METHOD AND DEVICE FOR FORMING A PATTERN ON A THIN METAL FOIL

Abstract: The invention relates to a method for forming a pattern of a dissolved substance on a thin metal foil, comprising the following steps: applying an adhesive but removable film to the metal foil, holes of a desired shape being provided in the film, filling the holes in the film with a solution incorporating the dissolved substance, drying the solution incorporating the dissolved substance so that the dried substance remains in the holes, and removing the film from the metal foil so that the dried substance remains as a pattern on the metal foil, the film having a thickness substantially corresponding to the level of the solution incorporating the dissolved substance to be introduced into the holes. The invention relates more particularly to a method of forming a cell having a non-aqueous electrolyte as well as to a device for forming a pattern of a dissolved substance on a thin metal foil and to a cell having a non-aqueous electrolyte.

Description: Method and Device for Forming a Pattern on a Thin Metal Foil BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method and a device for forming a pattern of a dissolved substance on a thin metal foil, and more particularly to a method for forming a cell with a non- aqueous electrolyte. The invention relates further to a device for forming a pattern of a dissolved substance on a metal foil as well as to a cell with a non-aqueous electrolyte. 2. Description of the Prior Art Electrochemical cells having a non-aqueous electrolyte are used, for example, in the fabrication of round cells or lithium ion batteries . To form such electrochemical cells it is necessary to coat a thin metal foil, serving as the negative electrode, with a substance serving as the positive electrode. Known from EP 0 627 780 Bl is an electrochemical secondary cell having a non-aqueous electrolyte. In the method described therein for producing the cell a lithium ion solution is coated onto a metal foil, e.g. a strip of copper foil. The solution is dried and the resulting laminate may be employed as the starting material, for example, for fabricating battery cells. To fabricate lithium ion battery cells it is necessary to apply a relatively thick coating to the metal foil. When, as in accordance with EP 0 627 780 Bl the whole surface of a strip of metal foil is to be coated with a lithium ion solution this may result in very long drying times and thus drawn-out methods of fabrication. One major drawback relates furthermore to the fact that after having stamped out the cells from the fully coated metal foil merely the underside of the metal or the very thin side surface areas of the stamped out metal foil remain as contact surface areas (e.g. as terminal surface areas). In addition to this, fully coating a strip of metal is principally a wasteful utilization of the lithium ion solution, since after the battery cells have been stamped out, the remaining strip needs to be disposed of. In an attempt to apply the lithium ion solution sec- tionwise as a pattern in once-only application the edges of the pattern would be irregular and fail to assume any exact geometric shapes, the lithium solution weeping namely at the edges of the pattern on being coated. One way of getting round this problem basically would be to apply the solution containing the lithium ions as a pattern to the thin metal foil via silk-screening or gravure printing. The solution containing lithium which in this arrangement needs to exhibit a relatively low viscosity could be applied to the metal foil in several steps in the procedure in sequence, i.e. by applying and drying a thin film of solution, followed by applying and drying a further film of solution, and so on until the full level of the printed pattern is achieved. In this way a dry pattern roughly 150 μm thick could be formed from a wet film level of approximately 300 μm applied during the above procedure. However, this procedure would be too slow. SUMMARY OF THE INVENTION It is the object of the present invention to provide a method of forming a pattern of a dissolved substance on a thin metal foil, which obviates the drawbacks as cited above. More particularly, the intention of the method in accordance with the invention is to enable relatively thick patterns having a precise, undamaged edge definition to be applied to a metal foil. A further object of the present invention is to define a method as aforementioned so that fast, more particularly continuous fabrication of a patterned metal foil is made possible . Yet a further object of the present invention is to provide a device for forming a pattern of a dissolved substance on a thin metal foil . The objects as cited above are achieved by methods and devices as they read from the independent claims, the sub- claims defining advantageous embodiments of the invention. The method for forming a pattern of a dissolved substance on a thin metal foil in accordance with the invention comprises the following steps: applying an adhesive but removable film to the metal foil, holes of a desired shape being provided in the film, filling the holes in the film with a solution incorporating the dissolved substance, drying the solution incorporating the dissolved substance so that the dried substance remains in the holes, and removing the film from the metal foil so that the dried substance remains as a pattern on the metal foil, the film having a thickness substantially corresponding to the level of the solution incorporating the dissolved substance to be introduced into the holes . The method in accordance with the invention as listed above has the advantage that the solution incorporating the dissolved substance can be applied in