Cylindrical secondary battery and electronic device

Abstract

This application provides a cylindrical secondary battery and electronic device, including an electrode assembly. The electrode assembly includes an electrode sheet, and the electrode sheet includes a first material layer. The first material layer includes a middle section and an edge section. The length of the middle section is L, and 50% ≤ L ≤ 70%. Both the middle section and the edge section are provided with protrusions. The height of the protrusion in the middle section is H1 μm, and the height of the protrusion in the edge section is H2 μm, where H1 > H2. The first material layer includes a middle region and an edge region, and the protrusions include a first protrusion and a second protrusion. The height of the first protrusion in the middle section is H. 11 μm, the height of the second protrusion in the middle section is H 12 μm, the height of the first protrusion located at the edge segment is H 21 μm, the height of the second protrusion located at the edge segment is H 22 μm, H 11 >H 12 H 21 >H 22 H 11 / H 12 >H 21 / H 22 The above settings reduce the risk of lithium plating in secondary batteries.

Description

Technical Field

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

[0002] Cylindrical secondary batteries, such as cylindrical lithium-ion batteries, are used in various high-rate discharge systems (such as discharge rates greater than 3C). They have the characteristics of high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the consumer electronics field.

[0003] Currently, high-power cylindrical lithium-ion batteries are typically designed with a full-tab design, where the positive and negative tabs extend from opposite directions and are fabricated using full-tab flattening or rolling techniques. However, in the later stages of cycling, the electrodes in full-tab cylindrical lithium-ion batteries expand, and the compression in the center of the electrode assembly can lead to electrolyte accumulation on both sides of the electrodes. This increases side reactions on the electrode surface, resulting in increased impedance, raising the risk of lithium plating, and reducing cycle performance. Summary of the Invention

[0004] The purpose of this application is to provide a cylindrical secondary battery and electronic device to reduce the side reactions that occur in the later stages of cycling due to the compression of the electrode, which leads to the accumulation of electrolyte on both sides of the electrode. This reduces the risk of lithium plating caused by the increased interfacial impedance due to side reactions, thereby improving the cycle performance of the cylindrical secondary battery and reducing the risk of short circuits caused by electrode expansion and indentation in the later stages of cycling.

[0005] It should be noted that the invention description in this application uses lithium-ion batteries 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.

[0006] The specific technical solution is as follows:

[0007] The first aspect of this application provides a cylindrical secondary battery, including an electrode assembly with a wound structure. The electrode assembly includes an electrode sheet, which includes a current collector and a first material layer. The first material layer is located on the surface of the current collector away from the winding center of the electrode assembly. Along the length direction of the unfolded electrode sheet and along the winding direction of the electrode assembly, the first material layer includes a middle section and two edge sections connected to the middle section. Based on the length of the first material layer, the length ratio of the middle section is L, 50% ≤ L ≤ 70%, optionally 54% ≤ L ≤ 64%. Multiple protrusions are provided on the surfaces of both the middle section and the two edge sections. Along the thickness direction of the electrode sheet, the average height of the multiple protrusions located in the middle section is H1 μm, and the average height of the multiple protrusions located in the two edge sections is H2 μm, where H1 > H2. Along the width direction of the unfolded electrode sheet, the first material layer includes a middle region and two edge regions connected to the middle region. The protrusions include a first protrusion and a second protrusion. The first protrusion is located on the surface of the middle region, and the second protrusion is located on the surfaces of the two edge regions. The average height of all the first protrusions located in the middle section is H. 11 μm, the average height of all second protrusions located in the middle section is H 12 μm, the average height of all first protrusions located on the edge segment is H 21 μm, the average height of all second protrusions located on the edge segment is H 22 μm, H 11 >H 12 H 21 >H 22 H 11 / H 12 >H 21 / H 22 By setting protrusions of different heights in different areas of the electrode, and making the first protrusion in the central area of ​​the middle section have the highest average height, expansion space can be reserved for the electrode. This reduces the side reactions caused by electrolyte accumulation on both sides of the electrode due to the electrode being squeezed in the later stages of cycling. In this way, the risk of lithium plating in the secondary battery due to increased interfacial impedance caused by side reactions is reduced, thereby improving the cycle performance of the cylindrical secondary battery. At the same time, it reduces the risk of short circuit due to electrode indentation in the later stages of cycling.

[0008] In one or more embodiments, 3.6 ≤ H 11 / H 12 ≤6.5, optionally, 4.5≤H 11 / H 12 ≤6.5; 1.2≤H 21 / H 22 ≤5.5, optionally, 2.2≤H 21 / H 22 ≤3.5. By adjusting H 11 / H 12 、H21 / H 22 Within the above range, the value reduces the side reactions that occur in the later stages of cycling due to the compression of the electrode, which leads to the accumulation of electrolyte on both sides of the electrode. This reduces the risk of short circuits caused by electrode indentation in the later stages of cycling. At the same time, it also reduces the risk of side reactions caused by the accumulation of electrolyte in the middle of the electrode due to excessive reserved space, which prevents effective flow. This reduces the risk of lithium plating in the secondary battery and improves the cycle performance of the secondary battery.

[0009] In one or more embodiments, along the thickness direction of the electrode, the sum of the thicknesses of the first material layer and the current collector is H0 μm, and 15% ≤ H 11 / H0×100%≤30%, optionally, 18%≤H 11 / H0×100%≤25%;2%≤H 21 / H0×100%≤10%, optionally, 5%≤H 21 / H0×100%≤8%. By adjusting H... 11 / H0×100%, H 21 The value of / H0×100% is within the above range, which reduces the side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stage of the cycle. At the same time, it reduces the risk of short circuit due to electrode indentation in the later stage of the cycle. While taking into account the energy density of the secondary battery, it reduces the risk of lithium plating in the secondary battery and improves the cycle performance of the secondary battery.

[0010] In one or more embodiments, 30 ≤ H0 ≤ 80; alternatively, 35 ≤ H0 ≤ 55. By adjusting the value of H0 within the above range, the secondary battery achieves high energy density while also ensuring the processing performance of the electrode sheets.

[0011] In one or more embodiments, along the thickness direction of the electrode, a single first protrusion has a first projection on the first material layer, a single second protrusion has a second projection on the first material layer, and the sum of the areas of the plurality of first projections is S1μm. 2 The sum of the areas of the multiple second projections is S2μm. 2 The S1 / S2 ratio is set to 5% ≤ S1 / S2 ≤ 70%, and optionally, 25% ≤ S1 / S2 ≤ 50%. By adjusting the S1 / S2 value within the above range, side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling are reduced. At the same time, the risk of electrode indentation and short circuit in the later stages of cycling is reduced, the risk of lithium plating in the secondary battery is reduced, and the cycle performance of the secondary battery is improved.

[0012] In one or more embodiments, along the thickness direction of the electrode, a single protrusion has a projection on the first material layer, and the diameter of the largest circumscribed circle of the projection is D mm, where 0.5 ≤ D ≤ 10, and optionally, 2 ≤ D ≤ 6. By controlling the diameter D of the largest circumscribed circle of the projection of the single protrusion within the above range, it is beneficial to reduce side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling. Simultaneously, it reduces the risk of electrode indentation and short circuit in the later stages of cycling, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. This application does not impose any particular limitation on the projection shape of the single protrusion, as long as it achieves the purpose of this application.

[0013] In one or more embodiments, the distance between any two adjacent protrusions along the length direction after the electrode is unfolded is A mm, where 1 ≤ A ≤ 10, and optionally, 1.5 ≤ A ≤ 5. By adjusting the distance A between two adjacent protrusions within the above range, it is beneficial to reduce side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling. Simultaneously, it reduces the risk of short circuits due to electrode indentation in the later stages of cycling, reduces the risk of lithium plating, and improves the cycle performance of the secondary battery. In one or more embodiments, the distance between any two adjacent protrusions along the length direction after the electrode is unfolded is equal.

