Cylindrical secondary battery and electric equipment

Abstract

The invention relates to a cylindrical secondary battery and electric equipment, and belongs to the technical field of secondary batteries. The initial winding section with the winding number of at least two circles is arranged at the initial end, exceeding the second pole piece, of the first pole piece, and the supporting layer with certain flexural rigidity is arranged on at least one surface of the initial winding section, so that the center of the electrode assembly can be well supported, extrusion generated by expansion is resisted, and the service life of the electrode assembly is prolonged. Therefore, the collapse probability of the electrode plate of the inner ring is reduced, and the safety performance of the battery is improved. Meanwhile, by controlling the flexural rigidity of the supporting layer of the first circle to be larger than the flexural rigidity of the supporting layers at the other positions, the collapse probability of the electrode plate of the inner circle is further reduced.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more specifically, to a cylindrical secondary battery and an electrical device. Background Technology

[0002] For cylindrical secondary batteries, the electrode plates will expand during cycling. The expanded electrode plates will cause the inner electrode plates of the cylindrical secondary battery to be squeezed and collapse. The collapsed electrode plates are prone to local interface lithium plating and electrode plate breakage. In severe cases, it can lead to the cylindrical secondary battery cycling down, burrs piercing the separator, and thermal runaway risks such as fire and explosion, resulting in a reduction in the safety performance of the cylindrical secondary battery. Summary of the Invention

[0003] This application provides a cylindrical secondary battery and an electrical device that can reduce the probability of inner ring collapse of the electrode plates of the cylindrical secondary battery, thereby improving the safety performance of the cylindrical secondary battery.

[0004] In a first aspect, embodiments of this application provide a cylindrical secondary battery, comprising: An electrode assembly is provided, which has a wound structure and includes stacked electrode plates, each including a first electrode plate and a second electrode plate with opposite polarities. Along the opposite direction of the winding direction of the electrode assembly, the first electrode plate includes a starting winding section extending beyond the starting end of the second electrode plate. The starting winding section has at least two turns, and at least one surface of the starting winding section is provided with a support layer. Along the winding direction of the electrode assembly, the bending stiffness of the support layer located on the first turn of the starting winding section is greater than the bending stiffness of the support layers located at other positions on the starting winding section.

[0005] In the technical solution of this application embodiment, by setting a starting winding section with at least two turns beyond the starting end of the second electrode sheet on the first electrode sheet, and providing a support layer with a certain bending stiffness on at least one surface of the starting winding section, the center of the electrode assembly can be well supported, resisting the compression caused by expansion, thereby reducing the probability of the inner electrode sheet collapsing and improving the safety performance of the battery. Simultaneously, by controlling the bending stiffness of the support layer in the first turn to be greater than that of the support layers in other positions, the probability of the inner electrode sheet collapsing is further reduced.

[0006] As an optional implementation, the bending stiffness of the support layer in the first turn of the initial winding section is not less than 0.23 N*cm. 2 .

[0007] In the above implementation process, the greater the bending stiffness of the support layer in the first turn of the initial winding section, the more beneficial it is to reduce the probability of the inner electrode sheet collapsing.

[0008] As an optional implementation, the bending stiffness of the support layer in the first turn of the initial winding section is set to 0.23 N*cm. 2 -0.96N*cm 2 .

[0009] As an alternative implementation, the bending stiffness of the support layer gradually decreases along the winding direction of the electrode assembly.

[0010] As an optional implementation, along the winding direction of the electrode assembly, the bending stiffness of the support layer in the initial winding section decreases with each turn, and the bending stiffness of the support layer in the first turn of the initial winding section is 1.9 to 8 times that of the support layer in the last turn of the initial winding section.

[0011] As an optional implementation, the thickness of the support layer in the first turn of the initial winding section is greater than the thickness of the support layer in the remaining positions of the initial winding section.

[0012] In the above implementation process, by controlling the thickness of the first ring of support layers to be greater than that of the support layers in other positions, it is possible to reduce the probability of the inner ring of electrode plates collapsing while reducing the impact on the energy density of the cylindrical secondary battery.

[0013] As an optional implementation, the thickness of the support layer in the first turn of the initial winding section is set to 130μm~205μm.

[0014] As an optional implementation, the thickness ratio of the starting winding segment and the support layer in the same turn is 0.77 to 1.51.

