Cylindrical secondary battery and electronic device

Abstract

The present application provides a cylindrical secondary battery and an electronic device. The cylindrical secondary battery comprises an electrode assembly, the electrode assembly comprises electrode sheets, and each electrode sheet comprises a first current collector and a first material layer located on a surface of the first current collector. Starting from the tail end of the electrode sheet, in the length direction of the unfolded electrode sheet, the first material layer comprises a first section and a second section which are connected in sequence. On the basis of the length of the first material layer, the length proportion of the first section is K, wherein 1%≤K≤10%, and the surface of the first section is provided with a plurality of protrusions. By means of the described arrangement, the safety performance and cycle performance of the cylindrical secondary battery are improved while actual production requirements are taken into account.

Description

A cylindrical secondary battery and electronic device

[0001] This application claims priority to Chinese Patent Application No. 202411983560.3, filed with the State Intellectual Property Office of China on December 30, 2024, entitled "A Cylindrical Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a cylindrical secondary battery and electronic device. Background Technology

[0003] Cylindrical secondary batteries, such as cylindrical lithium-ion batteries, are used in a variety of fields. 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.

[0004] However, in the later stages of lithium-ion battery cycling, the electrode expands, resulting in excessive tensile stress on the electrode, especially the outer ring. The current collector stretches and extends, making the electrode prone to breakage, which reduces the safety and cycle performance of the secondary battery. Summary of the Invention

[0005] The purpose of this application is to provide a cylindrical secondary battery and electronic device that helps to reduce the tensile stress generated by electrode expansion during cycling, thereby improving the safety and cycle performance of the cylindrical secondary battery.

[0006] 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:

[0007] The first aspect of this application provides a cylindrical secondary battery, which includes an electrode assembly, an electrode sheet, a first current collector, and a first material layer on one surface of the first current collector. Starting from the tail end of the electrode sheet, along the length direction of the unfolded electrode sheet, the first material layer includes a first segment and a second segment connected in sequence. Based on the length of the first material layer, the length percentage of the first segment is K, where 1% ≤ K ≤ 10%, optionally 4% ≤ K ≤ 10%. Multiple protrusions are provided on the surface of the first segment. By providing protrusions on the first segment and adjusting the length percentage of the first segment within the aforementioned range, the protrusions at the tail end of the electrode sheet provide expansion space on the outer ring of the electrode assembly. This reduces the tensile stress generated by the expansion of the electrode sheet during the secondary battery cycle, which helps to reduce the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, leading to breakage of the electrode sheet, especially the current collector such as aluminum foil, and the generation of burrs. Simultaneously, it improves the wetting effect of the electrolyte on the electrode sheet, thus improving the safety and cycle performance of the cylindrical secondary battery while meeting actual production requirements.

[0008] In one or more embodiments, along the length direction of the unfolded electrode sheet and away from the terminal end of the electrode sheet, the second segment includes a first region, a second region, and a third region connected in sequence. Based on the length of the first material layer, the length ratio of the first region is K1, and the length ratio of the second region is K2, where 10% ≤ K1 ≤ 40% and 20% ≤ K2 ≤ 60%, optionally, 30% ≤ K2 ≤ 50%. Multiple protrusions are provided only on the surface of the second region in the second segment. By providing protrusions on the second region of the first and second segments, the intermittent provision of protrusions allows for expansion space in the outer and inner rings of the electrode assembly. This helps to further reduce the tensile stress and compressive force generated by the electrode sheet expansion during the secondary battery cycle, reducing the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, leading to breakage of the electrode sheet, especially the current collector such as aluminum foil, and the generation of burrs. This further improves the safety and cycle performance of the cylindrical secondary battery.

[0009] In one or more embodiments, the average height of the plurality of protrusions is H μm, 10 ≤ H ≤ 160, and optionally, 35 ≤ H ≤ 110. By adjusting the average height H of the plurality of protrusions within the above range, the outer ring of the electrode assembly has expansion space, which helps to reduce the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, resulting in breakage of the electrode sheet, especially the current collector such as aluminum foil, and the generation of burrs. This improves the safety performance and cycle performance of the cylindrical secondary battery.

[0010] In one or more embodiments, the thickness of the first current collector is T μm, where 8 ≤ T ≤ 16. By adjusting the thickness T of the first current collector within the above range, it is beneficial to enhance the mechanical strength of the first current collector, thereby enhancing the mechanical strength of the first electrode and improving the safety performance of the cylindrical secondary battery.

[0011] In one or more embodiments, multiple protrusions are distributed in a dotted pattern on the first material layer. Along the thickness direction of the first electrode, the projection shape of a single protrusion on the first material layer is circular, elliptical, or polygonal. The diameter of the largest circumscribed circle of the projection is D1 mm, where 3 ≤ D1 ≤ 7. By adjusting the diameter D1 of the largest circumscribed circle of the projection to be within the above range, it is beneficial to reduce the risk of protrusion collapse during fabrication or cycling, which would reduce the reserved expansion space, thereby improving the safety and cycle performance of the secondary battery.

[0012] In one or more embodiments, along the length of the unfolded electrode, the distance between two adjacent protrusions is A1 mm, where 5 ≤ A1 ≤ 15. By adjusting the distance A1 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 reducing the energy density of the secondary battery, thereby improving the safety and cycle performance of the secondary battery.

[0013] In one or more embodiments, along the thickness direction of the electrode, the projection shape of a single protrusion on the first material layer is strip-shaped, and multiple protrusions extend along the width direction of the unfolded electrode and are spaced apart along the length direction of the unfolded electrode. The width of the projection along the length direction of the unfolded electrode is D2 mm, where 5 ≤ D2 ≤ 10. By adjusting the projection width D2 within the above range, it is beneficial to reduce the risk of protrusion collapse during fabrication or cycling, which could lead to a reduction in the reserved expansion space, thereby improving the safety and cycle performance of the secondary battery.

[0014] In one or more embodiments, along the length of the unfolded electrode, the distance between two adjacent protrusions is A2 mm, where 5 ≤ A2 ≤ 15. By adjusting the distance A2 between two adjacent protrusions within the above range, it is beneficial to reduce the processing difficulty of the first electrode during processing, reduce the risk of excessive powder shedding during the processing of the first electrode leading to loss of active material and thus reducing the energy density of the secondary battery, thereby improving the safety performance and cycle performance of the secondary battery.

[0015] In one or more embodiments, along the width direction after the electrode is unfolded, the first material layer has a first edge and a second edge, and the shortest distance between a single protrusion and the first edge or the second edge is L1 mm, where 5 ≤ L1 ≤ 15. By controlling the shortest distance L1 between a single protrusion and the first edge or the second edge within the above range, it is beneficial to reduce the risk of loss of active material due to excessive powder shedding from the first material layer during electrode processing, reduce the safety risks of actual production process operations, and thus improve the safety performance and cycle performance of the secondary battery.