one step to the metal foil. Due to the supporting frame formed by the film with the holes the solution is now unable to weep and is able to dry so that the edges of the resulting pattern feature a precise geometric shape. The procedure for applying or filling the solution implemented in but a single step accelerates the method considerably, merely the amount of solution required for the pattern in each case needing to be applied so that drying too can be be made relatively quickly. Also, there is no waste of solution. The viscosity of the solution can be low. In addition, the method as described above can be be sequenced continually. A further major advantage of the method in accordance with the invention as compared to applying coatings as a whole is that in subsequently stamping out the patterns use can be made of such tools which include a free margin of the metal foil in stamping out which can be made use of as a terminal section. In accordance with the invention several possibilities exist for producing the holes in the film. In a first possibility the holes can be produced in the film before the film is applied to the metal foil, the holes then being preferably stamped from the film. Another possibility is not to produce the holes in the film until the film has been applied to the metal foil. In this arrangement stamping tools can be employed with highly accurate guidance, each of which works only the film without penetrating as far as the metal foil. The stamped out film pieces are removed by a stripping device, for example by one such device working with vacuum suction. Yet another possibility of producing the holes in the film consists of etching the holes from the film, i.e. should an etchant be applied to the metal foil then, of course, one which does not attack the metal foil . By means of the method in accordance with the invention the formation of a pattern can be done on one or both sides of the metal foil . In accordance with one embodiment of the invention the metal foil is a thin foil of aluminum or copper having preferably a thickness of 10 to 50μm, more particularly 20μm. The film employed in one aspect of the method in accordance with the invention is a plastics film, more particularly a film of polyester. Polyester films are advantageously insoluble as regards the solvents used in such methods . The thickness of the film may be in the range of 50 to 800 μm, more particularly approximately 300 μm, the thickness depending on the level of the pattern later desired, it being as thick as the level of the applied solution in each case. In one preferred embodiment of the invention the sidewalls of the holes in the film extend substantially perpendicular to the main surfaces of the film, it being assured by such a configuration of the sidewalls that when the film is removed from the metal foil the sidewalls of the remaining pattern do not suffer any damage. In addition, in this embodiment the film can be removed relatively easily without any mechanical snagging needing to be overcome . Preferably the surface of the film facing away from the metal foil is treated more particularly by irradiation and/or chemically so that the solution incorporating the dissolved substance does not stick thereto. Such an anti-stick treatment facilitates on the one hand removing the metal foil, whilst on the other it also contributes towards enabling solution fluid weeping past the holes to be easily removed from the surface of the film. Prior to the film being applied to the metal foil an adhesive is preferably applied to the surface of the film facing the metall foil which adhers to the film considerably more than to the metal foil, an adhesive needing to be used in this case which provides a sufficient bond between film and metal foil to enable the filling and drying procedure to be implemented without difficulty. However, when the film is removed from the metal foil once the pattern has dried it needs to be assured that all of the adhesive readhers to the film and as little as possible or nothing at all thereof remains on the metal foil. More particularly an adhesive could be used with which the film is able to readher to a metal foil, once it has been released from a previously treated metal foil. Using such "repeat adhesives" would then permit repeat use of the film in the fabrication method, permitting more particularly a continual cyclic use thereof. Preferably the adhesive is insoluble by the solvent of the solution, it needing to be applied evenly and at the edges exactly on the underside of the film and to adher to the metal foil at least so strongly that the solution is unable to penetrate between the metal foil and the film applied thereto, i.e. excluding "undercreep" . In a preferred embodiment of the invention the dissolved substance contains lithium ions. The solvent for the dissolved substance in accordance with the invention is preferably N- methy1 -2 -pyrro1idone . In one advantageous aspect of the method in accordance with the invention an applicator is used for filling the holes in the film applied to the metal foil which particularly with the aid of a knife introduces the solution into the holes or smooths out the filling level in the holes, thus making a very simple procedure for filling the holes possible which is substantially less complicated than the majority of the coating methods currently employed. Use can be made to particular advantage of the "knife over roll" system or including the use of a flexible knife (blade) without damaging the film surface (and also as regards the choice of material) , this applying in particular when the surface of the film has been treated so that the solution does not adher thereto. It is furthermore conceivable in the scope