WO2011109878A1

WO2011109878A1 - Liquid metal salts

Info

Publication number: WO2011109878A1
Application number: PCT/BE2011/000010
Authority: WO
Inventors: Koen Binnemans; Niel Richard Brooks; Jan Fransaer; Stijn Schaltin
Original assignee: Katholieke Universiteit Leuven
Priority date: 2010-03-12
Filing date: 2011-03-14
Publication date: 2011-09-15
Also published as: GB201004092D0; TW201137185A

Abstract

A liquid metal salt in which a metal (M) ion is surrounded by neutral ligands (L), or by a combination of neutral ligands (L) and negatively charged ligands (Y) such that the total negative charge of the total number of negatively charged ligands (Y) is smaller than the oxidation state of the metal ion so that the metal complex has an overall positive charge, with at least one counter anion (X), wherein M is a metal selected from the group consisting of copper, zinc, silver, gold, platinum, cobalt, nickel, tungsten, molybdenum and aluminium.; L is a neutral ligand and is selected from the group consisting of aceto- nitrile, propionitrile, butyronitrile, isobutyronitrile, acrylonitrile, 2-hydroxycyano-ethane, phenylacetonitrile, benzonitrile benzylnitrile, DMF, acetamide, N,N-dimethylacetamide, formamide, N-methylformamide, N-methylacetamide, DMSO, dimethylsulfone, hexa- methylphosphoramide, N-methylpyrrolidone, pyridine, morpholine, THF, diethyl ether, dimethoxyethane, bis(2-methoxyethyl) ether, triglyme, tetraglyme, pentaglyme, hexa- glyme, 1,4-dioxane, methanol, ethanol, propanol, butanol, ethyleneglycol, polyethylene- glycol, water, trialkylphosphine oxides, triaryl-phosphine oxides, trialkylphosphate, pyrazole, 3-alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethylpyrazole, imidazole, 1-alkyl- imidazoles, 1,2-dimethylimidazole, 2-imidazolid-inone, thiabendazole, ammonia, tetramethylenesulfoxide, urea, Ν,Ν,Ν',Ν'-tetramethylurea, thiourea, lactams, hydroxypyridines, 2-pyridone, pyridine-N-oxide, picoline-N-oxide, 2,6-lutidine, 2,6- lutidine N-oxide, pyrazine, pyrazine-N-oxide, 1,4-dithiane monosulfoxide, 2,2'-bipyridine, 1,10-phenanthroline, 2,6,2', 2"-terpyridine, ethylenediamine, diethyl enetriamine, 1,2,3- triaminopropane, cyclam, crown ethers and thiacrown ethers; Y is selected from the group consisting of chloride, bromide, iodide, thiocyanate, formate, acetate, trifluoroacetate, propionate, butyrate, pentanoate, hexanoate, benzoate, glycolate, heptafluorobutanate, alkylsulfate, octylsulfate, dodecylsulfate, triflate, methanesulfonate, nitrate, dicyanamide, tricyano-methanide, bis(trifluoromethylsulfonyl)-imide or bis(perfluoroalkylsulfonyl)- imide, dimethylphosphate, diethylphosphate, dialkylphosphate, saccharinate, acesulfamate and tosylate; and X is a counter anion selected from the group consisting of hexafluoro- phosphate, tetrafluoroborate, bis(trifluoromethylsulfonyl)imide (bistriflimide), bis(tri- fluoroalkylsulfonyl)imide, dicyanamide, triflate, methanesulfonate and trifluoroacetate; and uses thereof in an electrodeposition process, for electrodeposition of a metal M, for battery application; for electrochromic device, in fuel cells, for electropolishing and for electroless deposition of a metal M.

Description

LIQUID METAL SALTS

FIELD OF THE INVENTION:

The present invention relates to novel low-melting metal salts, their methods of preparation and to their use as electrolytes in electrochemical devices such as batteries, photovoltaic cells, electrochromic devices, fuel cells, or as electrolytes for

electrodeposition or electropolishing. Using this invention, electrodeposition of metals can be achieved at very high current densities. BACKGROUND OF THE INVENTION:

Liquid metal salts are solvents that consist entirely of ions [1-3]. Typically they are low melting organic salts that are liquid at temperatures below 100 °C. Due to their intrinsic ionic conductivity and wide electrochemical window, liquid metal salts are interesting non-aqueous electrolytes for the electrodeposition of reactive metals which cannot be deposited from aqueous solutions [4-7]. The most convincing results have been obtained for the electrodeposition of aluminium, although the electrodeposition of other metals like titanium, magnesium and the rare-earth metals have been investigated as well [8-11]. Liquid metal salts also offer advantages to the electrodeposition of metals which can be deposited from water, such as zinc, copper, silver or gold, because liquid metal salts not only allow to deposit alloys of these metals with compositions not obtainable from aqueous solvents, but these ionic solvents also allow the use of electrodes made of materials that are passivated in the presence of water. Typical examples are titanium or tantalum. The wide electrochemical window of liquid metal salts is an advantage if one wants to electrodeposit at very large overpotentials to achieve a high nucleation density. Another advantage of electroplating in liquid metal salts is that no hydrogen evolution is possible so that hydrogen embrittlement of the coatings is avoided and therefore the coatings have better mechanical properties. Liquid metal salts are interesting electrolytes not only for the electroplating of metals but also as electrolytes for batteries.

DE 3328635 A discloses electrochemical storage cell or battery comprising at least one positive and at least one negative electrode, and an electrolyte containing an ionic or ionisable compound and possibly an organic electrolyte solvent, the active electrode material of both the positive and the negative electrode is made of electrochemically oxidisable and/or reducible polymers having an electrical conductivity of more than 10 ohm^cm^"1, at least in the charged state of the cell or of the battery, the ionic or ionisable compound in the electrolyte being a compound of the general formula (I) [X A X]⁺ Y^", wherin X is a monomeric, organic C-H acid compound containing at least one heteroatom or a dimer thereof obtained by oxidative, dehydrogenating coupling of such a C-H acidic compound, A is a hydrogen, alkaline metal or ammonium cation and X is a suitable anion.

DD 290889A discloses the preparation of tetrakisacetonitrile lithium salts of hexafluoro arsenic or phosphorus acids.

In 2001 Raab et al., in Journal of Molecular Catalysis A: Chemical, volume 175, pages 51-63 describes copper halides complexed with three or four N-methylimidazole ligands.

WO 2005/065398A discloses an ionic compound comprising a cation which is a complex of a neutral organic ligand with a metal ion and an anion which is a conjugate anion of the metal ion.

In 2006 Pedireddi et al. in Macromolecular Symposia, volume 241, pages 83-87, reported that a reaction carried out between Ni(N0₃)₂.6H₂0 yields a complex

[Ni(bpy')₂N0₃]⁺ (N0₃)^"'.

In 2006 Huang et al., in Journal of the Electrochemical Society, volume 153, pages J9-J13, reported room temperature ionic liquids with Ag and Zn complexed with alkyl amines and Tf₂N^' anions and conductivities at 24°C of up to 12.30 mS/cm and a viscosity at 23 °C of 36.52 mPa.s.for [Ag(I)(n-propylamine)₂]⁺ [Tf₂N]^" .

In 2009 Rach et al. in Chemical Reviews, volume 109, pages 2061 -2080 reported nitrile ligated transitional metal complexes with weakly coordinating counteranions.

In 2010 Schaltin et al. in ECS Transactions, volume 25, pages 119-128, available on the internet on March 5, 2010, reported on direct Cu-on Ta electroplating from liquid metal salts in high vacuum using Cu(Tf₂N) as the liquid metal salt. Here Cu(Tf₂N) is dissolved in the ionic liquids in the ionic liquids l-ethyl-3-methylimidazolium chloride ([C2mim]Cl), N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][Tf2N]), or in mixtures of the latter ionic liquid with N-butyl-N-methylpyrrolidinium chloride

([BMP]C1). The limited solubility of most metal salts in ionic liquids hampers the mass transport of the metal ions to the cathode where electrroreduction takes place.

