Process for the preparation of lithium metal and lithium alloy articles

Abstract

The present invention provides a process for the production of lithium metal and lithium alloy shaped articles, which comprises Li(NH3) where n=0-10. 4+n contacting an ammoniacal solution of metallic lithium having the composition: with a metallic or conductive deposition substrate and removing the ammonia by flowing an inert gas over the substrate at a temperature of -100 to 100°C or at a pressure of 0.001 to 700 mbar, so that the remaining lithium is deposited on the deposition substrate and / or is doped or alloyed with lithium.

Description

[Technical Field]

[0001] The present invention relates to a process for producing lithium metal and lithium alloy articles, particularly lithium metallic coated or doped substrates for use as negative electrodes in carbonic cells. [Background technology]

[0002] Liquid ammonia solutions of alkali metals, especially metallic lithium, have been known for a long time (e.g., W.C. Johnson, M.M. Piskur, J.Phys.Chem.37(1933)93-99). When such saturated solutions are cooled below -60°C, phase separation occurs, and a liquid layer with the composition Li(NH3)4, having a bronze metallic luster, so-called Li bronze, forms on top of the pale blue solution (H.Jaffe, Z.Phys.93,1935,741-761). The lithium / ammonia system is described in detail in R.Hoffmann et al., Angew.Chem.Int.Ed.2009,48,8198-8232.

[0003] Ammoniacal solutions of alkali metals, such as lithium, are metastable, 2M+2NH3→2MNH2+H2(M=Li, Na, K, Rb, Cs) (1) It thermally decomposes with the formation of metal amides according to the formula (R. Hoffmann et al., Angew. Chem. Int. Ed. 2009, 48, p. 8202). The decomposition proceeds very slowly in the absence of water and oxygen. However, in the presence of several transition metals (e.g., Fe 2+ ) catalyzes the decomposition reaction that occurs under hydrogen evolution (Hollemann, Wiberg, "Lehrbuch der Anorganischen Chemie", 102nd ed., De Gruyter Verlag Berlin 2007, p. 1296). Studies of the vapor pressure isotherms of compounds with the composition Li2(NH3)8 (dimeric lithium bronzes) reveal that in addition to the decomposition into metal amides according to equation (1), [ka] It is speculated that there may also be a temperature-dependent dissociation equilibrium due to the above (F. Benoit, Bl. Soc. Chim. 33 (1923) 908-917).

[0004] US 4,206,191A describes a method for preparing lithium amide, in which a mixture of lithium metal, a liquid aromatic solvent (toluene), anhydrous liquid ammonia, and a metal catalyst (finely divided metallic cobalt) for increasing the rate of formation of the lithium ammonia compound are reacted with stirring at low temperature (below 0°C to -60°C) to form a lithium ammonia solution, which is then converted to a finely divided dispersion of lithium amide in ammonia by heating to room temperature up to 60°C.

[0005] US2008 / 0237538A1 teaches a method for preparing lithium bronze in the presence of an organic solvent, such as THF, at a temperature below -33°C (the boiling point of NH3 at atmospheric pressure), which is then converted to lithium amide in the presence of a hydrogen acceptor (1,3-diene, or an aryl olefin, such as styrene) by thermal decomposition with hydrogen evolution.

[0006] Furthermore, it is known that lithium bronze can be prepared at room temperature by reacting lithium flakes in anhydrous ether and obtained in pure form by phase separation using a separatory funnel (VI Mel'nikova, KK Pivnitskii, J. Org. Chem. USSR (Engl. Transl.), 6, 2635, 1970).

[0007] EP 1 238 944 A1 describes the preparation of lithium bronzes at room temperature (RT) from a suspension of lithium granules and ammonia gas in hexane.

[0008] Finally, the formation of bronzes from lithium wire and ammonia gas at room temperature in the absence of solvent has been reported (RH Muller, JG Gilick, J. Org. Chem. 43 (1978) 4647-8).

[0009] Lithium batteries currently available on the market function by the principle of intercalation. Graphite materials (corresponding to the formula LiC6) with a maximum capacity of 372 mAh / g are used as the anode. Higher capacities, and therefore energy densities, can be obtained by partially or completely replacing the graphite with alloy materials (e.g., silicon or tin, "alloy anode materials"), or by completely replacing the graphite material with metallic lithium.

