Secondary battery, manufacturing method and electric device

Abstract

The invention relates to a secondary battery, a manufacturing method and a power utilization device. The secondary battery comprises an electrode assembly and a tab, the electrode assembly comprises a pole piece, and the pole piece comprises a current collector and an active material layer arranged on at least one side surface of the current collector; the active material layer is provided with a groove, the current collector is provided with an exposed part exposed out of the groove, the exposed part is provided with a notch, and one end of the tab is arranged in the notch and fixed with the notch through welding; according to the secondary battery provided by the invention, the notch is reserved in the exposed part, exposed out of the groove, of the current collector, and the accommodating area is provided for one end of the tab, so that the notch is filled with one end of the tab, and the end of the tab is welded and fixed with part of the exposed part which defines the notch, and the end, located in the groove, of the tab and the exposed part are arranged side by side in the second direction; therefore, the thickness of a part of the electrode assembly where the tab is located is reduced, and the energy density of the secondary battery is further improved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a secondary battery, a manufacturing method thereof, and an electrical device. Background Art

[0002] With the rapid development of electronic information technology, various electronic devices are also developing towards the direction of intelligence and multi-functionality, and the requirement for the energy density of secondary batteries is also getting higher and higher. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery, a manufacturing method thereof, and an electrical device, which can improve the energy density of the secondary battery.

[0004] According to the first aspect of this application, a secondary battery is provided, which includes an electrode assembly and a tab. The electrode assembly includes a pole piece, and the pole piece includes a current collector and an active material layer provided on at least one surface of the current collector. The active material layer is provided with a groove, the current collector has an exposed portion exposed in the groove, the exposed portion is provided with a notch, and one end of the tab is disposed in the notch and fixed to the notch by welding.

[0005] Compared with the related art, in which the portion of the tab located in the groove is stacked and welded to the groove, compared with the secondary battery having no notch in the exposed portion, for the secondary battery mentioned in this application, by reserving a notch in the exposed portion of the current collector exposed in the groove to accommodate one end of the tab, one end of the tab is filled in the notch and welded to the partial exposed portion surrounding the notch, so that one end of the tab located in the groove is arranged side by side with the exposed portion in the second direction, thereby thinning the thickness of the partial electrode assembly where the tab is located, and further improving the energy density of the secondary battery.

[0006] In one or more of the above optional embodiments, the periphery of one end of the tab and the periphery of the notch are fixed by welding. With this arrangement, the thickness of the partial electrode assembly where the tab is located is further thinned, and the energy density of the secondary battery is further improved.

[0007] In one or more of the above optional embodiments, the welding is laser welding. Since the laser welding process can precisely control the welding quality by adjusting parameters such as laser power, welding speed, and spot size, it can provide suitable welding tensile force and contact resistance between the tab and the exposed portion.

[0008] In one or more of the above optional embodiments, along the first direction, where the first direction is the thickness direction of the electrode tab, the orthographic projection area of the welding mark area formed by welding the electrode tab and the exposed portion is S1, and the orthographic projection area of the exposed portion is S2. S1 and S2 satisfy: 1% ≤ S1 / S2 ≤ 6%. By limiting the ratio of S1 / S2 within this numerical range, while thinning the thickness of the partial electrode assembly where the electrode tab is located, a good welding tensile force can be maintained between the electrode tab and the exposed portion.

[0009] In one or more of the above optional embodiments, 3% ≤ S1 / S2 ≤ 6%. By limiting the ratio of S1 / S2 within this numerical range, a relatively good welding tensile force can be maintained between the electrode tab and the exposed portion.

[0010] In one or more of the above optional embodiments, the width of the welding mark area is W, and W satisfies: 0.1 mm ≤ W ≤ 1.0 mm. By limiting the width W of the welding mark area within this numerical range, the situation where the repeated welding of solder joints at the same position affects the welding quality can be reduced.

[0011] In one or more of the above optional embodiments, the distance between the welding mark area and the inner peripheral edge of the groove is N, and N satisfies: N ≥ 1.5 mm. Thereby, the situation where the active material layer falls off due to the thermal influence generated during the welding process and the volume energy density decreases can be improved.

[0012] In one or more of the above optional embodiments, the current collector is a composite current collector. The composite current collector includes a polymer layer and a first metal layer and a second metal layer provided on opposite sides of the polymer layer. The active material layers are respectively provided on the surfaces of the first metal layer and the second metal layer facing away from the polymer layer. Both the first metal layer and the second metal layer have exposed portions. One end of the electrode tab is provided in the notch and is located between the exposed portion of the first metal layer and the exposed portion of the second metal layer. One end of the electrode tab is fixed to the first metal layer and the second metal layer by welding respectively.