[0016] In one or more embodiments, along the length direction after the electrode is unfolded, the end of the first material layer includes a first end face, and the shortest distance between a single protrusion in the first segment and the first end face is L2 mm, where 5 ≤ L2 ≤ 15. By controlling the shortest distance L2 between a single protrusion in the first segment and the first end face within the above range, it is beneficial to reduce the risk of loss of active material due to excessive powder shedding from the first material layer during electrode processing, reduce the safety risks of actual production process operations, and thus improve the safety performance and cycle performance of the secondary battery.

[0017] In one or more embodiments, the first material layer is located on the surface of the first current collector away from the center of the electrode assembly winding.

[0018] In one or more embodiments, the electrode further includes a second material layer located on the surface of the first current collector toward the center of the electrode assembly, and the surface of the second material layer is provided with a plurality of first recesses toward the direction of the first material layer.

[0019] In one or more embodiments, the first current collector has a plurality of second recesses in the direction of the first material layer.

[0020] 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 second recesses on the electrode, further reducing the tensile stress generated by electrode expansion during secondary battery cycling. This reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, leading to breakage of the electrode, especially the current collector such as aluminum foil, and the generation of burrs. This improves the safety and cycle performance of the secondary battery while meeting mass production manufacturability requirements.

[0021] In one or more embodiments, the electrode is a positive electrode.

[0022] In one or more embodiments, the electrode assembly further includes another electrode with the opposite polarity to the electrode, the other electrode including a second current collector and a third material layer located on at least one surface of the second current collector, the third material layer including silicon.

[0023] A second aspect of this application provides an electronic device comprising the cylindrical secondary battery of any of the foregoing embodiments. The cylindrical secondary battery of this application has good safety and cycle performance; therefore, the electronic device of this application has a long service life.

[0024] The beneficial effects of the embodiments of this application are as follows:

[0025] This application embodiment designs a protrusion at the tail of the electrode to reserve expansion space for the electrode, which effectively reduces the tensile stress generated by the expansion of the electrode during the secondary battery cycle. This helps to reduce the safety risk of short circuit caused by excessive tensile stress leading to breakage of the electrode, especially the current collector such as aluminum foil, and the generation of burrs. In addition, it improves the wetting effect of the electrolyte on the electrode, thereby improving the safety performance and cycle performance of the cylindrical secondary battery while taking into account the actual production requirements.

[0026] 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

[0027] 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.

[0028] Figure 1 is a computed tomography (CT) scan of the outer electrode of a cylindrical lithium-ion battery in the late stage of cycling in the prior art.

[0029] Figure 2 is a schematic diagram of the winding structure formed by the electrode assembly in one embodiment of this application;

[0030] Figure 3 is a schematic diagram of the winding structure formed by the electrode assembly in another embodiment of this application;

[0031] Figure 4 is a partial front view of the positive electrode sheet after the electrode assembly is unfolded in another embodiment of this application;

[0032] Figure 5 is a partial front view of the positive electrode sheet after the electrode assembly is unfolded in another embodiment of this application;

[0033] Figure 6 is a cross-sectional view of the positive electrode sheet in Figure 5 along the PP direction;

[0034] Figure 7 is a partial front view of the positive electrode sheet after the electrode assembly is unfolded in another embodiment of this application.

[0035] Reference numerals: Electrode assembly 001; Positive electrode 10; First current collector 11; First material layer 12; Second material layer 13; Negative electrode 20; Second current collector 21; Third material layer 22; Separator 30; Protrusion 121; First recess 131; Second recess 111; First edge 1201; Second edge 1202; First end face 1203. Detailed Implementation

[0036] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and 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.

[0037] 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.

[0038] In existing cylindrical secondary batteries, such as cylindrical lithium-ion batteries, the electrodes expand during the later stages of cycling. This expansion and contraction is particularly pronounced when the negative electrode material layer contains silicon. For example, as shown in Figure 1, excessive tensile stress on the outer ring of the electrode assembly causes the electrodes to be compressed and stretched, which can easily lead to electrode breakage, especially of the current collector (e.g., aluminum foil), and burrs during the later stages of cycling. This can also cause short circuits during charging and discharging, reducing the safety performance and cycle life of the cylindrical lithium-ion battery. Therefore, this application provides a cylindrical secondary battery and electronic device that helps reduce the safety risk of electrode breakage, especially of the current collector, due to excessive tensile stress, thereby improving the safety and cycle life of the cylindrical secondary battery.

[0039] A first aspect of this application provides a cylindrical secondary battery, the cylindrical secondary battery including an electrode assembly, the electrode assembly including an electrode sheet, the electrode sheet including a first current collector and a first material layer located on one surface of the first current collector. Starting from the end of the electrode sheet, along the length direction after the electrode sheet is unfolded, the first material layer includes a first segment and a second segment connected in sequence. Based on the length of the first material layer, the length ratio of the first segment is K, where 1% ≤ K ≤ 10%, or optionally, 4% ≤ K ≤ 10%. For example, the value of K can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10%, or a range of any two of these values. The surface of the first segment has multiple protrusions.

[0040] In this application, the electrode can be a positive electrode and / or a negative electrode. The electrode assembly, in its unfolded state, is defined with its length direction as the X direction, its width direction as the Y direction, and its thickness direction as the Z direction. It is 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. For example, the electrode is a positive electrode. As shown in FIG2, the electrode assembly 001 includes a positive electrode 10, a negative electrode 20, and a separator 30. The starting end of the positive electrode 10 is close to the central hole of the electrode assembly 001, and the ending end of the positive electrode 10 is away from the central hole of the electrode assembly 001. The positive electrode 10 includes a first current collector 11 and a first material layer 12. The ending end of the first material layer 12 includes a first end face 1203. From the first end face 1203, along the unfolded length direction of the positive electrode 10, the first material layer 12 includes a first segment and a second segment connected in sequence. The positive electrode 10 has a plurality of protrusions 121 on the surface of the first segment. For example, as shown in FIG2, the first segment is M to M' and the second segment is M' to N in the opposite direction to the winding direction W of the electrode assembly 001.

[0041] When the length ratio K of the first segment is too small, for example, below the lower limit of this application, the area of ​​the protrusions on the electrode is too small, resulting in a small reserved expansion space. This makes it impossible to effectively release the tensile stress caused by the expansion of the electrode during cycling. In the later stages of cycling, the outer electrode of the electrode assembly is overstretched, increasing the risk of electrode breakage and burr formation, especially in the current collector such as aluminum foil. This also makes short circuits more likely during charging and discharging, thus reducing the safety and cycle performance of the secondary battery. When the length ratio K of the first segment is too large, for example, above the upper limit of this application, the area of ​​the protrusions on the electrode is too large, resulting in a large reserved expansion space. This makes electrolyte bridging more likely to occur between the layers of some electrodes, leading to an increase in electrochemical impedance during cycling and a decrease in the cycle performance of the secondary battery. Furthermore, the diameter of the electrode assembly is too large at this time, resulting in a lower electrode assembly casing yield in actual production, a lower lithium-ion battery production qualification rate, which does not meet actual production requirements, increases production costs, reduces capacity, and results in a low cost-performance ratio.

