Electrolyte composition dependent Li-ion binding and degradation of organic radical battery material†

Electrolyte composition governs battery design due to its influence on ion dynamics, active material stability, and performance. Using electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR), complemented by density functional theory calculations, the impact of electrolyte properties on an organic redox unit, TEMPO methacrylate (TMA), is explored. EPR hyperfine spectroscopy revealed that the amount of TMA bound to Li ions can be altered depending on the solvent used, and a higher fraction of TMA are Li-bound in linear carbonates compared to cyclic carbonates. The active material itself can be involved in the solvation shell of electrolyte ions, and insight into active material–electrolyte interactions from pulsed EPR may enable tuning of ion dynamics in organic radical batteries. Furthermore, the impact of moisture-dependent electrolyte degradation on the stability of TMA, investigated using time-resolved NMR and continuous wave EPR spectroscopy, resulted in the identification of degradation products and a degradation pathway mediated by the electrolyte.