[0013] In one or more of the above optional embodiments, the electrode assembly has a wound structure. The electrode tab is a positive electrode tab or a negative electrode tab.

[0014] According to a second aspect of the present application, there is provided an electrical device including the secondary battery as described above.

[0015] According to a third aspect of the present application, there is provided a method for manufacturing a secondary battery, the secondary battery including an electrode assembly and a tab. The manufacturing method includes the following steps: providing a current collector; coating an active material on at least one surface of the current collector to form a pole piece; determining the position and size of a groove on one side of the pole piece, and removing the active material layer at the position corresponding to the groove to expose an exposed portion of the current collector; determining the size of a notch according to the size of the tab, and cutting out the notch at the position corresponding to the exposed portion; placing one end of the tab in the notch, and fixing one end of the tab and the notch by laser welding.

[0016] In one or more of the above optional embodiments, one end of the tab and the notch are fixed by laser welding at their peripheries.

[0017] Additional aspects and advantages of the embodiments of the present application will be described, shown, or elucidated in part in the following description, or through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] One or more embodiments are exemplarily illustrated by corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, unless otherwise stated, and the dimensions in the drawings do not constitute a proportional limitation.

[0019] Figure 1 FIG. 1 is a schematic structural diagram of a secondary battery provided by one embodiment of the present application;

[0020] Figure 2 FIG. 2 is a schematic diagram of a partially un-welded structure of a secondary battery provided by one embodiment of the present application;

[0021] Figure 3 FIG. 3 is a schematic diagram of a partially welded structure of a secondary battery provided by one embodiment of the present application;

[0022] Figure 4 FIG. 4 is a schematic diagram of a partially welded structure of a secondary battery provided by one embodiment of the present application;

[0023] Figure 5 FIG. 5 is a schematic cross-sectional structure diagram of a pole piece in a secondary battery provided by one embodiment of the present application;

[0024] Figure 6 FIG. 6 is a schematic cross-sectional structure diagram of a pole piece in a secondary battery provided by one embodiment of the present application;

[0025] REFERENCE SIGNS:

[0026] 1. Electrode assembly; 11. Electrode tab; 111. Current collector; 1111. Polymer layer; 1112. First metal layer; 1113. Second metal layer; 11101. Exposed portion; 111a. Notch; 112. Active material layer; 112a. Groove;

[0027] 2. Tab;

[0028] 3. Outer shell;

[0029] 4. Welding mark area;

[0030] X. First direction; Y. Second direction; Z. Third direction. Detailed implementation manners

[0031] The following detailed implementation manners are exemplary rather than restrictive, aiming to provide a basic understanding of the present application, and not aiming to identify the key or decisive elements of the present application or limit the scope to be protected. As long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way.

[0032] 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 at the same time. 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 at the same time.

[0033] 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 may be a state approximately vertical or equal between the 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 also 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 absolutely straight lines or planes, and may 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 as "straight lines" or "planes".

[0034] Unless otherwise defined, the term "plural" in this article, when used to describe the quantity of components, specifically means that the component is two or more.

[0035] As mentioned in the background art, with the rapid development of electronic information technology, batteries are gradually developing in the direction of high energy density and high power density.

[0036] Currently, the positive electrode sheet or the negative electrode sheet in the electrode assembly generally consists of a current collector and two active material layers respectively disposed on opposite sides of the current collector. Two opposite grooves are simultaneously formed on the two active material layers, and the tab is only accommodated in one of the grooves and welded and fixed to the current collector.

[0037] In order to reduce lithium plating in the secondary battery, it is necessary to make the area of the active material layer of the positive electrode sheet smaller than the area of the active material layer of the negative electrode sheet. Therefore, an insulating adhesive layer corresponding to the groove on the negative electrode active material layer is also provided on the positive electrode active material layer, and this insulating adhesive layer can further isolate the negative tab from the current collector of the positive electrode sheet. In order to further isolate the positive tab from the negative electrode sheet, an insulating adhesive layer corresponding to the positive tab is also provided on the active material layer of the negative electrode sheet. Therefore, when the positive electrode sheet, the separator, and the negative electrode sheet are laminated into an electrode assembly, the thickness at the tab of each electrode sheet is actually the sum of the thickness of the current collector, the thickness of the tab, the thickness of the insulating adhesive layer, and the thickness of the separator, resulting in a larger thickness of the partial electrode assembly where the tab is located and a lower energy density of the secondary battery.

