Cylindrical secondary battery and electronic device

Abstract

The invention provides a cylindrical secondary battery and an electronic device, the cylindrical secondary battery comprises an electrode assembly, the electrode assembly comprises a pole piece, the pole piece comprises a first material layer, the first material layer comprises a middle section and an edge section, the length ratio L of the middle section is greater than or equal to 50% and less than or equal to 70%; the middle section and the edge section are both provided with protrusions, the height of the protrusion located on the middle section is H1 [mu] m, the height of the protrusion located on the edge section is H2 [mu] m, and H1 is larger than H2. The first material layer comprises a middle area and an edge area, and the protrusions comprise first protrusions and second protrusions. The height of the first protrusion located in the middle section is H11 microns, the height of the second protrusion located in the middle section is H12 microns, the height of the first protrusion located in the edge section is H21 microns, the height of the second protrusion located in the edge section is H22 microns, H11 is larger than H12, H21 is larger than H22, and H11 / H12 is larger than H21 / H22. Through the arrangement, the risk of lithium precipitation of the secondary battery is reduced.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a cylindrical secondary battery and an electronic device. Background Art

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

[0003] At present, the design of high-power cylindrical lithium-ion batteries usually adopts a full-ear design, that is, the positive and negative pole ears extend from opposite directions, and are prepared by flattening or kneading the full-ears. However, in the late cycle of the full-ear cylindrical lithium-ion battery, the pole piece expands, and the middle of the electrode assembly is squeezed, which easily leads to the enrichment of electrolyte on both sides of the pole piece, increasing the side reactions on the surface of the pole piece, resulting in increased impedance, increasing the risk of lithium plating in the lithium-ion battery, and reducing the cycle performance. Summary of the invention

[0004] The purpose of the present application is to provide a cylindrical secondary battery and electronic device to reduce the side reaction caused by the enrichment of electrolyte on both sides of the electrode due to the squeezing of the electrode in the late cycle, thereby reducing the risk of lithium plating caused by the increase of interfacial impedance due to the side reaction of the secondary battery, thereby improving the cycle performance of the cylindrical secondary battery and reducing the risk of short circuit caused by the expansion and collapse of the electrode in the late cycle.

[0005] It should be noted that in the invention content of the present application, the present application is explained by taking a lithium ion battery as an example of a cylindrical secondary battery, but the cylindrical secondary battery of the present application is not limited to a lithium ion battery.

[0006] The specific technical solutions are as follows:

[0007] The first aspect of the present application provides a cylindrical secondary battery, including an electrode assembly with a winding structure, the electrode assembly including a pole piece, the pole piece including a current collector and a first material layer, the first material layer being located on the surface of the current collector away from the winding center of the electrode assembly. Along the length direction of the pole piece after unfolding, and along the winding direction of the electrode assembly, the first material layer includes a middle section and two edge sections connected to the middle section, based on the length of the first material layer, the length of the middle section accounts for L, 50%≤L≤70%, optionally, 54%≤L≤64%; a plurality of protrusions are arranged on the surface of the middle section and the two edge sections, along the thickness direction of the pole piece, the average height of the plurality of protrusions located in the middle section is H1μm, and the average height of the plurality of protrusions located in the two edge sections is H2μm, H1>H2. Along the width direction of the pole piece after unfolding, the first material layer includes a middle area and two edge areas connected to the middle area, the protrusions include a first protrusion and a second protrusion, the first protrusion is located on the surface of the middle area, and the second protrusion is located on the surface of the two edge areas. The average height of all first protrusions located in the middle section is H 11 μm, the average height of all the second protrusions in the middle section is H 12 μm, the average height of all first protrusions located at the edge segment is H 21 μm, the average height of all the second protrusions 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 By providing protrusions of different heights in different areas of the pole piece and making the average height of the first protrusion located in the central area of ​​the middle section the highest, expansion space can be reserved for the pole piece, reducing the side reaction caused by the enrichment of electrolyte on both sides of the pole piece due to the squeezing of the pole piece in the late cycle, thereby reducing the risk of lithium deposition caused by the increase of interface impedance due to the side reaction of the secondary battery, thereby improving the cycle performance of the cylindrical secondary battery and reducing the risk of the pole piece collapsing and short circuit in the late cycle.

[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 When the value is within the above range, the side reaction caused by the enrichment of electrolyte on both sides of the electrode due to the squeezing of the electrode in the late cycle is reduced, and the risk of the electrode collapsing and short circuit in the late cycle is reduced. At the same time, the risk of the electrolyte enriching in the middle of the electrode and being unable to circulate effectively due to the reserved space being too large and causing side reactions is reduced, thereby reducing the risk of lithium plating in the secondary battery and improving the cycle performance of the secondary battery.

[0009] In one or more embodiments, along the thickness direction of the pole piece, the sum of the thickness of the first material layer and the current collector is H0 μm, 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 When the value of / H0×100% is within the above range, the side reaction caused by the enrichment of electrolyte on both sides of the electrode due to the squeezing of the electrode in the late cycle is reduced, and the risk of short circuit due to the electrode collapse in the late cycle is reduced. While taking into account the energy density of the secondary battery, the risk of lithium plating in the secondary battery is reduced, and the cycle performance of the secondary battery is improved.

[0010] In one or more embodiments, 30≤H0≤80; optionally, 35≤H0≤55. By adjusting the value of H0 within the above range, the secondary battery has a higher energy density while taking into account the processing performance of the electrode sheet.

[0011] In one or more embodiments, along the thickness direction of the pole piece, 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 S1 μm 2 The sum of the areas of multiple second projections is S2μm 2 , 5%≤S1 / S2≤70%, optionally, 25%≤S1 / S2≤50%. By regulating the value of S1 / S2 within the above range, the side reaction caused by the enrichment of electrolyte on both sides of the electrode due to the extrusion of the electrode in the late cycle is reduced, and the risk of the electrode collapsing and short circuit in the late cycle is reduced, the risk of lithium deposition 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 pole piece, a single protrusion has a projection on the first material layer, and the diameter of the maximum circumscribed circle of the outer contour of the projection is D mm, 0.5≤D≤10, optionally, 2≤D≤6. By regulating the diameter D of the maximum circumscribed circle of the outer contour of the projection of a single protrusion within the above range, it is helpful to reduce the side reaction caused by the enrichment of electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle, and at the same time reduce the risk of the pole piece collapsing and short circuit in the late cycle, reduce the risk of lithium deposition in the secondary battery, and thus improve the cycle performance of the secondary battery. The present application has no special restrictions on the projection shape of a single protrusion, as long as the purpose of the present application can be achieved.

[0013] In one or more embodiments, along the length direction of the pole piece after it is unfolded, the spacing between any two adjacent protrusions is Amm, 1≤A≤10, optionally, 1.5≤A≤5. By regulating the spacing A between two adjacent protrusions within the above range, it is helpful to reduce the side reaction caused by the enrichment of electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle, while reducing the risk of the pole piece collapsing and short circuit in the late cycle, reducing the risk of lithium deposition and improving the cycle performance of the secondary battery. In one or more embodiments, along the length direction of the pole piece after it is unfolded, the spacing between any two adjacent protrusions is equal.

[0014] In one or more embodiments, the pole piece further includes a second material layer, the second material layer is located on the surface of the current collector facing the winding center of the electrode assembly, and a plurality of first recesses are provided on the surface of the second material layer in the direction of the first material layer. In one or more embodiments, a plurality of second recesses are provided on the current collector 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 arrangement, the side reaction caused by the enrichment of the electrolyte on both sides of the pole piece due to the squeezing of the pole piece in the late cycle is further reduced, while the risk of the pole piece collapsing and short circuiting in the late cycle is reduced, and the risk of lithium deposition in the cylindrical secondary battery is reduced, thereby improving the cycle performance of the secondary battery while meeting the mass production manufacturability.