[0014] In one or more embodiments, the electrode further includes a second material layer located on the surface of the current collector facing the winding center of the electrode assembly, and the surface of the second material layer has a plurality of first recesses in the direction of the first material layer. In one or more embodiments, the current collector has a plurality of second recesses in the direction of the first material layer. In one or more embodiments, at least some of the first recesses correspond to some of the protrusions; and / or, at least some of the second recesses correspond to some of the protrusions. Through the above configuration, side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling are further reduced, while the risk of electrode indentation and short circuit in the later stages of cycling is reduced, and the risk of lithium plating in cylindrical secondary batteries is reduced, thus improving the cycle performance of secondary batteries while meeting mass production manufacturability requirements.

[0015] In one or more embodiments, the electrode is a positive electrode. This configuration helps reduce the processing difficulty of the electrode during manufacturing, further improving the cycle performance of the secondary battery.

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

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

[0018] This application provides a cylindrical secondary battery and electronic device. By adjusting the length ratio of the middle section within the aforementioned range, and by providing a first protrusion and a second protrusion on the middle region and two edge regions of the first material layer, respectively, H... 11 >H 12 H 21 >H 22 H 11 / H 12 >H 21 / H 22 By creating protrusions of varying heights in different regions on the first material layer of the electrode, and ensuring that the protrusion in the center of the electrode has the maximum height to allow for expansion space, this design reduces side reactions caused by electrolyte accumulation on both sides of the electrode due to compression during later cycles. It also reduces the risk of short circuits due to electrode indentation during later cycles, thereby lowering the risk of lithium plating in the secondary battery due to increased interfacial impedance caused by side reactions. Furthermore, the appropriately sized expansion space keeps the distance between the positive and negative electrodes and between electrode layers within a suitable range during charging and discharging, resulting in lower electrochemical impedance in the secondary battery. In addition, the use of protrusions of varying heights in different regions on the first material layer ensures uniform stress on the electrode while maintaining the energy density of the secondary battery. This reduces the risk of electrode fracture due to stress when expansion occurs, thus improving the safety performance of the secondary battery. Therefore, the cylindrical secondary battery of this application exhibits excellent cycle performance.

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

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

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

[0022] Figure 2 This is a partial front view of the positive electrode sheet after the electrode assembly in another embodiment of this application has been unfolded.

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

[0024] Reference numerals: Electrode assembly 001; Positive electrode 10; Positive current collector 11; First positive electrode material layer 12; Second positive electrode material layer 13; Negative electrode 20; Negative current collector 21; First negative electrode material layer 22; Second negative electrode material layer 23; Separator 30; Protrusion 121; First protrusion 1211; Second protrusion 1212; First recess 131; Second recess 111. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] 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.

[0027] In existing cylindrical secondary batteries, such as cylindrical lithium-ion batteries, the electrodes expand during the later stages of cycling. This is especially true when the negative electrode active material includes silicon. During charge and discharge, the negative electrode undergoes significant expansion and contraction, squeezing the electrolyte in the center of the electrode to the sides. This electrolyte accumulates on both sides of the electrode, leading to side reactions, increasing interfacial impedance, and causing lithium plating. Furthermore, in the later stages of cycling, the electrode assembly expands outward but is constrained by the casing. The inner electrodes in the electrode assembly will then indent to release stress, further increasing the distance between the positive and negative electrodes. This can cause some electrodes to break, increasing the risk of short circuits in the secondary battery. At the same time, the increased distance between the positive and negative electrodes increases the impedance of the lithium-ion battery, accelerating the degradation of the battery's cycle performance. Based on this, this application provides a cylindrical secondary battery and electronic device, which helps to reduce the side reactions caused by the accumulation of electrolyte on both sides of the electrode due to the compression of the electrode in the later stage of cycling, and at the same time reduces the degree of electrode indentation in the later stage of cycling, thereby improving the cycle performance of the cylindrical secondary battery, while reducing the risk of lithium plating and short circuit caused by the increased interfacial impedance due to side reactions.

[0028] The first aspect of this application provides a cylindrical secondary battery, including an electrode assembly with a wound structure. The electrode assembly includes an electrode sheet, which includes a current collector and a first material layer. The first material layer is located on the surface of the current collector opposite to the winding center of the electrode assembly. Along the length direction of the unfolded electrode sheet and along the winding direction of the electrode assembly, the first material layer includes a middle section and two edge sections connected to the middle section. Based on the length of the first material layer, the length percentage of the middle section is L, where 50% ≤ L ≤ 70%, and optionally, 54% ≤ L ≤ 64%. For example, the value of L can be 50%, 52%, 54%, 55%, 58%, 60%, 62%, 64%, 65%, 68%, 70%, or a range of any two of these values. Multiple protrusions are provided on the surfaces of both the middle section and the two edge sections. Along the thickness direction of the electrode sheet, the average height of the multiple protrusions located in the middle section is H1 μm, and the average height of the multiple protrusions located in the two edge sections is H2 μm, where H1 > H2. Along the width direction after the electrode is unfolded, the first material layer includes a central region and two edge regions connected to the central region. The protrusions include a first protrusion and a second protrusion. The first protrusion is located on the surface of the central region, and the second protrusion is located on the surfaces of the two edge regions. The average height of all the first protrusions located in the central section is H. 11 μm, the average height of all second protrusions located in the middle section is H 12 μm, the average height of all first protrusions located on the edge segment is H 21 μm, the average height of all second protrusions located on the edge segment is H 22 μm, H 11 >H 12 H 21 >H 22 H 11 / H 12 >H 21 / H 22 .

[0029] In this application, the electrode sheet can be a positive electrode sheet and / or a negative electrode sheet. 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 sheet, positive electrode sheet, 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, as shown... Figures 1 to 3As shown, the electrode assembly 001 includes a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10 includes a positive current collector 11, a first positive electrode material layer 12, and a second positive electrode material layer 13. The negative electrode 20 includes a negative current collector 21, a first negative electrode material layer 22, and a second negative electrode material layer 23. The first positive electrode material layer 12 is located on the surface of the positive current collector 11 facing away from the winding center of the electrode assembly 001, and the second positive electrode material layer 13 is located on the surface of the positive current collector 11 facing towards the electrode assembly 001. On the surface of the winding center, the first negative electrode material layer 22 is located on the surface of the negative electrode current collector 21 away from the winding center of the electrode assembly 001, and the second negative electrode material layer 23 is located on the surface of the negative electrode current collector 21 facing the winding center of the electrode assembly 001. Along the length direction (X direction) of the unfolded positive electrode sheet 10 and along the winding direction (W direction) of the electrode assembly 001, the first positive electrode material layer 12 includes a middle section M' to N and two edge sections M to N and N to N' connected to the middle section. Multiple protrusions 121 are provided on the surfaces of the middle section M' to N and the two edge sections M to N and N to N'. Along the thickness direction (Z direction) of the positive electrode sheet 10, the average height of the multiple protrusions 121 located in the middle section M' to N is H1 μm, and the average height of the multiple protrusions 121 located in the two edge sections M to N and N to N' is H2 μm. Along the width direction (Y direction) of the unfolded positive electrode sheet 10, the first positive electrode material layer 12 includes a central region, i.e., the region between the line containing EE' and the line containing FF', and two edge regions connected to the central region (not shown in the figure). The protrusions 121 include a first protrusion 1211 and a second protrusion 1212. The first protrusion 1211 is located on the surface of the central region, and the second protrusion 1212 is located on the surfaces of the two edge regions. The average height of all the first protrusions 1211 located in the central segment M' to N is H. 11 μm, the average height of all second protrusions 1212 located in the middle section M' to N is H 12 μm, the average height of all first protrusions 1211 located in edge segments M to N and N to N' is H 21 μm, the average height of all second protrusions 1212 located in edge segments M to N and N to N' is H. 22 μm.