[0015] In the above implementation process, by controlling the thickness ratio of the starting winding section and the support layer located in the same circle to be 0.77~1.51, the bending stiffness ratio of the starting winding section and the support layer is better matched, which is more conducive to resisting the compression caused by expansion, reducing the probability of the inner circle electrode sheet collapsing, and thus improving the safety performance of the battery.

[0016] As an alternative implementation, the thickness of the support layer gradually decreases along the winding direction of the electrode assembly.

[0017] In the above implementation process, by gradually reducing the thickness of the support layer, the probability of the inner electrode plates collapsing can be reduced, while further reducing the impact on the energy density of the cylindrical secondary battery.

[0018] As an optional implementation, along the winding direction of the electrode assembly, the thickness of the support layer in the initial winding section decreases turn by turn, and the thickness of the support layer in the first turn of the initial winding section is 1.2 to 2 times the thickness of the support layer in the last turn of the initial winding section.

[0019] As an optional implementation, the number of turns in the initial winding section is 2.5 to 4.5.

[0020] In the above implementation process, the more turns the initial winding section has, the better it is at resisting the compression caused by expansion, thereby reducing the probability of the inner electrode plates collapsing. Conversely, the fewer turns the initial winding section has, the better the cylindrical secondary battery can maintain a high energy density. By controlling the number of turns in the initial winding section to 2.5 to 4.5, both the safety and energy density of the cylindrical secondary battery can be balanced.

[0021] As an optional implementation, the support layer includes an adhesive layer and a substrate layer, the adhesive layer being bonded to the starting winding segment, and the peel strength between the adhesive layer and the starting winding segment being less than the peel strength between the adhesive layer and the substrate layer.

[0022] In the above embodiments, by controlling the peel strength between the adhesive layer and the starting winding segment to be less than the peel strength between the adhesive layer and the substrate layer, the probability of the adhesive layer being exposed and bonding to the starting winding segment, resulting in the starting winding segment folding back, can be reduced.

[0023] As an optional implementation, the peel strength between the adhesive layer and the initial winding segment is 100 N / m to 300 N / m; and / or, The peel strength between the adhesive layer and the substrate layer is 300 N / m to 500 N / m.

[0024] As an optional implementation, the adhesive layer comprises at least one of the following: acrylic adhesive, epoxy resin, polyurethane, butyl rubber, rosin resin, polyacrylic acid, silicone, polypropylene, PEDOT:PSS, or polypyrrole.

[0025] As an optional implementation, the substrate layer comprises at least one of polyethylene terephthalate, polyimide, polypropylene, polyphenylene sulfide, polyethylene, or polyvinyl chloride.

[0026] As an optional implementation, the line connecting the starting end of the starting winding section and the winding center axis of the electrode assembly is the first line, the line connecting the ending end of the starting winding section and the winding center axis of the electrode assembly is the second line, and the line connecting the ending end of the outermost electrode sheet of the electrode assembly and the winding center axis of the electrode assembly is the third line. Along the winding direction of the electrode assembly, the angle between the first connecting line and the third connecting line is θ1, and the angle between the first connecting line and the second connecting line is θ2, where 30°≤θ1≤θ2.

[0027] In the above embodiments, by controlling the relationship between the angle θ1 between the third line and the first line and the angle θ2 between the second line and the first line to satisfy: 30°≤θ1≤θ2, that is, the end of the extruded electrode sheet is within the fan-shaped area formed by the beginning and end of the starting winding section, and avoids the more fragile beginning part of the starting winding section, so that the path of extrusion inward can pass through more layers of the starting winding section, thereby providing better resistance with fewer turns, reducing the probability of the inner electrode sheet collapsing, and improving the safety performance of the battery.

[0028] As an optional implementation, the first electrode is a negative electrode.

[0029] In the above embodiments, by controlling the first electrode to be a negative electrode, and utilizing its initial winding section, more deposition sites for active metal ions can be provided, reducing the probability of lithium dendrite formation and improving the safety of cylindrical secondary batteries.

[0030] Secondly, embodiments of this application provide an electrical device, which includes the cylindrical secondary battery provided in the first aspect. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of an electrode assembly provided in some embodiments of this application.

[0033] Figure 2 This is a schematic diagram of the structure of the adhesive layer and substrate layer provided in some embodiments of this application.

