Cylindrical secondary battery and electronic device

Abstract

The invention provides a cylindrical secondary battery and an electronic device, an electrode assembly comprises a positive pole piece, a negative pole piece and a diaphragm, the negative pole piece comprises a negative current collector, and a first negative material layer is arranged on the surface, deviating from the winding center of the electrode assembly, of the negative current collector; the first negative electrode material layer comprises a first section, a second section and a third section which are connected in sequence, and based on the length of the first negative electrode material layer, the length ratio of the first section is 10%-30%, the length ratio of the second section is 20%-60%, and the length ratio of the third section is 15%-30%; the first section, the second section and the third section are respectively provided with a plurality of first stripes, the average depth of the plurality of first stripes located at the first section is H1 [mu] m, the average depth of the plurality of first stripes located at the second section is H2 [mu] m, the average depth of the plurality of first stripes located at the third section is H3 [mu] m, and H2 is greater than H1 and less than H3. Through the arrangement, the lithium precipitation performance and the cycle performance of the cylindrical secondary battery can be improved.

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, meaning the positive and negative tabs extend from opposite directions and are fabricated using full-tab flattening or rolling techniques. For cylindrical lithium-ion batteries, existing technologies employ grooves on the electrodes to improve the wetting effect, thereby enhancing the battery's kinetic performance. 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, and improve the cycle performance of the cylindrical secondary battery while taking into account the overall lithium plating performance of the negative electrode sheet. Based on the CB change trend from the inner ring to the outer ring of the cylindrical secondary battery, the optimal balance between lithium plating performance and cycle performance of the cylindrical secondary battery is achieved.

[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. The electrode assembly includes 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, a second segment, and a third segment connected in sequence. Based on the length of the first negative electrode material layer, the length ratio of the first segment is 10% to 30%, the length ratio of the second segment is 20% to 60%, and the length ratio of the third segment is 15% to 30%. A plurality of first stripes are disposed on the first segment, the second segment, and the third segment. The plurality of first stripes extend along the width direction of the unfolded negative electrode and are spaced apart along the length direction of the unfolded negative electrode. The average depth of the plurality of first stripes located in the first segment is H1 μm, the average depth of the plurality of first stripes located in the second segment is H2 μm, and the average depth of the plurality of first stripes located in the third segment is H3 μm, where H1 < H2 < H3. This application adjusts the length ratio of the first, second, and third segments within the aforementioned range and sets the first stripe on the first, second, and third segments, making H1 < H2 < H3. This accelerates the flow of electrolyte on the negative electrode sheet. While the electrolyte has good wettability on the negative electrode sheet, the cylindrical secondary battery has good lithium plating performance and cycle performance. Based on the CB change trend from the inner circle to the outer circle of the cylindrical secondary battery, the optimal balance between lithium plating performance and cycle performance of the cylindrical secondary battery is achieved.

[0007] In one or more embodiments, the thickness of the first negative electrode material layer is H0 μm, 20 ≤ H0 ≤ 100, 0.2 ≤ H1 / H0 ≤ 0.35, 0.35 < H2 / H0 ≤ 0.45, and 0.45 < H3 / H0 ≤ 0.5. By adjusting the values ​​of H1 / H0, H2 / H0, H3 / H0, and H0 within the above ranges, it is beneficial to set the first stripe of stepped depth on the first negative electrode material layer, thereby accelerating the flow of electrolyte on the negative electrode sheet. While taking into account mechanical safety performance and energy density, it improves 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 W μm, where 10 ≤ W ≤ 400; optionally, 50 ≤ W ≤ 200. By adjusting the width of the single first stripe within the above range, it is beneficial to improve the wetting effect of the electrolyte on the negative electrode sheet, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery while maintaining energy density.

[0009] In one or more embodiments, along the length direction of the unfolded negative electrode sheet, the spacing between two adjacent first stripes is A mm, where 0.5 ≤ A ≤ 10; optionally, 3 ≤ A ≤ 7. By adjusting the spacing between two adjacent first stripes within the above range, it is beneficial to reduce the risk of insufficient wetting of the negative electrode sheet by the electrolyte, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0010] 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 ≤ P ≤ 1; optionally, 0.3 ≤ P1 ≤ 0.8. By adjusting the ratio P1 of the length of a single first stripe to the width of the negative electrode material layer within the above range, 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.

[0011] 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 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. By providing second stripes in the empty foil region, it is beneficial to provide more electrolyte flow channels for the empty foil region. The first and second stripes work synergistically to improve the cycle performance and lithium plating performance of the cylindrical secondary battery.

[0012] In one or more embodiments, along the width direction after the negative electrode sheet is unfolded, the ratio of the length of a single second stripe to the width of the empty foil area is P2, where 0.1 ≤ P2 ≤ 0.7; optionally, 0.2 ≤ P2 ≤ 0.5. By adjusting the ratio P2 of the length of a single second stripe to the width of the empty foil area within the above range, it is beneficial to improve the wetting effect of the electrolyte on the negative electrode sheet, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery while taking into account mechanical safety performance.

[0013] 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 second stripes in the empty foil area opposite to the first segment is T1 μm, the average depth of the plurality of second stripes in the empty foil area opposite to the second segment is T2 μm, and the average depth of the plurality of second stripes in the empty foil area opposite to the third segment is T3 μm, where 3 ≤ T0 ≤ 20, 0.2 ≤ T1 / T0 ≤ 0.35, 0.35 < T2 / T0 ≤ 0.45, and 0.45 < T3 / T0 ≤ 0.5. By adjusting the values ​​of T1 / T0, T2 / T0, T3 / T0, and T0 within the above ranges, it is beneficial to set the second stripes of stepped depth on the empty foil area, thereby improving the cycle performance of the cylindrical secondary battery while taking into account mechanical safety performance.

[0014] In one or more embodiments, 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 further includes a fourth segment connected to the third segment. Based on the length of the first negative electrode material layer, the length ratio of the fourth segment is 10% to 25%. The fourth segment is provided with a plurality of 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 average depth of the plurality of first stripes in the fourth segment is H4μm, where H3 < H4. This configuration facilitates further acceleration of electrolyte flow on the negative electrode sheet. While the electrolyte has good wettability on the negative electrode sheet, the cylindrical secondary battery exhibits better lithium plating performance and cycle performance.

