Cylindrical secondary battery and electronic device

Abstract

The present application provides a cylindrical secondary battery and an electronic device, the cylindrical secondary battery including an electrode assembly including a pole piece including a first current collector and a first material layer on one surface of the first current collector. The first material layer comprises a first section and a second section which are sequentially connected from the ending end of the pole piece along the length direction of the unfolded pole piece, the length ratio of the first section is K (1% < = K < = 10%) based on the length of the first material layer, and a plurality of bulges are arranged on the surface of the first section. Through the arrangement, actual production requirements are considered, and the safety performance and the cycle performance of the cylindrical secondary battery are improved.

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 fields and have the characteristics of large specific energy, high operating voltage, low self-discharge rate, small size, and light weight. They are widely used in the field of consumer electronics.

[0003] However, in the later stages of the lithium-ion battery cycle, the electrode expands, resulting in excessive tensile stress in the electrode, especially in the outer ring of the electrode, stretching and extending the current collector, making the electrode prone to breakage, and reducing the safety and cycle performance of the secondary battery. Summary of the invention

[0004] The purpose of the present application is to provide a cylindrical secondary battery and an electronic device, which are conducive to reducing the tensile stress generated by the expansion of the pole piece during the cycle and improving the safety performance and cycle performance of the cylindrical secondary battery.

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

[0006] The first aspect of the present application provides a cylindrical secondary battery, the cylindrical secondary battery includes an electrode assembly, the electrode assembly includes a pole piece, the pole piece includes a first current collector and a first material layer located on a surface of the first current collector. From the end of the pole piece, along the length direction of the pole piece after the pole piece is unfolded, the first material layer includes a first section and a second section connected in sequence, based on the length of the first material layer, the length of the first section accounts for K, 1%≤K≤10%, optionally, 4%≤K≤10%; a plurality of protrusions are provided on the surface of the first section. By providing a protrusion on the first section and adjusting the length of the first section to be within the above range, the protrusion is provided at the end of the pole piece, so that the outer ring of the electrode assembly has expansion space, reducing the tensile stress generated by the expansion of the pole piece during the cycle of the secondary battery, which is conducive to reducing the safety risk of the pole piece, especially the current collector such as aluminum foil, being broken and generating burrs due to excessive tensile stress. At the same time, it is conducive to improving the infiltration effect of the electrolyte on the pole piece, while taking into account the actual production requirements, the safety performance and cycle performance of the cylindrical secondary battery are improved.

[0007] In one or more embodiments, along the length direction of the pole piece after unfolding, and along the direction away from the end of the pole piece, the second section includes a first area, a second area and a third area connected in sequence; based on the length of the first material layer, the length of the first area accounts for K1, and the length of the second area accounts for K2, 10%≤K1≤40%; 20%≤K2≤60%, optionally, 30%≤K2≤50%. In the second section, a plurality of protrusions are arranged on the surface of only the second area. By arranging protrusions on the first section and the second area of ​​the second section, the protrusions are arranged intermittently so that the outer ring of the electrode assembly and the inner ring of the electrode assembly have expansion space, which is conducive to further reducing the tensile stress and extrusion force generated by the expansion of the pole piece during the cycle of the secondary battery, and reducing the safety risk of excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, which causes the pole piece, especially the current collector such as aluminum foil, to break, generate burrs and short circuit, thereby further improving the safety performance and cycle performance of the cylindrical secondary battery.

[0008] In one or more embodiments, the average height of the plurality of protrusions is Hμm, 10≤H≤160, optionally, 35≤H≤110. By regulating the average height H of the plurality of protrusions within the above range, the outer ring of the electrode assembly has expansion space, which is conducive to reducing the safety risk of excessive tensile stress and excessive stretching of the outer ring of the electrode assembly, which may cause the pole piece, especially the current collector such as aluminum foil, to break, generate burrs and cause short circuit, thereby improving the safety performance and cycle performance of the cylindrical secondary battery.

[0009] In one or more embodiments, the thickness of the first current collector is T μm, 8 ≤ T ≤ 16. By adjusting the thickness T of the first current collector within the above range, it is beneficial to enhance the mechanical strength of the first current collector, thereby enhancing the mechanical strength of the first pole piece, and further improving the safety performance of the cylindrical secondary battery.

[0010] In one or more embodiments, a plurality of protrusions are distributed in a dotted manner on the first material layer, and along the thickness direction of the first pole piece, the projection shape of a single protrusion on the first material layer is circular, elliptical or polygonal, and the diameter of the maximum circumscribed circle of the outer contour of the projection is D1 mm, 3≤D1≤7. By regulating the diameter D1 of the maximum circumscribed circle of the outer contour of the projection within the above range, it is helpful to reduce the risk of the reserved expansion space being reduced due to the collapse of the protrusions during the preparation or cycle process, thereby improving the safety performance and cycle performance of the secondary battery.

[0011] In one or more embodiments, along the length direction of the unfolded pole piece, the distance between two adjacent protrusions is A1mm, 5≤A1≤15. By adjusting the distance A1 between two adjacent protrusions within the above range, it is helpful to reduce the difficulty of processing the pole piece during processing, reduce the risk of active material loss due to excessive powder loss during pole piece processing and thus reduce the energy density of the secondary battery, thereby improving the safety performance and cycle performance of the secondary battery.

[0012] In one or more embodiments, along the thickness direction of the pole piece, the projection shape of a single protrusion on the first material layer is a strip, and multiple protrusions extend along the width direction of the pole piece after it is unfolded and are arranged at intervals along the length direction of the pole piece after it is unfolded. Along the length direction of the pole piece after it is unfolded, the width of the projection is D2 mm, 5≤D2≤10. By regulating the projection width D2 within the above range, it is helpful to reduce the risk of the reserved expansion space being reduced due to the collapse of the protrusions during the preparation or cycle process, thereby improving the safety performance and cycle performance of the secondary battery.

[0013] In one or more embodiments, along the length direction of the unfolded pole piece, the distance between two adjacent protrusions is A2 mm, 5≤A2≤15. By adjusting the distance A2 between two adjacent protrusions within the above range, it is helpful to reduce the difficulty of processing the first pole piece during processing, reduce the risk of active material loss due to excessive powder loss during the processing of the first pole piece, and thus reduce the energy density of the secondary battery, thereby improving the safety performance and cycle performance of the secondary battery.

[0014] In one or more embodiments, along the width direction of the unfolded pole piece, the first material layer has a first edge and a second edge relative to each other, and the shortest distance between a single protrusion and the first edge or the second edge is L1 mm, 5≤L1≤15. By regulating the shortest distance L1 between a single protrusion and the first edge or the second edge within the above range, it is helpful to reduce the risk of active material loss caused by excessive powder loss of the first material layer during pole piece processing, reduce the safety risk of actual production process operation, and thus improve the safety performance and cycle performance of the secondary battery.

[0015] In one or more embodiments, along the length direction of the pole piece after unfolding, the end of the first material layer includes a first end face, and the shortest distance between a single protrusion in the first section and the first end face is L2 mm, 5≤L2≤15. By regulating the shortest distance L2 between a single protrusion in the first section and the first end face within the above range, it is helpful to reduce the risk of active material loss caused by excessive powder loss of the first material layer during the pole piece processing, reduce the safety risk of actual production process operation, and thus improve the safety performance and cycle performance of the secondary battery.