[0034] Reference numerals: 1000 - Electrode assembly; 100 - Electrode sheet; 110 - First electrode sheet; 110a - Initial winding section; 120 - Second electrode sheet; 200 - Separating membrane; 300 - Support layer; 310 - Adhesive layer; 320 - Substrate layer; L1 - First connection line; L2 - Second connection line; L3 - Third connection line; A - Winding direction of the electrode assembly. Detailed Implementation

[0035] The present application is hereby disclosed in detail with appropriate reference to the accompanying drawings. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter of the claims.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if a method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined. In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0039] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0040] For cylindrical secondary batteries, the electrode plates will expand during cycling. The expanded electrode plates will cause the inner electrode plates of the cylindrical secondary battery to be squeezed and collapse. The collapsed electrode plates are prone to local interface lithium plating and electrode plate breakage. In severe cases, it can lead to the cylindrical secondary battery cycling down, burrs piercing the separator, and thermal runaway risks such as fire and explosion, resulting in a reduction in the safety performance of the cylindrical secondary battery.

[0041] This application aims to provide a cylindrical secondary battery and an electrical device that can reduce the probability of inner ring collapse of the electrode plates of the cylindrical secondary battery, thereby improving the safety performance of the cylindrical secondary battery.

[0042] Please see Figure 1 , Figure 1This is a schematic diagram of the structure of an electrode assembly provided in some embodiments of this application. Embodiments of this application provide a cylindrical secondary battery, including: an electrode assembly 1000, which has a wound structure. The electrode assembly 1000 includes stacked electrode plates 100, each including a first electrode plate 110 and a second electrode plate 120 with opposite polarities. Along the opposite direction of the winding direction A of the electrode assembly, the first electrode plate 110 includes a starting winding section 110a extending beyond the starting end of the second electrode plate 120. The starting winding section 110a has at least two winding turns. At least one surface of the starting winding section 110a is provided with a support layer 300. Along the winding direction A of the electrode assembly, the bending stiffness of the support layer 300 located on the first turn of the starting winding section 110a is greater than the bending stiffness of the support layers 300 located at other positions on the starting winding section 110a.

[0043] Those skilled in the art will understand that, depending on the type of secondary battery, such as a liquid battery or a solid-state battery, a separator 200 or a solid electrolyte membrane is disposed between the first electrode 110 and the second electrode 120. Taking a liquid battery as an example, the cylindrical wound structure of the electrode assembly 1000 means that the separator 200, the first electrode 110, the separator 200, and the second electrode 120 are wound around a central axis, or the first electrode 110, the separator 200, the second electrode 120, and the separator 200 are wound around a central axis. There can be two winding directions: clockwise winding and counterclockwise winding.

[0044] The winding direction A of the electrode assembly refers to the direction from the inside out, and the opposite direction of the winding direction A of the electrode assembly is the direction from the outside in.

[0045] Bending stiffness refers to a structural member's ability to resist bending deformation. It is expressed as the product of the elastic modulus of the member material and the moment of inertia of the member's cross-section about its central axis. Bending stiffness is positively correlated with the member's thickness. Bending stiffness σ = E * I, where E is the elastic modulus of the member material and I is the moment of inertia of the member's cross-section. The formula for the moment of inertia I is adjusted according to the cross-sectional shape, such as rectangular, circular, hollow circular tube, and I-beam. Specific formulas can be found in reference books.

[0046] The support layer 300 at other positions in the initial winding segment 110a refers to the support layer 300 disposed excluding the first turn of the initial winding segment 110a. In other words, the support layer 300 at other positions is disposed in the initial winding segment 110a, but not in the first turn of the initial winding segment 110a. For example, if the initial winding segment 110a has three turns, and along the winding direction, the initial winding segment 110a can be divided into the first turn, the second turn, and the third turn in sequence, then the support layer 300 at other positions in the initial winding segment 110a refers to the support layer 300 located in the second and third turns of the initial winding segment 110a.

[0047] This cylindrical secondary battery features a starting winding section 110a with at least two turns, extending beyond the starting end of the second electrode 120 beyond the first electrode 110. A support layer 300 with a certain bending stiffness is provided on at least one surface of the starting winding section 110a. This provides good support for the center of the electrode assembly 1000, resisting compression caused by expansion, thereby reducing the probability of collapse of the inner electrode 100 and improving battery safety. Furthermore, by controlling the bending stiffness of the first winding support layer 300 to be greater than that of the support layers 300 at other locations, the probability of collapse of the inner electrode 100 is further reduced.

