Secondary battery, preparation method thereof and electric equipment

Abstract

The invention discloses a secondary battery and a preparation method thereof and electric equipment, the secondary battery comprises a shell and a cylindrical electrode assembly, the electrode assembly is arranged in the shell, and the electrode assembly comprises a first pole piece, a second pole piece and an isolating membrane. And the polarity of the second pole piece is opposite to that of the first pole piece. The isolating membrane is arranged between the first pole piece and the second pole piece, the electrode assembly is provided with a winding axis, the electrode assembly is formed by winding the first pole piece, the isolating membrane and the second pole piece around the winding axis, a cavity is formed in the winding center, and the first pole piece, the second pole piece and the isolating membrane have overlapped parts. The overlapping part is provided with an overlapping initial position along the winding direction, the overlapping part comprises a first section, the overlapping initial position is positioned in the first section, the number of winding turns of the first section is at least one, and the isolating membrane positioned in the first section is adhered to the first pole piece and the second pole piece, so that the internal collapse is improved, and the influence on the performance of the secondary battery is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage, and in particular, to a secondary battery, a preparation method thereof, and an electrical device. Background Art

[0002] With the continuous update and development of secondary battery technologies, the application fields of secondary batteries are also constantly expanding. Subsequently, the safety issues of battery cells have attracted increasing public attention. After a hard-shell wound secondary battery expands, the cavity position of the electrode assembly is prone to internal collapse, affecting the normal use of the secondary battery. Summary of the Invention

[0003] In view of this, it is necessary to provide a secondary battery, a preparation method thereof, and an electrical device, which can improve the internal collapse of the cavity position of the electrode assembly and reduce the impact on the performance of the secondary battery.

[0004] An embodiment of the present application provides a secondary battery, including a housing and a cylindrical electrode assembly disposed in the housing. The electrode assembly includes a first electrode tab, a second electrode tab, and a separator. The polarity of the second electrode tab is opposite to that of the first electrode tab. The separator is disposed between the first electrode tab and the second electrode tab. The electrode assembly has a winding axis, and the electrode assembly is formed by winding the first electrode tab, the separator, and the second electrode tab around the winding axis, and a cavity is formed at the winding center. The first electrode tab, the second electrode tab, and the separator have an overlapping portion. Along the winding direction, the overlapping portion has an overlapping starting position, the overlapping portion includes a first section, the overlapping starting position is located in the first section, the number of turns of the first section is at least one turn, and the separator located in the first section bonds the first electrode tab and the second electrode tab. By bonding the separator of at least one turn of the first section to the first electrode tab and the second electrode tab, the strength of the first section is improved, the inward squeezing force is resisted, and the occurrence of internal collapse is reduced. Moreover, after the separator located in the inner circle bonds the first electrode tab and the second electrode tab, the further curvature non-uniformity caused by the rotation of the first section is reduced, so that the first section maintains a stable shape, which is beneficial to improving internal collapse and reducing the impact on the performance of the secondary battery.

[0005] In one or more of the above optional embodiments, the number of turns n of the first section is such that 2 ≤ n ≤ 8. This further improves the strength of the first section, reduces the occurrence of internal collapse, further helps the first section to maintain a stable shape, improves internal collapse, and reduces the impact on the performance of the secondary battery.

[0006] In one or more of the above optional embodiments, 3 ≤ n ≤ 8, which can significantly optimize the support performance of the first section, help the first section to better maintain a stable shape, better improve internal collapse, and reduce the impact on the performance of the secondary battery.

