A lithium battery based on a flexible thin film current collector

Abstract

The present invention discloses a lithium battery based on a flexible thin film current collector, comprising a rolled electrode sheet, an electrolyte and a packaging assembly. The electrode sheet comprises a flexible thin film current collector and an active substance; the middle of the flexible thin film current collector is a polymer base layer, and both the front and back surfaces are metal-plated; the flexible thin film current collector comprises a main body area and a plurality of overlapping structures integrated with the main body area; the active substance is coated on the surface of the main body area. The overlapping structures are bent and arranged toward the axial direction of the rolled electrode sheet, and at least a portion of the front and back surfaces of any two adjacent overlapping structures form an overlapping contact, so that the metal coatings on the front and back surfaces of the flexible thin film current collector are conductive. The packaging assembly comprises a protective cover and a battery shell, and the protective cover is in extrusion contact with at least one overlapping structure. The interior of the lithium battery of the present invention does not contain welding parts, which greatly improves the manufacturing yield of the battery and improves the safety of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage batteries, and in particular relates to a lithium battery based on a flexible thin film current collector. Background Art

[0002] In lithium batteries, 6μm-10μm copper foil and 8μm-15μm aluminum foil are typically used as current collectors for electrode sheets. Since copper and aluminum foil are electrical conductors, simply welding a metal tab to one side allows the active material on both sides of the current collector to participate in electron transfer with the external circuit. However, this metal foil current collector accounts for a high proportion of the battery cell's weight, hindering the improvement of the cell's energy density.

[0003] In order to improve the energy density of the battery cell, the relevant technology has proposed a composite current collector consisting of a polymer material layer and a metal layer with a thickness of more than 1μm located on both sides of the polymer material layer, which has improved the weight energy density of the battery cell to a certain extent. At present, this related technology is in the stage of industrial promotion.

[0004] However, the metal layers on both sides of the composite current collector in the related art are in an insulating state, which means that the metal layers on both sides of the composite current collector need to be welded to the tabs to achieve electronic conduction between the two sides. In this way, on the one hand, the thin metal coating and the low-melting-point polymer layer on the surface of the composite current collector are very prone to deformation and melt-through during the tab welding process, forming local hot spots, which greatly reduces the yield rate of pole piece manufacturing and hinders the industrialization process of the composite current collector. On the other hand, after the battery is assembled, the welding of the tabs and the caps forms another local hot spot, and the limited welding area of ​​the tabs and the caps exacerbates the temperature rise of the hot spot, resulting in excessive temperature difference in the battery, increased risk of thermal runaway, and low safety. Summary of the Invention

[0005] The present invention provides a lithium battery based on a flexible thin-film current collector. Multiple overlapping structures integral to the flexible thin-film current collector are placed in contact with each other on both the front and back sides to conduct active material between the front and back sides of the electrode sheet. Furthermore, a protective cover is provided that is in contact with the overlapping structures in a compressive manner to conduct an external circuit. This lithium battery eliminates the need for welding processes, significantly improving the battery's manufacturing yield and safety.

[0006] The present invention discloses a lithium battery based on a flexible thin film current collector, comprising an electrode sheet, an electrolyte, and a packaging assembly. The electrode sheet comprises a flexible thin film current collector and an active material; the middle of the flexible thin film current collector is a polymer base layer, and both the front and back surfaces are metal-plated, with a thickness of the metal plating being 0.8-1.5 μm; the flexible thin film current collector comprises a main body region and a plurality of overlapping structures integral with the main body region; the overlapping structures are rectangular teeth-shaped and arranged on one edge of the main body region; the active material is coated on the surface of the main body region; the electrode sheet is in a roll-like shape, and there are two of them. The overlapping structures are bent and arranged toward the axial direction of the rolled electrode sheet, and at least a portion of the front and back surfaces of any two adjacent overlapping structures form an overlapping contact, so that the metal plating on the front and back surfaces of the flexible thin film current collector is conductive, and the active materials on both the front and back surfaces of the flexible thin film current collector can participate in electron exchange. The electrolyte is disposed between the two electrode sheets. The packaging assembly includes a protective cover and a battery shell, and the protective cover is in extrusion contact with at least one overlapping structure; the interior of the lithium battery does not contain a welding part, and there is no welding connection between the overlapping structures and between the overlapping structures, the protective cover and the battery shell.

[0007] Optionally, the polymer substrate layer is selected from one of polyethylene terephthalate, polypropylene, polycarbonate, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polyethylene and polytetrafluoroethylene. In a preferred embodiment, the polymer substrate layer is polyethylene terephthalate or polycarbonate.

[0008] Optionally, the thickness of the polymer base layer is 1 μm-6 μm.