However, there are serious technological drawbacks related to the use of liquid metal salts as electrolytes for electrochemical devices or for electrochemical applications , which prevents their application in industrial processes. First of all, the mass transport in liquid metal salts is slow due to their high viscosity. Secondly, many metals salts are only sparingly soluble in liquid metal salts. As a result, the current densities that can be obtained are often too low for industrial applications. Different solutions have been proposed to solve these problems, but neither of them give satisfying results. The viscosity of an liquid metal salt can be reduced by addition of cosolvents such as toluene, but this approach results in an even further reduction of the solubility of metal salts in the electrolyte and moreover there is a decrease in electric conductivity. The viscosity of liquid metal salt solutions can also be reduced by heating the solution, but this is at the expense of a higher energy consumption in the electrodeposition process. Moreover, for photovoltaic, electrochromic and battery applications it is often impractical to increase the temperature in order to increase the mass transport. Higher concentrations of metal ions in liquid metal salts can be achieved by designing liquid metal salts which have a metal complex as part of their composition. Most liquid metal salts of this type contain anionic metal complexes. The concentration of anionic complexes close to the cathode is potential-dependent and at the very negative potentials required for the electrodeposition of reactive metals the metal concentration can be too low to initiate nucleation of the metal at the cathode. For instance, aluminium cannot be electrodeposited from Lewis basic chloroaluminate liquid metal salts in which aluminium is present as tetrachloroaluminate(III) ions [8]. Neither is it possible to deposit cobalt from liquid metal salts containing the tetracobaltate(II) anion [12]. Examples of liquid metal salts with metals as part of the cation are very rare. Iida et al. prepared the room temperature liquid metal salts bis(N-2-ethylhexylethylenediamine)silver(I) nitrate, and bis(N-hexylethylenediamine)silver(I) hexafluorophosphate [13]. Compounds with the [Cu(CH₃CN)₄]⁺ cation and BF₄ ^", PF₆ ^", C10₄ ^", or OTf anions have been described in the literature and they are useful precursors for the synthesis of other copper(I) coordination compounds or as catalysts [14-17]. In general, these compounds have very high melting points or even decompose without melting.

US 7,196,221 describes the use of mixtures of hydrated metal salts and choline chloride as electrolytes for the deposition of chromium, cobalt and silver. It is evident that the use of hydrated salts is restricted to the electrodeposition of metals of the so-called "aqueous group", i.e. metals that can be deposited from aqueous solutions [18]. US 7,423,164 describes ionic compounds consisting of a cation which is the complex of a neutral organic ligand with a metal ion and an anion which is the conjugate anion of the metal ion [19]. Here the organic ligand is an alkylamine or a crown ether. Huang et al. applied these electrolytes for the electrodeposition of silver and zinc [20].

Therefore, it is clear that there is still a need for further alternative ionic compounds with low melting points, which would overcome the current drawbacks of limited solubility of metal salts in liquid metal salts, slow mass transport and low current densities in electrodeposition processes.

SUMMARY OF THE INVENTION

The current invention provides a solution to the drawbacks of slow mass transport, low current densities and limited solubility of metal salts in liquid metal salts by using liquid metal salts with a metal-containing cationic core. By making the metal part of the liquid metal salt, the highest possible metal content of the electrolyte bath is achieved. By making the metal to be deposited part of the cation, the electric field in the electrolyte will enhance the mass transport during metal deposition due to electromigration. Because the cathodic decomposition reaction of the liquid metal salt is the reduction of the metal ion to the metallic state, very high current densities can be obtained. The liquid metal salts with metal-containing cations can be described as liquid metal salts '.

The design of liquid metal salts with metal in the cation rather than in the anion - since electrodeposition takes place at the negatively charges cathode, which themselves are capable of efficiently electrodepositing metal - is not straightforward, because they need to combine the following properties: (1) low melting point, (2) sufficient thermal stability, (3) electroactive. You can easily make low-melting compounds, but these are often not electroactive and do not allow to obtain metals by electrodeposition. Alternatively the ligand is so easily lost upon heating that a solid metal salt results rather than a molten complex. The liquid metal salts of the present invention surprisingly exhibit improved stability and increased mass transport over the ionic liquids with Ag⁺ and Zn²⁺ complexed with alkyl amines and Tf₂N^" anion reported in 2006 by Huang et al., in Journal of the Electrochemical Society, volume 153, pages J9-J13.

In order to obtain liquid metal salts, the metal (M) ion is surrounded by neutral ligands (L), or by a combination of neutral ligands (L) and negatively charged ligands (Y). In the case of a combination of neutral ligands and negatively charged ligands, the total negative charge of the total number of negatively charged ligands (L) has to be smaller than the oxidation state of the metal ion so that the metal complex has an overall positive charge. Preferably, the ligands (L and Y, if present) have to be weakly coordinating in order to facilitate their removal during the electroreduction to the metallic state. The counter anions (X) have to be weakly coordinating in order to reduce the melting point and to prevent their direct binding to the metal ion. During the electrodeposition process, the liquid metal salts act both as electrolyte and as metal source. At the cathode, the metal ion is reduced to the metallic state. The neutral ligands, the negative ligands and the counter anions do not react at the cathode. The anodic reaction is preferably the dissolution of a sacrificial anode.

A first aspect of the present invention relates to a liquid metal salt in which a metal

(M) ion is surrounded by neutral ligands (L), or by a combination of neutral ligands (L) and negatively charged ligands (Y) such that the total negative charge of the total number of negatively charged ligands (Y) is smaller than the oxidation state of the metal ion so that the metal complex has an overall positive charge, with counter anions (X), wherein M is a metal selected from the group consisting of copper, zinc, cadmium, nickel, cobalt, manganese, iron, chromium, tin, lead, bismuth, antimony, selenium, tellurium, thallium, silver, gold, platinum, palladium, rhodium, ruthenium, iridium, osmium, rhenium, aluminium, gallium, indium, silicium, germanium, beryllium, magnesium,

titanium,zirconium, hafnium, molybdenum, tungsten, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, thorium, uranium, plutonium and lithium; L is a neutral ligand and is selected from the group consisting of acetonitrile (AN), propionitrile, butyronitrile, isobutyronitrile, acrylonitrile, 2- hydroxycyanoethane, phenylacetonitrile, benzonitrile benzylnitrile, dimethylformamide (DMF), acetamide, Ν,Ν-dimethylacetamide, formamide, N-methylformamide, N- methylacetamide, dimethylsulfoxide (DMSO), dimethylsulfone (DMSO₂),

hexamethylphosphoramide (HMPA), N-methylpyrrolidone (NMP), pyridine (Py), morpholine, tetrahydrofuran (THF), diethyl ether, dimethoxyethane (DME, monoglyme), bis(2-methoxyethyl) ether (diglyme), triglyme, tetraglyme, pentaglyme, hexaglyme, 1,4- dioxane, methanol, ethanol, propanol, butanol, ethyleneglycol, polyethyleneglycol, water, trialkylphosphine oxides, triarylphosphine oxides, trialkylphosphate, pyrazole, 3- alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethylpyrazole, imidazole, 1-alkylimidazoles, 1,2- dimethylimidazole, 2-imidazolidinone, thiabendazole, ammonia, tetramethylenesulfoxide (TMSO), urea, Ν,Ν,Ν',Ν'-tetramethylurea (TMU), thiourea, lactams, hydroxypyridines, 2- pyridone, pyridine-N-oxide, picoline-N-oxide, 2,6-lutidine, 2,6-lutidine N-oxide, pyrazine, pyrazine-N-oxide, 1,4-dithiane monosulfoxide, 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), 2,6,2 ',2"-terpyridine (terpy), ethylenediamine, diethylenetriamine, 1 ,2,3- triaminopropane, cyclam, crown ethers and thiacrown ethers; Y is selected from the group consisting of chloride, bromide, iodide, thiocyanate, formate, acetate, trifluoroacetate, propionate, butyrate, pentanoate, hexanoate, benzoate, glycolate, heptafluorobutanate, alkylsulfate, octylsulfate, dodecylsulfate, triflate, methanesulfonate, nitrate, dicyanamide, tricyanomethanide, bis(trifluoromethylsulfonyl)imide (bistriflimide) or

bis(perfluoroalkylsulfonyl)imide, dimethylphosphate, diethylphosphate, dialkylphosphate, saccharinate, acesulfamate and tosylate; and X is a counter anion selected from the group consisting of hexafluorophosphate, tetrafluoroborate, chloride, bromide, iodide acetate, trifluoroacetate, triflate, methanesulfonate, nitrate, perchlorate, dicyanamide,

tricyanomethanide, bis(trifluoroalkylsulfonyl)imide, bis(trifluoromethylsulfonyl)imide (bistriflimide), bis(perfluoroalkylsulfonyl)imide, alkyltrifluoroborate, dimethylphosphate, diethylphosphate, dialkylphosphate tetrachloroaluminate, tetrachlorogallate,

tetrachloroindate, tetrachloroferrate, hexachloroarsenate, hexachlorantimonate(VI), hexachlorotantalate and hexachloroniobate.

