Functional Electrolytes: Recent Advances in Development of Additives for Resistance Reduction

The concept of "Functional Electrolytes" first reported in 1999 by Ube Industries, Ltd. provides improved battery performances by adding miniscule amounts of various additives to highly purified base-electrolytes, which deliberately induce additive decomposition to form "Controlled Thin Layer (CTL)" instead of uncontrolled formation of undesired thick SEI. Recently we examined various sulfonate esters and evaluated the influence of substituent groups on the battery resistance. The resistance reduction effect is found to be greater for highly branched structures or highly distortional structures of sulfonate esters. Interestingly, even Li salts containing a sulfonate ester structure shows a strong resistance reduction effect. Impedance measurements of the cathode and the anode reveal that additives suppress the cathode resistance increase by electrochemical process rather than chemical process.