[0016] In one or more embodiments, the first material layer is located on a surface of the first current collector facing away from a winding center of the electrode assembly.

[0017] In one or more embodiments, the pole piece further includes a second material layer, which is located on the surface of the first current collector facing the winding center of the electrode assembly, and a plurality of first recesses are provided on the surface of the second material layer facing the first material layer.

[0018] In one or more embodiments, the first current collector is provided with a plurality of second recesses toward the first material layer.

[0019] 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 the second recess on the pole piece is improved, and the tensile stress generated by the expansion of the pole piece during the cycle of the secondary battery is further reduced, thereby reducing the safety risk of the pole piece, especially the current collector such as aluminum foil, breaking, generating burrs and short circuiting due to excessive tensile stress and excessive stretching of the outer ring of the electrode assembly, thereby improving the safety performance and cycle performance of the secondary battery while meeting the mass production manufacturability.

[0020] In one or more embodiments, the pole piece is a positive pole piece.

[0021] In one or more embodiments, the electrode assembly further includes another pole piece having a polarity opposite to that of the pole piece, the other pole piece includes a second current collector and a third material layer located on at least one surface of the second current collector, the third material layer includes silicon.

[0022] 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 safety performance and cycle performance, so the electronic device of the present application has a long service life.

[0023] Beneficial effects of the embodiments of the present application:

[0024] The embodiment of the present application reserves expansion space for the pole piece by designing a protrusion at the tail of the pole piece, thereby effectively reducing the tensile stress generated by the expansion of the pole piece during the cycle of the secondary battery, which is beneficial to reducing the safety risk of short circuit caused by excessive tensile stress leading to breakage of the pole piece, especially the collector such as aluminum foil, generation of burrs, etc. In addition, the wetting effect of the electrolyte on the pole piece is improved, while taking into account the actual production requirements, thereby improving the safety performance and cycle performance of the cylindrical secondary battery.

[0025] 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

[0026] 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.

[0027] Figure 1This is a computer tomography (CT) image of a cylindrical lithium-ion battery with an outer ring pole piece fractured in the late cycle period in the prior art;

[0028] Figure 2 A schematic diagram of a winding structure formed by an electrode assembly in one embodiment of the present application;

[0029] Figure 3 A schematic diagram of a winding structure formed by an electrode assembly in another embodiment of the present application;

[0030] Figure 4 A partial front view of a positive electrode sheet after the electrode assembly in another embodiment of the present application is unfolded;

[0031] Figure 5 A partial front view of a positive electrode sheet after the electrode assembly in another embodiment of the present application is unfolded;

[0032] Figure 6 for Figure 5 The cross-sectional view of the positive electrode sheet along the PP direction;

[0033] Figure 7 It is a partial front view of the positive electrode sheet after the electrode assembly in another embodiment of the present application is unfolded.

[0034] Figure numerals: electrode assembly 001; positive electrode plate 10; first current collector 11; first material layer 12; second material layer 13; negative electrode plate 20; second current collector 21; third material layer 22; separator 30; protrusion 121; first recess 131; second recess 111; first edge 1201; second edge 1202; first end face 1203. DETAILED DESCRIPTION

[0035] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in 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.

[0036] It should be noted that in the specific embodiments 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.

[0037] In the prior art cylindrical secondary batteries, such as cylindrical lithium-ion batteries, the pole pieces expand in the later stages of the cycle. In particular, when the negative electrode material layer of the negative electrode piece contains silicon, the expansion and contraction of the negative electrode piece during the cycle is aggravated. For example, Figure 1As shown, the tensile stress of the outer ring of the electrode assembly is too large, and the pole piece is squeezed and stretched, which can easily cause the pole piece, especially the current collector such as aluminum foil, to break in the later stage of the cycle, resulting in burrs, and a short circuit during the charge and discharge process, which reduces the safety performance of the cylindrical lithium-ion battery and attenuates the cycle performance. Based on this, the present application provides a cylindrical secondary battery and an electronic device, which is conducive to reducing the safety risk of the pole piece, especially the current collector, breaking due to excessive tensile stress, thereby improving the safety performance and cycle performance of the cylindrical secondary battery.

[0038] A first aspect of the present application provides a cylindrical secondary battery, the cylindrical secondary battery comprising an electrode assembly, the electrode assembly comprising a pole piece, the pole piece comprising a first current collector and a first material layer located on a surface of the first current collector. Starting from the tail end of the pole piece, along the length direction of the pole piece after it is unfolded, the first material layer includes a first section and a second section connected in sequence. Based on the length of the first material layer, the length of the first section accounts for K, 1%≤K≤10%, optionally, 4%≤K≤10%, for example, the value of K can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10% or a range consisting of any two of the values. A plurality of protrusions are arranged on the surface of the first section.

[0039] 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. Exemplarily, the electrode sheet is a positive electrode sheet, such as Figure 2 As shown, the electrode assembly 001 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 30. The starting end of the positive electrode sheet 10 is close to the central hole of the electrode assembly 001, and the tail end of the positive electrode sheet 10 is away from the central hole of the electrode assembly 001. The positive electrode sheet 10 includes a first current collector 11 and a first material layer 12. The tail end of the first material layer 12 includes a first end face 1203. From the first end face 1203, along the length direction of the positive electrode sheet 10 after it is unfolded, the first material layer 12 includes a first section and a second section connected in sequence. The positive electrode sheet 10 is provided with a plurality of protrusions 121 on the surface of the first section. Among them, illustratively, as Figure 2 As shown, along the opposite direction of the winding direction W of the electrode assembly 001, the first section is from M to M', and the second section is from M' to N.

[0040] When the length of the first section accounts for K too small, for example, lower than the lower limit of the present application, the area of ​​the protrusion on the pole piece is too small, resulting in a small reserved expansion space, and the tensile stress caused by the expansion of the pole piece during the cycle cannot be effectively released. In the later stage of the cycle, the outer ring pole piece of the electrode assembly is overstretched, and the risk of the pole piece, especially the current collector such as aluminum foil, breaking and producing burrs increases, and short circuits are prone to occur during the charging and discharging process, which reduces the safety performance and cycle performance of the secondary battery. When the length of the first section accounts for K too large, for example, higher than the upper limit of the present application, the area of ​​the protrusion on the pole piece is too large, resulting in a large reserved expansion space, and the electrolyte is prone to breakage between the layers of some pole pieces, resulting in an increase in electrochemical impedance during the cycle of the secondary battery, which reduces the cycle performance of the secondary battery. At this time, the diameter of the electrode assembly is too large, which leads to a lower shell entry rate of the electrode assembly in the actual production process, and a low production qualification rate of lithium-ion batteries, which does not meet the actual production requirements, increases production costs and reduces production capacity, and has a low cost performance.

[0041] The present application sets a protrusion on the first section and adjusts the length ratio of the first section within the above range. The protrusion is set at the tail of the pole piece, so that the outer ring of the electrode assembly has expansion space, which reduces the tensile stress caused by the expansion of the pole piece during the cycle of the secondary battery, which is conducive to reducing the safety risk of excessive tensile stress, which causes the pole piece, especially the current collector such as aluminum foil, to break, produce burrs and short circuit due to excessive stretching of the outer ring of the electrode assembly. At the same time, it is conducive to increasing the infiltration speed of the electrolyte to the pole piece, thereby improving the safety performance and cycle performance of the cylindrical secondary battery; in addition, the above setting makes the average diameter of the electrode assembly within a suitable range, reduces the actual production cost and increases the production capacity. While taking into account the actual production requirements, the lithium-ion battery has good safety performance and cycle performance.

