A new class of electrochemically and thermally stable lithium salts for lithium battery electrolytes .4. Investigations of the electrochemical oxidation of lithium organoborates

Synthesis, analysis, and purification of lithium bis[2,2'-biphenyldiolato(2-)-O,O']borate lithium bis[salicylato(2-)]-borate, lithium phenolate, and dilithium-2,2'-biphenyldiolate are described. Electrochemical studies show that lithium organoborates are subject to anodic decomposition mechanisms, which depend on their chemical structure. The anodic decomposition of lithium benzenediolatoborates results in the formation of soluble products including chinones, whereas the anodic oxidation of lithium bis[2,2'-biphenyldiolato(2-)-O,O']borate lithium bis[salicylato(2-)]borate, and lithium phenolates entails the formation of thin electronically insulating lithium ion-conducting polymer films, preventing further anion decomposition as well as anodic decomposition of solvents which are sensitive to oxidation. These film-forming materials are useful to enlarge the electrochemical window of electrolyte solutions for lithium batteries and electrochemical capacitors.