Secondary battery, battery pack, and electronic device

Abstract

The utility model provides a secondary battery, which comprises an electrode assembly formed by laminating and winding a first diaphragm, a first pole piece, a second diaphragm and a second pole piece, and the starting end of the second pole piece exceeds the starting end of the first pole piece along the reverse direction of the winding direction of the electrode assembly. The first diaphragm comprises a first starting section exceeding the starting end of the second pole piece, the second diaphragm comprises a second starting section exceeding the starting end of the second pole piece, and the first diaphragm in the first starting section and the second diaphragm in the second starting section are at least partially fixed by an adhesive layer; the first diaphragm comprises a first base film, the second diaphragm comprises a second base film, and the first diaphragm further comprises a first adhesive layer located on at least one face of the first base film or the second diaphragm further comprises a second adhesive layer located on at least one face of the second base film. According to the secondary battery provided by the utility model, at least the collapse of the central hole can be avoided so as to improve the reliability and yield of a hole burning process. The embodiment of the utility model also provides a battery pack and an electronic device.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, provides secondary batteries, battery packs, and electronic devices. Background Technology

[0002] Currently, electrochemical devices are being used more and more widely, such as secondary batteries (e.g., lithium-ion batteries) in vehicles, energy storage, mobile phones, tablets, wearable devices, power banks, e-cigarettes, digital products, power tools, power devices, and energy storage devices, and are particularly important in the new energy field. One type of secondary battery is the cylindrical battery, which includes a casing and an electrode assembly. The electrode assembly consists of a positive electrode, a first separator, a negative electrode, and a second separator, which are stacked sequentially and wound to form the electrode assembly, which is then encapsulated in the casing. In the field of secondary battery manufacturing, improving yield is a key technical challenge. Utility Model Content

[0003] In view of the above-mentioned problems in the prior art, this application provides a secondary battery that can at least improve the reliability and yield of the hot-hole process in the production of secondary batteries.

[0004] According to one aspect of this application, a secondary battery is provided, the secondary battery including an electrode assembly formed by stacking and winding a first separator, a first electrode, a second separator, and a second electrode. In the opposite direction to the winding direction of the electrode assembly, the starting end of the second electrode extends beyond the starting end of the first electrode. The first separator includes a first starting section extending beyond the starting end of the second electrode. The second separator includes a second starting section extending beyond the starting end of the second electrode. The first starting section of the first separator and the second starting section of the second separator are at least partially fixed by an adhesive layer. The first separator includes a first base film and the second separator includes a second base film. The first separator also includes a first adhesive layer located on at least one side of the first base film, or the second separator also includes a second adhesive layer located on at least one side of the second base film.

[0005] In some embodiments, a first adhesive layer is located on the side of the first base film facing the second diaphragm, and a second adhesive layer is located on the side of the second base film facing the first diaphragm, such that the first adhesive layer in the first starting segment and the second adhesive layer in the second starting segment bond together to each other as an adhesive layer.

[0006] In some embodiments, the first separator further includes a first heat insulation layer located between the first adhesive layer and the first base film, the first heat insulation layer being located on the side of the first base film facing away from the nearest first electrode; the second separator further includes a second heat insulation layer located between the second base film and the second adhesive layer, the second heat insulation layer being located on the side of the second base film facing away from the nearest first electrode.

[0007] In some embodiments, the first diaphragm further includes a first heat insulation layer, wherein a first base film is located between the first heat insulation layer and the first adhesive layer, and the second diaphragm further includes a second heat insulation layer located between the second base film and the second adhesive layer.

[0008] In some embodiments, the first adhesive layer or the second adhesive layer is a polyvinylidene fluoride adhesive layer.

[0009] In some embodiments, the secondary battery further includes a housing, the housing including an end wall and a peripheral sidewall surrounding the end wall, the housing defining a receiving cavity for providing an electrode assembly; the ratio of the minimum diameter y of the central hole of the electrode assembly to the outer diameter x of the peripheral sidewall of the housing ranges from 0.08 to 0.16.

[0010] In some embodiments, the length of either the first starting segment or the second starting segment is 22 mm to 104 mm in the opposite direction to the winding direction of the electrode assembly.

