Cylindrical secondary battery and electronic device

Abstract

The invention provides a cylindrical secondary battery and an electronic device, and the cylindrical secondary battery comprises an electrode assembly, the electrode assembly comprises a pole piece, the pole piece comprises a first material layer, and the first material layer is located on the surface, away from the winding center of the electrode assembly, of a current collector; the first material layer comprises a first section, a second section and a third section which are sequentially connected, based on the length of the first material layer, the length ratio of the first section is L1, the length ratio of the second section is L2, the length ratio of the third section is L3, L1 is larger than or equal to 10% and smaller than or equal to 30%, L2 is larger than or equal to 20% and smaller than or equal to 40%, and L3 is larger than or equal to 40% and smaller than or equal to 60%. The first section, the second section and the third section are respectively provided with a plurality of bulges, along the thickness direction of the pole piece, the average height of the plurality of bulges positioned on the first section is H1 [mu] m, the average height of the plurality of bulges positioned on the second section is H2 [mu] m, the average height of the plurality of bulges positioned on the third section is H3 [mu] m, and H2 is more than H1 and less than H3. Through the arrangement, the sinking of the inner ring pole piece in the later cycle period of the secondary battery is improved, and the cycle performance of the secondary battery is 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. However, in the later stages of cycling, the electrodes in full-tab cylindrical lithium-ion batteries expand, which can cause the inner electrode rings of the battery's electrode assembly to sink inward, increasing the distance between the positive and negative electrodes. This leads to increased electrochemical impedance during charging and discharging, raising the risk of lithium plating and reducing cycle performance. Summary of the Invention

[0004] The purpose of this application is to provide a cylindrical secondary battery and electronic device to reduce the risk of lithium plating in the cylindrical secondary battery due to indentation of the inner electrode plate of the electrode assembly in the later stage of cycling, thereby improving the cycle performance of the cylindrical secondary battery.

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

[0006] The first aspect of the present application provides a cylindrical secondary battery. The cylindrical secondary battery includes an electrode assembly, and the electrode assembly includes a pole piece. The pole piece includes a current collector and a first material layer, and the first material layer is located on the surface of the current collector facing away from the winding center of the electrode assembly. Along the length direction of the pole piece after unfolding and along the winding direction of the electrode assembly, the first material layer includes a first section, a second section, and a third section connected in sequence. Based on the length of the first material layer, the length proportion of the first section is L1, the length proportion of the second section is L2, and the length proportion of the third section is L3, where 10% ≤ L1 ≤ 30%, 20% ≤ L2 ≤ 40%, and 40% ≤ L3 ≤ 60%. A plurality of protrusions are provided on each of the first section, the second section, and the third section. Along the thickness direction of the pole piece, the average height of the plurality of protrusions located on the first section is H1 μm, the average height of the plurality of protrusions located on the second section is H2 μm, and the average height of the plurality of protrusions located on the third section is H3 μm, and H1 < H2 < H3. In the present application, by regulating the length proportions of the first section, the second section, and the third section within the above ranges, providing protrusions on the first section, the second section, and the third section, and making H1 < H2 < H3, gradient-height protrusions are provided on the first material layer of the pole piece along the winding direction of the electrode assembly. From the outer circle to the inner circle of the electrode assembly, the stress continuously decreases, which can reduce the risk of the inner circle of the pole piece indenting due to stress concentration in the later stage of cycling, resulting in lithium deposition in the secondary battery. At the same time, the reserved expansion space is appropriate, and the distances between the positive and negative pole pieces and between the pole piece layers during the charge and discharge process are designed within a suitable range, thereby reducing the risk of lithium deposition and improving the cycle performance of the secondary battery.

[0007] In one or more embodiments, along the thickness direction of the pole piece, the sum of the thicknesses of the first material layer and the current collector is H0 μm, where 30 ≤ H0 ≤ 60, and 8% ≤ H2 / H0 × 100% ≤ 60%; optionally, 15% ≤ H2 / H0 × 100% ≤ 45%. By regulating the values of H0 and H2 / H0 × 100% within the above ranges, it is beneficial to improve the degree of indenting of the inner circle pole piece of the electrode assembly due to pole piece expansion in the later stage of cycling, and further reduce the risk of lithium deposition in the cylindrical secondary battery. The electrochemical impedance of the secondary battery during the charge and discharge process is small, and while taking into account the energy density of the secondary battery, the cycle performance of the secondary battery is improved.

[0008] In one or more embodiments, aH3 ≤ H2 ≤ bH1, where 0.5 ≤ a ≤ 0.8 and 1.1 ≤ b ≤ 1.6. By regulating the ratio relationship between H1, H^2, and H3, it is beneficial to improve the degree of indenting of the inner circle pole piece of the electrode assembly due to pole piece expansion in the later stage of cycling, and further reduce the risk of lithium deposition in the cylindrical secondary battery. The electrochemical impedance of the secondary battery during the charge and discharge process is small, and while taking into account a relatively high energy density, the secondary battery has good cycle performance and safety performance.

[0009] In one or more embodiments, along the length direction after the electrode sheet is unfolded, the distance between two adjacent protrusions is A mm, where 1 ≤ A ≤ 10; optionally, 3 ≤ A ≤ 7. By adjusting the distance A between two adjacent protrusions within the above range, the degree of inner electrode sheet indentation caused by electrode sheet expansion in the later stages of cycling is improved, thereby reducing the risk of lithium plating in cylindrical secondary batteries and improving the cycle performance of secondary batteries.

[0010] In one or more embodiments, along the thickness direction of the electrode, the diameter of the largest circumscribed circle of the projected outer contour of a single protrusion is D mm, where 0.5 ≤ D ≤ 10; optionally, 2 ≤ D ≤ 6. By controlling the diameter D of the largest circumscribed circle of the projected outer contour of a single protrusion within the above range, the risk of increased electrochemical impedance due to increased local electrolyte aggregation side reactions is reduced. It also improves the degree of inner electrode indentation caused by electrode expansion in the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries and improving the cycle performance of the secondary battery.

