C. Buhrmester, Lee Moshurchak, Richard L. C. Wang
Feb 1, 2006
Citations
1
Influential Citations
99
Citations
Quality indicators
Journal
Journal of The Electrochemical Society
Abstract
The molecules 10-methylphenothiazine, 10-ethylphenothiazine. 3-chloro-10-methylphenothiazine, 10-isopropylphenothiazine, and 10-acetylphenothiazine are shown to be stable redox shuttle additives in LiFePO 4 /graphite and LiFePO 4 /Li 4 / 3 Ti 5 / 3 O 4 Li-ion coin cells to protect against overcharge and overdischarge. The diffusion constant of 10-methylphenothiazine was measured using cyclic voltammetry to be 1.5 X 10 - 6 cm 2 /s, which translates to maximum shuttle-protected overcharge current densities near 2 mA/cm 2 in practical cells. Although the redox potentials of these molecules (near 3.5 V) are somewhat low for LiFePO 4 , 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 200 cycles 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.