[0011] In some embodiments, the secondary battery is a cylindrical battery, the first electrode is a positive electrode, the second electrode is a negative electrode, the secondary battery also includes a terminal post, and a positive current collector that electrically connects the positive electrode and the terminal post, and the positive current collector and the terminal post are welded together, and the solder mark is located on the side of the positive current collector close to the electrode assembly.

[0012] According to another aspect of this application, a battery pack is also provided, which includes the aforementioned secondary battery.

[0013] According to another aspect of this application, an electronic device is also provided, which includes the aforementioned secondary battery.

[0014] The above-described technical solution of this application, by fixing the initial sections of the first and second separators at the center hole of the electrode assembly with adhesive layers, improves the composite strength between the first and second separators during the hot-drilling process, preventing center hole collapse and improving the reliability and yield of the hot-drilling process. It also avoids problems such as center hole blockage, loose internal electrode sheets, and impaired electrolyte wetting caused by center hole collapse. In embodiments where the secondary battery is a cylindrical battery, fixing the initial sections of the first and second separators with adhesive layers to improve the composite strength between them during the hot-drilling process also prevents the separators from affecting the insertion of the welding pins. By providing a first heat-insulating layer and a second heat-insulating layer on opposite sides of the first and second adhesive layers facing each other, the heat resistance of the first and second separators can be improved, thus enhancing the reliability and yield of the hot-drilling process. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It is worth noting that, according to industry standard practice, the components are not drawn to scale and are only used for illustrative purposes. In fact, for clarity of discussion, the dimensions of the components can be arbitrarily increased or decreased.

[0016] Figure 1 A perspective view of a secondary battery according to an embodiment of this application is shown.

[0017] Figure 2 A cross-sectional view of a secondary battery according to an embodiment of this application is shown.

[0018] Figure 3 A more detailed cross-sectional schematic diagram of the electrode assembly according to an embodiment of this application is shown.

[0019] Figure 4 This is a cross-sectional view of the electrode assembly of a secondary battery according to an embodiment of this application in a section perpendicular to the axis.

[0020] Figure 5 A partially enlarged schematic diagram of the first and second diaphragms of an electrode assembly according to an embodiment of this application is shown.

[0021] Figure 6 A partially enlarged schematic diagram of the first and second diaphragms of an electrode assembly according to another embodiment of this application is shown.

[0022] Figure 7 A schematic diagram is shown when the electronic device according to an embodiment of this application is a vehicle. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0024] The following disclosure provides numerous different embodiments or instances for implementing various features of the provided subject matter. Specific examples of elements and arrangements will be described below to simplify the present invention. These are merely examples and are not intended to limit the present invention. For example, in the following description, forming a first component above or on a second component may include embodiments where the first and second components are in direct contact, or embodiments where an additional component is formed between the first and second components such that the first and second components are not in direct contact. Furthermore, reference numerals and / or letters may be repeated in various instances of the present invention. Such repetition is merely for brevity and clarity and does not in itself indicate a relationship between the various embodiments and / or configurations discussed.

[0025] Furthermore, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific structures shown in the figures are merely illustrative and are not intended to limit the scope of this application. Other structures not described in the figures may be provided according to actual needs when describing specific figures, and are not intended to limit the scope of this application.

[0026] In the field of new energy power batteries, the application of secondary batteries is becoming increasingly widespread. For example, secondary batteries (such as lithium-ion batteries) can be used in electronic devices such as cars, energy storage, mobile phones, tablets, wearable devices, power banks, e-cigarettes, digital products, power tools, power devices, and energy storage devices.

[0027] One type of rechargeable battery that has emerged in recent years is the cylindrical battery, such as the 46mm diameter series cylindrical batteries. Cylindrical cells, combined with CTC (Cell to Chassis) technology, can significantly improve the energy density of the entire battery pack. Because CTC technology requires steel casings for the cells, resulting in a heavier overall structure, the 46mm series large cylindrical cells often require high-energy-density positive and negative electrode materials to increase the cell's energy density. In this context, improving cell safety performance is particularly important. Another advantage of cylindrical cells is their production cycle time, offering a significant increase in production capacity compared to prismatic cells. Therefore, improving yield in the cylindrical battery manufacturing process is a crucial technical challenge to overcome.