[0048] In some embodiments, the bending stiffness of the support layer 300 in the first turn of the initial winding section 110a is not less than 0.23 N*cm. 2 The greater the bending stiffness of the support layer 300 in the first turn of the initial winding section 110a, the more beneficial it is to reducing the probability of the inner electrode sheet 100 collapsing. For example, the bending stiffness of the support layer 300 in the first turn of the initial winding section 110a can be 0.23 N*cm. 2 0.3 N*cm 2 0.4 N*cm 2 0.5 N*cm 2 0.6 N*cm 2 0.7N*cm 2 0.8 N*cm 2 0.9 N*cm 2 0.96 N*cm 2 etc., which can also be not less than 0.23 N*cm 2 Any value within the range.

[0049] Optionally, the bending stiffness of the support layer 300 in the first turn of the initial winding segment 110a is set to 0.23 N*cm. 2 -0.96N*cm 2 .

[0050] In some embodiments, the bending stiffness of the support layer 300 gradually decreases along the winding direction A of the electrode assembly.

[0051] Those skilled in the art will understand that the gradual reduction can be linear or step-like. A step-like reduction, also known as a non-linear reduction, can be a regular step-like reduction, such as a decrease in the bending stiffness of the support layer 300 along the winding direction A of the electrode assembly, turning by turning. It can also be an irregular step-like reduction, such as a higher bending stiffness in the first turn of the support layer 300 along the winding direction A than in the other positions, meaning that the bending stiffness of the support layer 300 is the same except for the first turn. Similarly, the magnitude of the step-like reduction can be regular, such as an equal multiple reduction or an arithmetic progression reduction, or it can be irregular.

[0052] In some embodiments, along the winding direction A of the electrode assembly, the bending stiffness of the support layer 300 provided in the initial winding section 110a decreases with each turn, and the bending stiffness of the support layer 300 provided in the first turn of the initial winding section 110a is 1.9 to 8 times that of the support layer 300 provided in the last turn of the initial winding section 110a.

[0053] For example, the bending stiffness of the support layer 300 in the first turn of the starting winding section 110a can be 1.9 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, 6 times, 7 times, 8 times, etc., which is the bending stiffness of the support layer 300 in the last turn of the starting winding section 110a, or it can be any value in the range of 1.9 times to 8 times.

[0054] In some embodiments, the thickness of the support layer 300 in the first turn of the initial winding section 110a is greater than the thickness of the support layers 300 in the remaining positions of the initial winding section 110a. By controlling the thickness of the support layer 300 in the first turn to be greater than that in the remaining positions, the probability of the inner electrode sheet 100 collapsing can be reduced, while the impact on the energy density of the cylindrical secondary battery can be reduced.

[0055] In some embodiments, the thickness of the support layer 300 in the first turn of the initial winding segment 110a is 130μm to 205μm. For example, the thickness of the support layer 300 in the first turn of the initial winding segment 110a can be 130μm, 135μm, 140μm, 145μm, 150μm, 155μm, 160μm, 165μm, 170μm, 175μm, 180μm, 185μm, 190μm, 195μm, 200μm, 205μm, etc., or it can be any value within the range of 130μm to 205μm.

[0056] In some embodiments, the thickness ratio of the initial winding segment 110a and the support layer 300 located in the same turn is 0.77 to 1.51. By controlling the thickness ratio of the initial winding segment 110a and the support layer 300 located in the same turn to 0.77 to 1.51, a better match is achieved in the bending stiffness ratio of the initial winding segment 110a and the support layer 300, which is more conducive to resisting the compression caused by expansion, reducing the probability of the inner electrode sheet 100 collapsing, and thus improving the safety performance of the battery. For example, the thickness ratio of the initial winding segment 110a and the support layer 300 located in the same turn can be 0.77, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.51, etc., or any value within the range of 0.77 to 1.51.

[0057] In some embodiments, the thickness of the support layer 300 gradually decreases along the winding direction A of the electrode assembly.

[0058] Those skilled in the art will understand that the gradual reduction can be linear or step-like. A step-like reduction can be a regular step-like reduction, such as decreasing the thickness of the support layer 300 around the winding direction A of the electrode assembly with each turn, or it can be an irregular step-like reduction, such as the thickness of the first turn of the support layer 300 being greater than the thickness of the support layer 300 at other positions along the winding direction A of the electrode assembly, i.e., the thickness of the support layer 300 is the same at other positions except for the first turn which is thicker. Similarly, the magnitude of the step-like reduction can be regular, i.e., it can be a multiple reduction, an arithmetic reduction, etc., or it can be irregular.

[0059] By gradually reducing the thickness of the support layer 300, the probability of the inner electrode plate 100 collapsing can be reduced, while further reducing the impact on the energy density of the cylindrical secondary battery.

