Method and system for producing an increased surface area of a metallic foil by embossing

Abstract

A method for producing an increased surface area of a metallic foil by embossing. The method comprises providing the metallic foil presenting an initial surface area on one of its faces and a determined thickness, and providing an embossing set-up. The embossing set-up comprises a first and a second embossing tool having respectively a first and a second base surface, and positioning tools for positioning the first and the second embossing tool for the first base surface to face the second base surface, and be separated by at least an embossing gap that receives the metallic foil during embossing of the metallic foil. The first embossing tool comprises on the first base surface first protruding embossing structures positioned on the first base surface, having respectively each a height that has at most a determined first height value above the first base surface, and any convex edge exposed by a corresponding one of the first protruding embossing structures has a curvature configured to prevent a tearing-up of the metallic foil during embossing. The second embossing tool comprises on the second base surface second protruding embossing structures positioned on the second base surface, and having a second height above the second base surface with a value inferior to the determined first height value, in order for the second protruding embossing structures to press the metallic foil towards the first embossing roller at spaces not occupied by any one of first embossing structure during the embossing of the metallic foil. The embossing gap is greater than the thickness of the metallic foil. The method further comprises embossing the metallic foil with the embossing set-up, and stretching the metallic foil during the embossing by exerting a stretching force through pressure of tops of protruding embossing structures of any one of the first and second embossing tools towards the base surface opposing the respective top on the corresponding second and first embossing tools, thereby producing the increased surface area of the metallic foil to be greater than the initial surface area of the metallic foil, the increased surface area comprising surfaces of stretched and non-stretched portions of the metallic foil.

Description

[0001] P4237PC01 / 0768-108 spec dpt

[0002] METHOD AND SYSTEM FOR PRODUCING AN INCREASED SURFACE AREA OF A METALLIC FOIL BY EMBOSSING

[0003] Technical field

[0004] The present invention is in the field of embossing a metallic foil in view of increasing a surface area that the embossed metallic foil presents.

[0005] Background

[0006] It is known to apply embossing technologies in the field of electrical batteries.

[0007] US publication US11,316,189B2 describes to provide a secondary battery that is suitable to a portable information terminal or a wearable device, and to provide an electronic device having a novel structure that can have various forms and a secondary battery that fits the forms of the electronic device. The secondary battery includes a film provided with depressions or projections that can ease stress on the film due to application of external force. The sizes of the depressions or projections are different between a center portion and an end portion of the film. The end portion of the film is sealed with an adhesive layer. The depressions or projections of the film are formed by pressing such as embossing. The embossing does not contribute to any electrical property of the secondary battery.

[0008] US publication US2024 / 0097245A1 relates to a battery cell including a pouch-shaped battery case configured to receive an electrode assembly therein. The pouch shaped battery case is provided at an outer periphery thereof surrounding an electrode assembly receiving portion with a sealed portion, and an embossed pattern is formed on the sealed portion in all direction. This, it is possible to increase sealing force of a pouch-shaped battery cell without the addition of a separate battery cell manufacturing process. The embossing does not contribute to any electrical property of the battery cell. P4237PC01 / 0768-108_dpt 2

[0009] US publication 6,946,362B2 discloses a method and apparatus for producing high surface area material films and membranes on substrates. In one application, patterns of spikes or bristles are produced on wafers and transferred to films, such as conductive polymer or metal films, by using repetitive processes, such as electroplating and embossing. Such a technique provides high surface area materials and allows reuse of expensive patterned silicon. Membranes with high surface area are extremely valuable in fuel cells since the power density is generally proportional to the surface area and the patterns may be used to cast inexpensive fuel cell electrodes. The embossing patterns provides from a silicon wafer which obtains grassy structures, which is then embossed to material films while the embossing assembly is heated in an oven to 140°C for 1 hour. The whole assembly including the embossed material film are subsequently cooled and soaked in order for the silicon wafer to fall off from the material film. The embossed material film is for example a conductive polymer film. The whole embossing process is rather slow and cumbersome, as it comprises lengthy transfer steps, and the embossing patterns on the silicium are random. In addition, it appears to be unsuitable to emboss metallic foils.

[0010] One aim of the invention is to provide a way of applying embossing to metallic foils, and obtaining an increased surface area of the metallic foil as controlled by the embossing.

[0011] A further aim of the invention is to provide a solution for manufacturing embossed metallic foils in view of modifying electrical properties thereof.

[0012] Summary of the invention

[0013] In a first aspect, the invention provides a method for producing an increased surface area of a metallic foil by embossing. The method comprises providing the metallic foil to be embossed presenting an initial surface area on one of its faces and a P4237PC01 / 0768-108_dpt 3 determined thickness, and providing an embossing set-up. The embossing set-up comprises a first and a second embossing tool having respectively a first and a second base surface, and positioning tools for positioning the first and the second embossing tool for the first base surface to face the second base surface, and be separated by at least an embossing gap that receives the metallic foil during embossing of the metallic foil. The first embossing tool comprises on the first base surface first protruding embossing structures positioned on the first base surface, having respectively each a height that has at most a determined first height value above the first base surface, and any convex edge exposed by a corresponding one of the first protruding embossing structures has a curvature configured to prevent a tearing-up of the metallic foil during embossing. The second embossing tool comprises on the second base surface second protruding embossing structures positioned on the second base surface, and having a second height above the second base surface with a value inferior to the determined first height value, in order for the second protruding embossing structures to press the metallic foil towards the first embossing roller at spaces not occupied by any one of the first embossing structures during the embossing of the metallic foil. The embossing gap is greater than the thickness of the metallic foil, wherein the embossing gap is a space between corresponding surfaces of the first and the second embossing tools which is not occupied by any of the embossing structures of the first and second embossing tools. The method further comprises embossing the metallic foil with the embossing set-up, and stretching the metallic foil during the embossing by exerting a stretching force through pressure of tops of protruding embossing structures of any one of the first and second embossing tools towards the base surface opposing the respective top on the corresponding second and first embossing tools, thereby producing the increased surface area of the metallic foil to be greater than the initial surface area of the metallic foil, the increased surface area of the metallic foil comprising surfaces of stretched and non-stretched portions of the metallic foil.

[0014] In a preferred embodiment, the embossing gap is greater than a sum of the determined first height value and the determined thickness of the metallic foil. P4237PC01 / 0768-108_dpt 4

[0015] In a further preferred embodiment, the first protruding embossing structures are aligned along first parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the first parallel lines for protruding structures being separated by a first separating distance (P) from one to the next in their first parallel line for protruding structures, the first parallel lines for protruding structures being separated from one to an adjacent one by a determined first period value (P1), the second protruding embossing structures are aligned along second parallel lines for protruding structures on the second embossing tool, and the second protruding embossing structures of each of the second parallel lines for protruding structure being separated by the first separating distance from one to the next in their second parallel line for protruding structures, the second parallel lines for protruding structures being separated from one to an adjacent one by the determined first period value.

[0016] In a further preferred embodiment, the first separating distance has a value in a range from 0,02 mm to 1 mm, and the determined first period value is in a range from 0,02 mm to 1 mm.

[0017] In a further preferred embodiment, of the protruding first and second embossing structures are described to have an embossing structure height value between a top of the protruding first or second embossing structure and respectively the first or second base surface, the embossing structure height value being in a range between 0,01 mm and 0,5 mm.

[0018] In a further preferred embodiment, the first embossing tool further comprises on the first base surface first recessed embossing structures with a depth of a determined first depth value below the first base surface, the second embossing tool further comprises on the second base surface second recessed embossing structures with a depth of a determined second depth value below the second base surface, the first protruding and recessed embossing structures respectively corresponding to second recessed and protruding embossing structures shaped such that first protruding P4237PC01 / 0768-108_dpt 5 embossing structures fit into the corresponding second recessed embossing structures, and the second protruding embossing structures fit into the corresponding first recessed embossing structures during the embossing, while allowing at least a distance greater than the determined thickness to separate opposing surfaces of the first and the second roller, the first protruding embossing structures being aligned along parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the parallel lines for protruding structures being separated by a first separating distance from one to the next in their parallel line for protruding structures, the parallel lines for protruding structures being separated from one to the adjacent by a determined first period value, and the first recessed embossing structures being aligned along parallel lines for recessed structures on the first embossing tool, and the first recessed embossing structures of each of the parallel lines for recessed embossing structures being separated by the first separating distance from one to the next in their parallel line for recessed structures, the parallel lines for recessed structures being separated from one to the adjacent by the determined first period value.

[0019] In a further preferred embodiment, the first separating distance has a value in a range from 0,02 mm to 1 mm, and the determined first period value is in a range from 0,02 mm to 1 mm.

[0020] In a further preferred embodiment, the parallel lines for protruding structures and the parallel lines for recessed structures are positioned relatively to each other such that first protruding embossing structures taken from successive parallel lines for protruding structures are aligned with first recessed embossing structures taken from successive parallel lines for recessed structures, along lines of alternating recessed and protruding embossing structures, the lines of alternating recessed and protruding embossing structures being parallel among each other. P4237PC01 / 0768-108_dpt 6

[0021] In a further preferred embodiment, the lines of alternating recessed and protruding embossing structures are perpendicular to the parallel lines for protruding structures and the parallel lines for recessed structures.

[0022] In a further preferred embodiment, the lines of alternating recessed and protruding embossing structures are in a determined non-perpendicular inclination angle to the parallel lines for protruding structures and the parallel lines for recessed structures.

[0023] In a further preferred embodiment, 11 . The method according to any one of claims 6 to 10, wherein each of the protruding first and second embossing structures and each of the recessed first and second embossing structures are described by a top of a protruding first or second embossing structure to a bottom of a recessed respectively first or second embossing structure height value situated in a range between 0,01 mm and 0,5 mm.

[0024] In a further preferred embodiment, the first protruding embossing structures are shaped as any one of a list of shapes comprising:

[0025] - a truncated pyramid with polygonal basis;

[0026] - a non-truncated pyramid with polygonal basis;

[0027] - a bowling cone;

[0028] - a truncated bowling cone;

[0029] - a paraboloid;

[0030] - a spherical dome.

[0031] In a further preferred embodiment, the first protruding embossing structure of truncated pyramid shape or of non-truncated pyramid shape comprises concave lateral flanks. P4237PC01 / 0768-108_dpt 7

[0032] In a further preferred embodiment, a first width of the first protruding embossing structures, at the first base surface, and a second width of the second protruding embossing structures, at the second base surface are in a range from 0,01 mm to 0,5 mm.