[0009] Optionally, the metal coating is composed of one or more selected from copper, aluminum, silver, nickel, molybdenum, titanium, niobium, iron, zinc, stainless steel, graphene, carbon nanotubes, Ketjen black, acetylene black, graphite powder and carbon fiber. In a preferred embodiment, the metal coating is composed of copper or aluminum.

[0010] Optionally, the metal plating layers prepared on the front and back sides of the polymer substrate have the same composition.

[0011] Optionally, the metal coatings on the front and back surfaces of the flexible thin film current collector are prepared by a method selected from vacuum coating, electroplating, and chemical plating. In some preferred embodiments, the metal coatings of the flexible thin film current collector are prepared by vacuum evaporation or vacuum magnetron sputtering.

[0012] Optionally, the front side of the overlapping structure is part of the front side of the flexible thin film current collector; and the back side of the overlapping structure is part of the back side of the flexible thin film current collector.

[0013] Optionally, the bending angle of the overlapping structure relative to the main body is less than 90 degrees. In this way, when the protective cover forms a pressing contact with the overlapping structure, it is conducive to ensuring full contact between the protective cover and the overlapping structure, thereby improving the conductive effect between the external circuit and the electrode sheet.

[0014] Optionally, multiple overlapping structures are arranged at intervals.

[0015] Optionally, an insulating material is provided between the overlapping structure and the rolled electrode sheet. In some preferred embodiments, the insulating material is an insulating tape or an insulating sheet.

[0016] Optionally, the flexible film current collector is cut by laser cutting, mechanical cutting or plasma cutting, thereby forming a plurality of overlapping structures on one side of the flexible film current collector, and the overlapping structures are integrally arranged with the flexible film current collector.

[0017] Optionally, the two electrode sheets have the same structure but opposite polarities; the electrode sheets are disposed within the battery housing; the overlapping structures of the two electrode sheets are located at opposite ends of the battery housing; and two protective covers are provided, one at each end of the battery housing, and each protective cover is in pressurized contact with at least one overlapping structure.

[0018] Optionally, the battery housing is made of insulating material with a density less than 2g / cm 3 Thus, the battery shell adopts a density of less than 2g / cm 3 The insulating material greatly reduces the overall weight of the battery, thereby greatly improving the energy density of the battery.

[0019] Optionally, the protective cover has a cylindrical structure.

[0020] Optionally, the protective cover includes a support and a conductor. The conductor is spliced ​​with the support, with the lower surface of the conductor and the lower surface of the support being coplanar, and the upper surface of the conductor and the upper surface of the support being coplanar. The lower surface of the conductor is in press-contact with the front surface of at least one overlapping structure.

[0021] Optionally, the conductor is made of copper, aluminum, nickel, or stainless steel.

[0022] Optionally, the conductor and the support are combined to form a protective cover by heat sealing, gluing or inlaying.

[0023] Optionally, an explosion-proof structure is provided around the support body, and the explosion-proof structure is in a groove shape.

[0024] Optionally, the support body is made of a brittle material.

[0025] Optionally, the support body is made of a thermally variable material; the support body has a breaking strength of 1.6 MPa or more at a temperature below 130° C., and a breaking strength of 10 kPa-30 kPa at a temperature above 160° C.

[0026] Optionally, the density of the support is less than 1.5 g / cm 3 .

[0027] Optionally, the ratio of the cross-sectional area of ​​the conductor to the cross-sectional area of ​​the protective cover is less than 40%, and the ratio of the cross-sectional area of ​​the support body to the cross-sectional area of ​​the protective cover is greater than 60%.

[0028] Optionally, the conductor includes a columnar central conductive block and circumferential conductive blocks. The shape of the central conductive block can be selected from a cylindrical shape, a polygonal prism shape, and the like. In a preferred embodiment, the central conductive block is cylindrical. The circumferential conductive blocks are circumferentially spaced around the central conductive block and correspond one-to-one with the overlapping structures. The thickness of the circumferential conductive blocks is less than that of the central conductive block, and the lower surface of the circumferential conductive blocks is flush with the lower surface of the central conductive block, together forming the lower surface of the conductor.

[0029] Optionally, the support body is an annular structure, the inner hole size of the annular structure is consistent with the outer size of the central conductive block, the lower surface of the support body is provided with a groove matching the circumferential conductive block, and the circumferential conductive block is clamped in the groove of the support body.

[0030] Optionally, the overhang length of the overlapping structure is greater than 80% of the rolled radius of the electrode sheet and less than 150% of the rolled radius of the electrode sheet, and the length, spacing and number of the overlapping structures are matched so that the sum of the areas of overlapping contact of multiple overlapping structures accounts for 90%-110% of the total area of ​​extruded contact between the conductor and the overlapping structure.