of the invention to make use of an applicator for filling the holes which does so by drip application, requiring the viscosity of the solution to be maintained relatively low. Drying the solution is implemented by infrared heating the metal foil side in one embodiment of the invention for a film applied one-sidedly, heating thus being applied to advantage to the metal foil side since heating the film side directly could cause a skin to form on the solution disturbing further homogenous drying . In the drying process a relatively weak flow of gas is passed over the film into which the solvent of the solution can evaporate, it being necessary in this case to ensure that the flow of gas is not too strong so that drying the solution is able to take place homogenously and without a skin forming. It is also conceivable for a single-sided film within the scope of the invention to implement drying of the solution at the metal foil side by means of hot gas heating, this requiring, however, preferably means for preventing an excessively strong overflow of the hot gas on the film side. Such means could involve e.g. baffle plates. It is also possibile that a part of the flow of hot gas is made use of to provide the necessary relatively weak gas flow over the film. In a preferred embodiment of the method in accordance with the invention the patterned metal foil and the film are separated from each other after drying by means of an air knife, the metal foil then being exited over a roll to advantage. Stripping the film from the metal foil is required 8 to be as gentle as possible without damaging the metal foil or the pattern existing thereon. An air knife permits such gentle stripping. Also conceivable is a suction of the metal foil and/or film by vacuum pressure in various directions or also by gentle mechanical strippers, however, which grip the edge of the foil or film. In one embodiment of the present invention the method results in the metal foil being configured as a negative electrode and the pattern of the dissolved substance as the positive electrode of a cell having a non-aqueous electrolyte. In keeping with the details as discussed above the present invention thus also defines a method of forming an (electrochemical) cell having a non-aqueous electrolyte by the following steps: applying an adhesive but removable film to a metal foil, preferably a thin aluminum or copper foil, holes of a desired shape being required to be produced in the film, filling the holes in the film with a lithium ion solution dissolved in a solvent with N-methyl-2 pyrrolidone, preferably with the aid of a knife, drying the solution so that the dried residue remains in the holes, and removing the film from the metal foil so that a pattern remains on the metal foil, the film having a thickness substantially corresponding to the level of the solution to be applied to the holes with the dissolved substance. In accordance with yet a further aspect of the present invention a device for forming a pattern of a dissolved substance on a thin metal foil is provided, this device comprising: a film in which holes of a desired shape are incorporated, and an adhesive for applying the film to the metal foil, the film having a thickness substantially corresponding to the level of the solution incorporating the dissolved substance to be introduced into the holes . Accordingly, the invention relates also to the film used as an expedient in fabricating a patterned metal foil which can be applied by an adhesive to the metal foil and advantageously forming a "mask" for the solution introduced which can thus be applied in a single step. The device in accordance with the invention thus permits achieving the advantages in the method of fabrication already discussed. In accordance with the invention the cited device may advantageously comprise one or more of the following features: the film is a plastics film, more particularly a film of polyester; the film has a thickness in the range 50 to 800 μm, more particularly 300 μm; the sidewalls of the holes in the film extend substantially perpendicular to the main surfaces; the surface of the film facing away from the metal foil is treated more particularly by irradiation and/or chemically so that the solution incorporating the dissolved substance does not adher thereto; the adhesive applied to the surface of the film facing the metal foil is such that it adhers substantially stronger to the film than to the metal foil so that the film can readher to a metal foil after having been once removed from the metal foil; the adhesive is insoluble due to the solvent of the solution and more particularly adhers to the metal foil at least so strongly that the solvent cannot penetrate between film and metal foil . The advantages achievable by the above features as regards a method of fabricating patterned metal foils have already been discussed. The invention relates furthermore to an (electrochemical) cell having a non-aqueous electrolyte which is fabricated by one of the methods or by a device as cited above. 10 The invention will now be detailled on the basis of an embodiment and with respect to the attached drawings. Brief Description of the Drawings The following is a brief description of the drawings in which: Fig. 1 is a plan view of a film which in accordance with the invention is applied to a metal foil to be patterned, with a center section illustrated below; Fig. 2 is a center section of the film just before being applied to a metal foil; Fig. 3 is a center section of the film and metal foil in the composite condition, a solution having been introduced into the holes in the film; Fig. 4 shows the metal foil with the dried pattern after stripping of the film; and Fig. 5 illustrates electrochemical cells fabricated from the patterned metal foil . Brief Description of the Preferred Embodiments Referring now to Fig. 1 there is illustrated in the upper illustration a plan view of a film 1 configured in accordance with an embodiment of the present invention as a film of polyester. The film of polyester 1 comprises holes 2 circular throughout spaced away from each other longitudinally. The lower illustration in Fig. 1 showing a center section of the film 1 likewise makes the through-holes 2 evident configured with vertical sidewalls 7. The remaining Figs . 