[0033] In a further preferred embodiment, the first and the second embossing tools are first and second flat embossing tools.

[0034] In a further preferred embodiment, the first and the second embossing tools are first and second embossing rollers.

[0035] In a further preferred embodiment, the step of providing the embossing set-up comprises mounting and adjusting the first and the second embossing rollers in a quick exchange cassette, whereby the quick exchange cassette is removably mounted in a frame.

[0036] In a further preferred embodiment, the first and the second embossing rollers are driven and synchronized by any means from a list of synchronization means comprising toothed-wheels gears, helicoidal gears, servomotors.

[0037] In a further preferred embodiment, the embossing set-up is part of a production chain for a manufacturing of the embossed metallic foil for an electric energy storage intended for use in electric appliances such as an electric vehicle, a robot, a cell phone, a portable computer, a hearing device, a power bank.

[0038] In a further preferred embodiment, the provided metallic foil to be embossed comprises any material from a list comprising copper, aluminum, lithium, silver, gold, iron, brass, lead, zinc and mixtures thereof. P4237PC01 / 0768-108_dpt 8

[0039] In a further preferred embodiment, the metallic foil is covered with at least a layer of polymer.

[0040] In a further preferred embodiment, the first and second embossing tool each comprise any one material of a list comprising steel, hardened steel, stainless steel, ceramic, any of the preceding materials coated with oxide, nitride, diamond like coatings, carbide.

[0041] In a second aspect, the invention provides an embossing system configured for producing an increased surface area of a metallic foil by embossing, the metallic foil to be embossed presenting an initial surface area on one of its faces and a determined thickness. The embossing system comprises an embossing set-up, which comprises a first and a second embossing tool having respectively a first and a second base surface, and positioning tools for positioning the first and the second embossing tool for the first base surface to face the second base surface, and be separated by at least an embossing gap that receives the metallic foil during embossing of the metallic foil. The first embossing tool comprises on the first base surface first protruding embossing structures positioned on the first base surface, having respectively each a height that has at most a determined first height value above the first base surface, and any convex edge exposed by a corresponding one of the first protruding embossing structures has a curvature configured to prevent a tearing-up of the metallic foil during embossing. The second embossing tool comprises on the second base surface second protruding embossing structures positioned on the second base surface, and having a second height above the second base surface with a value inferior to the determined first height value, in order for the second protruding embossing structures to press the metallic foil towards the first embossing roller at spaces not occupied by any one of the first embossing structures during the embossing of the metallic foil to be embossed, wherein the embossing gap is a space between corresponding surfaces of the first and the second embossing tools which is not occupied by any of the embossing structures of the first and second embossing tools. The embossing gap is greater than the thickness of the metallic foil. The embossing system is configured to emboss the P4237PC01 / 0768-108_dpt 9 metallic foil with the embossing set-up, thereby stretching the metallic foil during the embossing by exerting a stretching force through pressure of tops of protruding embossing structures of any one of the first and second embossing tools towards the base surface opposing the respective top on the corresponding second and first embossing tools, thereby producing the increased surface area of the metallic foil to be greater than the initial surface area of the metallic foil, the increased surface area comprising surfaces of stretched and non-stretched portions of the metallic foil.

[0042] In a further preferred embodiment, the embossing gap is greater than a sum of the determined first height value and the determined thickness of the metallic foil to be embossed.

[0043] In a further preferred embodiment, the first protruding embossing structures are aligned along first parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the first parallel lines for protruding structures being separated by a first separating distance (P) from one to the next in their first parallel line for protruding structures, the first parallel lines for protruding structures being separated from one to an adjacent one by a determined first period value (P1), the second protruding embossing structures are aligned along second parallel lines for protruding structures on the second embossing tool, and the second protruding embossing structures of each of the second parallel lines for protruding structure being separated by the first separating distance from one to the next in their second parallel line for protruding structures, the second parallel lines for protruding structures being separated from one to an adjacent one by the determined first period value.

[0044] In a further preferred embodiment, the first separating distance has a value in a range from 0,02 mm to 1 mm, and the determined first period value is in a range from 0,02 mm to 1 mm. P4237PC01 / 0768-108_dpt 10

[0045] In a further preferred embodiment, each of the protruding first and second embossing structures are described to have an embossing structure height value between a top of the protruding first or second embossing structure and respectively the first or second base surface, the embossing structure height value being in a range between 0,01 mm and 0,5 mm.

[0046] In a further preferred embodiment, the first embossing tool further comprises on the first base surface first recessed embossing structures with a depth of a determined first depth value below the first base surface, the second embossing tool further comprises on the second base surface second recessed embossing structures with a depth of a determined second depth value below the second base surface, the first protruding and recessed embossing structures respectively corresponding to second recessed and protruding embossing structures shaped such that first protruding embossing structures fit into the corresponding second recessed embossing structures, and the second protruding embossing structures fit into the corresponding first recessed embossing structures during the embossing, while allowing at least a distance greater than the determined thickness to separate opposing surfaces of the first and the second roller, the first protruding embossing structures being aligned along parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the parallel lines for protruding structures being separated by a first separating distance from one to the next in their parallel line for protruding structures, the parallel lines for protruding structures being separated from one to the adjacent by a determined first period value, and the first recessed embossing structures being aligned along parallel lines for recessed structures on the first embossing tool, and the first recessed embossing structures of each of the parallel lines for recessed embossing structures being separated by the first separating distance from one to the next in their parallel line for recessed structures, the parallel lines for recessed structures being separated from one to the adjacent by the determined first period value. P4237PC01 / 0768-108_dpt 11

[0047] In a further preferred embodiment, the first separating distance has a value in a range from 0,02 mm to 1 mm, and the determined first period value is in a range from 0,02 mm to 1 mm.

[0048] In a further preferred embodiment, the parallel lines for protruding structures and the parallel lines for recessed structures are positioned relatively to each other such that first protruding embossing structures taken from successive parallel lines for protruding structures are aligned with first recessed embossing structures taken from successive parallel lines for recessed structures, along lines of alternating recessed and protruding embossing structures, the lines of alternating recessed and protruding embossing structures being parallel among each other.

[0049] In a further preferred embodiment, the lines of alternating recessed and protruding embossing structures are perpendicular to the parallel lines for protruding structures and the parallel lines for recessed structures.

[0050] In a further preferred embodiment, the lines of alternating recessed and protruding embossing structures are in a determined non-perpendicular inclination angle to the parallel lines for protruding structures and the parallel lines for recessed structures.

[0051] In a further preferred embodiment, each of the protruding first and second embossing structures and each of the recessed first and second embossing structures are described by a top of a protruding first or second embossing structure to a bottom of a recessed respectively first or second embossing structure height value situated in a range between 0,01 mm and 0,5 mm.

[0052] In a further preferred embodiment, the first protruding embossing structures are shaped as any one of a list of shapes comprising:

[0053] - a truncated pyramid with polygonal basis;

[0054] - a non-truncated pyramid with polygonal basis; P4237PC01 / 0768-108_dpt 12

[0055] - a bowling cone;

[0056] - a truncated bowling cone;

[0057] - a paraboloid;

[0058] - a spherical dome.

[0059] In a further preferred embodiment, the first protruding embossing structure of truncated pyramid shape or of non-truncated pyramid shape comprises concave lateral flanks.

[0060] In a further preferred embodiment, a first width of the first protruding embossing structures, at the first base surface, and a second width of the second protruding embossing structures, at the second base surface are in a range from 0,01 mm to 0,5 mm.

[0061] In a further preferred embodiment, the first and the second embossing tools are first and second flat embossing tools.

[0062] In a further preferred embodiment, the first and the second embossing tools are first and second embossing rollers.

[0063] In a further preferred embodiment, the first and the second embossing rollers are mounted and adjusted in a quick exchange cassette, whereby the quick exchange cassette is removably mounted in a frame.

[0064] In a further preferred embodiment, the first and the second embossing rollers are driven and synchronized by any means from a list of synchronization means comprising toothed-wheels gears, helicoidal gears, servomotors. P4237PC01 / 0768-108_dpt 13

[0065] In a further preferred embodiment, a production chain for a manufacturing of the embossed metallic foil for an electric energy storage intended for use in electric appliances such as an electric vehicle, a robot, a cell phone, a portable computer, a hearing device, a power bank comprises the embossing system according to any of the embodiments of the invention.

[0066] In a further preferred embodiment, the metallic foil embossed by the embossing system comprises any material from a list comprising copper, aluminum, lithium, silver, gold, iron, brass, lead, zinc and mixtures thereof.

[0067] In a further preferred embodiment, the metallic foil is covered with at least a layer of polymer.

[0068] In a further preferred embodiment, the first and second embossing tool each comprise any one material of a list comprising steel, hardened steel, stainless steel, ceramic, any of the preceding materials coated with oxide, nitride, diamond like coatings, carbide.