[0031] Optionally, the protective cover has a thickness of 0.5 mm to 1.5 mm.

[0032] The lithium battery technology solution based on the flexible thin film current collector of the present invention can be applied to battery forms such as cylindrical batteries, square batteries, soft-pack batteries, and button batteries.

[0033] The present invention provides a lithium battery based on a flexible thin film current collector, which can achieve the following technical effects:

[0034] (1) The battery is composed of a flexible thin film current collector with a lapped structure. The spatial arrangement of the lapped structure can efficiently conduct the metal coatings on the front and back sides of the flexible thin film current collector, which can completely eliminate the tab welding process, thereby greatly improving the manufacturing yield of the battery and being more conducive to the industrial manufacturing of the battery.

[0035] (2) Since the flexible film current collector of the present invention is integrally arranged with the overlapping structure to form a conductive whole without interface transfer resistance, the problems of contact resistance between the flexible film current collector and the tab, welding point resistance, etc. existing in the tab welding process are avoided, thereby reducing the battery resistance and avoiding the ohmic heat generation of the battery to the greatest extent. The temperature rise rate of the battery and the battery tab and surface temperature ratio are greatly reduced, effectively improving the local temperature rise of the battery and improving the safety of the battery.

[0036] (3) By extruding the protective cover and the overlapping structure into contact, multi-path electron transmission can be achieved, further reducing the ohmic impedance of the battery and solving the hidden danger of thermal runaway inside the battery.

[0037] (4) By setting up the structure of the protective cover, the conductor of the protective cover is in squeeze contact with the overlapping structure of the electrode sheet. In the event of abnormal operation of the battery, the support body of the protective cover will quickly rupture and release pressure along the explosion-proof structure. When the support body ruptures, the squeeze contact between the conductor of the protective cover and the electrode sheet is quickly disconnected, achieving efficient disconnection between the electrode sheet and the external circuit, so that the battery stops providing current and continues to generate heat, effectively blocking the accident and further improving the safety of the battery. This avoids the phenomenon in the related art that when the battery is abnormal, the ordinary metal composite cap and the tab connected by welding are difficult to disconnect, making it difficult to disconnect the traditional battery from the electrical appliance in time, resulting in a great safety hazard.

[0038] (5) By providing a lighter protective cover and battery shell and replacing the separately provided tabs with a lap joint structure, the battery weight is greatly reduced, the specific gravity of inactive substances is reduced, and the battery energy density is improved.

[0039] The above general description and the following description are exemplary and explanatory only and are not intended to limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] One or more embodiments are exemplarily described by corresponding drawings, and these exemplary descriptions and drawings do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements, and the drawings do not constitute a scale limitation.

[0041] Figure 1 It is a schematic cross-sectional structure diagram of an embodiment of the flexible thin film current collector in the present invention.

[0042] Figure 2 It is a planar unfolding schematic diagram of an embodiment of the flexible thin film current collector in the present invention.

[0043] Figure 3 It is a structural schematic diagram of an embodiment of a lithium battery based on a flexible thin film current collector of the present invention.

[0044] Figure 4 It is a schematic structural diagram of the protective cover of the present invention in which the conductor and the support are in a separated state.

[0045] Figure 5 It is a structural schematic diagram of the protective cover of the present invention in which the conductor and the support are in a spliced ​​state.

[0046] Figure 6 It is a schematic diagram of the overlapping contact mode of the overlap structure in one embodiment of the present invention.

[0047] Figure 7 It is a schematic diagram of the overlapping contact mode of the overlap structure in another embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to provide a more detailed understanding of the features and technical content of the present invention, the implementation of the present invention is described in detail below with reference to the accompanying drawings. The accompanying drawings are for reference only and are not intended to limit the present invention. In the following technical description, for the sake of convenience of explanation, multiple details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. In other cases, to simplify the drawings, well-known structures and devices may be simplified.

[0049] The terms "includes" and "have" and any variations thereof in the description and claims of the present invention and the above-mentioned drawings are intended to cover a non-exclusive inclusion.

[0050] Unless otherwise stated, the term "plurality" means two or more.

[0051] The terms “front side” and “back side” are used for the convenience of distinction in description and are not used to limit the present invention.

[0052] The term "correspondence" may refer to an association relationship or a binding relationship. The correspondence between A and B means that there is an association relationship or a binding relationship between A and B.

[0053] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0054] The present invention provides a lithium battery based on a flexible thin film current collector, in which multiple overlapping structures are superimposed on each other to contact and conduct the active materials on the front and back sides of the electrode sheet, and the protective cover and the overlapping structures are squeezed and contacted with each other to conduct the external circuit and the active materials of the electrode sheet, thereby greatly improving the manufacturing yield of the battery and improving the safety of the battery.