The general formula of a metal-containing liquid metal salt, also being referred to as a liquid metal salt is MLYX, where M is a metal ion, L is a neutral ligand, Y is a negatively charged ligand and X is a counter anion. In some cases, e.g. when M has a charge of +1, Y is not present and the general formula of such liquid metal salt is MLX.

A particular embodiment of the first aspect of the present invention relates to novel liquid metal salts also referred to as metal-containing liquid metal salts which are represented as liquid metal salts of the formula (A):

[ML]X

wherein: [ML] is a cation complex

wherein M is a metal ion selected from the group consisting of copper, zinc, cadmium, nickel, cobalt, manganese, iron, chromium, tin, lead, bismuth, antimony, selenium, tellurium, thallium, silver, gold, platinum, palladium, rhodium, ruthenium, iridium, osmium, rhenium, aluminium, gallium, indium, silicium, germanium, beryllium, magnesium, titanium,zirconium, hafnium, molybdenum, tungsten, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, thorium, uranium, plutonium and lithium; L is a neutral ligand and is selected from the group consisting of acetonitrile (AN), propionitrile, butyronitrile, isobutyronitrile, acrylonitrile, 2-hydroxycyanoethane, phenylacetonitrile, benzonitrile benzylnitrile, dimethylformamide (DMF), acetamide, Ν,Ν-dimethylacetamide, formamide, N-methylformamide, N- methylacetamide, dimethylsulfoxide (DMSO), dimethylsulfone (DMS0₂),

hexamethylphosphoramide (HMPA), N-methylpyrrolidone (NMP), pyridine (Py), morpholine, tetrahydrofuran (THF), diethyl ether, dimethoxyethane (DME, monoglyme), bis(2-methoxyethyl) ether (diglyme), triglyme, tetraglyme, pentaglyme, hexaglyme, 1,4- dioxane, methanol, ethanol, propanol, butanol, ethyleneglycol, polyethyleneglycol, water, trialkylphosphine oxides, triarylphosphine oxides, trialkylphosphate, pyrazole, 3- alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethylpyrazole, imidazole, 1-alkylimidazoles, 1,2- dimethylimidazole, 2-imidazolidinone, thiabendazole, ammonia, alkylamines,

tetramethylenesulfoxide (TMSO), urea, Ν,Ν,Ν',Ν'-tetramethylurea (TMU), thiourea, lactams, hydroxypyridines, 2-pyridone, pyridine-N-oxide, picoline-N-oxide, 2,6-lutidine, 2,6-lutidine N-oxide, pyrazine, pyrazine-N-oxide, 1,4-dithiane monosulfoxide, 2,2'- bipyridine (bipy), 1,10-phenanthroline (phen), 2,6,2 ',2"-terpyridine (terpy),

ethylenediamine, diethylenetriamine, 1,2,3-triaminopropane, cyclam, crown ethers and thiacrown ethers; and X is a counter anion selected from the group consisting of hexafluorophosphate, tetrafluoroborate, chloride, bromide, iodide acetate, trifluoroac.etate, triflate, methanesulfonate, nitrate, perchlorate, dicyanamide, tricyanomethanide, bis(trifluoroalkylsulfonyl)imide, bis(trifluoromethylsulfonyl)imide (bistriflimide), bis(perfluoroalkylsulfonyl)imide, alkyltrifluoroborate, dimethylphosphate,

diethylphosphate, dialkylphosphate tetrachloroaluminate, tetrachlorogallate,

In a particular embodiment, the liquid metal salts of the present invention are further comprising a negatively charged ligand Y, said liquid metal salt represented by the formula (B):

[MLY]X

wherein [MLY] is a cation complex and X is a counter anion

wherein M is a metal ion selected from the group consisting of is copper, zinc, cadmium, nickel, cobalt, manganese, iron, chromium, tin, lead, bismuth, antimony, selenium, tellurium, thallium, silver, gold, platinum, palladium, rhodium, ruthenium, iridium, osmium, rhenium, aluminium, gallium, indium, silicium, germanium, beryllium, magnesium, titanium,zirconium, hafnium, molybdenum, tungsten, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, thorium, uranium, plutonium and lithium; L is a neutral ligand and is selected from the group consisting of acetonitrile (AN), propionitrile, butyronitrile, isobutyronitrile, acrylonitrile, 2-hydroxycyanoethane, phenylacetonitrile, benzonitrile benzylnitrile, dimethylformamide (DMF), acetamide, Ν,Ν-dimethylacetamide, formamide, N-methylformamide, N- methylacetamide, dimethylsulfoxide (DMSO), dimethylsulfone (DMS0₂),

ethylenediamine, diethylenetriamine, 1,2,3-triaminopropane, cyclam, crown ethers and thiacrown ethers; Y is selected from the group consisting of chloride, bromide, iodide, thiocyanate, formate, acetate, trifluoroacetate, propionate, butyrate, pentanoate, hexanoate, benzoate, glycolate, heptafluorobutanate, alkylsulfate, octylsulfate, dodecylsulfate, triflate, methanesulfonate, nitrate, dicyanamide, tricyanomethanide,

bis(trifluoromethylsulfonyl)imide (bistriflimide) or bis(perfluoroalkylsulfonyl)imide, dimethylphosphate, diethylphosphate, dialkylphosphate, saccharinate, acesulfamate and tosylate; and X is a counter anion selected from the group consisting of

hexafluorophosphate, tetrafluoroborate, chloride, bromide, iodide acetate, trifluoroacetate, triflate, methanesulfonate, nitrate, perchlorate, dicyanamide, tricyanomethanide, bis(trifluoroalkylsulfonyl)imide, bis(trifluoromethylsulfonyl)imide (bistriflimide), bis(perfluoralkylsulfonyl)imide, , methyltrifluoroborate, alkyltrifluoroborate,

diethylphosphate, dialkylphosphate, tetrachloroaluminate, tetrachlorogallate,

A second aspect of the present invention relates to the use of the liquid metal salts described herein in an electrodeposition process.

A third aspect of the present invention relates to a process for the preparation of the liquid metal salts described herein, said process can be any of the methods for preparation of liquid metal salts as described in the detailed description of this invention. A fourth aspect of the present invention relates to the use of the liquid metal salts described herein for battery applications.

A fifth aspect of the present invention relates to the use of the liquid metal salts described herein in electrochromic devices.

A sixth aspect of the present invention relates to the use of the liquid metal salts described herein in fuel cells.

A seventh aspect of the present invention relates to the use of the liquid metal salts described herein for electropolishing applications.

An eighth aspect of the present invention relates to the use of the liquid metal salts described herein for electroless deposition of a metal M. In a particular embodiment, said metal M is selected from the group consisting of copper, zinc, silver, gold, platinum, cobalt, nickel, tungsten, molybdenum, and aluminium, and in a more particular

embodiment, said metal M is copper or aluminium.

Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 : Cyclic voltammogram of the [Cu(CH₃CN)₄][Tf₂N] electrolyte at a platinum

working electrode at 90°C. The CV has been corrected for iR drop in-situ (by current interrupt techniques).

Figure 2: Linear potential scan of the [Cu(CH₃CN)₄][Tf₂N] electrolyte at a platinum

working electrode at 90°C.

Figure 3. Deposits from a [Cu(CH₃CN)₄][Tf₂N] electrolyte on a Pt working electrode for current density values of 1, 5 and 25 A/dm².

Figure 4. EDX spectrum of a copper deposit obtained from the [Cu(CH₃CN)₄][Tf₂N]

electrolyte at a current density of 25 A/dm². Figure 5. Cyclic voltammogram of the [Ag(CH₃CN)₂][Tf₂N] electrolyte on a Au working electrode at 90°C. The CV has been corrected for iR drop in-situ (by current interrupt techniques).

Figure 6. Deposits from a [Ag(CH₃CN)₂][Tf₂N] electrolyte on a Au working electrode for current density values of 0.5, 1, 2, 5 and 25 A/dm² at 50°C.

Figure 7. Cyclic voltammogram of [Cu(CH₃CN)₂][Tf₂N]₂ on a Pt working electrode at 90°C.

Figure 8. Cyclic voltammogram of [Cu(N-methylimidazole)₆][Tf₂N]₂ on a Pt working

electrode at 90°C.

Figure 9. Cyclic voltammogram of [Mn(N-butylimidazole)5]Cl₂ on a Pt working electrode at 90°C.

Figure 10. Deposition experiment of [Mn(N-butylimidazole)₅]Cl₂ on a Pt electrode at 90°C at -2.5 V vs Pt.

Figure 11. Cyclic voltammogram of [Fe(N-methylimidazole)6][N0₃]₃ xH₂0 on a Pt

working electrode at 90°C.

Figure 12. Deposition experiment of [Fe(N-methylimidazole)₆][N0₃]₃ xH₂0 on a Pt

electrode at 90°C at -2 V vs Pt.

