Aromatic Compounds as Redox Shuttle Additives for 4 V Class Secondary Lithium Batteries

Redox shuttle, a chemical overcharge protection that consumes the excess current during overcharge, has been studied. Aromatic compounds with two methoxy groups and a halogen directly substituted on the benzene were found to be stable up to about 4 V against lithium, and oxidize above this potential by means of cyclic voltammetry. Of these compounds, compounds with methoxy groups at adjacent positions and opposite positions showed reversible redox reactions. These compounds worked as redox shuttle overcharge protection when added to the electrolyte of a Li/LiCoO{sub 2} coin-type cell. The voltage leveled off right above the full charge voltage even when overcharge current was supplied. The current supplied over the full-charge voltage was not stored in the cell or consumed in a side reaction, but completely converted into heat, and the operation of a redox shuttle in a 4 V class battery was confirmed.