Evaluation of Cyclooctatetraene-Based Aliphatic Polymers as Battery Materials: Synthesis, Electrochemical, and...

Organic electrode materials for rechargeable batteries are becoming a viable alternative for existing technologies. In particular, redox polymers have shown great performances. While many cathode-active derivatives are known, the development of their anode-active counterparts, required for the design of full-organic batteries, lacks behind. Here we present investigation on the suitability of cyclooctatetraene (COT)-based aliphatic polymers as anode-active battery materials, inspired by the known reversible reduction chemistry of COT at low electrochemical potential. We found that both synthesized polystyrene derivatives, side-group functionalized with COT, showed limited electrochemical reversibility of the reduction processes, whereas reductions proceeded reversibly in model compounds of these polymers. Differential scanning calorimetry measurements and density-functional theory calculations showed that this incomplete reversibility was due to cross-linking reactions occurring between COT units in the polymers. For the future of COT-based redox polymers, we propose a molecular design that prevents these cross-linking reactions.