A combined computational/experimental study on tertbutyl- and methoxy-substituted benzene derivatives as redox shuttles for lithium-ion cells

Calculations were performed on a group of 43 t-butyl- and methoxy-substituted benzenes to assess their suitability as redox shuttle additives for lithium-ion cells. One molecule of this type has been previously shown to be excellent for overcharge protection of mesocarbon microbead (MCMB)/LiFePO4 and Li4/3Ti5/3O4/LiFePO4 lithium-ion cells. These calculations showed that 2,5-di-t-butyl- 1,4-dimethoxybenzene was the best molecule in this group, as far as oxidation potential and stability are concerned. Other molecules that showed promise were 2-t-butyl-1,4-dimethoxybenzene, 4-t-butyl-1,2-dimethoxybenzene, and 3,5-di-t-butyl- 1,2-dimethoxybenzene. These molecules were synthesized and tested in coin-type cells to confirm the results expected based on the calculations. The results of the calculations show that the substitution pattern on the molecule can be used to predict the most reactive sites on the oxidized molecule. For the dimethoxy-substituted molecules, the calculations predict that the ortho and para substitution pattern results in more stable oxidized molecules than the meta pattern. (c) 2007 The Electrochemical Society.