[0030] During charging and discharging, the degree of compression on the electrode sheet along its unfolded length is inconsistent, with the ends experiencing relatively less compression. When the length ratio L of the middle section is too small, for example, less than the lower limit of this application (i.e., the length ratio of the edge section is too large), the area of ​​the protrusions on the electrode sheet is too small, affecting the wetting of the middle part of the electrode sheet by the electrolyte and failing to effectively improve the cycle performance of the secondary battery. When the length ratio L of the middle section is too large, for example, greater than the upper limit of this application (i.e., the length ratio of the edge section is too small), there is more powder shedding during electrode processing, leading to loss of active material. Simultaneously, when the length ratio L of the middle section is too large, the number of electrode layers in an electrode assembly of the same diameter decreases, which in turn affects the energy density of the secondary battery, thus weakening the product's competitiveness. Furthermore, when the length ratio L of the middle section is too large, the average height of the corresponding protrusions is higher, which can easily lead to electrolyte bridging between some electrode layers, increasing the electrochemical impedance of the secondary battery and thus increasing the risk of lithium plating. When H... 11 ≤H 12 、H 21 ≤H 22 and / or H 11 / H 12 ≤H 21 / H 22 At this point, the height of the protrusion in the middle of the electrode is relatively small, and the expansion space reserved in the middle of the electrode is too small. During charge and discharge, this cannot effectively mitigate the risk of side reactions caused by electrolyte accumulation on both sides of the electrode due to compression during later stages of the cycle. This results in a higher risk of lithium plating in the secondary battery and poor cycle performance. This application addresses this by controlling the length ratio of the middle section within the aforementioned range, and by setting the first protrusion and the second protrusion on the middle region and two edge regions of the first material layer, respectively, and making H... 11 >H 12 H 21 >H 22 H 11 / H 12 >H 21 / H 22The first material layer of the electrode features protrusions of varying heights in different regions, with the central protrusion being the highest. This allows for expansion space, reducing side reactions caused by electrolyte accumulation on both sides of the electrode due to compression during later cycles. It also lowers the risk of short circuits due to electrode indentation during later cycles, thus reducing the risk of lithium plating caused by increased interfacial impedance due to side reactions, thereby improving the cycle performance of the secondary battery. Simultaneously, the appropriately designed expansion space keeps the distance between the positive and negative electrodes and between electrode layers within a suitable range during charging and discharging, resulting in lower electrochemical impedance of the secondary battery. Furthermore, the varying heights of the protrusions on the first material layer ensure uniform stress on the electrode while maintaining energy density. When the electrode expands, the risk of stress-induced fracture is reduced, improving the safety performance of the secondary battery. Therefore, the cylindrical secondary battery of this application exhibits excellent cycle performance.

[0031] It should be noted that the "surface" of the first material layer located on the surface of the current collector away from the winding center of the electrode assembly can be the entire area of ​​the current collector surface or a part of the current collector surface. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0032] In one or more embodiments, based on the length of the first material layer, the length percentage of any edge segment is L', where 15% ≤ L' ≤ 25%. For example, the value of L' can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or a range of any two of these values. During charging and discharging, the degree of compression on the electrode along its unfolded length is inconsistent, with the ends of the electrode experiencing relatively less compression. By adjusting the length percentage of any edge segment within the aforementioned range, expansion space is reserved at the edge segments of the electrode, improving the wetting of the electrolyte on the electrode edge segments while reducing side reactions caused by electrolyte accumulation on both sides of the electrode due to compression in the later stages of cycling. This also reduces the risk of short circuits due to electrode indentation in the later stages of cycling and reduces the risk of lithium plating in the secondary battery due to increased interfacial impedance caused by side reactions. This improves the cycle performance of the secondary battery while maintaining energy density.

[0033] In one or more embodiments, such as Figure 2As shown, based on the width of the first positive electrode material layer 12, the length ratio of the middle region, i.e., the region between the straight line containing EE' and the straight line containing FF', is L1, where 30% ≤ L1 ≤ 50%. For example, the value of L1 can be 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, or a range of any two of these values. By controlling the length ratio of the middle region within the above range, it is beneficial to reserve sufficient expansion space in the middle of the electrode, reducing the side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling. At the same time, it reduces the risk of electrode indentation and short circuit in the later stages of cycling, and reduces the risk of lithium plating in the secondary battery due to increased interfacial impedance caused by side reactions, thereby improving the cycle performance of the secondary battery.

[0034] In one or more embodiments, based on the width of the first material layer, the length percentage of any edge region is L'1, where 25% ≤ L'1 ≤ 35%. For example, the value of L'1 can be 25%, 28%, 30%, 32%, 35%, or a range consisting of any two of these values. By adjusting the length percentage of the edge region within the above range, expansion space is reserved in the edge region of the electrode, improving the wetting of the electrode edge region by the electrolyte while reducing side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling. This also reduces the risk of electrode indentation and short circuit in the later stages of cycling, and reduces the risk of lithium plating in the secondary battery due to increased interfacial impedance caused by side reactions, thereby improving the cycle performance of the secondary battery.

[0035] In one or more embodiments, 3.6 ≤ H 11 / H 12 ≤6.5, optionally, 4.5≤H 11 / H 12 ≤6.5; for example, H 11 / H 12 The value can be 3.6, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, or a range of any two of these values. 1.2 ≤ H 21 / H 22 ≤5.5, optionally, 2.2≤H 21 / H 22 ≤3.5; for example, H 11 / H 12 The value can be 1.2, 1.4, 1.5, 1.8, 2, 2.2, 2.4, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, or a range of any two of these values. This can be achieved by adjusting H... 11 / H 12 、H 21 / H22 Within the aforementioned range, the value of the expansion space is beneficial for reserving expansion space in the middle of the electrode, reducing the side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling, and reducing the risk of electrode indentation and short circuit in the later stages of cycling. At the same time, it also reduces the risk of side reactions caused by electrolyte accumulation in the middle of the electrode due to excessive reserved space, which prevents effective flow. In addition, the moderate reserved expansion space is beneficial for designing the distance between the positive and negative electrodes and between electrode layers within a suitable range during charging and discharging. The electrochemical impedance of the secondary battery is relatively small, reducing the risk of lithium plating caused by increased interfacial impedance due to side reactions, thereby improving the cycle performance of the secondary battery.

[0036] In one or more embodiments, along the thickness direction of the electrode, the sum of the thicknesses of the first material layer and the current collector is H0 μm, and 15% ≤ H 11 / H0×100%≤30%, optionally, 18%≤H 11 / H0×100%≤25%, for example, H 11 The value of / H0 can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range of any two of these values. 2% ≤ H 21 / H0×100%≤10%, optionally, 5%≤H 21 / H0×100%≤8%, for example, H 21 The value of / H0×100% can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range of any two of these values. By adjusting H... 11 / H0×100%, H 21 A value of / H0×100% within the above range is beneficial for reserving expansion space in the middle of the electrode, reducing side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling, and reducing the risk of electrode indentation and short circuit in the later stages of cycling. At the same time, it also reduces the risk of side reactions caused by electrolyte accumulation in the middle of the electrode due to excessive reserved space, which prevents effective flow. In addition, the reserved expansion space is moderate, which is beneficial for designing the distance between the positive and negative electrodes and between electrode layers within a suitable range during charging and discharging. The electrochemical impedance of the secondary battery is relatively small. While taking into account the energy density of the secondary battery, it reduces the risk of lithium plating caused by increased interfacial impedance due to side reactions, thus improving the cycle performance of the secondary battery.