[0042] In one or more embodiments, based on the length of the first material layer, the length of the second segment accounts for K' of 90% to 99%. For example, the value of K' can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or a range consisting of any two of these values. By regulating the length of the second segment to be within the above range, the average diameter of the electrode assembly is within a suitable range, which is beneficial to reduce the safety risk of excessive tensile stress, excessive stretching of the outer ring of the electrode assembly, causing the pole piece, especially the current collector such as aluminum foil, to break, generate burrs and short-circuit, while taking into account the production cost and production capacity of the secondary battery.

[0043] In one or more embodiments, along the length direction of the pole piece after unfolding, and along the direction away from the end of the pole piece, the second section includes a first region, a second region and a third region connected in sequence; based on the length of the first material layer, the length of the first region accounts for K1, and the length of the second region accounts for K2, 10%≤K1≤40%; 20%≤K2≤60%, optionally, 30%≤K2≤50%. For example, the value of K1 can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40% or a range consisting of any two of the values, and the value of K2 can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60% or a range consisting of any two of the values. In the second section, only the second region has a plurality of protrusions disposed on its surface. Figure 3 and Figure 4 As shown, the end of the first material layer 12 on the positive electrode sheet 10 includes a first end face 1203. Along the length direction (X direction) of the positive electrode sheet 10 after unfolding, and in the direction away from the first end face 1203, the second section includes a first area, a second area and a third area connected in sequence. In the second section, a plurality of protrusions 121 are only provided on the surface of the second area. Figure 3 As shown, along the opposite direction of the winding direction W of the electrode assembly 001, the first area of ​​the second section is M' to M", the second area of ​​the second section is M" to N', and the third area of ​​the second section is N' to N. By providing protrusions on the first section and the second area of ​​the second section, the protrusions are intermittently provided so that the outer ring of the electrode assembly and the inner ring of the electrode assembly have expansion space, so that the average diameter of the electrode assembly is within a suitable range, which is beneficial to further reduce the tensile stress and extrusion force generated by the expansion of the electrode piece during the cycle of the secondary battery, and reduce the safety risk of the electrode piece, especially the current collector such as aluminum foil, breaking and generating burrs due to excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress and short circuit. At the same time, it is beneficial to reduce the safety risk of lithium deposition in the secondary battery due to the indentation of the inner ring of the electrode assembly due to excessive extrusion pressure. In addition, the wetting effect of the electrolyte on the electrode piece is improved, while taking into account the actual production requirements, the safety performance and cycle performance of the cylindrical secondary battery are further improved.

[0044] In one or more embodiments, based on the length of the first material layer, the length proportion of the third region is K3, 0%≤K3≤69%. For example, the value of K3 can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 67%, 69% or a range consisting of any two of the values. By regulating the length proportion of the third region within the above range, the average diameter of the electrode assembly is within a suitable range, which is conducive to reducing the safety risk of excessive tensile stress, excessive stretching of the outer ring of the electrode assembly, causing the pole piece, especially the current collector such as aluminum foil, to break, generate burrs and short-circuit, that is, the cylindrical secondary battery has good safety performance and cycle performance while taking into account the production cost and production capacity of the secondary battery.

[0045] In one or more embodiments, the average height of the plurality of protrusions is H μm, such as Figure 6 As shown, the average height of the plurality of protrusions 121 is H μm. 10≤H≤160, optionally, 35≤H≤110. For example, the value of H can be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160 or a range consisting of any two of the values. By regulating the average height H of multiple protrusions within the above range, the outer ring of the electrode assembly has expansion space and the average diameter of the electrode assembly is within a suitable range, which is beneficial to reducing the tensile stress caused by the expansion of the electrode piece during the cycle of the secondary battery, and reducing the safety risk of excessive tensile stress, which causes the electrode piece, especially the current collector such as aluminum foil, to break and generate burrs and short circuit due to excessive stretching of the outer ring of the electrode assembly, while the reserved space is moderate, the positive and negative electrode pieces and the electrode piece layers can be tightly fitted during the charge and discharge process, the electrochemical impedance of the secondary battery during the charge and discharge process is small, and the wetting effect of the electrolyte on the electrode piece is improved, while taking into account the production cost and production capacity of the secondary battery, the safety performance and cycle performance of the cylindrical secondary battery are improved.

[0046] In one or more embodiments, the thickness of the first current collector is T μm, such as Figure 6As shown, the thickness of the first current collector 11 is Tμm. 8≤T≤16. For example, the value of T can be 8, 9, 10, 11, 12, 13, 14, 15, 16 or a range consisting of any two of these values. By regulating the thickness T of the first current collector within the above range, it is beneficial to enhance the mechanical strength of the first current collector, thereby enhancing the mechanical strength of the pole piece, further reducing the pole piece expansion during the cycle, causing the outer ring of the electrode assembly to be overstretched, causing the pole piece, especially the current collector, such as aluminum foil, to break, produce burrs and short-circuit safety risks, thereby improving the safety performance of the cylindrical secondary battery. In addition, under the same battery specifications, the gap between the positive and negative pole pieces is moderate, taking into account the energy density of the secondary battery. The present application does not particularly limit the method for regulating the thickness of the first 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 the thickness of the first current collector can be determined in combination with the test method of "H, T, A1, A2, D1, D2, L1, L2 test" in the present application, and then the first current collector of the required thickness is selected.

[0047] In one or more embodiments, a plurality of protrusions are distributed in a dotted manner on the first material layer. Along the thickness direction of the pole piece, the projection shape of a single protrusion on the first material layer is circular, elliptical or polygonal, and the diameter of the maximum circumscribed circle of the outer contour of the projection is D1 mm. For example, Figure 5 As shown, a plurality of protrusions 121 are distributed in a dotted manner on the first material layer 12. Along the thickness direction (Z direction) of the positive electrode sheet 10, the projection shape of a single protrusion 121 on the first material layer 12 is circular, and the diameter of the maximum circumscribed circle of the outer contour of the projection is D1 mm. 3≤D1≤7. For example, the value of D1 can be 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or a range consisting of any two of these values. By adjusting the diameter D1 of the maximum circumscribed circle of the projected outer contour within the above range, it is helpful to reduce the risk of reduction of reserved expansion space due to collapse of protrusions during preparation or circulation, so that the reserved space is moderate, which is beneficial to reduce the tensile stress caused by expansion of the electrode piece during the circulation of the secondary battery, and reduces the safety risk of excessive tensile stress, excessive stretching of the outer ring of the electrode assembly, causing the electrode piece, especially the current collector such as aluminum foil, to break and produce burrs and short circuit. In addition, the pits on the surface of the electrode piece are of moderate size, which reduces the risk of increased electrochemical impedance due to increased local aggregation side reactions of the electrolyte, while taking into account the production cost and production capacity of the secondary battery, while improving the safety performance and cycle performance of the secondary battery.