[0007] In one or more of the above optional embodiments, the peel strength F between the second electrode tab and the first electrode tab located in the first section1 where 1 N / m ≤ F 1 ≤ 15 N / m. When controlling F 1 ≥ 1 N / m, an effective bonding strength is formed between the first pole piece and the second pole piece. When the electrode assembly expands, the first pole piece and the second pole piece are not easily separated, which is beneficial to improving the stability of the electrode assembly and providing a certain support strength for the first section to improve internal collapse. When controlling F 1 ≤ 15 N / m, while ensuring the structural strength of the first section, the optimal benefit level for improving the internal collapse effect can be maintained. In this application, by 1 N / m ≤ F 1 ≤ 15 N / m, the strength of the first section is enhanced, the inward extrusion force is resisted, the occurrence of internal collapse is reduced, the further curvature non-uniformity caused by the rotation of the first section is decreased, and the first section maintains a stable shape, which is beneficial to improving internal collapse and further ensuring the stability of the secondary battery performance.

[0008] In one or more of the above optional embodiments, 5 N / m ≤ F 1 ≤ 15 N / m, further enhancing the strength of the first section, resisting the inward extrusion force, reducing the occurrence of internal collapse, decreasing the further curvature non-uniformity caused by the rotation of the first section, enabling the first section to better maintain a stable shape, which is beneficial to further improving internal collapse and further ensuring the stability of the secondary battery performance.

[0009] In one or more of the above optional embodiments, the separator includes a base material layer and an adhesive layer connecting the base material layer.

[0010] In one or more of the above optional embodiments, the material of the base material layer includes one or more of polyolefin, polypropylene, and polyimide, and the material of the adhesive layer includes one or more of polyvinylidene fluoride, polyurethane, ethylene-vinyl acetate copolymer, and polyolefin elastomer.

[0011] In one or more of the above optional embodiments, the secondary battery includes a cylindrical hard shell battery.

[0012] In one or more of the above optional embodiments, along the opposite direction of the winding direction, the parts of the separator exceeding the first pole piece and the second pole piece are adhesively bonded to each other. This helps to weaken the relative sliding inside the first section and reduce the risk of deformation of the first section.

[0013] The embodiments of this application provide a preparation method of the secondary battery in any one of the above embodiments, including sequentially stacking the first pole piece, the separator, and the second pole piece; thermally pressing the first section to bond the separator to the first pole piece and the second pole piece; winding the first pole piece, the separator, and the second pole piece, and placing them into the housing.

[0014] In some embodiments, before winding, the portion of the separator film extending beyond the first and second electrode tabs in the direction opposite to the winding direction is thermocompressed.

[0015] An embodiment of the present application provides an electrical device including the secondary battery in any one of the above embodiments.

[0016] By bonding at least one turn of the separator film in the first section to the first and second electrode tabs, the strength of the first section is enhanced, the inward squeezing force is resisted, the occurrence of internal collapse is reduced, and after the separator film in the inner circle is bonded to the first and second electrode tabs, the further curvature non-uniformity caused by the rotation of the first section is reduced, so that the first section maintains a stable shape, which is beneficial to improving internal collapse and reducing the impact on the performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A cross-sectional schematic view of a secondary battery in some embodiments is shown.

[0018] Figure 2 A schematic structural view of an overlapping portion of an electrode assembly in some embodiments is shown.

[0019] Figure 3 A schematic structural view of a separator film in some embodiments is shown.

[0020] Figure 4 A schematic structural view of a part of the first electrode tab in some embodiments is shown.

[0021] Figure 5 A schematic flow chart of a method for manufacturing a secondary battery in some embodiments is shown.

[0022] Figure 6 A schematic structural view of an electrical device in some embodiments is shown.

[0023] MAIN ELEMENT SYMBOL DESCRIPTION:

[0024] Secondary battery 100

[0025] Housing 10

[0026] Electrode assembly 20

[0027] Cavity 20a

[0028] Overlapping portion 20b

[0029] Overlapping start position 20c

[0030] First section 201

[0031] First electrode tab 21

[0032] First part 21a

[0033] The first current collector 211

[0034] The first active material layer 212

[0035] The first region 213

[0036] The second region 214

[0037] The third region 215

[0038] The first edge 210

[0039] The second edge 220

[0040] The second pole piece 22

[0041] The second part 22a

[0042] The second current collector 221

[0043] The second active material layer 222

[0044] The fourth region 223

[0045] The fifth region 224

[0046] The sixth region 225

[0047] The third edge 230

[0048] The fourth edge 240

[0049] The separator 23

[0050] The substrate layer 231

[0051] The adhesive layer 232

[0052] The electrical device 200

[0053] The following specific embodiments will further illustrate the present application in combination with the above-mentioned drawings. Specific embodiments

[0054] Next, the technical solutions in the embodiments of the present application will be described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0055] When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be an intermediate component.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application herein are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "or / and" used herein includes any and all combinations of one or more of the related listed items.

