Cylindrical secondary battery and electronic device

Abstract

The invention provides a cylindrical secondary battery and an electronic device, the cylindrical secondary battery comprises an electrode assembly, the electrode assembly comprises a first pole piece, and the first pole piece comprises a first current collector and a first material layer; the number of winding turns of the first material layer is N, and N is larger than or equal to 15 and smaller than or equal to 70. The first material layer sequentially includes a first region and a second region in a winding direction of the electrode assembly. Wherein the first area is located from the first circle to the 0.75 Nth circle of the first material layer, and a plurality of first concave parts are arranged on the surface of the first area; the second area is located from the 0.8 Nth circle to the Nth circle of the first material layer, and the surface of the second area is provided with a plurality of second concave parts. Through the arrangement, the safety risk of short circuit caused by burr generation due to collapse of the inner ring pole piece caused by overlarge extrusion force and breakage of the outer ring pole piece caused by overlarge tensile stress of the electrode assembly is reduced.

Description

Technical Field

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

[0002] Cylindrical secondary batteries, such as cylindrical lithium-ion batteries, are used in a variety of 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 cycle of cylindrical lithium-ion batteries, the pole pieces expand and the current collector stretches and extends, causing the outer pole pieces to be prone to breakage due to excessive tensile stress and the inner pole pieces to be prone to collapse due to excessive extrusion pressure, reducing the safety and cycle performance of the lithium-ion 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 and extrusion force generated by the expansion of the pole piece during the cycle process, 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, including an electrode assembly of a winding structure, the electrode assembly including a first pole piece, the first pole piece including a first current collector and a first material layer located on a surface of the first current collector; along the winding direction of the electrode assembly, the number of windings of the first material layer is N, 15≤N≤70, and N is a positive integer. Along the winding direction of the electrode assembly, the first material layer includes a first region and a second region in sequence. The first region is located at the 1st to 0.75Nth turns of the first material layer, and a plurality of first recesses are provided on the surface of the first region; the second region is located at the 0.8Nth to Nth turns of the first material layer, and a plurality of second recesses are provided on the surface of the second region. The present application can reduce the extrusion pressure caused by the expansion of the inner pole piece and the tensile stress caused by the expansion of the outer pole piece in the late cycle by making recessed portions in different regions within the range of the number of circles on the surface of the first material layer, effectively reducing the safety risk of the electrode assembly causing the inner pole piece to collapse due to excessive extrusion pressure and the outer pole piece to break due to excessive tensile stress, generating burrs and short circuit, and at the same time, improving the infiltration effect of the electrolyte on the pole piece, reducing the risk of lithium deposition in the secondary battery, thereby improving the cycle performance of the secondary battery. Therefore, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0007] In one or more embodiments, the first region is located between the 0.06Nth and 0.75Nth turns of the first material layer. In one or more embodiments, the first region is located between the 0.3Nth and 0.7Nth turns of the first material layer. In one or more embodiments, the first region is located between the 0.4Nth and 0.6Nth turns of the first material layer. When the first region is within the above number of turns, it is beneficial to further reduce the safety risk of the inner ring pole piece collapse due to excessive extrusion pressure of the electrode assembly, and thus, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0008] In one or more embodiments, the second region is located between the 0.9Nth and Nth turns of the first material layer. In one or more embodiments, the second region is located between the 0.95Nth and Nth turns of the first material layer. When the second region is within the above number of turns, it is beneficial to further reduce the safety risk of the electrode assembly causing the outer ring pole piece to break due to excessive tensile stress, generating burrs and short circuit, and thus, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0009] In one or more embodiments, based on the surface area of ​​the first material layer, the sum of the areas of the first region and the second region accounts for S, 2% ≤ S ≤ 55%; optionally, 10% ≤ S ≤ 20%; further optionally, 12% ≤ S ≤ 18%. By regulating the value of S within the above range, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0010] In one or more embodiments, along the thickness direction of the first pole piece, the thickness of the first pole piece is Tμm, 60≤T≤450; the average depth of the plurality of first recesses is H1μm, 1.5%≤H1 / T×100%≤35%, optionally, 3%≤H1 / T×100%≤15%; further optionally, 5%≤H1 / T×100%≤10%; and / or, the average depth of the plurality of second recesses is H2μm, 1.5%≤H2 / T×100%≤35%, optionally, 3%≤H2 / T×100%≤15%; further optionally, 5%≤H2 / T×100%≤10%. Through the above arrangement, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0011] In one or more embodiments, 0.1≤H1 / H2≤5; optionally, 0.2≤H1 / H2≤3; further optionally, 0.3≤H1 / H2≤1.5. By adjusting the value of H1 / H2 within the above range, the cylindrical secondary battery has good safety performance and cycle performance while taking into account the actual production requirements.

[0012] In one or more embodiments, along the thickness direction of the first pole piece, a single first recess has a first projection on the surface of the first material layer, and along the length direction of the first pole piece after it is unfolded, the shortest distance between the outer contours of two adjacent first projections is d1 mm, 0.1≤d1≤15; optionally, 0.5≤d1≤8; further optionally, 1≤d1≤5; and / or, along the thickness direction of the first pole piece, a single second recess has a second projection on the surface of the first material layer, and along the length direction of the first pole piece after it is unfolded, the shortest distance between the outer contours of two adjacent second projections is d2 mm, 0.1≤d2≤10; optionally, 0.3≤d2≤5; further optionally, 0.5≤d2≤2. Through the above settings, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0013] In one or more embodiments, a plurality of first recesses or a plurality of second recesses are distributed in a dotted manner on the surface of the first material layer, and along the thickness direction of the first pole piece, the shape of the first projection of a single first recess on the surface of the first material layer is a circle, an ellipse or a regular polygon, and the diameter of the maximum circumscribed circle of the outer contour of the single first projection is D1 mm, 0.2≤D1≤5; optionally, 0.5≤D1≤4.5; further optionally, 1≤D1≤4; and / or, along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is a circle, an ellipse or a regular polygon, and the diameter of the maximum circumscribed circle of the outer contour of the single second projection is D2 mm, 0.1≤D2≤6; optionally, 0.2≤D2≤5.5; further optionally, 0.5≤D2≤5. Through the above arrangement, while taking into account the production cost and production capacity of the secondary battery, the cylindrical secondary battery has good safety performance and cycle performance.

[0014] In one or more embodiments, along the thickness direction of the first pole piece, the shape of the first projection of a single first recess on the surface of the first material layer is a strip, and along the length direction of the first pole piece after it is unfolded, the average width of the multiple first projections is W1 mm, 0.2≤W1≤5; optionally, 0.6≤W1≤2; further optionally, 1≤W1≤1.5; and / or, along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is a strip, and along the length direction of the first pole piece after it is unfolded, the average width of the multiple second projections is W2 mm, 0.1≤W2≤6; optionally, 0.1≤W2≤3; further optionally, 0.2≤W2≤1. Through the above settings, while taking into account the production cost and production capacity of the secondary battery, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0015] In one or more embodiments, a plurality of first recesses extend along the width direction of the first pole piece after it is unfolded and are arranged at intervals along the length direction of the first pole piece after it is unfolded, and based on the width of the first pole piece after it is unfolded, the length of a single first projection accounts for L1, 5%≤L1≤95%; and / or, a plurality of second recesses extend along the width direction of the first pole piece after it is unfolded and are arranged at intervals along the length direction of the first pole piece after it is unfolded, and based on the width of the first pole piece after it is unfolded, the length of a single second projection accounts for L2, 10%≤L2≤95%. Through the above arrangement, while taking into account actual production and energy density, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0016] In one or more embodiments, along the width direction after the first pole piece is unfolded, the length of a single first projection is L3 mm, 9≤L3≤150; optionally, 15≤L3≤80; further optionally, 20≤L3≤55; and / or, along the width direction after the first pole piece is unfolded, the length of a single second projection is L4 mm, 18≤L4≤180; optionally, 30≤L4≤100; further optionally, 50≤L4≤80. Through the above settings, while taking into account actual production and energy density, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0017] In one or more embodiments, the first material layer is located on the surface of the first current collector facing the winding center of the electrode assembly. In one or more embodiments, the first pole piece further includes a second material layer, which is located on the surface of the first current collector away from the winding center of the electrode assembly; the surface of the second material layer in the area opposite to the first area is provided with a plurality of first convex portions, at least part of the first convex portions are arranged opposite to part of the first concave portions; and / or, the surface of the second material layer in the area opposite to the second area is provided with a plurality of second convex portions, at least part of the second convex portions are arranged opposite to part of the second concave portions. In one or more embodiments, the area opposite to the first area of ​​the first current collector is provided with a plurality of third convex portions in the direction of the second material layer; and / or, the area opposite to the second area of ​​the first current collector is provided with a plurality of fourth convex portions in the direction of the second material layer. In one or more embodiments, at least part of the third convex portions corresponds to part of the first concave portions; and / or, at least part of the fourth convex portions corresponds to part of the second concave portions. Through the above arrangement, the safety performance and cycle performance of the cylindrical secondary battery are improved while meeting the mass production manufacturability.

[0018] In one or more embodiments, the first pole piece is a positive pole piece.

[0019] The second aspect of the present application provides an electronic device, which includes the cylindrical secondary battery in any one of the above embodiments. Therefore, the electronic device of the present application has good performance.

[0020] Beneficial effects of the embodiments of the present application:

[0021] The embodiment of the present application can reduce the extrusion pressure caused by the expansion of the inner pole piece and the tensile stress caused by the expansion of the outer pole piece in the late cycle by making recessed portions in different regions within the range of the number of circles on the surface of the first material layer, effectively reducing the safety risk of the electrode assembly causing the inner pole piece to collapse due to excessive extrusion pressure and the outer pole piece to break due to excessive tensile stress, generating burrs and short circuit, and at the same time, improving the infiltration effect of the electrolyte on the pole piece, reducing the risk of lithium deposition in the secondary battery, thereby improving the cycle performance of the secondary battery. Therefore, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0022] 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

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and a person skilled in the art can also obtain other embodiments based on these drawings.

[0024] Figure 1 A schematic diagram of a winding structure formed by an electrode assembly in one embodiment of the present application;

[0025] Figure 2 A partial front view of a positive electrode sheet after the electrode assembly in another embodiment of the present application is unfolded;

[0026] Figure 3 A partial front view of a positive electrode sheet after the electrode assembly in another embodiment of the present application is unfolded;

[0027] Figure 4 for Figure 2 Cross-sectional view of the positive electrode sheet along the PP direction.

