation on the negative electrode current collector of the present application, as long as the object of the present application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). The first negative electrode material layer and the second negative electrode material layer of the present application contain a negative electrode active material, and there is no particular limitation on the negative electrode active material and the type of the negative electrode active material, as long as the object of the present application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x ≤ 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12The material comprises at least one of Li-Al alloy or metallic lithium. In this application, there are no particular limitations on the thickness of the negative electrode current collector, the first negative electrode material layer, and the second negative electrode material layer, as long as the purpose of this application is achieved. Optionally, the first negative electrode material layer and the second negative electrode material layer may further include a conductive agent and a negative electrode binder. This application does not particularly limit the type of conductive agent in the first and second negative electrode material layers, as long as the purpose of this application is achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (SuperP), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the type of negative electrode binder in the first and second negative electrode material layers, as long as it achieves the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, conductive agent, and negative electrode binder in the first and second negative electrode material layers, as long as it achieves the purpose of this application.

[0052] This application does not impose any particular restrictions on the preparation method of the negative electrode sheet, as long as it can achieve the purpose of this application. For example, the preparation method of the negative electrode sheet may include, but is not limited to, the following steps: (1) mixing the negative electrode active material, negative electrode binder, and conductive agent, adding solvent and stirring evenly to prepare a negative electrode slurry; (2) pre-determining the surface of the negative electrode current collector away from the winding center of the electrode assembly, coating the negative electrode slurry on the surface of the negative electrode current collector away from the winding center of the electrode assembly, and drying it to obtain a negative electrode sheet coated with the first negative electrode material layer; (3) after cold pressing and slitting, along the width direction of the unfolded negative electrode sheet and along the winding direction of the electrode assembly, determining the first segment and the second segment of the first negative electrode material layer, setting the first stripe on the first segment and setting the second stripe on the second segment, thus obtaining the negative electrode sheet.

[0053] In one or more embodiments, after step (2), the negative electrode slurry is coated onto another surface of the negative electrode current collector, and dried to obtain a negative electrode sheet coated with a first negative electrode material layer and a second negative electrode material layer. In one or more embodiments, in step (3), along the width direction after the negative electrode sheet is unfolded, an empty foil area of ​​the negative electrode current collector connected to the first negative electrode material layer is determined, and a first stripe is set on the first segment, a second stripe is set on the second segment, and a third stripe is set on the empty foil area. In one or more embodiments, in step (3), while setting the first stripe on the first segment and the second stripe on the second segment, a fourth stripe is set on the second negative electrode material layer. In one or more embodiments, in step (3), while setting the first stripe on the first segment and the second stripe on the second segment, a third stripe is set on the empty foil area and a fourth stripe is set on the second negative electrode material layer.

[0054] This application does not impose any particular limitation on the solid content of the slurry, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the drying temperature and time, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the process parameters for cold pressing and slitting, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the manner in which the first, second, third, and fourth stripes are set, as long as the purpose of this application can be achieved. For example, pulsed laser etching can be used to set the first, second, third, and fourth stripes. The average depth H1 of the multiple first stripes located in the first segment, the average depth H2 of the multiple second stripes located in the second segment, the average depth T1 μm of the multiple third stripes located in the empty foil area opposite to the first segment, the average depth T2 μm of the multiple third stripes located in the empty foil area opposite to the second segment, the average depth H4 of the multiple fourth stripes, the width W1 of a single first stripe, the width W2 of a single second stripe, the width W' of a single third stripe, and the width W4 of a single fourth stripe can be adjusted by the power and defocusing amount of the pulsed laser emitter; the ratio P1 of the length of a single first stripe to the width of the first negative electrode material layer, and the ratio P' of the length of a single second stripe to the width of the first negative electrode material layer are all adjustable by the power and defocusing amount of the pulsed laser emitter. 2. The ratio P3 of the length of a single third stripe to the width of the empty foil area can be adjusted by adjusting the width of the empty foil area, the power of the pulsed laser emitter, and the defocusing amount; the ratio P4 of the length of a single fourth stripe to the width of the second negative electrode material layer can be adjusted by adjusting the width of the second negative electrode material layer, the power of the pulsed laser emitter, and the defocusing amount; the spacing A1 between two adjacent first stripes, the spacing A2 between two adjacent second stripes, the spacing A' between two adjacent third stripes, and the spacing A4 between two adjacent fourth stripes can be adjusted by adjusting the spacing between the pulsed laser emitters or the laser emission frequency.

