Studies of Aromatic Redox Shuttle Additives for LiFePO[sub 4]-Based Li-Ion Cells

Abstract

Fifty eight aromatic organic molecules were screened as chemical shuttles to provide overcharge protection for LiFePO4 Li Fe P O 4 /graphite and LiFePO4/Li4/3Ti5/3O4 Li Fe P O 4 ∕ Li 4 ∕ 3 Ti 5 ∕ 3 O 4 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 3.9V 3.9 V vs Li/Li+ Li ∕ Li + and long-term stability during extended abusive overcharge totaling over 300cycles 300 cycles of 100% overcharge per cycle. The reasons for the success of this molecule are explored.