In the different figures, the same reference signs refer to the same or analogous elements.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

The following terms are provided solely to aid in the understanding of the invention.

Definitions and nomenclature

Low-melting metal salts are being used both as electrolyte and metal source in an electroplating bath, that can be operated at high current densities. The compounds consist of a metal surrounded with neutral weakly coordinating organic ligands and weakly coordinating anions. The electrolyte can be considered as a very concentrated solution of a metal salt in an inert coordinating solvent so that all solvent molecules are coordinated to the metal centre and no free solvent molecules remain in solution.

The term "alkyl" as used herein means normal, secondary, or tertiary hydrocarbon having 1 to 12 carbon atoms. Examples are methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2- methyl-l-propyl(i-Bu), 2-butyl (s-Bu) 2-methyl-2-propyl (t-Bu), 1-pentyl (n-pentyl), 2- pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3 -methyl- 1 -butyl, 2-methyl-l -butyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 3- methyl-3-pentyl, 2-methyl-3-pentyl, 2,3 -dimethyl -2-butyl, 3,3-dimethyl-2-butyl, cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. Preferably alkyl is a linear or branched alkyl chain with 6 or less carbon atoms.

The term "aryl" as used herein means 5 or 6 membered heterocyclic, oxyheterocyclic or thioheterocyclic rings, including arylalkyl, arylalkyloxy and arylalkylthio. Preferably aryl is phenyl.

A weakly coordinating neutral ligand is a ligand that is displaced by coordinating solvent molecules (= solvent molecules with donor atoms) upon dissolution. For instance, such ligands will not remain coordinated to the metal upon dissolution of the metal complex in for instance water. Weakly coordinating neutral ligands will only coordinate (bind) to the metal ion in the absence of competing solvent molecules.

An anion is weakly coordinating, if upon dissolution of a salt in a solvent, the anion is not making direct contact with the metal cation, the anion being present in the second coordination sphere and the first coordination sphere of the metal ion being formed by solvent molecules only. Weakly coordinating anions will only coordinate (bind) to the metal ion in the absence of competing solvent molecules. 11 000010

13

Tf N is a abbreviation for bis(trifluromethylsulfonyl)imide.

Bistriflimide is an abbreviated name for bis(trifluromethylsulfonyl)imide.

Triflate is an abbreviated name for trifluoromethylsulfonate.

The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope and spirit of this invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

Liquid metal salt In another preferred embodiment of the present invention, the negative charged ligand Y and the counter anion X are different.

M can be any metal, being a main-group metal (s-block or p-block), a d-block metal or an f-block metal in any oxidation state. Suitable metals include copper, zinc, cadmium, nickel, cobalt, manganese, iron, chromium, tin, lead, bismuth, antimony, selenium, tellurium, thallium, silver, gold, platinum, palladium, rhodium, ruthenium, iridium, osmium, rhenium, aluminium, gallium, indium, silicon, germanium, beryllium, magnesium, titanium, zirconium, hafnium, molybdenum, tungsten, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, thorium, uranium, plutonium and lithium. When the metals have different oxidation states, the lowest oxidation state is the preferred one when it is easily accessible, because of the lower electricity consumption for electrodeposition. For instance, copper(I) is preferred over copper(II), and cobalt(II) is preferred over cobalt(III). In another preferred embodiment of the present invention, M is selected from the group consisting of copper, zinc, silver, gold, platinum, cobalt, nickel, tungsten, molybdenum and aluminium.

In another preferred embodiment of the present invention, M is selected from the group consisting of copper, zinc and silver. In another particular embodiment, M is aluminium. In another preferred embodiment of the present invention, the metal M is selected from the group consisting of copper or silver. In another preferred embodiment of the present invention, the metal M is silver. In yet another preferred embodiment of the present invention the metal M is copper.

In another preferred embodiment of the present invention, metal (M) ion is copper(I);

L is 1-methylimidazole; and X is bis(trifluoromethylsulfonyl)imide.

In another preferred embodiment of the present invention, metal (M) ion is copper(I); L is 1-methylimidazole; and Y is bis(trifluoromethylsulfonyl)imide.

In another preferred embodiment of the present invention M (M) ion is silver(I); L is acetonitrile; and X is bis(trifluoromethylsulfonyl)imide.

In another preferred embodiment of the present invention, the liquid metal salts are selected from the group consisting of copper(I) tetrakis(acetonitrile)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(methylimidazole)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(butylimidazole)

bis(trifluoromethylsulfonyl)imide, copper(I) bis(2,2'-bipyridine)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(pyridine)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(3 -picoline)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(benzonitrile)

bis(trifluoromethylsulfonyl)imide, zinc(II) bis(trifluoromethylsulfonyl)imide hexahydrate, silver(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide, silver(I) tris(acetonitrile) bis(trifluoromethylsulfonyl)imide, silver(I) (acetonitrile)2.₅

bis(trifluoromethylsulfonyl)imide, silver(I) bis(acetonitrile)

bis(trifluoromethylsulfonyl)imide, silver(I)mono(acetonitrile)

bis(trifluoromethylsulfonyl)imide and copper(I) tetrakis(methylimidazole)

trifluoromethanesulfonate.

In another preferred embodiment of the present invention, the liquid metal salts are selected from the group consisting of silver(I) tetrakis(acetonitrile)

bis(trifluoromethylsulfonyl)imide, silver(I) tris(acetonitrile)

bis(trifluoromethylsulfonyl)imide, silver(I) (acetonitrile)2.5 bis(trifluoromethylsulfonyl)imide, silver(I) bis(acetonitrile)

bis(triflupromethylsulfonyl)imide and silver(I)mono(acetonitrile)

bis(trifluoromethylsulfonyl)imide.

The bis(trifluoromethylsulfonyl)imide anion is useful in this application because of its electrochemical stability and because it leads to metal complexes with a low melting point. The design of this type of compounds is not straightforward, because they need to combine the following properties: (1) low melting point, (2) sufficient thermal stability, (3) electroactive. It is easy to make low-melting compounds, but these are often not electroactive and do not allow metals to be obtained by electrodeposition. Alternatively the ligand is so easily lost upon heating that a solid metal salt results rather than a molten complex.

The melting point of the liquid metal salts is below 100°C, more preferable below 50 °C and most preferable below room temperature. The liquid metal salts should have a high thermal stability. They should be able to withstand prolonged heating (several hours or even days) at a temperature of 100°C or even at a temperature of 150°C without significant thermal decomposition. The liquid metals salts should have no or a limited volatility to facilitate the drying procedure, especially when they have to be used as precursor for the electrodeposition of reactive metals. For easy handling, the liquid metal salts should be air- stable, or they should have only a limited sensitivity for air or moisture. The molecular mass of the compounds should be as low as possible in order to get a high concentration of the metal ion. The metal complexes should not have a polymeric structure or should at least melt to a solution with non-polymeric species.

In a preferred embodiment of the present invention, the liquid metal salt has a melting point below 100°C, more preferably below 50°C, and even more preferably below room temperature.

In a preferred embodiment of the present invention, the liquid metal salt has an ionic conductivity in a liquid state of at least 5 x 10^"2 ohm^m^"1, preferably at least 10^"1 ohm^m^"1 and particularly preferably at least 1 ohm^m^"1. For example [Cu(CH₃CN)₂] [Tf₂N] has a conductivity at 90°C of 1.62 ohm^{' 1}.

In a preferred embodiment of the present invention, the liquid metal salt has a minimum viscosity below 100°C of below 100 mPa.s, with a viscosity below 10 mPa.s being preferred. For example [Cu(CH₃CN)₂] [Tf₂N] has a viscosity at 80°C of 9.0 mPa.s. A low viscosity enhances the mass transport during electrodeposition. T/BE2011/000010

16

In a preferred embodiment of the present invention, the liquid metal salt is stable in an inert atmosphere at 90°C for at least 2 days preferably at least 5 days.