[0037] In one or more embodiments, 30 ≤ H0 ≤ 80; optionally, 35 ≤ H0 ≤ 55. For example, the value of H0 can be 30, 32, 35, 40, 45, 50, 52, 55, 60, 65, 70, 75, 80, or a range of any two of these values. By adjusting the value of H0 within the above range, it is beneficial to the processing of the electrode sheets in actual production, reducing the risk of electrode powder shedding during production and the risk of short circuits in the secondary battery. The secondary battery has high energy density while also taking into account the processing performance of the electrode sheets.

[0038] In this application, the thickness of the first material layer can be controlled by means known to those skilled in the art. For example, when coating the slurry onto the surface of the current collector, given a certain solid content in the slurry, the thickness of the first material layer can be increased by increasing the coating weight, and decreased by decreasing the coating weight; alternatively, when cold pressing the electrode, the thickness of the first material layer can be decreased by increasing the cold pressing pressure, and increased by decreasing the cold pressing pressure. This application does not impose any particular limitation on the method of controlling the current collector thickness, as long as the purpose of this application can be achieved. For example, commercially available current collectors with different thicknesses can be selected, and combined with the "H" in this application... 11 、H 12 、H 21 、H 22 The thickness of the current collector is determined by the test method of "H0, S1, S2, A, D", and then the current collector with the required thickness is selected. In one or more embodiments, the thickness of the current collector can be from 8 μm to 20 μm along the thickness direction of the electrode.

[0039] In one or more embodiments, along the thickness direction of the electrode, a single first protrusion has a first projection on the first material layer, a single second protrusion has a second projection on the first material layer, and the sum of the areas of the plurality of first projections is S1μm. 2 The sum of the areas of the multiple second projections is S2μm. 25% ≤ S1 / S2 ≤ 70%, optionally, 25% ≤ S1 / S2 ≤ 50%. For example, the value of can be 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, or a range of any two of these values. By adjusting the values ​​of S1 / S2 within the aforementioned range, it is beneficial to reserve expansion space in the middle of the electrode, reducing side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling. This also reduces the risk of electrode indentation and short circuit in the later stages of cycling. At the same time, it also reduces the risk of side reactions caused by electrolyte accumulation in the middle of the electrode due to excessive reserved space, which prevents effective flow. In addition, the moderate reserved expansion space is conducive to designing the distance between the positive and negative electrodes and between electrode layers within an appropriate range during charging and discharging. This results in a lower electrochemical impedance of the secondary battery, reducing the risk of lithium plating caused by increased interfacial impedance due to side reactions, thereby improving the cycle performance of the secondary battery.

[0040] In one or more embodiments, along the thickness direction of the electrode, a single protrusion has a projection on the first material layer, the diameter of the largest circumcircle of the projected outer contour being D mm, as shown below. Figure 2 As shown, along the thickness direction (Z direction) of the positive electrode sheet 10, a single protrusion 121 has a projection on the first positive electrode material layer 12, and the diameter of the largest circumscribed circle of the outer contour of the projection of the single protrusion 121 is D mm. 0.5≤D≤10, optionally, 2≤D≤6. For example, the value of D can be 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two of these values. By controlling the diameter D of the maximum circumcircle of the projected outer contour of a single protrusion within the aforementioned range, it is beneficial to reduce the risk of protrusion collapse during preparation or cycling, which would reduce the reserved expansion space. This ensures a moderate reserved space, which helps reduce side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling. It also reduces the risk of electrode indentation and short circuits in the later stages of cycling. Furthermore, by ensuring that the pit size on the electrode surface facing the winding center of the electrode assembly is moderate, it reduces the risk of increased electrochemical impedance due to localized electrolyte accumulation and side reactions. It also improves the degree of inner electrode indentation caused by electrode expansion in the later stages of cycling, thereby reducing the risk of lithium plating in the secondary battery due to increased interfacial impedance caused by side reactions, thus improving the cycle performance of the secondary battery. This application does not impose any particular limitation on the projected shape of the single protrusion, as long as it achieves the purpose of this application. For example, the projected shape of a single protrusion can be at least one of a triangle, an arc (with an area smaller than a semicircle with the same radius), a semicircle, a rectangle, a trapezoid, a square, or a pentagon or more polygons.

[0041] In one or more embodiments, the spacing between any two adjacent protrusions is equal along the length direction of the unfolded electrode. This arrangement improves the operability of setting protrusions on the first material layer, reduces side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling, lowers the risk of short circuits due to electrode indentation in the later stages of cycling, and further reduces the risk of lithium plating in cylindrical secondary batteries due to increased interfacial impedance caused by side reactions. This improves the cycle performance of cylindrical secondary batteries while meeting mass production manufacturability requirements.

[0042] In one or more embodiments, the distance between two adjacent protrusions along the length direction of the unfolded electrode is A mm, such as... Figure 2 As shown, along the length direction (X direction) of the unfolded positive electrode plate 10, the distance between two adjacent protrusions 121 is A mm. 1 ≤ A ≤ 10, and optionally, 1.5 ≤ A ≤ 5. For example, the value of A 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. By adjusting the spacing A between two adjacent protrusions within the aforementioned range, it is beneficial to reduce the processing difficulty of the electrode sheet during manufacturing, reduce the risk of excessive powder shedding during electrode sheet manufacturing leading to loss of active materials and thus reduced energy density of the secondary battery, and ensure uniform pore distribution of the electrode sheet, which is conducive to the flow of electrolyte on the electrode sheet and improves the wetting effect of the electrolyte on the electrode sheet. It also helps to reduce side reactions caused by electrolyte accumulation on both sides of the electrode sheet due to electrode sheet compression in the later stages of cycling, reduces the risk of electrode sheet indentation and short circuit in the later stages of cycling, and improves the degree of inner-ring electrode sheet indentation caused by electrode sheet expansion in the later stages of cycling, thereby reducing the risk of lithium plating in cylindrical secondary batteries. Simultaneously, with appropriate reserved space, the positive and negative electrode sheets and electrode sheet layers can be tightly bonded during charging and discharging, resulting in lower electrochemical impedance of the secondary battery during charging and discharging, thus reducing the risk of lithium plating caused by increased interfacial impedance due to side reactions and improving the cycle performance of the secondary battery. In this application, the spacing between two adjacent protrusions refers to the distance between the geometric centers of two adjacent protrusions along the length direction after the electrode sheet is unfolded.

[0043] In one or more embodiments, the protrusions are distributed in a dotted pattern on the first material layer. In one or more embodiments, the protrusions are distributed in a matrix on the first material layer. In one or more embodiments, when the protrusions are distributed in a matrix on the first material layer, the spacing between adjacent rows in the same region is equal along the width direction of the unfolded electrode, i.e., equally spaced distribution. This application does not impose any particular limitation on the number of rows of the first protrusions and the second protrusions; those skilled in the art can set them according to the specifications of the actual electrode, as long as the purpose of this application can be achieved.

[0044] In one or more embodiments, multiple protrusions are located on the same side of the electrode along its thickness direction. This arrangement improves the operability of setting protrusions on the first material layer, reduces side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression during later stages of cycling, and lowers the risk of short circuits due to electrode indentation during later stages of cycling. Furthermore, it reduces the risk of lithium plating in cylindrical secondary batteries due to increased interfacial impedance caused by side reactions, thus improving the cycle performance of cylindrical secondary batteries while meeting mass production manufacturability requirements.

