An electrolyte for use in a rechargeable cell whose charging voltage exceeds 3.8 volts includes a redox chemical comprising a substituted aromatic molecule in which .alpha. hydrogens are either absent, or are sterically against loss from the ionized form of the molecule. Such as chemical can act as a redox shuttle during overcharge, suppressing damage to the cell and preventing the deposition of metallic lithium during the overcharge of a lithium ion cell, but does not affect normal operation of the cell during either charge or discharge. One such molecule is hexaethyl benzene.