[0028] Figure numerals: electrode assembly 001; positive electrode plate (first electrode plate) 10; first current collector 11; first material layer 12; second material layer 13; negative electrode plate 20; second current collector 21; negative electrode material layer 22; separator 30; first recess 121; first protrusion 131; third protrusion 111; second recess 122; second protrusion 132; fourth protrusion 112; winding starting end face 0011; winding ending end face 0012. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] In the prior art, cylindrical secondary batteries, such as cylindrical lithium-ion batteries, expand the pole pieces in the later stages of the cycle, especially when the negative pole pieces include negative active materials containing silicon elements, the expansion and contraction of the negative pole pieces in the cycle process intensifies. At this time, the inner pole piece of the electrode assembly is squeezed inward to cause collapse, and the tensile stress on the outer pole piece is too large, which can easily cause the pole piece, especially the current collector, to break and produce burrs. Short circuits are prone to occur during the charging and discharging process, and lithium deposition occurs at the local interface of the pole piece, affecting the cycle performance and safety performance of the secondary battery. At present, in order to solve this problem, the thickness of the foil is usually increased to increase the strength of the pole piece, but it will lead to a decrease in the energy density of the electrode assembly under the same specifications, and increase the production cost of the electrode assembly. At the same time, the improvement effect on the breakage and collapse of the pole piece in the later stages of the cycle is not obvious. Based on this, the present application provides a cylindrical secondary battery and an electronic device, which is conducive to reducing the safety risks of the outer pole piece breaking due to excessive tensile stress and the inner pole piece collapse due to excessive extrusion force, thereby improving the safety performance and cycle performance of the cylindrical secondary battery.

[0032] The first aspect of the present application provides a cylindrical secondary battery, including an electrode assembly of a winding structure, the electrode assembly including a first pole piece, the first pole piece including a first current collector and a first material layer located on one surface of the first current collector; along the winding direction of the electrode assembly, the number of windings of the first material layer is N, 15≤N≤70, and N is a positive integer. For example, the value of N can be 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, 65, 68, 70 or a range consisting of any two of the values. Along the winding direction of the electrode assembly, the first material layer includes a first region and a second region in sequence. Among them, the first region is located at the 1st to 0.75Nth turns of the first material layer, and a plurality of first recesses are provided on the surface of the first region; the second region is located at the 0.8Nth to Nth turns of the first material layer, and a plurality of second recesses are provided on the surface of the second region.

[0033] It can be understood that a circle of the first material layer refers to a circle with one end of the first material layer as the starting point and one end of the circle wound along the winding direction of the electrode assembly as the ending point, and the starting point and the ending point are aligned along the axial direction of the electrode assembly. In the present application, the starting point of the first circle of the first material layer is the starting end of the first material layer, and so on.

[0034] In the present application, the first electrode sheet can be a positive electrode sheet and / or a negative electrode sheet. It is defined that the electrode assembly is in an unfolded state, and 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 the negative electrode sheet, the positive electrode sheet and the separator are in an unfolded state. The 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 first electrode sheet is a positive electrode sheet, such as Figure 1 As shown, the electrode assembly 001 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 30. The positive electrode sheet 10 includes a first current collector 11 and a first material layer 12 located on a surface of the first current collector 11. Along the winding direction (W direction) of the electrode assembly 001, the electrode assembly 001 has a winding starting end face 0011 and a winding ending end face 0012. Along the radial direction of the electrode assembly 001, that is, the direction from the winding center of the electrode assembly 001 to the outside (not shown in the figure), the winding starting end face 0011 has a position M on the surface of the first material layer 12, and the winding ending end face 0012 has a position N on the surface of the first material layer 12. The first material layer 12 is wound along the winding direction (W direction) of the electrode assembly 001, and the first material layer 12 includes a first region and a second region in sequence. The first region is located in the first turn of the first material layer 12, the first region is M to N, and a plurality of first recesses 121 are arranged on the surface of the first region; the second region is located in the last turn of the first material layer 12, the second region is M' to N', and a plurality of second recesses 122 are arranged on the surface of the second region. Figure 1 The number of turns of the first material layer, the number, size, length and spacing of the first recesses and the second recesses are only exemplary, and the present application is not limited thereto. In the present application, the above-mentioned "multiple" refers to two or more.

[0035] When recesses are provided on the first material layer, the area of ​​the recesses provided on the electrode piece is too large, resulting in a large reserved expansion space. The electrolyte is easily broken between the layers of some electrode pieces, resulting in an increase in the electrochemical impedance during the cycle of the secondary battery. The resistance to ion conduction during the cycle is greater, which reduces the cycle performance of the secondary battery. At the same time, the electrolyte is in excessive contact with the electrode piece, resulting in a relatively increased number of side reactions of the secondary battery. The increase in the number of side reaction products leads to an increase in the thickness of the electrode piece and an increase in the corresponding hardness of the electrode piece. Furthermore, the improvement effect on the safety risk of the electrode assembly causing the inner ring electrode piece to collapse due to excessive extrusion pressure and the outer ring electrode piece to break due to excessive tensile stress, generating burrs and short circuit is also poor. At this time, the diameter of the electrode assembly is too large. In the actual production process, under the same shell specifications, the production qualification rate of lithium-ion batteries is low, which does not meet the actual production requirements. Or, when a larger shell is used, the capacity of the secondary battery is reduced, affecting the energy density of the secondary battery. Both situations will increase production costs and reduce production capacity, and the cost performance is too low. The present application makes recesses in different regions within the range of different circles on the surface of the first material layer, that is, the first recess is made in the first region near the starting end of the electrode assembly, and the second recess is made in the second region near the end of the electrode assembly. The inner and outer rings of the electrode assembly have expansion space, which can reduce the extrusion force generated by the expansion of the inner ring pole piece and the tensile stress generated by the expansion of the outer ring pole piece in the later stage of the cycle, effectively reducing the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion force and the outer ring pole piece to break due to excessive tensile stress, generating burrs and short circuit. At the same time, the infiltration effect of the electrolyte on the pole piece is improved, and the risk of lithium deposition in the secondary battery is reduced, thereby improving the cycle performance of the secondary battery; in addition, the reserved expansion space is moderate, and the distance between the positive and negative pole pieces and between the pole piece levels during the charge and discharge process is designed to be within a suitable range, so that the electrochemical impedance of the secondary battery is small, and the above-mentioned setting makes the average diameter of the electrode assembly within a suitable range, reducing the actual production cost and increasing the production capacity. Therefore, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0036] It should be noted that the "surface" of the first material layer located on one surface of the first current collector can be the entire area of ​​the surface of the first current collector or a partial area of ​​the surface of the first current collector. This application has no special restrictions as long as the purpose of this application can be achieved.

[0037] In one or more embodiments, the first region is located between the 0.06Nth and 0.75Nth turns of the first material layer. In one or more embodiments, the first region is located between the 0.3Nth and 0.7Nth turns of the first material layer. In one or more embodiments, the first region is located between the 0.4Nth and 0.6Nth turns of the first material layer. When the first region is located within the above number of turns, it is beneficial to further reduce the safety risk of the inner ring pole piece collapse due to excessive extrusion pressure of the electrode assembly, and also reduces the safety risk of the outer ring pole piece breaking due to excessive tensile stress, generating burrs and short circuiting. At the same time, it improves the wetting effect of the electrolyte on the pole piece, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. Furthermore, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0038] In one or more embodiments, the second region is located between the 0.9Nth and Nth turns of the first material layer. In one or more embodiments, the second region is located between the 0.95Nth and Nth turns of the first material layer. When the second region is within the above number of turns, it is beneficial to further reduce the safety risk of the electrode assembly causing the outer ring pole piece to break due to excessive tensile stress, the generation of burrs and short circuit, and also reduces the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the pole piece, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. Furthermore, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0039] In one or more embodiments, based on the surface area of ​​the first material layer, the sum of the areas of the first region and the second region accounts for S, 2%≤S≤55%; optionally, 10%≤S≤20%; further optionally, 12%≤S≤18%. For example, the value of S can be 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55% or a range consisting of any two of the values. By adjusting the value of S within the above range, it is helpful to reduce the safety risk of the electrode assembly causing the inner ring electrode sheet to collapse due to excessive extrusion pressure and the outer ring electrode sheet to break due to excessive tensile stress, and the generation of burrs and short circuit. At the same time, it improves the infiltration effect of the electrolyte on the electrode sheet, reduces the risk of lithium deposition in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, at this time, the distance between the positive and negative electrode sheets and between the electrode sheet layers during the charging and discharging process is within a suitable range, so that the electrochemical impedance of the secondary battery is small, and the average diameter of the electrode assembly is within a suitable range, which reduces the actual production cost and improves the production capacity. Therefore, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0040] In one or more embodiments, along the thickness direction of the first pole piece, the thickness of the first pole piece is T μm, 60 ≤ T ≤ 450, for example, the value of T can be 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700 30, 440, 450 or a range consisting of any two of them; the average depth of the plurality of first recesses is H1μm, 1.5%≤H1 / T×100%≤35%, optionally, 3%≤H1 / T×100%≤15%; further optionally, 5%≤H1 / T×100%≤10%; for example, the value of H1 / T×100% can be 1.5%, 2%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35% or a range consisting of any two of them. By adjusting the values ​​of T and H1 / T×100% within the above range, it is beneficial to further reduce the safety risk of the inner ring pole piece collapsing due to excessive extrusion pressure of the electrode assembly, and also reduce the safety risk of the outer ring pole piece breaking and burr short circuit due to excessive tensile stress. At the same time, it improves the infiltration effect of the electrolyte on the pole piece, reduces the risk of lithium deposition in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the gap between the positive and negative pole pieces and between the pole piece layers during the charge and discharge process is moderate, and thus the electrochemical impedance of the secondary battery is small, which further makes the average diameter of the electrode assembly within a suitable range, reduces the actual production cost and increases the production capacity. Therefore, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0041] In one or more embodiments, along the thickness direction of the first pole piece, the thickness of the first pole piece is T μm, 60≤T≤450, for example, the value of T can be 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450 or a range consisting of any two of them; the average depth of the plurality of second recesses is H2μm, 1.5%≤H2 / T×100%≤35%, optionally, 3%≤H2 / T×100%≤15%; further optionally, 5%≤H2 / T×100%≤10%, for example, the value of H2 / T×100% can be 1.5%, 2%, 3%, 5%, 6%, 7%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35% or a range consisting of any two of them. By adjusting the values ​​of T and H2 / T×100% within the above range, it is beneficial to further reduce the safety risk of the outer ring pole piece breaking and burr short circuit caused by excessive tensile stress of the electrode assembly, and also reduce the safety risk of the inner ring pole piece collapsing due to excessive extrusion pressure of the electrode assembly. At the same time, it improves the infiltration effect of the electrolyte on the pole piece, reduces the risk of lithium precipitation in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the gap between the positive and negative pole pieces and between the pole piece layers during the charge and discharge process is moderate, and thus the electrochemical impedance of the secondary battery is small, which further makes the average diameter of the electrode assembly within a suitable range, reduces the actual production cost and increases the production capacity. Therefore, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0042] In one or more embodiments, along the thickness direction of the first pole piece, the thickness of the first pole piece is T μm, 60≤T≤450, for example, the value of T can be 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450 or a range consisting of any two thereof; the average depth of the plurality of first recesses is H1 μm, 1.5% ≤ H1 / T×100% ≤ 35%, optionally, 3% ≤ H1 / T×100% ≤ 15%; further optionally, 5% ≤ H1 / T×100%≤10%; for example, the value of H1 / T×100% can be 1.5%, 2%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35% or a range consisting of any two of the values; and, the average depth of the plurality of second recesses is H2μm, 1.5%≤H2 / T×100%≤35% , optionally, 3%≤H2 / T×100%≤15%; further optionally, 5%≤H2 / T×100%≤10%, for example, the value of H2 / T×100% can be 1.5%, 2%, 3%, 5%, 6%, 7%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35% or a range consisting of any two of the values. For example, Figure 2 and Figure 4 As shown, Figure 2 The first pole piece in the PP direction is cut to obtain Figure 4 . Along the thickness direction (Z direction) of the first pole piece 10, the thickness of the first pole piece 10 is Tμm, the average depth of the plurality of first recesses 121 is H1μm, and the average depth of the plurality of second recesses 122 is H2μm. By regulating the values ​​of T, H1 / T×100% and H2 / T×100% within the above range, it is helpful to reduce the safety risk of the electrode assembly short-circuiting due to the collapse of the inner ring pole piece caused by excessive extrusion pressure and the breakage of the outer ring pole piece caused by excessive tensile stress, and the generation of burrs. At the same time, the infiltration effect of the electrolyte on the pole piece is improved, and the risk of lithium deposition in the secondary battery is reduced, thereby improving the cycle performance of the secondary battery; in addition, the gaps between the positive and negative pole pieces and between the pole piece layers during charging and discharging are moderate, so that the electrochemical impedance of the secondary battery is small, and the average diameter of the electrode assembly is further within a suitable range, which reduces the actual production cost and increases the production capacity. Therefore, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0043] In one or more embodiments, along the thickness direction of the first pole piece, the thickness of the first current collector may be 4 μm to 30 μm.