[0045] In one or more embodiments, the electrode further includes a second material layer located on the surface of the current collector facing the winding center of the electrode assembly, and the surface of the second material layer has a plurality of first recesses in the direction facing the first material layer. Figure 1 and Figure 3 As shown, the positive electrode 10 also includes a second positive electrode material layer 13. The second positive electrode material layer 13 is located on the surface of the positive current collector 11 facing the winding center of the electrode assembly 001. The surface of the second positive electrode material layer 13 has a plurality of first recesses 131 in the direction of the first positive electrode material layer 12. Through the above arrangement, the operability of setting protrusions and first recesses on the electrode is improved, which is beneficial to improving the wetting performance of the electrolyte on the electrode. It further reduces the side reactions caused by the electrolyte accumulation on both sides of the electrode due to the compression of the electrode in the later stage of cycling, reduces the risk of short circuit due to electrode indentation in the later stage of cycling, and improves the degree of inner electrode indentation caused by electrode expansion in the later stage of cycling. In addition, it reduces the risk of lithium plating caused by increased interfacial impedance due to side reactions in the cylindrical secondary battery. While meeting the manufacturability of mass production, it improves the cycle performance of the secondary battery. It should be noted that the "surface" of the second material layer located on the surface of the current collector facing the winding center of the electrode assembly can be the entire area of ​​the current collector surface or a part of the current collector surface. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0046] In one or more embodiments, the current collector has a plurality of second recesses in the direction toward the first material layer. For example... Figure 1 and Figure 3As shown, the positive electrode current collector 11 has multiple second recesses 111 in the direction of the first positive electrode material layer 12. This arrangement improves the operability of setting protrusions and second recesses on the electrode, further reduces side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling, reduces the risk of short circuits due to electrode indentation in the later stages of cycling, and improves the degree of inner electrode indentation caused by electrode expansion in the later stages of cycling. This further reduces the risk of lithium plating in cylindrical secondary batteries due to increased interfacial impedance caused by side reactions, thus improving the cycle performance of secondary batteries while meeting mass production manufacturability requirements.

[0047] In one or more embodiments, at least a portion of the first recess corresponds to a portion of the protrusion; and / or, at least a portion of the second recess corresponds to a portion of the protrusion. This configuration improves the operability of providing protrusions, first recesses, and / or second recesses on the electrode, further reduces side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling, reduces the risk of short circuits due to electrode indentation in the later stages of cycling, and improves the degree of inner-ring electrode indentation caused by electrode expansion in the later stages of cycling. This further reduces the risk of lithium plating in cylindrical secondary batteries due to increased interfacial impedance caused by side reactions, improving the cycle performance of secondary batteries while meeting mass production manufacturability requirements.

[0048] In one or more embodiments, the electrode is a positive electrode. This configuration helps reduce the processing difficulty of the electrode, minimizes the risk of excessive powder shedding during electrode processing leading to loss of active materials and consequently reduced energy density of the secondary battery, and further reduces side reactions caused by electrolyte accumulation on both sides of the electrode due to electrode compression in the later stages of cycling. It also reduces the risk of electrode indentation and short circuits in the later stages of cycling, and improves the degree of inner electrode indentation caused by electrode expansion in the later stages of cycling. This further reduces the risk of lithium plating in cylindrical secondary batteries due to increased interfacial impedance caused by side reactions. Simultaneously, the reserved expansion space is moderate, and the distance between the positive and negative electrodes and between electrode layers during charging and discharging is within a suitable range, resulting in lower electrochemical impedance of the secondary battery and further improving its cycle performance.

[0049] In this application, when the electrode is a positive electrode, there are no particular restrictions on the positive current collector, as long as it can achieve the purpose of this application. For example, the positive current collector can include aluminum foil, aluminum alloy foil, or composite current collector (e.g., aluminum-carbon composite current collector). In this case, both the first and second material layers are positive electrode material layers. The positive electrode material layer in this application includes a positive electrode active material. There are no particular restrictions on the type of positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there is no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of this application is achieved. In this application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. In this application, there is no particular limitation on the type of positive electrode binder in the positive electrode material layer, as long as the purpose of this application is achieved. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the type of conductive agent in the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and positive electrode binder in the positive electrode material layer; those skilled in the art can select according to actual needs, as long as it can achieve the purpose of this application.

[0050] In the present application, when the electrode sheet is a negative electrode sheet, there is no particular limitation on the negative electrode current collector as long as the object of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector (such as lithium-copper composite current collector, carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector, etc.). In the present application, there is no particular limitation on the thickness of the negative electrode current collector as long as the object of the present application can be achieved. At this time, both the first material layer and the second material layer are negative electrode material layers, and the negative electrode material layer of the present application contains negative electrode active material. There is no particular limitation on the type of the negative electrode active material in the present application as long as the object of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 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 the present application as long as the object of the present application can be achieved. For example, the conductive agent may be the same 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 the present application as long as the object of the present application can be achieved. For example, the negative electrode binder may be the same as the positive electrode binder in the above-mentioned positive electrode material layer. Optionally, the negative electrode material layer further includes a thickening agent. There is no particular limitation on the type of the thickening agent in the present application as long as the object of the present application can be achieved. For example, the thickening agent may include at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose. 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 the present application as long as the object of the present application can be achieved. There is no particular limitation on the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickening agent in the negative electrode material layer in the present application, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0051] This application does not impose any particular limitation on the preparation method of the electrode sheet, as long as it can achieve the purpose of this application. For example, the preparation method of the electrode sheet includes, but is not limited to, the following steps: (1) preparing a slurry; (2) coating the slurry on one surface of the current collector and drying it to form an electrode sheet including a first material layer; (3) coating the slurry on the other surface of the current collector and drying it to obtain an electrode sheet including a first material layer and a second material layer; (4) determining the middle section and two edge sections of the first material layer along the length direction of the unfolded electrode sheet and along the winding direction of the electrode assembly, determining the middle region of the first material layer and two edge regions connected to the middle region along the width direction of the unfolded electrode sheet, setting a first protrusion and a second protrusion on the surface of the middle section and the two edge sections respectively, and obtaining the electrode sheet after cutting and slitting.

[0052] This application does not impose any particular limitation on the solid content of the above-mentioned slurry. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the above-mentioned drying, cutting, and slitting process parameters. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved. In one or more embodiments, in step (4), when the first protrusion and the second protrusion are respectively provided on the surface of the middle section and the two edge sections, 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 the first protrusion and the second protrusion are respectively provided on the surface of the middle section and the two edge sections, a second recess is provided on the current collector in the direction towards the first material layer.

[0053] 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 makes the secondary battery manufacturing process easier, thereby improving the safety and cycle performance of the cylindrical secondary battery.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] In this application, when preparing the wound electrode assembly for the cylindrical secondary battery, an embossing roller can be installed on a winding device to form a first protrusion, a second protrusion, a first recess, and a second recess on the electrode sheet.

[0060] This application does not impose any particular limitation on the method of setting the first protrusion, the second 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 is achieved. For example, the first protrusion, the second 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 first protrusion and a single second protrusion onto the first material layer can be adjusted by the shape of the stainless steel needle on the embossing roller; the average height H of all the first protrusions located in the middle section... 11 The average height H of all the second protrusions located in the middle section 12 The average height H of all the first protrusions located on the edge segment 21 The average height H of all second protrusions located on the edge segment 22 The cold pressing pressure value set on the embossing roller or the height specification of the stainless steel needles on the embossing roller can be adjusted; the distance A between two adjacent protrusions (including the first protrusion and the second protrusion) can be adjusted by the distance between adjacent stainless steel needles on the embossing roller; the diameter D of the maximum circumscribed circle of the projection of a single protrusion (including the first protrusion and the second protrusion) on the first material layer can be adjusted by the diameter specification of the stainless steel needles on the embossing roller; a single first protrusion has a first projection on the first material layer, and the sum of the areas S1 of multiple first projections can be adjusted by the number of stainless steel needles and the number of roller turns on the embossing roller, as well as the number of rows of first protrusions set in the middle area along the width direction after the electrode sheet is unfolded; a single second protrusion has a first projection on the first material layer, and the sum of the areas S2 of multiple second projections can be adjusted by the number of stainless steel needles and the number of roller turns on the embossing roller, as well as the number of rows of second protrusions set in the two edge areas along the width direction after the electrode sheet is unfolded.

