Low Temperature Molten Salt Electrolytes Based on Quaternary Alkyl Phosphonium Salts

A new room temperature molten salt comprised of a 1:2 mixture of quaternary alkylphosphonium chloride and aluminum chloride has been discovered. Formation of a room temperature melt was unexpected due to the high melting point of tetramethylphosphonium chloride and the absence of an inversion vibration. The melt has good conductivity and also has higher stability toward electrochemical reduction than any previously studied room temperature melt. Aluminum metal can be reversibly plated and stripped from the melt.