[0069] Brief description of the figures

[0070] The invention will be better understood through the detailed description of preferred embodiments of the invention, and in reference to the drawings, wherein

[0071] Figure 1 contains a schematic illustration of an embossing system configured for producing an increased surface area of a metallic foil by embossing, according to an example embodiment of the invention;

[0072] Figure 2 contains a view of a first and a second embossing tool with a cross-sectional view thereof that also contains a metallic foil being embossed, according to an example embodiment of the invention; P4237PC01 / 0768-108_dpt 14

[0073] Figure 3 contains a view of a first and a second embossing tool with a cross-sectional view thereof that also contains a metallic foil being embossed, according to a further example embodiment of the invention;

[0074] Figure 4 shows embossing tools embodied as embossing rollers according to an example embodiment of the invention;

[0075] Figure 5 shows embossing rollers possessing at one end toothed wheels for drive and synchronization according to an example embodiment of the invention;

[0076] Figures 6(A)-6(F) contain examples of periodical arrangements of protruding embossing structures on an embossing tool for producing an increased surface area of a metallic foil according to an example embodiment of the invention;

[0077] Figures 7(A)-7(D) present further example embodiments for protruding embossing structures for use with an embossing tool for producing an increased surface area of a metallic foil, according to the invention;

[0078] Figure 8 contains an example embodiment of the invention, in which narrowed truncated square pyramids are present as protruding embossing structures on at least one embossing roller;

[0079] Figure 9 contains an example embodiment of the invention, in which smaller-base truncated square pyramids are present as protruding embossing structures on at least one embossing roller;

[0080] Figure 10 contains an example embodiment of the invention, in which larger-summit truncated square pyramids are present as protruding embossing structures on at least one embossing roller;

[0081] Figure 11 contains an example embodiment of the invention, in which smaller-based truncated square pyramids are present as protruding embossing structures on a first embossing roller, whereas larger-summit truncated square pyramids are present as protruding embossing structures on the second embossing roller;

[0082] Figure 12 contains an example embodiment of the invention, in which narrowed rounded-shaped protrusions are present as protruding embossing structures on at least one embossing roller; P4237PC01 / 0768-108_dpt 15

[0083] Figure 13 contains an example embodiment of the invention, in which roundedshaped protrusions are present as protruding embossing structures on at least one embossing roller;

[0084] Figure 14 contains an example embodiment of the invention, in which narrowed rounded-shaped protrusions are present as embossing structures on the first embossing roller, whereas rounded-shaped protrusions are present as embossing structures on the second embossing roller;

[0085] Figure 15 contains a view of an embossed metallic foil and magnified cross-section views of embossing rollers used for embossing according to the invention;

[0086] Figure 16 contains a view of a further embossed metallic foil and magnified crosssection views of embossing rollers used for embossing according to the invention;

[0087] Figure 17 contains a view of a further embossed metallic foil and magnified crosssection views of embossing rollers used for embossing according to the invention;

[0088] Figure 18 contains a view of a further embossed metallic foil and magnified crosssection views of embossing rollers used for embossing according to the invention;

[0089] Figure 19 contains top views of further examples of protruding embossing features that may be contained on an embossing tool used to emboss a metallic foil;

[0090] Figure 20 contains example embodiments of embossing rollers according to the invention;

[0091] Figure 21 contains a view of an example for a quick-exchange device configured for housing a set of embossing rollers according to the invention;

[0092] Figures 22(A)-22(C) show views of examples for using different configurations of embossing rollers in a cassette according to the invention;

[0093] Figures 23(A)-23(C) show an example for an adjustment and correction of a position of an embossing roller in a cassette;

[0094] Figure 24 illustrates an application of the invention in the field of electric mobility, more specifically for a battery of an electric vehicle;

[0095] Figure 25 illustrates an application of the invention in the field of chemistry, more specifically in the field of chemical reactions supported by a catalyst; P4237PC01 / 0768-108_dpt 16

[0096] Figure 26 illustrates applications of the invention in the field of mobile machinery, illustrated here by a lawnmower and by a robot;

[0097] Figure 27 illustrates applications of the invention in the field of mobile electronic devices, such a cell phone, a portable computers, and a household device;

[0098] Figure 28 illustrates an application of the invention in the field of the utilization of renewable energies; and

[0099] Figure 29 contains a flowchart illustrating an example of the method for producing an increased surface area of a metallic foil by embossing

[0100] Same reference signs will be used throughout the Figures to reference same of similar features.

[0101] Detailed description of preferred embodiments of the invention

[0102] Figure 1 shows an example of an embossing system configured for producing an increased surface area of a metallic foil by embossing, according to the invention. A metallic foil 101 presenting an initial surface area on one of its faces and a determined thickness, is embossed using an embossing set-up 105, in order to obtain an embossed metallic foil 109 with an increased surface area, and in which embossing tools are present in a preferred embodiment of embossing rollers. For ease of readability, the embossing set-up 105 is represented as comprising a frame 106, which accommodates two embossing rollers, 107 and 108. According to a feed direction 100, the metallic foil 101 to be embossed is guided using optionally at least a deflection roller 103 into a gap (not visible in Figure 1) between a first embossing roller 107 and a second embossing roller 108, comprising respectively first embossing structures and second embossing structures (not illustrated in Figure 1). An optional deflection roller 104 is also illustrated in Figure 1. For subsequent figures and considerations, a zone 110 on the embossed metallic foil 109, a figurative process input interface 102, and a figurative process output interface 111 are also represented in Figure 1. The embossing set-up 105 may be a component of an online production system (not illustrated), preceded at the interface 102, e.g., by an P4237PC01 / 0768-108_dpt 17 unwinding device (not represented) feeding the metallic foil 101 in the feed direction 100, and followed at the interface 111 , e.g., by a conditioning and coating system (not represented) providing the embossed metallic foil 109 with a thin metallic coating, e.g., a Lithium coating.

[0103] Referring to Figure 2, this illustrates a first 201 and a second 203 embossing tool to increase a surface area of a metallic foil by embossing, having respectively a first base surface 205 and a second base surface 206, and bearing respectively first protruding embossing structures 202 and second protruding embossing structures 204. A cross-section view 200, also illustrated in Figure 2, gives more insight on the particular shapes of the first protruding embossing structures 202 and second protruding embossing structures 204, and on the placement of the metallic foil 109 between the first embossing tool 201 and the second embossing tool 203. The crosssection view 200 shows the base surfaces 205 and 206 as well as the first and second heights hi and h2 of the protruding embossing structures 202 and 204. hi, the first height value, has at most a determined first height value above the first base surface, and h2, the second height value, has a value inferior to the determined first height value inferior to the determined first height value. Furthermore, top zones 207 and 211 of the protruding embossing structures are indicated, as well as transition zones or convex edges 208 and 210, where the metallic foil gets into contact with the protruding embossing structures 202 and 204. The metallic foil 109 endures a plastic deformation, and the protruding embossing structures are configured in such a manner to prevent the tearing of the metallic foil 109 during the embossing: (i) an embossing gap between the first 201 and the second 203 embossing tools shall be larger than a determined thickness of the metallic foil, optionally greater than a sum of the determined first height value and the determined thickness of the metallic foil, enabling the foil to glide on protruding structures in the top zones 207 and 211, and preventing the metallic foil to be pinched between the embossing tools; (ii) the protruding embossing features shall have in their transition zones 208 and 210 rounded, convex surfaces (e.g., radii R greater than 0,025 mm), preventing a tearing- up of the deformed metallic foil on sharp edges; (iii) the flank 212 of the protruding embossing feature 202 shall optionally have a concave shape, preventing any mechanical contact between the metallic foil 109 in a zone 209 of the metallic foil P4237PC01 / 0768-108_dpt 18 located between two tops of protruding embossing structures located respectively on different embossing rollers, which is a zone of maximal foil stretching and therefore of minimal foil thickness, and the embossing tools. Besides the first and second heights hi and h2, which may have preferred values in a range from 0,01 mm to 0,5 mm, a first embossing feature is described by a width D, which may have preferred values in a range from 0,01 mm to 0,5 mm, at the level of the base surface 205, and by a width d, whereas d < D, at the top zone 207. Furthermore, the magnified view 214 in the Figure 2 emphasizes the condition that the embossed metallic foil shall not be pinched between the first 201 and the second 203 embossing tools, clearly evidencing the space 213 between the metallic foil and the second embossing tool 203.

[0104] Geometrical considerations on the shape of the concave flank 212, which is assumed to be described by a radius Rc, yield the following equation having this theoretical radius as a solution:

[0105] Rc2( sin-1(L / 2Rc) - (L / 2Rc)( 1-(L / 2Rc)2)0 5) = (d t) / 2 whereas

[0106] L = hi / sina, and t is the thickness of the metallic foil.

[0107] Geometrical considerations on the dependence of the possible stretching of the embossed metallic foil 109, obtained after embossing, and the angle a from Figure 2, show that maximal stretching (i.e., surface area increase) is obtained for a = 90° and further reveal the following dependence:

[0108] Relative Increase (a) = 1 / 2 (1 + 1 / sina - 1 / tana), which as table of values has the following form:

[0109] Angle a [°] 45 50 55 60 65 70 75 80 85 90

[0110] Relative Increase 0,71 0,73 0,76 0,79 0,82 0,85 0,88 0,92 0,96 1

[0111] From the theoretical point of view, for preferred executions, the angle a should take values as close as possible to 90°, which however may be disadvantageous (i) from P4237PC01 / 0768-108_dpt 19 the manufacturing point of view, and (ii) considering the risk of metallic foil tearing. In preferred executions of the invention, values of the angle a in a range from 45° and 85°, more preferably between 50° and 80°, were used.

[0112] Referring now to Figure 3, this illustrates a further embodiment with a first 301 and a second 303 embossing tool to increase a surface area of a metallic foil by embossing, having respectively a first base surface 305 and a second base surface 306, and bearing respectively first protruding embossing structures 302 and second protruding embossing structures 304. A cross-section view 300, also illustrated in Figure 3, gives more insight on the shapes of the first protruding embossing structures 302 and second protruding embossing structures 304, on the placement of the metallic foil 109 between the first embossing tool 301 and the second embossing tool 303. The cross-section view 300 shows the base surfaces 305 and 306 as well as the first and the second heights hi and h2 of the protruding embossing structures 302 and 304. Furthermore, top zones 307 and 311 of the protruding embossing structures are indicated, as well the transition zones 308 and 310, where the metallic foil gets into contact with the protruding embossing structures 302 and 304. The metallic foil 109 endures a plastic deformation, and the protruding embossing structures are configured in such a manner to prevent the tearing-up of the metallic foil 109 during the embossing: (i) the gap between the first 301 and the second 303 embossing tools shall be larger than the thickness of the metallic foil, optionally greater than a sum of the determined first height value and the determined thickness of the metallic foil, enabling the foil to glide on protruding structures in the top zones 307 and 311 , and preventing the metallic foil to be pinched between the embossing tools; (ii) the second protruding embossing features shall have in their transition zones 310 rounded, convex surfaces (e.g. radii R greater than 0,025 mm), preventing a tearing-up of the deformed metallic foil on sharp edges. Besides the height first h 1 , which may have preferred values in a range from 0,01 mm to 0,5 mm, a first embossing feature, is described by a width D, which may have preferred values in a range from 0,01 mm to 0,5 mm, at the level of the base surface 305. In this particular embodiment, the rounded shape of the first protruding embossing structures 302 provides for a gliding of the metallic film without risk of tearing in the top 307 and transition 308 zones. The magnified view 312 in Figure 3 emphasizes the condition P4237PC01 / 0768-108_dpt 20 that the embossed metallic foil is not pinched between the first 301 and the second 303 embossing tools, clearly evidencing the space 313 between the metallic foil and the second embossing tool 303.

