Novel electrolyte design for high-efficiency vanadium redox flow batteries with enhanced 3.0 M V3+ stability at low temperatures

Abstract

Vanadium redox flow batteries (VRFB) are gradually becoming an important support to address the serious limitations of renewable energy development. The ideal electrolyte for vanadium batteries needs to ensure the stability of high-concentration vanadium ions in different oxidation states over a wide temperature range. A key issue to be resolved is to improve the stability of V⁵⁺ at high temperatures (50 °C) and V³⁺ at low temperatures (−5 °C). However, to date, no suitable electrolyte has been found that can simultaneously meet these requirements. Here, we report and validate a design strategy for a high-concentration, high-stability electrolyte prepared using raw materials containing both vanadium and chlorine. Notably, no external HCl was added as a chloride source in this study, allowing for controlled H⁺ content. Additionally, the complexation of Cl⁻ and SO₄²⁻ with V³⁺ inhibits the deprotonation of [V(H₂O)₆]³⁺ and prevents the nucleation process prior to precipitation. The developed 3.0 M electrolyte remains stable over a wide temperature range from −5 °C to 50 °C. At 80 mA cm⁻², the energy efficiency of the VRFB exceeds 80 %. Our design increases the vanadium concentration in the VRFB while ensuring stability. This advancement provides data support for high-concentration, high-stability, and high-performance VRFB.