[0044] In the present application, the thickness of the first pole piece can be controlled by means known to those skilled in the art. For example, when the slurry is coated on the surface of the first current collector on a certain basis, the solid content of the slurry is fixed, and the thickness of the first material layer can be increased by increasing the coating weight per unit area, and the thickness of the first pole piece increases accordingly; the coating weight per unit area can be reduced to reduce the thickness of the first material layer, and the thickness of the first pole piece decreases accordingly; and when the first pole piece is cold pressed, the thickness of the first material layer can be reduced by increasing the cold pressing pressure, and the thickness of the first pole piece can be reduced accordingly; the thickness of the first material layer can be increased by reducing the cold pressing pressure, and the thickness of the first pole piece can be increased accordingly.

[0045] In one or more embodiments, 0.1≤H1 / H2≤5; optionally, 0.2≤H1 / H2≤3; further optionally, 0.3≤H1 / H2≤1.5. For example, the value of H1 / H2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, 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, or a range consisting of any two of the values. The first and second recesses within the above-mentioned depth ratio range are provided in the inner and outer rings of the electrode assembly, which is conducive to further reducing the safety risk of the electrode assembly collapsing the inner ring pole piece due to excessive extrusion pressure and breaking the outer ring pole piece due to excessive tensile stress, generating burrs and short circuiting. At the same time, it improves the infiltration effect of the electrolyte on the pole piece, reduces the risk of lithium deposition in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the gaps between the positive and negative pole pieces and between the pole piece layers during charging and discharging are moderate, so that the electrochemical impedance of the secondary battery is small. At the same time, in the actual production process, the recesses with the above-mentioned corresponding depth ratios can be provided according to the actual tensile stress and extrusion pressure, which reduces the actual production cost and improves the production capacity. Therefore, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0046] In one or more embodiments, along the thickness direction of the first pole piece, a single first recess has a first projection on the surface of the first material layer, and along the length direction of the first pole piece after it is unfolded, the shortest distance between the outer contours of two adjacent first projections is d1 mm, 0.1≤d1≤15; optionally, 0.5≤d1≤8; further optionally, 1≤d1≤5, for example, the value of d1 can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range consisting of any two of these values. By adjusting the value of d1 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 processing of the first pole piece, and thus reduce the energy density of the secondary battery. The pore distribution of the first pole piece is uniform, which is conducive to the circulation of the electrolyte on the first pole piece, improves the infiltration effect of the electrolyte on the first pole piece, and thus improves the cycle performance of the secondary battery; it is helpful to further reduce the safety risk of the inner ring pole piece collapse due to excessive extrusion pressure of the electrode assembly, and also reduces the safety risk of the outer ring pole piece breaking due to excessive tensile stress, generating burrs and short circuit; in addition, the gap between the positive and negative pole pieces and between the pole piece layers during charging and discharging is moderate, which reduces the actual production cost and improves the production capacity. Therefore, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0047] In one or more embodiments, along the thickness direction of the first pole piece, a single second recess has a second projection on the surface of the first material layer, and along the length direction of the unfolded first pole piece, the shortest distance between the outer contours of two adjacent second projections is d2 mm, 0.1≤d2≤10; optionally, 0.3≤d2≤5; further optionally, 0.5≤d2≤2, for example, the value of d2 can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two of these values. By adjusting the value of d2 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 processing of the first pole piece, and thus reduce the energy density of the secondary battery. The pore distribution of the first pole piece is uniform, which is conducive to the circulation of the electrolyte on the first pole piece, improves the infiltration effect of the electrolyte on the first pole piece, and thus improves the cycle performance of the secondary battery; it is helpful to further reduce the safety risk of the outer ring pole piece breaking and burr generation due to excessive tensile stress of the electrode assembly, and also reduces the safety risk of the inner ring pole piece collapse due to excessive extrusion pressure of the electrode assembly; in addition, the gap between the positive and negative pole pieces and between the pole piece layers during charging and discharging is moderate, which reduces the actual production cost and improves the production capacity. Therefore, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0048] In one or more embodiments, along the thickness direction of the first pole piece, a single first recess has a first projection on the surface of the first material layer, and along the length direction of the first pole piece after the first pole piece is unfolded, the shortest distance between the outer contours of two adjacent first projections is d1 mm, 0.1≤d1≤15; optionally, 0.5≤d1≤8; further optionally, 1≤d1≤5, for example, the value of d1 can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range consisting of any two of the values; and, along the thickness direction of the first pole piece, a single second recess has a second projection on the surface of the first material layer, and along the length direction of the first pole piece after the first pole piece is unfolded, the shortest distance between the outer contours of two adjacent second projections is d2 mm, 0.1≤d2≤10; optionally, 0.3≤d2≤5; further optionally, 0.5≤d2≤2, for example, the value of d2 can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two of the values. For example, Figure 2 and Figure 3 As shown, along the thickness direction (Z direction) of the first pole piece 10, a single first recess 121 has a first projection on the surface of the first material layer 12, and along the length direction (X direction) after the first pole piece 10 is unfolded, the shortest distance between the outer contours of two adjacent first projections is d1 mm, and along the thickness direction (Z direction) of the first pole piece 10, a single second recess 122 has a second projection on the surface of the first material layer 12, and along the length direction (X direction) after the first pole piece 10 is unfolded, the shortest distance between the outer contours of two adjacent second projections is d2 mm. By adjusting the values ​​of d1 and d2 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 processing of the first pole piece, and thus reduce the energy density of the secondary battery. The pore distribution of the first pole piece is uniform, which is conducive to the circulation of the electrolyte on the first pole piece, improves the infiltration effect of the electrolyte on the first pole piece, and thus improves the cycle performance of the secondary battery; it is helpful to reduce the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure and the outer ring pole piece to break due to excessive tensile stress, produce burrs and short circuit; in addition, the gap between the positive and negative pole pieces and between the pole piece layers during charging and discharging is moderate, the pole piece is subjected to a relatively uniform force, which reduces the actual production cost and improves the production capacity. Therefore, while taking into account the actual production requirements, the cylindrical secondary battery has good safety performance and cycle performance.