[0011] In one or more embodiments, the electrode further includes a second material layer located on the surface of the current collector facing the winding center of the electrode assembly. The surface of the second material layer has a plurality of first recesses facing the first material layer. In one or more embodiments, the current collector has a plurality of second recesses facing the first material layer. In one or more embodiments, at least some of the first recesses correspond to some of the protrusions; and / or, at least some of the second recesses correspond to some of the protrusions. This configuration improves the operability of providing protrusions, first recesses, and second recesses on the first segment, which is beneficial for improving the wetting performance of the electrolyte on the electrode, further improving the degree of inner-ring electrode indentation caused by electrode expansion in the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries, and improving the cycle performance of secondary batteries while meeting mass production manufacturability requirements.

[0012] In one or more embodiments, the electrode is a positive electrode.

[0013] 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 cycle performance; therefore, the electronic device of this application has a long service life.

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

[0015] This embodiment of the application provides a gradient height protrusion on the first material layer along the winding direction of the electrode assembly. From the outer ring to the inner ring of the electrode assembly, the stress continuously decreases, which can improve the degree of inward sinking of the inner ring of the electrode due to stress concentration in the later stage of cycling. This reduces the risk of lithium plating in the secondary battery, and ensures that the distance between the positive and negative electrodes is within a suitable range during charging and discharging, resulting in a smaller electrochemical impedance of the secondary battery, thereby improving the cycle performance of the cylindrical secondary battery.

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

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

[0018] Figure 1 Computed tomography (CT) image of the inner electrode indentation in the late cycle stage of a cylindrical lithium-ion battery in the prior art;

[0019] Figure 2 This is a schematic diagram of the winding structure formed by the electrode assembly in one embodiment of this application;

[0020] Figure 3 This is a partial front view of the positive electrode sheet after the electrode assembly in another embodiment of this application has been unfolded.

[0021] Figure 4 for Figure 3 A cross-sectional view of the positive electrode sheet along the PP direction.

[0022] Reference numerals: Electrode assembly 001; Positive electrode 10; Positive current collector 11; First positive electrode material layer 12; Second positive electrode material layer 13; Negative electrode 20; Negative current collector 21; First negative electrode material layer 22; Second negative electrode material layer 23; Separator 30; Protrusion 121; First recess 131; Second recess 111. Detailed Implementation

[0023] 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.

[0024] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of a cylindrical secondary battery to explain the present application. However, the cylindrical secondary battery of the present application is not limited to lithium-ion batteries.

[0025] In the cylindrical secondary batteries in the prior art, such as cylindrical lithium-ion batteries, the electrode sheets expand in the later stage of cycling. Especially when the negative active material in the negative electrode sheet contains silicon elements, the negative electrode sheet expands and contracts significantly during the cycling process. When the electrode assembly expands outward and is restricted by the housing, the electrode sheets in the electrode assembly will sink inward to release stress, resulting in the inward indentation of the inner ring electrode sheets in the electrode assembly. As Figure 1 shown, at this time, the distance between the positive electrode sheet and the negative electrode sheet in the electrode assembly further increases, and some electrode sheets may break. Moreover, the impedance of the lithium-ion battery also increases during the charge and discharge process, increasing the risk of lithium deposition in the lithium-ion battery and affecting the cycling performance of the lithium-ion battery. Based on this, the present application provides a cylindrical secondary battery and an electronic device, which are beneficial to improving the degree of inward indentation of the inner ring electrode sheets caused by the expansion of the electrode sheets in the later stage of cycling, thereby reducing the risk of lithium deposition in the cylindrical secondary battery and ultimately improving the cycling performance of the cylindrical secondary battery.

[0026] In the first aspect of the present application, a cylindrical secondary battery is provided. The cylindrical secondary battery includes an electrode assembly. The electrode assembly includes electrode sheets. The electrode sheets include current collectors and a first material layer. The first material layer is located on the surface of the current collector facing away from the winding center of the electrode assembly. Along the length direction of the electrode sheet after unfolding and along the winding direction of the electrode assembly, the first material layer includes a first segment, a second segment, and a third segment connected in sequence. Based on the length of the first material layer, the length ratio of the first segment is L1, the length ratio of the second segment is L2, and the length ratio of the third segment is L3, where 10% ≤ L1 ≤ 30%, 20% ≤ L2 ≤ 40%, and 40% ≤ L3 ≤ 60%. A plurality of protrusions are provided on each of the first segment, the second segment, and the third segment. Along the thickness direction of the electrode sheet, the average height of the plurality of protrusions located on the first segment is H1 μm, the average height of the plurality of protrusions located on the second segment is H2 μm, and the average height of the plurality of protrusions located on the third segment is H3 μm, and H1 < H2 < H3.

[0027] In the present application, the electrode sheet can be a positive electrode sheet and / or a negative electrode sheet. It is defined that in the unfolded state of the electrode assembly, its own length direction is the X direction, its own width direction is the Y direction, and its own thickness direction is the Z direction. It can be understood that in the unfolded state, the length direction, width direction, and thickness direction of the negative electrode sheet, the positive electrode sheet, and the separator are the same as those of the electrode assembly, and the winding direction of the electrode assembly is the W direction. Exemplarily, as Figure 2 and Figure 3As shown, the electrode assembly 001 includes a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10 includes a positive current collector 11 and a first positive electrode material layer 12. The negative electrode 20 includes a negative current collector 21 and a first negative electrode material layer 22. Along the length direction (X direction) of the unfolded positive electrode 10 and along the winding direction (W direction) of the electrode assembly 001, the first positive electrode material layer 12 includes a first segment (not shown in the figure), a second segment (not shown in the figure), and a third segment (not shown in the figure) connected in sequence. Multiple protrusions 121 are provided on the first, second, and third segments. Figure 4 As shown, along the thickness direction Z of the positive electrode 10, the average height of the multiple protrusions 121 in the first segment is H1 μm, the average height of the multiple protrusions 121 in the second segment is H2 μm, and the average height of the multiple protrusions 121 in the third segment is H3 μm.