[0028] Cylindrical battery cells are typically manufactured by winding a separator, positive electrode, and negative electrode to form a hollow cylindrical electrode assembly. For this type of wound electrode assembly, due to the need for hot-drilling holes and the insertion of welding pins, torque welding is generally preferred. This process welds the electrode assembly to the casing. During this process, the welding pin must be fully inserted into the central hole of the cylindrical body. The condition of the separator around the central hole affects the insertion of the welding pin. Therefore, the existing central hole needs to be optimized to improve the yield of torque welding.

[0029] An embodiment of this application provides a secondary battery. Figure 1 A perspective view of a secondary battery 100 according to an embodiment of this application is shown. Figure 2 A cross-sectional view of a secondary battery 100 according to an embodiment of this application is shown. In the following description, a cylindrical battery is used as an example to illustrate the embodiments of this application.

[0030] Combination Figures 1 to 2 As shown, the secondary battery 100 includes a casing, which comprises a housing 200 and a cover plate 220. Specifically, the housing 200 includes a peripheral sidewall 109 and an end wall 111 connected to one end of the peripheral sidewall 109. An opening 205 is provided at the other end of the peripheral sidewall 109 opposite to the end wall 111, and the cover plate 220 covers the opening 205 of the housing 200. The cover plate 220 can be used to encapsulate the electrode assembly 120 and the electrolyte together with the housing 200. The housing 200 can be made of any of a variety of available materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. The housing 200 can be cylindrical and define a receiving cavity in which the electrode assembly 120 is disposed. The outer diameter of the housing 200 can be determined according to the specific diameter of the electrode assembly 120; for example, the outer diameter of the housing 200 can be, for example, 18 mm, 21 mm, 46 mm, etc. In some embodiments, the secondary battery 100 may be a 4680 cylindrical battery (outer diameter 46mm, height 80mm), or a 4695 cylindrical battery (outer diameter 46mm, height 95mm), or a 46120 cylindrical battery (outer diameter 46mm, height 120mm).

[0031] The electrode assembly 120 can be formed primarily by sequentially stacking and winding a positive electrode sheet, a negative electrode sheet, and a separator located between the positive and negative electrode sheets. The positive electrode sheet, negative electrode sheet, and separator can be wound around an axis Lc. Furthermore, the electrode assembly 120 also has a central hole 120c, and the axis Lc can be the axis of the central hole 120c. The wound electrode assembly 120 can have a central hole 120c. In some embodiments, the positive electrode sheet may include a positive current collector and a positive active material layer, the positive active material layer being coated on a portion of the surface of the positive current collector. The uncoated area of ​​the positive current collector not covered by the positive electrode coating area is used to form a positive electrode tab 125. The negative electrode sheet may include a negative current collector and a negative active material layer, the negative active material layer being coated on a portion of the surface of the negative current collector. The uncoated area of ​​the negative current collector not covered by the negative electrode coating area is used to form a negative electrode tab 124.

[0032] An inwardly protruding groove 113 (also referred to as a crimping portion) is formed on the peripheral sidewall of the housing 200 near the opening 205. The electrode assembly 120 is disposed between the end wall 111 and the groove 113, and the groove 113 restricts the movement of the electrode assembly 120 in the Z direction and its opposite direction between the end wall 111 and the groove 113. The direction from the opening 205 to the end wall 111 is the axial direction of the electrode assembly 120 and the height direction Z of the secondary battery. The end of the peripheral sidewall 109 of the housing 200 on the opening 205 side can be configured as a rolled edge 32, which extends radially inward into the housing 200, perpendicular to the Z direction. The rolled edge 32 and the groove 113 are spaced apart in the Z direction, and the groove 113 and the rolled edge 32 can together clamp the cover plate 220. The cover plate 220 can be electrically insulated from the housing 200.

[0033] The cover plate 220 may have a weak part. When the battery experiences thermal runaway, the high-temperature and high-pressure emissions inside can be discharged to the outside through the weak part on the cover plate 220 after breaking through the bottom of the battery, thereby achieving good discharge of the emissions.