[0057] It can be understood that the term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there can be a state approximately vertical or equal between two components. For example, in combination with numerical description, vertical can refer to the included angle range between two straight lines being between 90°±10°, vertical can also refer to the dihedral angle range between two planes being between 90°±10°, and vertical can further refer to the included angle range between a straight line and a plane being between 90°±10°. The two components described as "vertical" may not be absolute straight lines or planes, and can also be approximately straight lines or planes. From a macroscopic perspective, as long as the overall extension direction is a straight line or a plane, the components can be considered "straight lines" or "planes".

[0058] Unless otherwise defined, the term "plurality" used herein, when used to describe the quantity of components, specifically means that the component is two or more.

[0059] The following will describe in detail some embodiments of this application with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0060] Please refer to Figure 1 and Figure 2 , an embodiment of this application provides a secondary battery 100, including a housing 10 and a cylindrical electrode assembly 20, and the electrode assembly 20 is disposed in the housing 10.

[0061] In some embodiments, the electrode assembly 20 includes a first electrode tab 21, a second electrode tab 22, and a separator 23. The polarity of the first electrode tab 21 is opposite to that of the second electrode tab 22. The separator 23 is disposed between the first electrode tab 21 and the second electrode tab 22. The electrode assembly 20 has a winding axis, and the electrode assembly 20 is formed by winding the first electrode tab 21, the separator 23, and the second electrode tab 22 around the winding axis, and a cavity 20a is formed at the winding center P.

[0062] In some embodiments, the first electrode tab 21 is a positive electrode tab, and the second electrode tab 22 is a negative electrode tab. In some embodiments, the first electrode tab 21 is a negative electrode tab, and the second electrode tab 22 is a positive electrode tab.

[0063] This application takes the first electrode tab 21 as the positive electrode tab and the second electrode tab 22 as the negative electrode tab as an example for illustration.

[0064] In some embodiments, the first pole piece 21, the second pole piece 22, and the separator 23 have an overlapping portion 20b. Along the winding direction S, the overlapping portion 20b has an overlapping start position 20c. The overlapping portion 20b includes a first section 201. The overlapping start position 20c is located in the first section 201. The number of turns of the first section 201 wound is at least one turn. The separator 23 located in the first section 201 bonds the first pole piece 21 and the second pole piece 22.

[0065] When the electrode assembly 20 expands, the outer diameter of the wound electrode assembly 20 becomes larger. The outermost first pole piece 21 contacts the inner wall of the housing 10. The housing 10 forms a squeezing force towards the winding center P on the first pole piece 21. After the electrode assembly 20 is wound and formed, there is a situation of uneven curvature. The position with uneven curvature is prone to local instability and collapse towards the cavity 20a during the process of being squeezed inward, forming an internal collapse. In this application, by bonding the separator 23 of at least one turn of the first section 201 to the first pole piece 21 and the second pole piece 22, the strength of the first section 201 is enhanced to resist the inward squeezing force, reducing the occurrence of internal collapse. And after the separator 23 located in the inner circle bonds the first pole piece 21 and the second pole piece 22, the further uneven curvature caused by the rotation of the first section 201 is reduced, so that the first section 201 maintains a stable shape, which is beneficial to improving the internal collapse and reducing the impact on the performance of the secondary battery 100.

[0066] In some embodiments, the housing 10 is a hard shell. Optionally, the housing 10 is a cylindrical steel shell. In some embodiments, the secondary battery 100 is a cylindrical hard shell battery.