[0049] In one or more embodiments, a plurality of first recesses or a plurality of second recesses are distributed in a point-like manner on the surface of the first material layer. Along the thickness direction of the first pole piece, the shape of the first projection of a single first recess on the surface of the first material layer is circular, elliptical or regular polygonal, and the diameter of the maximum circumscribed circle of the outer contour of the single first projection is D1 mm, 0.2≤D1≤5; optionally, 0.5≤D1≤4.5; further optionally, 1≤D1≤4, for example, the value of D1 can be 0.2, 0.4, 0.5, 0.8, 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 or a range consisting of any two of these values. By regulating the value of D1 within the above range, it is beneficial to further reduce the safety risk of the inner ring electrode sheet of the electrode assembly collapsing due to excessive extrusion pressure, and also reduce the safety risk of the outer ring electrode sheet breaking, generating burrs and short circuiting due to excessive tensile stress. At the same time, it improves the wetting effect of the electrolyte on the electrode sheet, reduces the risk of lithium plating on the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first recess on the surface of the first electrode sheet is moderate, which reduces the risk of increased electrochemical impedance due to increased side reactions of local aggregation of the electrolyte. Furthermore, while taking into account the production cost and production capacity of the secondary battery, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0050] In one or more embodiments, multiple first recesses or multiple second recesses are distributed in a point-like manner on the surface of the first material layer. Along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is circular, elliptical or regular polygonal, and the diameter of the maximum circumscribed circle of the outer contour of the single second projection is D2 mm, 0.1≤D2≤6; optionally, 0.2≤D2≤5.5; further optionally, 0.5≤D2≤5, for example, the value of D2 can be 0.1, 0.2, 0.3, 0.5, 0.8, 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 or a range consisting of any two of these values. By regulating the value of D2 within the above range, it is beneficial to further reduce the safety risk of the electrode assembly causing the outer ring electrode piece to break and generate burrs and short circuit due to excessive tensile stress, and also reduce the safety risk of the inner ring electrode piece of the electrode assembly collapsing due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the electrode piece, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the size of the second recess on the surface of the first electrode piece is moderate, which reduces the risk of increased electrochemical impedance due to increased local aggregation side reactions of the electrolyte; further, while taking into account the production cost and production capacity of the secondary battery, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0051] In one or more embodiments, a plurality of first recesses or a plurality of second recesses are distributed in a point-like manner on the surface of the first material layer, and along the thickness direction of the first pole piece, the shape of the first projection of a single first recess on the surface of the first material layer is a circle, an ellipse or a regular polygon, and the diameter of the maximum circumscribed circle of the outer contour of the single first projection is D1 mm, 0.2≤D1≤5; optionally, 0.5≤D1≤4.5; further optionally, 1≤D1≤4, for example, the value of D1 can be 0.2, 0.4, 0.5, 0.8, 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 or a range consisting of any two of the values; and, along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is a circle, an ellipse or a regular polygon, and the diameter of the maximum circumscribed circle of the outer contour of the single second projection is D2 mm, 0.1≤D2≤6; optionally, 0.2≤D2≤5.5; further optionally, 0.5≤D2≤5, for example, the value of D2 can be 0.1, 0.2, 0.3, 0.5, 0.8, 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 or a range consisting of any two of the values. For example, Figure 2 As shown, along the thickness direction (Z direction) of the first pole piece 10, the shape of the first projection of a single first recess 121 on the surface of the first material layer 12 is circular, and the diameter of the maximum circumscribed circle of the outer contour of the single first projection is D1 mm, and the shape of the second projection of a single second recess 122 on the surface of the first material layer 12 is circular, and the diameter of the maximum circumscribed circle of the outer contour of the single second projection is D2 mm. By adjusting the values ​​of D1 and D2 within the above range, it is helpful to reduce the safety risk of the electrode assembly collapsing the inner ring pole piece due to excessive extrusion pressure and breaking the outer ring pole piece due to excessive tensile stress, generating burrs and short circuiting. At the same time, it improves the infiltration effect of the electrolyte on the pole piece, reduces the risk of lithium deposition in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the size of the first recess and the second recess on the surface of the first pole piece is moderate, which reduces the risk of increased electrochemical impedance due to increased local aggregation side reactions of the electrolyte; further, while taking into account the production cost and production capacity of the secondary battery, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0052] In one or more embodiments, along the thickness direction of the first pole piece, the shape of the first projection of a single first recess on the surface of the first material layer is a strip, and along the length direction of the first pole piece after it is unfolded, the average width of the multiple first projections is W1 mm, 0.2≤W1≤5; optionally, 0.6≤W1≤2; further optionally, 1≤W1≤1.5, for example, the value of W1 can be 0.2, 0.4, 0.5, 0.6, 0.8, 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 or a range consisting of any two of these values. By adjusting the value of W1 within the above range, it is beneficial to further reduce the safety risk of the inner ring electrode sheet of the electrode assembly collapsing due to excessive extrusion pressure, and also reduce the safety risk of the outer ring electrode sheet breaking, generating burrs and short circuiting due to excessive tensile stress. At the same time, it improves the wetting effect of the electrolyte on the electrode sheet, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first recess on the surface of the first electrode sheet is moderate, which reduces the risk of increased electrochemical impedance due to increased side reactions of local aggregation of the electrolyte. Furthermore, while taking into account the production cost and production capacity of the secondary battery, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0053] In one or more embodiments, along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is a strip, and along the length direction of the first pole piece after it is unfolded, the average width of the multiple second projections is W2 mm, 0.1≤W2≤6; optionally, 0.1≤W2≤3; further optionally, 0.2≤W2≤1, for example, the value of W2 can be 0.1, 0.15, 0.2, 0.4, 0.5, 0.8, 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 or a range consisting of any two of these values. By regulating the value of W2 within the above range, it is beneficial to further reduce the safety risk of the electrode assembly causing the outer ring electrode piece to break and generate burrs and short circuit due to excessive tensile stress, and also reduce the safety risk of the inner ring electrode piece of the electrode assembly collapsing due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the electrode piece, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the size of the second recess on the surface of the first electrode piece is moderate, which reduces the risk of increased electrochemical impedance due to increased local aggregation side reactions of the electrolyte; further, while taking into account the production cost and production capacity of the secondary battery, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0054] In one or more embodiments, along the thickness direction of the first pole piece, the shape of the first projection of a single first recess on the surface of the first material layer is a strip, and along the length direction of the first pole piece after it is unfolded, the average width of the multiple first projections is W1 mm, 0.2≤W1≤5; optionally, 0.6≤W1≤2; further optionally, 1≤W1≤1.5, for example, the value of W1 can be 0.2, 0.4, 0.5, 0.6, 0.8, 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 or a range consisting of any two of the values; and, along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is a strip, and along the length direction after the first pole piece is unfolded, the average width of the multiple second projections is W2 mm, 0.1≤W2≤6; optionally, 0.1≤W2≤3; further optionally, 0.2≤W2≤1, for example, the value of W2 can be 0.1, 0.15, 0.2, 0.4, 0.5, 0.8, 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 or a range consisting of any two of the values. For example, Figure 3 As shown, along the thickness direction (Z direction) of the first pole piece 10, the shape of the first projection of the single first recess 121 on the surface of the first material layer 10 is a strip, and along the length direction (X direction) after the first pole piece 10 is unfolded, the average width of the multiple first projections is W1 mm, and along the thickness direction (Z direction) of the first pole piece 10, the shape of the second projection of the single second recess 122 on the surface of the first material layer 12 is a strip, and along the length direction (X direction) after the first pole piece 10 is unfolded, the average width of the multiple second projections is W2 mm, by adjusting the values ​​of W1 and W2 within the above range, it is helpful to reduce the safety risks of the electrode assembly causing the inner ring electrode sheet to collapse due to excessive extrusion pressure and the outer ring electrode sheet to break due to excessive tensile stress, and the generation of burrs and short circuit. At the same time, the wetting effect of the electrolyte on the electrode sheet is improved, and the risk of lithium plating in the secondary battery is reduced, thereby improving the cycle performance of the secondary battery; in addition, the first recess and the second recess on the surface of the first electrode sheet are of moderate size, which reduces the risk of increased electrochemical impedance due to increased side reactions of local aggregation of the electrolyte; further, while taking into account the production cost and production capacity of the secondary battery, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0055] In one or more embodiments, a plurality of first recesses extend along the width direction of the first pole piece after it is unfolded and are spaced apart along the length direction of the first pole piece after it is unfolded. Based on the width of the first pole piece after it is unfolded, the length of a single first projection accounts for L1, 5%≤L1≤95%. For example, the value of L1 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a range consisting of any two of these values. By regulating the value of L1 within the above range, it is beneficial to further reduce the safety risk of the inner ring electrode sheet of the electrode assembly collapsing due to excessive extrusion pressure, and also reduce the safety risk of the outer ring electrode sheet breaking and generating burrs and short circuiting due to excessive tensile stress. At the same time, it improves the wetting effect of the electrolyte on the electrode sheet, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first recess on the surface of the first electrode sheet is moderate, which reduces the risk of increased electrochemical impedance due to increased local aggregation of the electrolyte and increased side reactions, and also reduces the risk of active material loss due to excessive powder loss during the processing of the first electrode sheet, thereby reducing the energy density of the secondary battery. Furthermore, while taking into account both actual production and energy density, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0056] In one or more embodiments, a plurality of second recesses extend along the width direction of the first pole piece after it is unfolded and are spaced apart along the length direction of the first pole piece after it is unfolded. Based on the width of the first pole piece after it is unfolded, the length of a single second projection accounts for L2, 10%≤L2≤95%. For example, the value of L2 can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a range consisting of any two of these values. By regulating the value of L2 within the above range, it is beneficial to further reduce the safety risk of the electrode assembly causing the outer ring electrode piece to break and generate burrs and short circuit due to excessive tensile stress, and also reduce the safety risk of the inner ring electrode piece of the electrode assembly collapsing due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the electrode piece, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the size of the second recess on the surface of the first electrode piece is moderate, which reduces the risk of increased electrochemical impedance due to increased local aggregation of the electrolyte and increased side reactions, and also reduces the risk of active material loss due to excessive powder loss during the processing of the first electrode piece, thereby reducing the energy density of the secondary battery; and thus, while taking into account both actual production and energy density, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0057] In one or more embodiments, a plurality of first recesses extend along the width direction of the first pole piece after it is unfolded and are spaced apart along the length direction of the first pole piece after it is unfolded. Based on the width of the first pole piece after it is unfolded, the length proportion of a single first projection is L1, 5%≤L1≤95%. For example, the value of L1 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or any two of them. A range of composition; and, multiple second recesses extend along the width direction of the first pole piece after it is unfolded and are spaced apart along the length direction of the first pole piece after it is unfolded. Based on the width of the first pole piece after it is unfolded, the length of a single second projection accounts for L2, 10%≤L2≤95%. For example, the value of L2 can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a range consisting of any two of these values. By regulating the values ​​of L1 and L2 within the above range, it is helpful to reduce the safety risks of the electrode assembly causing the inner ring electrode sheet to collapse due to excessive extrusion pressure and the outer ring electrode sheet to break due to excessive tensile stress, and the generation of burrs and short circuit. At the same time, the wetting effect of the electrolyte on the electrode sheet is improved, and the risk of lithium plating in the secondary battery is reduced, thereby improving the cycle performance of the secondary battery. In addition, the first and second recesses on the surface of the first electrode sheet are of moderate size, which reduces the risk of increased electrochemical impedance due to increased local aggregation of the electrolyte side reactions, and also reduces the risk of active material loss due to excessive powder loss during the processing of the first electrode sheet, thereby reducing the energy density of the secondary battery. Furthermore, while taking into account both actual production and energy density, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0058] In one or more embodiments, along the width direction of the first pole piece after unfolding, the length of a single first projection is L3 mm, 9≤L3≤150; optionally, 15≤L3≤80; further optionally, 20≤L3≤55, for example, the value of L3 can be 9, 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 or a range consisting of any two of these values. By regulating the value of L3 within the above range, it is beneficial to further reduce the safety risk of the inner ring electrode sheet of the electrode assembly collapsing due to excessive extrusion pressure, and also reduce the safety risk of the outer ring electrode sheet breaking and generating burrs and short circuiting due to excessive tensile stress. At the same time, it improves the wetting effect of the electrolyte on the electrode sheet, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery. In addition, the size of the first recess on the surface of the first electrode sheet is moderate, which reduces the risk of increased electrochemical impedance due to increased local aggregation of the electrolyte and increased side reactions, and also reduces the risk of active material loss due to excessive powder loss during the processing of the first electrode sheet, thereby reducing the energy density of the secondary battery. Furthermore, while taking into account both actual production and energy density, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0059] In one or more embodiments, along the width direction of the unfolded first pole piece, the length of a single second projection is L4 mm, 18≤L4≤180; optionally, 30≤L4≤100; further optionally, 50≤L4≤80, for example, the value of L4 can be 18, 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, 165, 170, 175, 180 or a range consisting of any two of the values. By regulating the value of L4 within the above range, it is beneficial to further reduce the safety risk of the electrode assembly causing the outer ring electrode piece to break and generate burrs and short circuit due to excessive tensile stress, and also reduce the safety risk of the inner ring electrode piece of the electrode assembly collapsing due to excessive extrusion pressure. At the same time, it improves the wetting effect of the electrolyte on the electrode piece, reduces the risk of lithium plating in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the size of the second recess on the surface of the first electrode piece is moderate, which reduces the risk of increased electrochemical impedance due to increased local aggregation of the electrolyte side reactions, and also reduces the risk of active material loss due to excessive powder loss during the processing of the first electrode piece, thereby reducing the energy density of the secondary battery; and thus, while taking into account both actual production and energy density, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0060] In one or more embodiments, along the width direction after the first pole piece is unfolded, the length of a single first projection is L3 mm, 9≤L3≤150; optionally, 15≤L3≤80; further optionally, 20≤L3≤55, for example, the value of L3 can be 9, 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 or a range consisting of any two of the values; and, along the width direction after the first pole piece is unfolded, the length of a single second projection is L4 mm, 18≤L4≤180; optionally, 30≤L4≤100; further optionally, 50≤L4≤80, for example, the value of L4 can be 18, 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, 165, 170, 175, 180 or a range consisting of any two of the values. For example, Figure 3 As shown, along the width direction (Y direction) after the first pole piece 10 is unfolded, the length of a single first projection is L3 mm, and the length of a single second projection is L4 mm. By adjusting the values ​​of L3 and L4 within the above range, it is helpful to reduce the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure and the outer ring pole piece to break due to excessive tensile stress, and the generation of burrs and short circuit. At the same time, it improves the infiltration effect of the electrolyte on the pole piece, reduces the risk of lithium deposition in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the size of the first recess and the second recess on the surface of the first pole piece is moderate, which reduces the risk of increased electrochemical impedance caused by increased local aggregation of the electrolyte side reactions, and also reduces the risk of active material loss and reduced energy density of the secondary battery due to more powder loss during the processing of the first pole piece; further, while taking into account the actual production and energy density, the cylindrical secondary battery of the present application has good safety performance and cycle performance.