[0113] Referring to Figure 4, this contains an example embodiment of the invention, in which the embossing tools to increase a surface area of a metallic foil have a cylindrical shape, corresponding to first and second embossing rollers 107 and 108, respectively. A zone 400 is represented in a magnified view, illustrating in crosssection a protruding embossing structure 202 of the first embossing roller 107, the space 402 between two protruding embossing structures 403 of the second embossing roller 108, as well as the embossing gap 401 , in which the metallic foil 109 is situated during the embossing process. In this embodiment, the embossing rollers do not comprise any toothed wheel and they are typically driven and synchronized by a servo motor mechanism (not represented) that directly rotates them.

[0114] Referring to Figure 5, this contains a further example embodiment of the invention, in which the embossing tools are the first and second embossing rollers 107 and 108, possessing at one end toothed wheels 501 for drive and synchronization. A zone 500 is represented in a magnified view, illustrating in cross-section a first base surface 507 and a second base surface 508, protruding 506 and recessed 503 embossing structures of the first embossing roller 107, as well as protruding 505 and recessed 502 embossing structures of the second embossing roller 108. Concave shaped flanks 504 and 509, as well as a separating distance p between two protruding embossing structures, which may have a value in a range from 0,02 mm to 1 mm, are equally shown in Figure 5.

[0115] Referring to Figures 6(A) - 6(F), these illustrate examples of periodical arrangements of protruding embossing structures on an embossing tool, used to increase the surface area of a metallic foil by embossing. The examples are illustrated in a schematic upper view of the arrangements. These arrangements are considered as P4237PC01 / 0768-108_dpt 21 examples and have a triangular shape 600 in Figure 6(A), a quadratic shape 602 in Figure 6(B), and a hexagonal 604 shape in Figure 6(C) and they are characterized by a same size a of their respective elementary cells, which respectively are triangles 601, squares 603, and hexagons 605. Considering the tridimensional shapes describing these example of protruding embossing structures, they are (i) triangular pyramids in Figure 6(D), which are described by apexes 606, by base edges 607, and by flank edges 608, (ii) truncated square pyramids in Figure 6(E), which are described by tops 609, by base edges 610, and by flank edges 611 , and (iii) truncated hexagonal pyramids in Figure 6(F), which are described by tops 612, by base edges 613, and by flank edges 614. The respective heights of the above mentioned and in Figures 6(A) - 6(F) depicted tridimensional shapes can be derived from basic geometrical considerations and are considered in detail.

[0116] Referring to Figures 7(A) - 7(D), these present further example embodiments for protruding embossing structures for an embossing tool configured to increase the surface area of a metallic foil through embossing, whilst presenting geometrical transformations facilitating their use on embossing tools according to the invention. Figure 7(A) illustrates a truncated square pyramid 700 characterized by a square base surface 603, by a base edge 610, by a top 609, and by a flank edge 611 , as well as a narrowed truncated square pyramid 701 derived from 700, characterized by the same square base surface 603, the base edge 610, and the top 609, however showing concave flank edges 702. Figure 7(B) illustrates the truncated square pyramid 700 and a smaller-base truncated square pyramid 702 derived from 700, characterized by a smaller base surface 703, by a base edge 704, by a flank edge 705, and by the top 609. Figure 7(C) illustrates the truncated square pyramid 700 and a larger-top truncated square pyramid 706 derived from 700, characterized by the square base surface 603, by the base edge 610, by a flank edge 707, and by a larger top 708 (larger than the top 609). Figure 7(D) illustrates a rounded-shaped (e.g., spherical, paraboloidal) protrusion 709 characterized by a circular base surface 710, and by a lateral surface 711 , as well as a narrowed rounded-shaped protrusion 712 derived from 709, characterized by a smaller circular base surface 713, and by a lateral surface 714. In preferred embodiments, narrowed truncated square pyramid 701 are accordingly placed both on the first embossing tool and on the second P4237PC01 / 0768-108_dpt 22 embossing tool, whereas in other preferred embodiments, smaller-base truncated square pyramid 702 are placed on one embossing tool and larger- top truncated square pyramid 706 are accordingly placed on the other embossing tool.

[0117] Furthermore, in further preferred embodiments, rounded-shaped protrusion 709 are placed on one embossing tool and narrowed rounded-shaped protrusions 712 are accordingly placed on the other embossing tools. The following figures will describe in more details preferred arrangements of protruding and recessed embossing structures on embossing tools used to increase a surface area of a metallic foil by embossing.

[0118] Referring to Figure 8, this contains an example embodiment of the invention, in which narrowed truncated square pyramids are present as protruding embossing structures on at least one of the first 107 and second 108 embossing rollers. In a detailed view from a zone 800 from the surface of embossing roller 107, 108 a base edge 610, a top 609, and a concave flank edge 702 are depicted, as well as a crosssection plane 802. In the corresponding cross-section view, the height h, the width d at the top, the width D at the base surface 801 , as well as a concave flank 803 are depicted. The separating distance p, which may have a value in a range from 0,02 mm to 1 mm, and the period value p’, which may have a value in a range from 0,02 mm to 1 mm, describe the arrangement of the narrowed truncated square pyramids on the roller base surface 801 and are also represented in Figure 8.

[0119] Referring to Figure 9, this contains a further example embodiment of the invention, in which smaller-base truncated square pyramids are present as protruding embossing structures on at least one of the first 107 and second 108 embossing rollers. In a detailed view from a zone 900 from the surface of the embossing roller 107, 108 a base edge 704, a top 609, and a flank edge 705 are depicted, as well as a crosssection plane 902. In the corresponding cross-section view, the height h, the width d at the top, the width D at the base surface 901, as well as a flank 903 are depicted. The separating distance p and the period value p’ describe the arrangement of the narrowed truncated square pyramids on the roller base surface 901 and are also represented in Figure 9. P4237PC01 / 0768-108_dpt 23

[0120] Referring to Figure 10, this contains another example embodiment of the invention, in which larger-top truncated square pyramids are present as protruding embossing structures on at least one of the first 107 and second 108 embossing rollers. In a detailed view from a zone 1000 from the surface of the embossing roller 107, 108 a base edge 610, a top 708, and a flank edge 707 are depicted, as well as a crosssection plane 1002. In the corresponding cross-section view, the height h, the width d at the top, the width D at a base surface 1001 , as well as a flank 1003 are depicted. The separating distance p and the period value p’ describe the arrangement of the narrowed truncated square pyramids on the roller base surface 1001 and are also represented in Figure 10.

[0121] Referring to Figure 11, this contains a preferred example embodiment of the invention, in which smaller-base truncated square pyramids are present as protruding embossing structures on the first embossing roller 107, whereas larger-top truncated square pyramids are present as protruding embossing structures on the second embossing roller 108. In a detailed view from a zone 1100 from the surface of the first embossing roller 107, a base surface 1102, a base edge 704, a top 609, and a flank edge 705 are depicted, whilst in a detailed view from a zone 1101 from the surface of the second embossing roller 108, a base surface 1103, a base edge 610, a larger top 708, and a flank edge 707 are shown. The separating distance p and the period value p’ describe the arrangement of the protruding embossing features on the base surface 1101 and 1102 and are also depicted in Figure 11.

[0122] Referring to Figure 12, this contains another example embodiment of the invention, in which narrowed rounded-shaped protrusions are present as protruding embossing structures on at least one of the first 107 and second 108 embossing rollers. In a detailed view from a zone 1200 from the surface of the embossing roller 107, 108 a base surface 1201 and a lateral surface 714 of a narrowed rounded-shaped protrusion, as well as a cross-section plane 1202 are shown. In the corresponding cross-section view, the height h, the width D at the base surface 1201, as well as a flank 1203 are depicted. The separating distance p and the period value p’ describe P4237PC01 / 0768-108_dpt 24 the arrangement of the narrowed rounded-shaped protrusions on the roller base surface 1201 and are also illustrated in Figure 12.

[0123] Referring to Figure 13, this contains an example embodiment of the invention, in which rounded-shaped protrusions are present as protruding embossing structures on at least one of the first 107 and second 108 embossing rollers. In a detailed view from a zone 1300 from the surface of the embossing roller 107, 108 a base surface 1301 and a lateral surface 711 of a rounded-shaped protrusion, as well as a crosssection plane 1302 are depicted. In the corresponding cross-section view, the height h, the width D at the base surface 1301, as well as a flank 1303 are depicted. The separating distance p and the period value p’ describe the arrangement of the narrowed rounded-shaped protrusions on the roller base surface 1301 and are also represented in Figure 13.

[0124] Referring to Figure 14, this contains a preferred example embodiment of the invention, in which narrowed rounded-shaped protrusions are present as protruding embossing structures on the first embossing roller 107, whereas rounded-shaped protrusions are present as protruding embossing structures on the second embossing roller 108. In a detailed view from a zone 1400 from the surface of the first embossing roller 107, a base surface 1402 of the first embossing roller 107, and a lateral surface 714 of a narrowed rounded-shaped protrusion are depicted, whilst in a detailed view from a zone 1401 from the surface of the second embossing roller 108, a base surface 1403 of the second embossing roller 108, and a lateral surface 711 of a rounded-shaped protrusion are shown. The separating distance p and the period value p’ describe the arrangement of the protruding embossing features on the base surface 1401 and 1402 and are also shown in Figure 14.

[0125] Referring now to Figure 15, this contains a representation of a preferred example of an embossed metallic foil 109 and several magnified cross-section views of embossing rollers used for embossing the metallic foil. Figure 15 illustrates a view from the above of the zone 110 from the embossed metallic foil 109, according to the P4237PC01 / 0768-108_dpt 25 invention, with an increased surface area, which further contains elevated embossed features 1505 and deepened embossed features 1506. The elevated embossed features 1505 are arranged in an array-like manner described by the dimensional periods I and I’, whereas, the deepened embossed features 1506 are arranged in the same manner, i.e. , in an array-like manner described by the dimensional periods I and I’. The solid and the dotted contours used for the representation of the embossed features 1505, 1506 are contours of the same height on the embossed metallic foils (representation not at scale), whereas the transitions zones between the solid and the dotted contours are to be considered as continuous height transition between elevated and deepened features (i.e. not height steps). The cross-sectional views shown in Figure 15 contain representations of the embossing structures present on the first and second embossing rollers 107 and 108 used to emboss the metallic foil and they correspond to symbolic lines chosen to pass along a line of elevated embossed structures 1502, along a line of deepened embossed structures 1501, and along lines of alternating elevated and deepened embossed structures 1500, 1503, and 1504. The base surfaces 1507 and 1508 of the first 107 and second 108 embossing rollers, respectively, are also depicted in the cross-sectional views 1500, 1501 , 1502, 1503, 1504. In this example, the lines of alternating elevated and deepened embossed structures are situated in an angle of 60° to the lines of elevated embossed structures.

