Temperature-Induced Precipitation of V2O5 in Vanadium Flow Batteries—Revisited

The maximum operation temperature of the vanadium solution in vanadium flow batteries is typically limited to 40 °C to prevent the damaging thermal precipitation of V2O5. Therefore, the operation of batteries at high ambient temperatures is an important aspect to tackle for stationary storage. In the present work, a comprehensive study of the high temperature stability of redox solutions for vanadium flow batteries was performed. In particular, focus was placed on a comparison between batch and in operando precipitation experiments. It was found that, despite being a widely used method in the literature, caution should be taken when assessing the precipitation through capacity fade due to the large influence of external oxidation and cycling parameters, plausibly leading to an incorrect interpretation of the results. The in operando experiments consistently show a precipitation temperature almost 10–20 °C higher than in the batch tests at a 100% state of charge for the same time lapse.