[0015] In one or more embodiments, the pole piece is a positive pole piece. The above arrangement is helpful to reduce the difficulty of processing the pole piece during the processing process, and further improves the cycle performance of the secondary battery.

[0016] The second aspect of the present application provides an electronic device, which includes the cylindrical secondary battery in any of the above embodiments. The cylindrical secondary battery of the present application has good cycle performance, so the electronic device of the present application has a long service life.

[0017] Beneficial effects of the embodiments of the present application:

[0018] The embodiment of the present application provides a cylindrical secondary battery and an electronic device, by adjusting the length ratio of the middle section within the above range, and respectively providing a first protrusion and a second protrusion on the middle area and two edge areas of the first material layer, and making H 11 >H 12 , H 21 >H 22 , H 11 / H 12 >H 21 / H 22 , protrusions of different heights are arranged in different regions on the first material layer of the pole piece, and the height of the protrusion in the middle of the pole piece is made to be the maximum to reserve expansion space, which can reduce the side reaction caused by the enrichment of electrolyte on both sides of the pole piece due to the squeezing of the pole piece in the late cycle, and at the same time reduce the risk of the pole piece sinking and short circuit in the late cycle, thereby reducing the risk of lithium precipitation caused by the increase of interface impedance due to side reactions in the secondary battery; at the same time, the reserved expansion space is moderate, and the distance between the positive and negative pole pieces and between the pole piece levels during the charging and discharging process is designed within a suitable range, and the electrochemical impedance of the secondary battery is small; in addition, protrusions of different heights are arranged in different regions on the first material layer, while taking into account the energy density of the secondary battery, the pole piece is evenly stressed, and when the pole piece expands, the risk of the pole piece being fractured due to stress is reduced, thereby improving the safety performance of the secondary battery. Therefore, the cylindrical secondary battery of the present application has good cycle performance.

[0019] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 A schematic diagram of a winding structure formed by an electrode assembly in one embodiment of the present application;

[0022] Figure 2 It is a partial front view of a positive electrode sheet after the electrode assembly in another embodiment of the present application is unfolded;

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

[0024] Figure numerals: electrode assembly 001; positive electrode plate 10; positive electrode collector 11; first positive electrode material layer 12; second positive electrode material layer 13; negative electrode plate 20; negative electrode 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 DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0026] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of a cylindrical secondary battery to explain the present application, but the cylindrical secondary battery of the present application is not limited to a lithium-ion battery.

[0027] In the prior art, cylindrical secondary batteries, such as cylindrical lithium-ion batteries, expand their pole pieces in the late stage of the cycle. Especially when the negative active material in the negative pole piece includes silicon, the negative pole piece undergoes relatively obvious expansion and contraction during the charge and discharge process, and the electrolyte in the middle of the pole piece is squeezed to both sides. The electrolyte is enriched on both sides of the pole piece and side reactions occur, which increases the interface impedance and causes lithium precipitation. In addition, in the late stage of the cycle, because the electrode assembly expands outward and is constrained by the shell, the inner ring pole piece in the electrode assembly will be concave inward to release stress, thereby causing the inner ring pole piece of the electrode assembly to be sunken. At this time, the distance between the positive pole piece and the negative pole piece in the electrode assembly is further increased, and some pole pieces may be broken, increasing the risk of short circuit of the secondary battery. At the same time, the increase in the distance between the positive and negative pole pieces will increase the impedance of the lithium-ion battery, and the cycle performance of the secondary battery will also decay rapidly. Based on this, the present application provides a cylindrical secondary battery and electronic device, which are beneficial to reducing the side reaction caused by the enrichment of electrolyte on both sides of the electrode due to the squeezing of the electrode in the late cycle, while reducing the degree of electrode collapse in the late cycle, thereby improving the cycle performance of the cylindrical secondary battery, and reducing the risk of lithium plating and short circuit caused by the increase of interface impedance due to side reactions in the secondary battery.

[0028] The first aspect of the present application provides a cylindrical secondary battery, including an electrode assembly with a winding structure, the electrode assembly including a pole piece, the pole piece including 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 pole piece after unfolding, 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 of the middle section accounts for L, 50%≤L≤70%, 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 consisting of any two of the values. A plurality of protrusions are arranged on the surface of the middle section and the two edge sections, and along the thickness direction of the pole piece, the average height of the plurality of protrusions located in the middle section is H1μm, and the average height of the plurality of protrusions located in the two edge sections is H2μm, H1>H2. Along the width direction of the unfolded pole piece, the first material layer includes a middle area and two edge areas connected to the middle area, and the protrusions include a first protrusion and a second protrusion. The first protrusion is located on the surface of the middle area, and the second protrusion is located on the surfaces of the two edge areas. The average height of all first protrusions located in the middle section is H 11 μm, the average height of all the second protrusions in the middle section is H 12 μm, the average height of all first protrusions located at the edge segment is H 21 μm, the average height of all the second protrusions 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 .

[0029] In the present application, the electrode sheet can be a positive electrode sheet and / or a negative electrode sheet. It is defined that when the electrode assembly is in the unfolded state, its own length direction is the X direction, its own width direction is the Y direction, and its own thickness direction is the Z direction. It can be understood that when the negative electrode sheet, the positive electrode sheet and the separator are in the unfolded state, their own length direction, width direction and thickness direction are the same as those of the electrode assembly, and the winding direction of the electrode assembly is the W direction. For example, Figures 1 to 3As shown, the electrode assembly 001 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 30. The positive electrode sheet 10 includes a positive electrode collector 11, a first positive electrode material layer 12 and a second positive electrode material layer 13. The negative electrode sheet 20 includes a negative electrode 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 electrode collector 11 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 electrode collector 11 toward the electrode assembly 00 1, the first negative electrode material layer 22 is located on the surface of the negative electrode 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 collector 21 facing the winding center of the electrode assembly 001. Along the length direction (X direction) of the positive electrode sheet 10 after unfolding, 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. A plurality of protrusions 121 are arranged on the surface 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 plurality of protrusions 121 located in the middle section M' to N is H1μm, and the average height of the plurality of protrusions 121 located in the two edge sections M to N and N to N' is H2μm. Along the width direction (Y direction) of the positive electrode sheet 10 after unfolding, the first positive electrode material layer 12 includes a middle area, that is, an area between the straight line EE' and the straight line FF' and two edge areas connected to the middle area (not shown in the figure), and the protrusion 121 includes a first protrusion 1211 and a second protrusion 1212. The first protrusion 1211 is located on the surface of the middle area, and the second protrusion 1212 is located on the surfaces of the two edge areas. The average height of all the first protrusions 1211 located in the middle section M' to N is H 11 μm, and the average height of all the second protrusions 1212 located in the middle section M' to N is H 12 μm, and the average height of all first protrusions 1211 located in the edge segments M to N and N to N' is H 21 μm, and the average height of all second protrusions 1212 located in the edge segments M to N and N to N' is H 22 μm.