[0038] Based on this, the embodiment of the present application provides a secondary battery, aiming to reduce the thickness of the partial electrode assembly where the tab is located to improve the energy density of the secondary battery.

[0039] Please refer to Figures 1 to 6 , a secondary battery provided by the embodiment of the present application includes a housing 3, an electrode assembly 1, and a tab 2. The housing 3 is a protective structure for the electrode assembly 1, and the electrode assembly 1 is accommodated in the housing 3. The electrode assembly 1 includes an electrode sheet 11. The electrode sheet 11 includes a current collector 111 and an active material layer 112 disposed on at least one surface of the current collector 111. The active material layer 112 is provided with a groove 112a. The current collector 111 has an exposed portion 11101 exposed in the groove 112a, and the exposed portion 11101 is provided with a notch 111a. When observed in the first direction X, the notch 111a is located in the groove 112a. One end of the tab 2 is disposed in the notch 111a and is fixed to the notch 111a by welding. The tab 2 is configured to be electrically connected to a power source to charge the secondary battery; or is configured to be electrically connected to a load to supply power to the load.

[0040] Compared with the secondary battery in the related art, in which the part of the tab 2 located in the groove 112a overlaps the exposed part 11101 without the notch 111a, for the secondary battery mentioned in the present application, by reserving the notch 111a in the exposed part 11101 where the current collector 111 is exposed in the groove 112a to accommodate one end of the tab 2, one end of the tab 2 is filled in the notch 111a and welded and fixed to the part of the exposed part 11101 surrounding the notch 111a, so that one end of the tab 2 located in the groove 112a is arranged side by side with the exposed part 11101 in the second direction Y. Thus, the thickness of the part of the electrode assembly 1 where the tab 2 is located is reduced, and further the energy density of the secondary battery is improved.

[0041] In some embodiments, any two of the first direction X, the second direction Y, and the third direction Z are perpendicular to each other, where the first direction X is the thickness direction of the electrode plate 11, and the third direction Z is the direction in which the tab 2 protrudes from the electrode plate 11.

[0042] As Figures 3 to 6 As shown in any of the accompanying drawings, in some embodiments, the periphery of the tab 2 and the notch 111a are fixed by welding, that is, when observed along the first direction X, one end of the tab 2 and the exposed part 11101 are integrally connected, and along the third direction Z, the exposed part 11101, the welding mark area 4 (the welding mark area formed by welding one end of the tab 2 and the part of the exposed part 11101 surrounding the notch 111a), and the tab 2 are arranged side by side. With such an arrangement, the thickness of the part of the electrode assembly 1 where the tab 2 is located is further reduced, and the energy density of the secondary battery is further improved.

[0043] In some embodiments, one end of the tab 2 is fixed to the part of the exposed part 11101 surrounding the notch 111a by laser welding. Since the laser welding process can precisely control the welding quality by adjusting parameters such as laser power, welding speed, and spot size, it can provide a suitable welding tensile force between the tab 2 and the exposed part 11101.

[0044] It can be understood that the secondary battery can be a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, etc., and the embodiments of the present application do not make specific limitations on this. In addition, the shape of the secondary battery can be cylindrical, flat, cuboid, or other shapes, etc., and the embodiments of the present application also do not make specific limitations on this.

[0045] For the convenience of description, some embodiments of the present application are described in detail. Without conflict, the following embodiments and the features in the embodiments can be combined with each other. Here, the present application takes a flat lithium-ion secondary battery as an example for illustration.

[0046] For the housing 3, as Figure 1As shown, in some embodiments, the housing 3 is a flexible packaging bag, such as an aluminum-plastic film. In other embodiments, the housing 3 is a rigid outer shell, such as a metal shell made of at least one of steel alloy, aluminum alloy, and copper alloy.

[0047] In some embodiments, the secondary battery includes an electrolyte (not shown in the figure), and the electrolyte is housed in the housing 3 and wets the electrode assembly 1. Among them, the electrolyte includes a solvent, an electrolyte salt, and an additive. The electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0048] For the electrode assembly 1, it includes a positive electrode sheet (not shown in the figure), a negative electrode sheet (not shown in the figure), and a separator (not shown in the figure) that separates the positive electrode sheet and the negative electrode sheet.