[0034] The negative electrode tab 124 of the electrode assembly 120 faces the opening 205 and can be electrically connected to the housing 200 via a negative electrode current collector 201 located between the cover plate 220 and the electrode assembly 120, thereby making the housing 200 negatively charged. The negative electrode current collector 201 can be welded to the housing 200 by laser welding. Specifically, the welding position of the negative electrode current collector 201 to the housing 200 is located on the side of the groove 113 facing the electrode assembly 120.

[0035] The secondary battery 100 may further include a terminal post 160 and a positive current collector 202, the terminal post 160 passing through and being insulated from the end wall 111. The positive current collector 202 may be located between the terminal post 160 and the electrode assembly 120, and the positive current collector 202 may be electrically connected to the positive electrode plate of the electrode assembly 120 (e.g., the positive electrode tab 125 connected to the positive electrode plate) and the terminal post 160, thereby making the terminal post 160 positively charged. In some embodiments, the terminal post 160 may be welded to the positive current collector 202 by laser penetration welding.

[0036] In one example of the secondary battery 100 in this application, the method for manufacturing the secondary battery 100 in this application includes the following steps:

[0037] Winding: A winding structure formed by stacking and winding negative electrode sheet, separator and positive electrode sheet, the uncoated part of the negative current collector of negative electrode sheet and the positive current collector of positive electrode sheet is used as positive electrode tab 125 and negative electrode tab 124, and the positive electrode tab 125 and negative electrode tab 124 are bent along the radial direction of electrode assembly 120.

[0038] Welding of current collectors to electrode assemblies: The positive current collector 202 and the negative current collector 201 are welded to the positive electrode sheet and the negative electrode sheet respectively, for example, by welding to the surface areas of the bent positive electrode tab 125 and the negative electrode tab 124.

[0039] Installation into the housing: The electrode assembly 120, which has been welded to the negative current collector 201 and the positive current collector 202, is installed into the housing 200 through the opening 205. The method of installing the electrode assembly 120 in this step is not limited. For example, it can be installed manually or by a robot.

[0040] The electrode post 160 is installed and welded to the positive current collector 202. In some embodiments, torque welding is used to weld the electrode post 160 to the positive current collector 202, wherein the weld mark formed is located on the side of the positive current collector 202 closer to the electrode assembly 120. This allows for torque welding, with the welding head inserted through a central hole and applied to one side of the positive current collector 202, thus welding the positive current collector 202 and the electrode post 160. The diaphragm is fixed with adhesive, which avoids interference from diaphragm wrinkles on the welding head.

[0041] Electrolyte injection: The method of electrolyte injection is not limited, and injection can be carried out through opening 205. In this embodiment, electrolyte is injected through opening 205, which reduces the step of opening an injection hole in the end wall 111. The existing opening 205 can be used directly for injection, simplifying the process and reducing costs.

[0042] Sealing: The cover plate 220 is sealed and installed on the opening 205. There are various sealing methods, and this is not limited to one. In some embodiments, a rolling groove 113 recessed towards the center of the housing 200 is first formed on the outer periphery of the housing 200 to restrict the movement of the electrode assembly 120 in the Z direction. Then, a mechanical sealing process is used to press and seal the cover plate 220 to form a rolled edge 32, thereby sealing and installing the cover plate 220 on the opening 205 of the housing 200. This step is a mature process, low in cost, and highly efficient.

[0043] Figure 3 A more detailed cross-sectional schematic diagram of the electrode assembly 120 according to an embodiment of this application is shown. Figure 4 This is a cross-sectional view of the electrode assembly 120 of a secondary battery according to an embodiment of this application, in a section perpendicular to the axis Lc. It should be understood that the wound electrode assembly 120 has a central hole 120c, the axis Lc of which extends in the Z direction (see...). Figure 3 ), Figure 3 The XY plane shown is a cross-section perpendicular to the axis Lc. The center hole 120c is located in... Figure 3 The cross-section shown can have a circular shape.

[0044] Combination Figure 3 and Figure 4 As shown, the electrode assembly 120 may include a first electrode 121, a first separator 141, a second electrode 122, and a second separator 142. Furthermore, the secondary battery may also include an electrolyte, which may be located between the first electrode 121, the first separator 141, the second electrode 122, and the second separator 142.

