Elucidating Charge Carrier Solvation in Biredox Eutectic Electrolytes for Nonaqueous Symmetrical Organic Redox Flow Batteries

Abstract

Charge carrier solvation is crucial for mass transfer rates and redox kinetics of redox couples in organic redox flow batteries (ORFBs), yet it remains underexplored. This study employs molecular dynamics simulations to investigate charge carrier solvation in biredox eutectic electrolytes (BEEs) under diverse solvent and salt conditions. Results demonstrate that acetonitrile (ACN) molecules preferentially occupy the primary solvation shell of the bis(trifluoromethanesulfonimide) anions (TFSI^–) in the catholyte and the tetrabutylammonium cations (TBA⁺) in the anolyte, forming charge carrier solvation, thus decoupling the molecular interactions within the BEEs and accelerating the redox kinetics in ORFBs. With an optimized ACN-TBATFSI electrolyte, a prototype symmetrical flow cell can achieve a high output voltage of 2.35 V, high material utilization of 93%, and stable cyclability with a capacity retention rate of 99.97% per cycle after 1200 cycles. This work highlights the potential of modulating the charge carrier solvation to enhance the electrochemical performance of ORFBs.