[0061] In one or more embodiments, along the thickness direction of the first pole piece, the shape of the first projection of the single first recess on the surface of the first material layer is a strip, along the width direction of the first pole piece after it is unfolded, the first material layer has two opposite edges, and the first recess extends from any one of the edges along the width direction of the first pole piece after it is unfolded; or, the first recess is located between the two edges. In one or more embodiments, along the thickness direction of the first pole piece, the shape of the second projection of the single second recess on the surface of the first material layer is a strip, along the width direction of the first pole piece after it is unfolded, the first material layer has two opposite edges, and the second recess extends from any one of the edges along the width direction of the first pole piece after it is unfolded; or, the second recess is located between the two edges. In one or more embodiments, along the thickness direction of the first pole piece, the shape of the first projection of a single first recess on the surface of the first material layer is a strip, and there is an angle between the first recess and the length direction of the first pole piece after the first pole piece is unfolded, and the angle is 15° to 90°; and / or, along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is a strip, and there is an angle between the second recess and the length direction of the first pole piece after the first pole piece is unfolded, and the angle is 15° to 90°. Through the above arrangement, it is beneficial to improve the consistency of the distribution of the electrolyte in the first pole piece, and when the secondary battery has a high energy density, it is beneficial to improve the infiltration performance of the electrolyte on the first pole piece, and improve the penetration efficiency of the electrolyte in the first pole piece. At the same time, it is beneficial to reduce the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure and the outer ring pole piece to break due to excessive tensile stress, generate burrs and short circuit. In addition, while meeting mass production manufacturability, the cycle performance and safety performance of the secondary battery are improved.

[0062] In one or more embodiments, the first material layer is located on the surface of the first current collector toward the winding center of the electrode assembly. Figure 1 As shown, the first material layer 12 is located on the surface of the first current collector 11 facing the winding center of the electrode assembly 001. Through the above arrangement, the safety risks of the electrode assembly causing the inner pole piece to collapse due to excessive extrusion pressure and the outer pole piece to break due to excessive tensile stress, generating burrs and short circuit are reduced, and the cycle performance of the secondary battery is improved, while taking into account the energy density and processing performance of the secondary battery.

[0063] In one or more embodiments, the first pole piece further includes a second material layer, and the second material layer is located on the surface of the first current collector away from the winding center of the electrode assembly; the surface of the second material layer in the area opposite to the first area is provided with a plurality of first protrusions, and at least some of the first protrusions are arranged opposite to some of the first recesses. Through the above arrangement, the operability of setting the first recess and the first protrusion on the first pole piece is improved, which is conducive to improving the wetting performance of the electrolyte on the pole piece, further reducing the safety risk of the inner ring pole piece collapsing due to excessive extrusion force of the electrode assembly, and improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0064] In one or more embodiments, the first pole piece further includes a second material layer, and the second material layer is located on the surface of the first current collector away from the winding center of the electrode assembly; the surface of the second material layer in the area opposite to the second area is provided with a plurality of second protrusions, and at least some of the second protrusions are arranged opposite to some of the second recesses. Through the above arrangement, the operability of setting the second recess and the second protrusion on the first pole piece is improved, which is conducive to improving the infiltration performance of the electrolyte to the pole piece, and further reduces the safety risk of the outer ring pole piece of the electrode assembly being broken and burred due to excessive tensile stress, thereby improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0065] In one or more embodiments, the first electrode sheet further includes a second material layer, the second material layer is located on the surface of the first current collector away from the winding center of the electrode assembly; the surface of the second material layer in the area opposite to the first area is provided with a plurality of first protrusions, at least some of the first protrusions are arranged opposite to some of the first concave parts; and the surface of the second material layer in the area opposite to the second area is provided with a plurality of second protrusions, at least some of the second protrusions are arranged opposite to some of the second concave parts. For example, Figure 1 and Figure 4 As shown, the first pole piece 10 further includes a second material layer 13, which is located on the surface of the first current collector 11 away from the winding center of the electrode assembly 001; the surface of the second material layer 13 in the area opposite to the first area is provided with a plurality of first convex portions 131, and the first convex portions 131 are arranged opposite to the first concave portion 121; the surface of the second material layer 13 in the area opposite to the second area is provided with a plurality of second convex portions 132, and the second convex portions 132 are arranged opposite to the second concave portion 122. Through the above arrangement, the operability of setting the first concave portion, the first convex portion, the second concave portion and the second convex portion on the first pole piece is improved, which is conducive to improving the infiltration performance of the electrolyte on the pole piece, and is conducive to reducing the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure and the outer ring pole piece to break due to excessive tensile stress, generating burrs and short circuit, and improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0066] In one or more embodiments, a plurality of third protrusions are provided in the region of the first current collector opposite to the first region toward the second material layer. Through the above arrangement, the operability of setting the first concave portion and the third protrusion on the first pole piece is improved, which is conducive to improving the infiltration performance of the electrolyte to the pole piece, further reducing the safety risk of the inner ring pole piece collapse caused by excessive extrusion force of the electrode assembly, and improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0067] In one or more embodiments, a plurality of fourth protrusions are provided in the region of the first current collector opposite to the second region in the direction of the second material layer. Through the above arrangement, the operability of setting the second concave portion and the fourth protrusion on the first pole piece is improved, which is conducive to improving the infiltration performance of the electrolyte to the pole piece, and further reduces the safety risk of the outer ring pole piece breaking and burr generation due to excessive tensile stress of the electrode assembly, thereby improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0068] In one or more embodiments, a region of the first current collector opposite to the first region is provided with a plurality of third protrusions toward the second material layer; and a region of the first current collector opposite to the second region is provided with a plurality of fourth protrusions toward the second material layer. Figure 1 and Figure 4 As shown, the area of ​​the first current collector 11 opposite to the first area is provided with a plurality of third protrusions 111 in the direction of the second material layer 13; and the area of ​​the first current collector 11 opposite to the second area is provided with a plurality of fourth protrusions 112 in the direction of the second material layer 13. Through the above arrangement, the operability of setting the first recess, the third protrusion, the second recess and the fourth protrusion on the first pole piece is improved, which is conducive to improving the infiltration performance of the electrolyte to the pole piece, and is conducive to further reducing the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure and the outer ring pole piece to break due to excessive tensile stress, generating burrs and short circuit, thereby improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0069] In one or more embodiments, at least part of the third protrusion corresponds to part of the first concave portion. Through the above arrangement, the operability of setting the first concave portion and the third protrusion on the first pole piece is improved, which is conducive to improving the infiltration performance of the electrolyte to the pole piece, further reducing the safety risk of the inner ring pole piece collapsing due to excessive extrusion force of the electrode assembly, and improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0070] In one or more embodiments, at least part of the fourth protrusion corresponds to part of the second concave portion. Through the above arrangement, the operability of setting the second concave portion and the fourth protrusion on the first pole piece is improved, which is conducive to improving the infiltration performance of the electrolyte to the pole piece, and further reduces the safety risk of the outer ring pole piece breaking and burr generation due to excessive tensile stress of the electrode assembly, thereby improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0071] In one or more embodiments, at least part of the third protrusion corresponds to part of the first concave portion; and, at least part of the fourth protrusion corresponds to part of the second concave portion. Through the above arrangement, the operability of setting the first concave portion, the third protrusion, the second concave portion and the fourth protrusion on the first pole piece is improved, which is conducive to improving the infiltration performance of the electrolyte to the pole piece, and is conducive to further reducing the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure and the outer ring pole piece to break due to excessive tensile stress, generating burrs and short circuit, thereby improving the safety performance and cycle performance of the cylindrical secondary battery while meeting the mass production manufacturability.