[0055] In this application, the different features of the stripes included in the negative electrode sheet can be combined, and the implementation methods or embodiments covered by the above combinations are all within the protection scope of this application.

[0056] This application does not impose any particular limitation on the positive electrode sheet, as long as the purpose of this application can be achieved. For example, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The aforementioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its own thickness direction, or it can be disposed on two surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or it can be a partial surface area of ​​the positive current collector; this application does not impose any particular limitation, as long as the purpose of this application can be achieved. Figure 1 As shown, the positive electrode 10 includes a positive current collector 11 and a positive electrode material layer 12 disposed on both surfaces of the positive current collector 11. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). The positive electrode material layer of this application includes a positive electrode active material. This application does not impose any particular limitation on the type of positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05 At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application is achieved. In this application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. In this application, there are no particular limitations on the type of positive electrode binder in the positive electrode material layer, as long as the purpose of this application is achieved; for example, the positive electrode binder may be the same type as the negative electrode binder in the first and second negative electrode material layers described above. This application does not impose any particular restrictions on the type of conductive agent in the positive electrode material layer, as long as it achieves the purpose of this application. For example, the conductive agent can be the same type as the conductive agent in the first negative electrode material layer and the second negative electrode material layer. This application does not impose any particular restrictions on the mass ratio of the positive electrode active material, the conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0057] The cylindrical secondary battery of this application includes an electrolyte comprising a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not limit the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. This application does not particularly limit the non-aqueous solvent, as long as it achieves the purpose of this application. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate, or vinylene carbonate. Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1,2-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0058] This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane. The diaphragm of this application may have a porous structure, and this application does not impose any particular limitation on the size of the pores in the porous structure of the diaphragm, as long as it achieves the purpose of this application. For example, the pore size may be from 0.01 μm to 1 μm. This application does not impose any particular limitation on the thickness of the diaphragm, as long as it achieves the purpose of this application. For example, the thickness of the diaphragm may be from 5 μm to 40 μm.

[0059] The cylindrical secondary battery of this application also includes a casing for housing the positive electrode, negative electrode, separator, and electrolyte, as well as other components known in the art for cylindrical secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it can achieve the purpose of this application.

[0060] The cylindrical secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one or more embodiments, the cylindrical secondary battery may include, but is not limited to, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0061] This application does not impose any particular limitation on the preparation method of the cylindrical secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the cylindrical secondary battery includes, but is not limited to, the following steps: stacking the separator, negative electrode, separator and positive electrode in sequence, and winding and folding them as needed to obtain a wound electrode assembly; placing the electrode assembly into the housing; welding the current collector and assembling the insulating sheet; and then injecting the electrolyte into the housing and sealing it to obtain the cylindrical secondary battery.

[0062] A second aspect of this application provides an electronic device comprising the cylindrical secondary battery of any of the foregoing embodiments. The cylindrical secondary battery of this application exhibits good cycle performance and lithium plating performance; therefore, the electronic device of this application has a long service life.

[0063] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0064] Example

[0065] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0066] Test methods and equipment:

[0067] Tests for T1, T2, H1, H2, T0, H0, H4, H'0, P1, P2, P3, P4, W1, W2, A1, A2, and A4:

[0068] At an ambient temperature of 25℃, the lithium-ion battery was discharged to 2.5V at 0.5C and then disassembled. The negative electrode sheet was removed, and the first and second negative electrode material layers were determined based on the orientation of the negative electrode sheet in the electrode assembly. The negative electrode sheet was soaked in dimethyl carbonate (DMC) for 20 minutes, and then placed in an oven and dried at 80℃ for 12 hours to obtain the negative electrode sheet sample.

[0069] Along the width direction after the negative electrode sheet is unfolded, the empty foil area of ​​the negative electrode current collector and the coating area on which the first negative electrode material layer is disposed are distinguished by the junction area between the negative electrode current collector and the first negative electrode material layer, and the boundary line between the empty foil area and the coating area is determined.

[0070] The negative electrode sheet was cut along its thickness direction and the boundary between the empty foil area and the coating area to obtain the longitudinal section of the coating area, i.e., the longitudinal section of the region containing the first and second negative electrode material layers (i.e., the cross-section of the negative electrode sheet along the PP direction); and the longitudinal section of the empty foil area, i.e., the cross-section of the negative electrode sheet along the QQ direction. Each longitudinal section was measured using a scanning electron microscope.