[0061] A second aspect of this application provides an electronic device comprising a cylindrical secondary battery as described in any of the foregoing embodiments. The cylindrical secondary battery of this application exhibits excellent cycle performance; therefore, the electronic device of this application has a long service life.

[0062] 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.

[0063] Example

[0064] 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.

[0065] Test methods and equipment:

[0066] H 11 、H 12 、H 21 、H 22 Tests for H0, S1, S2, A, and D:

[0067] At an ambient temperature of 25°C, the lithium-ion batteries of each embodiment and comparative example were discharged to 2.5V at 0.5C and then disassembled to obtain electrode assemblies. The positive and negative electrode sheets were taken out from the electrode assemblies and soaked in dimethyl carbonate (DMC) for 20 minutes. Then, the positive and negative electrode sheets were placed in an oven and dried at 80°C for 12 hours to obtain test samples of the positive and negative electrode sheets.

[0068] The surface of the electrode was observed using a scanning electron microscope (SEM). Measurements were taken along the thickness direction of the electrode, measuring the plane formed by the length and width directions after the electrode was unfolded. Due to the height difference between the protrusion and the material layer surface, a noticeable color difference was observed on the electrode surface. The protrusions projected irises onto the electrode surface, which could be used to distinguish the protrusions from the first material layer. Five irises were randomly selected, and the maximum circumcircle diameter of the projection of each iris onto the first material layer was measured. The average value was taken as the maximum circumcircle diameter D of the projection of a single protrusion. Along the length direction of the unfolded electrode, one protrusion was randomly selected, and the distance between the geometric center of that protrusion and the geometric center of the adjacent protrusion was measured. Five measurements were taken, and the average value was taken as the distance A between two adjacent protrusions.

[0069] The electrode with protrusions is ion-polished along its length and thickness directions after being unfolded, yielding a cross-section. Scanning electron microscopy (SEM) is used to measure this cross-section, revealing a clear boundary between the material layer and the current collector. The material layer with the protrusions is designated as the first material layer. Along the thickness direction of the electrode, based on the height variation of the protrusions along the length of the unfolded electrode, the middle section and two edge sections connected to the middle section of the first material layer are determined. Along the thickness direction of the electrode, based on the height variation of the protrusions along the width of the unfolded electrode, the middle region of the first material layer and two edge regions connected to the middle region are determined. The protrusion on the surface of the middle region is designated as the first protrusion, and the protrusions on the surfaces of the two edge regions are designated as the second protrusion.

[0070] In the middle region of the edge segment of the first material layer, randomly select 10 apertures, measure the area of ​​each aperture, and take the average value. This average value is the projected area of ​​a single first protrusion on the first material layer in the edge segment. Count the number of apertures in the middle region of the two edge segments, which is the number of first protrusions in the two edge segments. In the middle region of the middle segment of the first material layer, randomly select 10 apertures, measure the area of ​​each aperture, and take the average value. This average value is the projected area of ​​a single first protrusion in the middle segment on the first material layer. Count the number of apertures in the middle region of the middle segment, which is the number of first protrusions in the middle segment. The sum of the projected areas of the first protrusions on the first material layer = the projected area of ​​a single first protrusion on the edge segment × the number of first protrusions in the two edge segments + the projected area of ​​a single first protrusion on the middle segment × the number of first protrusions in the middle segment, which gives the sum of the areas of multiple first projections, S1.

[0071] In the edge region of the first material layer, randomly select 10 apertures and measure the area of ​​each aperture. Take the average value, which is the projected area of ​​a single second protrusion on the first material layer in the edge segment. Count the number of apertures on the two edge regions of the two edge segments, which is the number of second protrusions on the two edge segments. In the middle segment of the first material layer, randomly select 10 apertures and measure the area of ​​each aperture. Take the average value, which is the projected area of ​​a single second protrusion on the first material layer in the middle segment. Count the number of apertures on the two edge regions of the middle segment, which is the number of second protrusions on the middle segment. Then, the sum of the projected areas of the second protrusions on the first material layer = the projected area of ​​a single second protrusion on the edge segment × the number of second protrusions on the two edge segments + the projected area of ​​a single second protrusion on the middle segment × the number of second protrusions on the middle segment, which gives the sum of the areas of multiple second projections, S2.

[0072] Select any 10 first protrusions in the middle section, and measure the maximum height from the surface of the first material layer to each individual first protrusion along the thickness direction of the electrode. Take the average value, which is the average height H of all the first protrusions in the middle section. 11 Select any 10 second protrusions in the middle section, and measure the maximum height from the surface of the first material layer to each individual second protrusion along the thickness direction of the electrode. Take the average value, which is the average height H of all the second protrusions located in the middle section. 12 Select any two edge segments and choose 10 first protrusions. Along the thickness direction of the electrode, measure the maximum height from the surface of the first material layer to each individual first protrusion, and take the average value, which is the average height H of all the first protrusions located in the edge segments. 21 Select any two edge segments and choose 10 second protrusions. Along the thickness direction of the electrode, measure the maximum height from the surface of the first material layer to each individual second protrusion, and take the average value, which is the average height H of all second protrusions located in the edge segments.22 .

[0073] Along the thickness direction of the electrode, measure the distance from the surface of the first material layer to the surface of the current collector opposite to the first material layer, which is the sum of the thicknesses of the first material layer and the current collector, H0.

[0074] Cyclic performance test:

[0075] The lithium-ion batteries in the examples and comparative examples were subjected to charge-discharge cycle tests in a 25°C constant temperature chamber. The lithium-ion batteries were charged at a constant current of 2C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C. After resting for 5 minutes, they were discharged at a constant current of 6C to 2.5V. This was the first cycle, and the discharge capacity C1 of the first cycle was recorded. After 600 cycles following the above process, the discharge capacity C of the lithium-ion battery was recorded. 600 The capacity retention rate at 600 cycles was calculated as an indicator to evaluate the electrode wetting effect and the cycle performance of the lithium-ion battery, as shown in Equation (I). A lower capacity retention rate at 600 cycles (cls) indicates a poorer electrode wetting effect and worse cycle performance in the lithium-ion battery; conversely, a higher capacity retention rate at 600cls indicates a better electrode wetting effect and better cycle performance in the lithium-ion battery.

[0076] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0077] Lithium plating performance test:

[0078] The lithium-ion batteries from the examples and comparative examples were placed in a constant temperature chamber at 10°C for 60 minutes. They were then charged at a constant current of 2C to 4.2V, followed by constant voltage charging at 4.2V until the current reached 0.05C. After resting for 5 minutes, they were discharged at a constant current of 0.5C to 2.5V. This constituted one cycle. After 10 cycles of the above charge-discharge process, the batteries were charged again at a constant current of 2C to 4.2V, followed by constant voltage charging at 4.2V until the current reached 0.05C. After resting for 5 minutes, the lithium-ion batteries were disassembled, and the lithium plating on the electrode surface was observed. Areas without lithium plating appeared golden yellow, while areas with lithium plating appeared grayish-white.

[0079] The criteria for judging the degree of lithium plating in lithium-ion batteries are as follows: 0% lithium plating area is considered no lithium plating, i.e., the degree of lithium plating is zero; lithium plating area greater than 0 and less than or equal to 2% is considered mild lithium plating; lithium plating area greater than 2% and less than or equal to 20% is considered moderate lithium plating; and lithium plating area greater than 20% and less than or equal to 100% is considered severe lithium plating. The percentage of lithium plating area is calculated based on the total area of ​​the first material layer of the electrode.