[0072] In one or more embodiments, the first pole piece is a positive pole piece. When the first pole piece is a positive pole piece, it is helpful to reduce the processing difficulty of the first pole piece during the processing process, 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. It is also helpful to reduce the safety risk of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure and the outer ring pole piece to break due to excessive tensile stress, and the generation of burrs and short circuit. At the same time, it improves the infiltration effect of the electrolyte on the pole piece, reduces the risk of lithium deposition in the secondary battery, and thus improves the cycle performance of the secondary battery; in addition, the gaps between the positive and negative pole pieces and between the pole piece layers during the charge and discharge process are moderate, and the electrochemical impedance of the secondary battery is small, thereby further improving the safety performance and cycle performance of the secondary battery.

[0073] In the present application, the first electrode sheet can be a positive electrode sheet, in which case the first current collector is a positive electrode current collector. The present application has no particular 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), etc. 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 particular 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.

[0074] In the present application, the first pole piece may be a negative pole piece, in which case the first current collector is a negative current collector. The present application has no particular 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 particular 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, lithium titanate Li4Ti5O with spinel structure 12 , Li-Al alloy or metallic lithium. Optionally, the negative electrode material layer may further include a conductive agent and a negative electrode binder. There is no particular limitation on the type of the conductive agent in the negative electrode material layer of the present application, 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. There is no particular limitation on the type of the negative electrode binder in the negative electrode material layer of the present application, 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. There is no particular limitation on the mass ratio of the negative electrode active material, the conductive agent and the negative electrode binder in the negative electrode material layer of the present application, as long as the object of the present application can be achieved.

[0075] There is no particular limitation on the preparation method of the first electrode sheet of the present application, as long as the object of the present application can be achieved. For example, the preparation method of the first electrode sheet includes but is not limited to the following steps: (1) preparing a slurry; (2) coating the slurry on one surface of the first current collector and drying to form an electrode sheet including a first material layer; (3) coating the slurry on the other surface of the first current collector and drying to obtain a first electrode sheet including a first material layer and a second material layer; (4) cutting and slitting, etc., to obtain a first electrode sheet without a first recess and a second recess; (5) pre-winding the first electrode sheet, the prepared second electrode sheet and the separator in step (4), determining the number of winding turns of the first electrode sheet, i.e., the number of winding turns of the first material layer, and then along the pre-winding direction, confirming the first region and the second region of the first material layer, setting a first recess on the surface of the first region, and setting a second recess on the surface of the second region, to obtain the first electrode sheet.

[0076] The present application does not have any particular restrictions on the solid content of the above-mentioned slurry, and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. The present application does not have any particular restrictions on the process parameters of the above-mentioned drying, cutting and slitting, and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. In one or more embodiments, in step (5), when the first convex portion is set on the first area, the surface of the area of ​​the second material layer opposite to the first area is provided with a first convex portion in the direction of the first material layer. In one or more embodiments, in step (5), when the first concave portion is set on the first area, a third concave portion is provided in the direction of the first material layer in the area of ​​the first current collector opposite to the first area. In one or more embodiments, in step (5), when the second convex portion is set on the second area, a second convex portion is provided on the surface of the area of ​​the second material layer opposite to the second area in the direction of the first material layer. In one or more embodiments, in step (5), when the second concave portion is set on the second area, a fourth concave portion is provided in the direction of the first material layer in the area of ​​the first current collector opposite to the second area.

[0077] The present application does not particularly limit the method of setting the first concave portion, the second concave portion, the first convex portion, the second convex portion, the third convex portion, and the fourth convex portion. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the first pole piece can be cold-pressed by an embossing roller to set the first concave portion, the second concave portion, the first convex portion, the second convex portion, the third convex portion, and the fourth convex portion. The shape of the projection of a single first concave portion or a single second concave portion on the first material layer can be controlled by the shape of the protrusion on the embossing roller; the maximum depth H1 of a single first concave portion and the maximum depth H2 of a single second concave portion can be controlled by the cold pressing pressure value set by the embossing roller or the height specification of the protrusion on the embossing roller; the average height H1 of multiple first concave portions can be adjusted by the cold pressing pressure value set by the embossing roller or the height specification of the protrusion on the embossing roller; the average height H2 .... 11 , the average height H of the plurality of second recesses 12 It can be regulated by the cold pressing pressure value set by the embossing roller or the height specification of the protrusions on the embossing roller; the shortest distance d1 between the outer contours of two adjacent first projections and the shortest distance d2 between the outer contours of two adjacent second projections can be regulated by the spacing between adjacent protrusions on the embossing roller; the diameter D1 of the maximum circumscribed circle of the outer contour of a single first projection and the diameter D1 of the maximum circumscribed circle of the outer contour of a single second projection can be regulated by the specifications of the protrusions on the embossing roller; the average width W1 of multiple first projections, the average width W2 of multiple second projections, the length proportion L1 of a single first projection, the length proportion L2 of a single second projection, the length L3 of a single first projection, and the length L4 of a single second projection can be regulated by the specifications of the protrusions on the embossing roller.

[0078] In one or more embodiments, the first current collector includes a coating area provided with a first 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.

[0079] In the present application, the different features of the first pole piece including the first recess and the second recess may be combined, and the implementation methods or examples covered by the above combination are all within the protection scope of the present application.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] The second aspect of the present application provides an electronic device, which includes the cylindrical secondary battery in any one of the above embodiments. Therefore, the electronic device of the present application has good performance.

[0086] 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.

[0087] Example

[0088] 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.

[0089] Test methods and equipment:

[0090] Tests for H1, H2, T, D1, D2, d1, d2, W1, W2, L1, L2, L3, L4:

[0091] At an ambient temperature of 25°C, the lithium-ion batteries of the embodiments and comparative examples were discharged at 1C to 2.8V and then disassembled to obtain electrode assemblies. According to the winding center and the starting end of the electrode assembly, the number of windings of the positive electrode sheet and the negative electrode sheet was determined; the positive electrode sheet and the negative electrode sheet were taken out from the electrode assembly respectively, soaked in dimethyl carbonate (DMC) for 20 minutes, and 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. By visual observation, it was determined that the electrode sheet with a concave portion on the surface was the target electrode sheet, and the material layer with the concave portion was the first material layer. The first region and the second region of the first material layer were determined according to the winding traces and the starting and ending ends of the electrode sheet.

[0092] A scanning electron microscope (SEM) is used to observe the surface of the pole piece, that is, along the thickness direction of the pole piece, the plane formed by the length and width directions of the pole piece after it is unfolded is measured. Due to the height difference between the depth of the recess 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. There is a projected aperture on the surface of the pole piece for the recess, which can be used to distinguish the recess from the first material layer.

[0093] When the projected apertures on the first area 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 a single first projection. Select 1 aperture at random along the length direction of the unfolded pole piece, measure the shortest distance between the center of the maximum circumscribed circle of the outer contour of a single aperture and the outer contour of an adjacent aperture, measure 5 times, and take the average value, which is the shortest distance d1 between the outer contours of two adjacent first projections.

[0094] When the shape of the projected aperture on the first area 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 average width W1 of multiple first projections. 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 5 apertures at random along the width direction of the pole piece after it is unfolded, measure the length of the first projection, and take the average value, which is the length L3 of a single first projection; at the same time, measure the width of the first material layer after it is unfolded, and compare it with L3 to obtain the length of the single first projection based on the length of the first pole piece after it is unfolded. The proportion L1 of the length of the single first projection.

[0095] The pole piece with the protrusion is ion polished along the length direction and thickness direction of the pole piece after it is unfolded to obtain a cross section of the pole piece, and the cross section of the pole piece is measured using a scanning electron microscope (SEM).

[0096] Select any five first recesses in the first region, measure the maximum depth from the surface of the first material layer to a single first recess along the thickness direction of the pole piece, and take the average value, which is the average depth H1 of the multiple first recesses.

[0097] Select any five flat areas along the thickness direction of the pole piece, measure the thickness of the pole piece, and take the average value, which is the thickness T of the first pole piece.

[0098] By measuring the second recesses in the second area with reference to the above-mentioned test method, one can obtain the average depth H2 of the multiple second recesses, the shortest distance d2 between the outer contours of two adjacent second projections, the diameter D2 of the maximum circumscribed circle of the outer contour of a single second projection, or the average width W2 of the multiple second projections, the length L4 of a single second projection, and the length proportion L2 of a single second projection based on the length of the first pole piece after unfolding.

[0099] Cycle performance test:

[0100] The lithium-ion batteries in the examples and comparative examples were subjected to a charge-discharge cycle test in an environment of 25°C. The lithium-ion batteries were charged to 4.3V at a constant current of 0.5C, charged to 0.05V at a constant voltage of 4.3V, left to stand for 10 minutes, and then discharged to 2.8V at a constant current of 1C. This was the first cycle, and the first cycle discharge capacity C1 was recorded. After 400 cycles according to the above cycle process, the lithium-ion battery discharge capacity C 400 , the cycle capacity retention rate of the 400th cycle is calculated as an indicator for evaluating the cycle performance of the lithium-ion battery, and the formula is shown in formula (I). When the 400-cycle (cls) capacity retention rate is lower, it indicates that the cycle performance of the lithium-ion battery is worse; when the 400-cls capacity retention rate is higher, it indicates that the cycle performance of the lithium-ion battery is better.

[0101] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0102] Computerized tomography and pole piece indentation distance test:

[0103] Using industrial computed tomography technology (industrial CT, Zeiss Xradia 620Versa), a CT scan was performed on the lithium-ion batteries in the embodiments and comparative examples after the above-mentioned "cycle performance test" along the width direction of the electrode assembly after it was unfolded (or the axial direction of the electrode assembly), and the number of pole piece collapse circles and pole piece breakage circles of each electrode assembly were observed.

[0104] Example 1-1

[0105] <Preparation of negative electrode sheet>

[0106] The negative electrode active materials artificial graphite, sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97.7:1.3:1, and then deionized water is added as a solvent, stirred and mixed evenly 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 6μm, and dried at 105°C to obtain a negative electrode sheet coated with a 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 negative electrode material layer on both sides. Then, after cold pressing, cutting, laser cleaning, and pole ear welding, a negative electrode sheet with a specification of 210.5mm×2700mm is obtained for standby use. Among them, the coating weight of the negative electrode material layer is 340mg / 1540.25mm 2 The specifications of the negative electrode material layer are 194.5mm×2700mm, and the thickness of the negative electrode sheet after cold pressing is 140μm.