[0028] When the length of the first and / or second segment is too large, for example, exceeding the upper limit of this application, the length of the third segment is too small, resulting in a low height of the protrusions on the electrode sheet. This leads to a small reserved expansion space, which cannot effectively improve the indentation of the inner electrode sheet caused by electrode sheet expansion in the later stages of cycling. The distance between the positive and negative electrode sheets is large, and some electrode sheets may tear. Furthermore, the impedance of the secondary battery increases during charging and discharging, increasing the risk of lithium plating and failing to significantly improve the cycle performance of the secondary battery. When H1≥H2≥H3, the height of the protrusions on the inner electrode sheet near the winding center of the electrode assembly is large, resulting in a large reserved expansion space. This makes it easy for electrolyte bridging to occur between some electrode layers, leading to an increase in the electrochemical impedance of the secondary battery, increasing the risk of lithium plating and resulting in poor cycle performance. This application adjusts the length ratio of the first, second, and third segments within the aforementioned range, and sets protrusions on the first, second, and third segments, ensuring H1 < H2 < H3. A gradient height of protrusions is set on the first material layer of the electrode assembly along the winding direction of the electrode assembly. From the outer ring to the inner ring of the electrode assembly, the stress continuously decreases, reducing the risk of lithium plating and breakage of the secondary battery due to stress concentration in the later stages of cycling. Simultaneously, the reserved expansion space is moderate, designing the distance between the positive and negative electrodes and between electrode layers within an appropriate range during charging and discharging. This results in a lower electrochemical impedance of the secondary battery, thereby reducing the risk of lithium plating and improving the cycle performance. Furthermore, setting protrusions of different heights on the first material layer ensures uniform stress on the electrode while maintaining the energy density of the secondary battery. When the electrode expands, the risk of breakage due to stress is reduced, thus improving the safety performance of the secondary battery. Therefore, the cylindrical secondary battery of this application has excellent cycle performance. It should be noted that the "surface" of the first material layer located on the surface of the current collector away from the winding center of the electrode assembly can be the entire area of ​​the current collector surface or a part of the current collector surface. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0029] In one or more embodiments, along the thickness direction of the electrode, the sum of the thicknesses of the first material layer and the current collector is H0 μm, such as... Figure 4As shown, along the thickness direction (Z direction) of the positive electrode sheet 10, the sum of the thicknesses of the first positive electrode material layer 12 and the positive electrode current collector 11 is H0 μm. 30≤H0≤60, 8%≤H2 / H0×100%≤60%; optionally, 15%≤H2 / H0×100%≤45%. For example, the value of H0 can be 30, 32, 35, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, or a range of any two of these values; the value of H2 / H0×100% can be 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, or a range of any two of these values. By adjusting the values ​​of H0 and H2 / H0×100% within the aforementioned range, the inner ring of the electrode assembly has expansion space. This helps to mitigate the degree of inner ring electrode indentation caused by electrode expansion during the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries. Simultaneously, the reserved space is moderate, allowing for tight adhesion between the positive and negative electrodes and between electrode layers during charging and discharging. This results in lower electrochemical impedance of the secondary battery during charging and discharging, improving cycle performance while maintaining energy density. In this application, the thickness of the first material layer can be controlled using methods known to those skilled in the art. For example, when coating the slurry onto the surface of the current collector, given a fixed solid content in the slurry, the thickness of the first material layer can be increased by increasing the coating weight and decreased by decreasing the coating weight. Alternatively, during cold pressing of the electrode, the thickness of the first material layer can be decreased by increasing the cold pressing pressure and increased by decreasing the cold pressing pressure. This application does not impose any particular limitation on the method of adjusting the thickness of the current collector, as long as it can achieve the purpose of this application. For example, commercially available current collectors with different thicknesses can be selected, and the thickness of the current collector can be determined by combining the test method of "H1, H2, H3, H0, A, D test" in this application, and then the current collector with the required thickness can be selected. In one or more embodiments, the thickness of the current collector along the thickness direction of the electrode can be 10 μm to 15 μm.

[0030] In one or more embodiments, 2.4 ≤ H2 ≤ 36; optionally, 4.5 ≤ H2 ≤ 27. For example, the value of H2 can be 2.4, 2.5, 2.7, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 8, 10, 12, 15, 18, 20, 22, 25, 27, 28, 30, 32, 35, 36, or a range of any two of these values. By adjusting the value of H2 within the above range, the inner ring of the electrode assembly has expansion space, which helps to reduce the degree of inner ring electrode indentation caused by electrode expansion in the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries. At the same time, the reserved space is moderate, and the positive and negative electrode sheets and the electrode layers can be tightly attached during charging and discharging. The electrochemical impedance of the secondary battery is small during charging and discharging, thereby improving the cycle performance of the secondary battery.

[0031] In one or more embodiments, aH3≤H2≤bH1, 0.5≤a≤0.8, 1.1≤b≤1.6. For example, the value of a can be 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, or a range of any two of these values; the value of b can be 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3, 1.32, 1.35, 1.38, 1.4, 1.42, 1.45, 1.48, 1.5, 1.52, 1.55, 1.58, 1.6, or a range of any two of these values. By adjusting the ratio of H1, H2, and H3, a gradient height of protrusions is created on the first material layer. This helps mitigate the inward deformation of the inner electrode due to electrode expansion during later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries. Simultaneously, the appropriate space allows for tight adhesion between the positive and negative electrodes and between electrode layers during charging and discharging, resulting in lower electrochemical impedance and improved cycle performance. Furthermore, the moderate average height of the protrusions on the electrodes ensures uniform stress distribution, reducing the risk of electrode fracture due to stress during expansion while maintaining high energy density, thus enhancing battery safety. Therefore, the secondary battery exhibits both good cycle performance and safety while maintaining high energy density.