[0045] The first electrode 121 may include a first current collector 1211 and a first active material layer 1213, wherein a portion of the opposing surface of the first current collector 1211 along its thickness direction is covered by the first active material layer 1213. The uncoated areas of the first current collector 1211 not covered by the first active material layer 1213 may be bent and stacked on top of each other toward the central hole 120c to serve as first tabs (such as positive tab 125).

[0046] The second electrode 122 includes a second current collector 1221 and a second active material layer 1223, wherein at least a portion of the surface of the second current collector 1221 along its thickness direction is covered by the second active material layer 1223. Uncoated areas of the second current collector 1221 not covered by the second active material layer 1223 can be bent and stacked together toward the central hole 120c to serve as second tabs (such as negative tab 124).

[0047] In some embodiments, the first electrode 121 is the positive electrode, and the second electrode 122 is the negative electrode. The first current collector 1211 is the positive current collector, and the first active material layer 1213 is the positive active material layer; the second current collector 1221 is the negative current collector, and the second active material layer 1223 is the negative active material layer. Taking a lithium-ion battery as an example, the material of the positive current collector can be aluminum, and the positive active material layer can include the positive active material, which can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. For high-nickel ternary lithium batteries, the positive active material can be a ternary material composed of nickel, cobalt, and manganese (or aluminum), wherein the nickel content is usually relatively high, generally above 60%. Similarly, the negative electrode can include a negative current collector and negative active material layers coated on both sides of the negative current collector. The portion of the negative current collector not coated with the negative active material layer constitutes the negative electrode tab. The negative electrode current collector can be made of copper, and the negative electrode active material layer can include a negative electrode active material, which can be carbon or silicon, etc.

[0048] The first electrode 121, the first diaphragm 141, the second electrode 122, and the second diaphragm 142 are sequentially stacked and wound along the winding direction D to form the electrode assembly 120. Specifically, the first electrode 121 is wound from its starting end 121s to its ending end 121e along the winding direction D, and the second electrode 122 is wound from its starting end 122s to its ending end 122e. The first diaphragm 141 and the second diaphragm 142 isolate the first electrode 121 from the second electrode 122. In the winding direction D, the ending end 122e of the second electrode 122 extends beyond the ending end 121e of the first electrode 121, so that the second electrode 122 can cover the ending end 121e of the first electrode 121. Therefore, lithium ions detached from the positive active material layer of the first electrode 121 (positive electrode) can be smoothly inserted into the negative active material layer of the second electrode 122 (negative electrode), thereby avoiding lithium plating at the end of the negative electrode. Furthermore, the ends 141e of the first separator 141 and 142e of the second separator 142 extend beyond the end 122e of the second electrode 122 to provide insulation.

[0049] In the opposite direction to the winding direction D, the starting end 122s of the second electrode 122 extends beyond the starting end 121s of the first electrode 121. Therefore, lithium ions detached from the positive active material layer of the first electrode 121 (positive electrode) can be smoothly inserted into the negative active material layer of the second electrode 122 (negative electrode), avoiding lithium plating at the starting end on the negative electrode.

[0050] Furthermore, in the opposite direction to the winding direction D, the starting end 141s of the first diaphragm 141 and the starting end 142s of the second diaphragm 142 extend beyond the starting end 122s of the second electrode 122, respectively. Therefore, the first diaphragm 141 may include a first starting segment 141p extending beyond the starting end 122s of the second electrode 122, and the second diaphragm 142 may include a second starting segment 142p extending beyond the starting end 122s of the second electrode 122. The first starting segment 141p and the second starting segment 142p may form the inner ring of the central hole 120c. In some embodiments, the innermost ring of the electrode assembly is the first diaphragm 141, thus defining the sidewall of the central hole 120c. The first diaphragm 141 in the first starting segment 141p and the second diaphragm 142 in the second starting segment 142p are at least partially fixed by an adhesive layer. For example, the first starting segment 141p and the second starting segment 142p can be bonded together by an adhesive layer, or the first starting segment 141p and the second starting segment 142p can be fixed together by an adhesive tape including an adhesive layer.