[0030] During the charge and discharge process, the degree of extrusion of the pole piece along the length direction after unfolding is inconsistent, and the extrusion at both ends of the pole piece is relatively small. When the length proportion L of the middle section is too small, for example, less than the lower limit of the present application, that is, the length proportion of the edge section is too large, the area of ​​the protrusion set on the pole piece is too small, which affects the infiltration of the electrolyte into the middle of the pole piece and cannot effectively improve the cycle performance of the secondary battery. When the length proportion L of the middle section is too large, for example, greater than the upper limit of the present application, that is, the length proportion of the edge section is too small, at this time, more powder falls off during the processing of the pole piece, resulting in loss of active materials. At the same time, when the length proportion L of the middle section is too large, the number of pole piece layers in the electrode assembly of the same diameter is reduced, which will affect the energy density of the secondary battery, thereby weakening the competitiveness of the product; in addition, the length proportion L of the middle section is too large, that is, the average height of the corresponding protrusion is higher, which is easy to cause the phenomenon of electrolyte bridging between some pole piece layers, and the electrochemical impedance of the secondary battery increases, thereby increasing the risk of lithium precipitation in the secondary battery. When H 11 ≤H 12 , H 21 ≤H 22 and / or H 11 / H 12 ≤H 21 / H 22 At this time, the height of the protrusion set in the middle of the pole piece is small, and the expansion process reserved in the middle of the pole piece is too small. In the process of charging and discharging, it is impossible to effectively improve the risk of side reactions caused by the electrolyte enrichment on both sides of the pole piece due to the extrusion of the pole piece in the late cycle. The risk of lithium deposition in the secondary battery is high, and the cycle performance is poor. The present application adjusts the length ratio of the middle section within the above range, and sets the first protrusion and the second protrusion on the middle area and the two edge areas of the first material layer respectively, and makes H 11 >H 12 , H 21 >H 22 , H 11 / H 12 >H 21 / H 22, protrusions of different heights are arranged in different regions on the first material layer of the pole piece, and the height of the protrusion in the middle of the pole piece is made the largest, so that expansion space can be reserved, which can reduce the side reaction caused by the enrichment of electrolyte on both sides of the pole piece due to the squeezing of the pole piece in the late cycle, and reduce the risk of the pole piece sinking and short circuit in the late cycle, thereby reducing the risk of lithium precipitation caused by the increase of interface impedance due to side reactions in the secondary battery, thereby improving the cycle performance of the secondary battery; at the same time, the reserved expansion space is moderate, and the distance between the positive and negative pole pieces and between the pole piece levels during the charging and discharging process is designed within a suitable range, and the electrochemical impedance of the secondary battery is small; in addition, protrusions of different heights are arranged in different regions on the first material layer, while taking into account the energy density of the secondary battery, the pole piece is evenly stressed, and when the pole piece expands, the risk of the pole piece being fractured due to stress is reduced, thereby improving the safety performance of the secondary battery. Therefore, the cylindrical secondary battery of the present application has good cycle performance.

[0031] It should be noted that the "surface" of the first material layer located on the surface of the current collector facing away from the winding center of the electrode assembly can be the entire area of ​​the current collector surface or a partial area of ​​the current collector surface. This application has no special restrictions 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 of any edge segment accounts for L', 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 consisting of any two of these values. During the charging and discharging process, the degree of extrusion of the pole piece along the length direction after unfolding is inconsistent, wherein the extrusion at both ends of the pole piece is relatively small. By regulating the length of any edge segment to account for within the above range, expansion space is reserved at the edge segment of the pole piece, improving the infiltration of the electrolyte into the edge segment of the pole piece, while reducing the side reaction caused by the enrichment of the electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle, and at the same time reducing the risk of the pole piece collapsing and short circuiting in the late cycle, and reducing the risk of lithium precipitation caused by the secondary battery due to the increase of the interface impedance due to the side reaction, while taking into account the energy density, the cycle performance of the secondary battery is improved.

[0033] In one or more embodiments, Figure 2As shown, based on the width of the first material layer 10, the length of the middle area, that is, the area between the straight line where EE' and the straight line where FF' are located, accounts for L1, 30%≤L1≤50%. For example, the value of L1 can be 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50% or a range consisting of any two of these values. By regulating the length of the middle area within the above range, it is beneficial to reserve sufficient expansion space in the middle of the pole piece, reducing the side reaction caused by the enrichment of the electrolyte on both sides of the pole piece due to the squeezing of the pole piece in the late cycle, and at the same time reducing the risk of the pole piece collapsing and short circuiting in the late cycle, and reducing the risk of lithium precipitation caused by the secondary battery due to the increase of the interface impedance due to the side reaction, 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 ratio of any edge area is L'1, 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 values ​​therein. By regulating the length ratio of the edge area within the above range, expansion space is reserved in the edge area of ​​the electrode, which improves the infiltration of the electrolyte into the edge area of ​​the electrode, while reducing the side reaction caused by the enrichment of the electrolyte on both sides of the electrode due to the squeezing of the electrode in the late cycle. At the same time, the risk of the electrode collapse and short circuit in the late cycle is reduced, and the risk of lithium precipitation caused by the increase of the interface impedance of the secondary battery due to side reactions is reduced, 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 of 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 consisting 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 of 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 consisting of any two of them. 11 / H 12 , H 21 / H22 The value of within the above range is conducive to reserving expansion space in the middle of the electrode, reducing the risk of side reactions caused by the enrichment of electrolyte on both sides of the electrode due to the squeezing of the electrode in the late cycle, reducing the risk of the electrode collapsing and short circuit in the late cycle. At the same time, it also reduces the risk of side reactions caused by the enrichment of electrolyte in the middle of the electrode due to the inability to effectively circulate due to the reserved space being too large. In addition, the reserved expansion space is moderate, which is conducive to designing the distance between the positive and negative electrodes and between the electrode layers within a suitable range during the charge and discharge process. The electrochemical impedance of the secondary battery is small, reducing the risk of lithium precipitation caused by the increase of interface impedance due to side reactions in the secondary battery, thereby improving the cycle performance of the secondary battery.

[0036] In one or more embodiments, along the thickness direction of the pole piece, the sum of the thickness of the first material layer and the current collector is H0 μm, 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 consisting of any two of them. 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 consisting of any two of these values. 11 / H0×100%、H 21 The value of / H0×100% is within the above range, which is conducive to reserving expansion space in the middle of the electrode, reducing the side reaction caused by the enrichment of electrolyte on both sides of the electrode due to the squeezing of the electrode in the late cycle, reducing the risk of the electrode collapse and short circuit in the late cycle, and at the same time, it also reduces the risk of side reactions caused by the electrolyte enriching in the middle of the electrode and being unable to circulate effectively due to the reserved space being too large. In addition, the reserved expansion space is moderate, which is conducive to designing the distance between the positive and negative electrodes and between the electrode layers within a suitable range during the charge and discharge process. The electrochemical impedance of the secondary battery is small, while taking into account the energy density of the secondary battery, it reduces the risk of lithium precipitation caused by the increase of interface impedance due to side reactions in the secondary battery, thereby 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 consisting of any two of these values. By regulating the value of H0 within the above range, it is beneficial to the processing of the pole piece in the actual production process, reducing the risk of powder loss of the pole piece during the production process and the risk of short circuit of the secondary battery. The secondary battery has a higher energy density while taking into account the processing performance of the pole piece.

[0038] In the present application, the thickness of the first material layer can be regulated by means known to those skilled in the art. For example, when the slurry is coated on the surface of the current collector, the thickness of the first material layer can be increased by increasing the coating weight, and the thickness of the first material layer can be reduced by reducing the coating weight, based on a certain solid content of the slurry; when the electrode is cold-pressed, the thickness of the first material layer can be reduced by increasing the cold-pressing pressure, and the thickness of the first material layer can be increased by reducing the cold-pressing pressure. The present application does not have any particular restrictions on the method of regulating the thickness of the current collector, as long as the purpose of the present application can be achieved. For example, commercially available current collectors of different thicknesses can be selected, and combined with the "H 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 test", and then the current collector of the required thickness is selected. In one or more embodiments, the thickness of the current collector along the thickness direction of the pole piece can be 8μm to 20μm.