[0042] This application, by setting a protrusion on the first segment and adjusting the length ratio of the first segment within the aforementioned range, and setting a protrusion at the tail of the electrode sheet, provides expansion space for the outer ring of the electrode assembly. This reduces the tensile stress generated by the expansion of the electrode sheet during the secondary battery cycle, which helps to reduce the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, leading to breakage of the electrode sheet, especially the current collector such as aluminum foil, and the formation of burrs. Simultaneously, it helps to improve the wetting speed of the electrolyte on the electrode sheet, thereby improving the safety and cycle performance of the cylindrical secondary battery. Furthermore, the above-mentioned design ensures that the average diameter of the electrode assembly is within a suitable range, reducing actual production costs and increasing production capacity. While meeting practical production requirements, the lithium-ion battery exhibits good safety and cycle performance.

[0043] In one or more embodiments, the length ratio K' of the second segment is 90% to 99% based on the length of the first material layer. For example, the value of K' can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or a range of any two of these values. By adjusting the length ratio of the second segment within the above range, the average diameter of the electrode assembly is kept within a suitable range. This helps to reduce the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which could lead to breakage of the electrode sheet, especially the current collector such as aluminum foil, resulting in burrs. In other words, while ensuring good safety and cycle performance of the cylindrical secondary battery, the production cost and capacity of the secondary battery are also taken into account.

[0044] In one or more embodiments, along the length direction of the unfolded electrode and in the direction away from the terminal end of the electrode, the second segment includes a first region, a second region, and a third region connected in sequence; based on the length of the first material layer, the length percentage of the first region is K1, the length percentage of the second region is K2, 10%≤K1≤40%; 20%≤K2≤60%, optionally, 30%≤K2≤50%. For example, the value of K1 can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40% or a range of any two of these values, and the value of K2 can be 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. In the second segment, only the surface of the second region has multiple protrusions. For example, the electrode is a positive electrode. As shown in Figures 3 and 4, the end of the first material layer 12 on the positive electrode 10 includes a first end face 1203. Along the length direction (X direction) of the unfolded positive electrode 10, and in a direction away from the first end face 1203, the second segment includes a first region, a second region, and a third region connected in sequence. In the second segment, only the surface of the second region has multiple protrusions 121. As shown in Figure 3, along the opposite direction of the winding direction W of the electrode assembly 001, the first region of the second segment is M' to M'", the second region of the second segment is M'" to N', and the third region of the second segment is N' to N. By setting protrusions in the second region of the first and second sections, the intermittent setting of protrusions allows for expansion space in both the outer and inner rings of the electrode assembly. This keeps the average diameter of the electrode assembly within a suitable range, which helps to further reduce the tensile and compressive stresses generated by electrode expansion during the secondary battery cycle. It also reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which could lead to breakage of the electrode, especially the current collector such as aluminum foil, and the formation of burrs. At the same time, it helps to reduce the safety risk of lithium plating in the secondary battery due to indentation of the inner ring of the electrode assembly caused by excessive compressive stress. In addition, it improves the wetting effect of the electrolyte on the electrode, further enhancing the safety and cycle performance of the cylindrical secondary battery while taking into account actual production requirements.

[0045] In one or more embodiments, the length percentage of the third region is K3, based on the length of the first material layer, where 0% ≤ K3 ≤ 69%. For example, the value of K3 can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 67%, 69%, or a range of any two of these values. By adjusting the length percentage of the third region within the above range, the average diameter of the electrode assembly is kept within a suitable range. This helps to reduce the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which could lead to breakage of the electrode sheet, especially the current collector such as aluminum foil, resulting in burrs. In other words, while ensuring good safety and cycle performance of the cylindrical secondary battery, the production cost and capacity of the secondary battery are also considered.

[0046] In one or more embodiments, the average height of the plurality of protrusions is H μm, as shown in FIG6, where the average height of the plurality of protrusions 121 is H μm. 10 ≤ H ≤ 160, and optionally, 35 ≤ H ≤ 110. For example, the value of H can be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, or a range of any two of these values. By adjusting the average height H of multiple protrusions within the aforementioned range, the outer ring of the electrode assembly has expansion space, and the average diameter of the electrode assembly is within a suitable range. This helps to reduce the tensile stress generated by the expansion of the electrode sheets during the secondary battery cycle. It also reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which can lead to breakage of the electrode sheets, especially the current collector such as aluminum foil, and the generation of burrs. At the same time, the reserved space is moderate, allowing for tight adhesion between the positive and negative electrode sheets and between electrode layers during charging and discharging. This results in a lower electrochemical impedance of the secondary battery during charging and discharging. In addition, it improves the wetting effect of the electrolyte on the electrode sheets, balancing the production cost and capacity of the secondary battery while improving the safety and cycle performance of the cylindrical secondary battery.

[0047] In one or more embodiments, the thickness of the first current collector is T μm, as shown in Figure 6, where the thickness of the first current collector 11 is T μm. 8 ≤ T ≤ 16. For example, the value of T can be 8, 9, 10, 11, 12, 13, 14, 15, 16, or a range of any two of these values. By adjusting the thickness T of the first current collector within the above range, it is beneficial to enhance the mechanical strength of the first current collector, thereby enhancing the mechanical strength of the electrode sheet. This further reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to electrode sheet expansion during cycling, which could lead to breakage or burr formation in the electrode sheet, especially the current collector (e.g., aluminum foil). This improves the safety performance of the cylindrical secondary battery. Furthermore, for the same battery specifications, this results in a suitable gap between the positive and negative electrodes, balancing the energy density of the secondary battery. This application does not impose any particular restrictions on the method of adjusting the thickness of the first current collector, as long as the purpose of this application can be achieved. For example, commercially available current collectors with different thicknesses can be selected, and the thickness of the first current collector can be determined by combining the test method of "testing H, T, A1, A2, D1, D2, L1, L2" in this application, and then the first current collector with the required thickness can be selected.

[0048] In one or more embodiments, multiple protrusions are distributed in a dotted pattern on the first material layer. Along the thickness direction of the electrode sheet, the projection shape of a single protrusion on the first material layer is circular, elliptical, or polygonal, and the diameter of the largest circumscribed circle of the projection is D1 mm. For example, as shown in FIG5, multiple protrusions 121 are distributed in a dotted pattern on the first material layer 12. Along the thickness direction (Z direction) of the positive electrode sheet 10, the projection shape of a single protrusion 121 on the first material layer 12 is circular, and the diameter of the largest circumscribed circle of the projection is D1 mm. 3 ≤ D1 ≤ 7. For example, the value of D1 can be 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or a range consisting of any two of these values. By adjusting the diameter D1 of the maximum circumcircle of the projected outer contour 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 that the reserved space is moderate, which helps to reduce the tensile stress generated by electrode expansion during secondary battery cycling. It also reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which can lead to breakage of the electrode, especially the current collector such as aluminum foil, and the generation of burrs. In addition, the moderate size of the pits on the electrode surface reduces the risk of increased electrochemical impedance due to localized electrolyte aggregation and side reactions. This approach balances the production cost and capacity of secondary batteries while improving their safety and cycle performance.