[0051] In some embodiments, the first diaphragm 141 may include a first base film and a first adhesive layer located on at least one side of the first base film, and the second diaphragm 142 may include a second base film and a second adhesive layer located on at least one side of the second base film. Figure 5 A partially enlarged schematic diagram of a first diaphragm 141 and a second diaphragm 142 of an electrode assembly 120 according to an embodiment of this application is shown. Figure 4 and Figure 5 As shown, the first diaphragm 141 may include a first base film 101 and a first adhesive layer 103. The first adhesive layer 103 is located at least on a first side of the first base film 101 in the first starting segment 141p, i.e., on the surface 101a side of the first base film 101. The second diaphragm 142 includes a second base film 301 and a second adhesive layer 303. The second adhesive layer 303 is located at least on a first side of the second base film 301 in the second starting segment 142p, i.e., on the surface 301a side of the second base film 301. The first adhesive layer 103 and the second adhesive layer 303 are the outermost layers of the first starting segment 141p and the second starting segment 142p, respectively. Surface 301a faces surface 101a of the first diaphragm 141, and the first adhesive layer 103 and the second adhesive layer 303 face each other, such that the first adhesive layer 103 in the first starting section 141p and the second adhesive layer 203 in the second starting section 142p are bonded together (e.g., glued together) to form an adhesive layer, thereby fixing the first starting section 141p and the second starting section 142p to each other.

[0052] By fixing the first starting section 141p of the first diaphragm 141 and the second starting section 142p of the second diaphragm 142 at the center hole 120c of the electrode assembly with an adhesive layer, the composite strength between the first diaphragm 141 and the second diaphragm 142 can be improved during the hot-drilling process, thus avoiding the collapse of the center hole and improving the reliability and yield of the hot-drilling process. Furthermore, it can avoid problems such as center hole blockage, loose internal electrode sheets, and impact on electrolyte wetting caused by center hole collapse.

[0053] In embodiments where the secondary battery is a cylindrical battery, since the welding needle needs to be inserted into the central hole of the cylindrical body during the hot-filling process, this application improves the composite strength between the first and second separators by fixing the starting sections of the first and second separators together with an adhesive layer during the hot-filling process. This also further prevents the separator from affecting the insertion of the welding needle during the hot-filling process, thereby improving the reliability and yield of the hot-filling process for cylindrical batteries.

[0054] By designing the orientation of the first adhesive layer 103 and the second adhesive layer 303 within the first diaphragm 141 and the second diaphragm 142, the first adhesive layer 103 and the second adhesive layer 303 face each other and bond the first starting section 141p and the second starting section 142p together. Therefore, the composite strength between the first diaphragm 141 and the second diaphragm 142 can be improved during the hot-drilling process, and the diaphragm can be prevented from affecting the insertion of the welding pin.

[0055] In some embodiments, the first adhesive layer 103 or the second adhesive layer 303 may be a PVDF (polyvinylidene fluoride) adhesive layer. In other embodiments, the first adhesive layer 103 or the second adhesive layer 303 may also be made of other materials that provide an adhesive effect.

[0056] Furthermore, in some embodiments, the first diaphragm 141 may further include a first heat-insulating layer 102 located at least in the first starting segment 141p, the first heat-insulating layer 102 being located on the side of the first adhesive layer 103 facing away from the second adhesive layer 303, that is, on the side of the first base film 101 facing away from the nearest first electrode 121. The second diaphragm 142 further includes a second heat-insulating layer 302 located at least in the second starting segment 142p, the second heat-insulating layer 302 being located on the side of the second adhesive layer 303 facing away from the nearest first electrode 121, that is, on the side of the second base film 301 facing away from the nearest first electrode 121. In some embodiments, the first heat-insulating layer 102 and the second heat-insulating layer 302 may be used for heat insulation. In some embodiments, the first heat-insulating layer 102 and the second heat-insulating layer 302 may be ceramic layers. By providing a first heat insulation layer 102 and a second heat insulation layer 302 on opposite sides of the first adhesive layer 103 and the second adhesive layer 303 that face each other, the heat resistance of the first diaphragm 141 and the second diaphragm 142 can be improved, thereby improving the reliability and yield of the hot-hole process.