[0015] In one or more embodiments, 0.5 < H4 / H0 ≤ 0.7. This facilitates the formation of a first stripe of stepped depth on the first negative electrode material layer, further accelerating the flow of electrolyte on the negative electrode sheet. While maintaining mechanical safety and energy density, this further improves the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0016] A second aspect of this application provides an electronic device comprising a cylindrical secondary battery as described in any of the foregoing embodiments. The cylindrical secondary battery of this application exhibits good cycle performance and lithium plating resistance; therefore, the electronic device of this application has a long service life.

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

[0018] This application embodiment optimizes the setting of stripes on the negative electrode sheet, which can effectively reduce the risk of lithium plating caused by insufficient CB value due to the setting of stripes on the negative electrode sheet. At the same time, the electrolyte has good wetting performance on the negative electrode sheet, and the cylindrical secondary battery has good lithium plating performance and cycle performance. Based on the CB change characteristics from the inner circle to the outer circle of the cylindrical secondary battery, the best balance between lithium plating performance and cycle performance of the cylindrical secondary battery is achieved.

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

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

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

[0022] Figure 2 for Figure 1 A partial front view of the negative electrode sheet after the electrode assembly is unfolded;

[0023] Figure 3 for Figure 2 A cross-sectional view of the negative electrode sheet along the PP direction;

[0024] Figure 4 This is a partial front view of the negative electrode sheet in another embodiment of this application;

[0025] Figure 5 for Figure 4 A cross-sectional view of the negative electrode plate along the QQ direction;

[0026] Figure 6 This is a partial front view of the negative electrode sheet in another embodiment of this application;

[0027] Figure 7 This is a cross-sectional view of the negative electrode sheet along the PP direction in another embodiment of this application;

[0028] Figure 8 This is a cross-sectional view of the negative electrode sheet along the PP direction in another embodiment of this application.

[0029] 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; Empty foil area 210; Second stripe 211; Third stripe 231. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] For high-power cylindrical secondary batteries, typically full-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 facing away from the winding center of the electrode assembly, especially near the winding 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 grooving reduces the active material of the negative electrode sheet. Furthermore, the structure of the cylindrical electrode assembly, where the curvature gradually decreases with increasing winding turns, means that for the same winding, the length of the negative electrode sheet surface facing away from the winding center is slightly shorter than the length of the positive electrode sheet surface facing the winding center. For these reasons, insufficient inner loop (CB) of the electrode assembly in the later stages of cycling still leads to lithium plating, thus affecting the kinetic 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 good lithium plating and cycle performance. The specific technical solution is as follows:

[0033] The first aspect of this application provides a cylindrical secondary battery, which includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector. 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, a second segment, and a third segment connected in sequence. Based on the length of the first negative electrode material layer, the length ratio K1 of the first segment is 10% to 30%, the length ratio K2 of the second segment is 20% to 60%, and the length ratio K3 of the third segment is 15% to 30%. For example, the length percentage K1 of the first segment can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or any range of two of these values; the length percentage K2 of the second segment can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, or any range of two of these values; the length percentage K3 of the third segment can be 15%, 18%, 20%, 22%, 25%, 28%, 30%, or any range of two of these values. Multiple first stripes are provided on the first, second, and third segments. The multiple first stripes 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 average depth of the multiple first stripes in the first segment is H1μm, the average depth of the multiple first stripes in the second segment is H2μm, and the average depth of the multiple first stripes in the third segment is H3μm, where H1 < H2 < H3.

[0034] 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 opposite to 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), a second segment (not shown), and a third segment (not shown) connected in sequence. Multiple first stripes 221 are disposed on the first, second, and third segments. The multiple first stripes 221 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 H1 μm, the average depth of the multiple first stripes 221 located in the second segment is H2 μm, and the average depth of the multiple first stripes 221 located in the third segment is H3 μm.

[0035] When the length of the first and / or second segments is too large, for example, exceeding the upper limit of this application, the average depth of the first stripe set on the first negative electrode material layer is too small. This results in poor wetting of the negative electrode sheet by the electrolyte, deteriorating negative electrode sheet kinetics, and increased susceptibility to lithium plating. Consequently, the lithium plating performance and cycle performance of the secondary battery cannot be significantly improved. When H1≥H2≥H3, excessive loss of negative electrode active material occurs near the winding center of the electrode assembly. The area near the winding center of the electrode assembly (inner ring or winding start section) is prone to insufficient CB (carbon dioxide content), further increasing the risk of lithium plating at the negative electrode interface and thus affecting the cycle performance of the secondary battery. This application adjusts the length ratio of the first, second, and third segments within the aforementioned range and sets a first stripe on the first, second, and third segments, ensuring H1 < H2 < H3. This accelerates the flow of electrolyte on the negative electrode sheet, while maintaining the electrolyte's wetting effect on the negative electrode sheet. It also reduces the risk of lithium plating due to insufficient CB on the negative electrode sheet, especially near the winding center of the electrode assembly (inner ring or winding start section), caused by the stripe setting. This improves the lithium plating performance and cycle performance of the secondary battery. Through this setup, the electrolyte achieves good wetting of the negative electrode sheet, while the cylindrical secondary battery exhibits excellent lithium plating and cycle performance. Based on the CB variation characteristics from the inner to the outer ring of the cylindrical secondary battery, an optimal balance between lithium plating performance and cycle performance is achieved. 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 area of ​​the negative electrode current collector surface or a part of the negative electrode current collector surface. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0036] 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 .