[0048] In one or more embodiments, along the length direction of the pole piece after unfolding, the distance between two adjacent protrusions is A1mm. For example, Figure 5As shown, along the length direction (X direction) of the positive electrode plate 10 after unfolding, the spacing between two adjacent protrusions 121 is A1 mm. 5≤A1≤15. For example, the value of A1 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range consisting of any two values ​​therein. By regulating the spacing A1 between two adjacent protrusions within the above range, it is helpful to reduce the difficulty of processing the electrode during processing, reduce the risk of active material loss due to excessive powder loss during the processing of the electrode, and thus reduce the energy density of the secondary battery, so that the pore distribution of the electrode is uniform, which is conducive to the circulation of the electrolyte on the electrode and improves the infiltration effect of the electrolyte on the electrode. The tensile stress generated by the expansion of the pole piece during the cycle of the secondary battery is reduced, thereby reducing the safety risk of the pole piece, especially the current collector such as aluminum foil, being broken and generating burrs and short circuiting due to excessive tensile stress due to excessive stretching of the outer ring of the electrode assembly. 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, while taking into account the production cost and production capacity of the secondary battery, the safety performance and cycle performance of the secondary battery are improved. In this application, the spacing between two adjacent protrusions refers to the distance between the centers of the maximum circumscribed circles of the outer contours of the projections of the two adjacent protrusions on the first material layer along the thickness direction of the pole piece along the length direction after the first pole piece is unfolded.

[0049] In one or more embodiments, along the thickness direction of the pole piece, the projection shape of a single protrusion on the first material layer is a strip shape, and multiple protrusions extend along the width direction of the pole piece after it is unfolded and are arranged at intervals along the length direction of the pole piece after it is unfolded. Along the length direction of the pole piece after it is unfolded, the width of the projection is D2 mm. For example, Figure 7As shown, along the thickness direction (Z direction) of the positive electrode sheet 10, the projection shape of a single protrusion 121 on the first material layer 12 is a strip shape, and multiple protrusions 121 extend along the width direction (Y direction) of the positive electrode sheet 10 after it is unfolded and are arranged at intervals along the length direction (X direction) of the positive electrode sheet 10 after it is unfolded, and along the length direction (X direction) of the positive electrode sheet 10 after it is unfolded, the projection width is D2 mm. 5≤D2≤10. For example, the value of D2 can be 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or a range consisting of any two of these values. By regulating the width D2 of the projection within the above range, it is beneficial to reduce the risk of reduction of reserved expansion space due to collapse of protrusions during preparation or circulation, so that the reserved space is moderate, which is beneficial to reduce the tensile stress caused by expansion of the electrode piece during the circulation of the secondary battery, and reduce the safety risk of excessive tensile stress, excessive stretching of the outer ring of the electrode assembly, causing the electrode piece, especially the current collector such as aluminum foil, to break, produce burrs and short circuit. In addition, the pits on the surface of the electrode piece are of moderate size, which reduces the risk of increased electrochemical impedance due to increased side reactions of local aggregation of electrolyte, while taking into account the production cost and production capacity of the secondary battery, while improving the safety performance and cycle performance of the secondary battery.

[0050] In one or more embodiments, along the length direction of the pole piece after unfolding, the distance between two adjacent protrusions is A2mm. For example, Figure 7 As shown, along the length direction (X direction) of the positive electrode plate 10 after unfolding, the spacing between two adjacent protrusions 121 is A2 mm. 5≤A2≤15. For example, the value of A2 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range consisting of any two values ​​therein. By regulating the spacing A2 between two adjacent protrusions within the above range, it is helpful to reduce the difficulty of processing the electrode during processing, reduce the risk of excessive powder loss during the processing of the electrode, resulting in loss of active materials and thus reducing the energy density of the secondary battery, make the pore distribution of the electrode uniform, facilitate the circulation of the electrolyte on the electrode, and improve the infiltration effect of the electrolyte on the electrode. The tensile stress generated by the expansion of the pole piece during the cycle of the secondary battery is reduced, thereby reducing the safety risk of excessive tensile stress on the outer ring of the electrode assembly, which causes the pole piece, especially the current collector such as aluminum foil, to break, produce burrs and short circuit. At the same time, the reserved space is moderate, and the positive and negative pole pieces and the pole piece layers can fit tightly during the charging and discharging process. The electrochemical impedance of the secondary battery during the charging and discharging process is small, taking into account the production cost and production capacity of the secondary battery, while improving the safety performance and cycle performance of the secondary battery. In this application, the spacing between two adjacent protrusions refers to the distance between the width centers of two adjacent strip protrusions along the length direction of the pole piece after it is unfolded.

[0051] In one or more embodiments, along the width direction of the unfolded pole piece, the first material layer has a first edge and a second edge opposite to each other, and the shortest distance between a single protrusion and the first edge or the second edge is L1 mm. For example, Figure 5 As shown, along the width direction (Y direction) of the unfolded positive electrode sheet 10, the first material layer 12 has a first edge 1201 and a second edge 1202 opposite to each other, and the shortest distance between a single protrusion 121 and the first edge 1201 is L1 mm. Figure 7 As shown, along the width direction (Y direction) of the unfolded positive electrode sheet 10, the first material layer 12 has a first edge 1201 and a second edge 1202 opposite to each other, and the shortest distance between a single protrusion 121 and the second edge is L1 mm. 5≤L1≤15. For example, the value of L1 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range consisting of any two of these values. By regulating the shortest distance L1 between a single protrusion and the first edge or the second edge within the above range, it is helpful to reduce the risk of active material loss due to excessive powder loss of the first material layer during electrode processing, reduce the proximity of the protrusion to the first edge or the second edge, and change the strip edge from a straight line to a curve. In the preparation process, the risk of the extreme difference of the positive and negative electrode sheets exceeding the specification and thus failing to produce is reduced, and the tensile stress generated by the expansion of the electrode sheets during the cycle of the secondary battery is reduced, thereby reducing the safety risk of the electrode sheets, especially the current collectors such as aluminum foil, breaking and generating burrs due to excessive stretching of the outer ring of the electrode assembly due to excessive tensile stress, and short circuiting. At the same time, the reserved space is moderate, and the positive and negative electrode sheets and the electrode sheet layers can be tightly fitted during the charge and discharge process. The electrochemical impedance of the secondary battery is small during the charge and discharge process, while taking into account the actual production requirements, the safety performance and cycle performance of the secondary battery are improved.

[0052] In one or more embodiments, along the length direction of the pole piece after unfolding, the end of the first material layer includes a first end surface, and the shortest distance between a single protrusion in the first section and the first end surface is L2 mm. For example, Figure 5 and Figure 7As shown, along the length direction (X direction) of the positive electrode sheet 10 after unfolding, the end of the first material layer 12 includes the first end face 1203, and the shortest distance between the single protrusion 121 in the first section and the first end face 1203 is L2 mm. 5≤L2≤15. For example, the value of L2 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range consisting of any two of these values. By regulating the shortest distance L2 between a single protrusion in the first section and the first end face within the above range, it is helpful to reduce the risk of active material loss due to excessive powder loss of the first material layer during electrode processing, and reduce the safety risk that the edge of the first material layer is deformed due to the protrusion being too close to the first end face, affecting the extreme value test of the positive and negative electrode sheets and thus preventing production, and reduce the tensile stress generated by the expansion of the electrode sheet during the cycle of the secondary battery, thereby reducing the safety risk that the electrode sheet, especially the current collector such as aluminum foil, breaks and generates burrs and short circuits due to excessive tensile stress and excessive stretching of the outer ring of the electrode assembly. At the same time, the reserved space is moderate, and the positive and negative electrode sheets and the electrode sheet layers can be tightly fitted during the charge and discharge process. The electrochemical impedance of the secondary battery is small during the charge and discharge process, while taking into account the actual production requirements, the safety performance and cycle performance of the secondary battery are improved.