[0055] The present invention provides a lithium battery based on a flexible film current collector, combined with Figures 1 to 3As shown, the lithium battery includes an electrode sheet 2, an electrolyte, and a packaging assembly 20. The electrode sheet 2 includes a flexible thin film current collector 10 and an active material. The flexible thin film current collector 10 has a polymer base layer 1 in the middle, and a metal coating 3 on both the front and back surfaces, with a thickness of 0.8-1.5 μm. The flexible thin film current collector 10 includes a main body region 101 and multiple overlapping structures 102 integral with the main body region 101. The overlapping structures 102 are rectangular teeth and are arranged on one edge of the main body region 101. The active material is coated on the surface of the main body region 101. The electrode sheet 2 is in the form of a roll, and there are two of them. The overlapping structures 102 are bent and arranged toward the axis 201 of the rolled electrode sheet 2, and at least a portion of the front and back surfaces of any two adjacent overlapping structures form an overlapping contact, so that the metal coatings on the front and back surfaces of the flexible thin film current collector are conductive. The electrolyte is provided between the two electrode sheets. The packaging assembly 20 includes a protective cover 21 and a battery housing 22 , wherein the protective cover 21 is in press contact with at least one overlapping structure 102 .

[0056] By sequentially stacking and pressing multiple overlapping structures integrally formed with the flexible thin-film current collector, the metal coatings on the front and back surfaces of the flexible thin-film current collector are electrically conductive, eliminating the need for welding the tabs. Furthermore, after battery assembly, a protective cover is provided to contact the overlapping structures through compression, achieving electrical continuity between the active materials on the front and back surfaces of the electrode sheet and the external circuit without welding the protective cover to the tabs. This lithium battery contains no internal welds, and no welds exist between the overlapping structures, nor between the overlapping structures, the protective cover, and the battery case. This design replaces the existing state-of-the-art approach of requiring additional tabs, welding them to the current collector, and then welding the tabs to a conventional metal composite cap and / or battery case. This design addresses the issues of cold welds, high resistance, and high local temperatures at the welds caused by the tab welding process. It also addresses the problem of limited welding area between the tabs and the conventional metal composite cap and / or battery case, creating additional localized hot spots that can easily lead to thermal runaway and safety accidents. The overlapping structures integrated with the flexible film current collector are then pressed into contact with each other and then connected to the conductive body of the protective cover through extrusion. This contact connection method efficiently and directly connects the external circuit to the electrode sheet, avoiding the welding resistance generated by the tab welding, which increases the battery resistance. This helps to reduce the internal resistance of the battery and improve battery efficiency. It also avoids deformation and melt-through of the flexible film current collector during welding, which can cause localized hot spots, thereby improving the manufacturing yield of the electrode sheet. At the same time, the present invention uses a lighter and thinner protective cover to replace the conventional metal composite cap of the related art, an insulating material battery shell to replace the metal conductive shell of the related art, and an overlapping structure to replace the separately provided metal foil tabs of the related art, thereby significantly reducing the weight of the battery itself and significantly improving the battery's energy density.

[0057] Optionally, the polymer substrate layer is selected from one of polyethylene terephthalate, polypropylene, polycarbonate, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polyethylene and polytetrafluoroethylene. In a preferred embodiment, the polymer substrate layer is polyethylene terephthalate or polycarbonate.

[0058] Optionally, the thickness of the polymer base layer is 1 μm-6 μm.

[0059] Optionally, the metal coating is composed of one or more selected from copper, aluminum, silver, nickel, molybdenum, titanium, niobium, iron, zinc, stainless steel, graphene, carbon nanotubes, Ketjen black, acetylene black, graphite powder and carbon fiber. In a preferred embodiment, the metal coating is composed of copper or aluminum.

[0060] Optionally, the metal plating layers prepared on the front and back sides of the polymer substrate have the same composition.

[0061] Optionally, a metal coating is formed on the front and back surfaces of the polymer substrate layer by vacuum coating, electroplating, or chemical plating to form a flexible thin film current collector. In some preferred embodiments, the metal coating is formed by vacuum evaporation or vacuum magnetron sputtering to form a flexible thin film current collector.

[0062] Optionally, the front side of the overlapping structure is part of the front side of the flexible thin film current collector, and the back side of the overlapping structure is part of the back side of the flexible thin film current collector. In this way, by overlapping the front side of at least one overlapping structure with the back side of another overlapping structure, the front and back sides of the flexible thin film current collector can be electrically connected. After packaging into a battery, the conductive portion of the protective cover only needs to be pressed into contact with at least one overlapping structure to achieve external circuit conduction through the metal coating on the front and back sides of the entire flexible thin film current collector, thereby achieving electrical conduction between the external circuit and the active materials on the front and back sides of the electrode sheet, allowing the active materials on the front and back sides of the electrode sheet to participate in electron exchange.