[0037] In one or more embodiments, such as Figure 3As shown, the thickness of the first negative electrode material layer 22 is H0 μm, where 20 ≤ H0 ≤ 100, 0.2 ≤ H1 / H0 ≤ 0.35, 0.35 < H2 / H0 ≤ 0.45, and 0.45 < H3 / H0 ≤ 0.5. For example, the value of H0 can be 20, 23, 25, 28, 30, 33, 35, 38, 40, 43, 45, 48, 50, 53, 55, 58, 60, 62, 65, 68, 70, 72, 75, 78, 80, 83, 85, 88, 90, 92, 95, 98, 100, or a range consisting of any two of these values; the value of H1 / H0 can be 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, or a range consisting of any two of these values. The range of values ​​for H2 / H0 can be 0.351, 0.353, 0.355, 0.358, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, or any two of these values; the range of values ​​for H3 / H0 can be 0.451, 0.453, 0.455, 0.458, 0.46, 0.47, 0.48, 0.49, 0.50, or any two of these values. By adjusting the values ​​of H1 / H0, H2 / H0, H3 / H0, and H0 within the aforementioned ranges, it is beneficial to set the first stripe of stepped depth on the first negative electrode material layer, thereby accelerating the flow of electrolyte on the negative electrode sheet, improving the wetting effect of the electrolyte on the negative electrode sheet, and reducing the risk of lithium plating due to insufficient CB caused by the setting of stripes on the negative electrode sheet, especially near the winding center of the electrode assembly (inner ring or winding start section of the negative electrode sheet). At the same time, it is beneficial to reduce the risk of the first negative electrode material layer being punctured by the first stripe when it is set. In addition, the loss of negative electrode active material is less, and the energy density of the secondary battery is higher. While taking into account mechanical safety performance and energy density, it improves the lithium plating performance and cycle performance of the cylindrical secondary battery. Based on the CB change characteristics from the inner ring to the outer ring of the cylindrical secondary battery, the best balance between lithium plating performance and cycle performance of the cylindrical secondary battery is 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, with a certain solid content of the negative electrode slurry, the thickness H0 of the first negative electrode material layer can be increased by increasing the coating weight, and the thickness H0 of the first negative electrode material layer can be 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 the thickness H0 of the first negative electrode material layer can be increased by decreasing the cold pressing pressure.

[0038] In one or more embodiments, 4 ≤ H1 ≤ 35, 7 < H2 ≤ 45, and 9 < H3 ≤ 50. For example, the value of H1 can be 4, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, or a range of any two of these values; the value of H2 can be 7.1, 7.5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, or a range of any two of these values; and the value of H3 can be 9.1, 9.5, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, or a range of any two of these values. By adjusting the values ​​of H1, H2, and H3 within the aforementioned range, it is beneficial to set the first stripe of stepped depth on the first negative electrode material layer, thereby accelerating the flow of electrolyte on the negative electrode sheet, improving the wetting effect of the electrolyte on the negative electrode sheet, and reducing the risk of lithium plating due to insufficient CB caused by the setting of stripes on the negative electrode sheet, especially near the winding center of the electrode assembly (inner ring or winding start section of the negative electrode sheet). At the same time, it is beneficial to reduce the risk of the first negative electrode material layer being punctured by the first stripe when it is set. In addition, the loss of negative electrode active material is less, and the energy density of the secondary battery is higher. While taking into account mechanical safety performance and energy density, it improves the lithium plating performance and cycle performance of the cylindrical secondary battery. Based on the CB change characteristics from the inner ring to the outer ring of the cylindrical secondary battery, the best balance between lithium plating performance and cycle performance of the cylindrical secondary battery is achieved.

[0039] In one or more embodiments, such as Figure 2 As shown, along the length direction (X direction) of the unfolded negative electrode sheet 20, the width of a single first stripe 221 is W μm, where 10 ≤ W ≤ 400; optionally, 50 ≤ W ≤ 200. For example, the value of W can be 10, 30, 50, 80, 100, 120, 150, 180, 200, 220, 250, 280, 300, 320, 350, 380, 400, or a range consisting of any two of these values. By controlling the width of the single first stripe within the above range, it is beneficial to achieve a uniform distribution of stripes on the surface of the negative electrode sheet, improve the wetting effect of the electrolyte on the negative electrode sheet, effectively improve the wetting performance of the electrolyte on the negative electrode sheet, and at the same time reduce the risk of excessive loss of negative electrode active material content in the first negative electrode material layer leading to lithium plating in the secondary battery. While taking into account energy density, it improves the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0040] In one or more embodiments, such as Figure 2As shown, along the length direction (X direction) of the unfolded negative electrode sheet 20, the distance between two adjacent first stripes 221 is A mm, where 0.5 ≤ A ≤ 10; optionally, 3 ≤ A ≤ 7. For example, the value of A can be 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two of these values. By adjusting the distance between two adjacent first stripes within the above range, the distance between the two adjacent first stripes is moderate, which helps to reduce the risk of insufficient wetting of the negative electrode sheet by the electrolyte. It also helps to reduce the processing difficulty of the grooving process and the risk of local collapse of the material layer, improving the wetting performance of the electrolyte on the negative electrode sheet and thus improving the lithium plating performance and cycle performance of the cylindrical secondary battery. In this application, the distance between two adjacent first stripes refers to the distance between the centers of the widths of two adjacent first stripes along the length direction of the unfolded negative electrode sheet.

[0041] 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 ≤ P ≤ 1; optionally, 0.3 ≤ P1 ≤ 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 consisting of any two of these values. By adjusting the ratio P1 of the length of a single first stripe to the width of the negative electrode material layer to be within the above range, it is beneficial for the flow of electrolyte on the first negative electrode material layer, improving the wetting effect of the electrolyte on the negative electrode sheet, effectively improving the wetting efficiency and performance of the electrolyte on the negative electrode sheet, while reducing the processing difficulty in the actual production process, 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, thereby improving the lithium plating performance and cycle performance of the cylindrical secondary battery.

[0042] 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 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. Figure 4As 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 a plurality of second 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 second 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 second stripes in the empty foil region have little impact on the capacity of the secondary battery and can effectively reduce the electrochemical impedance. By setting the first stripe and the second stripe together, the first stripe and the second stripe achieve a 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.

[0043] In one or more embodiments, along the length of the unfolded negative electrode sheet, the center line of a portion of the second stripe coincides with the center lines of multiple first stripes. For example... Figure 4 As shown, along the length direction (X direction) of the unfolded negative electrode 20, the center lines of the multiple second stripes 211 coincide with the center lines of the multiple first stripes 221. 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 length of the unfolded negative electrode sheet, the center line of the second fringe does not coincide with the center line of the first fringe. For example... Figure 6 As shown, along the length direction (X direction) of the unfolded negative electrode plate 20, the center lines of the multiple second stripes 211 do not coincide with the center lines of the multiple first stripes 221.