[0053] In one or more embodiments, the first material layer is located on the surface of the first current collector away from the winding center of the electrode assembly. Figure 2 and Figure 3 As shown, the first material layer 12 is located on the surface of the first current collector 11 away from the winding center of the electrode assembly 001. Through the above arrangement, while reducing the safety risk of excessive tensile stress on the outer ring of the electrode assembly causing the pole piece, especially the current collector such as aluminum foil, to break, generate burrs and short circuit, the energy density and processing performance of the secondary battery are taken into account. It should be noted that the "surface" where the first material layer is located on the surface of the current collector away from the winding center of the electrode assembly can be the entire area of ​​the current collector surface or a partial area of ​​the current collector surface. This application is not particularly limited as long as the purpose of this application can be achieved.

[0054] 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 first 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 2 and Figure 3As shown, the positive electrode sheet 10 also includes a second material layer 13, which is located on the surface of the first current collector 11 facing the winding center of the electrode assembly 001, and the surface of the second material layer 13 is provided with a plurality of first recesses 131 in the direction of the first 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, and further reducing the tensile stress generated by the expansion of the electrode sheet during the cycle of the secondary battery, thereby reducing the safety risk of the electrode sheet, especially the current collector such as aluminum foil, breaking, generating burrs and short circuiting due to excessive tensile stress and excessive stretching of the outer ring of the electrode assembly, while meeting the mass production manufacturability and improving the safety performance and cycle performance of the secondary battery. It should be noted that the "surface" of the second material layer located on the surface of the current collector facing the winding center of the electrode assembly can be the entire area of ​​the current collector surface or a part of the current collector surface. There is no special limitation in this application, as long as the purpose of this application can be achieved.

[0055] In one or more embodiments, the first current collector is provided with a plurality of second recesses in the direction of the first material layer. Figure 2 and Figure 3 As shown, the first current collector 11 is provided with a plurality of second recesses 111 in the direction of the first 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 tensile stress generated by the expansion of the pole piece during the cycle of the secondary battery is further reduced, thereby reducing the safety risk of the pole piece, especially the current collector such as the aluminum foil, being broken, generating burrs and short circuiting due to excessive tensile stress and excessive stretching of the outer ring of the electrode assembly, thereby improving the safety performance and cycle performance of the secondary battery while meeting the mass production manufacturability.

[0056] 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. Figure 6 As shown, part of the first recess 131 corresponds to part of the protrusion 121, and part of the second recess 111 corresponds to part of the protrusion 121. 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 tensile stress generated by the expansion of the pole piece during the cycle of the secondary battery is further reduced, thereby reducing the safety risk of the pole piece, especially the current collector such as aluminum foil, breaking, generating burrs and short circuiting due to excessive tensile stress and excessive stretching of the outer ring of the electrode assembly, thereby improving the safety performance and cycle performance of the secondary battery while meeting the mass production manufacturability.

[0057] In one or more embodiments, the pole piece is a positive pole piece. When the pole piece is a positive pole piece, it is beneficial to reduce the difficulty of processing the pole piece during processing, reduce the risk of active material loss due to excessive powder loss during pole piece processing, and thus reduce the energy density of the secondary battery, and further reduce the tensile stress generated by the expansion of the pole piece during the cycle of the secondary battery, thereby reducing the safety risk of the pole piece, especially the current collector such as aluminum foil, breaking and generating burrs due to excessive tensile stress and excessive stretching of the outer ring of the electrode assembly, and short circuiting. 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 safety performance and cycle performance of the secondary battery.

[0058] In one or more embodiments, the electrode assembly further includes another electrode sheet having a polarity opposite to that of the electrode sheet, the other electrode sheet includes a second current collector and a third material layer located on at least one surface of the second current collector, and the third material layer includes silicon. Figure 2 and Figure 3 As shown, the electrode assembly 001 also includes a negative electrode sheet 20 with a polarity opposite to that of the positive electrode sheet 10, and the negative electrode sheet 20 includes a second current collector 21 and a third material layer 22 located on both surfaces of the second current collector 21. When the third material layer contains silicon, the expansion and contraction of the electrode sheet during the cycle is more obvious. At this time, a protrusion is set at the tail end of the electrode sheet to reduce the safety risk of excessive tensile stress, which causes the electrode sheet, especially the current collector such as aluminum foil, to break, generate burrs and short circuit due to excessive stretching of the outer ring of the electrode assembly, which is more significant, and is conducive to further improving the safety performance and cycle performance of the cylindrical secondary battery. When the third material layer contains silicon, the third material layer includes active materials, and the active materials include silicon-containing substances, and the silicon-containing substances include at least one of silicon, silicon-carbon materials or silicon-oxygen materials.

[0059] In the present application, when the electrode sheet is a positive electrode sheet, the first current collector is a positive electrode current collector. 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 electrode 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, 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 and 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.

[0060] In the present application, when the pole piece is a negative pole piece, the first current collector is a negative current collector. The present application has no special restrictions on the negative current collector, as long as the purpose of the present application can be achieved. For example, the negative current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or 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.). At this time, the first material layer and the second material layer are both negative electrode material layers, and the negative electrode material layer of the present application contains negative electrode active materials. The present application has no special restrictions on the type of negative electrode active materials, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO x(0 < x < 2), at least one of Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and spinel-structured lithium titanate Li4Ti5O 12 、Li-Al alloy or metallic lithium. Optionally, the negative electrode material layer may further include a conductive agent and a negative electrode binder. The present application does not particularly limit the type of the conductive agent in the negative electrode material layer, as long as the object of the present 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. The present application does not particularly limit the type of the negative electrode binder in the negative electrode material layer, as long as the object of the present 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. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, and the negative electrode binder in the negative electrode material layer, as long as the object of the present application can be achieved.

[0061] The present application does not particularly limit the method for preparing the electrode sheet, as long as the object of the present application can be achieved. For example, the method for preparing the electrode sheet includes but is not limited to the following steps: (1) preparing a slurry; (2) coating the slurry on one surface of a first current collector and drying to form an electrode sheet including a first material layer; (3) coating the slurry on the other surface of the first current collector and drying to obtain an electrode sheet including a first material layer and a second material layer; (4) identifying the end of the electrode sheet, starting from the end of the electrode sheet, along the length direction after the electrode sheet is unfolded, determining the first section and the second section of the first material layer, setting a protrusion on the surface of the first section, and cutting and striping to obtain the electrode sheet.

[0062] The present application does not particularly limit the solid content of the above-mentioned slurry, and those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved. The present application does not particularly limit the process parameters of the above-mentioned drying, cutting, and striping, and those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved. In one or more embodiments, in step (4), when setting a protrusion on the surface of the first section, a first recess is provided on the surface of the second material layer in the direction towards the first material layer. In one or more embodiments, in step (4), when respectively setting protrusions on the surface of the first section, a second recess is provided on the first current collector in the direction towards the first material layer. In one or more embodiments, in step (4), while determining the first section and the second section of the first material layer, along the length direction after the electrode sheet is unfolded and in the direction away from the end of the electrode sheet, identifying the first region, the second region, and the third region of the second section, and while setting a protrusion on the surface of the first section, setting a protrusion on the surface of the second region.