[0049] In one or more embodiments, the distance between two adjacent protrusions along the length direction of the unfolded electrode sheet is A1 mm. For example, as shown in FIG5, the distance between two adjacent protrusions 121 along the length direction (X direction) of the unfolded positive electrode sheet 10 is A1 mm. 5 ≤ A1 ≤ 15. For example, the value of A1 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range of any two values ​​therein. By adjusting the distance A1 between two adjacent protrusions within the above range, it is beneficial to reduce the processing difficulty of the electrode sheet during processing, reduce the risk of excessive powder shedding during electrode sheet processing leading to loss of active materials and thus reduced energy density of the secondary battery, make the electrode sheet pore distribution uniform, facilitate the flow of electrolyte on the electrode sheet, and improve the wetting effect of electrolyte on the electrode sheet. This reduces the tensile stress generated by electrode expansion during secondary battery cycling, thereby lowering the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which can lead to breakage of the electrode, especially the current collector such as aluminum foil, and the formation of burrs. 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 of the secondary battery during charging and discharging. This approach balances production cost and capacity while improving the safety and cycle performance of the secondary battery. In this application, the distance between two adjacent protrusions refers to the distance between the centers of the largest circumcircle of the projection of the outer contours of two adjacent protrusions onto the first material layer along the thickness direction of the electrode after the first electrode has been unfolded.

[0050] In one or more embodiments, along the thickness direction of the electrode sheet, the projection shape of a single protrusion on the first material layer is a strip, and multiple protrusions extend along the width direction of the unfolded electrode sheet and are spaced apart along the length direction of the unfolded electrode sheet. The projection width along the length direction of the unfolded electrode sheet is D2mm. For example, as shown in FIG7, along the thickness direction (Z direction) of the positive electrode sheet 10, the projection shape of a single protrusion 121 on the first material layer 12 is a strip, and multiple protrusions 121 extend along the width direction (Y direction) of the unfolded positive electrode sheet 10 and are spaced apart along the length direction (X direction) of the unfolded positive electrode sheet 10. The projection width along the length direction (X direction) of the unfolded positive electrode sheet 10 is D2mm. 5≤D2≤10. For example, the value of D2 can be 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range consisting of any two of these values. By adjusting the projection width D2 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 that the reserved space is moderate, which helps to reduce the tensile stress generated by electrode expansion during secondary battery cycling. It also reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which can lead to breakage of the electrode, especially the current collector such as aluminum foil, and the generation of burrs. In addition, the moderate size of the pits on the electrode surface reduces the risk of increased electrochemical impedance due to localized electrolyte aggregation and side reactions. This approach balances the production cost and capacity of secondary batteries while improving their safety and cycle performance.

[0051] In one or more embodiments, the distance between two adjacent protrusions along the length direction of the unfolded electrode sheet is A2 mm. For example, as shown in FIG7, the distance between two adjacent protrusions 121 along the length direction (X direction) of the unfolded positive electrode sheet 10 is A2 mm. 5 ≤ A2 ≤ 15. For example, the value of A2 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range of any two of these values. By adjusting the distance A2 between two adjacent protrusions within the above range, it is beneficial to reduce the processing difficulty of the electrode sheet during processing, reduce the risk of excessive powder shedding during electrode sheet processing leading to loss of active materials and thus reduced energy density of the secondary battery, make the electrode sheet pore distribution uniform, facilitate the flow of electrolyte on the electrode sheet, and improve the wetting effect of electrolyte on the electrode sheet. This reduces the tensile stress caused by electrode expansion during secondary battery cycling, thereby lowering the safety risk of short circuits due to excessive stretching of the outer ring of the electrode assembly caused by excessive tensile stress, which can lead to breakage of the electrode, especially the current collector such as aluminum foil, and the formation of burrs. 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 of the secondary battery during charging and discharging. This approach balances production cost and capacity while improving the safety and cycle performance of the secondary battery. In this application, the distance between two adjacent protrusions refers to the distance between the centers of the widths of two adjacent strip protrusions along the length direction after the electrode is unfolded.

[0052] In one or more embodiments, along the width direction of the unfolded electrode sheet, the first material layer has opposing first and second edges, and the shortest distance between a single protrusion and the first or second edge is L1 mm. For example, as shown in FIG5, along the width direction (Y direction) of the unfolded positive electrode sheet 10, the first material layer 12 has opposing first edges 1201 and second edges 1202, and the shortest distance between a single protrusion 121 and the first edge 1201 is L1 mm. As shown in FIG7, along the width direction (Y direction) of the unfolded positive electrode sheet 10, the first material layer 12 has opposing first edges 1201 and second edges 1202, and the shortest distance between a single protrusion 121 and the second edge is L1 mm. 5 ≤ L1 ≤ 15. For example, the value of L1 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of these values. By adjusting the shortest distance L1 between a single protrusion and the first or second edge within the aforementioned range, it is beneficial to reduce the risk of excessive powder shedding from the first material layer during electrode processing, which could lead to loss of active material. It also reduces the risk of the protrusion being too close to the first or second edge, causing the slit edge to change from a straight line to a curve, resulting in the positive and negative electrode sheet exceeding specifications and thus being unable to be produced. Furthermore, it reduces the tensile stress generated by electrode sheet expansion during secondary battery cycling, thereby reducing the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, leading to breakage of the electrode sheet, especially the current collector such as aluminum foil, and the generation of burrs. Simultaneously, with appropriate reserved space, the positive and negative electrode sheets and electrode layers can be tightly bonded during charging and discharging, resulting in lower electrochemical impedance of the secondary battery during charging and discharging. This approach improves the safety and cycle performance of the secondary battery while meeting actual production requirements.

[0053] In one or more embodiments, along the length direction of the unfolded electrode sheet, the end of the first material layer includes a first end face, and the shortest distance between a single protrusion in the first segment and the first end face is L2mm. For example, as shown in Figures 5 and 7, along the length direction (X direction) of the unfolded positive electrode sheet 10, the end of the first material layer 12 includes a first end face 1203, and the shortest distance between a single protrusion 121 in the first segment and the first end face 1203 is L2mm. 5 ≤ L2 ≤ 15. For example, the value of L2 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of these values. By adjusting the shortest distance L2 between a single protrusion in the first segment and the first end face within the aforementioned range, it is beneficial to reduce the risk of excessive powder shedding from the first material layer during electrode processing, which could lead to loss of active material. It also reduces the safety risk that the edge deformation of the first material layer caused by the protrusion being too close to the first end face could affect the range test of the positive and negative electrode sheets, thus preventing production. Furthermore, it reduces the tensile stress generated by electrode sheet expansion during secondary battery cycling, thereby reducing the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which could lead to breakage of the electrode sheets, especially the current collector such as aluminum foil, and the generation of burrs. At the same time, with a moderate reserved space, the positive and negative electrode sheets and the electrode layers can be tightly bonded during charging and discharging. The electrochemical impedance of the secondary battery is relatively low during charging and discharging. While taking into account actual production requirements, it improves the safety performance and cycle performance of the secondary battery.