[0071] The cross-section of the negative electrode sheet along the PP direction is ion-polished and observed using an electron scanning microscope. This reveals clear boundaries between the first and second negative electrode material layers and the negative electrode current collector. The thickness H0 of the first negative electrode material layer is measured along the thickness direction of the negative electrode sheet. Based on the variation in stripe depth along the thickness direction of the negative electrode sheet, the first and second stripes are determined, thus identifying the first and second segments of the first negative electrode material layer. The stripe with the greater depth is the second stripe. Five first stripes from the first segment are randomly selected. Along the width direction of the unfolded negative electrode sheet, the positions of the two ends and the midpoint of each individual first stripe in the first segment are identified. Then, along the thickness direction of the negative electrode sheet, the distances from the surface of the first negative electrode material layer to the bottom surface at the two ends and the midpoint of each individual first stripe in the first segment are measured. The average of these distances is the depth of the individual first stripe in the first segment. The average depth H1 of the five individual first stripe depths in the first segment is obtained. Select any 5 second stripes from the second segment. Along the width direction of the unfolded negative electrode sheet, identify the positions of the two ends and the midpoint of each individual second stripe in the second segment. Then, along the thickness direction of the negative electrode sheet, measure the distance from the surface of the first negative electrode material layer to the bottom surface at the two ends and the midpoint of each individual second stripe in the second segment. Take the average value; this is the depth of a single second stripe in the second segment. Take the average depth of the five individual second stripes in the second segment; this is the average depth H2 of the multiple second stripes in the second segment. Select any single first stripe from the first segment. Along the width direction of the unfolded negative electrode sheet, select any 5 positions on the stripe. Then, along the length direction of the unfolded negative electrode sheet, measure the width at the 5 selected positions on the stripe. Take the average value; this is the width W1 of a single first stripe. Along the length direction of the unfolded negative electrode sheet, measure the distance between the center of the width of a single first stripe and the center of the width of an adjacent first stripe. Select 5 positions and measure once for each. Take the average value; this is the spacing A1 between two adjacent first stripes. Select any single second stripe from the second segment. Along the width direction of the unfolded negative electrode sheet, randomly select 5 positions on this stripe. Then, along the length direction of the unfolded negative electrode sheet, measure the width at the 5 selected positions on the stripe and take the average value to obtain the width W2 of the single second stripe. Along the length direction of the unfolded negative electrode sheet, measure the distance between the center of the width of the single second stripe and the center of the width of the adjacent second stripe, and take the average value. This is the spacing A2 between two adjacent second stripes.

[0072] Along the width direction of the negative electrode sheet, measure the width of the first negative electrode material layer. Then, randomly select a single first fringe from the first segment and measure its length. This length is the length of a single first fringe. Divide this length by the width of the first negative electrode material layer to obtain the ratio P1. Similarly, randomly select a single second fringe from the second segment and measure its length along the width direction of the negative electrode sheet. This length is the length of a single second fringe. Divide this length by the width of the first negative electrode material layer to obtain the ratio P2.

[0073] By replacing the first negative electrode material layer with the second negative electrode material layer and following the above testing method, the thickness H'0 of the second negative electrode material layer and the fourth stripes H4, P4, W4, and A4 can be obtained.