[0060] In some embodiments, along the winding direction A of the electrode assembly, the thickness of the support layer 300 in the initial winding section 110a decreases with each turn, and the thickness of the support layer 300 in the first turn of the initial winding section 110a is 1.2 to 2 times the thickness of the support layer 300 in the last turn of the initial winding section 110a.

[0061] For example, the thickness of the support layer 300 in the first turn of the starting winding segment 110a can be 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2 times, etc., the thickness of the support layer 300 in the last turn of the starting winding segment 110a, or it can be any value in the range of 1.2 times to 2 times.

[0062] In some embodiments, the number of turns of the initial winding section 110a is 2.5 to 4.5 turns.

[0063] The more turns the initial winding section 110a has, the better it resists the compression caused by expansion, thus reducing the probability of the inner electrode sheet 100 collapsing. Conversely, the fewer turns the initial winding section 110a has, the better the cylindrical secondary battery can maintain a high energy density. By controlling the number of turns in the initial winding section 110a to be 2.5 to 4.5, both the safety and energy density of the cylindrical secondary battery can be balanced.

[0064] For example, the number of turns of the initial winding section 110a can be 2.5 turns, 2.6 turns, 2.8 turns, 3 turns, 3.2 turns, 3.4 turns, 3.6 turns, 3.8 turns, 4 turns, 4.2 turns, 4.4 turns, 4.5 turns, etc., or it can be any value in the range of 2.5 to 4.5 turns.

[0065] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of the adhesive layer 310 and the substrate layer 320 provided in some embodiments of this application. In some embodiments, the support layer 300 includes an adhesive layer 310 and a substrate layer 320, wherein the adhesive layer 310 is bonded to the starting winding section 110a, and the peel strength between the adhesive layer 310 and the starting winding section 110a is less than the peel strength between the adhesive layer 310 and the substrate layer 320.

[0066] Peel strength refers to the force required to separate two bonded layers of a certain width (such as adhesive layer 310 and starting wound section 110a, adhesive layer 310 and substrate layer 320) at a specified angle and speed. In this application, the peel strength of adhesive layer 310 and starting wound section 110a, and adhesive layer 310 and substrate layer 320 can be tested using a tensile testing machine, with standard sample preparation and testing according to ASTM D3330, at a testing speed of 300 mm / min.

[0067] By controlling the peel strength between the adhesive layer 310 and the starting winding segment 110a to be less than the peel strength between the adhesive layer 310 and the substrate layer 320, the probability of the starting winding segment 110a being exposed and bonded to the adhesive layer can be reduced, thus reducing the probability of the starting winding segment 110a folding back.

[0068] In some embodiments, the peel strength between the adhesive layer 310 and the starting winding section 110a is 100 N / m to 300 N / m; the peel strength between the adhesive layer 310 and the substrate layer 320 is 300 N / m to 500 N / m.

[0069] For example, the peel strength between the adhesive layer 310 and the starting winding section 110a can be 100 N / m, 110 N / m, 120 N / m, 130 N / m, 140 N / m, 150 N / m, 160 N / m, 170 N / m, 180 N / m, 190 N / m, 200 N / m, 210 N / m, 220 N / m, 230 N / m, 240 N / m, 250 N / m, 260 N / m, 270 N / m, 280 N / m, 290 N / m, 300 N / m, etc., or it can be any value in the range of 100 N / m to 300 N / m. The peel strength between the adhesive layer 310 and the substrate layer 320 can be 300 N / m, 310 N / m, 320 N / m, 330 N / m, 340 N / m, 350 N / m, 360 N / m, 370 N / m, 380 N / m, 390 N / m, 400 N / m, 410 N / m, 420 N / m, 430 N / m, 440 N / m, 450 N / m, 460 N / m, 470 N / m, 480 N / m, 490 N / m, 500 N / m, etc., or any value within the range of 300 N / m to 500 N / m. For example, the adhesive layer 310 can be made of acrylic adhesive. For example, the material of the substrate layer 320 can be polyethylene terephthalate (PET), polyimide (PI), or polyphenylene sulfide (PPS).

[0070] In some embodiments, the adhesive layer 310 comprises at least one of acrylic adhesive, epoxy resin, polyurethane, butyl rubber, rosin resin, polyacrylic acid, silicone, polypropylene, PEDOT:PSS, or polypyrrole.

[0071] In some embodiments, the substrate layer 320 comprises at least one of polyethylene terephthalate, polyimide, polypropylene, polyphenylene sulfide, polyethylene, or polyvinyl chloride.