[0063] The present application does not particularly limit the method for setting the protrusion, the first concave portion, and the second concave portion. Those skilled in the art can choose 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 protrusion, the first concave portion, and the second concave portion. The shape of the projection of a single protrusion on the first material layer can be regulated by the shape of the stainless steel needle on the embossing roller; the average height H of multiple protrusions can be regulated by the cold pressing pressure value set by the embossing roller or the height specification of the stainless steel needle on the embossing roller; the spacing A1 between two adjacent protrusions or the spacing A2 between two adjacent protrusions can be regulated by the spacing between adjacent stainless steel needles on the embossing roller; the diameter D1 of the maximum circumscribed circle of the outer contour of the projection of a single protrusion on the first material layer or the projection width D2 of a single strip protrusion on the first material layer can be regulated by the specifications of the stainless steel needle on the embossing roller; the shortest distance L1 between a single protrusion and the first edge or the second edge of the first material layer, and the shortest distance L2 between a single protrusion in the first section and the first end face can be regulated by the position where the embossing roller starts cold pressing on the first material layer.

[0064] 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 part 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, is conducive to high-rate charging and discharging of the secondary battery, reduces internal resistance and heat generation, and thus improves the safety performance and cycle performance of the cylindrical secondary battery.

[0065] In the present application, the different features of the protrusions included in the first pole piece can be combined, and the implementation methods or examples covered by the above combination are all within the protection scope of the present application.

[0066] 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 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 non-aqueous solvents, 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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, folding and other operations 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.

[0071] 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 safety performance and cycle performance, so the electronic device of the present application has a long service life.

[0072] 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.

[0073] Example

[0074] 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.

[0075] Test methods and equipment:

[0076] Tests for H, T, A1, A2, D1, D2, L1, L2:

[0077] 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. Then, 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. The electrode sheet with protrusions on the surface was determined to be the target electrode sheet by naked eye observation.

[0078] A scanning electron microscope (SEM) is used to observe the surface of the pole piece, that is, the plane formed by the length and width directions of the pole piece after it is unfolded is measured along the thickness direction of the pole piece. Due to the height difference between 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.

[0079] When the projected apertures are distributed in a dotted pattern on the first material layer, select 5 apertures at random, measure the maximum circumscribed circle diameter of the outer contour of a single aperture, and take the average value, which is the diameter D1 of the maximum circumscribed circle of the outer contour of the projection of a single protrusion. Select 1 aperture at random along the length direction of the unfolded pole piece, measure the distance between the center of the maximum circumscribed circle of the outer contour of the single aperture and the center of the maximum circumscribed circle of the outer contour of the adjacent aperture, measure 5 times, and take the average value, which is the spacing A1 between two adjacent protrusions.

[0080] When the shape of the projected aperture is a strip, select 5 apertures at random, measure the width of a single aperture along the length direction of the pole piece after it is unfolded, and take the average value, which is the width D2 of the projection of a single protrusion. The measurement of the width of a single aperture includes dividing the aperture into 10 segments along the width direction of the pole piece after it is unfolded, measuring the values ​​of both ends of each segment along the length direction of the pole piece after it is unfolded, a total of 11 values, and taking the average value, which is the width of a single aperture. Select 1 aperture at random along the length direction of the pole piece after it is unfolded, measure the closest distance between its width center and the width center of the adjacent aperture, measure 5 times, and take the average value, which is the spacing A2 between two adjacent protrusions.

[0081] The pole piece with the protrusion is ion polished along the length direction and thickness direction 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 first current collector. Among them, the material layer with the protrusion is the first material layer. Along the length direction after the pole piece is unfolded, the first section and the second section of the first material layer are determined according to the setting of the protrusion; if there are two parts with protrusions on the first material layer, along the length direction after the pole piece is unfolded, according to the setting of the protrusion, the first section, the first area of ​​the second section, the second area and the third area of ​​the first material layer are determined. During the measurement, the first section and the first area are separated by the edge of the protrusion, the first area and the second area are separated by the edge of the protrusion, and the second area and the third area are separated by the edge of the protrusion.

[0082] Select any five protrusions, measure the maximum height from the surface of the first material layer to a single protrusion along the thickness direction of the pole piece, and take the average value, which is the average height H of the multiple protrusions.

[0083] Five flat areas are randomly selected along the thickness direction of the pole piece, and the thickness of the first current collector is measured. The average value is taken as the thickness T of the first current collector.

[0084] Observe with naked eyes along the width direction of the unfolded pole piece to confirm the first edge and the second edge of the first material layer, measure the distance between a single protrusion and the first edge and the distance between a single protrusion and the second edge respectively, and take the minimum value, which is L1. Confirm the end of the first material layer, and measure the shortest distance between a single protrusion and the end of the first material layer, which is L2.

[0085] Aluminum foil breaking cycle test:

[0086] The lithium-ion batteries in the embodiments and comparative examples were subjected to charge and discharge cycle tests in a 60°C thermostat, and the lithium-ion batteries were charged to 4.2V at 1C constant current, 4.2V constant voltage was charged to 0.05C, and after standing for 5 minutes, they were discharged to 2.5V at 2C constant current, which was the first cycle. According to the above-mentioned cycle process, the cycle was circulated to 50 laps, and industrial computed tomography (industrial CT, Zeiss Xradia 620Versa) was used to scan and shoot the cross section of the lithium-ion battery along the axial direction of the cylindrical lithium-ion battery, and then the cycle was continued. The industrial CT was used to scan and shoot every 5 laps, and the cycle was stopped when the electrode assembly pole piece broke in the scanned structural image, and the number of cycles was recorded, which was the number of cycles when the aluminum foil in the electrode assembly broke. The more cycles when the aluminum foil broke, the better the cycle performance and safety performance of the lithium-ion battery.

[0087] Shell quality test:

[0088] Prepare the wound electrode assemblies in each group of embodiments and comparative examples according to the preparation steps, and select different positions along the circumferential direction of the electrode assembly at the same height of a single electrode assembly using an inductively coupled device test (CCD test) to measure the diameter of the electrode assembly, measure 20 points, and take the maximum diameter of the single electrode assembly. Prepare 100 electrode assemblies of each group, and take the average value of the maximum diameters of the single electrode assemblies of each group, which is the average value of the maximum diameters of the electrode assemblies corresponding to the group. Place each group of electrode assemblies into a steel shell with an internal diameter of 33.5±0.1mm and a height of 203.9±0.1mm, and record the number of lithium-ion batteries that can be successfully placed in the shell in each group. The shell entry rate (%) = the number of lithium-ion batteries successfully placed in the shell / 100×100%.

[0089] Among them, the higher the shell quality rate, the higher the production qualification rate of lithium-ion batteries; when the shell quality rate is lower than 50%, the production qualification rate of lithium-ion batteries is too low and does not meet the actual production requirements, which is recorded as <50%.

[0090] Example 1

[0091] <Preparation of positive electrode sheet>

[0092] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.91 Co 0.05 Mn 0.04O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 97.1:1.6:1.3, and 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 T of 14μm, and dried at 105°C to obtain a positive electrode sheet coated with the first positive electrode material layer on one side. Afterwards, 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 the first positive electrode material layer and the second positive electrode material layer.