Neutral ligands

The neutral ligand L is preferably a weakly coordinating molecule that is also used as a solvent for non-aqueous electrochemistry. Solvents that can be used as ligands to solvate a metal ion, include acetonitrile (AN), dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylsulfone (DMS0₂), hexamethylphosphoramide (HMPA), N- methylpyrrolidone (NMP), pyridine (Py), tetrahydrofuran (THF), diethyl ether, dimethoxyethane (DME, monoglyme), bis(2-methoxyethyl) ether (diglyme), 1,4-dioxane, methanol, ethanol, propanol, butanol or water. This list is not limiting. For instance, acetonitrile can be replaced by other nitrile solvents such as propionitrile, butyronitrile, benzonitrile or benzylnitrile. DMSO and DMS0₂ can be replaced by other sulfoxides and sulfones with longer alkyl chains than methyl groups. Pyridine can be replaced by substituted pyridines like picoline. Other compounds that can act as ligand L include acetamide, N,N-dimethylacetamide, trialkylphosphine oxides, triarylphosphine oxides, trialkylphosphate (e.g. tributylphosphate), pyrazole, 3-alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethylpyrazole, imidazole, 1-alkylimidazoles, 1,2-dimethylimidazole, 2- imidazolidinone, thiabendazole, ammonia, alkylamines, tetramethylenesulfoxide (TMSO), urea, N^A^iV etramethylurea (TMU), thiourea, lactams, hydroxypyridines, 2-pyridone, pyridine-N-oxide, picoline-N-oxides, 2,6-lutidine, 2,6-lutidine N-oxide, pyrazine, pyrazine-jV-oxide, 1,4-dithiane monosulfoxide. Less favorable are neutral bidentate or polydentate ligands like 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), 2,6,2',2"- terpyridine (terpy), ethylene diamine, diethylenetriamine, 1,2,3-triaminopropane, cyclam, crown ethers, thiacrown ethers, glymes, polyethyleneglycols, and the like. The reduction potential for reducing the metal ion to the metallic state can be tuned by a suitable choice of the ligand L. In general, the reduction potential will shift to more negative potentials for more strongly coordinating ligands.

In another preferred embodiment of the present invention, L is selected from the group consisting of acetonitrile (AN), dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylsulfone (DMS0₂), hexamethylphosphoramide (HMPA), N- methylpyrrolidone (NMP), pyridine (Py), tetrahydrofuran (THF), diethyl ether, dimethoxyethane (DME, monoglyme), bis(2-methoxyethyl) ether (diglyme), 1,4-dioxane, methanol, ethanol, propanol, butanol and water.

In another preferred embodiment of the present invention, L is selected from the group consisting of 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), 2,6,2 ',2"- terpyridine (terpy), ethylene diamine, diethylenetriamine, 1,2,3-triaminopropane, cyclam, crown ethers, thiacrown ethers, glymes and polyethyleneglycol.

In another more preferred embodiment of the present invention, L is selected from the group consisting of acetamide, N,N-dimethylacetamide, trialkylphosphine oxides, triarylphosphine oxides, trialkylphosphate (e.g. tributylphosphate), pyrazole, 3- alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethyIpyrazole, imidazole, 1-alkylimidazoles, 1,2- dimethylimidazole, 2-imidazolidinone, thiabendazole, ammonia, alkylamines,

tetramethylenesulfoxide (TMSO), urea, N,N,A^,A -tetramethylurea (TMU), thiourea, lactams, hydroxypyridines, 2-pyridone, pyridine-N-oxide, picoline-N-oxides, 2,6-lutidine, 2,6-lutidine N-oxide, pyrazine, pyrazine-N-oxide, 1,4-dithiane monosulfoxide,

propionitrile, butyronitrile, benzonitrile and benzylnitrile.

In another preferred embodiment L is selected from the group consisting of acetonitrile (AN), dimethylformamide (DMF), dimethylsulfoxide (DMSO),

dimethylsulfone (DMS0₂), hexamethylphosphoramide (HMPA), N-methylpyrrolidone (NMP), pyridine (Py), tetrahydrofuran (THF), diethyl ether, dimethoxyethane (DME, monoglyme), bis(2-methoxyethyl) ether (diglyme), 1,4-dioxane, methanol, ethanol, propanol, butanol and water.

In another preferred embodiment L is selected from the group consisting of acetonitrile, propionitrile, butyronitrile, isobutyronitrile, acrylonitrile, 2- hydroxycyanoethane, phenylacetonitrile, benzonitrile and benzylnitrile.

In another preferred embodiment of the present invention, L is acetonitrile.

Negatively charged ligands

The negatively charged ligands Y are of importance in reducing the overall positive charge of the cation in the case of dipositive, tripositive and tetrapositive metal ion or multiple monopositive metal ions. A lower overall positive charge leads in general to lower melting points. Typical examples of Y ligands are chloride and bromide, but also weakly coordinating ligands with charge -1, e.g. acetate, trifluoroacetate, triflate, methanesulfonate or bis(trifluoromethylsulfonyl)imide (bistriflimide), are suitable. In another preferred embodiment of the present invention Y is bis(trifluoromethylsulfonyl)imide.

In another preferred embodiment of the present invention Y is chloride or bromide.

Counter anions

The counter anion X can be a weakly coordinating anion, such as

hexafluorophosphate, tetrafluoroborate, bis(trifluoromethylsulfonyl)imide (bistriflimide), bis(trifluoroalkylsulfonyl)imides, dicyanamide, triflate, methanesulfonate or

trifluoroacetate. The counter anion can also be a metal-containing anion that cannot be reduced at the cathode and that preferably has a low overall charge. Typical examples are tetrachloroaluminate(III) and tetracobaltate(II).

In a preferred embodiment of the present invention, X is a large asymmetric anion.

In a preferred embodiment of the present invention, X is selected from the group consisting of hexafluorophosphate, tetrafluoroborate, bis(trifluoromethylsulfonyl)imide (bistriflimide), bis(trifluoroalkylsulfonyl)imide, dicyanamide, triflate, methanesulfonate and trifluoroacetate.

In a preferred embodiment of the present invention, X is selected from the group consisting of tetrachloroaluminate, tetrachlorogallate, tetrachloroindate, tetrachloroferrate, hexachloroarsenate, hexachlorantimonate(VI), hexachlorotantalate, hexachloroniobate.

In another preferred embodiment of the present invention, X is

bis(trifluoromethylsulfonyl)imide.

Methods of preparation

The liquid metal salts can be prepared via different synthetic methods. A first method is by dissolving a metal salt in a coordinating solvent and to remove all the non- coordinated solvent molecules under reduced pressure. Preferably, the metal salt is anhydrous. A hydrated metal salt can also be dried in solution by adding a chemical drying agent such a triethylorthoformate or dimethoxypropane. Another drying method is by using molecular sieves. A second method is by dissolving the metal salt in the coordinating solvent and to add a second solvent from which the metal salt with the coordinated solvent molecules precipitates. A third method is by adding an acid to a dispersion of a metal oxide or metal hydroxide in the coordinating solvent, followed by removal of the water and of the excess of solvent. A fourth method is to dissolve a metal oxide or a metal hydroxide in a protonated liquid metal salt. During the dissolution process water is generated and the free base of the protic liquid metal salts coordinates to the metal ion and the anion of the protic liquid metal salt becomes the anion of the liquid metal salt. This method is limited to coordinated solvents with a strong basicity which can uptake a proton from an added acid to form a protic liquid metal salt. A fifth method is applicable to metal halide salts. The metal halide salt is dissolved in a coordinating solvent and a strong Lewis acid (e.g. A1C1₃, FeCl₃ or SbCl ) is added to this solution. The Lewis acid abstracts halide ions from the metal salts so that coordination solvent molecules can enter the first coordination sphere. This will generate salts with [A1C1₄]^", [FeCl₄]^" or [SbCl₆]^" anions, which are not electro- active.

Use of liquid metal salts in an electrodeposition process A second aspect of the present invention relates to the use of the liquid metal salts described herein in an electrodeposition process.

In a preferred embodiment of the second aspect of the present invention, the electrodeposition process relates to the electrodeposition of a metal M.

In another preferred embodiment of the second aspect of the present invention, the liquid metal salts are used in an electrodeposition process together with a non-coordinating solvent, such as toluene.

In another preferred embodiment of the second aspect of the present invention, the electrodeposition process is performed without an additional electrolyte.

In another preferred embodiment of the second aspect of the present invention, the electrodeposition process is performed without an additional metal salt.

In another preferred embodiment of the second aspect of the present invention, said metal M is selected from the group consisting of copper, zinc, silver, gold, platinum, cobalt, nickel, tungsten, molybdenum, and aluminium, and in a more particular embodiment, said metal M is copper or aluminium. In another particular embodiment, said metal M is silver. In another embodiment of the second aspect of the present invention, said metal M is selected from the group consisting of manganese, iron, copper and silver.

The deposition takes place under controlled electric current or under controlled electric potential. The current densities lie between 10^" A/dm and 100 A/dm , and preferably between 1 A dm 2 and 50 A/dm 2. The temperature duri ·ng electrodeposition is between 0 and 200°C, and preferably between 18°C and 100°C. The electrolyte solution may or may not be stirred.

