Poly(vinylphenoxazine) as Fast-Charging Cathode Material for Organic Batteries

Organic cathode materials are attractive for a new generation of more sustainable batteries due to their comparably low environmental footprint and toxicity. There is a continued quest for new compounds that meet the requirements of a competitive potential and a good cycling performance. We herein present phenoxazine-based polymers as cathode materials with good cycling stability, excellent rate performance, and a high discharge potential of 3.52 V vs Li vertical bar Li+ in composite electrodes. At the ultra-fast rate of 100C, a cross-linked phenoxazine poly(vinylene) showed only slow capacity decay over 10 000 cycles with a capacity retention of 74% in cycle 10 000. Mechanistic investigations using UV/vis/near-infrared (NIR) spectroscopy and density functional theory (DFT) calculations unveiled that unlike in the homologous phenothiazine polymers, pi-interactions played a minor role in phenoxazine-based polymers. Our study is the first to present phenoxazine as a redox-active unit for cathode materials and shows that an elemental change of one atom (S vs O compared to known phenothiazine-based polymers) can have a profound effect on electrochemical performance.