[0039] In one or more embodiments, along the thickness direction of the pole piece, 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 S1 μm 2 The sum of the areas of multiple second projections is S2μm 2, 5%≤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 consisting of any two of the values. By regulating the value of S1 / S2 within the above range, it is beneficial to reserve expansion space in the middle of the electrode, reduce the side reaction caused by the enrichment of electrolyte on both sides of the electrode due to the squeezing of the electrode in the late cycle, and reduce the risk of the electrode collapsing and short circuit in the late cycle. At the same time, it also reduces the risk of side reactions caused by the electrolyte enriching in the middle of the electrode and being unable to circulate effectively due to the reserved space being too large. In addition, the reserved expansion space is moderate, which is beneficial to designing the distance between the positive and negative electrodes and between the electrode layers within a suitable range during the charge and discharge process. The electrochemical impedance of the secondary battery is small, which reduces the risk of lithium precipitation caused by the increase of interface impedance due to side reactions in the secondary battery, thereby improving the cycle performance of the secondary battery.

[0040] In one or more embodiments, along the thickness direction of the pole piece, a single protrusion has a projection on the first material layer, and the diameter of the maximum circumscribed circle of the outer contour of the projection is D mm, such as 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 maximum 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 consisting of any two of the values. By regulating the diameter D of the maximum circumscribed circle of the outer contour of the projection of a single protrusion within the above range, it is beneficial to reduce the risk of the reserved expansion space being reduced due to the collapse of the protrusion during the preparation or cycle, so that the reserved space is moderate, which is beneficial to reduce the side reaction caused by the enrichment of the electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle, and at the same time reduce the risk of the pole piece being sunken and short-circuited in the late cycle; in addition, the size of the pit on the pole piece surface facing the winding center of the electrode assembly is moderate, reducing the risk of increased electrochemical impedance due to the increase of local electrolyte aggregation side reactions, and also improving the degree of indentation of the inner ring pole piece due to the expansion of the pole piece in the late cycle of the electrode assembly, thereby reducing the risk of lithium precipitation caused by the increase of the interface impedance of the secondary battery due to the side reaction, thereby improving the cycle performance of the secondary battery. The present application does not have any special restrictions on the projection shape of a single protrusion, as long as the purpose of the present application can be achieved. For example, the projection shape of a single protrusion can be at least one of a triangle, an arc (the area is smaller than a semicircle with the same radius), a semicircle, a rectangle, a trapezoid, a square or a pentagon and the above polygons.

[0041] In one or more embodiments, along the length direction of the pole piece after unfolding, the spacing between any two adjacent protrusions is equal. The above arrangement is conducive to improving the operability of setting the protrusions on the first material layer, and is conducive to reducing the side reaction caused by the enrichment of electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle, reducing the risk of the pole piece collapsing and short circuit in the late cycle, thereby reducing the risk of lithium deposition caused by the increased interface impedance of the cylindrical secondary battery due to the side reaction, and improving the cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0042] In one or more embodiments, along the length direction of the unfolded pole piece, the distance between two adjacent protrusions is A mm. Figure 2 As shown, along the length direction (X direction) of the positive electrode sheet 10 after unfolding, the spacing between two adjacent protrusions 121 is A mm. 1≤A≤10, 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 consisting of any two of the values. By regulating the spacing A between two adjacent protrusions within the above range, it is beneficial to reduce the processing difficulty of the pole piece during the processing process, reduce the risk of active material loss caused by excessive powder loss during the processing of the pole piece, and thus reduce the energy density of the secondary battery, so that the pore distribution of the pole piece is uniform, which is beneficial to the circulation of the electrolyte on the pole piece, and improves the infiltration effect of the electrolyte on the pole piece. It is beneficial to reduce the side reaction caused by the enrichment of the electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle, reduce the risk of the pole piece inwardly sinking and short circuit in the late cycle, and improve the degree of the inner circle pole piece inwardly sinking due to the expansion of the pole piece in the late cycle of the electrode assembly, thereby reducing the risk of lithium deposition in the cylindrical secondary battery. At the same time, the reserved space is moderate, and the positive and negative pole pieces and the pole piece layers can be tightly fitted during the charging and discharging process. The electrochemical impedance of the secondary battery during the charging and discharging process is small, thereby reducing the risk of lithium deposition caused by the secondary battery due to the increase of the interface impedance due to the side reaction 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 the two adjacent protrusions along the length direction after the pole piece 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 pattern on the first material layer. In one or more embodiments, when the protrusions are distributed in a matrix pattern on the first material layer, the spacing between adjacent rows in the same area along the width direction after the pole piece is unfolded is equal, that is, the distribution is equidistant. This application does not have any special restrictions on the number of rows of the first protrusions and the second protrusions, and those skilled in the art can set them according to the specifications of the actual pole piece, as long as the purpose of this application can be achieved.

[0044] In one or more embodiments, along the thickness direction of the pole piece, multiple protrusions are located on the same side of the pole piece. The above arrangement is conducive to improving the operability of setting the protrusions on the first material layer, and is conducive to reducing the side reaction caused by the enrichment of electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle, and reducing the risk of the pole piece collapsing and short circuit in the late cycle; thereby reducing the risk of lithium deposition caused by the increased interface impedance of the cylindrical secondary battery due to the side reaction, and improving the cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0045] In one or more embodiments, the electrode sheet further includes a second material layer, the second material layer is located on the surface of the current collector facing the winding center of the electrode assembly, and a plurality of first recesses are provided on the surface of the second material layer facing the first material layer. Figure 1 and Figure 3 As shown, the positive electrode sheet 10 also includes a second positive electrode material layer 13, which is located on the surface of the positive current collector 11 facing the winding center of the electrode assembly 001, and the surface of the second positive electrode material layer 13 is provided with 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 the protrusions and the first recesses on the electrode sheet is improved, which is conducive to improving the wetting performance of the electrolyte on the electrode sheet, further reducing the side reaction caused by the enrichment of the electrolyte on both sides of the electrode sheet due to the extrusion of the electrode sheet in the late cycle, reducing the risk of the electrode sheet sinking and short circuit in the late cycle, and improving the degree of the inner circle electrode sheet sinking due to the expansion of the electrode sheet in the late cycle of the electrode assembly, thereby reducing the risk of lithium precipitation caused by the side reaction of the cylindrical secondary battery due to the increase of the interface impedance, and improving the cycle performance of the secondary battery while meeting the mass production manufacturability. 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 it can be a partial area of ​​the current collector surface. There is no special limitation in this application, as long as the purpose of this application can be achieved.

[0046] In one or more embodiments, the current collector is provided with a plurality of second recesses in the direction of the first material layer. Figure 1 and Figure 3As shown, the positive electrode current collector 11 is provided with a plurality of second recesses 111 in the direction of the first positive electrode material layer 12. Through the above arrangement, the operability of providing the protrusions and the second recesses on the pole piece is improved, and the side reaction caused by the enrichment of the electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle is further reduced, and the risk of the pole piece sinking and short circuit in the late cycle is reduced, and the degree of the inner circle pole piece sinking due to the expansion of the pole piece in the late cycle of the electrode assembly is improved, thereby reducing the risk of lithium deposition caused by the increased interface impedance due to the side reaction of the cylindrical secondary battery, and improving the cycle performance of the secondary battery while meeting the mass production manufacturability.

