Electrochemical Alloying of Lithium in Organic Electrolytes

Lithium metal was found to alloy with the other metals including noble metals in an organic electrolyte lectrochemical cell: Li/1M LiC104 in pro-pylene carbonate/metal at ambient emperature with the evolution of elec-trical energy. The alloying occurred in many organic electrolytes containing l ithium ions. Both the coulombic efficiency and the rate of alloying were found to be high. The alloys were gray to dark gray and brittle. Chemical and x-ray analysis indicated that they were intermetall ic compounds. It was observed (1, 2) earlier in our laboratory that a cathodic chronopotentiogram in the organic electro-lyte consisting of 1M LiC104 in propylene carbonate consisted of several voltage plateaus prior to the l ith-ium deposition. It was postulated that one of these plateaus might be due to the alloying of l ithium with the substrate. In this paper, I wish to present some ex-perimental evidence to show that l ithium undergoes spontaneous electrochemical loying (SEA) at am-bient temperature with various metals including noble metals at appreciable rates in the organic electrolytes containing l ithium salts. The phenomenon results in the dissolution of the l ithium anode and the simultaneous deposition and alloying of l ithium on the metal cathode, and the evolution of energy in a manner similar to a primary cell. Experimental Materials.--Propylene carbonate (PC) (Eastman Kodak) was vacuum distilled at 12O ~ 1.2 mm Hg. Anhydrous LiC10 ~ was used as received from G. Fredrick Smith Company. The water content of the electrolyte consisting of 1M LiC104 in PC was found to be 0.01 % (volume). The other organic solvents such as ~-butyrolacetone, dimethyl sulfoxide, N, N-dimethyl formamide, methyl formate, tetrahydrofuran, and acetonitrile were used as received. Electrodes.--The l i thium anodes were made by pressing a rectangular piece of l ithium ribbon (0.02 in. thick, Foote Mineral Company Inc.) on the expanded stainless steel current collector. The cathodes of the