[0010] Lithium metal has an extremely high electrochemical capacity of 3862 mAh / g. Because common cathode materials have much lower capacities (only 150–300 mAh / g), this leads to very low areal loadings of less than 10 mAh / g on the Li metal-based anode side in equalized battery cells (i.e., cathode / anode capacity ratios N / P close to 1). This corresponds to Li films with thicknesses of 5–20 μm. However, today's commercially available films, manufactured by extrusion and possibly subsequent rolling processes, are only available in layer thicknesses of 50 μm, with the thinnest being 30 μm. When using 50 μm lithium foil, N / P ratios of 50 or more exist. This unnecessarily high lithium loading reduces energy density (most of the lithium remains electrochemically unused, thus creating inactive "dead" capacity). Furthermore, the unnecessarily high input of metallic lithium represents an avoidable cost factor, which deteriorates the safety characteristics of such battery cells due to their high reactivity (J. Liu et al., Nature Energy 4, 180, 2019; P. Shi et al., Adv. Mater. Technol. 2020, 5, 1900806).

[0011] Therefore, for the production of the thin lithium electrodes required for future lithium metal batteries, it is necessary to resort to inconvenient and costly processes, mostly PVD (plasma vapor deposition) techniques, or processes operating at higher temperatures (e.g., fused lithium deposition on current collectors above 180°C).

[0012] the purpose The present invention aims to provide a low-cost, scalable process that can be performed under mild conditions for producing lithium metal-containing shaped articles (objects / stamps), such as lithium or lithium alloy foils. Summary of the Invention

[0013] The process according to the present invention involves the synthesis of Li(NH3) 4+n The ammoniacal solution of metallic lithium having the composition Bar (hereinafter sometimes referred to as "bar") The ammonia is removed at a pressure of 0.15 MPa, so that the remaining lithium deposits on the deposition substrate and / or it becomes doped or alloyed with lithium.

[0014] The lithium metal and lithium alloy shaped articles (objects / imprints) according to the present invention are prepared by pyrolysis of an ammoniacal solution of pure metallic lithium, preferably pure liquid lithium bronze (Li(NH3)4), in contact with a deposition substrate in the absence of a transition metal-containing catalyst or hydrogen acceptor, at temperatures up to 100°C, preferably up to 60°C, particularly preferably up to 40°C. In this process, ammonia is completely removed via the gas phase in the reverse of the formation reaction, leaving behind elemental Li metal, which is deposited on the surface of the application equipment and the deposition substrate placed therein. The deposition substrate is, in particular, a metallic or merely conductive object, in the form of a powder, granules, foil, thin plate, or a three-dimensional object with a hollow structure, such as a sponge. The deposition of lithium can be purely physical (for example, for metals that cannot be alloyed with lithium, such as copper, iron, or nickel), or it can be physicochemical, reaching the "internal volume" of the material (for example, in the case of sponge-like substances or certain carbon materials, such as graphite and graphene), or it can involve an alloy-forming reaction (for example, in the case of lithium-alloyable deposition substrates made of silicon, germanium, tin, boron, aluminum, magnesium, antimony, etc.).

[0015] Surprisingly, and contrary to conventional principles, it has been found that there is little decomposition to lithium amide when the process conditions described in more detail below are observed, and instead pure metallic lithium is produced.

[0016] Lithium bronze with a Li:NH molar ratio of 1:4 has the lowest ammonia content and therefore requires the least ammonia for production, making this compound the ideal starting material for the process according to the invention: Li(NH3)4→Li 0 +4NH3↑ (3) On the other hand, the composition Li(NH3) 4+n When a blue ammoniacal solution of lithium with ammonia is used, the stoichiometric excess of ammonia (n molar equivalents) is first removed until the most concentrated liquid form—Li bronze—is obtained. As the ammonia content increases, the process efficiency deteriorates and the undesired lithium amide-forming decomposition reaction increases. For these reasons, although dilute liquid ammoniacal solutions of lithium can in principle be used, the use of lithium bronze is preferred for an economical process.

[0017] The process is preferably carried out under reduced pressure, i.e., in the pressure range of 0.001 to 700 mbar. Alternatively, the ammonia can be removed by passing a stream of inert gas over it. This process is generally less cost-effective than the vacuum process because the volatilization gas reduces the ammonia concentration, making ammonia recovery more difficult.