[0054] In one or more embodiments, the first material layer is located on the surface of the first current collector away from the winding center of the electrode assembly. As shown in Figures 2 and 3, the first material layer 12 is located on the surface of the first current collector 11 away from the winding center of the electrode assembly 001. This arrangement reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, leading to breakage of the electrode sheet, especially the current collector (e.g., aluminum foil), resulting in burrs. It also balances the energy density and processing performance of the secondary battery. 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 surface of the current collector or only a portion thereof. This application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0055] In one or more embodiments, the electrode further includes a second material layer located on the surface of the first 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. Exemplarily, as shown in Figures 2 and 3, the positive electrode 10 further includes a second material layer 13 located on the surface of the first current collector 11 facing the winding center of the electrode assembly 001. The surface of the second material layer 13 has a plurality of first recesses 131 facing the first material layer 12. This configuration improves the operability of providing protrusions and first recesses on the electrode, enhances the wetting performance of the electrolyte on the electrode, and further reduces the tensile stress generated by electrode expansion during secondary battery cycling. This reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, leading to breakage of the electrode, especially the current collector such as aluminum foil, and the generation of burrs. This improves the safety and cycle performance of the secondary battery while meeting mass production manufacturability requirements. It should be noted that the "surface" of the second material layer on the surface of the current collector facing the center of the electrode assembly can be the entire surface of the current collector or a part of the surface of the current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0056] In one or more embodiments, the first current collector has a plurality of second recesses in the direction toward the first material layer. For example, as shown in Figures 2 and 3, the first current collector 11 has a plurality of second recesses 111 in the direction toward the first material layer 12. This configuration improves the operability of providing protrusions and second recesses on the electrode, further reducing the tensile stress generated by electrode expansion during secondary battery cycling. This reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, leading to breakage of the electrode, especially the current collector such as aluminum foil, and the generation of burrs. This improves the safety and cycle performance of the secondary battery while meeting mass production manufacturability requirements.

[0057] 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. As shown in FIG6, a portion of the first recess 131 corresponds to a portion of the protrusion 121, and a portion of the second recess 111 corresponds to a portion of the protrusion 121. Through the above arrangement, the operability of setting protrusions, first recesses, and / or second recesses on the electrode sheet is improved, and the tensile stress generated by the expansion of the electrode sheet during the cycle of the secondary battery is further reduced. This reduces the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which may lead to breakage of the electrode sheet, especially the current collector such as aluminum foil, and the generation of burrs. While meeting the manufacturability requirements for mass production, the safety performance and cycle performance of the secondary battery are improved.

[0058] 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 loss of active materials due to excessive powder shedding during electrode processing, and thus reduces the energy density of the secondary battery. It also further reduces the tensile stress generated by the expansion of the electrode during the cycle of the secondary battery, thereby reducing the safety risk of short circuits caused by excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which may lead to breakage of the electrode, especially the current collector such as aluminum foil, and the generation of burrs. At the same time, the reserved expansion space is moderate, and the distance between the positive and negative electrodes and between electrode layers is within a suitable range during charging and discharging. As a result, the electrochemical impedance of the secondary battery is relatively small, thereby further improving the safety performance and cycle performance of the secondary battery.

[0059] In one or more embodiments, the electrode assembly further includes another electrode with the opposite polarity to the positive electrode 10. This other electrode includes a second current collector and a third material layer located on at least one surface of the second current collector. The third material layer includes silicon. Exemplarily, as shown in Figures 2 and 3, the electrode assembly 001 also includes a negative electrode 20 with the opposite polarity to the positive electrode 10. The negative electrode 20 includes a second current collector 21 and a third material layer 22 located on both surfaces of the second current collector 21. When the third material layer contains silicon, the degree of expansion and contraction of the electrode during cycling is more pronounced. In this case, providing a protrusion at the tail end of the electrode significantly reduces the safety risk of short circuits caused by excessive tensile stress leading to overstretching of the outer ring of the electrode assembly, especially the current collector (e.g., aluminum foil), resulting in breakage and burrs. This is beneficial for further improving the safety and cycle performance of the cylindrical secondary battery. When the third material layer contains silicon, it includes an active material, which includes a silicon-containing substance, including at least one of silicon, silicon-carbon materials, or silicon-oxygen materials.

[0060] In this application, when the electrode is a positive electrode, the first current collector is a positive current collector. 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). At this time, both the first material layer and the second material layer are positive material layers. The positive material layer in this application includes a positive active material. This application does not impose any particular limitation on the type of positive active material, as long as it achieves the purpose of this application. For example, the positive active material may 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, the positive electrode material layer may also include a positive electrode binder and a conductive agent. This application does not particularly limit the type of positive electrode binder in the positive electrode material layer, as long as it can achieve the purpose of this application. 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.

[0061] In this application, when the electrode is a negative electrode, the first current collector is a negative current collector. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. For example, the negative current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (e.g., lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). In this case, 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. This application does not impose any particular limitation on the type of negative electrode active material, as long as it achieves the purpose of this application. For example, the negative electrode active material may 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. 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-mentioned 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-mentioned 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.

[0062] There is no particular limitation on the preparation method of the electrode in this application, as long as the object of this application can be achieved. For example, the preparation method of the electrode includes but is not limited to the following steps: (1) preparing a slurry; (2) coating the slurry on one surface of the first current collector and drying to form an electrode including the first material layer; (3) coating the slurry on the other surface of the first current collector and drying to obtain an electrode including the first material layer and the second material layer; (4) confirming the end of the electrode, starting from the end of the electrode, along the length direction after the electrode is unfolded, determining the first section and the second section of the first material layer, setting a protrusion on the surface of the first section, and cutting and slitting to obtain the electrode.

[0063] There is no particular limitation on the solid content of the above-mentioned 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-mentioned 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 a protrusion on the surface of the first section, a first recess is provided on the surface of the second material layer in the direction towards the first material layer. In one or more embodiments, in step (4), when respectively setting protrusions on the surface of the first section, a second recess is provided on the first current collector in the direction towards the first material layer. In one or more embodiments, in step (4), while determining the first section and the second section of the first material layer, along the length direction after the electrode is unfolded and in the direction away from the end of the electrode, confirming the first region, the second region and the third region of the second section, and while setting a protrusion on the surface of the first section, setting a protrusion on the surface of the second region.