[0045] In one or more embodiments, along the width direction of the unfolded negative electrode sheet, the ratio of the length of a single second stripe to the width of the empty foil area is P2, where 0.1 ≤ P2 ≤ 0.7; optionally, 0.2 ≤ P2 ≤ 0.5. For example, the value of P2 can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, or a range consisting of any two of these values. By adjusting the ratio P2 of the length of a single second stripe to the width of the empty foil area 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.

[0046] In one or more embodiments, such as Figure 5As 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 second stripes 211 set in the empty foil area 210 opposite to the first segment is T1 μm, the average depth of the plurality of second stripes 211 set in the empty foil area 210 opposite to the second segment is T2 μm, the average depth of the plurality of second stripes 211 set in the empty foil area 210 opposite to the third segment is T3 μm, 3≤T0≤20, 0.2≤T1 / T0≤0.35, 0.35<T2 / T0≤0.45, 0.45<T3 / T0≤0.5. For example, the value of T0 can be 3, 5, 8, 10, 12, 15, 18, 20, or a range of any two values; the value of T1 / T0 can be 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, or a range of any two values; the value of T2 / T0 can be 0.351, 0.353, 0.355, 0.358, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, or a range of any two values; the value of T3 / T0 can be 0.451, 0.453, 0.455, 0.458, 0.46, 0.47, 0.48, 0.49, 0.50, or a range of any two values. By adjusting the values ​​of T1 / T0, T2 / T0, T3 / T0, and T0 within the aforementioned range, it is beneficial to set a second stripe of stepped depth 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 second 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 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, T3, T4, H1, H2, H3, H4, H5, H'0, T0, H0, P1, P2, P3, W, A, W', A', W3, A3," thereby selecting a negative electrode current collector of the desired thickness.

[0047] In one or more embodiments, 0.6 ≤ T1 ≤ 7, 1.05 < T2 ≤ 9, and 1.35 < T3 ≤ 10. For example, the value of T1 can be 0.6, 0.8, 1, 2, 3, 4, 5, 6, 7, or a range of any two values ​​therein; the value of T2 can be 1.051, 1.055, 1.06, 1.1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or a range of any two values ​​therein; and the value of T3 can be 1.351, 1.355, 1.36, 1.4, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two values ​​therein. By adjusting the values ​​of T1, T2, and T3 within the aforementioned range, it is beneficial to set a second stripe of stepped depth on the empty foil area, thereby improving the diffusion efficiency of the electrolyte to the empty foil area of ​​the negative electrode current collector, improving the wetting effect of the electrolyte on the negative electrode sheet, and reducing the risk of the empty foil area being punctured by the second stripe when it is set. This improves the cycle performance of the cylindrical secondary battery while taking into account mechanical safety performance.

[0048] In one or more embodiments, along the length direction of the unfolded negative electrode sheet, the width of a single second stripe is W' μm, where 10 ≤ W' ≤ 400; optionally, 50 ≤ W' ≤ 200. For example, the value of W' can be 10, 30, 50, 80, 100, 120, 150, 180, 200, 220, 250, 280, 300, 320, 350, 380, 400, or a range of any two of these values. By controlling the width W' of a single second stripe within the above range, the wetting performance of the electrolyte on the negative electrode sheet is effectively improved, while reducing the processing difficulty in the actual production process and reducing the risk of reduced mechanical safety performance of the secondary battery due to decreased strength in the empty foil area during secondary battery preparation. While maintaining mechanical safety performance, the lithium plating performance and cycle performance of the cylindrical secondary battery are improved.

[0049] In one or more embodiments, along the length direction of the unfolded negative electrode sheet, the spacing between two adjacent second stripes is A' mm, where 0.5 ≤ A' ≤ 10; optionally, 3 ≤ A' ≤ 7. For example, the value of A' can be 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two of these values. By adjusting the spacing between two adjacent second stripes within the above range, the distance between the two adjacent second stripes is moderate, which helps reduce the risk of insufficient wetting of the negative electrode sheet by the electrolyte. It also helps reduce the processing difficulty of the grooving process and the risk of local collapse in the empty foil area, improving the wetting performance of the electrolyte on the negative electrode sheet and thus improving the lithium plating performance and cycle performance of the cylindrical secondary battery. In this application, 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 of the unfolded negative electrode sheet.

[0050] In one or more embodiments, 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 further includes a fourth segment connected to the third segment. Based on the length of the first negative electrode material layer, the length percentage K4 of the fourth segment is 10% to 25%; for example, the length percentage K4 of the fourth segment can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, or a range consisting of any two of these values. Figure 7 As shown, the fourth segment (not shown in the figure) has multiple first stripes 221. These first stripes 221 extend along the width direction (Y direction) of the unfolded negative electrode sheet 20 and are spaced apart along the length direction (X direction) of the unfolded negative electrode sheet 20. The average depth of the multiple first stripes 221 in the fourth segment is H4μm, where H3 < H4. This arrangement helps to further accelerate the flow of electrolyte on the negative electrode sheet. While ensuring the electrolyte's wetting effect on the negative electrode sheet, it reduces the risk of lithium plating due to insufficient CB on the negative electrode sheet, especially near the winding center of the electrode assembly (inner ring or winding start section), caused by the stripes. This improves the lithium plating performance and cycle performance of the secondary battery. With good electrolyte wetting of the negative electrode sheet, the cylindrical secondary battery exhibits better lithium plating and cycle performance. Based on the CB variation characteristics from the inner to the outer ring of the cylindrical secondary battery, the optimal balance between lithium plating performance and cycle performance is achieved.