[0126] Concerning the embossing tools used for embossing the metallic foil, the first embossing tool 107 comprises on the first base surface first protruding embossing structures with the first height value, and first recessed embossing structures with a depth of a determined first depth value below the first base surface, the second embossing tool 108 comprises on the second base surface second protruding embossing structures with the second height value, and second recessed embossing structures with a depth of a determined second depth value below the second base surface. The first protruding and recessed embossing structures respectively correspond to second recessed and protruding embossing structures shaped such that first protruding embossing structures fit into the corresponding second recessed embossing structures, and the second protruding embossing structures fit into the corresponding first recessed embossing structures during the embossing, while P4237PC01 / 0768-108_dpt 26 allowing at least a distance greater than the determined thickness to separate opposing surfaces of the first and the second roller.

[0127] Regarding now the result of the embossing shown in Figure 15, an embossed elevated feature 1505 is obtained for a combination between a first protruding embossing structure and a second recessed embossing structure, whereas an embossed deepened feature 1506 is obtained for a combination between a recessed first embossing structure and a second protruding embossing structure. Hence, the parallel lines describing the arrangement of the embossed features shown in Figure

[0128] 15 are describing in the same manner the parallel lines chosen for the arrangement of first and second protruding and recessed embossing feature.

[0129] Referring now to Figure 16, this contains a representation of a yet preferred example of an embossed metallic foil and several magnified cross-section views of embossing rollers used for embossing. Figure 16 illustrates a view from the above of the zone 110 from the embossed metallic foil 109, according to the invention, with an increased surface area, which further contains elevated embossed features 1605 and deepened embossed features 1606. The elevated embossed features 1605 are arranged in an array-like manner described by the dimensional periods I and I’, whereas, the deepened embossed features 1606 are arranged in the same manner, i.e. in an array-like manner described by the dimensional periods I and I’. The solid and the dotted contours used for the representation of the embossed features 1605, 1606 are contours of the same height on the embossed metallic foils (representation not at scale), whereas the transitions zones between the solid and the dotted contours are to be considered as continuous height transition between elevated and deepened features (i.e. not height steps). The cross-sectional views shown in Figure

[0130] 16 contain representations of the embossing structures present on the embossing rollers 107 and 108 used to emboss the metallic foil and they correspond to symbolic lines chosen to pass along a line of elevated embossed structures 1600, along a line of deepened embossed structures 1601 , and along lines of alternating elevated and deepened embossed structures 1602, 1603, and 1604. The base surfaces 1607 and 1608 of the first 107 and second 108 embossing rollers, respectively, are also P4237PC01 / 0768-108_dpt 27 depicted in the cross-sectional views 1600, 1601 , 1602, 1603, 1604. In this example, the lines of alternating elevated and deepened embossed structures are perpendicular to the lines of elevated embossed structures.

[0131] Concerning the embossing tools used for embossing the metallic foil, the first embossing tool 107 comprises on the first base surface first protruding embossing structures with the first height value, and first recessed embossing structures with a depth of a determined first depth value below the first base surface, the second embossing tool 108 comprises on the second base surface second protruding embossing structures with the second height value, and second recessed embossing structures with a depth of a determined second depth value below the second base surface. The first protruding and recessed embossing structures respectively correspond to second recessed and protruding embossing structures shaped such that first protruding embossing structures fit into the corresponding second recessed embossing structures, and the second protruding embossing structures fit into the corresponding first recessed embossing structures during the embossing, while allowing at least a distance greater than the determined thickness to separate opposing surfaces of the first and the second roller.

[0132] Considering now the result of the embossing shown in Figure 16, an embossed elevated feature 1605 is obtained for a combination between a first protruding embossing structure and a second recessed embossing structure, whereas an embossed deepened feature 1606 is obtained for a combination between a first recessed embossing structure and a second protruding embossing structure. Hence, the parallel lines describing the arrangement of the embossed features shown in Figure 16 are describing in the same manner the parallel lines chosen for the arrangement of first and second protruding and recessed embossing feature.

[0133] The first protruding embossing structures are aligned along parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the parallel lines for protruding structures are separated by a P4237PC01 / 0768-108_dpt 28 first separating distance I from one to the next in their parallel line for protruding structures, the parallel lines for protruding structures being separated from one to the adjacent by a determined first period value I’. Further, the first recessed embossing structures are aligned along parallel lines for recessed structures on the first embossing tool, and the first recessed embossing structures of each of the parallel lines for recessed embossing structures are separated by the first separating distance I from one to the next in their parallel line for recessed structures, the parallel lines for recessed structures being separated from one to the adjacent by the determined first period value I’.

[0134] Referring now to Figure 17, this contains a representation of a preferred example of an embossed metallic foil and several magnified cross-section views of embossing rollers used for the embossing. Figure 17 illustrates a view from the above of the zone 110 from the embossed metallic foil 109, according to the invention, with an increased surface area, which further contains elevated embossed features 1705 and deepened embossed features 1706. The elevated embossed features 1705 are arranged in an array-like manner described by the dimensional periods I and I’, whereas, the deepened embossed features 1706 are arranged in the same manner, i.e. in an array-like manner described by the dimensional periods I and I’. The solid and the dotted contours used for the representation of the embossed features 1705, 1706 are contours of the same height on the embossed metallic foils (representation not at scale), whereas the transitions zones between the solid and the dotted contours are to be considered as continuous height transition between elevated and deepened features (i.e. not height steps). The cross-sectional views shown in Figure 17 contain representations of the embossing structures present on the embossing rollers 107 and 108 used to emboss the metallic foil and they correspond to symbolic lines chosen to pass along a line of elevated embossed structures 1702, along a line of deepened embossed structures 1701, and along lines of alternating elevated and deepened embossed structures 1700, 1703, and 1704. The base surfaces 1707 and 1708 of the first 107 and second 108 embossing rollers, respectively, are also depicted in the cross-sectional views 1700, 1701 , 1702, 1703, 1704. In the example shown in Figure 17, the lines of alternating elevated and deepened embossed P4237PC01 / 0768-108_dpt 29 structures are situated in an angle of 60° to the lines of elevated embossed structures.

[0135] In a yet preferred embodiment example of the invention, the metallic foil consists of copper and has an initial thickness value of 0,01 mm, the period I and the period I’ have a same value of 0,06 mm, as angle between the lines of alternating elevated and deepened embossed structures and the lines of elevated embossed structures was chosen to be 45°. In this preferred embodiment example, the elevated embossed features had heights between 0,02 mm and 0,03 mm, whereas the deepened embossed features had depths between 0,02 mm and 0,03 mm.

[0136] Concerning the embossing tools used for embossing the metallic foil, the first embossing tool 107 comprises on the first base surface first protruding embossing structures with the first height value, and first recessed embossing structures with a depth of a determined first depth value below the first base surface, the second embossing tool 108 comprises on the second base surface second protruding embossing structures with the second height value, and second recessed embossing structures with a depth of a determined second depth value below the second base surface. The first protruding and recessed embossing structures respectively correspond to second recessed and protruding embossing structures shaped such that first protruding embossing structures fit into the corresponding second recessed embossing structures, and the second protruding embossing structures fit into the corresponding first recessed embossing structures during the embossing, while allowing at least a distance greater than the determined thickness to separate opposing surfaces of the first and the second roller.

[0137] Regarding now the result of the embossing shown in Figure 17, an embossed elevated feature 1705 is obtained for a combination between a first protruding embossing structure and a second recessed embossing structure, whereas an embossed deepened feature 1706 is obtained for a combination between a recessed first embossing structure and a second protruding embossing structure. Hence, the P4237PC01 / 0768-108_dpt 30 parallel lines describing the arrangement of the embossed features shown in Figure 17 are describing in the same manner the parallel lines chosen for the arrangement of first and second protruding and recessed embossing feature.

[0138] Referring now to Figure 18, this contains a representation of a yet preferred example of an embossed metallic foil and several magnified cross-section views of embossing rollers used for embossing. Figure 18 illustrates a view from the above of the zone 110 from the embossed foil 109, according to the invention, with an increased surface area, which further contains elevated embossed features 1805 and deepened embossed features 1806. The elevated embossed features 1805 are arranged in an array-like manner described by the dimensional periods I and I’, whereas, the deepened embossed features 1806 are arranged in the same manner, i.e. in an array-like manner described by the dimensional periods I and I’. The solid and the dotted contours used for the representation of the embossed features 1805, 1806 are contours of the same height on the embossed metallic foils (representation not at scale), whereas the transitions zones between the solid and the dotted contours are to be considered as continuous height transition between elevated and deepened features (i.e. not height steps). The cross-sectional views shown in Figure 18 contain representations of the embossing structures present on the embossing rollers 107 and 108 used to emboss the metallic foil and they correspond to symbolic lines chosen to pass along a line of elevated embossed structures 1800, along a line of deepened embossed structures 1801, and along lines of alternating elevated and deepened embossed structures 1802, 1803, and 1804. The base surfaces 1807 and 1808 of the first 107 and second 108 embossing rollers, respectively, are also depicted in the cross-sectional views 1800, 1801 , 1802, 1803, 1804. In this example, the lines of alternating elevated and deepened embossed structures are perpendicular to the lines of elevated embossed structures.