[0072] In some embodiments, the line connecting the starting end of the starting winding segment 110a and the winding center axis of the electrode assembly 1000 is the first connecting line L1, the line connecting the ending end of the starting winding segment 110a and the winding center axis of the electrode assembly 1000 is the second connecting line L2, and the line connecting the ending end of the outermost electrode plate 100 of the electrode assembly 1000 and the winding center axis of the electrode assembly 1000 is the third connecting line L3; along the winding direction A of the electrode assembly, the angle between the first connecting line L1 and the third connecting line L3 is θ1, the angle between the first connecting line L1 and the second connecting line L2 is θ2, and 30°≤θ1≤θ2<360°.

[0073] By controlling the relationship between the angle θ1 between the first connection L1 and the third connection L3 and the angle θ2 between the first connection L1 and the second connection L2, the following condition is met: 30°≤θ1≤θ2. That is, the end of the extruded electrode sheet 100 is within the fan-shaped area formed by the beginning and end of the starting winding section 110a, and avoids the more fragile beginning part of the starting winding section 110a. This allows the path of extrusion to be transmitted inward to pass through more layers of the starting winding section 110a, thereby providing better resistance with fewer turns, reducing the probability of the inner electrode sheet 100 collapsing, and improving the safety performance of the battery.

[0074] For example, the included angle θ2 between the first line L1 and the second line L2 can be 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°, 185°, 190°, 200°, or 2... 05°, 210°, 215°, 220°, 225°, 230°, 235°, 240°, 245°, 250°, 255°, 260°, 265°, 270°, 275°, 280°, 285°, 290°, 295°, 300°, 305°, 310°, 315°, 320°, 325°, 330°, 335°, 340°, 345°, 350°, 355°, or 359°, etc., which can also be any value within the range of 30°≤θ2<360°. The angle θ1 between the first line L1 and the third line L3 can be 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°, 185°, 190°, 200°, or 205°. °, 210°, 215°, 220°, 225°, 230°, 235°, 240°, 245°, 250°, 255°, 260°, 265°, 270°, 275°, 280°, 285°, 290°, 295°, 300°, 305°, 310°, 315°, 320°, 325°, 330°, 335°, 340°, 345°, 350°, 355°, or 359°, etc., which can also be any value within the range of 30°≤θ1≤θ2.

[0075] To provide more deposition sites for active metal ions and reduce the probability of lithium dendrite formation, in some embodiments, the first electrode 110 is a negative electrode. By controlling the first electrode 110 to be a negative electrode, and utilizing its initial winding section 110a, more deposition sites for active metal ions can be provided, reducing the probability of lithium dendrite formation and improving the safety of the cylindrical secondary battery. Similarly, in some embodiments, the outermost electrode 100 of the electrode assembly 1000 is a negative electrode.

[0076] This application also provides an electrical device, which includes the cylindrical secondary battery provided above.

[0077] In some embodiments, the electrical equipment can be a drone, power tool, electric vehicle, electric car, ship, spacecraft, etc. Among these, drones can be drones for photography, agricultural drones, transportation drones, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0078] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0079] Example 1 Preparation of the positive electrode sheet The positive electrode active material NCM622, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5, and N was added. Methylpyrrolidone (NMP) was used as a solvent to prepare a slurry with a solid content of 75 wt%, which was then stirred evenly. The slurry was uniformly coated onto one surface of an aluminum foil with a thickness of 15 μm, and then dried at 120 °C to obtain a positive electrode sheet with a single-sided coating of the positive active material layer. When preparing a double-sided coated positive electrode sheet, the above coating steps were repeated on the other surface of the aluminum foil. The single-sided coating weight of the positive active material layer was 190 mg / 1540.25 mm. 2 Then, through cold pressing, die cutting, and slitting, a positive electrode sheet with a thickness of 140μm is obtained.

[0080] Preparation of the negative electrode sheet Artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:1.5:2.5, with deionized water added as a solvent to prepare a slurry with a weight percentage of 50 wt%. The slurry was then uniformly coated onto one surface of a 6 μm thick copper foil and dried at 110 °C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer. To prepare a double-sided coated negative electrode sheet, the above steps were repeated on the other surface to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. The single-sided coating weight of the negative electrode active material layer was 160 mg / 1540.25 mm. 2 Then, through cold pressing, die cutting, and slitting, a negative electrode sheet with a thickness of 135μm is obtained.