2 to 5 each show center sections with no true-to-scale representation of the dimensional relationships, more particularly as regards the thicknesses 11 involved. To simplify the illustration the metal foil 3 and the film 1 are depicted the same in thickness. In reality the metal foil 3 has a thickness of approximately 10 to 50μm, preferably 20 μm whilst the film 1 is as thick as the desired level of the solution introduced into the holes 2, namely approximately 50 to 800 μm, more particularly 300 μm. Referring now to Fig. 2 there is illustrated the condition just before the film 1 is applied to a metal foil 3. On the underside of the portions of the film 1 from which small holes have been stamped, the film 1 comprises an adhesive layer 8 distributed homogenously and true to edge. The adhesive 8 sticks excellently to the film 1 and is furthermore configured so that although it can adher to the metal foil 3 where it prevents the ingress of solution fluid between metal foil 3 and film 1 but can be easily removed from the metal foil 3. The film 1 is applied to the metal foil 3 in the direction of the arrows as shown in Fig. 2. Referring now to Fig. 3 there is illustrated a film 1 already sticking to the metal foil 1, a lithium ion solution 4 for the fabrication of lithium ion cells then being introduced into the holes 2. One such solution 4 may contain, for example, N-methyl-2 -pyrrolidone as the solvent. The solution 4 is applied by a simple system, for example a knife system. When the upper surface of the film 1 is treated so that the solution 4 cannot adher thereto, it can be assured by very simple means that only the holes are filled with the solution 4 without any solution 4 remaining of the surface of the film 1. In the condition as shown in Fig. 3 the drying procedure is introduced, for example, by heating the metal foil side 3 by irradiation so that the solvent evaporates from the solution 4. Referring now to Fig. 4 there is illustrated a patterned metal plate 3 after drying of the solvent and stripping of the 12 film, leaving circular patterns 5 from the dried solution on the metal foil 3. Although the patterns 5 are depicted the same in level as the level of the solution 4 as shown in Fig. 3, to make for a better overview, in reality a reduction in level is to be assumed due to evaporation of the solvent. The edge geometry of the patterns 5 is precise since the plastics film easily releases from the patterns as the side edges 7 of the holes 2, too, this being more particularly the case when also the side edges 7 of the holes 2 are treated by irradiation or chemically so that neither the solution 4 nor the dried patterns 5 stick thereto. The metal foil 3 with the deposited patterns 5 can then be machine stamped. Due to patterning in accordance with the invention there is the advantageous possibility of working with stamping knives or molds which, as evident from the cells depicted in Fig. 5, include a free margin 9 of the metal foil 3 in stamping. This free margin 9 of the metal foil 3 can then be made use of as the terminal section, for example, for lithium ion cells in lithium ion batteries. The shape of the margin 9 stamped out free can be freely defined by the design of the stamping tool . By filling the solution into the holes 2 of the film 1 in a single step it can thus be assured in accordance with the invention that a very fast method of fabricating such cells is made available. The film 2 which is stripped from the metal foil 3 after drying of the patterns can be more particularly re-applied to a new metal foil 3 together with the adhesive sticking thereto for the same procedure; this applying more particularly when a so-called "repeat ad-hesive" is employed.

Claims: 13 Claims 1. A method for forming a pattern of a dissolved substance on a thin metal foil, comprising the following steps: applying an adhesive but removable film to said metal foil, holes of a desired shape being provided in said film, filling said holes in said film with a solution incorporating said dissolved substance, drying said solution incorporating said dissolved substance so that said dried substance remains in said holes, and removing said film from said metal foil so that said dried substance remains as a pattern on said metal foil, said film having a thickness substantially corresponding to the level of said solution incorporating said dissolved substance to be introduced into said holes. 2. The method as set forth in claim 1, wherein said holes are fabricated in said film before said film is applied to said metal foil . 3. The method as set forth in claim 2, wherein said holes are stamped from said film. 4. The method as set forth in claim 1, wherein said holes are fabricated in said film after said film has been applied to said metal foil . 5. The method as set forth in claim 4 , wherein said holes are stamped from said film or etched out with an etchant not aggressive to said metal foil . 6. The method as set forth in claim 1, wherein said pattern is formed on one or both sides of said metal foil . 