[0063] Optionally, the deformation angle of the overlapping structure relative to the main body area is less than 90 degrees.

[0064] Optionally, multiple overlapping structures are arranged at intervals.

[0065] Optionally, an insulating material is provided between the overlapping structure and the rolled electrode sheet to prevent short circuit and improve battery safety. In some preferred embodiments, the insulating material is an insulating tape or an insulating sheet.

[0066] Optionally, the flexible film current collector is cut by laser cutting, mechanical cutting or plasma cutting, thereby forming a plurality of overlapping structures on one side of the flexible film current collector, and the overlapping structures are integrated with the flexible film current collector.

[0067] Optionally, the two electrode sheets have the same structure but opposite polarities; the electrode sheets are disposed inside the battery housing 22. The overlapping structures of the two electrode sheets are located at both ends of the battery housing; and there are two protective covers, each disposed at both ends of the battery housing and in pressurized contact with at least one overlapping structure.

[0068] By providing two electrode sheets, one for the positive electrode and the other for the negative electrode, and the overlapping structures of the two electrode sheets are connected to the two protective covers at both ends of the battery shell by extrusion contact, the structure of the present invention does not require the battery shell to participate in the conduction between the battery and the external circuit, that is, it can achieve conduction between the external circuit and the two electrode sheets. Therefore, the present invention can design the battery shell as an insulating non-metallic material, thereby reducing the weight of the battery and thereby increasing the energy density of the battery. Optionally, the battery shell is made of an insulating material with a density of less than 2g / cm 3 .

[0069] Optionally, the protective cover has a cylindrical structure.

[0070] Optionally, the cross-sectional area of ​​the protective cover is the same as the rolled area of ​​the rolled electrode sheet, so that the protective cover can completely wrap the end of the electrode sheet having the overlapping structure.

[0071] Optionally, combined Figure 4 、 Figure 5 As shown, the protective cover 21 includes a support body 221 and a conductor 222. The conductor 222 is spliced ​​with the support body 221, with the lower surface of the conductor 222 and the lower surface of the support body 221 coplanar, and the upper surface of the conductor 222 and the upper surface of the support body 221 coplanar. During battery assembly, the lower surface of the conductor 222 is in pressurized contact with the front surface of at least one overlapping structure.

[0072] Optionally, the conductor is made of copper, aluminum, nickel, or stainless steel.

[0073] The protective cover is formed by splicing the support body and the conductor, so that a part of the protective cover is the conductor. On the one hand, due to the extrusion contact between the conductor and the overlapping structure, the conductive effect between the electrode sheet and the external circuit can be ensured. On the other hand, optionally, the density of the support body is less than 1.5g / cm 3 Due to the participation of the support body, the overall weight of the protective cover is reduced, thereby improving the energy density of the battery.

[0074] Optionally, the conductor and the support are combined to form a protective cover by heat sealing, gluing or inlaying.

[0075] Optionally, combined Figure 4 、 Figure 5As shown, an explosion-proof structure 2212 is provided around the support body 221. The explosion-proof structure 2212 is groove-shaped. In this way, when an abnormality occurs to the battery, the protective cover 21 can be quickly broken along the explosion-proof structure 2212, thereby accelerating the response speed of the protective cover 21.

[0076] Optionally, the support body is made of a brittle material.

[0077] Optionally, the support body is made of a thermally variable material; the support body has a breaking strength of 1.6 MPa or greater at temperatures below 130°C, and a breaking strength of 10 kPa to 30 kPa at temperatures above 160°C. By using a thermally variable material for the support body, the strength of the support body of the protective cover will be greatly reduced under the action of heat in the event of thermal runaway, causing it to rupture in a timely manner, releasing pressure and preventing battery explosion or combustion, which could lead to greater safety accidents.

[0078] Optionally, the ratio of the cross-sectional area of ​​the conductor to the cross-sectional area of ​​the protective cover is less than 40%, and the ratio of the cross-sectional area of ​​the support body to the cross-sectional area of ​​the protective cover is greater than 60%. Thus, by setting the ratio of the support body area, sufficient pressure relief channels are ensured, and the strength of the protective cover is further reduced, which is more conducive to the effective and rapid pressure relief of the protective cover before an accident occurs.