In another preferred embodiment of the second aspect of the present invention, said use of the liquid metal salts for electrodeposition of a metal M is at a current density of at least 1 A/dm . In a more particular embodiment said current density is at least 10 A/ dm , more particularly said current density is at least 40 A/dm . In another particular embodiment said current density can reach values up to 100 A/dm².

The electrodeposition takes place using either a two-electrode or a three-electrode configuration. The cathode can consists of any suitable conducting material, preferably a metallic surface. The anode can be either a sacrificial anode, consisting of the same metal as the one being deposited (for instance a copper anode in the case of copper deposition) or an inert anode such as platinum. These metals can be deposited as single metals or as alloys. Additives may or may not be added to improve the nucleation density or to act as a brightener. The cathodic reaction is the decomposition of the cationic complex of the liquid metal salt, giving rise to reduction of the metal ion to the metallic state. Because of the high concentration of metal ions and the high current efficiency, the electrodeposition process can be run at high current densities to ensure a fast growth of the deposited layer. The neutral ligands, the negatively charged ligands and the counter anions do not undergo reduction at the cathode. They will either escape from the electrolyte bath when they are volatile (and they can be recycled for reuse) or they can be transported to the anode to assist the dissolution process of the sacrificial anode. If an inert anode is being used, the anodic reaction will be the oxidation of ligands or counter ions. For instance, chloride ions can be oxidized to chlorine gas. Also, more than one liquid metal salt can be present in one electrolyte in order to electrodeposit alloys. The composition of the alloy can be varied by changing the relative concentration of the different metal ions, the applied potential or the coordination of the different metal ions. The liquid metal salts can also be used as electrolytes in the electropolishing of metals e.g. stainless steel, titanium and titanium alloys and aluminium and aluminium alloys. Description of liquid metal salts and applications

The liquid metals salts can be considered as very concentrated solutions of metals salts in an inert coordinating solvent. All the solvents molecules are used for coordinating the metal centre, so that no free solvent molecules are available in solution. Coordination of the solvent molecules to the metal ion considerably changes the properties of the solvent molecules, in the sense that the coordinated solvent is no longer volatile. The liquid metal salts serve as both the electrolyte and the metal source in an electroplating bath. It is of importance that the solvent molecules have coordinating properties, because otherwise no adduct formation between the metal ion and the solvent can occur. The coordinating ability of the solvent molecules also aids to the dissolution of a sacrificial anode. The dissolution process is facilitated by solvation of the dissolved metal ion by coordinating solvent molecules. The coordination of the solvent molecules to the metal ion increases the effective size of the cation. This decreases the strength of the electrostatic interaction between the metal ion and the anion, which results in a lowering of the melting point and an increase in electric conductivity. It is possible that the composition of the electrolyte at the temperature at which the electrodeposition is carried differs from the composition at room temperature, because one or more coordinated ligands are lost during the heating process. However, after the initial loss of the weakly coordinated ligands, the electrolyte can have a long-term stability.

The liquid metal salts can be used as electrolyte and metal source for electroless deposition. In this case a reducing agent like LiBH₄, NaBH₄, KBtL_t, LiAlH₄, hydrazine, formaldehyde or a titanium(III) salt is added to the molten electrolyte.

The liquid metal salts can find application as electrolytes in batteries, provided that the electrodeposition process is reversible. Of special interest are here liquid metal salts that containing lithium, magnesium or aluminium ions.

However, it should be understood that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only. Since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. It is to be understood that both the foregoing general and detailed description and the following examples are exemplary and explanatory only and are not restrictive of the invention, as claimed. EXAMPLES

EXAMPLE 1. Preparation of copper(I) tetrakis(acetonitrile)

bis(trifluoromethylsulfonyl)imide. Hydrogen bis(trifluoromethylsulfonyl)imide (80% solution in water, 53.02 g, 150.66 mmol) was added to copper(II) oxide (6.10 g, 76.69 mmol) in distilled water (100ml) and the mixture heated at 80°C for 16 hours. The remaining solids were removed by filtration and the water removed in vacuo giving copper(II) bis(trifluoromethylsulfonyl)imide hydrate. This solid was dissolved in 100 ml of acetonitrile and powdered copper metal (5 g, 78.68 mmol) was added and the mixture stirred at room temperature for 16 hours. The remaining solids were removed by filtration and the liquid removed in vacuo to give copper(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide (72.17 g, 142.09 mmol, 94.3%) as a white solid with a melting point of 66°C.

EXAMPLE 2. Preparation of copper(I) tetrakis(N-methylimidazole)

bis(trifluoromethylsulfonyl)imide.

N-methylimidazole (6.47 g, 78.76 mmol) was added to copper(I)

tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide (10.00 g, 19.69 mmol) and the mixture heated to 90° C in vacuo giving copper(I) tetrakis(N-methylimidazole)

bis(trifluoromethylsulfonyl)imide (11.92 g, 17.74 mmol, 90.1%) as a dark green liquid.

EXAMPLE 3. Preparation of copper(I) tetrakis(N-butylimidazole)

bis(trifluoromethylsulfonyl)imide.

N-butylimidazole (2.45 g, 19.69 mmol) was added to copper(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide (2.50g, 4.92mmol) and the mixture heated to 90° C in vacuo giving copper(I) tetrakis(N-butylimidazole) bis(trifiuoromethylsulfonyl)imide (3.98 g, 4.47 mmol, 90.9%) as a dark green liquid. EXAMPLE 4. Preparation of copper(I) bis(2,2'-bipyridine)

bis(trifluoromethylsulfonyl)imide.

2,2'-bipyridine (1.18 g, 7.56 mmol) was added to copper(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide (1.92 g, 3.78mmol) and the mixture heated to 90° C in vacuo to give copper(I) tetrakis(2,2'-bipyridine) bis(trifluoromethylsulfonyl)imide (2.27 g, 3.46 mmol, 91.5%) as an orange solid with a melting point of 125°C.

EXAMPLE 5. Preparation of copper(I) tetrakis(pyridine)

bis(trifluoromethylsulfonyl)imide. Pyridine (3.02 g, 38.12 mmol) was added to copper(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide (4.84 g, 9.53 mmol) and the mixture heated to 90° C in vacuo giving copper(I) tetrakis(pyridine) bis(trifluoromethylsulfonyl)imide (6.01 g, 9.10 mmol, 95.5%) as a brown solid with a melting point of 83°C

EXAMPLE 6. Preparation of copper(I) tetrakis(3-picoline)

bis(trifluoromethylsulfonyl)imide.

3-picoline (1.24 g, 13.31 mmol) was added to copper(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide (1.69 g, 3.33 mmol) and the mixture heated to 90° C in vacuo giving copper(I) tetrakis(3-picoline) bis(trifluoromethylsulfonyl)imide (2.12 g, 2.96 mmol, 88.9%) as a brown liquid.

EXAMPLE 7. Preparation of copper(I) tetrakis(benzonitrile)

bis(trifluoromethylsulfonyl)imide.

Benzonitrile (0.85 g, 8.24 mmol) was added to copper(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide (1.05 g, 2.0 7mmol) and the mixture heated to 90° C in vacuo giving copper(I) tetrakis(benzonitrile) bis(trifluoromethylsulfonyl)imide (11.92 g, 17.74 mmol, 90.1%) as a pale yellow liquid. After standing for several days crystals formed with a melting point of 65°C.

EXAMPLE 8. Preparation of zinc(II) bis(trifluoromethylsulfonyl)imide hexahydrate.

Hydrogen bis(trifluoromethylsulfonyl)imide (80% solution in water, 5.18g, 14.74 mmol) was added to zinc(II) oxide (0.70 g, 8.60 mmol) in distilled water (50 ml) and the mixture heated at 80°C for 16 hours. The remaining solids were removed by filtration and the water removed in vacuo giving zinc(II) bis(trifluoromethylsulfonyl)imide hexahydrate (72.17 g, 142.09 mmol, 94.3%) as a white solid with a melting point of 105°C.

EXAMPLE 9. Preparation of zinc(II) bis(trifluoromethylsulfonyl)imide tetrafluoroborate. hexahydrate

Hydrogen tetrafluoroborate (50% solution in water, 2.16 g, 12.28 mmol) was added to zinc(II) oxide (0.60 g, 7.37 mmol) in distilled water (50ml) and the mixture heated at 80°C for 16 hours. The remaining solids were removed by filtration and the water removed in vacuo giving zinc(II) tetrafluoroborate hexahydrate (2.87 g, 10.59 mmol, 86.2%) as a white solid with a melting point of 91°C.

EXAMPLE 10. Preparation of silver(I) tetrakis(acetonitrile)

bis(trifluoromethylsulfonyl)imide.