[0074] The longitudinal section of the empty foil area is subjected to ion polishing treatment. The longitudinal section of the empty foil area is observed using an electron scanning microscope. The thickness T0 of the negative electrode current collector is measured along the thickness direction of the negative electrode sheet. Based on the depth variation of the third fringe along the thickness direction of the negative electrode sheet, the empty foil areas corresponding to each segment of the first negative electrode material layer are determined. Five third fringes of the empty foil areas corresponding to the first segment are randomly selected. Along the width direction of the unfolded negative electrode sheet, the positions of the two ends and the midpoint of each individual third fringe of the empty foil area corresponding to the first segment are confirmed. Then, along the thickness direction of the negative electrode sheet, the distances from the surface of the empty foil area to the bottom surface at the two ends and the midpoint of each individual third fringe of the empty foil area corresponding to the first segment are measured. The average value is taken as the depth of the individual third fringe of the empty foil area corresponding to the first segment. The average value of the five individual third fringes of the empty foil areas corresponding to the first segment is taken as the average depth T1 of the multiple third fringes of the empty foil areas corresponding to the first segment. Choose any 5 third stripes in the empty foil area opposite to the second segment. Along the width direction after the negative electrode sheet is unfolded, determine the positions of the two ends and the midpoint of a single third stripe in the empty foil area opposite to the second segment. Then, along the thickness direction of the negative electrode sheet, measure the distance between the surface of the empty foil area and the bottom surface at the two ends and the midpoint of a single third stripe in the empty foil area opposite to the second segment. Take the average value, which is the depth of a single third stripe in the empty foil area opposite to the second segment. Take the average value of the 5 single third stripes in the empty foil area opposite to the second segment, which is the average depth T2 of the multiple third stripes in the empty foil area opposite to the second segment. Select any single third stripe in the empty foil area opposite the first segment. Along the width direction of the unfolded negative electrode sheet, select any 5 positions on this stripe. Then, along the length direction of the unfolded negative electrode sheet, measure the width at these 5 selected positions and take the average value to obtain the width of the single third stripe. Along the length direction of the unfolded negative electrode sheet, measure the distance between the center of the width of the single third stripe and the center of the width of the adjacent third stripe, and take the average value. This is the spacing between two adjacent third stripes in the empty foil area opposite the first segment. Select any single third stripe in the empty foil area opposite the second segment. Along the width direction of the unfolded negative electrode sheet, select any 5 positions on this stripe. Along the length direction of the unfolded negative electrode sheet, measure the width at these 5 selected positions and take the average value to obtain the width of the single third stripe. Along the length direction of the unfolded negative electrode sheet, measure the distance between the center of the width of the single third stripe and the center of the width of the adjacent third stripe. Measure once at each of the 5 selected positions and take the average value. This is the spacing between two adjacent third stripes in the empty foil area opposite the second segment.

[0075] Measure the width of the empty foil area along the width direction of the negative electrode sheet, and randomly select a single third stripe in the empty foil area and measure the length of the stripe. This is the length of the single third stripe. Divide the length of the single third stripe by the width of the empty foil area to obtain the ratio P3 of the length of the single third stripe to the width of the empty foil area.

[0076] Cyclic performance test:

[0077] The lithium-ion batteries in the examples and comparative examples were subjected to charge-discharge cycle tests in a 25°C constant temperature chamber. The lithium-ion batteries were charged at a constant current of 2C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C. After resting for 5 minutes, they were discharged at a constant current of 6C to 2.5V. This was the first cycle, and the discharge capacity C1 of the first cycle was recorded. After 600 cycles following the above process, the discharge capacity C of the lithium-ion battery was recorded. 600 The capacity retention rate at 600 cycles was calculated as an indicator to evaluate the wetting effect of the negative electrode and the cycle performance of the lithium-ion battery, as shown in Equation (I). A lower capacity retention rate at 600 cycles (cls) indicates a poorer wetting effect of the negative electrode in the lithium-ion battery, resulting in poorer cycle performance; conversely, a higher capacity retention rate at 600cls indicates a better wetting effect of the negative electrode in the lithium-ion battery, resulting in better cycle performance.

[0078] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0079] Lithium plating performance test:

[0080] The lithium-ion batteries from the examples and comparative examples were placed in a constant temperature chamber at 10°C for 60 minutes. They were then charged at a constant current of 2C to 4.2V, and then charged at a constant voltage of 4.2V to a current of 0.05C. After resting for 5 minutes, they were discharged at a constant current of 0.5C to 2.5V. This constitutes one cycle. After 10 cycles of the above charge-discharge process, the batteries were charged again at a constant current of 2C to 4.2V, and then charged at a constant voltage of 4.2V to a current of 0.05C. After resting for 5 minutes, the lithium-ion batteries were disassembled, and the lithium plating state on the surface of the first negative electrode material layer of the negative electrode sheet was observed. The non-lithium-plated areas were golden yellow, while the lithium-plated areas were grayish-white.

[0081] The criteria for judging the degree of lithium plating in lithium-ion batteries are as follows: 0% lithium plating area is considered no lithium plating, i.e., the degree of lithium plating is zero; lithium plating area greater than 0 and less than or equal to 2% is considered mild lithium plating; lithium plating area greater than 2% and less than or equal to 20% is considered moderate lithium plating; and lithium plating area greater than 20% and less than or equal to 100% is considered severe lithium plating. The percentage of lithium plating area is calculated based on the total area of ​​the negative electrode material layer.

[0082] In this application, those skilled in the art will understand that "C" refers to the rated capacity of the finished lithium-ion battery at the time of manufacture. "1C" is the current value that completely discharges the lithium-ion battery capacity in 1 hour, "0.1C" is the current value that completely discharges the lithium-ion battery capacity in 10 hours, and other rates follow the same principle.