[0032] In one or more embodiments, 4.8 ≤ H3 ≤ 45, and 1.5 ≤ H1 ≤ 32.7. For example, the value of H3 can be 4.8, 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 H1 can be 1.5, 1.8, 2, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 32.2, 32.5, 32.7, or a range of any two of these values. By adjusting the ratio of H1, H2, and H3, a gradient height of protrusions is created on the first material layer. This helps mitigate the inward deformation of the inner electrode due to electrode expansion during later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries. Simultaneously, the appropriate space allows for tight adhesion between the positive and negative electrodes and between electrode layers during charging and discharging, resulting in lower electrochemical impedance and improved cycle performance. Furthermore, the moderate average height of the protrusions on the electrodes ensures uniform stress distribution, reducing the risk of electrode fracture due to stress during expansion while maintaining high energy density, thus enhancing battery safety. Therefore, the secondary battery exhibits both good cycle performance and safety while maintaining high energy density.

[0033] In one or more embodiments, the distance between two adjacent protrusions along the length direction of the unfolded electrode is A mm, such as... Figure 3 As shown, along the length direction (X direction) of the unfolded positive electrode 10, the distance between two adjacent protrusions 121 is A mm. 1≤A≤10; optionally, 3≤A≤7. For example, the value of A can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two values. By adjusting the distance A between two adjacent protrusions within the above range, it is beneficial to reduce the processing difficulty of the electrode during processing, reduce the risk of excessive powder shedding during electrode processing leading to loss of active materials and thus reduced energy density of the secondary battery, and make the electrode pore distribution uniform, which is conducive to the flow of electrolyte on the electrode and improves the wetting effect of electrolyte on the electrode. It improves the degree of inner electrode indentation caused by electrode expansion in the later stage of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries. At the same time, the reserved space is moderate, and the positive and negative electrodes and the electrode layers can be tightly attached during charging and discharging. The electrochemical impedance of the secondary battery is small during charging and discharging, thereby reducing the risk of lithium plating and improving the cycle performance of the secondary battery. In this application, the spacing between two adjacent protrusions refers to the distance between the geometric centers of two adjacent protrusions along the length direction after the electrode is unfolded.

[0034] In one or more embodiments, the spacing between any two adjacent protrusions is equal along the length direction after the electrode sheet is unfolded. This arrangement improves the operability of setting protrusions on the first material layer, reduces the degree of inner electrode sheet indentation caused by electrode sheet expansion during later stages of cycling, and thus reduces the risk of lithium plating in cylindrical secondary batteries. This improves the cycle performance of cylindrical secondary batteries while meeting mass production manufacturability requirements.

[0035] In one or more embodiments, along the thickness direction of the electrode sheet, the diameter of the largest circumcircle of the projected outer contour of a single protrusion is D mm, as shown below. Figure 3 As shown, along the thickness direction Z of the positive electrode 10, a single protrusion 121 has a projection on the first positive electrode material layer 12, and the diameter of the largest circumscribed circle of the projection of the single protrusion 121 is D mm. 0.5≤D≤10; optionally, 2≤D≤6. For example, the value of D 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 controlling the diameter D of the maximum circumcircle of the projected outer contour of a single protrusion within the aforementioned range, it is beneficial to reduce the risk of reduced reserved expansion space due to protrusion collapse during preparation or cycling. This ensures a moderate reserved space, effectively mitigating the risk of inner electrode plate indentation in the later stages of cycling. Furthermore, by ensuring the pit size on the electrode surface facing the winding center of the electrode assembly is moderate, the risk of increased electrochemical impedance due to localized electrolyte aggregation and side reactions is reduced. This also mitigates the degree of inner electrode plate indentation caused by electrode plate expansion in the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries and improving the cycle performance of the secondary battery. This application does not impose any particular limitation on the projected shape of a single protrusion, as long as it achieves the purpose of this application. For example, the projected shape of a single protrusion can be at least one of a triangle, an arc (with an area smaller than a semicircle with the same radius), a semicircle, a rectangle, a trapezoid, a square, or a pentagon or more polygons.

[0036] In one or more embodiments, the protrusions are distributed in a dotted pattern on the first material layer. In one or more embodiments, the protrusions are distributed in a matrix on the first material layer. In one or more embodiments, when the protrusions are distributed in a matrix on the first material layer, the spacing between adjacent rows is equal along the width direction after the electrode is unfolded. This application does not impose a particular limitation on the number of rows of protrusions; those skilled in the art can set the number according to the specifications of the actual electrode, as long as the purpose of this application can be achieved.

[0037] In one or more embodiments, multiple protrusions are located on the same side of the electrode along its thickness direction. This arrangement improves the operability of setting protrusions on the first material layer, reduces the degree of inner electrode indentation caused by electrode expansion during later stages of cycling, and thus reduces the risk of lithium plating in cylindrical secondary batteries. This improves the cycle performance of cylindrical secondary batteries while meeting mass production manufacturability requirements.

[0038] In one or more embodiments, the electrode further includes a second material layer located on the surface of the current collector facing the winding center of the electrode assembly, and the surface of the second material layer has a plurality of first recesses in the direction facing the first material layer. Figure 2 and Figure 4 As shown, the positive electrode 10 also includes a second positive electrode material layer 13. The second positive electrode material layer 13 is located on the surface of the positive current collector 11 facing the winding center of the electrode assembly 001. The surface of the second positive electrode material layer 13 has a plurality of first recesses 131 in the direction of the first positive electrode material layer 12. Through the above arrangement, the operability of setting protrusions and first recesses on the electrode is improved, which is beneficial to improving the wetting performance of the electrolyte on the electrode, further improving the degree of inner ring electrode sinking caused by electrode expansion in the later stage of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries, and improving the cycle performance of secondary batteries while meeting the manufacturability of mass production. It should be noted that the "surface" of the second material layer located on the surface of the current collector facing the winding center of the electrode assembly can be the entire area of ​​the current collector surface or a part of the current collector surface. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0039] In one or more embodiments, the current collector has a plurality of second recesses in the direction toward the first material layer. For example... Figure 2 As shown, the positive electrode current collector 11 has a plurality of second recesses 111 in the direction of the first positive electrode material layer 12. This arrangement improves the operability of setting protrusions and second recesses on the electrode sheet, further reduces the degree of inner electrode sheet indentation caused by electrode sheet expansion in the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries and improving the cycle performance of secondary batteries while meeting mass production manufacturability requirements.

