Investigation of modified deep eutectic solvent for high performance vanadium redox flow battery

Amidst the growing need for sustainable energy solutions, the vanadium redox flow battery (VRFB) emerges as a promising technology for large-scale grid energy storage. Compared to conventional aqueous electrolyte system, deep eutectic solvents (DES) have the potential to be considered as the smart electrolyte system for VRFB, owing to its exceptional features such as broad electrochemical window, facile synthesis, low vapor pressure , and economically viable. Unfortunately, original DES have inherently low ionic conductivity and high viscosity, limiting their applicability in flow batteries . To address this issue, we propose deep eutectic solvent (DES)-based vanadium electrolytes containing an optimal amount of aqueous acid and dispersed sulfonated multi-walled carbon nanotubes (sMWCNT) in a 1:6 choline chloride:ethylene glycol mixture (Eu-sMWCNT V III /V IV ) and in detail, evaluate the performance of a single-cell VRFB using this electrolyte. In this work, it is demonstrated that DES electrolyte can be made more conducting and less viscous with subtle modifications. The prepared electrolyte exhibits excellent electrochemical properties , showcasing high-capacity retention (90.0 % over 400 charge/discharge cycles at an applied current density of 30 mA cm -2 ) and efficiencies (average Coulombic and energy efficiencies of 84.0 % and 70.0 % over 400 cycles, respectively). This modified DES system holds potential as the future electrolyte for various flow battery technologies, enabling operation at higher applied current densities compared to reported DES-based flow batteries .