Phenothiazine Molecules

The molecules 10-methylphenothiazine, 10-ethylphenothiazine, 3-chloro-10-methylphenothiazine, 10-isopropylphenothiazine, and 10-acetylphenothiazine are shown to be stable redox shuttle additives in /graphite and Li-ion coin cells to protect against overcharge and overdischarge. The diffusion constant of 10-methylphenothiazine was measured using cyclic voltammetry to be , which translates to maximum shuttle-protected overcharge current densities near in practical cells. Although the redox potentials of these molecules (near ) are somewhat low for , their stability over repeated overcharge and overdischarge cycles is about equal to that of 2,5-di- tert -butyl-1,4-dimethoxybenzene that has been shown to provide protection for over of 100% overcharge at C/10. Given the stability of these oxidized molecules, we believe that phenothiazine represents an attractive core for ligand substitution to adjust the redox potential to more practical values.