[0083] Example 1-1

[0084] <Preparation of Negative Electrode Sheets>

[0085] Artificial graphite, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 97:1.7:1.3, and then deionized water was added as a solvent. The mixture was stirred until homogeneous, resulting in a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was uniformly coated onto one surface of a copper foil with a current collector thickness T0 of 10 μm and dried at 105 °C to obtain a negative electrode sheet with a single-sided coating of the first negative electrode material layer. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with both the first and second negative electrode material layers. After cold pressing and slitting, the empty foil area of ​​the negative electrode current collector was determined along the width direction of the unfolded negative electrode sheet. The coating weight of the negative electrode material layer was 107 mg / 1540.25 mm. 2 The thickness of both the first and second negative electrode material layers is H0, which is 70 μm. Along the width direction after the negative electrode sheet is unfolded, the width of the empty foil area is 5.45 mm, the width of the first negative electrode material layer is 62 mm, and the width of the second negative electrode material layer is 62 mm.

[0086] Along the length of the unfolded negative electrode sheet, determine the first and second segments of the first negative electrode material layer. Based on the unfolded length of the first negative electrode material layer, the length ratio K1 of the first segment is 40%, and the length ratio K2 of the second segment is 60%. A first stripe is formed on the first segment, and a second stripe is formed on the second segment. The specific shapes of the first and second stripes are as follows... Figure 2 As shown. Along the width direction after the negative electrode sheet is unfolded, the ratio P2 of the length of a single second stripe to the width of the first negative electrode material layer is set to 0.6, the width W2 of the second stripe is 100 μm, and the spacing A2 between two adjacent second stripes along the length direction after the negative electrode sheet is unfolded is 5 mm. The average depth H2 of the multiple second stripes located in the second segment is 35 μm, and H2 / H0 is 0.5. Along the width direction after the negative electrode sheet is unfolded, the ratio P1 of the length of a single first stripe to the width of the first negative electrode material layer is 0.6, the width W1 of the first stripe is 90 μm, and the spacing A1 between two adjacent first stripes along the length direction after the negative electrode sheet is unfolded is 5 mm. The average depth H1 of the multiple first stripes located in the first segment is 28 μm, H1 / H2 is 0.8, A1 / A2 is 1, and W1 / W2 is 0.9. The first stripe is laser-etched on the first segment according to the above parameters, and the second stripe is laser-etched on the second segment.

[0087] The average depth H4 of the fourth stripe is set to 35 μm, H4 / H'0 is 0.5, the ratio P4 of the length of a single fourth stripe to the width of the second negative electrode material layer along the width direction after the negative electrode sheet is unfolded is 0.6, the width W4 of the fourth stripe is 100 μm, and the spacing A4 between two adjacent fourth stripes along the length direction after the negative electrode sheet is unfolded is 5 mm. The shape of the fourth stripe is the same as that of the second stripe. The fourth stripe is laser-etched on the second negative electrode material layer according to the above parameters.

[0088] The final negative electrode sheet has a size of 67.45mm × 1436mm.

[0089] <Preparation of the positive electrode>

[0090] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1 O2), polyvinylidene fluoride (PVDF) binder, and conductive carbon black were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94.8:2.8:2.4 and thoroughly mixed to obtain a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated onto one surface of a 15 μm thick aluminum foil current collector and dried at 105 °C to obtain a single-sided coated positive electrode sheet. The above steps were then repeated on the other surface of the same aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 105 °C for 4 hours to obtain a positive electrode sheet with dimensions of 64.5 mm × 1422 mm for later use. The coating weight of the positive electrode material layer was 234 mg / 1540.25 mm. 2 The compaction density of the positive electrode material layer is 3.4 g / cm³. 3 The width of the positive electrode material layer is 60mm, and the width of the empty foil area of ​​the positive electrode sheet is 4.5mm.

[0091] <Septum>

[0092] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0093] <Preparation of Electrolyte>

[0094] In a dry argon-atmospheric glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 to obtain a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, with the remainder being the base solvent.