[0067] In some embodiments, the number of turns n of the first section 201 wound satisfies 2 ≤ n ≤ 8, further enhancing the strength of the first section 201, reducing the occurrence of internal collapse, further facilitating the first section 201 to maintain a stable shape, improving the internal collapse, and reducing the impact on the performance of the secondary battery 100.

[0068] Optionally, n can be any one of 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8.

[0069] In some embodiments, 3 ≤ n ≤ 8 can significantly optimize the support performance of the first section 201, help the first section 201 to better maintain a stable shape, better improve the internal collapse, and reduce the impact on the performance of the secondary battery 100.

[0070] In some embodiments, the peel strength F between the second pole piece 22 and the first pole piece 21 located in the first section 201 1 , 1 N / m ≤ F 1 ≤ 15 N / m. When controlling F 1When it is ≥ 1 N / m, an effective bonding strength is formed between the first pole piece 21 and the second pole piece 22. When the electrode assembly 20 expands, the first pole piece 21 and the second pole piece 22 are not easily separated, which is beneficial to improving the stability of the electrode assembly 20 and providing a certain support strength for the first section 201 to improve internal collapse. When controlling F 1 ≤ 15 N / m, while ensuring the structural strength of the first section 201, the optimal benefit level for improving the internal collapse effect can be maintained. In this application, by 1 N / m ≤ F 1 ≤ 15 N / m, the strength of the first section 201 is enhanced to resist the inward squeezing force, reduce the occurrence of internal collapse, and reduce the further curvature non-uniformity caused by the rotation of the first section 201, so that the first section 201 maintains a stable shape, which is beneficial to improving internal collapse and further ensuring the stable performance of the secondary battery 100.

[0071] Optionally, F 1 can be any one of 1 N / m, 2 N / m, 3 N / m, 4 N / m, 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, 15 N / m or the range composed of any two of them.

[0072] In some embodiments, 5 N / m ≤ F 1 ≤ 15 N / m, further enhancing the strength of the first section 201 to resist the inward squeezing force, reducing the occurrence of internal collapse, further reducing the further curvature non-uniformity caused by the rotation of the first section 201, so that the first section 201 maintains a stable shape, and further being beneficial to improving internal collapse. The peel strength is set to be less than or equal to 15 N / m, which is beneficial to balancing the electrolyte infiltration performance.

[0073] Please refer to Figure 3 , in some embodiments, the separator 23 includes a base material layer 231 and an adhesive layer 232. Along the thickness direction of the separator 23, the adhesive layer 232 connects both sides of the base material layer 231. One side of the adhesive layer 232 is used to connect the first pole piece 21, and the other side of the adhesive layer 232 is used to connect the second pole piece 22. The adhesive layer 232 is configured to have viscosity after being heated.

[0074] Specifically, the first pole piece 21, the separator 23 and the second pole piece 22 are stacked in sequence, and the first section 201 is hot-pressed, so that the adhesive layer 232 is heated and melted to connect the first pole piece 21 and the second pole piece 22. The micron-level gaps between the first pole piece 21 and the separator 23 and between the second pole piece 22 and the separator 23 can be eliminated in the hot-pressed first section 201, shortening the lateral diffusion path of the electrolyte and reducing the overall infiltration time.

[0075] In some embodiments, the material of the adhesive layer 232 includes one or more of polyvinylidene fluoride, polyurethane, ethylene-vinyl acetate copolymer, and polyolefin elastomer.

[0076] Please refer to Figure 4 , in some embodiments, the first electrode tab 21 includes a first current collector 211 and a first active material layer 212 disposed on the first current collector 211. The first electrode tab 21 includes a first portion 21a, and both side surfaces of the first portion 21a are provided with the first active material layer 212 along the thickness direction of the first electrode tab 21.

[0077] In some embodiments, along the width direction of the first electrode tab 21, the first portion 21a includes a first edge 210 and a second edge 220. The surface of the first portion 21a facing the separator 23 is sequentially connected with a first region 213, a second region 214, and a third region 215. One edge of the first region 214 coincides with the first edge 210 in the width direction of the first electrode tab 21, and one edge of the third region 215 coincides with the second edge 220 in the width direction of the first electrode tab 21.

