Evaluation of Cyclooctatetraene‐Based Aliphatic Polymers as Battery Materials: Synthesis, Electrochemical, and Thermal Characterization Supported by DFT Calculations

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. COT battery? Two aliphatic polymers, side‐group‐functionalized with cyclooctatetraene (COT) units, and four COT model compounds were synthesized and investigated towards their ability to serve as an electrode material in organic batteries (see figure). Although the model compounds showed promising electrochemical reversibility, the polymers suffered from thermal dimerization and cross‐linking reactions between the COT units.