[0095] <Preparation of Lithium-ion Batteries>

[0096] The prepared separator, negative electrode sheet, and positive electrode sheet are stacked sequentially and pre-wound to ensure the separator is positioned between the negative and positive electrodes. Simultaneously, the first negative electrode material layer is positioned away from the center of the pre-wound electrode assembly, and the first segment of the first negative electrode material layer is located close to the center of the pre-wound electrode assembly. Afterwards, the process involves winding, flattening, current collector welding, casing, bottom penetration welding, inkjet coding, vacuum drying, electrolyte injection, sealing, and high-temperature settling followed by capacity testing to obtain the lithium-ion battery. The upper limit of the formation voltage is 3.6V, the formation temperature is 45℃, and after formation, the battery is left to stand at room temperature (25℃) for 24 hours.

[0097] Examples 1-2 to Examples 1-34

[0098] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0099] Examples 1-35

[0100] Except that the parameters for setting stripes in the second negative electrode material layer in the <Preparation of Negative Electrode Sheet> are exactly the same as those for setting stripes in the first negative electrode material layer, i.e., the first negative electrode material layer and the second negative electrode material layer are exactly the same, everything else is the same as in Example 1-1.

[0101] Examples 1-36

[0102] Except for the absence of stripes in the second negative electrode material layer during the preparation of the negative electrode sheet, the rest is the same as in Example 1-1.

[0103] Example 2-1

[0104] Except for the step of adding a third stripe in the empty foil area according to the following steps in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1-1. The third stripe is set in the empty foil area, and the shape of the third stripe is as follows... Figure 5As shown. The average depth T' of the third stripe is set to 5 μm. The average depth T1 of multiple third stripes in the empty foil area opposite the first segment is 5 μm, and the average depth T2 of multiple third stripes in the empty foil area opposite the second segment is 5 μm. T' / T0 is 0.5. Along the width direction of the unfolded negative electrode sheet, the ratio P3 of the length of a single third stripe to the width of the empty foil area is 0.3. The width W'1 of the third stripe in the empty foil area opposite the first segment is 90 μm, and the width W'2 of the third stripe in the empty foil area opposite the second segment is 100 μm. Along the length direction of the unfolded negative electrode sheet, the spacing A'1 between two adjacent third stripes in the empty foil area opposite the first segment is 5 mm, and the spacing A'2 between two adjacent third stripes in the empty foil area opposite the second segment is 5 mm. According to the above parameters, the first stripe is laser-etched on the first segment, the second stripe is laser-etched on the second segment, and the third stripe is laser-etched in the empty foil area to obtain a negative electrode sheet with a size of 67.45mm×1436mm.

[0105] Example 2-2

[0106] Except for setting the average depth T2 of the third stripe in the empty foil area opposite to the second segment to 5 μm and T2 / T0 to 0.5, and the average depth T1 of the third stripe in the empty foil area opposite to the first segment to 4 μm and T1 / T2 to 0.8, the rest is the same as in Example 2-1.

[0107] Examples 2-3 to 2-13

[0108] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 2-2.

[0109] Comparative Example 1

[0110] Except for the fact that no stripes are set on the first and second negative electrode material layers in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1-1.

[0111] Comparative Example 2

[0112] Except for the absence of stripes on the first negative electrode material layer in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1-1.

[0113] Comparative Examples 3 to 4

[0114] The relevant preparation parameters were adjusted according to Table 1, and except that no stripes were set on the second negative electrode material layer, the rest was the same as in Example 1-1.

[0115] Comparative Example 5

[0116] Except for the fact that in the <Preparation of Negative Electrode Sheet> only the second stripe is set in the second section and no stripe is set on the second negative electrode material layer, the rest is the same as in Example 1-1.

[0117] Comparative Example 6

[0118] Except for the fact that in the <Preparation of Negative Electrode Sheet> only the first stripe is set in the first section and no stripe is set on the second negative electrode material layer, the rest is the same as in Example 1-1.

[0119] Comparative Example 7

[0120] The relevant preparation parameters were adjusted according to Table 1, and except that no stripes were set on the second negative electrode material layer, the rest was the same as in Example 1-1.