[0040] In one or more embodiments, at least a portion of the first recess corresponds to a portion of the protrusion; and / or, at least a portion of the second recess corresponds to a portion of the protrusion. This configuration improves the operability of providing protrusions, first recesses, and / or second recesses on the electrode sheet, further reduces the degree of inner electrode sheet indentation due to electrode sheet expansion in the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries and improving the cycle performance of secondary batteries while meeting mass production manufacturability requirements.

[0041] In one or more embodiments, the electrode is a positive electrode. When the electrode is a positive electrode, it helps to reduce the processing difficulty of the electrode during the manufacturing process, reduces the risk of excessive powder shedding during electrode processing leading to loss of active materials and thus a decrease in the energy density of the secondary battery, and further improves the degree of inner electrode sinking caused by electrode expansion in the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries. At the same time, the reserved expansion space is moderate, and the distance between the positive and negative electrodes and between electrode layers during charging and discharging is within a suitable range, resulting in a lower electrochemical impedance of the secondary battery, thereby further improving the cycle performance of the secondary battery.

[0042] In this application, when the electrode is a positive electrode, there are no particular restrictions on the positive current collector, as long as it can achieve the purpose of this application. For example, the positive current collector can include aluminum foil, aluminum alloy foil, or composite current collector (e.g., aluminum-carbon composite current collector). In this case, both the first and second material layers are positive electrode material layers. The positive electrode material layer in this application includes a positive electrode active material. There are no particular restrictions on the type of positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there is no particular limitation on the thickness of the positive electrode current collector, 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 is no particular limitation 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 include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the type of conductive agent in the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and positive electrode binder in the positive electrode material layer; those skilled in the art can select according to actual needs, as long as it can achieve the purpose of this application.

[0043] In this application, when the electrode is a negative electrode, there are no particular restrictions on the negative current collector, as long as it can achieve the purpose of this application. For example, the negative current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (such as lithium copper composite current collectors, carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.). At this time, both the first material layer and the second material layer are negative electrode material layers, and the negative electrode material layer in this application includes a negative electrode active material. There are no particular restrictions on the type of negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material can include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO2, etc. x(0 < x < 2), at least one of Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O with spinel structure 12 , Li-Al alloy or metallic lithium. In this application, there is no particular limitation on the thickness of the negative electrode current collector, as long as the object of this application can be achieved. Optionally, the negative electrode material layer may further include a conductive agent and a negative electrode binder. There is no particular limitation on the type of the conductive agent in the negative electrode material layer in this application, as long as the object of this application can be achieved. For example, the conductive agent may be of the same type as the conductive agent in the above positive electrode material layer. There is no particular limitation on the type of the negative electrode binder in the negative electrode material layer in this application, as long as the object of this application can be achieved. For example, the negative electrode binder may be of the same type as the positive electrode binder in the above positive electrode material layer. There is no particular limitation on the mass ratio of the negative electrode active material, the conductive agent and the negative electrode binder in the negative electrode material layer in this application, as long as the object of this application can be achieved.

[0044] There is no particular limitation on the method for preparing the electrode sheet in this application, as long as the object of this application can be achieved. For example, the method for preparing the electrode sheet includes but is not limited to the following steps: (1) preparing a slurry; (2) coating the slurry on one surface of the current collector and drying to form an electrode sheet including a first material layer; (3) coating the slurry on the other surface of the current collector and drying to obtain an electrode sheet including a first material layer and a second material layer; (4) determining the first segment, the second segment and the third segment of the first material layer along the length direction after the electrode sheet is unfolded and along the winding direction of the electrode assembly winding, setting protrusions on the surfaces of the first segment, the second segment and the third segment, and then cutting and slitting to obtain the electrode sheet.

[0045] There is no particular limitation on the solid content of the above slurry in this application, and those skilled in the art can select according to actual needs, as long as the object of this application can be achieved. There is no particular limitation on the process parameters of the above drying, cutting and slitting in this application, and those skilled in the art can select according to actual needs, as long as the object of this application can be achieved. In one or more embodiments, in step (4), when setting protrusions on the surfaces of the first segment, the second segment and the third segment respectively, a first recess is provided on the surface of the second material layer facing the first material layer. In one or more embodiments, in step (4), when setting protrusions on the surfaces of the first segment, the second segment and the third segment respectively, a second recess is provided on the current collector facing the first material layer.

[0046] This application does not impose any particular limitation on the method of setting the protrusion, the first recess, and the second recess. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the protrusion, the first recess, and the second recess can be set by cold pressing the electrode sheet with an embossing roller. The shape of the projection of a single protrusion on the first material layer can be controlled by the shape of the stainless steel needle on the embossing roller; the average height H1 of multiple protrusions in the first segment, the average height H2 of multiple protrusions in the second segment, and the average height H3 of multiple protrusions in the third segment can be controlled by the cold pressing pressure value set on the embossing roller or the height specification of the stainless steel needle on the embossing roller; the distance A between two adjacent protrusions can be controlled by the distance between adjacent stainless steel needles on the embossing roller; the diameter D of the maximum circumscribed circle of the outer contour of the projection of a single protrusion on the first material layer can be controlled by the specification of the stainless steel needle on the embossing roller.

[0047] In one or more embodiments, the current collector includes a coated region having a material layer and an empty foil region connected to the coated region, with at least a portion of the empty foil region forming a flattened portion. This arrangement facilitates the placement of the tabs and makes the secondary battery manufacturing process easier, thereby improving the safety and cycle performance of the cylindrical secondary battery.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] In this application, when preparing a wound electrode assembly for a cylindrical secondary battery, an embossing roller can be installed on a winding device to create protrusions, a first recess, and a second recess on the electrode sheet.

