• • Ion association in weakly solvating electrolytes lowers the onset temperature of exothermic reactions by ~94 °C, directly linking electrolyte microstructure to thermal runaway risk.
• • The solvent-relay electrolyte enables a 4.5-V graphite-NCM811 pouch cell (1.1 Ah) to achieve 1,000 cycles at 0.45 C with ~81.9% capacity retention over 4,100 hours, demonstrating exceptional longevity.
• • The strategy decouples SEI formation (promoted by ion association at room temperature) from thermal stability (enhanced by ion dissociation at elevated temperatures), addressing the core safety-longevity trade-off.
• • The design relies on a temperature-sensitive 'passing solvent' and a temperature-insensitive 'receiving solvent', enabling precise regulation of ion solvation microenvironments, which is scalable to other high-energy electrode systems.