[0018] The lithium source used is commercially available industrial lithium metal, or preferably pure battery or alloy grade. Such metal grades are available, for example, from Sigma-Aldrich-Fluka (SAF). For example, there is a 99% "high sodium" industrial grade, which contains up to 15,000 ppm of metal impurities, with a much higher proportion of sodium. On the other hand, transition metals (especially Fe, Ag, Cu, and Zn) are present only in the low ppm range (1-20 ppm). The total amount of transition metal impurities is typically in the 100 ppm range or less. Furthermore, SAF offers battery-grade lithium, i.e., with a Li content of 99.9% (based on metallic trace elements). Such particularly pure battery-grade lithium contains up to 1500 ppm of other metal impurities, again dominated by sodium.

[0019] For the process according to the invention, metallic lithium is used with a cumulative transition metal impurity content of at most 200 ppm, preferably at most 100 ppm, particularly preferably at most 50 ppm. On the other hand, impurities of main group metals, in particular alkali and alkaline earth metals, as well as metals of the boron and carbon groups (groups 13 and 14), do not in principle interfere with the process. Therefore, they may be present in higher amounts, i.e., in the percentage range.

[0020] A notable advantage of the process according to the invention is that it allows the production of low purity and correspondingly low amounts of transition metal elements. Even lithium metal grades containing high amounts of ammonium can be used after simple pretreatment. In this case, simple filtration, centrifugation, and / or decantation steps precede the thermally induced dissociation process. Because transition metals, especially iron, are generally insoluble in liquid ammonia and do not form ammonia complexes, they remain in solid form and can therefore be separated from the ammoniacal lithium solution or lithium bronze, respectively, by a solid / liquid separation process. This prepurification step can be carried out over the entire liquid range of the lithium-ammonia solution used. For lithium bronze, this ranges from -185°C to approximately 70°C. A temperature range of -40°C to 40°C is preferred. When filters are used, the preferred pore size is a maximum of 10 μm, preferably a maximum of 2 μm, and particularly preferably a maximum of 0.5 μm. The total (cumulative) content of transition metal elements in the lithium ammonia composition purified as described is a maximum of 200 ppm, preferably a maximum of 100 ppm, and particularly preferably a maximum of 50 ppm, based on the lithium content.

[0021] The thermal decomposition or dissociation of lithium ammonia solutions and compounds, particularly the defined lithium bronzes, can occur in the presence of additional organic solvents (e.g., hydrocarbons, ethers, or amines) or without such additives. The presence of such liquid solvents represents a preferred embodiment of the present invention, since in the presence of a solvent that is inert to lithium metal or at least kinetically stable, the process heat released during the ammonia complex formation reaction can be dissipated more easily than in the absence of such additives. In particular, saturated hydrocarbons, such as pentane, hexane, heptane, octane, or common commercial mixtures of such compounds (industrial "petroleum ether," "white oil," "benzine"), are suitable as solvents. Aromatic hydrocarbons can be used to a limited extent, as they may promote undesirable decomposition with lithium amide formation, and aromatic compounds are less preferred. The use of ether compounds, such as diethyl ether, dibutyl ether, methyl tert-butyl ether, tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, glyme, etc., is also possible, but is less preferred than the use of hydrocarbons. This is because lithium metal may react with ether compounds under unfavorable conditions, resulting in the cleavage of C-O bonds. This is a kinetically controlled process, but it is highly exothermic. Accidents have been reported when using lithium / THF systems on an industrial scale. Therefore, although cyclic ethers are in principle feasible, they are particularly inconvenient on an industrial scale. The volume of organic solvent that can be used to produce the defined lithium bronzes is 20-500% of the volume of the lithium bronze.

[0022] It has surprisingly been found that the subsequent use of pure lithium (i.e. lithium metal with a total transition metal content of at most 200 ppm, preferably at most 100 ppm, particularly preferably at most 50 ppm) or lithium / ammonia solutions or lithium bronzes suitably purified by solid / liquid separation during pyrolysis at mild temperatures above 100° C. and preferably under reduced pressure leads to the production of very pure, i.e. low-amide or amide-free, lithium forms. The lithium amide content relative to the total amount of deposited lithium is at most 1% by weight, preferably at most 0.1% by weight.