[0080] In this application, those skilled in the art will understand that "C" refers to the rated capacity of the finished lithium-ion battery at the time of manufacture. "1C" is the current value that completely discharges the lithium-ion battery capacity in 1 hour, "0.1C" is the current value that completely discharges the lithium-ion battery capacity in 10 hours, and other rates follow the same principle.

[0081] Computed tomography (CT) scan and electrode indentation distance test:

[0082] The lithium-ion batteries in the examples and comparative examples were subjected to charge-discharge cycle tests in a 25°C constant temperature chamber. The lithium-ion batteries were charged at a constant current of 2C to 4.2V, charged at a constant voltage of 4.2V to 0.05C, and left to stand for 5 minutes. Then, they were discharged at a constant current of 6C to 2.5V. This was the first cycle. After 600 cycles according to the above cycle process, the lithium-ion batteries were disassembled to obtain the wound electrode assembly.

[0083] Using industrial computed tomography (industrial CT, Zeiss Xradia 620Versa), a CT scan is performed on the wound electrode assembly along the width direction (or the axis of the electrode assembly) after the electrode assembly is unfolded. The distance from the innermost ring of the electrode assembly to the outermost ring where the electrode deformation occurs is measured, which is the electrode indentation distance.

[0084] Example 1

[0085] <Preparation of the positive electrode>

[0086] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi). 0.91 Co 0.01 Mn 0.08 O2), polyvinylidene fluoride (PVDF) binder, and conductive carbon black were dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94.8:2.8:2.4 and thoroughly mixed to obtain a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated onto one surface of a 13 μm thick aluminum foil current collector and dried at 105 °C to obtain a positive electrode sheet with a first positive electrode material layer coated on one side. The above steps were then repeated on the other surface of the same aluminum foil to obtain a positive electrode sheet coated with both the first and second positive electrode material layers. After cold pressing, cutting, and slitting, the sheets were dried under vacuum at 105 °C for 4 hours to obtain positive electrode sheets with dimensions of 66.5 mm × 1422 mm for use. The coating weight of the positive electrode material layer was 234 mg / 1540.25 mm. 2 The compaction density of the positive electrode material layer is 3.6 g / cm³. 3 The specifications of the second positive electrode material layer are the same as those of 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 45 μm. The width of the empty foil area of ​​the positive electrode sheet is 4.5 mm.

[0087] <Preparation of Negative Electrode Sheets>

[0088] Artificial graphite (anode active material), SiO₂ (anode active material), sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 84:13:1.7:1.3. Deionized water was then added as a solvent, and the mixture was stirred until homogeneous, yielding a negative electrode slurry with a solid content of 50 wt%. This slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector and dried at 105 °C to obtain a negative electrode sheet with a first negative electrode material layer coated on one side. The same steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with both the first and second negative electrode material layers. After cold pressing, cutting, and slitting, negative electrode sheets with dimensions of 67.45 mm × 1436 mm were obtained for later use. The coating weight of the first and second negative electrode material layers was 110 mg / 1540.25 mm. 2 The first negative electrode material layer has a size of 62mm × 1436mm, the second negative electrode material layer has the same size as the first negative electrode material layer, the sum of the thickness of the first negative electrode material layer and the negative electrode current collector is 40μm, and the width of the empty foil area of ​​the negative electrode sheet is 5.45mm.

[0089] <Preparation of the diaphragm>

[0090] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0091] <Preparation of Electrolyte>

[0092] 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.

[0093] <Preparation of Lithium-ion Batteries>

[0094] The prepared separator, negative electrode sheet, separator, and positive electrode sheet are stacked sequentially and pre-wound to ensure the separator is positioned between the negative and positive electrodes, while ensuring the first positive electrode material layer is away from the center of the pre-wound electrode assembly, and the first segment of the first positive electrode material layer is located close to the center of the pre-wound electrode assembly. Along the length of the unfolded positive electrode sheet, the middle segment and two edge segments of the first positive electrode material layer are determined. Based on the length of the first positive electrode material layer, the length proportion L of the middle segment is 60%, and the length proportion L' of any edge segment is 20%. Based on the width of the first positive electrode material layer, the length proportion L1 of the middle region is 40%, and the length proportion L'1 of any edge segment is 30%. Along the thickness direction of the positive electrode sheet, the projection shape of a single protrusion on the first material layer is set to be circular, and the diameter D of the largest circumcircle of the projection of a single protrusion is 4mm. The average height H of all first protrusions located in the middle segment is... 11 The average height H of all the first protrusions located on the edge segment is 9 μm. 21 The average height H of all the second protrusions located in the middle section is 2.7 μm. 12 The average height H of all the second protrusions located on the edge segment is 1.636 μm. 22 The diameter is 0.9 μm; the distance A between two adjacent protrusions is 3 mm along the length direction of the unfolded positive electrode sheet; along the width direction of the unfolded positive electrode sheet, eight rows of first protrusions are set in the middle area, and ten rows of second protrusions are set in each of the two edge areas. Using embossing rollers of the corresponding specifications, the positive electrode sheet is cold-pressed on a winding machine according to the above parameters to obtain a positive electrode sheet with protrusions, a first concave portion, and a second concave portion. The electrode assembly is obtained by winding the core, and after flattening, current collector welding, casing, bottom penetration welding, inkjet coding, vacuum drying, electrolyte injection, sealing, and high-temperature standing, a lithium-ion battery is obtained after capacity formation. The upper limit of the formation voltage is 3.6V, the formation temperature is 45℃, and after formation, it is left to stand at room temperature (25℃) for 24 hours.

[0095] Examples 2 to 37

[0096] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1. Specifically, when S1 / S2 changes, the number of rows of the first protrusions set in the middle region along the width direction after the positive electrode sheet is unfolded is adjusted so that the values ​​of S1 / S2 are as shown in Table 1.

[0097] Example 38

[0098] Except that in the <Preparation of Lithium-ion Batteries>, when protrusions, a first recess, and a second recess are provided on the positive electrode sheet, and embossing rollers of the corresponding specifications are installed on the winding equipment according to the parameters in Table 1, and protrusions, a first recess, and a second recess are also provided on the negative electrode sheet, the rest is the same as in Example 1.

[0099] Comparative Example 1

[0100] Except that no protrusions are provided on the surface of the first material layer, the rest is the same as in Example 1.

[0101] Comparative Examples 2 to 4

[0102] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0103] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0104]

[0105]

[0106] As can be seen from Examples 1 to 38 and Comparative Examples 1 to 4, by adjusting the length ratio of the middle segment within the scope of this application, and by setting a first protrusion and a second protrusion on the middle region and two edge regions of the first material layer respectively, and making H 11 >H 12 H 21 >H 22 H 11 / H 12 >H 21 / H 22 The electrode indentation distance is shorter, resulting in less lithium plating in the lithium-ion battery, and the 600cls capacity retention rate is improved. This indicates that the lithium-ion battery of this application can effectively improve the electrode indentation caused by electrode expansion in the later stages of cycling, reduce the risk of lithium plating in the lithium-ion battery, and the lithium-ion battery has good cycle performance. In Comparative Example 1, no protrusions are provided on the first material layer; in Comparative Examples 2 and 3, the length ratio of the middle section is not within the scope of this application; in Comparative Example 4, H... 11 / H 12 <H 21 / H 22The lithium-ion batteries in Comparative Examples 1 to 3 exhibited longer electrode indentation distances, more severe lithium plating, and / or lower 600cls capacity retention. In contrast, the lithium-ion batteries in Examples 1 to 38 showed shorter electrode indentation distances, less severe lithium plating, and higher 600cls capacity retention, indicating less indentation of the inner electrode rings in the later stages of cycling, a lower risk of lithium plating, and good cycle performance.

