A Molten-Salt Electrolysis Approach for the Recycling of Spent Lithium-Ion Batteries

Abstract

Recycling spent lithium-ion batteries can close the strategic metal cycle while averting ecological and environmental footprints. High-temperature molten salts could act as both a promising electrolyte and a solvent to recover valuable Li and transition metals assisted by an electrochemical method that use electrons to break down the crystal structure and thereby sperate the Li and transition metal. In this paper, the molten salt paired electrolysis method employs electrons as both reducing and oxidizing agents and the molten salt as the solvent to separate the desired products without producing any hazardous secondary waste. Since the valence of Fe in LiFePO4 is 2+, the valence can be moved at both directions if proper electrolytes are chosen and appropriate potentials are applied. Moreover, molten salt electrolytes have a wide electrochemical potential range (e.g., electrochemical window) and considerable capability for dissolving lithium salt, which can be used as an electrolyzer to entail specific electrochemical reactions and solvent extraction processes. A molten salt electrolyzer with a solid LiFePO4 cathode and three types of anodes. All the three electrolyzers work well to electrochemically split LiFePO4 to Fe, Li+, and PO4 3 −. Besides molten carbonates, other types of molten salts such as halides, hydroxide, sulfates can be used. The anodic products are CO2, O2 and Fe3O4 if graphite, Ni10Cu11Fe alloy and LiFePO4 anodes are employed, respectively. To minimize the energy consumption and CO2 emissions, the paired electrolysis cells with dual LiFePO4 electrodes is preferable. In all types of eletrolyzers, the recovery rates of both Li and Fe are over 95.2%. Beside LiFePO4, the molten-salt electrolysis approach can be used to treat a variety of cathode materials of LIBs.