[0064] 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 H of multiple protrusions can be controlled by the cold pressing pressure value set by the embossing roller or the height specification of the stainless steel needle on the embossing roller; the distance A1 or the distance A2 between two adjacent protrusions can be controlled by the distance between adjacent stainless steel needles on the embossing roller; the diameter D1 of the maximum circumscribed circle of the projection of a single protrusion on the first material layer or the projection width D2 of a single strip protrusion on the first material layer can be controlled by the specification of the stainless steel needle on the embossing roller; the shortest distance L1 between a single protrusion and the first edge or the second edge of the first material layer, and the shortest distance L2 between a single protrusion in the first segment and the first end face can be controlled by the position where the cold pressing of the embossing roller begins on the first material layer.

[0065] 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 configuration facilitates the placement of the tabs and the processing of the secondary battery, promotes high-rate charging and discharging of the secondary battery, reduces internal resistance and heat generation, and thereby improves the safety and cycle performance of the cylindrical secondary battery.

[0066] In this application, the different features of the protrusions included in the first electrode can be combined, and the implementation methods or embodiments covered by the above combinations are all within the protection scope of this application.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] A second aspect of this application provides an electronic device comprising the cylindrical secondary battery of any of the foregoing embodiments. The cylindrical secondary battery of this application has good safety and cycle performance; therefore, the electronic device of this application has a long service life.

[0073] 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.

[0074] Example

[0075] 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.

[0076] Test methods and equipment:

[0077] Tests for H, T, A1, A2, D1, D2, L1, and L2:

[0078] 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. Positive and negative electrode sheets were removed from the electrode assemblies and immersed 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. Electrodes with raised surfaces were identified as target electrodes by visual inspection.

[0079] The surface of the electrode was observed using a scanning electron microscope (SEM). Specifically, the plane formed by the length and width directions of the unfolded electrode was measured along the thickness direction of the electrode. Due to the height difference between the protrusion itself and the surface of the material layer, a relatively obvious color difference can be seen on the surface of the electrode. The protrusion has a projection aperture on the surface of the electrode, which can be used to distinguish the protrusion from the first material layer.

[0080] When the projection apertures are distributed in a dotted pattern on the first material layer, select any 5 apertures and measure the maximum circumcircle diameter of the outer contour of each aperture. Take the average value, which is the diameter D1 of the maximum circumcircle of the projection of a single protrusion. Along the length direction after the electrode is unfolded, select any 1 aperture and measure the distance between the center of the maximum circumcircle of the outer contour of the single aperture and the center of the maximum circumcircle of the outer contour of the adjacent aperture. Take 5 measurements and take the average value, which is the distance A1 between two adjacent protrusions.

[0081] When the projection aperture is strip-shaped, randomly select 5 apertures and measure the width of each aperture along the length of the unfolded electrode. The average of these measurements is the width D2 of the projection of a single protrusion. The measurement of the width of a single aperture includes dividing the aperture into 10 equal segments along the width of the unfolded electrode, measuring the values ​​at both ends of each segment along the length of the unfolded electrode, for a total of 11 values. The average of these 11 values ​​is the width of a single aperture. Then, randomly select one aperture along the length of the unfolded electrode and measure the shortest distance between its width center and the width center of the adjacent aperture. Perform 5 measurements and take the average of these 5 measurements. This average value is the distance A2 between two adjacent protrusions.

[0082] The electrode with protrusions is ion-polished along its length and thickness 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 first current collector. The material layer with protrusions is designated as the first material layer. Based on the placement of the protrusions, the first and second segments of the first material layer are determined along the unfolded length of the electrode. If two parts of the first material layer have protrusions, the first, second, and third regions of the first segment and second segment are determined along the unfolded length of the electrode, based on the placement of the protrusions. During measurement, the first segment and first region are separated by the edge of the protrusion; the first and second regions are separated by the edge of the protrusion; and the second and third regions are separated by the edge of the protrusion.

[0083] Select any 5 protrusions and measure the maximum height from the surface of the first material layer to each protrusion along the thickness direction of the electrode. Take the average value, which is the average height H of the multiple protrusions.

[0084] Along the thickness direction of the electrode, select any 5 flat areas and measure the thickness of the first current collector. Take the average value, which is the thickness T of the first current collector.

[0085] By visually observing along the width direction of the unfolded electrode, identify the first and second edges of the first material layer. Measure the distance between a single protrusion and the first edge, and the distance between a single protrusion and the second edge, respectively. The minimum value is taken as L1. Identify the end of the first material layer and measure the shortest distance between a single protrusion and the end of the first material layer, which is taken as L2.

[0086] Aluminum foil breakage cycle test:

[0087] The lithium-ion batteries in the examples and comparative examples were subjected to charge-discharge cycle tests in a 60°C constant temperature chamber. The lithium-ion batteries were charged at a constant current of 1C 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 2C to 2.5V, marking the first cycle. This cycle was repeated for 50 cycles. Then, using industrial computed tomography (CT) technology (Zeiss Xradia 620 Versa), a CT scan of the cross-section of the cylindrical lithium-ion battery was performed along its axial direction. The cycle continued, with a scan performed every 5 cycles until the electrode assembly showed signs of breakage in the scanned structural image. The number of cycles was recorded as the number of cycles required for the aluminum foil in the electrode assembly to break. A higher number of cycles at which the aluminum foil breaks indicates better cycle performance and safety of the lithium-ion battery.

[0088] Shell fitment efficiency test:

[0089] The wound electrode assemblies used in the examples and comparative examples were prepared according to the preparation steps. Along the outer circumference of the electrode assembly, the diameter of the electrode assembly was measured at different locations at the same height of a single electrode assembly using an inductively coupled plasma (CCD) device. 20 measurements were taken, and the maximum diameter of a single electrode assembly was recorded. 100 electrode assemblies were prepared for each group, and the average maximum diameter of each single electrode assembly in each group was taken as the average maximum diameter of the electrode assemblies for that group. Each group of electrode assemblies was placed into a steel shell with an internal diameter of 33.5 ± 0.1 mm and a height of 203.9 ± 0.1 mm. The number of lithium-ion batteries that could be successfully placed into the shell in each group was recorded. The success rate (%) was calculated as: (Number of lithium-ion batteries successfully placed into the shell / 100) × 100%.

[0090] Among them, the higher the casing quality rate, the higher the production qualification rate of lithium-ion batteries; when the casing quality rate is less than 50%, the production qualification rate of lithium-ion batteries is too low and does not meet the actual production requirements, and is recorded as <50%.

[0091] Example 1

[0092] <Preparation of the positive electrode>

[0093] Lithium nickel cobalt manganese oxide (LiNi) is used as the positive electrode active material. 0.91 Co 0.05 Mn 0.04O2), 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 onto one surface of a positive electrode current collector aluminum foil with a thickness T of 14 μm 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 positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with both the first and second positive electrode material layers.