[0049] In some embodiments, the number of the positive electrode sheet 11 and the negative electrode sheet 11 is one each. A negative electrode sheet 11, a separator, and a positive electrode sheet 11 are sequentially stacked and wound to form a flat wound structure.

[0050] As Figure 5 shown, the electrode sheet 11 can be at least one of a positive electrode sheet in the wound structure and a negative electrode sheet in the wound structure. A positive electrode sheet 11 and a negative electrode sheet 11 both include the current collector 111 and the active material layer 112 provided on at least one surface of the current collector 111. For example, along the first direction X, active material layers 112 are provided on both opposite surfaces of the current collector 111, and the separator is disposed between the active material layer 112 of the positive electrode sheet 11 and the active material layer 112 of the negative electrode sheet 11.

[0051] Taking the electrode sheet 11 as the positive electrode sheet 11 and the electrode tab 2 as the positive electrode tab 2 as an example, the current collector 111 can be at least one of metal foils such as aluminum, nickel, tantalum, and titanium, such as aluminum foil. The active material layer 112 includes a positive electrode active material, and the positive electrode active material can include at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganate. The material of the positive electrode tab 2 includes at least one of aluminum, aluminum alloy, nickel, nickel-plated aluminum, silver-plated aluminum, etc.

[0052] In specific implementation, a part of the active material layer 112 on the positive electrode sheet 11 is removed to form the groove 112a, and the part of the current collector 111 exposed in the groove 112a is the exposed part 11101. The groove 112a is open on one side along the third direction Z. By removing a part of the exposed part 11101 on the same side as the opening to form the notch 111a, thus, when observed along the first direction X, the notch 111a is located within the groove 112a. One end of the positive electrode tab 2 is disposed in the notch 111a and is fixedly welded to the part of the exposed part 11101 that encloses the notch 111a, and the other end of the positive electrode tab 2 passes through the opening and extends out of the electrode assembly 1. In some embodiments, the extending direction of the positive electrode tab 2 is parallel to the third direction Z. Optionally, the periphery of one end of the positive electrode tab 2 and the notch 111a are fixedly welded together.

[0053] Taking the electrode sheet 11 as the negative electrode sheet 11 and the electrode tab 2 as the negative electrode tab 2 as an example, at this time, the current collector 111 can be at least one of metal foils such as copper, nickel, tantalum, and titanium, such as copper foil. The active material layer 112 includes a negative electrode active material, and the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon oxide material, and silicon carbon material. The material of the negative electrode tab 2 includes at least one of copper, nickel, copper-nickel alloy, nickel-chromium alloy, copper-plated nickel, nickel-plated copper, silver-plated copper, stainless steel (such as 304 stainless steel), etc.

[0054] In specific implementation, a part of the active material layer 112 on the negative electrode sheet 11 is removed to form the groove 112a, and the part of the current collector 111 exposed in the groove 112a is the exposed part 11101. The groove 112a is open on one side along the third direction Z. By removing a part of the exposed part 11101 on the same side as the opening to form the notch 111a, thus, when observed along the first direction X, the notch 111a is located within the groove 112a. One end of the negative electrode tab 2 is disposed in the notch 111a and is fixedly welded to the part of the exposed part 11101 that encloses the notch 111a, and the other end of the negative electrode tab 2 extends out of the electrode assembly 1. In some embodiments, the extending direction of the negative electrode tab 2 is parallel to the third direction Z. Optionally, the periphery of one end of the negative electrode tab 2 and the notch 111a are fixedly welded together.

[0055] It can be understood that the electrode sheet 11 is not limited to the specific forms mentioned above. For example, as Figure 6 shown, in some other embodiments, the electrode sheet 11 is a composite electrode sheet 11, that is, at least one of a positive electrode sheet 11 in a winding structure and a negative electrode sheet 11 in a winding structure is a composite electrode sheet 11.

[0056] The composite electrode sheet 11 includes a composite current collector 111 and an active material layer 112. The composite current collector 111 includes a polymer layer 1111, and a first metal layer 1112 and a second metal layer 1113 disposed on opposite sides of the polymer layer 1111. The active material layer 112 is disposed on the surfaces of the first metal layer 1112 and the second metal layer 1113 facing away from the polymer layer 1111, respectively.

[0057] In some embodiments, the first metal layer 1112 and the second metal layer 1113 may be at least one of aluminum, copper, nickel, cobalt, tungsten, tin, lead, iron, silver, gold, platinum, or an alloy thereof.

