PNNL

Abstract

Herein we report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide (TFSI-) , hexafluorophosphate (PF6-), perchlorate (ClO4-), tetrafluoroborate (BF4-), and dicyanamide (N(CN)2-) on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Finally, the electrochemical performance of these ionized Fc-species was evaluated and shown to have excellent cell efficiency and superior cycling stability.