Overcoming the temperature limitation of lithium-ion batteries: Local dynamics in supported ionic liquid–polymer electrolytes

Lithium-ion batteries designed for operation under harsh conditions require electrolytes that mitigate the volatility, flammability, and thermal instability of organic electrolytes. In this work, we study a high-temperature supported polymer electrolyte based on the tetrabutylphosphonium (trifluoromethylnonafluorobutylsulfonyl) imide (P4444IM14) ionic liquid with the LiTFSI salt, confined within polyacrylonitrile (PAN) membrane. Ion dynamics were studied using multinuclear NMR, combining diffusion and FFC-NMR on 1H, 19F, and 7Li, complemented by solid-state 13C NMR of the PAN host. PFG-NMR shows that LiTFSI reduces ionic self-diffusion in the liquid electrolyte, while incorporation into the PAN membrane does not further limit diffusion. Consistently, NMRD profiles remain essentially unchanged upon confinement with the polymer membrane, with no evidence of additional relaxation mechanisms associated with confinement, indicating weak dynamic coupling at the polymer–electrolyte interface. Thermal and electrochemical properties were also investigated confirming minimal influence of the PAN on electrolyte performance.