[0081] Preparation of Electrolyte In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent, dissolved, and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0082]

Separation membrane 200

[0083] [Preparation of Cylindrical Secondary Cells] The initial winding section 110a of the negative electrode is set to have 2 turns, and a support layer 300 is provided on the inner side of the initial winding section 110a. The prepared positive electrode, negative electrode, and separator 200 are wound together, and the negative electrode forms an initial winding section 110a extending beyond the starting end of the positive electrode along the opposite direction of the winding direction A of the electrode assembly. The bending stiffness of the support layer 300 in the first turn of the initial winding section 110a is 0.96 N*cm along the winding direction A of the electrode assembly. 2 The support layer 300, with a thickness of 205μm and made of PET (200μm) + acrylic adhesive (5μm), has a bending stiffness of 0.12 N*cm at the remaining positions of the initial winding section 110a. 2 It has a thickness of 105μm and is made of PET (100μm) + acrylic adhesive (5μm).

[0084] The electrode assembly 1000 is encapsulated in a housing, and electrolyte is injected into the assembled electrode assembly 1000. After vacuum encapsulation, standing, hot pressing formation, shaping and other processes, a cylindrical secondary battery with a diameter of 35mm, a length of 205mm and a central hole diameter of 4.5mm is obtained.

[0085] Example 2 Except for the setting of the support layer, all other contents of this embodiment are the same as those of Embodiment 1.

[0086] Parameters of the support layer: Along the winding direction A of the electrode assembly, the bending stiffness of the support layer 300 in the first turn of the initial winding segment 110a is set to 0.41 N*cm. 2 The support layer 300, with a thickness of 155μm and made of PET (150μm) + acrylic adhesive (5μm), has a bending stiffness of 0.12 N*cm at the remaining positions of the initial winding section 110a. 2 It has a thickness of 105μm and is made of PET (100μm) + acrylic adhesive (5μm).

[0087] Example 3 Except for the setting of the support layer, all other contents of this embodiment are the same as those of Embodiment 1.

[0088] Parameters of the support layer: Along the winding direction A of the electrode assembly, the bending stiffness of the support layer 300 in the first turn of the initial winding segment 110a is set to 0.23 N*cm. 2 The support layer 300, with a thickness of 130μm and made of PET (125μm) + acrylic adhesive (5μm), has a bending stiffness of 0.12 N*cm at the remaining positions of the initial winding section 110a. 2 It has a thickness of 105μm and is made of PET (100μm) + acrylic adhesive (5μm).

[0089] Example 4 Except for the number of turns in the initial winding section being 2.5 turns, this embodiment is the same as embodiment 2.

[0090] Example 5 Except for the number of turns in the initial winding section being 4.5 turns, all other aspects of this embodiment are the same as in Embodiment 2.

[0091] Comparative Example 1 Except for the setting of the support layer, the contents of this comparative example are the same as those of Example 1.

[0092] Support layer parameters: The flexural stiffness of the support layer with a diameter of 300 mm in all rings is 0.12 N*cm. 2It has a thickness of 105μm and is made of PET (100μm) + acrylic adhesive (5μm).

[0093] Comparative Example 2 This comparative example is identical to Example 1 except that it does not have a support layer.

[0094] The main parameter controls for each embodiment and comparative example are shown in Table 1.

[0095] The cylindrical secondary batteries provided in each embodiment and comparative example were tested, including: Cyclic collapse test: At 25℃, the cylindrical secondary battery is charged at a constant current of 1C to the charging cutoff voltage of 4.2V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 4C to the discharge cutoff voltage of 2.7V, left to stand for 5 minutes. This constitutes one cycle. This cycle is repeated 100 times. Using industrial computed tomography (CT) technology (Zeiss Xradia 620 Versa), a CT scan of the battery cross-section is performed along the axial direction of the cylindrical secondary battery. The cycle continues, with scanning performed every 10 cycles until wrinkles appear in the inner ring of the electrode assembly or the electrode sheets bend and protrude in the scanned structural image. The cycle is stopped when the inner ring of the electrode assembly collapses. The higher the number of cycles when the electrode assembly collapses, the better the cycle performance and safety performance of the cylindrical secondary battery.

[0096] The test results are shown in Table 1.

[0097] Table 1

[0098] In the table, " / " indicates that the material or parameter does not exist.

[0099] As can be seen from the table above, the secondary battery provided in this application embodiment has a larger number of cycles when the inner ring collapses, and has better safety.

