Studies of aromatic redox shuttle additives for LiFePO4-based Li-ion cells

Fifty eight aromatic organic molecules were screened as chemical shuttles to provide overcharge protection for LiFePO4/graphite and LiFePO4/Li4/3Ti5/3O4 Li-ion cells. The majority of the molecules were based on methoxybenzene and on dimethoxybenzene with a variety of ligands added to explore their effect. The added ligands affect the redox potential of the molecules through their electron-withdrawing effect and affect the stability of the radical cation. Of all the molecules tested, only 2,5-di-tert-butyl-1,4-dimethoxybenzene shows an appropriate redox potential of 3.9 V vs Li/Li+ and long-term stability during extended abusive overcharge totaling over 300 cycles of 100% overcharge per cycle. The reasons for the success of this molecule are explored. (c) 2005 The Electrochemical Society.