[0057] In this embodiment, the first heat insulation layer 102 is located between the first base film 101 and the first adhesive layer 103. The second heat insulation layer 302 is located between the second base film 301 and the second adhesive layer 303. Compared with the method of using the heat insulation layer as the outermost layer of the separator, by respectively setting the first heat insulation layer 102 and the second heat insulation layer 302 between the corresponding first base film 101, the second base film 301 and the corresponding first adhesive layer 103, the heat resistance temperature of the first separator 141 and the second separator 142 can be increased, the process boundary of the hot-drilling process can be improved, and thus the reliability and yield of the hot-drilling process can be improved.

[0058] Figure 6 A partially enlarged schematic diagram of a first diaphragm 141 and a second diaphragm 142 of an electrode assembly 120 according to another embodiment of this application is shown. In this embodiment, with Figure 5Similar to the illustrated embodiment, the first heat insulation layer 102 is located on the side of the first adhesive layer 103 facing the nearest first electrode 121, and on the side of the first base film 101 facing the nearest first electrode 121. The second heat insulation layer 302 is located on the side of the second adhesive layer 303 facing the nearest first electrode 121, and on the side of the second base film 301 facing away from the nearest first electrode 121. The first adhesive layer 103 of the first separator 141 is located on the surface 101a of the first base film 101. The second adhesive layer 303 of the second separator 142 is located on the surface 301a of the second base film 301. The first adhesive layer 103 and the second adhesive layer 303 face each other. Figure 5 The difference in the illustrated embodiment is that the first base film 101 in the first diaphragm 141 is located between the first heat insulation layer 102 and the first adhesive layer 103. The first heat insulation layer 102, used for heat insulation, is the outermost layer of the first diaphragm 141, and the first heat insulation layer 102 can be the sidewall of the central hole 120c. The second heat insulation layer 302 of the second diaphragm 142 is still located between the second base film 301 and the second adhesive layer 303. By designing the orientation of the first adhesive layer 103 and the second adhesive layer 303 within the first diaphragm 141 and the second diaphragm 142, so that the first adhesive layer 103 and the second adhesive layer 303 face each other, the composite strength between the first diaphragm 141 and the second diaphragm 142 can be improved during the hot-drilling process, preventing the diaphragm from affecting the insertion of the welding pin.

[0059] To ensure the reliability of the central hole, this application also optimizes the relationship between the diameter of the cylindrical battery and the diameter of the central hole. The outer diameter of the peripheral sidewall 109 of the secondary battery casing is x, and the minimum diameter of the central hole 120c is y. The ratio of y to x (y / x) ranges from 0.08 to 0.16. If y / x is less than 0.08, the central hole is too small, affecting the insertion of the welding pin into the central hole 120c; if y / x is greater than 0.16, the central hole is too large, reducing energy density. In the embodiment where the positive current collector 202 and the electrode post 160 are welded by torque welding, and the weld mark is located on the side of the positive current collector 202 closer to the electrode assembly 120, the above-mentioned range of y / x facilitates the insertion of the welding pin into the central hole 120c, optimizing the torque welding process while maintaining the battery's energy density. In some embodiments, the minimum diameter y of the center hole 120c ranges from 0.1968x-2 mm to 0.1968x-2.2 mm. For example, y can be determined by the following formula: y = 0.1968x-2.1042 mm. Table 1 below lists the center hole diameter values ​​for some example cylindrical batteries with different outer diameters.

[0060] Table 1. Outer diameter and minimum diameter of the central hole of a cylindrical battery

[0061]

[0062] In some embodiments, in the opposite direction of the winding direction D, the length of either the first starting segment 141p or the second starting segment 142p is 22mm-104mm. This length range is more suitable for 46-series cylindrical batteries; for example, the lengths of the first starting segment 141p and the second starting segment 142p can preferably be 55mm. The aforementioned length range of the first starting segment 141p and the second starting segment 142p ensures that the inner ring separator around the center hole 120c is firmly and reliably welded after hot-drilling, facilitating the insertion of the welding pin, thus optimizing the torque welding process while having a lower cost impact.