[0051] In one or more embodiments, 0.5 < H4 / H0 ≤ 0.7. For example, the value of H4 / H0 can be 0.501, 0.505, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, or a range of any two of these values. By adjusting the H4 / H0 value within the aforementioned range, it is beneficial to set the first stripe of stepped depth on the first negative electrode material layer, further accelerating the flow of electrolyte on the negative electrode sheet, improving the wetting effect of the electrolyte on the negative electrode sheet, and reducing the risk of lithium plating due to insufficient CB caused by the setting of stripes on the negative electrode sheet, especially near the winding center of the electrode assembly (inner ring or winding start section of the negative electrode sheet). At the same time, it is beneficial to reduce the risk of the first negative electrode material layer being punctured by the first stripe when it is set. In addition, the loss of negative electrode active material is less, and the energy density of the secondary battery is higher. While taking into account mechanical safety performance and energy density, it further improves the lithium plating performance and cycle performance of the cylindrical secondary battery. Based on the CB change characteristics from the inner ring to the outer ring of the cylindrical secondary battery, the best balance between lithium plating performance and cycle performance of the cylindrical secondary battery is achieved.

[0052] In one or more embodiments, 10 < H4 ≤ 70. For example, the value of H4 can be 10.1, 10.5, 11, 13, 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. By adjusting the value of H4 within the aforementioned range, it is beneficial to set the first stripe of stepped depth on the first negative electrode material layer, further accelerating the flow of electrolyte on the negative electrode sheet, improving the wetting effect of the electrolyte on the negative electrode sheet, and reducing the risk of lithium plating due to insufficient CB on the negative electrode sheet, especially near the winding center of the electrode assembly (i.e., the inner ring of the negative electrode sheet), caused by the setting of stripes. At the same time, it is beneficial to reduce the risk of the first negative electrode material layer being punctured by the first stripe when it is set. In addition, the loss of negative electrode active material is less, and the energy density of the secondary battery is higher. While taking into account mechanical safety performance and energy density, it further improves the lithium plating performance and cycle performance of the cylindrical secondary battery. Based on the CB change characteristics from the inner ring to the outer ring of the cylindrical secondary battery, the best balance between lithium plating performance and cycle performance of the cylindrical secondary battery is achieved.

[0053] In one or more embodiments, a second stripe is provided in the empty foil area opposite to the fourth segment. The average depth of the multiple second stripes provided in the empty foil area opposite to the fourth segment is T4 μm, and 0.5 < T4 / T0 ≤ 0.7. By adjusting the value of T4 / T0 within the above range, it is beneficial to set the second stripe of stepped depth on the empty foil area, further improving the diffusion efficiency of the electrolyte to the empty foil area of ​​the negative electrode current collector, improving the wetting effect of the electrolyte on the negative electrode sheet, and at the same time, reducing the risk of the empty foil area being punctured by the second stripe when it is set in the empty foil area. While taking into account mechanical safety performance, it further improves the cycle performance of the cylindrical secondary battery.

[0054] In one or more embodiments, 1.5 < T4 ≤ 14. By adjusting the value of T4 within the above range, it is beneficial to set a second stripe of stepped depth on the empty foil area, further improving the diffusion efficiency of the electrolyte to the empty foil area of ​​the negative electrode current collector, improving the wetting effect of the electrolyte on the negative electrode sheet, and at the same time reducing the risk of the empty foil area being punctured by the second stripe when it is set. While taking into account mechanical safety performance, it further improves the cycle performance of the cylindrical secondary battery.

[0055] In this application, the negative electrode sheet may further include a second negative electrode material layer, such as... Figure 1 As 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 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. In one or more embodiments, as... Figure 8 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 third stripes is H5 μm, 0.5 < H5 / H'0 ≤ 0.7, 20 ≤ 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 P3, 0.2 ≤ P3 ≤ 1. In one or more embodiments, as... Figure 8 As shown, along the length direction (X direction) of the unfolded negative electrode plate 20, the width of a single third stripe 231 is W3μm, where 10≤W3≤400. In one or more embodiments, as... Figure 8As shown, along the length direction (X direction) of the unfolded negative electrode sheet 20, the spacing between two adjacent third stripes 231 is A3 mm, 0.5≤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 at the negative electrode sheet, especially near the winding center of the electrode assembly (inner ring or 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 third stripes refers to the distance between the centers of the widths of two adjacent third stripes along the length direction of the unfolded negative electrode sheet.

[0056] In this application, the cross-section of a single first fringe, a single second fringe, and a single third fringe refers to the plane formed by the first fringe, the second fringe, and the third fringe along their length direction and their own thickness direction after being unfolded along the negative electrode sheet (or the cross-section obtained by viewing the first fringe and the second fringe along their length direction and thickness direction after being unfolded along the negative electrode sheet). This application does not impose any particular limitation on the cross-sectional shape of the single first fringe, the single second fringe, and the single third fringe, as long as the purpose of this application can be achieved. For example, the cross-section of each of the single first fringe, the single second fringe, and the single third fringe can be independently selected from at least one of the following: triangle, arc (area smaller than a semicircle with the same radius), semicircle, rectangle, trapezoid, or square.

[0057] This application does not impose any particular limitation on the cross-sectional shape of the first, second, and third stripes after they have been unfolded along the length and width directions of the negative electrode sheet. Any shape that achieves the purpose of this application is acceptable. For example, the cross-sectional shape of the first, second, and third stripes after they have been unfolded along the length and width directions of the negative electrode sheet can be straight, curved, or other specific shapes. Figure 2 , Figure 4 and Figure 6 As shown, the cross-sectional shape of the first and second stripes after being sectionally viewed along the length and width directions of the unfolded negative electrode sheet is straight.

[0058] The present application does not particularly limit the negative electrode current collector, as long as the object of the present application can be achieved. For example, the negative electrode current collector may include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a 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. The present application does not particularly limit 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 may include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), a Li-Sn alloy, a Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , a Li-Al alloy, or at least one of metallic lithium. In the present application, there is no particular limit 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 object of the present application can be 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. The present application does not particularly limit the type of the conductive agent in the first negative electrode material layer and the second negative electrode material layer, as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (SuperP), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, a metal material, or a conductive polymer. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above metal material may include, but is not limited to, metal powder and / or metal fiber. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The present application does not particularly limit the type of the negative electrode binder in the first negative electrode material layer and the second negative electrode material layer, as long as the object of the present application can be achieved. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, and the negative electrode binder in the first negative electrode material layer and the second negative electrode material layer, as long as the object of the present application can be achieved.

