Electrochemical characteristics of negative electrodes made of ozone-treated graphite for lithium-ion batteries

Electrochemical characteristics of negative electrodes made of graphite treated in ozone-oxygen environment are studied in an operating lithium-ion battery. Successively treating graphite with ozone and then with a sec-butyllithium solution in cyclohexane dramatically reduces the irreversible capacity and stabilizes discharge characteristics of graphite electrodes cycled in a propylene carbonate-based electrolyte. An ozone-oxygen gaseous mixture containing 5 vol % O-3 is Most effective for the stabilization. According to IR spectroscopy, the treatment gives rise largely to -COLi groups, which ex situ form a passivating solid-electrolyte film on the graphite surface. The film hampers the electroreduction of the organic solvent and reduces the irreversible lithium consumption.