Hydrogen bistriflimide (80% solution in water, 3.12 g, 8.88 mmol) was added to silver(I) oxide (1.10 g, 8.88 mmol) in acetonitrile (50ml) and the mixture heated at 80°C for 16 hours. The remaining solids were removed by filtration and the solvents removed in vacuo giving silver(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide (4.50 g, 8.15 mmol, 91.8%) as a white solid with a melting point of 48°C.

EXAMPLE 11. Preparation of silver(I) bis(acetonitrile) bis(trifluoromethylsulfonyl)imide.

Hydrogen bistriflimide (80% solution in water, 11.63 g, 33.1 mmol) was added to silver(I) oxide (3.83 g, 16.5 mmol) in acetonitrile (50ml) and the mixture stirred at room temperature for 1 hour. The remaining solids were removed by filtration and the solvents removed in vacuo on a rotary evaporator. The mixture was subsequently cooled to -78 °C and further solvent removed on a vacuum line giving silver(I) bis(acetonitrile)

bis(trifluoromethylsulfonyl)imide (14.76 g, 31.4 mmol, 94.9%) as a white solid with a melting point of 19°C.

EXAMPLE 12. Preparation of silver(I) (acetonitrile) bis(trifluoromethylsulfonyl)imide.

Silver(I) bis(acetonitrile) bis(trifluoromethylsulfonyl)imide (14.76 g, 31.4 mmol) was attached to a vacuum line at 50 °C for 16 hours giving silver(I) (acetonitrile) bis(trifluoromethylsulfonyl)imide (13.42g, 31.27 mmol, 99.6%) as a white solid with a melting point of 90°C.

EXAMPLE 13. Preparation of silver(I) 2.5 (acetonitrile) triflate.

Triflic acid (1.41 g, 9.39 mmol) was added to silver(I) oxide (1.09 g, 4.70 mmol) in acetonitrile (20ml) and the mixture stirred at room temperature for 1 hour. The remaining solids were removed by filtration and the solvents removed in vacuo on a rotary evaporator and then on a vacuum line for 16 hours giving silver(I) bis(acetonitrile) triflate (3.16 g, 8.79mmol, 93.6%) as a white solid with a melting point of 51°C. EXAMPLE 14. Preparation of copper(I) tetrakis(acetonitrile) trifluoromethanesulfonate.

Powdered copper metal (0.5g, 7.87 mmol) was added to copper(II)

trifluoromethanesulfonate (2.30 g, 6.36 mmol) in acetonitrile (50ml) and the mixture stirred at room temperature for 16 hours. The remaining solids were removed by filtration and the liquid removed in vacuo giving copper(I) tetrakis(acetonitrile) trifluoromethanesulfonate (4.26 g, 11.30 mmol, 88.9%) as a white solid with a melting point of 124°C.

EXAMPLE 15. Preparation of copper(I) tetrakis(N-methylimidazole)

trifluoromethanesulfonate.

N-methylimidazole (0.97 g, 11.78 mmol) was added to copper(I)

tetrakis(acetonitrile) trifluoromethanesulfonate (1.11 g, 2.95 mmol) and the mixture heated to 90° C in vacuo giving copper(I) tetrakis(N-methylimidazole) trifluoromethanesulfonate (1.35 g, 2.50 mmol, 84.7%) as a dark green solid with a melting point of 123°C. EXAMPLE 16: Preparation of copper(I) bis(acetonitrile)

bis(trifluoromethylsulfonyl)imide

Copper(I) bis(acetonitrile) bis(trifluoromethylsulfonyl)imide (10.05g, 19.79 mmol) was heated to 90 °C in vacuo for 24 hours giving copper(I) bis(acetonitrile)

bis(trifluoromethylsulfonyl)imide (8.38 g, 19.69 mmol, 99.5%) as a white solid with a melting point of 65 °C. Analysis gave a copper content of 14.5 wt.% (14.9 wt.% calc. for copper(I) bis(acetonitrile) bis(trifluoromethylsulfonyl)imide.

EXAMPLE 17. Electrodeposition of copper

The electrochemical behaviour of [Cu(CH₃CN)₄][Tf₂N] was investigated by cyclic voltammetry (see Figure 1) and electrodeposition experiments (see Figure 3) on a platinum-covered silicon wafer as working electrode. The pretreatment of the electrodes consisted of rinsing with acetone.. A Solartron instruments SI 1287 electrochemical interface was used for the electrochemical experiments. The temperature was held constant at 90°C. All the electrochemical experiments were done in a glove box under an argon atmosphere. Despite the fact that it is a pure liquid metal salt, the cyclic voltammogram does not show an area of zero current as a classic liquid metal salt would do. The characteristic reduction and oxidation peaks of a copper solution are clearly visible. This liquid metal salt can be very promising to achieve a high nucleation density, since the concentration of copper ions is high without the need to dissolve a copper salt. The cathodic decomposition limit corresponds to the reduction of cuprous ions to copper and new cuprous ions dissolving at the anode, thereby compensating for the decomposition of the liquid metal salt. A linear potential scan (see Figure 2) shows that current densities of 25 A/dm² could be achieved. Copper deposition experiments were performed

galvanostatically at current densities of 1, 5 and 25 A/dm². The smoothest deposits were obtained at the highest current densities, due to a higher nucleation density under these conditions. Figure 4 shows the EDX spectrum of a copper deposit obtained at a current density of 25 A/dm .

EXAMPLE 18. Electrodeposition of silver

The electrochemical behaviour of [Ag(CH₃CN)₂][Tf₂N] was investigated by cyclic voltammetry (see Figure 5) and electrodeposition experiments (see Figure 6) on a gold- covered silicon wafer as working electrode. The pretreatment of the electrodes consisted of rinsing with acetone. A Solartron instruments SI 1287 electrochemical interface was used for the electrochemical experiments. All electrochemical experiments were done in a glove box under an argon atmosphere. The characteristic reduction and oxidation peaks of a silver solution was clearly visible at a potential of 0 V vs a silver pseudo-reference electrode. These reduction and oxidation peaks showed a relatively high current density. Such high current density is appealing for achieving a high nucleation density, since the concentration of silver ions is high without the addition of a silver salt. The cathodic decomposition limit corresponded to the reduction of silver ions to silver and new silver ions dissolving at the anode, thereby compensating for the decomposition of the liquid metal salt. Current densities of 25 A/dm² could be achieved. Silver deposition experiments were performed galvanostatically at current densities of 0.5, 1, 2, 5 and 25 A/dm . The smoothest deposits were obtained at the highest current densities, due to a higher nucleation density at these conditions.

EXAMPLE 19. Electrodeposition of copper

The electrochemical behaviour of [Cu(CH₃CN)₂] [Tf₂N] was investigated by cyclic voltammetry (see Figure 7) and electrodeposition experiments on a platinum-covered silicon wafer as working electrode. The pretreatment of the electrodes consisted of rinsing with acetone.. A Solartron instruments SI 1287 electrochemical interface was used for the electrochemical experiments. The temperature was held constant at 90°C. All the electrochemical experiments were done in a glove box under an argon atmosphere. Despite the fact that it is a pure liquid metal salt, the cyclic voltammogram does not show an area of zero current as a classic liquid metal salt would do. Compared with

[Cu(CH₃CN)₄][Tf₂N], [Cu(PhCN)₂][Tf₂N] and [Cu(PhCN)₄][Tf₂N], [Cu(CH₃CN)₂][Tf₂N] was the easiest to reduce. The characteristic reduction and oxidation peaks of a copper solution are clearly visible. The cathodic decomposition limit corresponds to the reduction of cuprous ions to copper and new cuprous ions dissolving at the anode, thereby compensating for the decomposition of the liquid metal salt. Copper deposition experiments were performed galvanostatically at current densities up to 25 A/dm in unstirred conditions. The resulting copper deposits from [Cu(CH₃CN)₂][Tf₂N] had a smooth appearance, did not show cracks, and were free from incorporated species.

EXAMPLE 20. Electrodeposition of copper

The electrochemical behaviour of [Cu(N-methylimidazole)₆] [Tf₂N]₂ was investigated by cyclic voltammetry (see Figure 8) on a platinum-covered silicon wafer as working electrode. All electrochemical experiments were done in a glove box under an argon atmosphere. Despite the fact that it is a pure liquid metal salt, the cyclic voltammogram did not show an area of zero current as a classic liquid metal salt would do. The characteristic reduction and oxidation peaks for the Cu²⁺/Cu couple were clearly visible.