[0121] Comparative Example 8

[0122] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0123] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0124]

[0125]

[0126]

[0127] As can be seen from Examples 1-1 to 1-36 and Comparative Examples 1 to 8, by adjusting the length ratio of the first segment and the second segment within the scope of this application, setting the first stripe on the first segment and the second stripe on the second segment, and ensuring that the values ​​of H0, H2 / H0, and H1 / H2 are within the scope of this application, the lithium-ion battery exhibits a lighter degree of lithium plating, and the 600cls capacity retention rate of the lithium-ion battery is improved. This indicates that the electrolyte has a good wetting effect on the negative electrode sheet of this application, and the lithium-ion battery has good lithium plating performance and cycle performance. In Comparative Example 1, no stripes were set on either the first or second negative electrode material layer; in Comparative Example 2, no stripes were set on the first negative electrode material layer; in Comparative Example 3, second stripes were set on all of the first negative electrode material layer; in Comparative Example 4, first stripes were set on all of the first negative electrode material layer; in Comparative Example 5, second stripes were set only on the second segment of the first negative electrode material layer; in Comparative Example 6, first stripes were set only on the first segment of the first negative electrode material layer; in Comparative Example 7, the parameters of the first and second stripes were opposite to those in Example 1-1; in Comparative Example 8, second stripes were set on all of the first negative electrode material layer and stripes were set on the second negative electrode material layer. The lithium-ion batteries in Comparative Examples 1 to 8 exhibited more severe lithium plating and / or lower 600cls capacity retention. In contrast, the lithium-ion batteries in Examples 1-1 to 1-36 showed less severe lithium plating and higher 600cls capacity retention, indicating that the electrolyte had a better wetting effect on the negative electrode sheet, and the lithium-ion batteries exhibited good lithium plating performance and cycle performance.

[0128] The values ​​of A2 and A1 / A2 typically affect the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-17 to 1-23, when the values ​​of A2 and A1 / A2 are within the range of this application, the lithium plating degree of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high. This indicates that the electrolyte in the examples of this application has a good wetting effect on the electrode, resulting in good lithium plating performance and cycle performance of the lithium-ion battery.

[0129] The values ​​of W2 and W1 / W2 typically affect the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-24 to 1-30, when the values ​​of W2 and W1 / W2 are within the range of this application, the degree of lithium plating in the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high. This indicates that the electrolyte in the examples of this application has a good wetting effect on the electrode, resulting in good lithium plating performance and cycle performance of the lithium-ion battery.

[0130] The values ​​of P1 and P2 typically affect the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-31 to 1-34, when the values ​​of P1 and P2 are within the range of this application, the degree of lithium plating in the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is high. This indicates that the electrolyte in the examples of this application has a good wetting effect on the electrode, resulting in good lithium plating performance and cycle performance of the lithium-ion battery.

[0131] The arrangement of stripes on the second negative electrode material layer typically affects the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-35 to 1-36, when the stripes on the second negative electrode material layer are arranged within the scope of this application, the lithium plating degree of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high. This indicates that the electrolyte in the embodiments of this application has a better wetting effect on the electrode, resulting in better lithium plating performance and cycle performance of the lithium-ion battery.

[0132] Table 2

[0133] Example 1-1 / 10 / / / / none 82.0 Example 2-1 0.3 10 0.5 5 1 5 none 82.4 Example 2-2 0.3 10 0.5 5 0.8 4 none 85.1 Example 2-3 0.3 10 0.15 1.5 0.8 1.2 none 83.9 Examples 2-4 0.3 10 0.7 7 0.8 5.6 none 84.2 Examples 2-5 0.3 10 0.5 5 0.45 2.25 none 84.5 Examples 2-6 0.3 10 0.5 5 0.95 4.75 none 83.1 Examples 2-7 0.3 3 0.5 1.5 0.8 1.2 none 85.5 Examples 2-8 0.3 20 0.5 10 0.8 8 none 84.8 Examples 2-9 0.1 10 0.5 5 0.8 4 none 83.4 Example 2-10 0.2 10 0.5 5 0.8 4 none 84.1 Example 2-11 0.5 10 0.5 5 0.8 4 none 86.1 Example 2-12 0.7 10 0.5 5 0.8 4 none 82.5 Example 2-13 0.8 10 0.5 5 0.8 4 Mild 82.2

[0134] Note: " / " in Table 2 indicates that there are no relevant preparation parameters.

[0135] The placement of the third stripe typically affects the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-13, when the third stripe is placed within the scope of this application, the lithium plating degree of the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is high. This indicates that the electrolyte in the embodiments of this application has a better wetting effect on the electrode, resulting in better lithium plating performance and cycle performance of the lithium-ion battery.

[0136] The values ​​of T2 / T0, T1 / T2, and T0 typically affect the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-2 to 2-8, when the values ​​of T2 / T0, T1 / T2, and T0 are within the range of this application, the degree of lithium plating in the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is high. This indicates that the electrolyte in the embodiments of this application has a good wetting effect on the electrode, resulting in good lithium plating performance and cycle performance of the lithium-ion battery.