[0059] 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, the second segment, and the third segment of the first negative electrode material layer, and setting the first stripe on the first segment, the second segment, and the third segment to obtain the negative electrode sheet.

[0060] 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 of the unfolded negative electrode sheet, 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, second, and third segments, while a second stripe is set on the empty foil area. In one or more embodiments, in step (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, a first segment, a second segment, a third segment, and a fourth segment of the first negative electrode material layer are determined, and a first stripe is set on the first, second, third, and fourth segments to obtain the negative electrode sheet. In one or more embodiments, in step (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, the first segment, second segment, third segment, and fourth segment of the first negative electrode material layer are determined. While setting the first stripe on the first segment, second segment, third segment, and fourth segment, a second 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, second segment, and third segment, a third 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, second segment, and third segment, a second stripe is set on the empty foil area and a third stripe is set on the second negative electrode material layer. In one or more embodiments, in step (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, the first segment, second segment, third segment, and fourth segment of the first negative electrode material layer are determined. While setting the first stripe on the first segment, second segment, third segment, and fourth segment, a second stripe is set on the empty foil area and a third stripe is set on the second negative electrode material layer.

[0061] 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 method of setting the first, second, and third stripes, as long as the purpose of this application can be achieved; for example, pulsed laser etching can be used to set the first, second, and third stripes. The average depth H1 of multiple first stripes located in the first segment, the average depth H2 of multiple first stripes located in the second segment, the average depth H3 of multiple first stripes located in the third segment, the average depth H4 of multiple first stripes located in the fourth segment, the average depth T1 μm of multiple second stripes located in the empty foil area opposite to the first segment, the average depth T2 μm of multiple second stripes located in the empty foil area opposite to the second segment, the average depth T3 μm of multiple second stripes located in the empty foil area opposite to the third segment, the average depth T4 μm of multiple second stripes located in the empty foil area opposite to the fourth segment, the average depth H5 of multiple third stripes, the width W of a single first stripe, the width W' of a single second stripe, and the width W3 of a single third stripe can be obtained through pulses. The power and defocusing amount of the pulsed laser emitter can be adjusted; the ratio P1 of the length of a single first stripe to the width of the first negative electrode material layer can be adjusted by adjusting the width of the material layer, the power of the pulsed laser emitter, and the defocusing amount; the ratio P2 of the length of a single second 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 P3 of the length of a single third 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 A between two adjacent first stripes, the spacing A' between two adjacent second stripes, and the spacing A3 between two adjacent third stripes can be adjusted by adjusting the spacing between the pulsed laser emitters or the laser emission frequency.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] A second aspect of this application provides an electronic device comprising a cylindrical secondary battery as described in any of the foregoing embodiments. The cylindrical secondary battery of this application exhibits excellent lithium plating performance and cycle performance; therefore, the electronic device of this application has a long service life.

[0070] 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.

[0071] Example

[0072] 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.

[0073] Test methods and equipment:

[0074] Tests for T1, T2, T3, T4, H1, H2, H3, H4, H5, H'0, T0, H0, P1, P2, P3, W, A, W', A', W3, A3:

[0075] 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.

[0076] 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.

[0077] Measure the width of the first negative electrode material layer along the width direction of the negative electrode sheet, and randomly select a single first stripe and measure the length of the stripe, which is the length of the single first stripe. Divide the length of the single first stripe by the width of the first negative electrode material layer to obtain the ratio P1 of the length of the single first stripe to the width of the first negative electrode material layer.

[0078] Measure the width of the empty foil area along the width direction of the negative electrode sheet, and randomly select a single second stripe and measure the length of the stripe. This is the length of the single second stripe. Divide the length of the single second stripe by the width of the empty foil area to obtain the ratio P2 of the length of the single second stripe to the width of the empty foil area.

[0079] 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.

[0080] The cross-section of the negative electrode sheet along the PP direction is subjected to ion polishing. Observation using an electron scanning microscope reveals clear boundaries between the first negative electrode material layer and the negative electrode current collector, as well as between the second negative electrode material layer 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. A single first fringe is randomly selected. Along the width direction of the unfolded negative electrode sheet, five positions are randomly selected on the fringe. Then, along the length direction of the unfolded negative electrode sheet, the width at each of the five selected positions is measured, and the average value is taken to obtain the width W of the single first fringe. Along the length direction of the unfolded negative electrode sheet, the distance between the center of the width of the single first fringe and the center of the width of the adjacent first fringe is measured. Measurements are taken once at five selected positions, and the average value is taken to obtain the spacing A between two adjacent first fringes.

[0081] Along the thickness direction of the negative electrode sheet, determine the first, second, third, and fourth segments of the first negative electrode material layer based on the depth variation of the first fringe (when the first fringe has only three depths, the first negative electrode material layer has only three segments). Randomly select five first fringe segments from the first segment. Along the width direction of the unfolded negative electrode sheet, confirm the positions of the two ends and the midpoint of each individual first fringe in the first segment. Then, along the thickness direction of the negative electrode sheet, measure 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 fringe in the first segment. Take the average value; this is the depth of the individual first fringe in the first segment. Take the average depth of the individual first fringe depths of the five first segments; this is the average depth H1 of the multiple first fringe depths in the first segment. Replace the first segment of the first negative electrode material layer with the second, third, and fourth segments respectively, and follow the above testing method to obtain the average depth H2 of the multiple first fringe depths in the second segment, the average depth H3 of the multiple first fringe depths in the third segment, and the average depth H4 of the multiple first fringe depths in the fourth segment.

[0082] 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 third stripes H5, P3, W3, and A3 can be obtained.