EXAMPLE 21. Electrodeposition of manganese

The electrochemical behaviour of [Mn( -butylimidazole) ]Cl₂ was investigated by cyclic voltammetry (see Figure 9) and electrodeposition experiments (see Figure 10) on a platinum-covered silicium wafer as working electrode. All electrochemical experiments were done in a glove box under an argon atmosphere. Despite the fact that it is a pure liquid metal salt, the cyclic voltammogram did not show an area of zero current as a classic liquid metal salt would do. The characteristic reduction and oxidation peaks of a Mn /Mn couple were clearly visible.

EXAMPLE 22. Electrodeposition of iron

The electrochemical behaviour of [Fe(N-methylimidazole)₆][N0₃]₃ xH₂0 was investigated by cyclic voltammetry (see Figure 11) and electrodeposition experiments (see Figure 12) on a platinum-covered silicon wafer as working electrode. All electrochemical experiments were done in a glove box under an argon atmosphere. Despite the fact that it is a pure liquid metal salt, the cyclic voltammogram did not show an area of zero current as a classic liquid metal salt would do. The characteristic reduction and oxidation peaks of a Fe /Fe couple were clearly visible.

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Claims

A liquid metal salt in which a metal (M) ion is surrounded by neutral ligands (L), or by a combination of neutral ligands (L) and negatively charged ligands (Y) such that the total negative charge of the total number of negatively charged ligands (Y) is smaller than the oxidation state of the metal ion so that the metal complex has an overall positive charge, with at least one counter anion (X),

wherein M is a metal selected from the group consisting of copper, zinc, silver, gold, platinum, cobalt, nickel, tungsten, molybdenum and aluminium.;

L is a neutral ligand and is selected from the group consisting of acetonitrile (AN), propionitrile, butyronitrile, isobutyronitrile, acrylonitrile, 2-hydroxycyanoethane, phenylacetonitrile, benzonitrile benzylnitrile, dimethylformamide (DMF), acetamide, N,N-dimethylacetamide, formamide, N-methylformamide, N-methylacetamide, dimethylsulfoxide (DMSO), dimethylsulfone (DMS0₂), hexamethylphosphoramide (HMPA), N-methylpyrrolidone (NMP), pyridine (Py), morpholine, tetrahydrofuran (THF), diethyl ether, dimethoxyethane (DME, monoglyme), bis(2-methoxyethyl) ether (diglyme), triglyme, tetraglyme, pentaglyme, hexaglyme, 1,4-dioxane, methanol, ethanol, propanol, butanol, ethyleneglycol, polyethyleneglycol, water, trialkylphosphine oxides, triarylphosphine oxides, trialkylphosphate, pyrazole, 3- alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethylpyrazole, imidazole, 1- alkylimidazoles, 1,2-dimethylimidazole, 2-imidazolidinone, thiabendazole, ammonia, tetramethylenesulfoxide (TMSO), urea, Ν,Ν,Ν',Ν'-tetramethylurea (TMU), thiourea, lactams, hydroxypyridines, 2-pyridone, pyridine-N-oxide, picoline- N-oxide, 2,6-lutidine, 2,6-lutidine N-oxide, pyrazine, pyrazine-N-oxide, 1,4-dithiane monosulfoxide, 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), 2,6,2',2"- terpyridine (terpy), ethylenediamine, diethylenetriamine, 1,2,3-triaminopropane, cyclam, crown ethers and thiacrown ethers;

Y is selected from the group consisting of chloride, bromide, iodide, thiocyanate, formate, acetate, trifluoroacetate, propionate, butyrate, pentanoate, hexanoate, benzoate, glycolate, heptafluorobutanate, alkylsulfate, octylsulfate, dodecylsulfate, triflate, methanesulfonate, nitrate, dicyanamide, tricyanomethanide,

bis(trifluoromethylsulfonyl)imide (bistriflimide) or bis(perfluoroalkylsulfonyl)imide, dimethylphosphate, diethylphosphate, dialkylphosphate, saccharinate, acesulfamate and tosylate; and X is a counter anion selected from the group consisting of hexafluorophosphate, tetrafluoroborate, bis(trifluoromethylsulfonyl)imide (bistriflimide),

bis(trifluoroalkylsulfonyl)imide, dicyanamide, triflate, methanesulfonate and trifluoroacetate.

The liquid metal salt of any of claim 1, wherein L is selected from the group consisting of acetamide, N,N-dimethylacetamide, trialkylphosphine oxides, triarylphosphine oxides, trialkylphosphate (e.g. tributylphosphate), pyrazole, 3- alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethylpyrazole, imidazole, 1-alkylimidazoles, 1,2-dimethylimidazole, 2-imidazolidinone, thiabendazole, ammonia, alkylamines, tetramethylenesulfoxide (TMSO), urea, N,N,A ,A^-tetramethylurea (TMU), thiourea, lactams, hydroxypyridines, 2-pyridone, pyridine-N-oxide, picoline-N-oxides, 2,6- lutidine, 2,6-lutidine N-oxide, pyrazine, pyrazine-JV-oxide, 1,4-dithiane

monosulfoxide, propionitrile, butyronitrile, benzonitrile and benzylnitrile.

The liquid metal salt of any of claim 1, wherein L is selected from the group consisting of acetonitrile, propionitrile, butyronitrile, isobutyronitrile, acrylonitrile, 2- hydroxycyanoethane, phenylacetonitrile, benzonitrile and benzylnitrile.

The liquid metal salt of any of claims 1 and 3, wherein L is acetonitrile.

The liquid metal salt according to any one of claims 1 to 4, wherein said negative charged ligand, Y, and said counter anion X are different.

The liquid metal salt of any of claims 1 to 5, wherein X is

bis(trifluoromethylsulfonyl)imide.

The liquid metal salt of any of claims 1 to 5, wherein Y is

bis(trifluoromethylsulfonyl)imide.

The liquid metal salt of any of claims 1 to 6, wherein Y is chloride or bromide.

The liquid metal salt of any of claims 1, 2, 4 and 6, wherein said metal (M) ion is copper(I); L is 1-methylimidazole; and X is bis(trifluoromethylsulfonyl)imide.

10. The liquid metal salt of any of claims 1, 2, 4 to 7, wherein metal (M) ion is copper(I); L is 1-methylimidazole; and Y is bis(trifluoromethylsulfonyl)imide.

11. The liquid metal salt of any of claims 1, 3, 4 and 6, wherein said metal (M) ion is silver(I); L is acetonitrile; and X is bis(trifluoromethylsulfonyl)imide.

12. The liquid metal salt of claim 1, wherein the liquid metal salt isbeing selected from the group consisting of copper(I) tetrakis(acetonitrile)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(methylimidazole)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(butylimidazole)

bis(trifluoromethylsulfonyl)imide, copper(I) bis(2,2'-bipyridine)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(pyridine)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(3-picoline)

bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(benzonitrile)

bis(trifluoromethylsulfonyl)imide, zinc(II) bis(trifluoromethylsulfonyl)imide hexahydrate, silver(I) tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide, silver(I) tris(acetonitrile) bis(trifluoromethylsulfonyl)imide, silver(I) (acetonitrile)₂.5

bis(trifluoromethylsulfonyl)imide, silver(I) bis(acetonitrile)

bis(trifluoromethylsulfonyl)imide, silver(I)mono(acetonitrile)

bis(trifluoromethylsulfonyl)imide and copper(I) tetrakis(methylimidazole) trifluoromethanesulfonate.

13. The liquid metal salt of any of claims 1 to 12 with a melting point below 100°C.

14. The liquid metal salt of any of claims 1 to 12 with a melting point below 50°C.

15. The liquid metal salt of any of claims 1 to 12 with a melting point below room

temperature.

16. The use of the liquid metal salts of any of claims 1 to 15 in an electrodeposition

process.

17. The use of the liquid metal salts of any of claims 1 to 15 for electrodeposition of a metal M.

18. The use of claim 17, wherein the metal M is selected from the group consisting of copper, zinc, silver, gold, platinum, cobalt, nickel, tungsten, molybdenum, and aluminium.

19. The use of any of claims 16 to 18 at a current density of at least 10 A/dm . 20. The use of the liquid metal salts of any of claims 1 to 15 for battery applications.

21. The use of the liquid metal salts of any of claims 1 to 15 in electrochromic devices.

22. The use of the liquid metal salts of any of claims 1 to 15 in fuel cells.

23. The use of the liquid metal salts of any of claims 1 to 15 for electropolishing

applications.

24. The use of the liquid metal salts of any of claims 1 to 15 for electroless deposition of a metal M.

25. The use of claim 24, wherein the metal M is selected from the group consisting of copper, zinc, silver, gold, platinum, cobalt, nickel, tungsten, molybdenum, and aluminium.