[0047] In one or more embodiments, at least part of the first recess corresponds to part of the protrusion; and / or, at least part of the second recess corresponds to part of the protrusion. Through the above arrangement, the operability of setting the protrusion, the first recess and / or the second recess on the pole piece is improved, and the side reaction caused by the enrichment of the electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle is further reduced, and the risk of the pole piece sinking and short circuit in the late cycle is reduced, and the degree of the inner ring pole piece sinking due to the expansion of the pole piece in the late cycle of the electrode assembly is improved, thereby reducing the risk of lithium deposition caused by the increase of the interface impedance due to the side reaction of the cylindrical secondary battery, and improving the cycle performance of the secondary battery while meeting the mass production manufacturability.

[0048] In one or more embodiments, the pole piece is a positive pole piece. The above arrangement is conducive to reducing the difficulty of pole piece processing during processing, reducing the risk of active material loss due to excessive powder loss during pole piece processing and thus reducing the energy density of the secondary battery, and further reducing the side reaction caused by the enrichment of electrolyte on both sides of the pole piece due to the extrusion of the pole piece in the late cycle, reducing the risk of short circuit due to the inward collapse of the pole piece in the late cycle, improving the degree of inward collapse of the inner ring pole piece due to the expansion of the pole piece in the late cycle of the electrode assembly, thereby reducing the risk of lithium precipitation caused by the increase of interface impedance due to side reactions in the cylindrical secondary battery, and at the same time, the reserved expansion space is moderate, and the distance between the positive and negative pole pieces and between the pole piece layers during the charge and discharge process is within a suitable range, so that the electrochemical impedance of the secondary battery is small, thereby further improving the cycle performance of the secondary battery.

[0049] In the present application, when the electrode sheet is a positive electrode sheet, the present application has no special restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). At this time, the first material layer and the second material layer are both positive electrode material layers. The positive electrode material layer of the present application contains positive electrode active materials. The present application has no special restrictions on the type of positive electrode active materials, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganate, lithium iron manganese phosphate or lithium titanate, etc. In the present application, the positive active material may also contain non-metallic elements, for example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive current collector, as long as the purpose of the present application can be achieved. In the present application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. The present application does not particularly limit the type of positive electrode binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal 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 above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the mass ratio of the positive active material, the conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0050] In this 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 purpose of this 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 a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). In this application, there is no particular limitation on the thickness of the negative electrode current collector as long as the purpose of this 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 this application contains a negative electrode active material. There is no particular limitation on the type of the negative electrode active material in this application as long as the purpose of this 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, lithium titanate with a spinel structure Li4Ti5O 12 , Li-Al alloy, or at least one of 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 of this application as long as the purpose of this application can be achieved. For example, the conductive agent may be of the same type as the conductive agent in the above-mentioned positive electrode material layer. There is no particular limitation on the type of the negative electrode binder in the negative electrode material layer of this application as long as the purpose of this application can be achieved. For example, the negative electrode binder may be of the same type as the positive electrode binder in the above-mentioned positive electrode material layer. Optionally, the negative electrode material layer further includes a thickening agent. There is no particular limitation on the type of the thickening agent in this application as long as the purpose of this 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 of this application as long as the purpose of this 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 of this application. Those skilled in the art can select according to actual needs as long as the purpose of this application can be achieved.

[0051] The present application has no particular restrictions on the preparation method of the electrode sheet, as long as the purpose of the present application can be achieved. For example, the preparation method of the electrode sheet includes but is not limited to the following steps: (1) preparing slurry; (2) coating the slurry on one surface of the current collector, and drying to form a electrode sheet including a first material layer; (3) coating the slurry on the other surface of the current collector, and drying to obtain a 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 electrode sheet after unfolding and along the winding direction of the electrode assembly, and determining the middle area of ​​the first material layer and two edge areas connected to the middle area along the width direction of the electrode sheet after unfolding, respectively setting a first protrusion and a second protrusion on the surface of the middle section and the two edge sections, and obtaining the electrode sheet after cutting the sheet into strips.

[0052] The present application has no special restrictions on the solid content of the above-mentioned slurry, and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the process parameters of the above-mentioned drying, cutting, and striping, and those skilled in the art can choose according to actual needs, as long as the purpose of the present 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 toward 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 toward the first material layer.

[0053] In one or more embodiments, the current collector includes a coating area provided with a material layer and an empty foil area connected to the coating area, and at least a portion of the empty foil area forms a flattened portion. The above arrangement is conducive to the arrangement of the tabs and facilitates the processing of the secondary battery, thereby improving the safety performance and cycle performance of the cylindrical secondary battery.

[0054] The cylindrical secondary battery in the present application includes an electrolyte, and the electrolyte includes 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(oxalate borate) (LiBOB), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) or lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or ethyl methyl carbonate. The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate or vinyl ethylene carbonate. Fluorinated carbonate compounds may include but are not limited to at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2-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 above-mentioned carboxylate compound may include but is 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, valerolactone or caprolactone. The above-mentioned ether compound may include but is 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 above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0055] The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or at least one of aramid. The type of diaphragm may include at least one of woven membranes, non-woven membranes, microporous membranes, composite membranes, rolled membranes or spun membranes. The diaphragm of the present application may have a porous structure, and the present application has no particular restrictions on the size of the pore size of the porous structure of the diaphragm, as long as the purpose of the present application can be achieved. For example, the size of the pore size can be 0.01 μm to 1 μm. The present application has no particular restrictions on the thickness of the diaphragm, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm can be 5 μm to 40 μm.

[0056] The cylindrical secondary battery of the present application also includes a shell for accommodating a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, as well as other components known in the art in the cylindrical secondary battery, and the present application does not limit the above other components. The present application does not specifically limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of the present application.

[0057] The cylindrical secondary battery of the present application is not particularly limited, and may include any device that generates an electrochemical reaction. In one or more embodiments, the cylindrical secondary battery may include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0058] The present application has no particular restrictions on the preparation method of the cylindrical secondary battery, and a preparation method known in the art can be selected as long as the purpose of the present application can be achieved. For example, the preparation method of the cylindrical secondary battery includes but is not limited to the following steps: stacking the diaphragm, the negative electrode sheet, the diaphragm and the positive electrode sheet in order, and winding and folding them as needed to obtain an electrode assembly with a winding structure, placing the electrode assembly in a shell, welding the collector plate, assembling the insulating sheet, and then injecting the electrolyte into the shell and sealing it to obtain a cylindrical secondary battery.

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

[0060] The present application does not particularly limit the method for setting the first protrusion, the second protrusion, the first concave portion, and the second concave portion. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the pole piece can be cold-pressed by an embossing roller to set the first protrusion, the second protrusion, the first concave portion, and the second concave portion. The shape of the projection of a single first protrusion or a single second protrusion on the first material layer can be controlled by the shape of the stainless steel needle on the embossing roller; the average height H of all the first protrusions located in the middle section is 11 , the average height H of all the second protrusions located in the middle section 12 , the average height H of all first protrusions located in the edge segment 21 , the average height H of all the second protrusions located in the edge segment 22 It can be regulated by the cold pressing pressure value set by the embossing roller or the height specification of the stainless steel needles on the embossing roller; the spacing A between two adjacent protrusions (including the first protrusion and the second protrusion) can be regulated by the spacing between adjacent stainless steel needles on the embossing roller; the diameter D of the maximum circumscribed circle of the outer contour of the projection of a single protrusion (including the first protrusion and the second protrusion) on the first material layer can be regulated 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 regulated 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 arranged in the middle area along the width direction of the electrode after the electrode 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 regulated 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 arranged in the two edge areas along the width direction after the electrode is unfolded.