[0107] H 11 / H 12 、H 21 / H 22 The value of H typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 6 to 11, when H... 11 / H 12 、H 21 / H 22 When the value is within the range of this application, the electrode indentation distance in the lithium-ion battery is relatively short, the degree of lithium plating is relatively mild, and the 600cls capacity retention rate is relatively high. This indicates that the degree of indentation of the inner electrode of the electrode assembly is relatively mild in the later stage of cycling, the risk of lithium plating in the lithium-ion battery is low, and the lithium-ion battery has good cycle performance.

[0108] The value of H0 typically affects the cycle performance of lithium-ion batteries. As seen in Examples 1, 12 to 15, when the value of H0 is within the range specified in this application, the electrode indentation distance in the lithium-ion battery is shorter, the degree of lithium plating is less, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode assembly is less in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery exhibits good cycle performance. In Example 12, the value of H0 is relatively small. When the first and second protrusions are provided on the electrode, the uneven distribution of the negative electrode active material particles within a unit area can easily lead to insufficient CB value in the later stages of cycling, resulting in lithium plating in the lithium-ion battery. In this application, the CB value refers to the ratio between the capacity of a unit area of ​​negative electrode and the capacity of a unit area of ​​positive electrode under the same conditions, such as an ambient temperature of 25°C and a discharge rate of 0.1C. CB = (Specific capacity of negative electrode active material × Mass of negative electrode active material per unit area of ​​negative electrode sheet) / (Specific capacity of positive electrode active material × Mass of positive electrode active material per unit area of ​​positive electrode sheet). The unit area mentioned above refers to 1 mm². 2 .

[0109] H 11 / H0×100%, H 21 The value of / H0×100% typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 16 to 21, when H... 11 / H0×100%, H 21When the value of / H0×100% is within the range of this application, the electrode indentation distance in the lithium-ion battery is relatively short, the degree of lithium plating is relatively mild, and the 600cls capacity retention rate is relatively high. This indicates that the degree of indentation of the inner electrode of the electrode assembly is relatively mild in the later stage of cycling, the risk of lithium plating in the lithium-ion battery is low, and the lithium-ion battery has good cycle performance.

[0110] The value of S1 / S2 typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 22 to 26, when the value of S1 / S2 is within the range of this application, the electrode indentation distance in the lithium-ion battery is shorter, the degree of lithium plating is less, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode assembly is less in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0111] The value of A typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 27 to 31, when the value of A is within the range of this application, the electrode indentation distance in the lithium-ion battery is shorter, the degree of lithium plating is milder, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode of the electrode assembly is milder in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0112] The value of D typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1, 32 to 37, when the value of D is within the range of this application, the electrode indentation distance in the lithium-ion battery is shorter, the degree of lithium plating is milder, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode of the electrode assembly is milder in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0113] The type of electrode used (positive or negative) typically affects the cycle performance of lithium-ion batteries. As seen in Examples 1 and 38, when the electrode is a positive or negative electrode, the electrode indentation distance in the lithium-ion battery is shorter, the degree of lithium plating is less, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode assembly is less in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery exhibits good cycle performance. In Example 38, both the positive and negative electrode plates are provided with a first protrusion and a second protrusion. This increases the amount of electrolyte stored on the positive and negative electrode plates, further improving electrolyte wetting of the electrode plates in the later stages of cycling and enhancing the cycle performance of the lithium-ion battery.

[0114] The presence of a first recess and / or a second recess typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1 to 38, when the first recess and / or the second recess are present, the electrode indentation distance in the lithium-ion battery is shorter, the degree of lithium plating is less, and the 600cls capacity retention rate is higher. This indicates that the degree of indentation of the inner electrode assembly is less in the later stages of cycling, the risk of lithium plating in the lithium-ion battery is lower, and the lithium-ion battery exhibits good cycle performance.

[0115] 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.

[0116] 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.

[0117] 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 having a wound structure, the electrode assembly comprising an electrode sheet, the electrode sheet comprising a current collector and a first material layer, the first material layer being located on the surface of the current collector opposite to the winding center of the electrode assembly; Along the length direction of the unfolded electrode sheet and along the winding direction of the electrode assembly, the first material layer includes a middle section and two edge sections connected to the middle section. Based on the length of the first material layer, the length ratio of the middle section is L, where 50% ≤ L ≤ 70%. Multiple protrusions are provided on the surfaces of the middle section and the two edge sections. Along the thickness direction of the electrode sheet, the average height of the multiple protrusions located in the middle section is H1 μm, and the average height of the multiple protrusions located in the two edge sections is H2 μm, where H1 > H2. Along the width direction of the unfolded electrode sheet, the first material layer includes a central region and two edge regions connected to the central region. The protrusion includes a first protrusion and a second protrusion. The first protrusion is located on the surface of the central region, and the second protrusion is located on the surface of the two edge regions. The average height of all the first protrusions located in the middle section is H. 11 μm, the average height of all the second protrusions located in the middle section is H 12 μm, the average height of all the first protrusions located in the edge segment is H 21 μm, the average height of all the second protrusions located in the edge segment is H 22 μm, H 11 >H 12 H 21 >H 22 H 11 / H 12 >H 21 / H 22 .

2. The cylindrical secondary battery according to claim 1, wherein, 3.6≤H 11 / H 12 ≤6.5,1.2≤H 21 / H 22 ≤5.5。 3. The cylindrical secondary battery according to claim 2, wherein it satisfies at least one of the following characteristics: (1)54％≤L≤64％； (2)4.5≤H 11 / H 12 ≤6.5; (3)2.2≤H 21 / H 22 ≤3.5。 4. The cylindrical secondary battery according to any one of claims 1 to 3, wherein, Along the thickness direction of the electrode, the sum of the thicknesses of the first material layer and the current collector is H0 μm, and 15% ≤ H 11 / H0×100%≤30%, 2%≤H 21 / H0×100%≤10%.

5. The cylindrical secondary battery according to claim 4, wherein, 18% ≤ H 11 / H0×100%≤25%; and / or, 5%≤H 21 / H0×100%≤8%.

6. The cylindrical secondary battery according to claim 4, wherein, 30≤H0≤80。 7. The cylindrical secondary battery according to claim 6, wherein, 35≤H0≤55。 8. The cylindrical secondary battery according to claim 1, wherein, Along the thickness direction of the electrode, a single first protrusion has a first projection on the first material layer, a single second protrusion has a second projection on the first material layer, and the sum of the areas of the plurality of first projections is S1μm. 2 The sum of the areas of the multiple second projections is S2μm 2 5% ≤ S1 / S2 ≤ 70%.

9. The cylindrical secondary battery according to claim 8, wherein, 25% ≤ S1 / S2 ≤ 50%.

10. The cylindrical secondary battery according to claim 1, wherein, Along the thickness direction of the electrode, each protrusion has a projection on the first material layer, and the diameter of the largest circumcircle of the outer contour of the projection is D mm, 0.5≤D≤10.

11. The cylindrical secondary battery according to claim 10, wherein, 2≤D≤6。 12. The cylindrical secondary battery according to claim 1, wherein, Along the length of the unfolded electrode, the distance between any two adjacent protrusions is A mm, where 1 ≤ A ≤ 10.

13. The cylindrical secondary battery according to claim 12, wherein, 1.5≤A≤5。 14. The cylindrical secondary battery according to claim 1, wherein, The electrode further includes a second material layer, which is located on the surface of the current collector facing the winding center of the electrode assembly. The surface of the second material layer is provided with a plurality of first recesses in the direction of the first material layer.

15. The cylindrical secondary battery according to claim 14, wherein, The 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 claim 1, wherein, The electrode is a positive electrode.

18. An electronic device comprising a cylindrical secondary battery as described in any one of claims 1 to 17.

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