[0054] 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 cycle performance; therefore, the electronic device of this application has a long service life.

[0055] 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.

[0056] Example

[0057] 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.

[0058] Test methods and equipment:

[0059] Tests for H1, H2, H3, H0, A, and D:

[0060] At an ambient temperature of 25°C, the lithium-ion batteries of each embodiment and comparative example were discharged to 2.5V at 0.5C and then disassembled to obtain electrode assemblies. The positive and negative electrode sheets were taken out from the electrode assemblies and soaked in dimethyl carbonate (DMC) for 20 minutes. Then, the positive and negative electrode sheets were placed in an oven and dried at 80°C for 12 hours to obtain test samples of the positive and negative electrode sheets.

[0061] The surface of the electrode was observed using a scanning electron microscope (SEM). Measurements were taken along the thickness direction of the electrode, measuring the plane formed by the length and width directions after the electrode was unfolded. Due to the height difference between the protrusion and the material layer surface, a noticeable color difference was observed on the electrode surface. The protrusions projected irises onto the electrode surface, which could be used to distinguish the protrusions from the first material layer. Five irises were randomly selected, and the maximum circumcircle diameter of the projection of each iris onto the first material layer was measured. The average value was taken as the maximum circumcircle diameter D of the projection of a single protrusion. Along the length direction of the unfolded electrode, one protrusion was randomly selected, and the distance between the geometric center of that protrusion and the geometric center of the adjacent protrusion was measured. Five measurements were taken, and the average value was taken as the distance A between two adjacent protrusions.

[0062] The electrode with protrusions is ion-polished along its length and thickness directions after being unfolded, yielding a cross-section. Scanning electron microscopy (SEM) is used to measure this cross-section, revealing a clear boundary between the material layer and the current collector. The material layer with protrusions is designated as the first material layer. Based on the variation in the height of the protrusions along the thickness direction of the electrode, the first, second, and third segments of the first material layer are determined.

[0063] Select any 5 protrusions in the first segment, and measure the maximum height from the surface of the first material layer to each individual protrusion along the thickness direction of the electrode. Take the average value, which is the average height H1 of the multiple protrusions in the first segment. Select any 5 protrusions in the second segment, and measure the maximum height from the surface of the first material layer to each individual protrusion along the thickness direction of the electrode. Take the average value, which is the average height H2 of the multiple protrusions in the second segment. Select any 5 protrusions in the third segment, and measure the maximum height from the surface of the first material layer to each individual protrusion along the thickness direction of the electrode. Take the average value, which is the average height H3 of the multiple protrusions in the third segment.

[0064] Along the thickness direction of the electrode, measure the distance from the surface of the first material layer to the surface of the current collector opposite to the first material layer, which is the sum of the thicknesses of the first material layer and the current collector, H0.

[0065] Cyclic performance test:

[0066] The lithium-ion batteries in the examples and comparative examples were subjected to charge-discharge cycle tests in a 25°C constant temperature chamber. The lithium-ion batteries were charged at a constant current of 2C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C. After resting for 5 minutes, they were discharged at a constant current of 6C to 2.5V. This was the first cycle, and the discharge capacity C1 of the first cycle was recorded. After 600 cycles following the above process, the discharge capacity C of the lithium-ion battery was recorded. 600 The capacity retention rate at 600 cycles was calculated as an indicator to evaluate the electrode wetting effect 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 electrode wetting effect and worse cycle performance in the lithium-ion battery; conversely, a higher capacity retention rate at 600cls indicates a better electrode wetting effect and better cycle performance in the lithium-ion battery.

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

[0068] Computed tomography (CT) scan and electrode indentation distance test:

[0069] 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, charged at a constant voltage of 4.2V to 0.05C, and left to stand for 5 minutes. Then, they were discharged at a constant current of 6C to 2.5V. This was the first cycle. After 600 cycles according to the above cycle process, the lithium-ion batteries were disassembled to obtain the wound electrode assembly.

[0070] Using industrial computed tomography (ICT) technology (Zeiss Xradia 620 Versa), a CT scan of the wound electrode assembly is performed along its unfolded width (or axial direction). The distance from the innermost ring of the electrode assembly to the outermost ring where the electrode deformation occurs is measured. Figure 1 As shown, the distance between point M and point N is the electrode indentation distance.

[0071] Example 1

[0072] <Preparation of the positive electrode>

[0073] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi). 0.91 Co 0.05 Mn 0.04 O2), polyvinylidene fluoride (PVDF) binder, and conductive carbon black were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97.1:1.6:1.3 and thoroughly mixed to obtain a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated on one surface of a 13 μm thick aluminum foil for the positive electrode current collector and dried at 105 °C to obtain a positive electrode sheet with a first positive electrode material layer coated on one side. The above steps were then repeated on the other surface of the same aluminum foil to obtain a positive electrode sheet with both a first and a second positive electrode material layer coated.

[0074] Along the length of the unfolded positive electrode sheet, the first, second, and third segments of the first positive electrode material layer are determined. Based on the unfolded length of the first positive electrode material layer, the length ratio L1 of the first segment is 20%, the length ratio L2 of the second segment is 20%, and the length ratio L3 of the third segment is 60%. Protrusions are respectively provided on the first, second, and third segments. Along the thickness direction of the positive electrode sheet, the projection shape of a single protrusion on the first material layer is set to be circular, and the diameter D of the largest circumcircle of the projection of a single protrusion is 4 mm. The average height H1 of multiple protrusions in the first segment is 9.643 μm, the average height H2 of multiple protrusions in the second segment is 13.5 μm, and the average height H3 of multiple protrusions in the third segment is 22.5 μm. Along the length of the unfolded positive electrode sheet, the spacing A between two adjacent protrusions is 5 mm. The positive electrode sheet is cold-pressed using an embossing roller of appropriate specifications according to the above parameters. After cutting and slitting, a positive electrode sheet with protrusions, a first recess, and a second recess is obtained. The coating weight of the first and second positive electrode material layers is 234 mg / 1540.25 mm. 2 The positive electrode sheet has a size of 64.5mm × 1422mm, the first positive electrode material layer has a size of 60mm × 1422mm, the second positive electrode material layer has the same size as the first positive electrode material layer, the sum of the thicknesses of the first positive electrode material layer and the positive current collector H0 is 45μm, and the width of the empty foil area of ​​the positive electrode sheet is 4.5mm.