[0058] In some embodiments, both the first metal layer 1112 and the second metal layer 1113 have exposed portions exposed in the groove 112a. The exposed portion of the first metal layer 1112 is provided with a notch, and the exposed portion of the second metal layer 1113 is provided with a notch.

[0059] In some embodiments, the polymer layer 1111 includes one or more of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyether ether ketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic olefin copolymer, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride - hexafluoropropylene), poly(vinylidene fluoride - co - chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone and derivatives, sodium carboxymethyl cellulose, styrene - butadiene rubber, fluororubber, polyvinyl alcohol, polyvinylidene fluoride, etc.

[0060] When the composite electrode sheet is used as the positive electrode sheet of a wound structure, the first metal layer 1112 and the second metal layer 1113 can be made of metal aluminum or an aluminum alloy material; when the composite electrode sheet is used as the negative electrode sheet of a wound structure, the first metal layer 1112 and the second metal layer 1113 can be made of metal copper or a copper alloy material. The metal thin films formed by rolling the first metal layer 1112 and the second metal layer 1113 are adhered to the surface of the polymer layer 1111 by an adhesive.

[0061] Specifically, during implementation, a part of the active material layer 112 coated on the first metal layer 1112 and the second metal layer 1113 is removed to form the groove 112a. The part of the first metal layer exposed in the groove 112a is the exposed portion of the first metal layer 1112, and the part of the second metal layer exposed in the groove 112a is the exposed portion of the second metal layer 1113. One side of the groove 112a along the third direction Z is open, and a notch is formed by removing a part of the exposed portions of the first metal layer 1112 and the second metal layer 1113 on the same side as the open end.

[0062] One end of the positive electrode tab is disposed at the notch 111a. When observing along the third direction Z, the positive electrode tab 2 is located between the exposed portions of the first metal layer 1112 and the second metal layer 1113, and is respectively welded and fixed to the first metal layer 1112 and the second metal layer 1113 to enclose a partially exposed portion of the notch 111a. The other end of the positive electrode tab extends out of the electrode assembly 1. In some embodiments, the extending direction of the positive electrode tab 2 is parallel to the third direction Z. Thus, not only can the energy density of the secondary battery be improved to a certain extent, but also the first metal layer 1112 and the second metal layer 1113 can be directly conducted through the electrode tab, and no other electrical connectors need to be provided.

[0063] Alternatively, in some other embodiments, a notch is provided in one of the exposed portions of the first metal layer 1112 and the exposed portion of the second metal layer 1113, and no notch is provided in the other. The positive electrode tab 2 is welded and fixed to the exposed portion with the notch 111a and the exposed portion without the notch 111a, and it can still reduce the thickness of the partial electrode assembly 1 where the electrode tab 2 is located to improve the energy density of the secondary battery.

[0064] Optionally, the periphery of one end of the positive electrode tab and the inner periphery of the notch 111a are fixed by welding.

[0065] Continuing as Figure 3 or Figure 4 shown, in some embodiments, along the first direction X, the orthographic projection area of the welding mark area 4 formed by welding the electrode tab 2 and the exposed portion 11101 is S1, and the orthographic projection area of the exposed portion 11101 is S2. S1 and S2 satisfy: 1% ≤ S1 / S2 ≤ 6%. The orthographic projection area of the welding mark area 4 is positively correlated with the welding tensile force between the electrode tab 2 and the exposed portion 11101. By limiting the ratio of S1 / S2 within this numerical range, while reducing the thickness of the partial electrode assembly 1 where the electrode tab 2 is located, a good welding tensile force can be maintained between the electrode tab 2 and the exposed portion 11101.

[0066] Exemplarily, S1 / S2 can be within the range defined by any two of 1%, 2%, 3%, 4%, 5%, 6%.

[0067] Further, 3% ≤ S1 / S2 ≤ 6%. By limiting the ratio of S1 / S2 within this numerical range, a relatively good welding tensile force can be maintained between the electrode tab 2 and the exposed portion 11101.

[0068] Continuing as Figure 3As shown, in some embodiments, the width of the welding mark area 4 is W, and W satisfies: 0.1 mm ≤ W ≤ 1.0 mm. Limiting the width W of the welding mark area 4 within this numerical range can reduce the situation where the repeated welding of solder joints at the same position affects the welding quality. It should be noted here that the width W of the welding mark area 4 mentioned herein specifically refers to the distance between the boundary line of the welding mark area 4 and the exposed part 11101 to the boundary line with the tab 2.