[0094] Along the length of the unfolded positive electrode sheet, the first and second 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 K of the first segment is 4%, and the length ratio K' of the second segment is 96%. A protrusion is provided in the first segment. Along the thickness direction of the positive electrode sheet, the projection shape of a single protrusion on the first positive electrode material layer is set to be circular, as shown in Figure 6. The diameter D1 of the largest circumcircle of the projection of a single protrusion is 5 mm, and the average height H of multiple protrusions is 70 μm. Along the unfolded length of the positive electrode sheet, the spacing A1 between two adjacent protrusions is 10 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 mm². 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, the width of the empty foil area of ​​the positive electrode sheet is 4.5mm, the shortest distance L1 between the protrusion and the first edge of the first positive electrode material layer is 8mm, and the shortest distance L2 between the protrusion and the first end face of the first positive electrode material layer is 8mm.

[0095] <Preparation of Negative Electrode Sheets>

[0096] Artificial graphite (anode active material), SiO₂ (silicon oxide), 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 a 10 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 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, 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.

[0097] <Septum>

[0098] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0099] <Preparation of Electrolyte>

[0100] 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.

[0101] <Preparation of Lithium-ion Batteries>

[0102] 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 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 near the end segment of the pre-wound electrode assembly. This winding process yields a wound electrode assembly. Afterwards, the assembly undergoes flattening, current collector welding, casing, bottom penetration welding, inkjet coding, vacuum drying, electrolyte injection, sealing, and high-temperature settling before formation and capacity testing to obtain a lithium-ion battery. The formation upper limit voltage is 3.6V, the formation temperature is 45℃, and after formation, the battery is settling at room temperature (25℃) for 24 hours.

[0103] Examples 2 to 5

[0104] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0105] Example 6

[0106] Except for determining the first and second segments of the first positive electrode material layer in the <Preparation of the Positive Electrode Sheet>, and determining the first, second, and third regions of the second segment, based on the length of the first positive electrode material layer after unfolding, the length ratio of the first region K1 is 10%, the length ratio of the second region K2 is 30%, and the length ratio of the third region K3 is 56%, and a protrusion is set on the second region while setting a protrusion in the first segment, the rest is the same as in Example 1.

[0107] Examples 7 to 10

[0108] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 6.

[0109] Examples 11 to 20

[0110] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0111] Example 21

[0112] Except for adjusting the projection shape of a single protrusion on the first material layer to a strip shape in the <Preparation of the Positive Electrode> section, as shown in Figure 7, and adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1.

[0113] Examples 22 to 25

[0114] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 21.

[0115] Examples 26 to 29

[0116] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0117] Example 30

[0118] 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.

[0119] <Preparation of Negative Electrode Sheets>

[0120] Artificial graphite (anode active material), SiO₂ (silicon oxide), 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 negative electrode slurry was uniformly coated onto one surface of a copper foil current collector with a thickness T 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 same copper foil to obtain a negative electrode sheet coated with both the first and second negative electrode material layers.

[0121] Along the length of the unfolded negative electrode sheet, the first and second 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 K of the first segment is 4%, and the length ratio K' of the second segment is 96%. Protrusions are provided on the first segment. Along the thickness direction of the negative electrode sheet, the projection shape of a single protrusion on the first negative electrode material layer is set to be circular. The diameter D1 of the largest circumcircle of the projection of a single protrusion is 5 mm, and the average height H of multiple protrusions is 70 μm. Along the unfolded length of the negative electrode sheet, the spacing A1 between two adjacent protrusions is 10 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 110mg / 1540.25mm2. The specifications of the negative electrode sheet are 67.45mm×1436mm. The specifications of the first negative electrode material layer are 62mm×1436mm. The specifications of the second negative electrode material layer are the same as those of 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. The width of the empty foil area of ​​the negative electrode sheet is 5.45mm. The shortest distance L1 between the protrusion and the first edge of the first negative electrode material layer is 8mm. The shortest distance L2 between the protrusion and the first end face of the first negative electrode material layer is 8mm.

[0122] <Preparation of Lithium-ion Batteries>

[0123] 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. Furthermore, the first segment of the first positive electrode material layer is located near the center of the pre-wound electrode assembly, and the first segment of the first negative electrode material layer is located near the end segment of the pre-wound electrode assembly. Afterward, a wound electrode assembly is obtained. Following this, the assembly undergoes flattening, current collector welding, casing, bottom penetration welding, inkjet coding, vacuum drying, electrolyte injection, sealing, and high-temperature settling before formation capacity testing to obtain a lithium-ion battery. The upper limit of the formation voltage is 3.6V, the formation temperature is 45℃, and after formation, the battery is set at room temperature (25℃) for 24 hours.

[0124] Comparative Example 1

[0125] Except that no protrusions are provided on the surface of the first material layer, the rest is the same as in Example 1.

[0126] Comparative Example 2

[0127] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0128] Comparative Example 3

[0129] Except for the fact that a protrusion is provided on the second segment of the first material layer and no protrusion is provided on the first segment, the rest is the same as in Example 1.

[0130] Comparative Example 4

[0131] Except for the fact that the length of the first segment is 100%, that is, the entire first material layer is provided with protrusions, the rest is the same as in Example 1.

[0132] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0133] As can be seen from Examples 1 to 30 and Comparative Examples 1 to 4, by adjusting the length ratio of the first segment within the scope of this application and setting protrusions on the first segment, the average maximum diameter of the electrode assembly is moderate, the casing yield of the lithium-ion battery is high, and the number of cycles when the aluminum foil breaks is increased. This indicates that the above-mentioned settings reduce the safety risk of electrode breakage due to excessive stretching of the outer ring of the electrode assembly caused by excessive tensile stress, which is beneficial to reducing actual production costs and increasing production capacity. The lithium-ion battery has good safety performance and cycle performance. In Comparative Example 1, no protrusions are set on the first material layer; in Comparative Example 2, the length ratio of the first segment is not within the scope of this application; in Comparative Example 3, no protrusions are set on the first segment, but protrusions are set on the second segment; in Comparative Example 4, protrusions are set on all parts of the first material layer. In Comparative Example 1, the number of cycle cycles when the aluminum foil breaks is relatively low, indicating poor safety and cycle performance of the lithium-ion battery. Comparative Example 2 shows significant energy density loss, large-scale defective casing, and a low casing yield, resulting in low production cost-effectiveness. Comparative Example 3 also shows significant energy density loss, large-scale defective casing, and a low casing yield, and fails to address the safety risk of electrode breakage, especially in current collectors like aluminum foil, due to excessive stretching of the outer ring of the electrode assembly during cycling, resulting in low production cost-effectiveness. Comparative Example 4 shows significant energy density loss, large-scale defective casing, and an even lower casing yield than Comparative Example 3, making it impossible to produce finished batteries, resulting in excessively low production cost-effectiveness and failing to meet actual production requirements. In contrast, the lithium-ion batteries in Examples 1 to 30 show improved cycle cycles when the aluminum foil breaks, along with a higher casing yield, thus meeting actual production requirements and demonstrating good safety and cycle performance.