[0139] Concerning the embossing tools used for embossing the metallic foil, the first embossing tool 107 comprises on the first base surface first protruding embossing structures with the first height value, and first recessed embossing structures with a depth of a determined first depth value below the first base surface, the second P4237PC01 / 0768-108_dpt 31 embossing tool 108 comprises on the second base surface second protruding embossing structures with the second height value, and second recessed embossing structures with a depth of a determined second depth value below the second base surface. The first protruding and recessed embossing structures respectively correspond to second recessed and protruding embossing structures shaped such that first protruding embossing structures fit into the corresponding second recessed embossing structures, and the second protruding embossing structures fit into the corresponding first recessed embossing structures during the embossing, while allowing at least a distance greater than the determined thickness to separate opposing surfaces of the first and the second roller.

[0140] Considering now the result of the embossing shown in Figure 18, an embossed elevated feature 1805 is obtained for a combination between a first protruding embossing structure and a second recessed embossing structure, whereas an embossed deepened feature 1806 is obtained for a combination between a first recessed embossing structure and a second protruding embossing structure. Hence, the parallel lines describing the arrangement of the embossed features shown in Figure 18 are describing in the same manner the parallel lines chosen for the arrangement of first and second protruding and recessed embossing feature.

[0141] The first protruding embossing structures are aligned along parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the parallel lines for protruding structures are separated by a first separating distance I from one to the next in their parallel line for protruding structures, the parallel lines for protruding structures being separated from one to the adjacent by a determined first period value I’. Further, the first recessed embossing structures are aligned along parallel lines for recessed structures on the first embossing tool, and the first recessed embossing structures of each of the parallel lines for recessed embossing structures are separated by the first separating distance I from one to the next in their parallel line for recessed structures, the parallel lines for recessed structures being separated from one to the adjacent by the determined first period value I’. P4237PC01 / 0768-108_dpt 32

[0142] Referring now to Figures 19(A) - 19(C), these show top-views of further examples of protruding embossing structures 1902, 1906, 1910, with their respective tops 1903, 1907, 1911, which may be comprise in an embossing tool used to emboss a metallic foil to increase a surface area of the metallic foil. The protruding embossing structures 1902 are arranged according to the parallel lines 1900 and 1901, the protruding embossing structures 1906 are arranged according to the parallel lines 1904 and 1905, whereas the protruding embossing structures 1910 are arranged according to the parallel lines 1908 and 1909.

[0143] Referring to Figure 20(A), this illustrates an example embodiment for any one of embossing rollers 107 and 108, which comprises a rotation axis 2003, a roller surface 2000 and a toothed wheel 2001 at one extremity of the embossing roller 107, 108 enabling the embossing rollers 107, 108 to be driven by a motor assembly having a corresponding toothed wheel (not represented in Figure 20). The roller surface 2000 may carry embossing features (as illustrated in previous figures) which protrude from or recess in a base surface (features not explicitly represented) of the embossing roller 107, 108. Referring now to Figure 20(B), this shows a further example embodiment for any one of embossing rollers 107 and 108, which doesn't comprise any toothed wheel. The roller surface 2002 may carry embossing features (as illustrated in previous figures) which protrude from or recess in a base surface (features not explicitly represented) of the embossing roller 107, 108. In this example, the embossing roller 107, 108 is typically driven by a servo motor mechanism (not represented) that directly rotates the rotation axis 2003.

[0144] Referring to Figure 21 , this contains a view of an example for a quick-exchange device 2100 configured for housing a set of embossing rollers according to the invention. The rollers 107 and 108 are mounted in a cassette 2101, which contains means (not represented) for adjusting and correcting the positions and the rotation axes of the rollers 107 and 108, and which is mounted in a removable manner in a frame 2102. In preferred embodiments, the roller 107 is driven by the externally driven roller 108 via gearwheels (not represented) located at one end of the rollers. However, other synchronizing means, e.g., electric servomotors, may also be used. P4237PC01 / 0768-108_dpt 33

[0145] Referring to Figures 22(A) - 22(C), these contain views of examples for using different configurations of embossing rollers 107, 108 in a cassette 2101 , which is a component of a quick-exchange device (not represented). The embossing rollers 107, 108 may have different diameters, typically in a range between 50 mm to 300 mm. Figure 22(A) illustrates an example embodiment with rollers 2200 and 2201 having substantially a same diameter, which may be for example 100 mm, and a length of 1 m. In addition, Figure 22(A) shows gear wheels 2202 mounted on the respective axes of the rollers and configured to couple the rollers among each other. Figure 22(B) illustrates a further example with rollers 2203 and 2204 having substantially a same diameter, larger than that used in Figure 22(A), and which may for example be 180 mm. Furthermore, Figure 22(B) shows gearwheels 2205 mounted on respective axis of the rollers and configured to couple the rollers among each other. Figure 22(C) illustrates a further example with rollers 2206 and 2207 having different diameters from one to the other, one having for example 90 mm diameter, and the other 180 mm diameter. In addition, Figure 22(C) shows gear wheels 2208 mounted on respective axis of the rollers and configured to couple the rollers among each other.

[0146] To compensate for the flexion of the embossing rollers that may occur during the embossing of the metallic film (not represented), the rollers 107, 108 may be cambered in order to achieve a uniform embossing across the width of the rollers. This is well known in the art and not further illustrated in the figures. Generally speaking, depending on the needs for the quality of embossing, the embossing rollers may be cylindrical, convex, or concave. The rollers may comprise stainless steel and be laser engraved on their surfaces with the embossing structures, whereas the stainless steel may be hardened in the whole volume or on a superficial layer (<0.5 mm). The embossing rollers may of ceramic material or be either powder metallurgic or casted, with initial hardness from 55 to 65 HRC and may be engraved with laser sources with wavelengths between 265 nm and 1065 nm and pulse durations between 0.1 ps and 20 ps. In a preferred embodiment, the embossing rollers may receive a hard coating (e.g. vacuum deposition of oxides, nitrides, carbides) or another surface treatment, in order to increase their wear resistance. For P4237PC01 / 0768-108_dpt 34 instance, the embossing rollers may be foreseen with a vacuum-deposited diamondlike coating, reducing their wear during the embossing process.

[0147] Referring to Figures 23(A) - 23(C), these illustrate an example for the adjustment and correction of the position of an embossing roller 107, 108 in a cassette (like 2101 , not represented here for readability reasons) which is a component of a quickexchange device (not represented). The adjustment and correction of the position of the rotation axis 2300 of an embossing roller 107, 108 in x-direction at one of the ends 2301 of one of the at least two rollers may for example be adjusted and corrected by ±0,1 mm by means of an off-centered pin 2302. This enables a precision of alignment between the rotation axes of the first roller and the second roller of 0,01 mm, i.e., 2 arcsec. The other of the ends 2303 of the roller is rotatably fixed at a fixed rotation center device 2304, which is configured to let the rotation axis 2300 rotate around the fixed rotation center 2304 around an axis perpendicular to the rotation axis 200 (the former is not represented). In Figure 23(A), the off-centered pin 2302 is adjusted in a central position, in Figure 23(B) the off-centered pin 2302 is adjusted to move the rotation axis 2300 in a direction away from a turning center 2305 of the off-centered pin, whereas in Figure 23(C) the off-centered pin 2302 is adjusted to move the rotation axis 2300 in a direction towards the turning center 2305. After adjusting the off-centered pin 2302, this is then locked in the correct position by means of fixture screws (not represented).

[0148] These precise adjustment and position-correction means are necessary for an embodiment of the invention, in order to ensure the homogeneous embossing of the protruding and recessed embossing structures from the embossed rollers into the embossed metallic foil, enabling for the elevated embossed features and the deepened embossed features to maintain a constant height, respective depth, over the entire width of the embossed metallic foil, which will maximize the overall surface area increase of the metallic foil through embossing.

[0149] Referring now to Figure 24, this illustrates an application of the invention in the field of electric mobility, more specifically for a battery of an electric vehicle 2400. Such a vehicle contains and is alimented by a battery 2403, which may contain modules P4237PC01 / 0768-108_dpt 35

[0150] 2402 that are built from cells 2401 , which include electrodes fabricated using thin metallic films 109 embossed according to the invention, and which possess an enlarged overall active surface area, exhibiting thus an increased energy storage capacity and enabling an increased number of charge cycles.

[0151] In a preferred embodiment of the invention, cathodes for secondary battery cells were fabricated using copper foil having an initial thickness of 10 pm, embossed according to the invention. The embossed copper foil had elevated and deepened embossed features with an overall peak-to-valley height of 45 pm, was coated on one side with a 20 pm layer of Lithium and further used in the fabrication of secondary battery cells. The cells produced with embossed metallic foil were compared with secondary battery cells of the same type, using cathodes made of the same time of copper, however non-embossed. The comparison evidenced a 2,5 times larger number of charging cycles for the secondary battery cells containing copper foil embossed according to the invention.

[0152] Referring now to Figure 25, this illustrates an application of the invention in the field of chemistry, more specifically in the field of chemical reactions supported by a catalyst. These chemical reactions may take place in a reactor 2500, which is alimented with the reactants 2501, and which delivers the products and the unreacted materials 2504 to separation. The reactor 2500 may include a catalyst 2503 consisting of a thin metallic film 109 embossed according to the invention, mounted on a support (not represented) inside the reactor 2500. The embossed film 109 possesses an enlarged surface, which represents an enlarged overall catalytic surface for the chemical processes taking place in the reactor 2500, yielding eventually increased reaction rates for these processes.

[0153] Referring now to Figure 26, this illustrates applications of the invention in the field of mobile machinery, illustrated here by a lawnmower 2602 and by a robot 2603. These devices are to be understood as examples and do not represent an exhaustive list of possible applications. Such devices may contain modules 2601 , which are built from secondary battery cells 2600, which were fabricated using metallic thin films 109 P4237PC01 / 0768-108_dpt 36 embossed according to the invention, exhibiting thus an increased energy storage capacity and enabling increased number of charge cycles.

[0154] Referring now to Figure 27, this illustrates applications of the invention in the field of mobile electronic devices, such as cell phones 2701 , portable computers 2702, household devices 2703. These devices may contain secondary battery pouch cells 2700, which are fabricated using metallic thin films 109 embossed according to the invention, and which therefore exhibit an increased energy storage capacity and allow an increased number of charge cycles.

[0155] Referring now to Figure 28, this illustrates an application of the invention in the field of the utilization of renewable energies. A home solar battery storage system 2802, which is fed by solar panels 2803, may contain modules 2801 that are built from secondary battery cells 2800, which were fabricated using metallic thin films 109 embossed according to the invention, exhibiting thus an increased energy storage capacity and enabling increased number of charge cycles.

