Accelerating reaction kinetics of AlCl₃/acetamide electrolyte by co-solvation for Al-S batteries

Deep eutectic solvents such as AlCl₃/acetamide (AcA) have demonstrated great potential as room-temperature electrolytes for Al-S batteries, but their high viscosities and low ionic conductivities severely impede the electrochemical reaction kinetics. Herein, we report an effective strategy to optimize AlCl₃/AcA by screening fluorobenzene co-solvents. The optimal 1,2,3-trifluorobenzene (tFBn) effectively dilutes AlCl₃/AcA and has a crowding effect that creates a local high-concentration zone for efficient transport of electro-active ions. Rather than merely functioning as a diluent, tFBn induces the localized aggregation of neutral molecules and ion clusters, which reduces the bulk viscosity by 50% and doubles the ionic conductivity. This localized high concentration, coupled with the rapid migration of ion clusters, accelerates the reaction kinetics and improves the long-cycling stability of Al stripping/plating. tFBn also promotes the transportation of Al-Cl species onto Al to regulate the interphase structures and reduce the resistance. Due to the accelerated reaction kinetics, the tFBn-modified AlCl₃/AcA further improves the S utilization, reduces the polarization, and enhances the capacity retention of Al-S batteries. This study provides important insights into the design of high-performance electrolytes toward practical Al-S batteries.