[0093] The first section and the second section of the first positive electrode material layer are determined along the length direction of the positive electrode sheet after it is unfolded. Based on the length of the first positive electrode material layer after it is unfolded, the length of the first section accounts for K 4%, and the length of the second section accounts for K' 96%. A protrusion is set in the first section, and the projection shape of a single protrusion on the first positive electrode material layer is set to be circular along the thickness direction of the positive electrode sheet. Specifically, Figure 6 As shown, the diameter D1 of the maximum circumscribed circle of the outer contour of the projection of a single protrusion is 5mm, and the average height H of multiple protrusions is 70μm; along the length direction of the unfolded positive electrode sheet, the spacing A1 between two adjacent protrusions is 10mm. According to the above parameters, the positive electrode sheet is cold pressed using an embossing roller of corresponding specifications, and the positive electrode sheet with protrusions, first concave parts and second concave parts is obtained after the sheet is cut into strips. Among them, the coating weight of the first positive electrode material layer and the second positive electrode material layer is 234mg / 1540.25mm 2 The specifications of the positive electrode sheet are 64.5mm×1422mm, the specifications of the first positive electrode material layer are 60mm×1422mm, 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 collector is 45μm, the width of the empty foil area of ​​the positive electrode sheet is 4.5mm, the shortest distance L1 between the protrusion and the first edge of the first positive electrode material layer is 8mm, and the shortest distance L2 between the protrusion and the first end face of the first positive electrode material layer is 8mm.

[0094] <Preparation of negative electrode sheet>

[0095] The negative electrode active material artificial graphite, 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 10μm, 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 striping, 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.

[0096] <Diaphragm>

[0097] A polyethylene (PE) film with a thickness of 12 μm was used as the separator.

[0098] <Preparation of Electrolyte>

[0099] 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.

[0100] <Preparation of lithium-ion batteries>

[0101] 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 electrode assembly formed by pre-winding, and the first section of the first positive electrode material layer is located near the end section of the electrode assembly formed by pre-winding, and the wound electrode assembly is obtained by winding. After that, after flattening, current collecting plate welding, shelling, bottom penetration welding, coding, vacuum drying, electrolyte injection, sealing, high-temperature standing, and forming 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.

[0102] Example 2 to Example 5

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

[0104] Example 6

[0105] In addition to determining the first and second sections of the first positive electrode material layer in <Preparation of Positive Electrode Sheet>, determining the first area, second area and third area of ​​the second section, based on the length of the first positive electrode material layer after unfolding, the length of the first area accounts for K1 of 10%, the length of the second area accounts for K2 of 30%, and the length of the third area accounts for K3 of 56%, and the protrusion is set on the second area while the protrusion is set on the first section, and the rest is the same as Example 1.

[0106] Example 7 to Example 10

[0107] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 6.

[0108] Example 11 to Example 20

[0109] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0110] Embodiment 21

[0111] In addition to adjusting the projection shape of the single protrusion on the first material layer to a strip shape in <Preparation of the positive electrode sheet>, the specific Figure 7 Except for adjusting the relevant preparation parameters as shown in Table 1, the rest is the same as Example 1.

[0112] Example 22 to Example 25

[0113] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 21.

[0114] Example 26 to Example 29

[0115] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0116] Embodiment 30

[0117] Except for preparing the negative electrode sheet and lithium-ion battery according to the following steps, the rest is the same as Example 1.

[0118] <Preparation of negative electrode sheet>

[0119] The negative electrode active material artificial graphite, 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 and mixed 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 T of 10μm, and dried at 105°C to obtain a negative electrode sheet coated with a first negative electrode material layer on one side. Afterwards, 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.

[0120] Along the length direction of the unfolded negative electrode sheet, determine the first section and the second section of the first negative electrode material layer. Based on the length of the unfolded first negative electrode material layer, the length of the first section accounts for K 4%, and the length of the second section accounts for K' 96%. Protrusions are set on the first section, and the projection shape of a single protrusion on the first negative electrode material layer is set to be circular along the thickness direction of the negative electrode sheet. The diameter D1 of the maximum circumscribed circle of the outer contour of the projection of a single protrusion is 5mm, and the average height H of multiple protrusions is 70μm; along the length direction of the unfolded negative electrode sheet, the spacing A1 between two adjacent protrusions is 10mm. According to the above parameters, the negative electrode sheet is cold pressed using an embossing roller of corresponding specifications, and the negative electrode sheet with protrusions, first recesses and second recesses is obtained after the sheet is cut into strips. 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 negative electrode sheet are 67.45mm×1436mm, the specifications of the first negative electrode material layer are 62mm×1436mm, the specifications of the second negative electrode material layer are the same as those of the first negative electrode material layer, the sum of the thicknesses H0 of the first negative electrode material layer and the negative electrode current collector is 40μm, the width of the empty foil area of ​​the negative electrode sheet is 5.45mm, the shortest distance L1 between the protrusion and the first edge of the first negative electrode material layer is 8mm, and the shortest distance L2 between the protrusion and the first end face of the first negative electrode material layer is 8mm.

[0121] <Preparation of lithium-ion batteries>

[0122] 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 electrode assembly formed by pre-winding, and the first negative electrode material layer is away from the center of the electrode assembly formed by pre-winding; and the first section in the first positive electrode material layer is located near the center of the electrode assembly formed by pre-winding, and the first section in the first negative electrode material layer is located near the end section of the electrode assembly formed by pre-winding. After that, a wound electrode assembly is obtained by winding. After that, after flattening, current collector welding, shelling, bottom penetration welding, coding, vacuum drying, electrolyte injection, sealing, high-temperature standing, and then forming 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.

[0123] Comparative Example 1

[0124] Except that no protrusions are provided on the surface of the first material layer, the rest is the same as that of Example 1.

[0125] Comparative Example 2

[0126] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0127] Comparative Example 3

[0128] Except that a protrusion is provided on the second section of the first material layer, and no protrusion is provided on the first section, the rest is the same as that of Example 1.

[0129] Comparative Example 4

[0130] Except that the length of the first section accounts for 100%, that is, the protrusions are all arranged on the first material layer, the rest is the same as the first embodiment.

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

[0132]

[0133]

[0134] Note: “ / ” in Table 1 indicates no relevant preparation or result parameters.

[0135] From Examples 1 to 30 and Comparative Examples 1 to 4, it can be seen that by adjusting the length ratio of the first section within the scope of this application and setting a protrusion on the first section, the average value of the maximum diameter of the electrode assembly is moderate, the shell entry rate of the lithium-ion battery is high, and the number of cycles when the aluminum foil breaks is increased, indicating that the above-mentioned setting reduces the safety risk of the electrode sheet breaking due to excessive tensile stress and excessive stretching of the outer ring of the electrode assembly, which is conducive to reducing the actual production cost and increasing production capacity. The lithium-ion battery has good safety performance and cycle performance. In Comparative Example 1, no protrusions are set on the first material layer; in Comparative Example 2, the length ratio of the first section is not within the scope of this application; in Comparative Example 3, no protrusions are set on the first section, but protrusions are set on the second section; in Comparative Example 4, protrusions are set on all the first material layers. At this time, the number of cycles when the aluminum foil breaks in Comparative Example 1 is small, indicating that the safety performance and cycle performance of the lithium-ion battery are poor; in Comparative Example 2, the energy density loss is large, and the shell entry is poor in large quantities, the shell entry rate is low, and the production cost performance is low; in Comparative Example 3, the energy density loss is large, and the shell entry is poor in large quantities, the shell entry rate is low, and it cannot solve the safety risk of excessive stretching of the outer ring of the electrode assembly during the cycle, causing the pole piece, especially the current collector such as aluminum foil, to break, and the production cost performance is low; in Comparative Example 4, the energy density loss is large, and the shell entry is poor in large quantities, the shell entry rate is lower than that of Comparative Example 3, and it cannot be made into a finished battery. The production cost performance is too low and does not meet the actual production requirements. While the number of cycles when the aluminum foil breaks in the lithium-ion batteries of Examples 1 to 30 is improved, the shell entry rate is high, taking into account the actual production requirements, and the lithium-ion batteries have good safety performance and cycle performance.