[0137] The value of P3 typically affects the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-2, 2-9 to 2-13, when the value of P3 is within the range of this application, the degree of lithium plating in the lithium-ion battery is relatively mild, and the 600cls capacity retention rate is relatively high. This indicates that the electrolyte in the examples of this application has a good wetting effect on the electrode, resulting in good lithium plating performance and cycle performance of the lithium-ion battery.

[0138] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0139] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0140] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A cylindrical secondary battery, comprising an electrode assembly, the electrode assembly comprising a positive electrode, a negative electrode and a separator, the negative electrode comprising a negative current collector, and a first negative electrode material layer disposed on the surface of the negative current collector opposite to the winding center of the electrode assembly; Along the length direction of the unfolded negative electrode sheet and along the winding direction of the electrode assembly, the first negative electrode material layer includes a first segment and a second segment connected in sequence. Based on the length of the first negative electrode material layer, the length of the first segment accounts for 9% to 75%, and the length of the second segment accounts for 25% to 91%. The first segment has multiple first stripes, which extend along the width direction of the unfolded negative electrode sheet and are spaced apart along the length direction of the unfolded negative electrode sheet. The second segment has multiple second stripes, which extend along the width direction of the unfolded negative electrode sheet and are spaced apart along the length direction of the unfolded negative electrode sheet. Along the thickness direction of the negative electrode sheet, the average depth of the multiple first stripes in the first segment is H1 μm, the average depth of the multiple second stripes in the second segment is H2 μm, the thickness of the first negative electrode material layer is H0 μm, 50≤H0≤100, 0.15≤H2 / H0≤0.7, and 0.45≤H1 / H2≤0.

95.

2. The cylindrical secondary battery according to claim 1, wherein, Based on the length of the first negative electrode material layer, the length of the first segment accounts for 17% to 60%, and the length of the second segment accounts for 40% to 83%. And / or, 0.3≤H2 / H0≤0.6, 0.7≤H1 / H2≤0.

85.

3. The cylindrical secondary battery according to claim 1 or 2, wherein, Along the length of the unfolded negative electrode sheet, the distance between two adjacent first stripes is A1 mm, the distance between two adjacent second stripes is A2 mm, 0.2≤A1 / A2≤3, 2≤A2≤10.

4. The cylindrical secondary battery according to claim 3, wherein, 0.5≤A1 / A2≤1.

5.

5. The cylindrical secondary battery according to any one of claims 1 to 4, wherein, Along the length direction after the negative electrode sheet is unfolded, the width of a single first stripe is W1μm, the width of a single second stripe is W2μm, 0.1≤W1 / W2≤1.5, and 70≤W2≤120.

6. The cylindrical secondary battery according to claim 5, wherein, 0.6≤W1 / W2≤1.

2.

7. The cylindrical secondary battery according to any one of claims 1 to 6, wherein, Along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single first stripe to the width of the first negative electrode material layer is P1, 0.2≤P1≤1; or, the ratio of the length of a single second stripe to the width of the first negative electrode material layer is P2, 0.2≤P2≤1.

8. The cylindrical secondary battery according to claim 7, wherein, 0.3≤P1≤0.8; and / or, 0.3≤P2≤0.

8.

9. The cylindrical secondary battery according to any one of claims 1 to 8, wherein, Along the width direction of the unfolded negative electrode sheet, the negative current collector includes an empty foil area connected to the first negative electrode material layer. The empty foil area is provided with a plurality of third stripes, which extend along the width direction of the unfolded negative electrode sheet and are spaced apart along the length direction of the unfolded negative electrode sheet.

10. The cylindrical secondary battery according to claim 9, wherein, Along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single third stripe to the width of the empty foil area is P3, where 0.1≤P3≤0.

7.

11. The cylindrical secondary battery according to claim 10, wherein, 0.2≤P3≤0.5。 12. The cylindrical secondary battery according to claim 9, wherein, Along the thickness direction of the negative electrode sheet, the thickness of the negative electrode current collector is T0 μm, the average depth of the plurality of third stripes in the empty foil area opposite to the first segment is T1 μm, the average depth of the plurality of third stripes in the empty foil area opposite to the second segment is T2 μm, 3≤T0≤20, 0.15≤T2 / T0≤0.7, 0.45≤T1 / T2≤0.

95.

13. An electronic device comprising a cylindrical secondary battery as described in any one of claims 1 to 12.

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