7. The method as set forth in claim 1, wherein said said 14 metal foil is a thin foil of aluminum or copper featuring preferably a thickness of 10 to 50 μm, more particularly 20 μm. 8. The method as set forth in claim 1, wherein a plastics film, more particularly a film of polyester, is used. 9. The method as set forth in claim 1, wherein a film is used having a thickness in the range 50 to 800 μm, more particularly approximately 300 μm. 10. The method as set forth in claim 1, wherein the sidewalls of said holes in said film extend substantially vertically to the main surfaces of said film. 11. The method as set forth in claim 1, wherein the surface of said film facing away from said metal foil is treated more particularly by irradiation and/or chemically so that said solution incorporating said dissolved substance does not adher thereto. 12. The method as set forth in claim 1, wherein an adhesive is applied to said surface of said film facing said metal foil, said adhesive adhering substantially stronger to said film than to said metal foil so that said film more particularly can readher to a metal foil after having been once removed from said metal foil. 13. The method as set forth in claim 1, wherein said adhesive is non-soluble to said solvent of said solution and more particularly adhers to said metal foil at least so strongly that said solution cannot penetrate between film and metal foil. 14. The method as set forth in claim 1, wherein said dissolved substance contains lithium ions. 15 15. The method as set forth in claim 1, wherein said solvent for said dissolved substance contains N-methyl-2 -pyrrolidone. 16. The method as set forth in claim 1, wherein for filling said holes in said film applied to said metal foil an applicator is used which more particularly with the aid of a knife introduces said solution into said holes or equalizes the filling level in said holes. 17. The method as set forth in claim 1, wherein for filling said holes in said film applied to said metal foil an applicator is used which fills said holes with said solution more particularly with the aid of drip application. 18. The method as set forth in claim 1, wherein drying said solution in the case of a single-sided applied film is implemented by means of irradiation heating said metal foil side. 19. The method as set forth in claim 1, wherein drying said solution in the case of a single-sided applied film is implemented by means of hot gas heating said metal foil side, means being provided to prevent excessive overflow of said hot gas to said film side. 20. The method as set forth in claim 1, wherein during drying a relatively weak flow of gas is passed over said film into which said solvent of said solution can evaporate. 21. The method as set forth in claim 1, wherein said metal foil provided with said pattern and said film are separated from each other after drying with the aid of an air knife, said metal foil then being preferably exited via a roll. 22. The method as set forth in claim 1, wherein said metal foil is configured as the negative electrode and said pattern of said dried substance is configured as the positive electrode 16 of a cell having a non-aqueous electrolyte. 23. A method of forming a cell having a non-aqueous electrolyte, comprising the following steps: applying an adhesive but removable film to a metal foil, preferably a thin aluminum or copper foil, holes of a desired shape being required to be fabricated in said film, filling said holes in said film with a solution incorporating lithium ions dissolved in a solvent with N-methyl-2 -pyrrolidone, preferably with the aid of a knife, drying said solution so that the dried residue remains in said holes, and removing said film from said metal foil so that a pattern remains on said metal foil, said film having a thickness substantially corresponding to the level of said solution incorporating said dissolved substance to be applied to said holes. 24. A device for forming a pattern of a dissolved substance on a thin metal foil, comprising: a film in which holes of a desired shape are incorporated, and an adhesive for applying said film to said metal foil, said film having a thickness substantially corresponding to the level of said solution incorporating said dissolved substance to be introduced into said holes. 25. The device as set forth in claim 24, wherein said film is a plastics film, more particularly a film of polyester. 26. The device as set forth in claim 24, wherein a film is used having a thickness in the range 50 to 800 μm, more particularly approximately 300 μm. 17 27. The device as set forth in claim 24, wherein the sidewalls of said holes in said film extend substantially vertically to the main surfaces of said film. 28. The device as set forth in claim 24, wherein the surface of said film facing away from said metal foil is treated more particularly by irradiation and/or chemically so that said solution incorporating said dissolved substance does not adher thereto. 29. The device as set forth in claim 24, wherein said adhesive applied to said surface of said film facing said metal foil adhers substantially stronger to said film than to said metal foil so that said film more particularly can readher to a metal foil after having been once removed from said metal foil. 30. The device as set forth in claim 24, wherein said adhesive is not dissolved by said solvent of said solution and more particularly adhers to said metal foil at least so strongly that said solution cannot penetrate between film and metal foil. 31. A cell having a non-aqueous electrolyte formed by a method as set forth in claim 1.

Inventors: KARTHAUS MICHAEL, KARTHAUS, MICHAEL
Applicants: AIR PROD & CHEM, KARTHAUS MICHAEL, AIR PRODUCTS AND CHEMICALS, INC., KARTHAUS, MICHAEL
Application year: 1998
Main classification: H01M6
IPC codes: B05D1, H01M4, H01M6, H01M10