[0078] In some embodiments, the second electrode tab 22 includes a second current collector 221 and a second active material layer 222 disposed on the second current collector 221. The second electrode tab 22 includes a second portion 22a, and both side surfaces of the second portion 22a are provided with the second active material layer 222 along the thickness direction of the second electrode tab 22.

[0079] In some embodiments, along the width direction of the second electrode tab 22, the second portion 22a includes a third edge 230 and a fourth edge 240. The surface of the second portion 22a facing the separator 23 is sequentially connected with a fourth region 223, a fifth region 224, and a sixth region 225. One edge of the fourth region 223 coincides with the third edge 230 in the width direction of the second electrode tab 22, and one edge of the sixth region 225 coincides with the fourth edge 240 in the width direction of the second electrode tab 22.

[0080] In some embodiments, one side of the separator 23 is adhered to the first region 213 and the third region 215, and the other side is adhered to the fourth region 223 and the sixth region 225 of the second electrode tab 22.

[0081] In some embodiments, one side of the separator 23 is adhered to the first region 213, the second region 214, and the third region 215, and the other side is adhered to the fourth region 223, the fifth region 224, and the sixth region 225 of the second electrode tab 22.

[0082] In some embodiments, in the opposite direction of the winding direction, the portions of the separator 23 that extend beyond the first electrode tab 21 and the second electrode tab 22 are adhesively bonded to each other. This helps to weaken the relative sliding inside the first section 201 and reduce the risk of deformation of the first section 201.

[0083] Please refer to Figure 5 , an embodiment of the present application provides a method for manufacturing a secondary battery 100, including the following steps:

[0084] Step 1, stack the first electrode tab 21, the separator 23, and the second electrode tab 22 in sequence;

[0085] Step 2, perform hot pressing on the first section 201 to bond the separator 23 to the first electrode tab 21 and the second electrode tab 22;

[0086] Step 3, wind the first electrode tab, the separator, and the second electrode tab, and wind and collect them into the housing 10.

[0087] In some embodiments, winding is performed with the first section 201 as the starting part of winding.

[0088] In some embodiments, before winding, hot pressing is performed on the portions of the separator 23 that extend beyond the first electrode tab 21 and the second electrode tab 22 in the opposite direction of the winding direction.

[0089] In some embodiments, the number of turns of winding around the winding axis at the overlapping starting position 20c of the first section 201 is at least one turn, which improves the strength of the first section 201, resists the inward squeezing force of the housing 10 on the electrode assembly 20, reduces the occurrence of inner collapse, and after the separator 23 located in the inner circle bonds the first electrode tab 21 and the second electrode tab 22, it reduces the further curvature non-uniformity caused by the rotation of the first section 201, so that the first section 201 maintains a stable shape, which is beneficial to improving inner collapse and reducing the impact on the performance of the secondary battery 100.

[0090] The present application will be further described below through specific embodiments.

[0091] The manufacturing process of the secondary battery 100 in Embodiment 1 includes the following steps:

[0092] Preparation of the positive electrode tab: Dissolve the positive electrode active material lithium cobaltate, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) solution in a weight ratio of 97.5:1:1.5 to form a positive electrode slurry. Use aluminum foil as the positive electrode current collector, coat the positive electrode slurry on the positive electrode current collector, and obtain the positive electrode tab after drying, cold pressing, and slitting.

[0093] Preparation of the negative electrode sheet: Artificial graphite as the negative active material, sodium carboxymethyl cellulose (CMC) as the thickener, and styrene-butadiene rubber (SBR) as the binder are mixed in a weight ratio of 96:1.5:2.5. Deionized water is added and stirred evenly under the action of a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry is evenly coated on the negative current collector copper foil; dried, and then obtained the negative electrode sheet after cold pressing, slicing, and slitting.