[0023] Due to the high reactivity of metallic lithium and the Li / NH3 mixture, all process steps are carried out under an inert gas atmosphere (preferably argon, helium) or under vacuum conditions.

[0024] The process according to the invention is particularly suitable for the direct production of thin lithium layers on current conductor foils made of copper, iron, nickel or certain carbon forms, such as carbon nanotube foils (CNT foils, CNT = carbon nanotubes) or graphene-based foils. Some commercially available forms of substrates are poorly wettable by lithium and it may be necessary to pretreat them. This pretreatment can be carried out, for example, by washing with a grease-soluble organic solvent to remove any grease that may be present. This involves removing the base film, cleaning with running water and / or mechanical cleaning processes, such as polishing or polishing. In the case of copper, optimal results are achieved by special lithiation processes, such as the application of a defined oxide layer by thermal pretreatment under oxidizing conditions, as described, for example, in DE 10 2017 208 218 A1.

[0025] When a liquid ammoniacal solution of lithium, or in particular lithium bronze, comes into contact with a metallic substrate M that can alloy with lithium, it surprisingly produces the corresponding alloy Li x M yHowever, under mild conditions, ammonia is released and the resulting alloy body is formed. To form such an alloy body, the desired metal M, preferably in powder or granular form, is added to lithium bronze. The added particles expand to form the alloy. After distillation of the ammonia, a lithium-containing alloy material is obtained. Main group elements that can be alloyed with lithium, i.e., Be, Mg, Ca, Sr, Ba, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, or any mixture thereof, are particularly suitable for this alloy formation process. Alloyable subgroup metals, such as Zn, Ti, or Zr, can also be used, although it may be difficult to avoid undesirable amide formation.

[0026] The alloy powder thus produced can be applied to a current conductor foil by the known purely mechanical pressing process (calendering) or by a dispersed binder process ("slurry coating") and thus processed into a negative electrode strip.

[0027] Freshly deposited metallic lithium from a lithium-NH3 solution under vacuum or in an inert gas atmosphere is highly reactive to air and moisture. To ensure its safe further processing in industrial applications, such as the construction of battery cells, passivation of the metal surface, i.e., the addition of a thin protective layer, is a significant additional process step. Such processes involve contact with a gaseous or liquid substance that forms stable polymers and / or salts upon contact with lithium. Such processes are described, for example, in WO 2011 / 073324 A1.

[0028] The ammonia released during ammonia complex dissociation can be liquefied and reused in the plant, or preferably used directly in gaseous form to form new lithium bronze, thus making it possible to reuse the ammonia without the energetically inconvenient liquefaction step.

[0029] Lithium metal and lithium alloy castings are used for the manufacture of negative electrodes of lithium batteries, as metallic materials (preferably Li-Mg or Li-Al alloys), for getter purposes or in chemical synthesis.

[0030] The embodiments of the present invention are summarized below:

[0031] · A process wherein the cumulative transition metal content of such solution is no more than a maximum of 200 ppm based on the lithium contained therein.

[0032] · A process wherein the total (cumulative) transition metal content of such solution is no more than 100 ppm based on the lithium contained therein.

[0033] The process wherein the ammonia is removed at a temperature in the range of -20 to 80°C.

[0034] A process wherein the separation of ammonia is carried out with the addition of an organic solvent selected from the group consisting of hydrocarbons, ethers or amines, and in the case of the production of lithium bronze Li(NH3)4, the volume of the organic solvent is 20-500% of the volume of the lithium bronze.

[0035] The process wherein the organic solvent is a saturated hydrocarbon.

[0036] a process in which a metallic or merely electrically conductive object having an impression such as a powder, granules, foil, thin plate or a three-dimensional object with a hollow structure is used as the deposition substrate, and the deposition of lithium is carried out physicochemically on a non-lithium-alloyable metal selected from the group consisting of copper, iron, nickel or carbon-based materials and / or as an alloy formation process in the case of a lithium-alloyable deposition substrate selected from the group consisting of silicon, germanium, tin, lead, boron, aluminum, magnesium or antimony.

[0037] A process wherein the carbon-based material used is based on carbon nanotubes or graphene.

[0038] The process wherein the lithium-alloyable deposition substrate comprises powders or granules of alloying elements having an average particle size range of 0.1 mm to 5 cm.