[0100] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A cylindrical secondary battery, characterized in that, include: An electrode assembly having a wound structure, the electrode assembly comprising stacked electrode plates, the electrode plates comprising a first electrode plate and a second electrode plate with opposite polarities; In the opposite direction to the winding direction of the electrode assembly, the first electrode includes a starting winding segment extending beyond the starting end of the second electrode. The starting winding segment has at least two turns, and at least one surface of the starting winding segment is provided with a support layer. In the winding direction of the electrode assembly, the bending stiffness of the support layer located on the first turn of the starting winding segment is greater than the bending stiffness of the support layer located at other positions of the starting winding segment.

2. The cylindrical secondary battery according to claim 1, characterized in that, The bending stiffness of the support layer in the first turn of the initial winding section is set to be no less than 0.23 N*cm. 2 .

3. The cylindrical secondary battery according to claim 1 or 2, characterized in that, The bending stiffness of the support layer in the first turn of the initial winding section is set to 0.23 N*cm. 2 -0.96N*cm 2 .

4. The cylindrical secondary battery according to any one of claims 1 to 3, characterized in that, Along the winding direction of the electrode assembly, the bending stiffness of the support layer gradually decreases.

5. The cylindrical secondary battery according to any one of claims 1 to 4, characterized in that, Along the winding direction of the electrode assembly, the bending stiffness of the support layer in the initial winding section decreases with each turn. The bending stiffness of the support layer in the first turn of the initial winding section is 1.9 to 8 times that of the support layer in the last turn of the initial winding section.

6. The cylindrical secondary battery according to any one of claims 1 to 5, characterized in that, The thickness of the support layer in the first turn of the initial winding segment is greater than the thickness of the support layer in the remaining positions of the initial winding segment.

7. The cylindrical secondary battery according to any one of claims 5 to 6, characterized in that, The thickness of the support layer in the first turn of the initial winding section is set to be 130μm~205μm.

8. The cylindrical secondary battery according to any one of claims 5 to 7, characterized in that, The thickness ratio of the starting winding segment and the support layer located in the same loop is 0.77 to 1.

51.

9. The cylindrical secondary battery according to any one of claims 5 to 8, characterized in that, The thickness of the support layer gradually decreases along the winding direction of the electrode assembly.

10. The cylindrical secondary battery according to any one of claims 5 to 9, characterized in that, Along the winding direction of the electrode assembly, the thickness of the support layer in the initial winding section decreases with each turn, and the thickness of the support layer in the first turn of the initial winding section is 1.2 to 2 times the thickness of the support layer in the last turn of the initial winding section.

11. The cylindrical secondary battery according to any one of claims 1 to 10, characterized in that, The number of turns in the initial winding section is 2.5 to 4.

5.

12. The cylindrical secondary battery according to any one of claims 1 to 11, characterized in that, The support layer includes an adhesive layer and a substrate layer. The adhesive layer is bonded to the starting winding section, and the peel strength between the adhesive layer and the starting winding section is less than the peel strength between the adhesive layer and the substrate layer.

13. The cylindrical secondary battery according to claim 12, characterized in that, The peel strength between the adhesive layer and the initial winding section is 100 N / m to 300 N / m; and / or, The peel strength between the adhesive layer and the substrate layer is 300 N / m to 500 N / m.

14. The cylindrical secondary battery according to claim 12 or 13, characterized in that, The adhesive layer comprises at least one of acrylic adhesive, epoxy resin, polyurethane, butyl rubber, rosin resin, polyacrylic acid, silicone, polypropylene, PEDOT:PSS, or polypyrrole; and / or, The substrate layer includes at least one of polyethylene terephthalate, polyimide, polypropylene, polyphenylene sulfide, polyethylene, or polyvinyl chloride.

15. The cylindrical secondary battery according to any one of claims 1 to 14, characterized in that, The line connecting the starting end of the starting winding segment and the winding center axis of the electrode assembly is the first line; the line connecting the ending end of the starting winding segment and the winding center axis of the electrode assembly is the second line; and the line connecting the ending end of the outermost electrode sheet of the electrode assembly and the winding center axis of the electrode assembly is the third line. Along the winding direction of the electrode assembly, the angle between the first connecting line and the third connecting line is θ1, and the angle between the first connecting line and the second connecting line is θ2, where 30°≤θ1≤θ2.

16. The cylindrical secondary battery according to any one of claims 1 to 15, characterized in that, The first electrode is the negative electrode.

17. An electrical appliance, characterized in that, The cylindrical secondary battery includes any one of claims 1 to 16.

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