[0075] <Preparation of Negative Electrode Sheets>

[0076] Artificial graphite (anode active material), SiO₂ (anode active material), sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 84:13:1.7:1.3. Deionized water was then added as a solvent, and the mixture was stirred until homogeneous, yielding a negative electrode slurry with a solid content of 50 wt%. This slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector and dried at 105 °C to obtain a negative electrode sheet with a first negative electrode material layer coated on one side. The same steps were 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, cutting, and slitting, negative electrode sheets with dimensions of 67.45 mm × 1436 mm were obtained for later use. The coating weight of the first and second negative electrode material layers was 110 mg / 1540.25 mm. 2 The first negative electrode material layer has a size of 62mm × 1436mm, the second negative electrode material layer has the same size as the first negative electrode material layer, the sum of the thickness of the first negative electrode material layer and the negative electrode current collector is 40μm, and the width of the empty foil area of ​​the negative electrode sheet is 5.45mm.

[0077] <Septum>

[0078] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0079] <Preparation of Electrolyte>

[0080] 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.

[0081] <Preparation of Lithium-ion Batteries>

[0082] The prepared separator, negative electrode, and positive electrode are stacked sequentially and pre-wound to ensure the separator is positioned between the negative and positive electrodes. Simultaneously, the first positive electrode material layer is positioned away from the center of the pre-wound electrode assembly, and the first segment of the first positive electrode material layer is located close to the center of the pre-wound electrode assembly. Afterwards, the process involves winding, flattening, current collector welding, casing, bottom penetration welding, inkjet coding, vacuum drying, electrolyte injection, sealing, and high-temperature settling followed by formation testing to obtain the lithium-ion battery. The upper limit of the formation voltage is 3.6V, the formation temperature is 45℃, and after formation, the battery is left to stand at room temperature (25℃) for 24 hours.

[0083] Examples 2 to 30

[0084] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1. Among them, when the sum of the thicknesses H0 of the first positive electrode material layer and the positive electrode current collector changes, the thickness of the positive electrode current collector remains unchanged, and the coating weight is adjusted so that H0 is as shown in Table 1.

[0085] Example 31

[0086] Except for the preparation of the negative electrode and lithium-ion battery according to the steps described below, the rest is the same as in Example 1.

[0087] <Preparation of Negative Electrode Sheets>

[0088] Artificial graphite (anode active material), SiO₂ (anode active material), sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 84:13:1.7:1.3. Deionized water was then added as a solvent, and the mixture was stirred until homogeneous, yielding a cathode slurry with a solid content of 50 wt%. This cathode slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector and dried at 105 °C to obtain a cathode sheet with a single-sided coating of the first cathode material layer. The above steps were then repeated on the other surface of the same copper foil to obtain a cathode sheet coated with both the first and second cathode material layers.

[0089] 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 ratio L1 of the first segment is 20%, the length ratio L2 of the second segment is 20%, and the length ratio L3 of the third segment is 60%. Protrusions are respectively provided on the first, second, and third segments. Along the thickness direction of the negative electrode sheet, the projection shape of a single protrusion on the first material layer is set to be circular, and the diameter D of the largest circumcircle of the projection of a single protrusion is 4 mm. The average height H1 of multiple protrusions in the first segment is 8.571 μm, the average height H2 of multiple protrusions in the second segment is 12 μm, and the average height H3 of multiple protrusions in the third segment is 20 μm. Along the length of the unfolded negative electrode sheet, the spacing A between two adjacent protrusions is 5 mm. The negative electrode sheet is cold-pressed using an embossing roller of appropriate specifications according to the above parameters. After cutting and slitting, a negative electrode sheet with protrusions, a first recess, and a second recess is obtained. The coating weight of the first negative electrode material layer and the second negative electrode material layer is 110 mg / 1540.25 mm. 2 The negative electrode sheet has a size of 67.45mm × 1436mm, the first negative electrode material layer has a size of 62mm × 1436mm, the second negative electrode material layer has the same size as the first negative electrode material layer, the sum of the thicknesses of the first negative electrode material layer and the negative electrode current collector H0 is 40μm, and the width of the empty foil area of ​​the negative electrode sheet is 5.45mm.

[0090] <Preparation of Lithium-ion Batteries>

[0091] 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 positive electrode material layer and the first negative electrode material layer are positioned away from the center of the pre-wound electrode assembly; the first segment of the first positive electrode material layer and the first segment of the first negative electrode material layer are located close to the center of the pre-wound electrode assembly. Afterwards, the process involves winding, flattening, current collector welding, casing, bottom penetration welding, inkjet coding, vacuum drying, electrolyte injection, sealing, and high-temperature settling followed by formation testing to obtain the lithium-ion battery. The upper limit of the formation voltage is 3.6V, the formation temperature is 45℃, and after formation, the battery is left to stand at room temperature (25℃) for 24 hours.

[0092] Comparative Example 1

[0093] Except that no protrusions are provided on the surface of the first material layer, the rest is the same as in Example 1.

[0094] Comparative Example 2

[0095] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0096] Comparative Example 3

[0097] Except that the length of the first segment on the first material layer is 100%, that is, only the H1 height protrusion is provided on the first material layer, the rest is the same as in Example 1.

[0098] Comparative Example 4

[0099] Except that the length of the second segment on the first material layer is 100%, that is, the H2 height protrusion is only provided on the first material layer, the rest is the same as in Example 1.