[0061] The second aspect of the present application provides an electronic device, which includes the cylindrical secondary battery in any of the above embodiments. The cylindrical secondary battery of the present application has good cycle performance, so the electronic device of the present application has a long service life.

[0062] The electronic device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. For example, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0063] Example

[0064] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0065] Test methods and equipment:

[0066] H 11 , H 12 , H 21 , H 22 , H0, S1, S2, A, D tests:

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

[0068] A scanning electron microscope (SEM) is used to observe the surface of the pole piece, that is, along the thickness direction of the pole piece, the plane formed by the length direction and the width direction after the pole piece is unfolded is measured. Due to the height difference between the height of the protrusion itself and the surface of the material layer, it can be seen that there is a relatively obvious color difference on the surface of the pole piece. The protrusion has a projected aperture on the surface of the pole piece, which can be used to distinguish the protrusion from the first material layer. Five apertures are selected, and the maximum circumscribed circle diameter of the outer contour of the projection of a single aperture on the first material layer is measured. The average value is the diameter D of the maximum circumscribed circle of the outer contour of the projection of a single protrusion. Along the length direction of the pole piece after unfolding, select a protrusion and measure the distance between the geometric center of the protrusion and the geometric center of the adjacent protrusion. Measure 5 times and take the average value, which is the spacing A between two adjacent protrusions.

[0069] The pole piece with the protrusion is ion polished along the length and thickness directions after the pole piece is unfolded to obtain the cross section of the pole piece. The cross section of the pole piece is measured by a scanning electron microscope (SEM), and it can be observed that there is a relatively clear boundary between the material layer and the current collector. Among them, the material layer with the protrusion is the first material layer. Along the thickness direction of the pole piece, according to the height change of the protrusion along the length direction after the pole piece is unfolded, the middle section of the first material layer and the two edge sections connected to the middle section are determined. Along the thickness direction of the pole piece, according to the height change of the protrusion along the width direction after the pole piece is unfolded, the middle area of ​​the first material layer and the two edge areas connected to the middle area are determined. The protrusion arranged on the surface of the middle area is the first protrusion, and the protrusion arranged on the surface of the two edge areas is the second protrusion.

[0070] Select any 10 apertures in the middle area of ​​the edge segment of the first material layer, measure the area of ​​each aperture, take the average value, which is the projection area of ​​each first protrusion on the edge segment on the first material layer, count the number of apertures in the middle area of ​​the two edge segments, that is, the number of first protrusions on the two edge segments; select any 10 apertures in the middle area of ​​the middle segment of the first material layer, measure the area of ​​each aperture, take the average value, which is the projection area of ​​each first protrusion on the middle segment on the first material layer, count the number of apertures in the middle area of ​​the pole piece, that is, the number of first protrusions on the middle segment; then the sum of the projection areas of the first protrusions on the first material layer = the projection area of ​​each first protrusion on the edge segment on the first material layer × the number of first protrusions on the two edge segments + the projection area of ​​each first protrusion on the middle segment on the first material layer × the number of first protrusions on the middle segment, that is, the sum of the areas of multiple first projections S1 is obtained.

[0071] Select any 10 apertures in the edge area of ​​the edge segment of the first material layer, measure the area of ​​a single aperture, take the average, which is the projection area of ​​a single second protrusion on the edge segment on the first material layer, count the number of apertures on the two edge areas of the two edge segments of the pole piece, that is, the number of second protrusions on the two edge segments; select any 10 apertures in the edge area of ​​the middle segment of the first material layer, measure the area of ​​a single aperture, take the average, which is the projection area of ​​a single second protrusion on the middle segment on the first material layer, count the number of apertures on the two edge areas of the pole piece, that is, the number of second protrusions on the middle segment; then the sum of the projection areas of the second protrusions on the first material layer = the projection area of ​​a single second protrusion on the edge segment on the first material layer × the number of second protrusions on the two edge segments + the projection area of ​​a single second protrusion on the middle segment on the first material layer × the number of second protrusions on the middle segment, that is, the sum of the areas of multiple second projections S2 is obtained.

[0072] Select 10 first protrusions in the middle section, and measure the maximum height from the surface of the first material layer to a single first protrusion along the thickness direction of the pole piece, and take the average value, that is, the average height H of all first protrusions in the middle section. 11 ; Select 10 second protrusions in the middle section, measure the maximum height from the surface of the first material layer to a single second protrusion along the thickness direction of the pole piece, and take the average value, that is, the average height H of all the second protrusions in the middle section 12 Select 10 first protrusions of any two edge segments, measure the maximum height from the surface of the first material layer to a single first protrusion along the thickness direction of the pole piece, and take the average value, that is, the average height H of all first protrusions located in the edge segment. 21 ; Select 10 second protrusions of any two edge segments, measure the maximum height from the surface of the first material layer to a single second protrusion along the thickness direction of the pole piece, and take the average value, that is, the average height H of all second protrusions located in the edge segment22 .

[0073] The distance measured from the surface of the first material layer to the surface of the current collector facing away from the first material layer along the thickness direction of the pole piece is the sum of the thicknesses H0 of the first material layer and the current collector.

[0074] Cycle performance test:

[0075] The lithium-ion batteries in the examples and comparative examples were subjected to a charge-discharge cycle test in a 25°C constant temperature box. The lithium-ion batteries were charged to 4.2V at a constant current of 2C, and then charged to 0.05V at a constant voltage of 4.2V. After standing for 5 minutes, they were discharged to 2.5V at a constant current of 6C. This was the first cycle, and the first cycle discharge capacity C1 was recorded. After 600 cycles according to the above cycle process, the lithium-ion battery discharge capacity C 600 , the cycle capacity retention rate of the 600th cycle is calculated as an indicator for evaluating the electrode wetting effect and the cycle performance of the lithium-ion battery, and the formula is shown in formula (I). When the 600-cycle (cls) capacity retention rate is lower, it indicates that the electrode wetting effect in the lithium-ion battery is worse, and the cycle performance of the lithium-ion battery is worse; when the 600cls capacity retention rate is higher, it indicates that the electrode wetting effect in the lithium-ion battery is better, and the cycle performance of the lithium-ion battery is better.

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

[0077] Lithium deposition performance test:

[0078] The lithium-ion battery in the embodiment and the comparative example is placed in a thermostat at 10°C. After 60 minutes, it is charged to 4.2V at 2C constant current, charged to 0.05C at 4.2V constant voltage, and left to stand for 5 minutes. Then, it is discharged to 2.5V at 0.5C constant current. This is one cycle. After 10 cycles of the above charge and discharge process, it is charged to 4.2V at 2C constant current, charged to 0.05C at 4.2V constant voltage, and left to stand for 5 minutes. After that, the lithium-ion battery is disassembled and the lithium deposition state of the electrode surface is observed. The surface area without lithium deposition is golden yellow, and the lithium deposition area is grayish white.