[0094] Preparation of the separator 23: The base layer of the separator 23 is polyethylene (PE). Alumina ceramic layers are coated on both sides of the base layer 231 of the separator 23, and then polyvinylidene fluoride (PVDF) is coated on both sides of the coated ceramic layers, and dried.

[0095] Preparation of the electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 3:5:2, and the lithium salt LiPF 6 is added. After mixing evenly, the electrolyte is obtained. Among them, the mass percentage concentration of LiPF 6 is 12.5%.

[0096] Preparation of the electrode assembly 20: The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, hot-pressed for the first section 201, and then wound and formed around the winding center P along the winding direction S.

[0097] Assembly of the secondary battery 100: The wound electrode assembly 20 is placed in the housing 10, and the electrolyte is injected for encapsulation, thus obtaining the secondary battery 100.

[0098] Peeling strength test method:

[0099] The experimental temperature is 20±5°C. Disassemble the secondary battery 100, take out the electrode assembly 20, unfold the electrode sheet of the electrode assembly 20, take out a part of the inner ring, and this inner ring contains the first section 201. Use a standard pressure roller (diameter 200 mm, width 50 mm, mass 2000 g) to roll once on this inner ring to ensure the flatness of this inner ring. Cut this inner ring into specimens with a length of 50 mm and a width of 25 mm, and the specimens include the first section 201. Then, fix the first electrode sheet 21 of the specimen on the upper fixture, and fix the second electrode sheet 22 of the specimen on the lower fixture to ensure that the specimen will not break or break away from the fixture during the peeling process. Use a load sensor to record the force applied to the specimen, and record the deformation of the specimen through a displacement sensor. Set the peeling angle to 180°, and set the peeling speed to 3 mm / min. Stretch the specimen until it is completely pulled apart to stop the test, record the force value and displacement data during the peeling process, and the peeling strength = maximum peeling force (N) / specimen width (mm). Test 5 parallel samples, and take the average value as the test result.

[0100] Inner collapse test method:

[0101] The secondary battery 100 is subjected to a cycling test. After the test is completed, a cross-sectional morphology diagram of the middle part of the secondary battery 100 is taken by CT. It is required that the inner pole pieces of the secondary battery 100 do not collapse inward to pass.

[0102] In this application, a cycling test is carried out on a battery cell with the diameter of the secondary battery 100 being 40 mm, the length of the secondary battery 100 being 100 mm, and the total number of winding turns of the electrode assembly 20 being 40. The number of battery cells in each test group is 50.

[0103] It can be understood that by adjusting the crystallinity and molecular weight of polyvinylidene fluoride (PVDF) in the adhesive layer of the separator, the viscosity of the separator is changed, thereby changing the peel strength between the first pole piece 21 and the second pole piece 22 in the first section after hot pressing. For example, increasing the molecular weight of polyvinylidene fluoride (PVDF) and decreasing the crystallinity of polyvinylidene fluoride (PVDF).

[0104] It should be noted that except for the different parameters in the table, other parameters of Comparative Examples 1-2 are the same as those of Example 1.

[0105] Table 1 (Other parameters of Examples 1 to 13 except for the parameters involved in Table 1 are the same as those of Example 1)

[0106] Number of turns (n) <![CDATA[Peeling strength (F 1 )]]> Pass rate Comparative example 1 \ \ 54％ Comparative example 2 0.5 10 60％ Example 1 1 10 72％ Example 2 2 10 84％ Example 3 3 10 90％ Example 4 4 10 92％ Example 5 5 10 94％ Example 6 6 10 96％ Example 7 8 10 98％ Example 8 9 10 98％ Example 9 5 0.5 70％ Example 10 5 1 86％ Example 11 5 5 92％ Example 12 5 15 96％ Example 13 5 20 96％

[0107] From the passing rates of the inner collapse tests of the secondary batteries 100 in Examples 1 to 13 in Table 1, which are all higher than the passing rates of the inner collapse tests in Comparative Examples 1 and 2, it can be known that when the number of winding turns of the first section 201 is from 1 to 8 turns and the peel strength F1 satisfies 1 N / m ≤ F 1 ≤ 15 N / m, it is beneficial to improve inner collapse and reduce the impact on the performance of the secondary battery 100. When the number of turns is greater than 8 turns and / or the peel strength F 1 is greater than 15 N / m, the benefit of improving inner collapse decreases.

