Poly(viologen halide)s: both cationic main-chain and counter anions are active for high-performance organic cathodes

Abstract

Redox-active ionic polymers show low solubility in organic electrolytes and high ionic/electronic conductivity, but most of them coupling with non-active counter ions present low specific capacity. Herein, we design polyviologens with halides (Br⁻ or I⁻) as counter anions, which are also redox-active and can participate in energy storage. Poly(viologen halide) electrodes exhibit high initial specific capacity (192 mA h g⁻¹) and high discharge voltage (∼3.7 V). When using carbon cloth as a current collector, the cathode with high mass loading (80 wt%) of poly(viologen iodide) presents high capacity, improved cycling stability (89% capacity retention after 600 cycles at 0.1 A g⁻¹) and rate performance (110 mA h g⁻¹ at 2 A g⁻¹). In addition, the charge storage mechanism is investigated by in situ Raman and ex situ X-ray photoelectron spectroscopy.