[0134] The length ratio of different regions in the second segment typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 1, 6 to 10, when the length ratio of different regions in the second segment falls within the scope of this application, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery casing yield is high, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application possesses good safety and cycle performance.

[0135] The average height H of multiple protrusions typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 1, 11 to 14, when the average height H of the multiple protrusions is within the range of this application, the average maximum diameter of the electrode assembly is moderate, the casing yield of the lithium-ion battery is high, and the number of cycle cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application has good safety and cycle performance. In Example 14, the number of cycle cycles when the aluminum foil breaks is high, but the casing yield is 98%. When the casing yield is lower than 99%, it will have a significant impact on production efficiency and cost during actual production.

[0136] The thickness T of the first current collector typically affects the safety and cycle performance of a lithium-ion battery. As can be seen from Examples 1, 15, and 16, when the thickness T of the first current collector is within the range specified in this application, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery casing yield is high, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application possesses good safety and cycle performance.

[0137] The value of D1 typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 1, 17, and 18, when the projection shape of a single protrusion on the first material layer is circular, and the diameter D1 of the maximum circumscribed circle of the projection of the single protrusion is within the range of this application, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery has a high casing yield, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0138] The value of A1 typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 1, 19, and 20, when the projection shape of a single protrusion on the first material layer is circular, and the distance A1 between two adjacent protrusions is within the range of this application, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery casing yield is high, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0139] The value of D2 typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 21 to 23, when the projection shape of a single protrusion on the first material layer is strip-shaped, and the width D2 of the projection of a single protrusion is within the range of this application, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery casing yield is high, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0140] The value of A2 typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 22, 24, and 25, when the projection shape of a single protrusion on the first material layer is strip-shaped, and the spacing A2 between two adjacent protrusions is within the range of this application, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery casing yield is high, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0141] The value of L1 typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 1, 26, and 27, when the shortest distance L1 between a single protrusion and the first or second edge is within the range of this application, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery casing yield is high, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0142] The value of L2 typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 1, 28, and 29, when the shortest distance L2 between a single protrusion in the first segment and the first end face is within the range of this application, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery casing yield is high, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0143] The use of positive and / or negative electrodes typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 1 and 30, when the electrodes are positive and / or negative, the average maximum diameter of the electrode assembly is moderate, the battery casing yield is high, and the number of cycles when the aluminum foil breaks is high. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application exhibits good safety and cycle performance.

[0144] The presence of a first recess and / or a second recess typically affects the safety and cycle performance of lithium-ion batteries. As can be seen from Examples 1 to 30, when the first recess and / or the second recess are provided, the average maximum diameter of the electrode assembly is moderate, the lithium-ion battery casing yield is high, and the number of cycles when the aluminum foil breaks is large. This indicates that while taking into account actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0145] 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.

[0146] 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.

[0147] 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 first current collector and a first material layer located on a surface of the first current collector; Starting from the end of the electrode sheet, along the length direction after the electrode sheet is unfolded, the first material layer includes a first segment and a second segment connected in sequence. Based on the length of the first material layer, the length ratio of the first segment is K, where 1% ≤ K ≤ 10%. Multiple protrusions are provided on the surface of the first segment.

2. The cylindrical secondary battery according to claim 1, wherein, Along the length direction of the unfolded electrode sheet, and in the direction away from the end of the electrode sheet, the second segment includes a first region, a second region, and a third region connected in sequence; based on the length of the first material layer, the length ratio of the first region is K1, the length ratio of the second region is K2, 10%≤K1≤40%, 20%≤K2≤60%, and only the surface of the second region in the second segment is provided with multiple protrusions.

3. The cylindrical secondary battery according to claim 2, wherein, 30％≤K2≤50％。 4. The cylindrical secondary battery according to any one of claims 1 to 3, wherein, The average height of the plurality of protrusions is H μm, and 10 ≤ H ≤ 160.

5. The cylindrical secondary battery according to claim 4, wherein, 35≤H≤110。 6. The cylindrical secondary battery according to any one of claims 1 to 5, wherein, The thickness of the first current collector is T μm, where 8 ≤ T ≤ 16.

7. The cylindrical secondary battery according to any one of claims 1 to 6, wherein, The plurality of protrusions are distributed in a dotted pattern on the first material layer. Along the thickness direction of the electrode, the projection shape of a single protrusion on the first material layer is circular, elliptical, or polygonal. The diameter of the largest circumcircle of the projection is D1 mm, where 3 ≤ D1 ≤ 7.

8. The cylindrical secondary battery according to claim 7, wherein, Along the length of the unfolded electrode, the distance between two adjacent protrusions is A1 mm, where 5 ≤ A1 ≤ 15.

9. The cylindrical secondary battery according to any one of claims 1 to 6, wherein, Along the thickness direction of the electrode sheet, the projection shape of a single protrusion on the first material layer is a strip. The plurality of protrusions extend along the width direction of the unfolded electrode sheet and are spaced apart along the length direction of the unfolded electrode sheet. Along the length direction of the unfolded electrode sheet, the width of the projection is D2 mm, 5≤D2≤10.

10. The cylindrical secondary battery according to claim 9, wherein, Along the length of the unfolded electrode, the distance between two adjacent protrusions is A2 mm, where 5 ≤ A2 ≤ 15.

11. The cylindrical secondary battery according to any one of claims 1 to 10, wherein, Along the width direction after the electrode is unfolded, the first material layer has a first edge and a second edge, and the shortest distance between a single protrusion and the first edge or the second edge is L1 mm, where 5 ≤ L1 ≤ 15.

12. The cylindrical secondary battery according to any one of claims 1 to 11, wherein, Along the length direction after the electrode is unfolded, the end of the first material layer includes a first end face, and the shortest distance between a single protrusion in the first segment and the first end face is L2 mm, where 5≤L2≤15.

13. The cylindrical secondary battery according to any one of claims 1 to 12, wherein, The first material layer is located on the surface of the first current collector away from the winding center of the electrode assembly.

14. The cylindrical secondary battery according to claim 13, wherein, The electrode further includes a second material layer, which is located on the surface of the first 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.

15. The cylindrical secondary battery according to claim 14, wherein, The first current collector has multiple second recesses in the direction of the first material layer.

16. The cylindrical secondary battery according to claim 15, 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.

17. The cylindrical secondary battery according to any one of claims 1 to 16, wherein it satisfies at least one of the following conditions: (1)4％≤K≤10％； (2) The electrode is a positive electrode.

18. The cylindrical secondary battery according to claim 1, wherein, The electrode assembly further includes another electrode with the opposite polarity to the first electrode, the other electrode including a second current collector and a third material layer located on at least one surface of the second current collector, the third material layer including silicon.

19. An electronic device comprising a cylindrical secondary battery according to any one of claims 1 to 18.

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