[0083] The longitudinal section of the empty foil area is subjected to ion polishing. 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. A single second fringe is randomly selected. Along the width direction of the unfolded negative electrode sheet, five positions are randomly selected on this fringe. Then, along the length direction of the unfolded negative electrode sheet, the width at these five selected positions is measured, and the average value is taken as the width W' of the single second fringe. Along the length direction of the unfolded negative electrode sheet, the distance between the center of the width of the single second fringe and the center of the width of the adjacent second fringe is measured. Five positions are selected, and each measurement is taken once. The average value is taken as the spacing A' between two adjacent second fringes. Along the thickness direction of the negative electrode sheet, based on the depth variation of the second fringe, the empty foil areas corresponding to each segment of the first negative electrode material layer are determined. Five second stripes from any empty foil area opposite 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 second stripe in the empty foil area opposite the first segment are determined. 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 second stripe in the empty foil area opposite the first segment are measured. The average value is taken as the depth of the individual second stripe in the empty foil area opposite the first segment. The average value of the five individual second stripes in the empty foil areas opposite the first segment is taken as the average depth T1 of the multiple second stripes in the empty foil area opposite the first segment. The empty foil areas opposite the first segment are replaced with empty foil areas opposite the second, third, and fourth segments, respectively. Following the above testing method, the average depths T2, T3, and T4 of the multiple second stripes in the empty foil area opposite the second, third, and fourth segments can be obtained.

[0084] Cyclic performance test:

[0085] 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. 600The 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.

[0086] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0087] Lithium plating performance test:

[0088] 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. 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.

[0089] 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.

[0090] In this application, those skilled in the art will understand that "1C" is the current value that completely discharges the capacity of a lithium-ion battery in 1 hour, "0.1C" is the current value that completely discharges the capacity of a lithium-ion battery in 10 hours, and other rates are deduced accordingly.

[0091] Example 1-1

[0092] <Preparation of Negative Electrode Sheets>

[0093] 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 the first negative electrode material layer is H0, which is 60 μm, and the thickness of the second negative electrode material layer is H'0, which is 60 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.

[0094] Along the length of the unfolded negative electrode sheet, the first, second, and third segments of the first negative electrode material layer are determined. Based on the unfolded length of the first negative electrode material layer, the length percentage K1 of the first segment is 20%, the length percentage K2 of the second segment is 60%, and the length percentage K3 of the third segment is 20%. A first stripe is formed on the first, second, and third segments. The shape of the first stripe is as follows... Figure 2 As shown. 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 set to 0.6, the width W of the first stripe is 120 μm, and the spacing A 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 18 μm, and H1 / H0 is 0.3; the average depth H2 of the multiple first stripes located in the second segment is 24 μm, and H2 / H0 is 0.4; the average depth H3 of the multiple first stripes located in the third segment is 28.8 μm, and H3 / H0 is 0.48. First stripes are laser-etched on the first, second, and third segments according to the above parameters.

[0095] The average depth H5 of the third stripe is set to 36 μm, H4 / H'0 to 0.6, the ratio P3 of the length of a single third stripe to the width of the second negative electrode material layer along the width direction of the unfolded negative electrode sheet is 0.6, the width W3 of the third stripe is 120 μm, and the spacing A3 between two adjacent third stripes along the length direction of the unfolded negative electrode sheet is 5 mm. The shape of the third stripe is the same as that of the first stripe. The third stripe is laser-etched on the second negative electrode material layer according to the above parameters.

[0096] The final negative electrode sheet has a size of 67.45mm × 1436mm.

[0097] <Preparation of the positive electrode>

[0098] 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.

[0099] <Septum>

[0100] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0101] <Preparation of Electrolyte>

[0102] 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.

[0103] <Preparation of Lithium-ion Batteries>

[0104] 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 includes winding, flattening, current collector welding, casing, bottom penetration welding, inkjet printing, vacuum drying, electrolyte injection, cap welding, sealing, high-temperature settling, and 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 settling at room temperature (25℃) for 24 hours.

[0105] Examples 1-2 to 1-25

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

[0107] Examples 1-26

[0108] Except for setting the first stripe on the first negative electrode material layer according to the following steps, the rest is the same as in Example 1-1.

[0109] <Preparation of Negative Electrode Sheets>

[0110] Along the length of the unfolded negative electrode sheet, the first, second, third, and fourth segments of the first negative electrode material layer are determined. Based on the unfolded length of the first negative electrode material layer, the length percentage K1 of the first segment is 20%, K2 of the second segment is 50%, K3 of the third segment is 15%, and K4 of the fourth segment is 15%. First stripes are formed on the first, second, third, and fourth segments. The specific shape of the first stripes is as follows... Figure 2 As shown. 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 set to 0.6, the width W of the first stripe is 120 μm, and the spacing A 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 in the first segment is 18 μm, H1 / H0 is 0.3; the average depth H2 of the multiple first stripes in the second segment is 24 μm, H2 / H0 is 0.4; the average depth H3 of the multiple first stripes in the third segment is 28.8 μm, H3 / H0 is 0.48; and the average depth H4 of the multiple first stripes in the fourth segment is 36 μm, H4 / H0 is 0.6. First stripes are laser-etched on the first, second, third, and fourth segments according to the above parameters.

[0111] Examples 1-27 to Examples 1-30

[0112] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Examples 1-26.

[0113] Examples 1-31

[0114] 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.

[0115] Examples 1-32

[0116] 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.

[0117] Example 2-1

[0118] Except for the step of adding a second 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. A second stripe is added to the empty foil area, and the shape of the second stripe is specifically as follows... Figure 4 As shown. The average depth T' of the second stripe is set to 3 μm, T' / T0 to 0.3, the ratio P2 of the length of a single second stripe to the width of the empty foil area along the width direction of the unfolded negative electrode sheet is 0.3, the width W' of the second stripe is 120 μm, and the spacing A' between two adjacent second stripes along the length direction of the unfolded negative electrode sheet is 5 mm. The second stripe is laser-etched in the empty foil area according to the above parameters.

[0119] Example 2-2

[0120] Except for setting the average depth T1 of the second stripe in the empty foil area opposite to the first segment to 3 μm and T1 / T0 to 0.3, the average depth T2 of the second stripe in the empty foil area opposite to the second segment to 4 μm and T2 / T0 to 0.4, and the average depth T3 of the second stripe in the empty foil area opposite to the third segment to 4.8 μm and T2 / T0 to 0.48, the rest is the same as in Example 2-1.

[0121] Examples 2-3 to 2-11

[0122] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 2-2.