[0079] Optionally, combined Figure 4 、 Figure 5 As shown, the conductor 222 includes a cylindrical central conductive block 2221 and circumferential conductive blocks 2222. The circumferential conductive blocks 2222 are circumferentially spaced around the central conductive block 2221 and correspond one-to-one with the overlapping structures. The thickness of the circumferential conductive blocks 2222 is less than that of the central conductive block 2221, and the lower surface of the circumferential conductive blocks 2222 is flush with the lower surface of the central conductive block 2221, together forming the lower surface of the conductor 222.

[0080] By arranging the circumferential conductive blocks in a one-to-one correspondence with the overlapping structures, the contact area between the conductor and the overlapping structure can be ensured, making the contact area between the conductor and the overlapping structure consistent with the contact area between multiple overlapping structures. In addition, the thickness of the circumferential conductive blocks is thinner than that of the central conductive blocks. While ensuring the contact area between the conductor and the overlapping structure, the proportion of the conductor is reduced. This not only ensures the volume ratio of the support body in the protective cover, further reducing the strength of the protective cover, but also reduces the weight of the protective cover, thereby improving the mass energy density of the battery.

[0081] Optionally, combined Figure 4 、 Figure 5As shown, the support body 221 is an annular structure, the inner diameter of the annular structure is consistent with the outer diameter of the central conductive block 2221, and the lower surface of the support body 221 is provided with a groove 2211 that matches the circumferential conductive block 2222, and the circumferential conductive block 2222 is clamped in the groove 2211 of the support body 221.

[0082] Optionally, the overhang length of the overlapping structure is greater than 80% of the rolled radius of the electrode sheet and less than 150% of the rolled radius of the electrode sheet. By matching the length, spacing and number of the overlapping structures, the sum of the areas of overlapping and contacting multiple overlapping structures accounts for 90%-110% of the total area of ​​extruded contact between the conductor and the overlapping structure.

[0083] The inventors discovered that the overlapping contact area between the overlapping structures and the extrusion contact area between the conductor and each overlapping structure are respectively associated with the degree of conduction between the active material on the front and back sides of the electrode sheet and the external circuit. If the overlapping contact area between the overlapping structures is significantly different from the extrusion contact area between the conductor and the overlapping structure, the efficiency of the active material of the electrode sheet cannot be fully exerted, affecting the energy density of the battery performance, and also causing a large temperature difference between the front and back sides of the electrode sheet or causing local overheating. In addition, the uneven degree of participation of the active material on the front and back sides of the electrode sheet in conduction will also cause the aging process of the active material on both sides to be different, affecting the service life of the battery. Therefore, by controlling the sum of the areas of the overlapping contact of multiple overlapping structures to account for 90%-110% of the total area of ​​the conductor and the overlapping structure extrusion contact, the area of ​​the overlapping contact of multiple overlapping structures is close to the total area of ​​the conductor and the overlapping structure extrusion contact, so that the efficiency of the active material of the electrode sheet can be fully exerted, the energy density of the battery performance is improved, and the service life of the battery is extended.

[0084] Optionally, the protective cover has a thickness of 0.5 mm to 1.5 mm.

[0085] By setting the protective cover to the above-mentioned structure, the structure is simple and easy to use, and the risk of safety hazards such as insufficient pressure relief, blockage, and failure caused by the high strength of traditional ordinary battery caps can be reduced. In addition, the protective cover has multiple practical functions, including: conductive interface between the positive and negative poles of the battery, high temperature protection, pressure relief and explosion protection, sealing, and because the thickness of the protective cover is small and the material density of the support body is small, the weight of the protective cover is greatly reduced, thereby greatly improving the energy density of the battery. During the application of the present invention, if the battery operation is abnormal, the support body of the protective cover will quickly rupture along the explosion-proof structure to release pressure, and when the support body ruptures, the extrusion contact between the conductor of the protective cover and the electrode sheet is quickly disconnected, thereby achieving efficient disconnection of the electrode sheet from the external circuit, causing the battery to stop providing current and continuing to generate heat, effectively blocking the accident.

[0086] Figure 6is a schematic diagram of the overlapping contact mode of the overlap structure in one embodiment of the present invention. Figure 6 In the embodiment shown, the electrode sheet is in a roll shape, and the front and back surfaces of the five overlapping structures are sequentially overlapped and contacted to form an end-to-end connection, so that the electrode sheet forms an electronic path with the external circuit. Figure 6 As shown, taking the positive electrode sheet as an example, the aluminum layer on the back side of the first overlapping structure 1021 contacts the aluminum layer on the front side of the second overlapping structure 1022, the aluminum layer on the back side of the second overlapping structure 1022 contacts the aluminum layer on the front side of the third overlapping structure 1023, the aluminum layer on the back side of the third overlapping structure 1023 contacts the aluminum layer on the front side of the fourth overlapping structure 1024, the aluminum layer on the back side of the fourth overlapping structure 1024 contacts the aluminum layer on the front side of the fifth overlapping structure 1025, and the aluminum layer on the back side of the fifth overlapping structure 1025 contacts the aluminum layer on the front side of the first overlapping structure 1021. The overlapping contact of multiple raised portions allows the active materials on the front and back sides of the composite current collector film to participate in electron transmission in a balanced manner through multiple pathways, which helps to reduce the impedance of the battery, improve battery performance, and reduce local resistive heating.