[0107] <Preparation of Separator>

[0108] 8 μm thick polyethylene (PE) was selected as the diaphragm substrate, and ceramic particles of aluminum oxide (Al2O3), binder styrene-butadiene rubber (Mw = 7×10 6 ) and solvent deionized water in a mass ratio of 35:10:55 to obtain a ceramic coating slurry. The binder polyvinylidene fluoride (PVDF, Mw = 8.5 × 10 6 ) and thickener sodium carboxymethyl cellulose (Mw = 8 × 10 5 ) are mixed in a mass ratio of 98.5:1.5, deionized water is added as a solvent, and a bonding layer slurry with a solid content of 75wt% is formed after being stirred evenly. Ceramic coating slurry is applied on one surface of the substrate, and after drying at 60°C, a ceramic coating is formed on one surface of the substrate, and the bonding layer slurry is applied on the surface of the ceramic coating away from the substrate, and after drying at 60°C, a diaphragm coated with a ceramic coating and a bonding layer on one side is obtained; thereafter, the above steps are repeated on the other surface of the substrate to obtain a diaphragm. Among them, the thickness of the single-sided ceramic coating is 2μm, and the coating weight of the single-sided bonding layer is 2.5mg / 5000m 2 .

[0109] <Preparation of positive electrode sheet>

[0110] The first electrode is the positive electrode, which contains positive electrode active materials (LiMn2O4), lithium nickel cobalt manganese oxide (LiNi 0.91 Co 0.05 Mn 0.04 Aluminum oxide (Al2O2), conductive carbon black and binder polyvinylidene fluoride (PVDF) are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 58:38:2:2, and the mixture is stirred thoroughly to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 15μm, and dried at 105°C to obtain a positive electrode sheet coated with a first material layer. Thereafter, the above steps are repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with a first material layer and a second material layer. Aluminum oxide and polyvinylidene fluoride are dissolved in N-methylpyrrolidone (NMP) solution in a weight ratio of 90:10 to obtain a ceramic slurry with a solid content of 60wt%. A layer of ceramic slurry is applied on the edge of the empty foil area of ​​the positive electrode current collector where the positive electrode material layer is not provided, close to the positive electrode material layer, to obtain a protective coating. The positive electrode sheet is then obtained after drying, cold pressing and cutting. Among them, the positive electrode current collector that is close to and coated with a protective coating is retained during cutting, and the positive electrode current collector that is not coated with a protective coating is used as a pole ear.

[0111] The positive electrode sheet, the separator, the prepared negative electrode sheet and another separator are stacked and wound. After the winding is completed, the number of windings of the first material layer and the first electrode sheet, that is, the number of windings of the first material layer, is determined. The number of windings N of the first material layer is 42. Then, along the pre-winding direction, the first area and the second area of ​​the first material layer are determined. The first area is located between the 20th and 25th turns, and the second area is located between the 40th and 41st turns. Setting: multiple first recesses are set on the first area, and multiple second recesses are set on the second area. Based on the surface area of ​​the first material layer, the sum of the areas of the first area and the second area accounts for 16%; the average depth H1 of the multiple first recesses is 11.2μm, and the average depth H2 of the multiple second recesses is 11.2μm. Along the thickness direction of the first pole piece, a single first recess has a first projection on the surface of the first material layer, and the first projection is circular. A single second recess has a second projection on the surface of the first material layer, and the second projection is circular. The diameter D1 of the maximum circumscribed circle of the outer contour of the single first projection is 3mm, the diameter D2 of the maximum circumscribed circle of the outer contour of the single second projection is 3mm, the shortest distance d1 between the outer contours of two adjacent first projections is 3mm, and the shortest distance d2 between the outer contours of two adjacent second projections is 1mm.

[0112] According to the above parameters, the positive electrode sheet is cold pressed using an embossing roller of corresponding specifications, and the sheet is cut into strips to obtain a positive electrode sheet with a first concave portion, a second concave portion, a first convex portion, a second convex portion, a third convex portion and a fourth convex portion. The coating weight of the first material layer and the second material layer is 600.5mg / 1540.25mm 2 The specifications of the positive electrode sheet are 200.5mm×2650mm, the specifications of the first material layer are 192.5mm×2650mm, the specifications of the second material layer are the same as those of the first material layer, the thickness T of the first electrode sheet is 140μm, and the specifications of the protective coating are 2mm×2650mm.

[0113] <Preparation of Electrolyte>

[0114] In an environment with a water content of less than 10ppm, organic solvents ethylene carbonate (EC) and propylene carbonate (PC) are mixed at a weight ratio of 50:50 to obtain a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added to the base solvent and mixed thoroughly to obtain an electrolyte. The concentration of the lithium salt LiPF6 is 1.15mol / L.

[0115] <Preparation of lithium-ion batteries>

[0116] The separator, negative electrode sheet, separator, and positive electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain an electrode assembly. The electrode lugs of the electrode assembly are flattened and welded to the collector plate. The electrode assembly is encapsulated in a steel shell, and after dehydration at 80°C, the above electrolyte is injected, and a lithium-ion battery is obtained through a process of formation, sealing pin welding, etc.

[0117] Example 1-2 to Example 1-31

[0118] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. Among them, when the thickness of the first electrode sheet changes, the thickness of the first current collector remains unchanged, and the coating weight is adjusted so that the thickness T of the first electrode sheet is as shown in Table 1. In Example 1-6 and Example 1-7, as the value of T and the value of N change, the specifications of the positive and negative electrode sheets change accordingly. In Example 1-6, the length of the positive electrode sheet is 956.59 mm, and the length of the negative electrode sheet is 981.78 mm; in Example 1-7, the length of the positive electrode sheet is 4260.79 mm, and the length of the negative electrode sheet is 4283.26 mm.

[0119] Examples 2-1 to 2-7

[0120] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.

[0121] Comparative Example 1

[0122] Except that no recess is provided on the surface of the first material layer in <Preparation of the Positive Electrode Sheet>, the rest is the same as Example 1-1.

[0123] Comparative Example 2

[0124] Except that only the first recess is provided on the surface of the first material layer from the 1st circle to the 42nd circle in <Preparation of the Positive Electrode Sheet>, the rest is the same as Example 1-1.

[0125] Comparative Example 3

[0126] Except that only the second recessed portion is provided on the surface of the first material layer from the 1st circle to the 42nd circle in <Preparation of the Positive Electrode Sheet>, the rest is the same as Example 1-1.

[0127] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0128]

[0129]

[0130]

[0131] Note: “ / ” in Table 1 indicates no relevant preparation or result parameters.

[0132] It can be seen from Examples 1-1 to 1-31 and Comparative Examples 1 to 3 that by respectively arranging the first recess and the second recess on the surface of the first material layer with different numbers of turns, the number of pole piece collapse turns and the number of pole piece breakage turns are reduced, and the 400cls capacity retention rate of the lithium-ion battery is improved, indicating that the lithium-ion battery of the present application can effectively reduce the safety risks of the electrode assembly short-circuiting due to collapse of the inner pole piece caused by excessive extrusion pressure and breakage of the outer pole piece caused by excessive tensile stress, and the generation of burrs, and the lithium-ion battery has good cycle performance. In Comparative Example 1, no recesses are set on the first material layer, and the number of pole piece collapse circles and pole piece breakage circles of the lithium ion battery in Comparative Example 1 is more, and the 400cls capacity retention rate of the lithium ion battery is lower; in Comparative Example 2, all circles on the first material layer are set with first recesses, and in Comparative Example 3, all circles on the first material layer are set with second recesses. In Comparative Examples 2 and 3, by setting recesses in all areas on the first material layer, the gap between the pole piece layers is increased, the impedance of the lithium ion battery is increased, the resistance to ion conduction during the cycle is greater, the 400cls capacity retention rate is also lower, and the cycle performance of the lithium ion battery is reduced; at the same time, excessive contact between the electrolyte and the pole piece leads to a relatively increased number of side reactions of the lithium ion battery, an increase in the number of side reaction products, an increase in the thickness of the pole piece, and an increase in the corresponding hardness of the pole piece. Furthermore, the improvement effect on the safety risk of the electrode assembly causing the collapse of the inner ring pole piece due to excessive extrusion pressure and the breakage of the outer ring pole piece due to excessive tensile stress, the generation of burrs and short circuit is poor. The number of pole piece collapse circles and pole piece breakage circles in the lithium-ion batteries in Examples 1-1 to 1-31 is relatively small, and the 400cls capacity retention rate is relatively high, indicating that the lithium-ion battery of the present application can effectively reduce the safety risks of electrode assemblies short-circuiting due to collapse of the inner pole piece caused by excessive extrusion pressure and breakage of the outer pole piece caused by excessive tensile stress, and the generation of burrs, and the lithium-ion battery has good cycle performance and safety performance.

[0133] The value of S usually affects the cycle performance and safety performance of lithium-ion batteries. It can be seen from Examples 1-1 to 1-7 that when the value of S is within the range of this application, the number of pole piece collapse circles and pole piece break circles is small, and the 400cls capacity retention rate is high, indicating that the lithium-ion battery of this application can effectively reduce the safety risks of the electrode assembly due to excessive extrusion pressure causing the inner ring pole piece to collapse and excessive tensile stress causing the outer ring pole piece to break, burrs and short circuit, and the lithium-ion battery has good cycle performance and safety performance.

[0134] The values ​​of T, H1 / T×100%, and H2 / T×100% usually affect the cycle performance and safety performance of lithium-ion batteries. It can be seen from Example 1, Example 1-6 to Example 1-13 that when the values ​​of T, H1 / T×100%, and H2 / T×100% are within the scope of this application, the number of pole piece collapse circles and pole piece breakage circles are small, and the 400cls capacity retention rate is high, indicating that the lithium-ion battery of this application can effectively reduce the safety risk of short circuit caused by excessive extrusion pressure causing collapse of the inner ring pole piece and excessive tensile stress causing breakage of the outer ring pole piece, burrs, etc., and the lithium-ion battery has good cycle performance and safety performance.

[0135] The value of H1 / H2 usually affects the cycle performance and safety performance of lithium-ion batteries. It can be seen from Example 1, Example 1-14 to Example 1-19 that when the value of H1 / H2 is within the range of this application, the number of pole piece collapse circles and pole piece break circles is small, and the 400cls capacity retention rate is high, indicating that the lithium-ion battery of this application can effectively reduce the safety risk of short circuit caused by excessive extrusion pressure causing collapse of the inner ring pole piece and excessive tensile stress causing breakage of the outer ring pole piece, burrs, etc., and the lithium-ion battery has good cycle performance and safety performance.