[0079] The criteria for judging the degree of lithium deposition in lithium-ion batteries are as follows: a lithium deposition area of ​​0% means no lithium deposition, i.e., the degree of lithium deposition is none; a lithium deposition area greater than 0 and less than or equal to 2% means mild lithium deposition, i.e., the degree of lithium deposition is mild; a lithium deposition area greater than 2% and less than or equal to 20% means moderate lithium deposition, i.e., the degree of lithium deposition is moderate; a lithium deposition area greater than 20% and less than or equal to 100% means severe lithium deposition, i.e., the degree of lithium deposition is severe, wherein the percentage of the lithium deposition 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 when it leaves the factory. "1C" is the current value that fully discharges the capacity of the lithium-ion battery within 1 hour, "0.1C" is the current value that fully discharges the capacity of the lithium-ion battery within 10 hours, and other multiples are similar.

[0081] Computerized tomography and pole piece indentation distance test:

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

[0083] Using industrial computed tomography (industrial CT, Zeiss Xradia 620Versa), the electrode assembly with a wound structure is CT scanned along the width direction of the electrode assembly after it is unfolded (or the axial direction of the electrode assembly), and the distance from the innermost circle of the electrode assembly to the outermost circle where the pole piece is deformed is measured, which is the pole piece indentation distance.

[0084] Example 1

[0085] <Preparation of positive electrode sheet>

[0086] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.91 Co 0.01 Mn 0.08 O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.8:2.8:2.4, and are fully stirred and mixed to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 105°C to obtain a positive electrode sheet coated with a first positive electrode material layer on one side. After that, the above steps are repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with a first positive electrode material layer and a second positive electrode material layer. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 105°C for 4h, and the positive electrode sheet with a size of 66.5mm×1422mm is ready for use. Among them, the coating weight of the positive electrode material layer is 234mg / 1540.25mm 2 The compaction density of the positive electrode material layer is 3.6g / cm 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 H0 of the first positive electrode material layer and the positive electrode current collector is 45 μm, and the width of the empty foil area of ​​the positive electrode sheet is 4.5 mm.

[0087] <Preparation of negative electrode sheet>

[0088] The negative electrode active material artificial graphite, the negative electrode active material silicon oxide material SiO, sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 84:13:1.7:1.3, and then deionized water is added as a solvent, and the mixture is stirred to obtain a negative electrode slurry with a solid content of 50wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm, and dried at 105°C to obtain a negative electrode sheet coated with a first negative electrode material layer on one side. After that, the above steps are repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet coated with a first negative electrode material layer and a second negative electrode material layer. Then, after cold pressing, cutting and stripping, a negative electrode sheet with a specification of 67.45mm×1436mm is obtained for standby use. Among them, the coating weight of the first negative electrode material layer and the second negative electrode material layer is 110mg / 1540.25mm 2 The specifications of the first negative electrode material layer are 62mm×1436mm, the specifications of the second negative electrode material layer are the same as those of the first negative electrode material layer, the sum of the thicknesses of the first negative electrode material layer and the negative electrode collector is 40μm, and the width of the empty foil area of ​​the negative electrode sheet is 5.45mm.

[0089] <Preparation of Separator>

[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 atmosphere glove box, organic solvents 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, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the base solvent, and the electrolyte was obtained after being fully mixed. Based on the mass of the electrolyte, the mass percentage of LiPF6 is 12.5%, and the balance is the base solvent.

[0093] <Preparation of lithium-ion batteries>

[0094] The prepared diaphragm, negative electrode sheet, diaphragm, and positive electrode sheet are stacked in order, and pre-wound first to ensure that the diaphragm is between the negative electrode and the positive electrode, and at the same time ensure that the first positive electrode material layer is away from the center of the pre-wound electrode assembly, and the first section of the first positive electrode material layer is located near the center of the pre-wound electrode assembly. Along the length direction of the unfolded positive electrode sheet, the middle section and two edge sections of the first positive electrode material layer are determined. Based on the length of the first positive electrode material layer, the length of the middle section accounts for L60%, and the length of any edge section accounts for L'20%. Based on the width of the first positive electrode material layer, the length of the middle area accounts for L1 to 40%, and the length of any edge section accounts for L'1 to 30%. Set the projection shape of a single protrusion on the first material layer along the thickness direction of the positive electrode sheet to be circular, the diameter D of the maximum circumscribed circle of the outer contour of the projection of a single protrusion is 4 mm, and the average height H of all first protrusions located in the middle section 11 The average height H of all the first protrusions located at the edge segment is 9 μm. 21 The average height H of all the second protrusions in the middle section is 2.7 μm. 12 The average height H of all the second protrusions located at the edge segment is 1.636 μm. 22 is 0.9μm; along the length direction of the positive electrode sheet after it is unfolded, the spacing A between two adjacent protrusions is 3mm; along the width direction of the positive electrode sheet after it is unfolded, 8 rows of first protrusions are set in the middle area, and 10 rows of second protrusions are set in each of the two edge areas. According to the above parameters, an embossing roller of corresponding specifications is installed on the winding equipment to cold press the positive electrode sheet to obtain a positive electrode sheet with protrusions, first recesses and second recesses. The electrode assembly is obtained by winding the core, and after flattening, current collector welding, shelling, bottom penetration welding, coding, vacuum drying, electrolyte injection, sealing, high-temperature standing, and then forming the capacity, a lithium-ion battery can be obtained. Among them, the upper limit voltage of formation is 3.6V, the formation temperature is 45°C, and after formation, it is left to stand at room temperature 25°C for 24 hours.

[0095] Example 2 to Example 37

[0096] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1. When S1 / S2 changes, the number of rows of the first protrusions arranged on the middle area along the width direction of the unfolded positive electrode sheet is adjusted so that the value of S1 / S2 is as shown in Table 1.

[0097] Embodiment 38

[0098] Except that in <Preparation of Lithium-ion Battery>, when the protrusion, the first recess and the second recess are set on the positive electrode sheet, an embossing roller of corresponding specifications is also used according to the parameters in Table 1, and an embossing roller that meets the above specifications is installed on the winding equipment to also set the protrusion, the first recess and the second recess on the negative electrode sheet, the rest is the same as 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 that of Example 1.

[0101] Comparative Example 2 to Comparative Example 4

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

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

[0104]

[0105]