[0087] The beneficial effects of the present invention will be further described below by way of specific examples. In addition, these examples are intended to illustrate the present invention and do not limit the scope of the present invention.

[0088] Example 1

[0089] An 18650 cylindrical battery having the structural characteristics of a lithium battery based on a flexible thin film current collector of the present invention is manufactured.

[0090] The battery consists of two electrode sheets, one for the positive electrode and one for the negative electrode. The flexible thin-film current collectors of these sheets consist of a 4.5μm-thick polyethylene terephthalate (PET) film in the center, with a 1μm-thick metal coating on both the front and back surfaces. The positive electrode sheet is coated with aluminum, while the negative electrode sheet is coated with copper. The flexible thin-film current collectors consist of a main body and five overlapping structures integrally formed with the main body. The active material is applied to both the front and back surfaces of the main body.

[0091] The electrode sheet is in a roll shape, and the overlap structure is bent toward the axis of the rolled electrode sheet, and the five overlap structures are arranged in a Figure 6 The electrodes are sequentially stacked and contacted in the manner shown, so that an electronic path is formed between the electrode sheets and the external circuit.

[0092] The electrolyte is disposed between the positive electrode sheet and the negative electrode sheet.

[0093] The packaging assembly includes a protective cover and a battery shell having the structural features of the present invention, which wraps the electrode sheet. The battery shell is made of insulating material with a density of 0.9g / cm 3 .

[0094] Example 2

[0095] An 18650 cylindrical battery having the structural characteristics of a lithium battery based on a flexible thin film current collector of the present invention is manufactured.

[0096] The difference between this battery and Example 1 is that the arrangement of the electrode sheet overlap structure is based on Figure 7 The contact is stacked in the manner shown. Figure 7 As shown, taking the positive electrode sheet as an example, the aluminum layer on the back side of the first lap joint structure 1026 contacts the aluminum layer on the front side of the second lap joint structure 1027 and the third lap joint structure 1028 respectively, the aluminum layer on the back side of the fourth lap joint structure 1029 contacts the aluminum layer on the front side of the second lap joint structure 1027 and the fifth lap joint structure 1020 respectively, and the aluminum layer on the front side of the fifth lap joint structure 1020 contacts the aluminum layer on the back side of the third lap joint structure 1028.

[0097] Comparative Example

[0098] The difference from Example 1 and Example 2 is that an ordinary composite current collector film (without a tooth-shaped portion) is used, and the tabs are welded on both sides of the composite current collector film. The composite current collector is composed of a 4.5 μm thick polyethylene terephthalate (PET) in the middle and a 1 μm metal plating layer on the front and back. Active material is coated on the composite current collector film to form a positive electrode sheet and a negative electrode sheet. The electrode sheet is rolled into an electrode sheet roll, and an electrolyte is provided. An ordinary battery cap and battery casing are used for packaging to form an 18650 cylindrical battery.

[0099] Table 1. Performance comparison of Example 1, Example 2 and Comparative Example

[0100]

[0101] As shown in Table 1, compared to a conventional cylindrical battery (Comparative Example) lacking the structural features of the present invention, the internal resistance between the positive and negative electrodes of the lithium batteries based on flexible thin-film current collectors (Examples 1 and 2) of the present invention is reduced by over 50 mΩ. When discharged at a current of 10 A, the surface and tab temperature rise rates of the batteries are reduced by over 70%, and the ratio of the tab to surface temperature decreases from 2.35 to 1.06 and 1.18, respectively, achieving consistent tab and surface temperatures. Compared to the comparative example using a conventional battery cap, the cylindrical batteries of the present invention, using protective caps (Examples 1 and 2), exhibited cap rupture and pressure release during the initial stages of the battery compression experiment. No flames were observed in the batteries, and no damage was posed to surrounding batteries.