[0136] The values ​​of d1 and d2 usually affect the cycle performance and safety performance of lithium-ion batteries. It can be seen from Example 1, Example 1-20 to Example 1-25 that when the values ​​of d1 and d2 are within the range of this application, the number of pole piece collapse circles and pole piece break circles is small, and the 400cls capacity retention rate is high, indicating that the lithium-ion battery of this application can effectively reduce the safety risks of the electrode assembly due to excessive extrusion pressure causing the inner ring pole piece to collapse and excessive tensile stress causing the outer ring pole piece to break, burrs and short circuit, and the lithium-ion battery has good cycle performance and safety performance.

[0137] The values ​​of D1 and D2 usually affect the cycle performance and safety performance of lithium-ion batteries. It can be seen from Example 1, Example 1-26 to Example 1-31 that when the values ​​of D1 and D2 are within the range of this application, the number of pole piece collapse circles and pole piece breakage circles is small, and the 400cls capacity retention rate is high, indicating that the lithium-ion battery of this application can effectively reduce the safety risks of the electrode assembly due to excessive extrusion pressure causing the inner ring pole piece to collapse and excessive tensile stress causing the outer ring pole piece to break, burrs and short circuit, and the lithium-ion battery has good cycle performance and safety performance.

[0138] Table 2

[0139]

[0140] Note: “ / ” in Table 2 indicates no relevant preparation or result parameters.

[0141] The values ​​of W1 and W2 usually affect the cycle performance and safety performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-1 to 2-7 that when the values ​​of W1 and W2 are within the range of this application, the number of pole piece collapse circles and pole piece break circles is small, and the 400cls capacity retention rate is high, indicating that the lithium-ion battery of this application can effectively reduce the safety risks of the electrode assembly due to excessive extrusion pressure causing the inner ring pole piece to collapse and excessive tensile stress causing the outer ring pole piece to break, burrs and short circuit, and the lithium-ion battery has good cycle performance and safety performance.

[0142] The values ​​of L1 and L2 usually affect the cycle performance and safety performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-1 to 2-7 that when the values ​​of L1 and L2 are within the range of this application, the number of pole piece collapse circles and pole piece fracture circles is small, and the 400cls capacity retention rate is high, indicating that the lithium-ion battery of this application can effectively reduce the safety risks of the electrode assembly due to excessive extrusion pressure causing the inner ring pole piece to collapse and excessive tensile stress causing the outer ring pole piece to fracture, burrs and short circuit, and the lithium-ion battery has good cycle performance and safety performance.

[0143] The values ​​of L3 and L4 usually affect the cycle performance and safety performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-1 to 2-7 that when the values ​​of L3 and L4 are within the range of this application, the number of pole piece collapse circles and pole piece fracture circles is small, and the 400cls capacity retention rate is high, indicating that the lithium-ion battery of this application can effectively reduce the safety risks of the electrode assembly causing the inner ring pole piece to collapse due to excessive extrusion pressure and the outer ring pole piece to fracture due to excessive tensile stress, and the generation of burrs and short circuits, and the lithium-ion battery has good cycle performance and safety performance.

[0144] 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.

[0145] 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.

[0146] 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 of a wound structure, the electrode assembly comprising a first pole piece, the first pole piece comprising a first current collector and a first material layer located on one surface of the first current collector; Along the winding direction of the electrode assembly, the number of winding turns of the first material layer is N, 15≤N≤70, and N is a positive integer; Along the winding direction of the electrode assembly, the first material layer sequentially includes a first region and a second region; Wherein, the first region is located at the 1st circle to the 0.75Nth circle of the first material layer, and a plurality of first recesses are arranged on the surface of the first region; The second region is located from the 0.8Nth circle to the Nth circle of the first material layer, and a plurality of second recesses are respectively disposed on the surface of the second region.

2. The cylindrical secondary battery according to claim 1, which satisfies one of the following characteristics: (1) The first region is located between the 0.06Nth circle and the 0.75Nth circle of the first material layer; (2) the first region is located between the 0.3Nth circle and the 0.7Nth circle of the first material layer; (3) The first region is located between the 0.4Nth circle and the 0.6Nth circle of the first material layer.

3. The cylindrical secondary battery according to claim 1 or 2, which satisfies one of the following characteristics: (1) The second region is located between the 0.9Nth circle and the Nth circle of the first material layer; (2) The second region is located from the 0.95Nth circle to the Nth circle of the first material layer.

4. The cylindrical secondary battery according to any one of claims 1 to 3, wherein: Based on the surface area of ​​the first material layer, the sum of the areas of the first region and the second region accounts for S, and 2%≤S≤55%.

5. The cylindrical secondary battery according to claim 4, wherein: 10%≤S≤20%; or, 12%≤S≤18%.

6. The cylindrical secondary battery according to any one of claims 1 to 5, wherein: Along the thickness direction of the first pole piece, the thickness of the first pole piece is Tμm, 60≤T≤450; the average depth of the multiple first recesses is H1μm, 1.5%≤H1 / T×100%≤35%; and / or the average depth of the multiple second recesses is H2μm, 1.5%≤H2 / T×100%≤35%.

7. The cylindrical secondary battery according to claim 6, which satisfies one of the following characteristics: (1) 3% ≤ H1 / T×100% ≤ 15%; or, 5% ≤ H1 / T×100% ≤ 10%; (2) 3% ≤ H2 / T×100% ≤ 15%; or, 5% ≤ H2 / T×100% ≤ 10%.

8. The cylindrical secondary battery according to claim 6, wherein: 0.1≤H1 / H2≤5.

9. The cylindrical secondary battery according to claim 8, wherein: 0.2≤H1 / H2≤3; or, 0.3≤H1 / H2≤1.

5.

10. The cylindrical secondary battery according to any one of claims 1 to 9, wherein Along the thickness direction of the first pole piece, a single first recess has a first projection on the surface of the first material layer, and along the length direction of the first pole piece after unfolding, the shortest distance between the outer contours of two adjacent first projections is d1 mm, 0.1≤d1≤15; and / or, Along the thickness direction of the first pole piece, a single second recess has a second projection on the surface of the first material layer, and along the length direction of the unfolded first pole piece, the shortest distance between the outer contours of two adjacent second projections is d2 mm, 0.1≤d2≤10.

11. The cylindrical secondary battery according to claim 10, which satisfies at least one of the following characteristics: (1) 0.5≤d1≤8; or, 1≤d1≤5; (2) 0.3≤d2≤5; or, 0.5≤d2≤2.

12. The cylindrical secondary battery according to any one of claims 1 to 11, wherein The plurality of first recesses or the plurality of second recesses are distributed in a dotted manner on the surface of the first material layer, and along the thickness direction of the first pole piece, the shape of a first projection of a single first recess on the surface of the first material layer is a circle, an ellipse or a regular polygon, and the diameter of the maximum circumscribed circle of the outer contour of a single first projection is D1 mm, 0.2≤D1≤5; and / or, Along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is circular, elliptical or regular polygonal, and the diameter of the maximum circumscribed circle of the outer contour of the single second projection is D2 mm, 0.1≤D2≤6.

13. The cylindrical secondary battery according to claim 12, which satisfies at least one of the following characteristics: (1) 0.5 ≤ D1 ≤ 4.5; or, 1 ≤ D1 ≤ 4; (2) 0.2≤D2≤5.5; or, 0.5≤D2≤5.

14. The cylindrical secondary battery according to any one of claims 1 to 11, wherein: Along the thickness direction of the first pole piece, the shape of a first projection of a single first recess on the surface of the first material layer is a strip, and along the length direction of the first pole piece after unfolding, the average width of the plurality of first projections is W1 mm, 0.2≤W1≤5; and / or, Along the thickness direction of the first pole piece, the shape of the second projection of a single second recess on the surface of the first material layer is a strip, and along the length direction of the unfolded first pole piece, the average width of the multiple second projections is W2mm, 0.1≤W2≤6.

15. The cylindrical secondary battery according to claim 14, which satisfies at least one of the following characteristics: (1) 0.6 ≤ W1 ≤ 2; or, 1 ≤ W1 ≤ 1.5; (2) 0.1≤W2≤3; or, 0.2≤W2≤1.

16. The cylindrical secondary battery according to claim 14, wherein The plurality of first recesses extend along the width direction of the first pole piece after unfolding and are spaced apart along the length direction of the first pole piece after unfolding, and based on the width of the first pole piece after unfolding, the length proportion of a single first projection is L1, 5%≤L1≤95%; and / or, The multiple second recesses extend along the width direction of the first pole piece after it is unfolded and are spaced apart along the length direction of the first pole piece after it is unfolded. Based on the width of the first pole piece after it is unfolded, the length of a single second projection accounts for L2, 10%≤L2≤95%.

17. The cylindrical secondary battery according to claim 16, wherein: Along the width direction of the first pole piece after unfolding, the length of a single first projection is L3 mm, 9≤L3≤150; and / or, along the width direction of the first pole piece after unfolding, the length of a single second projection is L4 mm, 18≤L4≤180.

18. The cylindrical secondary battery according to claim 17, which satisfies at least one of the following characteristics: (1) 15 ≤ L3 ≤ 80; or, 20 ≤ L3 ≤ 55; (2) 30≤L4≤100; or, 50≤L4≤80.

19. The cylindrical secondary battery according to any one of claims 1 to 18, wherein: The first material layer is located on a surface of the first current collector facing the winding center of the electrode assembly.

20. The cylindrical secondary battery according to claim 19, wherein The first pole sheet further includes a second material layer, the second material layer is located on the surface of the first current collector away from the winding center of the electrode assembly; a surface of the second material layer in an area opposite to the first area is provided with a plurality of first protrusions, at least some of the first protrusions are arranged opposite to some of the first concave parts; and / or, A plurality of second convex portions are disposed on a surface of a region of the second material layer opposite to the second region, and at least some of the second convex portions are disposed opposite to some of the second concave portions.

21. The cylindrical secondary battery according to claim 20, wherein A region of the first current collector opposite to the first region is provided with a plurality of third protrusions in the direction of the second material layer; and / or, A plurality of fourth protrusions are disposed in a region of the first current collector opposite to the second region toward the second material layer.

22. The cylindrical secondary battery according to claim 21, wherein At least part of the third convex portion corresponds to part of the first concave portion; and / or at least part of the fourth convex portion corresponds to part of the second concave portion.

23. The cylindrical secondary battery according to any one of claims 1 to 22, wherein: The first pole piece is a positive pole piece. 24 . An electronic device comprising the cylindrical secondary battery according to claim 1 .

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