[0106] It can be seen from Examples 1 to 38 and Comparative Examples 1 to 4 that by adjusting the length ratio of the middle section within the scope of the present application, and respectively providing the first protrusion and the second protrusion on the middle area and the two edge areas of the first material layer, and making H 11 >H 12 , H 21 >H 22 , H 11 / H 12 >H 21 / H 22 , the distance of the pole piece indentation is short, the lithium deposition degree of the lithium-ion battery is light, and the 600cls capacity retention rate is improved, indicating that the lithium-ion battery of the present application can effectively improve the pole piece indentation caused by the expansion of the pole piece in the electrode assembly in the late cycle, reduce the risk of lithium deposition in the lithium-ion battery, and the lithium-ion battery has good cycle performance. In Comparative Example 1, no protrusions are set on the first material layer; the length proportion of the middle section in Comparative Examples 2 and 3 is not within the scope of this application; in Comparative Example 4, H 11 / H 12 <H 21 / H 22. The lithium-ion batteries in Comparative Examples 1 to 3 have a longer pole piece indentation distance; a heavier degree of lithium deposition; and / or a lower 600cls capacity retention rate. However, the pole piece indentation distance in the lithium-ion batteries in Examples 1 to 38 is shorter, the degree of lithium deposition is lighter, and the 600cls capacity retention rate is higher, indicating that the degree of pole piece indentation in the inner circle of the electrode assembly is lighter in the later stage of the cycle, the risk of lithium deposition in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0107] H 11 / H 12 , H 21 / H 22 The value of usually affects the cycle performance of lithium-ion batteries. From Examples 1, 6 to 11, it can be seen that when H 11 / H 12 , H 21 / H 22 When the value is within the range of this application, the electrode plate indentation distance in the lithium-ion battery is shorter, the degree of lithium precipitation is lighter, and the 600cls capacity retention rate is higher, indicating that the degree of electrode plate indentation in the inner circle of the electrode assembly is lighter in the later stage of the cycle, the risk of lithium precipitation in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0108] The value of H0 usually affects the cycle performance of lithium-ion batteries. It can be seen from Examples 1, 12 to 15 that when the value of H0 is within the scope of this application, the indentation distance of the pole piece in the lithium-ion battery is shorter, the degree of lithium precipitation is lighter, and the 600cls capacity retention rate is higher, indicating that the degree of indentation of the inner ring pole piece of the electrode assembly is lighter in the later stage of the cycle, the risk of lithium precipitation in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance. Among them, the value of H0 in Example 12 is smaller. At this time, when the first protrusion and the second protrusion are set on the pole piece, due to the uneven distribution of the particles of the negative electrode active material per unit area, the CB value is easily insufficient in the later stage of the cycle, and lithium ion batteries undergo lithium precipitation. In this application, the CB value refers to the ratio between the capacity of the negative electrode pole piece per unit area and the capacity of the positive electrode pole piece per unit area under the same conditions, for example, at an ambient temperature of 25°C and a discharge rate of 0.1C. CB = (gram capacity of negative electrode active material × mass of negative electrode active material per unit area of ​​negative electrode sheet) / (gram capacity of positive electrode active material × mass of positive electrode active material per unit area of ​​positive electrode sheet). The above unit area refers to 1mm 2 .

[0109] H 11 / H0×100%、H 21 The value of / H0×100% usually affects the cycle performance of lithium-ion batteries. It can be seen from Examples 1, 16 to 21 that when H 11 / H0×100%、H 21When the value of / H0×100% is within the scope of the present application, the indentation distance of the pole piece in the lithium-ion battery is shorter, the degree of lithium precipitation is lighter, and the 600cls capacity retention rate is higher, indicating that the degree of indentation of the inner circle pole piece of the electrode assembly is lighter in the later stage of the cycle, the risk of lithium precipitation in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0110] The value of S1 / S2 usually affects the cycle performance of lithium-ion batteries. It can be seen from Examples 1 and 22 to 26 that when the value of S1 / S2 is within the range of this application, the distance of the pole piece in the lithium-ion battery is short, the degree of lithium precipitation is light, and the 600cls capacity retention rate is high, indicating that the degree of the inner ring pole piece of the electrode assembly is light in the later stage of the cycle, the risk of lithium precipitation in the lithium-ion battery is low, and the lithium-ion battery has good cycle performance.

[0111] The value of A usually affects the cycle performance of lithium-ion batteries. It can be seen from Examples 1 and 27 to 31 that when the value of A is within the range of this application, the pole piece indentation distance in the lithium-ion battery is shorter, the degree of lithium precipitation is lighter, and the 600cls capacity retention rate is higher, indicating that the degree of indentation of the inner ring pole piece of the electrode assembly is lighter in the later stage of the cycle, the risk of lithium precipitation in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0112] The value of D usually affects the cycle performance of lithium-ion batteries. It can be seen from Examples 1 and 32 to 37 that when the value of D is within the range of this application, the indentation distance of the pole piece in the lithium-ion battery is short, the degree of lithium precipitation is light, and the 600cls capacity retention rate is high, indicating that the degree of indentation of the inner ring pole piece of the electrode assembly is light in the later stage of the cycle, the risk of lithium precipitation in the lithium-ion battery is low, and the lithium-ion battery has good cycle performance.

[0113] The fact that the pole piece is a positive pole piece and / or a negative pole piece usually affects the cycle performance of the lithium-ion battery. It can be seen from Example 1 and Example 38 that when the pole piece is a positive pole piece and / or a negative pole piece, the pole piece in the lithium-ion battery has a shorter indentation distance, a lighter degree of lithium precipitation, and a higher 600cls capacity retention rate, indicating that the inner ring pole piece of the electrode assembly has a lighter indentation degree in the later stage of the cycle, and the risk of lithium precipitation in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance. Among them, in Example 38, the first protrusion and the second protrusion are provided on both the positive pole piece and the negative pole piece. At this time, the electrolyte stored on the positive and negative pole pieces increases, which further improves the infiltration of the electrolyte into the pole piece in the later stage of the cycle, and improves the cycle performance of the lithium-ion battery.

[0114] When the first recess and / or the second recess are provided, the cycle performance of the lithium-ion battery is usually affected. From Examples 1 to 38, it can be seen that when the first recess and / or the second recess are provided, the indentation distance of the pole piece in the lithium-ion battery is shorter, the degree of lithium precipitation is lighter, and the 600cls capacity retention rate is higher, indicating that the degree of indentation of the inner ring pole piece of the electrode assembly is lighter in the later stage of the cycle, the risk of lithium precipitation in the lithium-ion battery is lower, and the lithium-ion battery has good cycle performance.

[0115] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method or article.

[0116] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0117] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A cylindrical secondary battery, comprising an electrode assembly having a winding structure, the electrode assembly comprising a pole piece, the pole piece comprising a current collector and a first material layer, the first material layer being located on a surface of the current collector away from the winding center of the electrode assembly; Along the length direction of the pole piece after unfolding and along the winding direction of the electrode assembly, the first material layer includes a middle section and two edge sections connected to the middle section, based on the length of the first material layer, the length of the middle section accounts for L, 50%≤L≤70%; a plurality of protrusions are arranged on the surface of the middle section and the two edge sections, along the thickness direction of the pole piece, the average height of the plurality of protrusions located in the middle section is H1μm, and the average height of the plurality of protrusions located in the two edge sections is H2μm, H1>H2; Along the width direction of the pole piece after unfolding, the first material layer includes a middle area and two edge areas connected to the middle area, the protrusion includes a first protrusion and a second protrusion, the first protrusion is located on the surface of the middle area, and the second protrusion is located on the surfaces of the two edge areas; 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, which 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 pole piece, the sum of the thickness of the first material layer and the current collector is H0 μm, 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 any one of claims 1 to 7, wherein: Along the thickness direction of the pole piece, 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 S1 μm 2 The sum of the areas of the plurality of second projections is S2 μm 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 any one of claims 1 to 9, wherein: Along the thickness direction of the pole piece, a single protrusion has a projection on the first material layer, and the diameter of the maximum circumscribed circle 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 any one of claims 1 to 11, wherein: Along the length direction of the pole piece after unfolding, the distance between any two adjacent protrusions is Amm, 1≤A≤10.

13. The cylindrical secondary battery according to claim 12, wherein: 1.5≤A≤5。 14. The cylindrical secondary battery according to any one of claims 1 to 13, wherein: The pole piece further includes a second material layer, which is located on the surface of the current collector facing the winding center of the electrode assembly, and a plurality of first recesses are provided on the surface of the second material layer toward the first material layer.

15. The cylindrical secondary battery according to claim 14, wherein: The current collector is provided with a plurality of second recesses toward the first material layer.

16. The cylindrical secondary battery according to claim 15, wherein: At least part of the first recess corresponds to part of the protrusion; And / or, at least part of the second recess corresponds to part of the protrusion.

17. The cylindrical secondary battery according to any one of claims 1 to 16, wherein: The pole piece is a positive pole piece. 18 . An electronic device comprising the cylindrical secondary battery according to claim 1 .

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