[0069] Exemplarily, W can be 0.1 mm, 0.2 mm, 0.3 mm, 0.5 mm, 0.7 mm, 0.8 mm, 1.0 mm, and within the range defined by any two numerical values.

[0070] Continuing as Figure 3 As shown, in some embodiments, the spacing between the welding mark area 4 and the inner peripheral edge of the groove 112a is N, satisfying: N ≥ 1.5 mm. This can improve the situation where the active material layer 112 falls off due to the thermal influence generated during the welding process, resulting in a decrease in the volumetric energy density. It should be noted here that the spacing between the welding mark area 4 and the inner peripheral edge of the groove 112a mentioned herein specifically refers to the distance between the boundary line of the welding mark area 4 and the exposed part 11101 to the inner peripheral edge of the groove 112a.

[0071] Exemplarily, N can be any value of 1.5 mm, 2 mm, 3 mm, 5 mm, 7 mm, 8 mm or more.

[0072] One embodiment of the present application provides a method for manufacturing a secondary battery, including the following steps.

[0073] Step S1, providing a current collector 111;

[0074] The current collector 111 includes a metal foil or a composite current collector 111.

[0075] Step S2, coating an active material on at least one surface of the current collector 111 to form a pole piece 11;

[0076] Step S3, determining the position and size of the groove 112a on one side of the pole piece 11 along the third direction Z, and removing the active material layer 112 at the corresponding position of the groove 112a to expose the exposed part 11101 of the current collector 111;

[0077] Step S4, determining the size of the notch 111a according to the size of the tab 2, and cutting out the notch 111a at the corresponding position on the exposed part 11101;

[0078] Step S5, placing one end of the tab 2 in the notch 111a, and fixing one end of the tab 2 and the notch 111a by laser welding.

[0079] In some embodiments, in step S5, it specifically includes: fixing the periphery of one end of the tab 2 and the notch 111a by laser welding.

[0080] The present application will be further described below in conjunction with examples and comparative examples. Various tests and evaluations are carried out according to the following methods. It should be understood that these examples are only used to illustrate the present application and not to limit the present application.

[0081] Example 1-1

[0082] The preparation method of the secondary battery is as follows:

[0083] (1) Preparation of the positive electrode sheet: Lithium cobaltate, a conductive agent, and a binder polyvinylidene fluoride (PVDF) are dissolved in an N-methylpyrrolidone (NMP) solution according to a mass ratio of 97.2:1.5:1.3 to form a slurry for the positive electrode active material layer. Pass through a 200-mesh sieve to form a slurry for the positive electrode active material layer, and the solid content of the slurry is 70%-75%. Use a coater to coat the slurry for the positive electrode active material layer on the surface of the positive electrode current collector. After drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0084] (2) Assembly of the positive electrode sheet and the positive electrode tab: Determine the position and size of the groove on one side of the electrode sheet along the third direction, remove the active material layer at the corresponding position of the groove to expose the exposed part of the current collector; determine the size of the notch according to the size of the tab, cut out a notch at the corresponding position of the exposed part, place one end of the tab in the notch, and fix it to the notch by laser circumferential welding.

[0085] (3) Preparation and assembly of the adhesive tape: Use a microgravure printing method to coat an aqueous polyacrylate as an adhesive on one side of a polypropylene substrate layer, coat a release agent on the other side of the substrate layer, wind it up and slit it to prepare an adhesive tape roll stock. Cut the adhesive tape and attach the adhesive tape to the positive electrode active material layer so that the adhesive tape covers a part of the positive electrode tab.

[0086] (4) Preparation of the negative electrode sheet: Mix the negative electrode active material graphite, the negative electrode thickener sodium carboxymethyl cellulose, and the negative electrode binder styrene-butadiene rubber according to a mass ratio of 98:1:1, add deionized water and stir evenly to form a slurry for the negative electrode active material layer. Pass through a 200-mesh sieve to form a slurry for the negative electrode active material layer, and the solid content of the slurry is 40%-45%. Use a copper foil as the negative electrode current collector and coat the slurry for the negative electrode active material layer on the negative electrode current collector. After drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0087] (5) Assembly of the negative electrode sheet and the negative electrode tab: Prepare the negative electrode tab and connect the negative electrode tab to the negative electrode sheet.

[0088] (6) Preparation of the separator: The base material of the separator is polyethylene (PE) with a thickness of 5 μm. On both surfaces of the opposite sides of the base material, an alumina ceramic layer with a thickness of 2 μm is coated. Finally, a binder polyvinylidene fluoride (PVDF) with a coating amount of 2.5 mg / cm 2 is coated on both sides of the coated ceramic layer, and after drying, it is slit.

