Harnessing Solvation Chemistry of Pentavalent Vanadium for Wide-Temperature Range Vanadium Flow Batteries

Vanadium flow batteries (VFBs) are safe, cost-effective, and scalable solutions for storing renewable energies. However, the poor thermal stability of pentavalent vanadium [V(V)] electrolyte, manifested as V₂O₅ precipitation at high temperatures, leads to more critical heat management, low energy density, and even low reliability. The unclear dynamic solvation chemistry of V(V) ions brings difficulties in solving the above issues intrinsically. Herein, we investigated solvation structures and dynamic evolution of V(V) electrolyte using ab initio molecular dynamics (AIMD) and in situ liquid time-of-flight secondary ion mass spectrometry (ToF-SIMS). For the first time, we clarified the transformation from [VO₂(H₂O)₃]⁺ to VO(OH)₃, identifying the second deprotonation as the rate-determining step. Based on this, we developed stabilization strategies through anion coordination and proton concentration control. The incorporation of HCl and trifluoromethanesulfonic acid improved the thermal stability of V(V) electrolytes remarkably. The optimized electrolyte showed no precipitation during 30-day static tests at 50 °C, enabling stable cycling performance of 3000 cycles in VFB single cells. Further demonstration in a kW-scale stack achieved over 1000 cycles, validating the scalability and viability. Our work provides insights into the solvation chemistry of V(V) species, paving the way to improve the reliability and energy density of a VFB system.