[0063] See Figure 7 This application also provides an electronic device 1000. For ease of explanation, the following embodiments use a vehicle as an example. A battery pack 1002 is installed inside the vehicle. The battery pack 1002 can be located at the bottom, front, or rear of the vehicle body 1001. The battery pack 1002 can be used to power the vehicle; for example, it can serve as the vehicle's operating power source. The working part of the electronic device 1000 is electrically connected to the battery pack 1002 to obtain electrical power. The vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, but are not limited thereto. The working part is the vehicle body, and the battery pack 1002 is located at the bottom of the vehicle body, providing electrical power for the vehicle's movement or the operation of its internal electrical components. However, in other embodiments, the electronic device 1000 can also be a mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, power tool, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; the working unit can obtain electrical energy from the battery pack 1002 and perform corresponding work, such as the fan blade rotation unit of a fan, the vacuuming unit of a vacuum cleaner, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application embodiment does not impose special limitations on the above-described electronic device 1000. The battery pack 1002 may include multiple of the above-described secondary batteries 100, such as cylindrical batteries.

[0064] It should be understood that the various features of the embodiments of this application can be replaced and combined. The above description is only a preferred embodiment of this application and is not intended to limit this application. Any combination of embodiments within the spirit and principles of this application, as well as any modifications, equivalent substitutions, improvements, etc., made to the embodiments, should be included within the protection scope of this application.

Claims

1. A secondary battery, characterized in that, It includes an electrode assembly formed by stacking and winding a first diaphragm, a first electrode, a second diaphragm, and a second electrode. In the opposite direction to the winding direction of the electrode assembly, the starting end of the second electrode extends beyond the starting end of the first electrode, the first diaphragm includes a first starting section extending beyond the starting end of the second electrode, and the second diaphragm includes a second starting section extending beyond the starting end of the second electrode. The first starting section of the first diaphragm and the second starting section of the second diaphragm are at least partially fixed by an adhesive layer. The first diaphragm includes a first base membrane and the second diaphragm includes a second base membrane. The first diaphragm also includes a first adhesive layer located on at least one side of the first base membrane, or the second diaphragm also includes a second adhesive layer located on at least one side of the second base membrane.

2. The secondary battery according to claim 1, characterized in that, The first adhesive layer is located on the side of the first base film facing the second diaphragm, and the second adhesive layer is located on the side of the second base film facing the first diaphragm, such that the first adhesive layer in the first starting segment and the second adhesive layer in the second starting segment are bonded to each other to form the adhesive layer.

3. The secondary battery according to claim 2, characterized in that, The first diaphragm further includes a first heat insulation layer located between the first adhesive layer and the first base film, the first heat insulation layer being located on the side of the first base film facing away from the nearest first electrode sheet; The second diaphragm further includes a second heat insulation layer located between the second base film and the second adhesive layer, the second heat insulation layer being located on the side of the second base film facing away from the nearest first electrode.

4. The secondary battery according to claim 2, characterized in that, The first diaphragm further includes a first heat insulation layer, wherein the first base film is located between the first heat insulation layer and the first adhesive layer. The second diaphragm also includes a second heat insulation layer located between the second base film and the second adhesive layer.

5. The secondary battery according to claim 1, characterized in that, The first adhesive layer or the second adhesive layer is a polyvinylidene fluoride adhesive layer.

6. The secondary battery according to claim 1, characterized in that, Also includes: A housing, including an end wall and a peripheral sidewall surrounding the end wall, the housing defining a receiving cavity for housing the electrode assembly; The ratio of the minimum diameter y of the center hole of the electrode assembly to the outer diameter x of the peripheral sidewall of the housing ranges from 0.08 to 0.

16.

7. The secondary battery according to claim 1, characterized in that, In the opposite direction to the winding direction of the electrode assembly, the length of either the first starting segment or the second starting segment is 22mm-104mm.

8. The secondary battery according to any one of claims 1-7, characterized in that, The secondary battery is a cylindrical battery, with the first electrode being the positive electrode and the second electrode being the negative electrode. The secondary battery also includes a terminal post and a positive current collector that electrically connects the positive electrode plate and the terminal post. The positive current collector and the terminal post are welded together, and the solder mark is located on the side of the positive current collector close to the electrode assembly.

9. A battery pack, characterized in that, The secondary battery includes any one of claims 1 to 8.

10. An electronic device, characterized in that, The secondary battery includes any one of claims 1 to 8.

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