[0136] The length ratio of different regions in the second section usually affects the safety performance and cycle performance of the lithium-ion battery. It can be seen from Examples 1, 6 to 10 that when the length ratio of different regions in the second section is within the scope of this application, the average value of the maximum diameter of the electrode assembly is moderate, the shell entry rate of the lithium-ion battery is high, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety performance and cycle performance.

[0137] The average height H of multiple protrusions usually affects the safety performance and cycle performance of lithium-ion batteries. It can be seen from Example 1, Example 11 to Example 14 that when the average height H of multiple protrusions is within the scope of this application, the average value of the maximum diameter of the electrode assembly is moderate, the shell entry rate of the lithium-ion battery is high, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety performance and cycle performance. Among them, in Example 14, the number of cycles when the aluminum foil breaks is large, but at this time the shell entry rate is 98%. When the shell entry rate is lower than 99%, it will have a greater impact on production efficiency, cost, etc. in the actual production process.

[0138] The thickness T of the first current collector usually affects the safety performance and cycle performance of the lithium-ion battery. It can be seen from Example 1, Example 15 to Example 16 that when the thickness T of the first current collector is within the range of this application, the average value of the maximum diameter of the electrode assembly is moderate, the shell entry rate of the lithium-ion battery is high, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety performance and cycle performance.

[0139] The value of D1 usually affects the safety and cycle performance of lithium-ion batteries. It can be seen from Example 1, Example 17 to Example 18 that when the projection shape of a single protrusion on the first material layer is circular, when the diameter D1 of the maximum circumscribed circle of the outer contour of the projection of the single protrusion is within the scope of this application, the average value of the maximum diameter of the electrode assembly is moderate, the lithium-ion battery has a high shell entry rate, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0140] The value of A1 usually affects the safety and cycle performance of lithium-ion batteries. It can be seen from Example 1, Example 19 to Example 20 that when the projection shape of a single protrusion on the first material layer is circular, when the spacing A1 between two adjacent protrusions is within the scope of this application, the average value of the maximum diameter of the electrode assembly is moderate, the lithium-ion battery has a high shell entry rate, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0141] The value of D2 usually affects the safety and cycle performance of lithium-ion batteries. From Example 21 to Example 23, it can be seen that when the projection shape of a single protrusion on the first material layer is a strip, and the width D2 of the projection of a single protrusion is within the scope of this application, the average value of the maximum diameter of the electrode assembly is moderate, the shell entry rate of the lithium-ion battery is high, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0142] The value of A2 usually affects the safety and cycle performance of lithium-ion batteries. It can be seen from Examples 22, 24 and 25 that when the projection shape of a single protrusion on the first material layer is a strip, and the spacing A2 between two adjacent protrusions is within the scope of this application, the average value of the maximum diameter of the electrode assembly is moderate, the lithium-ion battery has a high shell entry rate, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0143] The value of L1 usually affects the safety and cycle performance of lithium-ion batteries. It can be seen from Example 1, Example 26 to Example 27 that when the shortest distance L1 between a single protrusion and the first edge or the second edge is within the scope of this application, the average value of the maximum diameter of the electrode assembly is moderate, the lithium-ion battery has a high shell entry rate, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0144] The value of L2 usually affects the safety and cycle performance of lithium-ion batteries. It can be seen from Example 1, Example 28 to Example 29 that when the shortest distance L2 between a single protrusion in the first section and the first end face is within the scope of this application, the average value of the maximum diameter of the electrode assembly is moderate, the shell entry rate of the lithium-ion battery is high, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of this application has good safety and cycle performance.

[0145] Whether the pole piece is a positive pole piece and / or a negative pole piece usually affects the safety performance and cycle performance of the lithium-ion battery. It can be seen from Example 1 and Example 30 that when the pole piece is a positive pole piece and / or a negative pole piece, the average value of the maximum diameter of the electrode assembly is moderate, the lithium-ion battery has a high shell entry rate, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of the present application has good safety performance and cycle performance.

[0146] The first recess and / or the second recess usually affect the safety and cycle performance of the lithium-ion battery. From Examples 1 to 30, it can be seen that when the first recess and / or the second recess are provided, the average value of the maximum diameter of the electrode assembly is moderate, the lithium-ion battery has a high shell entry rate, and the number of cycles when the aluminum foil breaks is large, indicating that while taking into account the actual production requirements, the lithium-ion battery of the present application has good safety and cycle performance.

[0147] 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.

[0148] 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.

[0149] 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, the electrode assembly comprising a pole piece, the pole piece comprising a first current collector and a first material layer located on a surface of the first current collector; Starting from the tail end of the pole piece, along the length direction of the pole piece after it is unfolded, the first material layer includes a first section and a second section connected in sequence. Based on the length of the first material layer, the length of the first section accounts for K, 1%≤K≤10%, and a plurality of protrusions are arranged on the surface of the first section.

2. The cylindrical secondary battery according to claim 1, wherein: Along the length direction of the pole piece after it is unfolded, and along the direction away from the tail end of the pole piece, the second section includes a first area, a second area and a third area connected in sequence; based on the length of the first material layer, the length of the first area accounts for K1, and the length of the second area accounts for K2, 10%≤K1≤40%, 20%≤K2≤60%, and in the second section, only the second area has multiple protrusions on its surface.

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

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

7. The cylindrical secondary battery according to any one of claims 1 to 6, wherein: The multiple protrusions are distributed in a point-like manner on the first material layer. Along the thickness direction of the pole piece, the projection shape of a single protrusion on the first material layer is circular, elliptical or polygonal, and the diameter of the maximum circumscribed circle of the outer contour of the projection is D1 mm, 3≤D1≤7.

8. The cylindrical secondary battery according to claim 7, wherein: Along the length direction of the pole piece after unfolding, the distance between two adjacent protrusions is A1 mm, 5≤A1≤15.

9. The cylindrical secondary battery according to any one of claims 1 to 6, wherein: Along the thickness direction of the pole piece, the projection shape of a single protrusion on the first material layer is a strip, and the multiple protrusions extend along the width direction of the pole piece after it is unfolded and are arranged at intervals along the length direction of the pole piece after it is unfolded. Along the length direction of the pole piece after it is unfolded, the width of the projection is D2 mm, 5≤D2≤10.

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

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

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 tail end of the first material layer includes a first end surface, and the shortest distance between a single protrusion in the first section and the first end surface is L2 mm, 5≤L2≤15.

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

14. The cylindrical secondary battery according to claim 13, wherein: The pole piece further includes a second material layer, which is located on a surface of the first 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 first 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, which satisfies at least one of the following conditions: (1)4％≤K≤10％； (2) The electrode is a positive electrode.

18. The cylindrical secondary battery according to claim 1, wherein The electrode assembly further includes another pole piece with a polarity opposite to that of the pole piece, the other pole piece includes a second current collector and a third material layer located on at least one surface of the second current collector, the third material layer includes silicon. 19 . An electronic device comprising the cylindrical secondary battery according to claim 1 .

Images