[0089] (7) Preparation of the electrolyte: In an environment with a water content of less than 10 ppm, lithium hexafluorophosphate is mixed with a non-aqueous organic solvent (propylene carbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:1:0.5:1, by weight ratio) to prepare a basic electrolyte, and LiPF6 is added and mixed evenly to obtain the electrolyte, where the concentration of LiPF6 is 1 mol / L.

[0090] (8) Preparation of the secondary battery: The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, with the separator placed in the middle of the positive electrode sheet and the negative electrode sheet to play a role in isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer packaging aluminum-plastic film, dehydrated at 80 °C, then the above-mentioned electrolyte is injected and sealed, and after processes such as formation, degassing, and edge trimming, the secondary battery is obtained.

[0091] Comparative Example 1-1

[0092] In the secondary battery of Comparative Example 1-1, no notch is opened in the exposed part of the positive electrode sheet. One end of the positive electrode tab is placed in the groove and fixed by laser welding to the exposed part exposed in the groove. Except for this, all other parameters in the secondary battery of Comparative Document 1-1 are the same as those in the secondary battery of Example 1-1.

[0093] Example 1-2

[0094] The difference between the secondary battery of Example 1-2 and the secondary battery of Example 1-1 is only the type of current collector, and all other parameters are the same.

[0095] Comparative Example 1-2

[0096] The difference between the secondary battery of Comparative Example 1-2 and the secondary battery of Example 1-1 is only the type of current collector, and all other parameters are the same.

[0097] Examples 2-1 to 2-7

[0098] The differences between Examples 2-1 to 2-7 and Example 1-2 are that, except for adjusting the relevant parameters according to Table 2, the rest are the same as Example 1-2.

[0099] Examples 3-1 and 3-2

[0100] Examples 3-1 and 3-2 are different from Example 1-2 in that, except for adjusting the relevant parameters according to Table 3, the rest are the same as Example 1-2.

[0101] The following describes the test methods for each parameter of the embodiments of the present application.

[0102] Test method for volumetric energy density:

[0103] Prepare a square secondary battery by the above preparation method, charge the battery to 4.5V at a constant current of 1C, then charge the battery to 0.05C at a constant voltage of 4.5V, discharge the battery to 3.0V at a constant current of 0.2C, and record the discharge energy E; measure the external dimensions of the square secondary battery and calculate its volume, which is V; then the energy density W = E / V. The test results are shown in Table 1 and Table 3 below.

[0104] Test method for welding tensile strength:

[0105] Disassemble the secondary battery to obtain the connection structure between the positive electrode plate and the positive electrode tab, remove the active material layer of the positive electrode plate, fix the positive electrode tab at the lower end of the tensile testing machine using a high-precision tensile testing machine, and fix the current collector of the positive electrode plate at the upper end of the high-precision tensile testing machine, keeping both ends on the same vertical plane. Set the speed of the tensile testing machine to 50 mm / min, pull the current collector of the positive electrode tab and the positive electrode plate, and record the tensile force F (in N) when the positive electrode tab and the current collector of the positive electrode plate are separated.

[0106] Table 1

[0107]

[0108]

[0109] As can be seen from Table 1, the volumetric energy density of the secondary battery of Example 1-1 is better than that of the secondary battery of Comparative Example 1-1, and the volumetric energy density of the secondary battery of Example 1-2 is better than that of Comparative Example 1-2. It can be seen that by reserving a notch at the exposed portion of the current collector exposed in the groove to receive one end of the electrode tab, one end of the electrode tab is filled in the notch and welded and fixed to the partial exposed portions surrounding the notch, the thickness of the partial electrode assembly where the electrode tab is located is reduced, and thus the energy density of the secondary battery is improved.

[0110] Table 2

[0111]

[0112] Observing Example 1-2, Examples 2-1 to 2-3, it can be seen that the welding tensile strength between the electrode tab and the exposed portion increases with the increase of the S1 / S2 ratio.

[0113] Comparing Example 2-1 to Example 2-3 with Example 1-2, it can be seen that when S2 remains unchanged, S1 and S2 satisfy: 1% ≤ S1 / S2 ≤ 6%. While reducing the thickness of the partial electrode assembly where the tab is located, a good welding tensile force can be maintained between the tab and the exposed portion. It should be noted that the reason for limiting the ratio of S1 / S2 within this numerical range is that when S1 / S2 < 1%, it is difficult to ensure the welding strength between the tab and the exposed portion in the welding process; when S1 / S2 > 6%, it is difficult for the current equipment to achieve complex processing.

