A pentakis-fused tetrathiafulvalene system extended by cyclohexene-1,4-diylidenes: a new positive electrode material for rechargeable batteries utilizing ten electron redox

Abstract

Pentakis-fused TTF derivatives extended with two cyclohexene-1,4-diylidenes (2a and 2b) have been successfully synthesized. Cyclic voltammetry of the tetrakis(2-ethylhexylthio) derivative (2b) has revealed that it exhibits five stages of the redox process to form 2b¹⁰⁺. A coin-type cell composed of a positive electrode incorporating the tetrakis(methylthio) derivative (2a) exhibits a discharge capacity of 196 mA h g⁻¹, which corresponds to participation of a ten electron redox. It shows a high performance of energy density of 700 mW h g⁻¹ and an output power density of 69 W g⁻¹ with a relatively stable cycle-life performance (72% of the initial discharge capacity after 30 cycles).