[0156] Fig. 29 contains a flowchart illustrating an example of the method for producing an increased surface area of a metallic foil 2900 by embossing. The method comprises providing 2901 the metallic foil 2900 presenting an initial surface area on one of its faces and a determined thickness, providing an embossing set-up 2902 comprising

[0157] • a first and a second embossing tool having respectively a first and a second base surface, and

[0158] • positioning tools for positioning the first and the second embossing tool for the first base surface to face the second base surface, and be separated by at least an embossing gap that receives the metallic foil during embossing of the metallic foil.

[0159] The first embossing tool comprises on the first base surface first protruding embossing structures positioned on the first base surface, having respectively each a P4237PC01 / 0768-108_dpt 37 height that has at most a determined first height value above the first base surface, and any convex edge exposed by a corresponding one of the first protruding embossing structures has a curvature configured to prevent a tearing-up of the metallic foil during embossing. The second embossing tool comprising on the second base surface second protruding embossing structures positioned on the second base surface, and having a second height above the second base surface with a value inferior to the determined first height value, in order for the second protruding embossing structures to press the metallic foil towards the first embossing roller at spaces not occupied by any one of first embossing structure during the embossing of the metallic foil. The embossing gap is greater than the thickness of the metallic foil.

[0160] The method further comprises embossing the metallic foil 2903 with the embossing set-up, and stretching the metallic foil 2904 during the embossing by exerting a stretching force through pressure of tops of protruding embossing structures of any one of the first and second embossing tools towards the base surface opposing the respective top on the corresponding second and first embossing tools, thereby producing the increased surface area of the metallic foil 2905 to be greater than the initial surface area of the metallic foil, the increased surface area comprising surfaces of stretched and non-stretched portions of the metallic foil.

[0161] P4237PC01 / 0768-108_dpt 38

[0162] Glossary

[0163] With regard to an embossing set-up

[0164] - flat embossing tool: a tool containing at least a substantially flat surface, which can be positioned and adjusted by positioning and adjusting means, which belongs to an embossing set-up, and which contains protruding or recessed embossing structures on its substantially flat surface;

[0165] - embossing roller: an embossing tool with a cylindrical symmetry, possessing a rotation axis, which can be positioned and adjusted by positioning and adjusting means, which belongs to an embossing roller system, and which contains protruding or recessed embossing structures on its cylindrical surface;

[0166] - positioning means: mechanical means for the adjustment and correction of a position of an embossing roller inside the embossing roller system, ensuring maintaining a chosen position for the roller;

[0167] - embossing gap: a space between the corresponding surfaces of the embossing tools of an embossing set-up, which is not occupied by any of the embossing structures of the embossing tools, and which accommodates the metallic foil during the embossing;

[0168] - cassette for quick-exchange: a mechanical device, part of an embossing roller system, configured for housing a set of embossing rollers, containing mechanical means for adjusting and correcting the positions and the rotation axes of the rollers, further configured to be inserted in a removable manner in a frame, part of the embossing roller system;

[0169] With regard to the embossing structures

[0170] - embossing structures: determined tridimensional modifications on a surface of a tool, having a chosen shape, arranged in a determined manner on the tool surface and intended to emboss the determined shape to a metallic foil, by means of a plastic deformation of the foil; P4237PC01 / 0768-108_dpt 39

[0171] - protruding structures: embossing structures situated above a base surface of an embossing tool;

[0172] - recessed structures: embossing structures situated below a base surface of an embossing tool;

[0173] - top of a protruding structure: the highest point or zone of a protruding embossing structure, seen above the base surface of an embossing tool, which comprises the protruding embossing structure;

[0174] - bottom of a recessed structure: the lowest point or zone of a recessed embossing structure, seen below the base surface of an embossing tool, which comprises the recessed embossing structure;

[0175] With regard to the embossed foil

[0176] - thickness: an intrinsic property of the metallic foil expressing its physical extension in one dimension, which presents an initial value prior to embossing and a reduced value after embossing;

[0177] - stretching: a process occurring when a metallic foil is subjected to stretching forces, resulting in an elongation and a plastic deformation of the metallic foil, and enabling the foil change shape and stretch without breaking;

[0178] - tearing: a phenomenon that occurs when the amount of stretching of a foil exceeds a material-specific property (the ultimate tensile strength) when the foil material will fracture and fail;

[0179] - increased surface area vs. initial surface area: an expansion of the overall metallic foil surface area, obtained by the elongation and the tridimensional plastic deformation of a metallic foil that is subjected to embossing;

[0180] With regard to the applications of the invention

[0181] - secondary battery: a type of battery that is reversible, converting electrical energy back into chemical energy when charged; P4237PC01 / 0768-108_dpt 40

[0182] - catalyst: a substance or a device that causes or accelerates a chemical reaction, without itself being affected;

[0183] - pouch battery cell: a soft cell (often flexible), in which most of the cell components are enclosed in an aluminum-coated plastic film;

[0184] - charging cycle of a battery: the process of charging and discharging a secondary battery into a load, which is typically used to specify a battery's expected lifetime, as the number of charging cycles indicates how many times the secondary battery can undergo the charging and discharging until failure or starting to lose capacity;

[0185] - capacity of a battery: a characteristic measure of a battery's ability to store electrical energy, given by the electrical charge that can be stored, and expressed in physical measuring units for electrical charge (e.g. Ah).

Claims

P4237PC01 / 0768-108_dpt 41Claims1 . Method for producing an increased surface area of a metallic foil by embossing, comprising providing the metallic foil to be embossed, the metallic foil presenting an initial surface area on one of its faces and a determined thickness, providing an embossing set-up comprising a first and a second embossing tool having respectively a first and a second base surface, and positioning tools for positioning the first and the second embossing tool for the first base surface to face the second base surface, and be separated by at least an embossing gap that receives the metallic foil during embossing of the metallic foil, the first embossing tool comprising on the first base surface first protruding embossing structures positioned on the first base surface, having respectively each a height that has at most a determined first height value above the first base surface, and any convex edge exposed by a corresponding one of the first protruding embossing structures has a curvature configured to prevent a tearing-up of the metallic foil during embossing, the second embossing tool comprising on the second base surface second protruding embossing structures positioned on the second base surface, and having a second height above the second base surface with a value inferior to the determined first height value, in order for the second protruding embossing structures to press the metallic foil towards the first embossing roller at spaces not occupied by any one of the first embossing structures during the embossing of the metallic foil, and the embossing gap is greater than the thickness of the metallic foil, wherein the embossing gap is a space between correspondingP4237PC01 / 0768-108_dpt 42 surfaces of the first and the second embossing tools which is not occupied by any of the embossing structures of the first and second embossing tools, the method further comprising embossing the metallic foil with the embossing set-up, and stretching the metallic foil during the embossing by exerting a stretching force through pressure of tops of protruding embossing structures of any one of the first and second embossing tools towards the base surface opposing the respective top on the corresponding second and first embossing tools, thereby producing the increased surface area of the metallic foil to be greater than the initial surface area of the metallic foil, the increased surface area of the metallic foil comprising surfaces of stretched and non-stretched portions of the metallic foil.

2. The method according to claim 1, wherein the embossing gap is greater than a sum of the determined first height value and the determined thickness of the metallic foil.

3. The method according to claim 1, wherein the first protruding embossing structures are aligned along first parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the first parallel lines for protruding structures being separated by a first separating distance (P) from one to the next in their first parallel line for protruding structures, the first parallel lines for protruding structures being separated from one to an adjacent one by a determined first period value (P1), the second protruding embossing structures are aligned along second parallel lines for protruding structures on the second embossing tool, and the second protruding embossing structures of each of the second parallel lines for protruding structure being separated by the first separatingP4237PC01 / 0768-108_dpt 43 distance from one to the next in their second parallel line for protruding structures, the second parallel lines for protruding structures being separated from one to an adjacent one by the determined first period value.

4. The method according to claim 3, wherein the first separating distance has a value in a range from 0,02 mm to 1 mm, and the determined first period value is in a range from 0,02 mm to 1 mm.

5. The method according to any one of claims 1 to 4, wherein each of the protruding first and second embossing structures are described to have an embossing structure height value between a top of the protruding first or second embossing structure and respectively the first or second base surface, the embossing structure height value being in a range between 0,01 mm and 0,5 mm.

6. The method according to claim 1 , wherein the first embossing tool further comprises on the first base surface first recessed embossing structures with a depth of a determined first depth value below the first base surface, the second embossing tool further comprises on the second base surface second recessed embossing structures with a depth of a determined second depth value below the second base surface, the first protruding and recessed embossing structures respectively corresponding to second recessed and protruding embossing structures shaped such that first protruding embossing structures fit into the corresponding second recessed embossing structures, and the second protruding embossing structures fit into the corresponding first recessed embossing structures during the embossing, while allowing at least aP4237PC01 / 0768-108_dpt 44 distance greater than the determined thickness to separate opposing surfaces of the first and the second roller, the first protruding embossing structures being aligned along parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the parallel lines for protruding structures being separated by a first separating distance from one to the next in their parallel line for protruding structures, the parallel lines for protruding structures being separated from one to the adjacent by a determined first period value, the first recessed embossing structures being aligned along parallel lines for recessed structures on the first embossing tool, and the first recessed embossing structures of each of the parallel lines for recessed embossing structures being separated by the first separating distance from one to the next in their parallel line for recessed structures, the parallel lines for recessed structures being separated from one to the adjacent by the determined first period value.

7. The method according to claim 6, wherein the first separating distance has a value in a range from 0,02 mm to 1 mm, and the determined first period value is in a range from 0,02 mm to 1 mm.

8. The method according to any one of claims 6 or 7, wherein the parallel lines for protruding structures and the parallel lines for recessed structures are positioned relatively to each other such that first protruding embossing structures taken from successive parallel lines for protruding structures are aligned with first recessed embossing structures taken from successive parallel lines for recessed structures, along lines of alternating recessed and protruding embossing structures, the lines of alternating recessed and protruding embossing structures being parallel among each other.P4237PC01 / 0768-108_dpt 459. The method according to claim 8, wherein the lines of alternating recessed and protruding embossing structures are perpendicular to the parallel lines for protruding structures and the parallel lines for recessed structures.

