Lithium metal oxides may be regenerated under ambient conditions from materials recovered from partially or fully depleted lithium-ion batteries. Recovered lithium and metal materials may be reduced to nanoparticles and recombined to produce regenerated lithium metal oxides. The regenerated lithium metal oxides may be used to produce rechargeable lithium ion batteries.

Compositions suitable for reversibly storing heat in thermal energy systems (TES) include a salt hydrate represented by the formula: MX.sub.q.nH.sub.2O. M is a cation selected from Groups 1 to 14 of the IUPAC Periodic Table, X is a halide of Group 17, q ranges from 1 to 4, and n ranges from 1 to 12. The cation (M) may have an electronegativity of ≤ about 1.8 and a molar mass ≤ about 28 g/mol. The anion (X) may have an electronegativity of ≥ about 2.9 to ≤ about 3.2. A distance between a cation (M) and coordinating water molecules (H.sub.2O) is ≤ about 2.1 Å. Thermal energy systems (TES) incorporating such compositions are also provided that are configured to reversibly store heat in the thermal energy system (TES) via an endothermic dehydration reaction and to release heat in in the thermal energy system (TES) via an exothermic hydration reaction.

Compositions suitable for reversibly storing heat in thermal energy systems (TES) include a salt hydrate represented by the formula: MX.sub.q.nH.sub.2O. M is a cation selected from Groups 1 to 14 of the IUPAC Periodic Table, X is a halide of Group 17, q ranges from 1 to 4, and n ranges from 1 to 12. The cation (M) may have an electronegativity of ≤ about 1.8 and a molar mass ≤ about 28 g/mol. The anion (X) may have an electronegativity of ≥ about 2.9 to ≤ about 3.2. A distance between a cation (M) and coordinating water molecules (H.sub.2O) is ≤ about 2.1 Å. Thermal energy systems (TES) incorporating such compositions are also provided that are configured to reversibly store heat in the thermal energy system (TES) via an endothermic dehydration reaction and to release heat in in the thermal energy system (TES) via an exothermic hydration reaction.

Provided is an active material for a fluoride-ion secondary battery, the active material containing a composite fluoride. The composite fluoride has a layered structure and is represented by a composition formula A.sub.mM.sub.nF.sub.x, where A is an alkali metal, M is a transition metal, 0<m≤2, 1≤n≤2, and 3≤x≤4. The alkali metal may be at least one kind selected from the group consisting of Na, K, Rb, and Cs. The transition metal may be a 3d transition metal.

Provided is an active material for a fluoride-ion secondary battery, the active material containing a composite fluoride. The composite fluoride has a layered structure and is represented by a composition formula A.sub.mM.sub.nF.sub.x, where A is an alkali metal, M is a transition metal, 0<m2, 1n2, and 3x4. The alkali metal may be at least one kind selected from the group consisting of Na, K, Rb, and Cs. The transition metal may be a 3d transition metal.

Method embodiments useful for recycling spent lithium-ion battery (LIB) electrodes to extract critical and/or valuable elements from LIBs are provided and involve mechanochemical processing of spent LIB electrodes in the presence of certain chemical agents to recover products that can include, but are not limited to, metallic solids such as elemental metals or metal alloys, and/or inorganic compounds, metal salts, or organometallic derivatives. The desired products can be separated from by-products and contaminants and further processed into LIB electrode materials or/and other substances.

The invention relates to a method for producing a metal chalcogenide thin film electrode, comprising the steps: (a) contacting a metal or metal oxide with an elementary halogen in a non-aqueous solvent, producing a metal halide compound in the solution, (b) applying a negative electric voltage to an electrically conducting or semiconducting substrate which is in contact with the solution from step (a), and (c) during and/or after step (b) contacting the substrate with an elementary chalcogen forming a metal chalcogenide layer on the substrate. The invention also relates to a metal chalcogenide thin film electrode which can be produced by the method and its use as an anode for releasing oxygen during (photo)electrochemical water splitting.

The invention relates to a method for producing a metal chalcogenide thin film electrode, comprising the steps: (a) contacting a metal or metal oxide with an elementary halogen in a non-aqueous solvent, producing a metal halide compound in the solution, (b) applying a negative electric voltage to an electrically conducting or semiconducting substrate which is in contact with the solution from step (a), and (c) during and/or after step (b) contacting the substrate with an elementary chalcogen forming a metal chalcogenide layer on the substrate. The invention also relates to a metal chalcogenide thin film electrode which can be produced by the method and its use as an anode for releasing oxygen during (photo)electrochemical water splitting.

An aqueous cobalt chloride solution refinement method, in which metallic nickel is washed with an acidic liquid having a pH of not more than 2.5 before the metallic nickel is brought into contact with the aqueous solution containing cobalt chloride. Since the metallic nickel is washed with the acidic liquid having a pH of not more than 2.5, a passive film on a surface of the metallic nickel is removed and therefore, when the metallic nickel comes in contact with the aqueous solution containing cobalt chloride, an impurity more noble than the metallic nickel can be precipitated by a cementation reaction. In addition, since the metallic nickel is only washed with acid to be brought into contact with the aqueous solution containing cobalt chloride, impurities can be easily removed from the aqueous solution containing cobalt chloride.

An aqueous cobalt chloride solution refinement method, in which metallic nickel is washed with an acidic liquid having a pH of not more than 2.5 before the metallic nickel is brought into contact with the aqueous solution containing cobalt chloride. Since the metallic nickel is washed with the acidic liquid having a pH of not more than 2.5, a passive film on a surface of the metallic nickel is removed and therefore, when the metallic nickel comes in contact with the aqueous solution containing cobalt chloride, an impurity more noble than the metallic nickel can be precipitated by a cementation reaction. In addition, since the metallic nickel is only washed with acid to be brought into contact with the aqueous solution containing cobalt chloride, impurities can be easily removed from the aqueous solution containing cobalt chloride.