[0102] The above results show that, on the one hand, the present invention uses a cylindrical battery formed by a flexible thin-film current collector with an overlap structure. The spatial arrangement of the overlap structure can efficiently conduct the metal coating on the front and back surfaces of the flexible thin-film current collector. At the same time, the overlap method is more flexible and can completely eliminate the tab welding process, thereby significantly improving the battery manufacturing yield. On the other hand, because the flexible thin-film current collector of the present invention is integrated with the overlap structure, forming a conductive whole without interface transfer resistance, it avoids the problems of contact resistance between the flexible thin-film current collector and the tab and welding point resistance that exist in the tab welding process, thereby reducing the battery resistance and minimizing the battery's ohmic heating. The battery's temperature rise rate and the ratio of the battery tab to the surface temperature are significantly reduced, effectively improving the local temperature rise of the battery. In addition, the protective cover and the overlap structure are connected by extrusion contact, which can achieve multi-path electron transmission, further reducing the battery's ohmic impedance and solving the hidden dangers of high temperature and high pressure inside the battery caused by battery extrusion test. When the temperature rises to a specific temperature, the fracture strength of the support body decreases instantly, blocking the battery's current output and timely releasing the pressure, thereby improving the battery safety.

Claims

1. A lithium battery based on a flexible thin film current collector, characterized in that: include: An electrode sheet, including a flexible thin film current collector and an active material; The flexible thin film current collector has a polymer base layer in the middle and metal coatings on both the front and back sides; The flexible thin film current collector includes a main body region and a plurality of overlapping structures integral with the main body region; the overlapping structures are rectangular teeth-shaped and disposed on one edge of the main body region; the active material is coated on the surface of the main body region; the electrode sheets are in the form of a roll, and there are two of them; the overlapping structures are bent and arranged toward the axis of the rolled electrode sheet, and at least a portion of the front and back surfaces of any two adjacent overlapping structures form an overlapping contact, so that the metal coatings on the front and back surfaces of the flexible thin film current collector are conductive; The electrolyte is placed between the electrodes; A packaging assembly including a protective cover in compression contact with at least one overlapping structure; The interior of the lithium battery does not contain any welding parts; The protective cover includes a support and a conductor, the conductor and the support are spliced ​​together, and the lower surface of the conductor and the lower surface of the support are in the same plane, and the upper surface of the conductor and the upper surface of the support are in the same plane; the lower surface of the conductor is in extrusion contact with the front surface of at least one overlapping structure; the material of the conductor is one of copper, aluminum, nickel, and stainless steel; The support body is provided with an explosion-proof structure on its circumference, and the explosion-proof structure is in the shape of a groove; The support is made of a thermally variable material; the support has a breaking strength of 1.6 MPa or more at a temperature below 130°C, and a breaking strength of 10 kPa-30 kPa at a temperature above 160°C; In the event of an abnormal operation of the lithium battery, the support body will rapidly rupture along the explosion-proof structure to release pressure. When the support body ruptures, the extrusion contact between the conductor of the protective cover and the electrode sheet will be quickly disconnected, thereby disconnecting the electrode sheet from the external circuit. The conductor includes a columnar central conductive block and circumferential conductive blocks; the circumferential conductive blocks are distributed circumferentially around the central conductive block and correspond one-to-one to the overlapping structures; the length of the overlapping structure is greater than 80% of the rolled radius of the electrode sheet and less than 150% of the rolled radius of the electrode sheet, the length, spacing and number of the overlapping structures match, and the sum of the areas of overlapping contact of multiple overlapping structures accounts for 90%-110% of the total area of ​​squeeze contact between the conductor and the overlapping structure.

2. The lithium battery based on the flexible thin film current collector according to claim 1, characterized in that: The packaging assembly also includes a battery shell; the two electrode sheets have the same structure and opposite polarity; the electrode sheets are arranged in the battery shell, and the overlapping structures in the two electrode sheets are respectively located at the two ends of the battery shell; the number of protective covers is 2, and the two protective covers are respectively arranged at the two ends of the battery shell, and are respectively in extrusion contact with at least one overlapping structure.

3. The lithium battery based on the flexible thin film current collector according to claim 1, characterized in that: The thickness of the circumferential conductive block is smaller than that of the central conductive block, and the lower surface of the circumferential conductive block is flush with the lower surface of the central conductive block, and together constitute the lower surface of the conductor.

4. The lithium battery based on the flexible thin film current collector according to claim 3, characterized in that: The support body is an annular structure, the inner hole size of the annular structure is consistent with the outer size of the central conductive block, the lower surface of the support body is provided with a groove matching the circumferential conductive block, and the circumferential conductive block is clamped in the groove of the support body.

5. The lithium battery based on the flexible thin film current collector according to claim 1, characterized in that: The ratio of the cross-sectional area of ​​the conductor to the cross-sectional area of ​​the protective cover is less than 40%.

6. The lithium battery based on a flexible thin film current collector according to claim 2, characterized in that: The battery shell is made of insulating material with a density of less than 2g / cm 3 ;The thickness of the protective cover is 0.5mm-1.5mm.

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