10. The method according to claim 8, wherein the lines of alternating recessed and protruding embossing structures are in a determined non-perpendicular inclination angle to the parallel lines for protruding structures and the parallel lines for recessed structures.

11. The method according to any one of claims 6 to 10, wherein each of the protruding first and second embossing structures and each of the recessed first and second embossing structures are described by a top of a protruding first or second embossing structure to a bottom of a recessed respectively first or second embossing structure height value situated in a range between 0,01 mm and 0,5 mm.

12. The method according to any one of claims 1 to 11, wherein the first protruding embossing structures are shaped as any one of a list of shapes comprising:- a truncated pyramid with polygonal basis;- a non-truncated pyramid with polygonal basis;- a bowling cone;- a truncated bowling cone;- a paraboloid;- a spherical dome.P4237PC01 / 0768-108_dpt 4613. The method according to claim 12, wherein the first protruding embossing structure of truncated pyramid shape or of nontruncated pyramid shape comprises concave lateral flanks.

14. The method according to any one of claims 1 to 13, wherein a first width of the first protruding embossing structures, at the first base surface, and a second width of the second protruding embossing structures, at the second base surface are in a range from 0,01 mm to 0,5 mm.

15. The method according to any one of the previous claims, wherein the first and the second embossing tools are first and second flat embossing tools.

16. The method according to any one of claims 1 to 14, wherein the first and the second embossing tools are first and second embossing rollers.

17. The method according to claim 16, wherein the step of providing the embossing set-up comprises mounting and adjusting the first and the second embossing rollers in a quick exchange cassette, whereby the quick exchange cassette is removably mounted in a frame.

18. The method according to any one of claims 16 to 17, wherein the first and the second embossing rollers are driven and synchronized by any means from a list of synchronization means comprising toothed-wheels gears, helicoidal gears, servomotors.

19. The method according to any one of the preceding claims, wherein the embossing set-up is part of a production chain for a manufacturing of theP4237PC01 / 0768-108_dpt 47 embossed metallic foil for an electric energy storage intended for use in electric appliances such as an electric vehicle, a robot, a cell phone, a portable computer, a hearing device, a power bank.

20. The method according to any one of the preceding claims, wherein the provided metallic foil to be embossed comprises any material from a list comprising copper, aluminum, lithium, silver, gold, iron, brass, lead, zinc and mixtures thereof.

21. The method according to claim 20, wherein the metallic foil is covered with at least a layer of polymer.

22. The method according to anyone of claims 1 to 21 , wherein the first and second embossing tool each comprise any one material of a list comprising steel, hardened steel, stainless steel, ceramic, any of the preceding materials coated with oxide, nitride, diamond like coatings, carbide.

23. An embossing system configured for producing an increased surface area of a metallic foil by embossing, the metallic foil to be embossed presenting an initial surface area on one of its faces and a determined thickness, the embossing system comprising an embossing set-up comprising a first and a second embossing tool having respectively a first and a second base surface, and positioning tools for positioning the first and the second embossing tool for the first base surface to face the second base surface, and be separated by at least an embossing gap that receives the metallic foil during embossing of the metallic foil,P4237PC01 / 0768-108_dpt 48 the first embossing tool comprising on the first base surface first protruding embossing structures positioned on the first base surface, having respectively each a height that has at most a determined first height value above the first base surface, and any convex edge exposed by a corresponding one of the first protruding embossing structures has a curvature configured to prevent a tearing-up of the metallic foil during embossing, the second embossing tool comprising on the second base surface second protruding embossing structures positioned on the second base surface, and having a second height above the second base surface with a value inferior to the determined first height value, in order for the second protruding embossing structures to press the metallic foil towards the first embossing roller at spaces not occupied by any one of the first embossing structures during the embossing of the metallic foil, and the embossing gap is greater than the thickness of the metallic foil to be embossed, wherein the embossing gap is a space between corresponding surfaces of the first and the second embossing tools which is not occupied by any of the embossing structures of the first and second embossing tools, the embossing system being configured to emboss the metallic foil with the embossing set-up, thereby stretching the metallic foil during the embossing by exerting a stretching force through pressure of tops of protruding embossing structures of any one of the first and second embossing tools towards the base surface opposing the respective top on the corresponding second and first embossing tools, thereby producing the increased surface area of the metallic foil to be greater than the initial surface of the metallic foil, the increased surface area comprising surfaces of stretched and non-stretched portions of the metallic foil.P4237PC01 / 0768-108_dpt 4924. The embossing system according to claim 23, wherein the embossing gap is greater than a sum of the determined first height value and the determined thickness of the metallic foil to be embossed.

25. The embossing system according to claim 23, wherein the first protruding embossing structures are aligned along first parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the first parallel lines for protruding structures being separated by a first separating distance (P) from one to the next in their first parallel line for protruding structures, the first parallel lines for protruding structures being separated from one to an adjacent one by a determined first period value (P1), the second protruding embossing structures are aligned along second parallel lines for protruding structures on the second embossing tool, and the second protruding embossing structures of each of the second parallel lines for protruding structure being separated by the first separating distance from one to the next in their second parallel line for protruding structures, the second parallel lines for protruding structures being separated from one to an adjacent one by the determined first period value.

26. The embossing system according to claim 25, wherein the first separating distance has a value in a range from 0,02 mm to 1 mm, and the determined first period value is in a range from 0,02 mm to 1 mm.

27. The embossing system according to any one of claims 23 to 26, wherein each of the protruding first and second embossing structures are described to have an embossing structure height value between a top of the protruding first or second embossing structure and respectively the first or second base surface, the embossing structure height value being in a range between 0,01 mm and 0,5 mm.P4237PC01 / 0768-108_dpt 5028. The embossing system according to claim 23, wherein the first embossing tool further comprises on the first base surface first recessed embossing structures with a depth of a determined first depth value below the first base surface, the second embossing tool further comprises on the second base surface second recessed embossing structures with a depth of a determined second depth value below the second base surface, the first protruding and recessed embossing structures respectively corresponding to second recessed and protruding embossing structures shaped such that first protruding embossing structures fit into the corresponding second recessed embossing structures, and the second protruding embossing structures fit into the corresponding first recessed embossing structures during the embossing, while allowing at least a distance greater than the determined thickness to separate opposing surfaces of the first and the second roller, the first protruding embossing structures being aligned along parallel lines for protruding structures on the first embossing tool, and the first protruding embossing structures of each of the parallel lines for protruding structures being separated by a first separating distance from one to the next in their parallel line for protruding structures, the parallel lines for protruding structures being separated from one to the adjacent by a determined first period value, the first recessed embossing structures being aligned along parallel lines for recessed structures on the first embossing tool, and the first recessed embossing structures of each of the parallel lines for recessed embossing structures being separated by the first separating distance from one to the next in their parallel line for recessed structures, the parallel lines for recessed structures being separated from one to the adjacent by the determined first period value.P4237PC01 / 0768-108_dpt 5129. The embossing system according to claim 28, wherein the first separating distance has a value in a range from 0,02 mm to 1 mm, and the determined first period value is in a range from 0,02 mm to 1 mm.

30. The embossing system according to any one of claims 28 or 29, wherein the parallel lines for protruding structures and the parallel lines for recessed structures are positioned relatively to each other such that first protruding embossing structures taken from successive parallel lines for protruding structures are aligned with first recessed embossing structures taken from successive parallel lines for recessed structures, along lines of alternating recessed and protruding embossing structures, the lines of alternating recessed and protruding embossing structures being parallel among each other.

31. The embossing system according to claim 30, wherein the lines of alternating recessed and protruding embossing structures are perpendicular to the parallel lines for protruding structures and the parallel lines for recessed structures.

32. The embossing system according to claim 30, wherein the lines of alternating recessed and protruding embossing structures are in a determined non-perpendicular inclination angle to the parallel lines for protruding structures and the parallel lines for recessed structures.

33. The embossing system according to any one of claims 23 to 32, wherein each of the protruding first and second embossing structures and each of the recessed first and second embossing structures are described by a top of a protruding first or second embossing structure to a bottom of a recessedP4237PC01 / 0768-108_dpt 52 respectively first or second embossing structure height value situated in a range between 0,01 mm and 0,5 mm.

34. The embossing system according to any one of claims 23 to 33, wherein the first protruding embossing structures are shaped as any one of a list of shapes comprising:- a truncated pyramid with polygonal basis;- a non-truncated pyramid with polygonal basis;- a bowling cone;- a truncated bowling cone;- a paraboloid;- a spherical dome.

35. The embossing system according to claim 34, wherein the first protruding embossing structure of truncated pyramid shape or of nontruncated pyramid shape comprises concave lateral flanks.

36. The embossing system according to any one of claims 23 to 35, wherein a first width of the first protruding embossing structures, at the first base surface, and a second width of the second protruding embossing structures, at the second base surface are in a range from 0,01 mm to 0,5 mm.

37. The embossing system according to any one of the previous claims, wherein the first and the second embossing tools are first and second flat embossing tools.P4237PC01 / 0768-108_dpt 5338. The embossing system according to any one of claims 23 to 36, wherein the first and the second embossing tools are first and second embossing rollers.

39. The embossing system according to claim 38, wherein the first and the second embossing rollers are mounted and adjusted in a quick exchange cassette, whereby the quick exchange cassette is removably mounted in a frame.

40. The embossing system according to any one of claims 38 to 39, wherein the first and the second embossing rollers are driven and synchronized by any means from a list of synchronization means comprising toothed-wheels gears, helicoidal gears, servomotors.

41. A production chain for a manufacturing of an embossed metallic foil for an electric energy storage intended for use in electric appliances such as an electric vehicle, a robot, a cell phone, a portable computer, a hearing device, a power bank, wherein the production chain comprises the embossing system according to any one of the previous claims 23 to 40.

42. A metallic foil embossed by the embossing system according to any one of the preceding claims 23 to 40, wherein the metallic foil comprises any material from a list comprising copper, aluminum, lithium, silver, gold, iron, brass, lead, zinc and mixtures thereof.

43. The metallic foil according to the previous claim , wherein the metallic foil is covered with at least a layer of polymer.

44. The embossing system according to anyone of claims 23 to 40, wherein the first and second embossing tool each comprise any one material of a listP4237PC01 / 0768-108_dpt 54 comprising steel, hardened steel, stainless steel, ceramic, any of the preceding materials coated with oxide, nitride, diamond like coatings, carbide.

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