[0039] The ammoniacal solution of lithium metal is pre-purified by solid / liquid separation at a temperature between -185°C and 70°C, preferably between -40°C and 40°C.

[0040] · A process in which filters with pore sizes in the range of 0.1-10 μm are used.

[0041] The process wherein lithium bronze Li(NH3)4 is used.

[0042] A process in which the surface passivation of the formed lithium coating or alloyed body is carried out by contacting it with a gaseous coating selected from the group consisting of N2, CO2, CO, O2, N2O, NO, NO2, HF, F2, PF3, PF5, POF3, or with a liquid coating selected from carbonate esters, lithium chelate borate solutions in organic solvents, organic sulfur compounds, N-containing organic compounds, phosphoric acid, organic phosphorus-containing compounds, fluorine-containing organic and inorganic compounds, partially fluorinated hydrocarbons, BF3, LiPF6, LiBF4 or silicon-containing compounds.

[0043] The process, wherein the organic solvent is selected from the group consisting of an oxygen-containing heterocycle, a carbonate, a nitrile, a carboxylic acid ester, or a ketone, and the organic sulfur compound is selected from the group consisting of a sulfite, a sulfone, or a sultone.

[0044] A process in which a coating of metallic lithium on a current collector foil made of Cu, Fe, Ni or a carbon-based material is produced as the lithium metal molding, and the thickness of the applied lithium layer is in the range of 2 to 40 μm, preferably 5 to 20 μm. [Example]

[0045] Example 1: Preparation of lithium bronze from pure (transition metal-poor) lithium metal In a 1 / 2 L inert (i.e., dried and filled with Ar) double-jacketed glass reactor equipped with a mechanical stirrer and a carbon dioxide snow cooler, 200 mL of technical-grade hexane containing 1.5 g (215 mmol) of Li granules (3 mm diameter, 0.45% Na, 26 ppm Fe, 2 ppm Zn, and less than 10 ppm Cu) was placed at room temperature. Then, 22 L (920 mmol) of ammonia gas was introduced into the reactor within 3 hours with vigorous stirring. After a few minutes, the reaction began, as indicated by the release of heat of solvation and the discoloration of the lithium surface from silvery white to bronze. The reaction heat was dissipated by jacket cooling, maintaining the temperature of the reaction mixture in the range of 18–30 °C.

[0046] After all the lithium had liquefied and been converted to lithium bronze, the ammonia injection was terminated, the two liquid phases were separated by decantation, and the upper, lighter phase, i.e., lithium bronze, was filled into an inertized glass bottle with a septum closure. Yield: 15.8 g (98% of theoretical value of bronze liquid)

[0047] Example 2: Purification of lithium bronze Lithium metal granules with an iron content of 210 ppm were used in a manner similar to that described in Example 1. After the reaction to give Li(NH3)4 was completed, the bronze was separated by decantation and filtered through a membrane filter with a pore size of 0.45 μm. The filtered product had the following analysis: Li=13.2mmol / g Fe=2 ppm, equivalent to 0.04 μmol / g This indicates that 90% of the iron content introduced by the lithium source could be removed by the filtration process.

[0048] Example 3: Thermal dissociation of pure Li-bronze under vacuum To a 50 mL inertized glass Schlenk flask equipped with a glass jacket and stirrer core was added 3.63 g (48.4 mmol) of pure lithium bronze from Example 1. With good stirring, a vacuum was applied to the flask using a diaphragm pump. The liquid began to boil and splash. A silvery-white metallic film formed on the glass walls. After applying a vacuum of 0.1 mbar for 1 hour, the vacuum was finally released and replaced with argon. The mass of the non-evaporable residue was determined by differential gravitation. Result: 0.31g (44.7mol of lithium, equivalent to 92% of the theoretical value)

[0049] Example 4: Deposition of lithium metal films on iron sheets A stainless steel sheet measuring 2 × 4 × 0.3 cm was mechanically cleaned with fine abrasive paper and degreased by rinsing first with acetone and then with hexane. The sheet was then immersed in lithium bronze at ambient temperature for approximately 10 seconds. The wetted sheet was placed in an air-excluded desiccator, and the ammonia was removed, first at 500 mbar and then at full oil pump vacuum. This resulted in an iron sheet partially coated with a thin, silvery-white lithium film. Because the steel surface was not completely lithiated, some areas were not wetted by the lithium bronze and therefore not coated with lithium.