[0123] Comparative Example 1

[0124] 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.

[0125] Comparative Example 2

[0126] 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.

[0127] Comparative Examples 3 to 5

[0128] Except for adjusting the relevant preparation parameters according to Table 1 and not setting stripes on the second negative electrode material layer, the rest is the same as in Example 1-1.

[0129] Comparative Example 6

[0130] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0131] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0132]

[0133]

[0134]

[0135] As can be seen from Examples 1-1 to 1-32 and Comparative Examples 1 to 6, by adjusting the length ratio of the first, second, and third segments within the scope of this application, and setting first stripes on the first, second, and third segments, and ensuring that H1 < H2 < H3, 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 first stripes are set on either the first or second negative electrode material layer; in Comparative Example 2, no stripes are set on the first negative electrode material layer; in Comparative Example 3, the average depth of all first stripes on the first negative electrode material layer is consistent; in Comparative Example 4, only the first and second segments are on the first negative electrode material layer; in Comparative Example 5, H1 > H2 > H3; and in Comparative Example 6, H1 > H2 > H3, and stripes are set on the second negative electrode material layer. The lithium-ion batteries in Comparative Examples 1 to 6 exhibited more severe lithium plating and / or lower 600cls capacity retention. In contrast, the lithium-ion batteries in Examples 1-1 to 1-32 showed less severe lithium plating and higher 600cls capacity retention, indicating that the electrolyte had a better wetting effect on the negative electrode, and that the lithium-ion batteries possessed good lithium plating performance and cycle performance.

[0136] The values ​​of H1 / H0, H2 / H0, H3 / H0, and H0 typically affect the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-4 to 1-8, when the values ​​of H1 / H0, H2 / H0, H3 / H0, and H0 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 P1 typically affects the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-9 to 1-13, when the value of P1 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] The value of W typically affects the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-14 to 1-19, when the width of a single first stripe is within the range specified in 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 good wetting effect on the electrode, resulting in good lithium plating performance and cycle performance of the lithium-ion battery.

[0139] The value of A typically affects the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-20 to 1-25, when the widths of two adjacent first stripes are within the range specified in 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 better lithium plating performance and cycle performance of the lithium-ion battery.

[0140] The length ratio of the fourth segment and the values ​​of H3 and H4 typically affect the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-26 to 1-28, when the length ratio of the fourth segment is within the range of this application and H3 < H4, 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 good wetting effect on the electrode, resulting in good lithium plating performance and cycle performance of the lithium-ion battery.

[0141] The H4 / H0 ratio typically affects the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-26, 1-29 to 1-30, when the H4 / H0 ratio is within the range specified in 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 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.

[0142] 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, 1-31 to 1-32, 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.

[0143] Table 2

[0144]

[0145] Note: " / " in Table 2 indicates that there are no relevant preparation parameters.

[0146] The placement of the second 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 2-9, when the second stripe is placed within the scope of this application, the degree of lithium plating in the lithium-ion battery is less, and the 600cls capacity retention rate is higher. 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.

[0147] The values ​​of T1 / T0, T2 / T0, T3 / T0, 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 2-6, when the values ​​of H1 / H0, H2 / H0, H3 / H0, and H0 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.

[0148] The value of P2 typically affects the lithium plating performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-2, 2-7 to 2-11, when the value of P2 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.

[0149] 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.

[0150] 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.

[0151] 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, a second segment, and a third segment connected in sequence. Based on the length of the first negative electrode material layer, the length ratio of the first segment is 10% to 30%, the length ratio of the second segment is 20% to 60%, and the length ratio of the third segment is 15% to 30%. The first segment, the second segment, and the third segment are each provided with a plurality of first stripes. The plurality of first stripes 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 average depth of the plurality of first stripes in the first segment is H1 μm, the average depth of the plurality of first stripes in the second segment is H2 μm, and the average depth of the plurality of first stripes in the third segment is H3 μm, where H1 < H2 < H3.

2. The cylindrical secondary battery according to claim 1, wherein, The thickness of the first negative electrode material layer is H0 μm, 20≤H0≤100, 0.2≤H1 / H0≤0.35, 0.35<H2 / H0≤0.45, and 0.45<H3 / H0≤0.

5.

3. The cylindrical secondary battery according to claim 1 or 2, wherein, Along the length direction of the unfolded negative electrode sheet, the width of a single first stripe is W μm, 10≤W≤400.

4. The cylindrical secondary battery according to claim 3, wherein, 50≤W≤200。 5. The cylindrical secondary battery according to any one of claims 1 to 4, wherein, Along the length of the unfolded negative electrode sheet, the distance between two adjacent first stripes is A mm, where 0.5 ≤ A ≤ 10.

6. The cylindrical secondary battery according to claim 5, wherein, 3≤A≤7。 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, where 0.2≤P≤1.

8. The cylindrical secondary battery according to claim 7, wherein, 0.3≤P1≤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 second stripes. The plurality of second stripes 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 second stripe to the width of the empty foil area is P2, where 0.1≤P2≤0.

7.

11. The cylindrical secondary battery according to claim 10, wherein, 0.2≤P2≤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 current collector is T0 μm, the average depth of the plurality of second stripes in the empty foil area opposite to the first segment is T1 μm, the average depth of the plurality of second stripes in the empty foil area opposite to the second segment is T2 μm, the average depth of the plurality of second stripes in the empty foil area opposite to the third segment is T3 μm, 3≤T0≤20, 0.2≤T1 / T0≤0.35, 0.35<T2 / T0≤0.45, 0.45<T3 / T0≤0.

5.

13. The cylindrical secondary battery according to claim 1, wherein, 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 further includes a fourth segment connected to the third segment. Based on the length of the first negative electrode material layer, the length ratio of the fourth segment is 10% to 25%. The fourth segment is provided with a plurality of 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 average depth of the plurality of first stripes located in the fourth segment is H4μm, where H3 < H4.

14. The cylindrical secondary battery according to claim 13, wherein, 0.5 < H4 / H0 ≤ 0.

7.

15. An electronic device comprising a cylindrical secondary battery as described in any one of claims 1 to 14.

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