[0114] Observing Example 2-5 to Example 2-7, it can be seen that when W is 1.2 mm, the welding tensile force between the tab and the exposed portion is actually less than when W is 1 mm. This is because after W > 1 mm, there is a situation of welding breakage caused by repeated welding of the solder joints at the same position, reducing the welding tensile force between the tab and the exposed portion. Therefore, limiting the width W of the solder print area within this numerical range can reduce the situation where the repeated welding of the solder joints at the same position affects the welding quality.

[0115] Table 3

[0116] Number Type of current collector N (mm) Volume energy density (Wh / L) Examples 1-2 Composite current collector 1.5 817.2 Example 3-1 Composite current collector 1 816.3 Example 3-2 Composite current collector 2 817.1

[0117] Comparing Example 1-2 and Example 3-1, it can be seen that the volume energy density of the secondary battery when N is 1 mm is less than that of the secondary battery when N is 1.5 mm. After disassembling the secondary batteries of both examples, it is found that this is because part of the active material layer near the inner periphery of the groove falls off due to the heat generated by welding, resulting in a decrease in the volume energy density.

[0118] Observing Example 3-1 and 3-2, it is found that after N ≥ 1.5 mm, the volume energy density of the secondary battery is less affected by welding.

[0119] Based on the same technical concept as the above secondary battery, the present application also provides an electrical device including the above-mentioned secondary battery. The electrical device of the present application may be, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0120] The above are only the embodiments of the present application, and do not thus limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall similarly be included within the patent protection scope of the present application.

Claims

1. A secondary battery, comprising an electrode assembly and a tab, the electrode assembly including a pole piece, the pole piece including a current collector and an active material layer provided on at least one surface of the current collector; characterized in that, the active material layer is provided with a groove; the current collector has an exposed portion exposed in the groove, the exposed portion is provided with a notch, and one end of the tab is provided in the notch and is fixed to the notch by welding.

2. The secondary battery according to claim 1, characterized in that, The periphery of one end of the tab and the periphery of the notch are fixed by welding.

3. The secondary battery according to claim 2, characterized in that, The welding is laser welding.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, Along a first direction, the first direction being the thickness direction of the pole piece, the orthographic projection area of the weld mark region formed by welding the tab and the exposed portion is S1, and the orthographic projection area of the exposed portion is S2, 1% ≤ S1 / S2 ≤ 6%.

5. The secondary battery according to claim 4, characterized in that, 3% ≤ S1 / S2 ≤ 6%.

6. The secondary battery according to claim 4, characterized in that, The width of the weld mark region is W, 0.1 mm ≤ W ≤ 1.0 mm.

7. The secondary battery according to claim 4, wherein The distance between the weld mark region and the inner periphery of the groove is N, N ≥ 1.5 mm.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The current collector is a composite current collector, the composite current collector including a polymer layer and a first metal layer and a second metal layer provided on opposite sides of the polymer layer, and the active material layer is respectively provided on the surface of the first metal layer facing away from the polymer layer and the surface of the second metal layer facing away from the polymer layer; Both the first metal layer and the second metal layer have the exposed portion; one end of the tab is provided in the notch and is located between the exposed portion of the first metal layer and the exposed portion of the second metal layer, and one end of the tab is fixed to the first metal layer and the second metal layer respectively by welding.

9. The secondary battery according to any one of claims 1-8, characterized in that, The electrode assembly is of a wound structure, and the pole piece is a positive pole piece or a negative pole piece.

10. An electrical device, characterized in that, Including the secondary battery according to any one of claims 1-9.

11. A method for manufacturing a secondary battery, characterized in that, The secondary battery includes an electrode assembly and a tab, and the manufacturing method includes the following steps: Provide a current collector; Coat an active material on at least one surface of the current collector to form a pole piece; Determine the position and size of the groove on one side of the pole piece, and remove the active material layer at the corresponding position of the groove to expose the exposed portion of the current collector; Determine the size of the notch according to the size of the tab, and cut out the notch at the corresponding position of the exposed portion; Place one end of the tab in the notch, and fix one end of the tab to the notch by laser welding.

12. The manufacturing method according to claim 11, characterized in that, The periphery of one end of the tab and the notch are fixed by laser welding.

Images