[0108] From Examples 3-7, 5, 11, and 12 in Table 1, it can be known that when the number of winding turns of the first section 201 is from 3 to 8 turns and the peel strength F 1 satisfies 5 N / m ≤ F 1 ≤ 15 N / m, it is further beneficial to improve inner collapse and further reduce the impact on the performance of the secondary battery 100.

[0109] Please refer to Figure 6, the present application also provides an electrical device 200 using the above secondary battery 100. In one embodiment, the electrical device 200 of the present application may be, but is not limited to, an electronic device, a drone, a backup power supply, an electric vehicle, an electric motorcycle, an electric assist bicycle, an electric tool, a large household battery module, etc.

[0110] Those of ordinary skill in the art of this technology should recognize that the above embodiments are only used to illustrate the present application, rather than to limit the present application. As long as appropriate changes and variations made to the above embodiments fall within the scope of the spirit of the present application, they fall within the scope disclosed by the present application.

Claims

1. A secondary battery, characterized in that: The invention comprises a shell and a cylindrical electrode assembly, wherein the electrode assembly is arranged in the shell, and the electrode assembly comprises: First pole piece; a second pole piece having a polarity opposite to that of the first pole piece; and a separation film, wherein the separation film is disposed between the first pole piece and the second pole piece, the electrode assembly has a winding axis, the electrode assembly is formed by winding the first pole piece, the separation film and the second pole piece around the winding axis, and a cavity is formed at the winding center, and the first pole piece, the second pole piece and the separation film have an overlapping portion; Along the winding direction, the overlapping part has an overlapping starting position, the overlapping part includes a first section, the overlapping starting position is located in the first section, the number of turns of the first section is at least one turn, and the isolation film located in the first section bonds the first pole piece and the second pole piece.

2. The secondary battery according to claim 1, wherein: The number of turns of the first section is n, 2≤n≤8.

3. The secondary battery according to claim 2, characterized in that: 3≤n≤8。 4. The secondary battery according to claim 1, wherein: The peel strength between the second pole piece located in the first section and the first pole piece is F1, 1N / m≤F1≤15N / m.

5. The secondary battery according to claim 4, characterized in that: 5N / m≤F1≤15N / m.

6. The secondary battery according to claim 1, wherein: The isolation film includes a substrate layer and an adhesive layer connecting the substrate layer.

7. The secondary battery according to claim 6, characterized in that: The material of the substrate layer includes one or more of polyolefin, polypropylene and polyimide, and the material of the adhesive layer includes one or more of polyvinylidene fluoride, polyurethane, ethylene-vinyl acetate copolymer and polyolefin elastomer.

8. The secondary battery according to claim 1, wherein: The secondary battery includes a cylindrical hard case battery.

9. The secondary battery according to claim 1, wherein: In the opposite direction of the winding direction, the portions of the isolation film that extend beyond the first pole piece and the second pole piece are bonded to each other.

10. A method for preparing a secondary battery according to any one of claims 1 to 9, characterized in that: include: Step 1, stacking the first pole piece, the isolation film and the second pole piece in sequence; Step 2, hot pressing the first section so that the isolation film is bonded to the first pole piece and the second pole piece; Step 3: Wind the first pole piece, the isolation film and the second pole piece, and place them into the shell.

11. The method for preparing a secondary battery according to claim 10, characterized in that: Before winding, a portion of the isolation film that exceeds the first pole piece and the second pole piece in the opposite direction of the winding direction is hot pressed.

12. An electrical equipment, characterized in that: Comprising the secondary battery as claimed in any one of claims 1 to 9.

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