[0050] Example 5: Preparation of lithium / aluminum alloy Into an inert 25 mL Schlenk flask with a glass-enclosed magnetic stirrer core was placed 2.9 g (39 mmol) of pure lithium bronze from Example 1 and cooled to 0° C. using an ice bath. Then, 0.61 g of aluminum grid was added and stirred for 1 h at 0° C. After this period, the mixture was warmed to room temperature and the ammonia was removed under vacuum (final 0.02 mbar). Yield: 0.86 g of alloy (98% of theoretical) with a silvery appearance

Claims

1. 1. A process for the production of lithium metal and lithium alloy shaped articles, comprising: Li(NH 3 ) 4 A solution of metallic lithium containing Li(NH) is contacted with a metallic or conductive deposition substrate and heated at a temperature of -20 to 80°C under a flow of inert gas or at a pressure of 0.001 to 700 mbar. 3 ) 4 and removing ammonia from Li(NH 3 ) 4 Lithium from the deposition substrate is deposited on the deposition substrate and / or the deposition substrate is doped or alloyed with lithium. The process, characterized by:

2. The cumulative transition metal content of the solution is Li(NH 3 ) 4 Only 200 ppm of lithium in the The process according to claim 1, characterized in that

3. The cumulative transition metal content of the solution is Li(NH 3 ) 4 Up to only 100 ppm based on lithium from The process according to claim 2, characterized in that

4. The removal of the ammonia is carried out with the addition of an organic solvent selected from the group consisting of hydrocarbons, ethers and amines, to give lithium bronze Li(NH 3 ) 4 In the case of preparing the lithium bronze, the volume of the organic solvent is 20 to 500% of the volume of the lithium bronze. The process according to claims 1 to 3, characterized in that

5. 5. The process of claim 4, wherein the organic solvent is a saturated hydrocarbon.

6. A metallic or merely electrically conductive object in the form of a powder, granules, foil, thin plate or a three-dimensional object with a hollow structure is used as the deposition substrate, said depositing of lithium physicochemically performed on a non-lithium alloyable metal selected from the group consisting of copper, iron, nickel and carbon-based materials; and / or and wherein the alloying process is carried out in the case of a lithium-alloyable deposition substrate selected from the group consisting of silicon, germanium, tin, lead, boron, aluminum, magnesium, and antimony. The process according to claims 1 to 5, characterized in that

7. The carbon-based material used is based on carbon nanotubes or graphene. The method according to claim 6, characterized in that

8. The lithium-alloyable deposition substrate is a powder or granule of alloying elements having an average particle size ranging from 0.1 mm to 5 cm.

7. The process according to claim 6, characterized in that

9. The pre-purification of the lithium metal ammonia solution is carried out by solid / liquid separation in the temperature range of -185°C to 70°C. The process according to claims 1 to 8, characterized in that

10. 10. The process according to claim 9, characterized in that a filter is used with a pore size in the range of 0.1 to 10 μm.

11. Surface passivation of lithium-coated or alloyed moldings Those, N 2 , CO 2 , CO, O 2 , N 2 O, NO, NO 2 , H.F., F. 2 , P.F. 3 , P.F. 5 , POF 3 a gas or liquid coating selected from the group consisting of: Carbonate esters, lithium chelate borate solutions in organic solvents, organic sulfur compounds, N-containing organic compounds, phosphoric acid, organic phosphorus-containing compounds, fluorine-containing organic and inorganic compounds, partially fluorinated hydrocarbons, BF 3 , LiPF 6 , LiBF 4 and a liquid coating agent selected from the group consisting of silicon-containing compounds. to come into contact with The process according to claims 1 to 10, characterized in that it is carried out by

12. The organic solvent is selected from the group consisting of an oxygen-containing heterocycle, a carbonate, a nitrile, a carboxylic acid ester, and a ketone, and the organic sulfur compound is selected from the group consisting of a sulfite, a sulfone, and a sultone. The process according to claim 11, characterized in that

13. The lithium metal molding is characterized by being produced by comprising a coating layer of metallic lithium on a current collector foil made of Cu, Fe, Ni or a carbon-based material; The thickness of the coating layer is in the range of 2 to 40 μm. The process according to claims 1 to 12.

Images