[0100] Comparative Example 5

[0101] Except that the length of the third segment on the first material layer is 100%, that is, the H3 height protrusion is only set on the first material layer, the rest is the same as in Example 1.

[0102] Comparative Example 6

[0103] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0104] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0105] Table 1

[0106]

[0107]

[0108] Note: " / " in Table 1 indicates that there are no relevant preparation parameters.

[0109] As can be seen from Examples 1 to 31 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 by setting protrusions on the first, second, and third segments, and making H1 < H2 < H3, the electrode indentation distance is shorter, and the 600cls capacity retention rate of the lithium-ion battery is improved. This indicates that the lithium-ion battery of this application can effectively improve the degree of inner electrode indentation caused by electrode expansion in the later stage of cycling, reduce the risk of lithium plating in the lithium-ion battery, and the lithium-ion battery has good cycle performance. In Comparative Example 1, no protrusions are provided on the first material layer; in Comparative Example 2, the length ratios of the first, second, and third segments are all outside the scope of this application; in Comparative Example 3, the average height of all protrusions on the first material layer is consistent with the average height of the protrusions on the first segment in Example 1; in Comparative Example 4, the average height of all protrusions on the first material layer is consistent with the average height of the protrusions on the second segment in Example 1; in Comparative Example 5, the average height of all protrusions on the first material layer is consistent with the average height of the protrusions on the third segment in Example 1; in Comparative Example 6, H1 > H2 > H3; the electrode indentation distance of the lithium-ion batteries in Comparative Examples 1 to 6 is longer; and / or, the 600cls capacity retention rate is lower. In contrast, the electrode indentation distance of the lithium-ion batteries in Examples 1 to 31 is shorter, and the 600cls capacity retention rate is higher, indicating that the degree of indentation of the inner electrode of the electrode assembly is less severe in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0110] The values ​​of H0 and H2 / H0×100% typically affect the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 7 to 13, when the values ​​of H0 and H2 / H0×100% are within the range of this application, the electrode indentation distance in the lithium-ion battery is shorter, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode assembly is less severe in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery exhibits good cycle performance.

[0111] The ratio between H1, H2, and H3, as well as the values ​​of a and b, typically affect the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 14 to 19, when aH3≤H2≤bH1, and a and b are within the range of this application, the electrode indentation distance in the lithium-ion battery is shorter, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode assembly is less severe in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery exhibits good cycle performance.

[0112] The value of A typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 20 to 24, when the value of A is within the range of this application, the electrode indentation distance in the lithium-ion battery is shorter and the 600cls capacity retention rate is higher, indicating that the degree of indentation of the inner electrode of the electrode assembly is less in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0113] The value of D typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 25 to 30, when the value of D is within the range of this application, the electrode indentation distance in the lithium-ion battery is shorter, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode assembly is less severe in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery exhibits good cycle performance.

[0114] The type of electrode used (positive or negative) typically affects the cycle performance of lithium-ion batteries. As seen in Examples 1 and 31, when the electrode is a positive or negative electrode, the electrode indentation distance in the lithium-ion battery is shorter, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode rings in the electrode assembly is less severe in the later stages of cycling, resulting in a lower risk of lithium plating and good cycle performance.

[0115] The presence of a first recess and / or a second recess typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1 to 31, when the first recess and / or the second recess are present, the electrode indentation distance in the lithium-ion battery is shorter, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode assembly is less severe in the later stages of cycling, resulting in a lower risk of lithium plating and good cycle performance.

[0116] 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.

[0117] 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.

[0118] 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 an electrode sheet, the electrode sheet comprising a current collector and a first material layer, the first material layer being located on the surface of the current collector opposite to the winding center of the electrode assembly; Along the length direction of the unfolded electrode sheet and along the winding direction of the electrode assembly, the first material layer includes a first segment, a second segment, and a third segment connected in sequence. Based on the length of the first material layer, the length ratio of the first segment is L1, the length ratio of the second segment is L2, and the length ratio of the third segment is L3, where 10%≤L1≤30%, 20%≤L2≤40%, and 40%≤L3≤60%. The first segment, the second segment, and the third segment are each provided with a plurality of protrusions. Along the thickness direction of the electrode sheet, the average height of the plurality of protrusions in the first segment is H1 μm, the average height of the plurality of protrusions in the second segment is H2 μm, and the average height of the plurality of protrusions in the third segment is H3 μm, where H1 < H2 < H3.

2. The cylindrical secondary battery according to claim 1, wherein, Along the thickness direction of the electrode, the sum of the thicknesses of the first material layer and the current collector is H0 μm, 30≤H0≤60, and 8%≤H2 / H0×100%≤60%.

3. The cylindrical secondary battery according to claim 2, wherein, 15% ≤ H2 / H0 × 100% ≤ 45%.

4. The cylindrical secondary battery according to claim 2, wherein, aH3≤H2≤bH1, 0.5≤a≤0.8, 1.1≤b≤1.

6.

5. The cylindrical secondary battery according to any one of claims 1 to 4, wherein, Along the length of the unfolded electrode, the distance between two adjacent protrusions is A mm, where 1 ≤ 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 thickness direction of the electrode sheet, the diameter of the largest circumcircle of the outer contour of the projection of a single protrusion is D mm, where 0.5 ≤ D ≤ 10.

8. The cylindrical secondary battery according to claim 7, wherein, 2≤D≤6。 9. The cylindrical secondary battery according to any one of claims 1 to 8, wherein, The electrode further includes a second material layer, which is located on the surface of the current collector facing the winding center of the electrode assembly. The surface of the second material layer is provided with a plurality of first recesses in the direction of the first material layer.

10. The cylindrical secondary battery according to claim 9, wherein, The current collector has multiple second recesses in the direction of the first material layer.

11. The cylindrical secondary battery according to claim 10, wherein, At least a portion of the first recess corresponds to a portion of the protrusion; and / or, at least a portion of the second recess corresponds to a portion of the protrusion.

12. The cylindrical secondary battery according to claim 11, wherein, The electrode is a positive electrode.

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

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