Vanadium flow batteries (VFBs) are among the most promising technologies for large-scale energy storage due to their high safety, long cycle life, and flexible scalability. However, their deployment in cold climate is hindered by the poor low-temperature stability of vanadium electrolytes. In particular, precipitation of divalent vanadium (V(II)) ions in the negative electrolyte can lead to capacity loss and performance degradation, severely limiting the operating temperature range of VFB systems.
Recently, a research team led by Prof. LI Xianfeng from the Dalian Institute of Chemical Physics(DICP), Chinese Academy of Sciences (CAS) uncovered the origin of low-temperature instability in VFB electrolytes and developed a strategy to suppress precipitation through solvation-shell engineering. The study was published in Angewandte Chemie International Edition.
By combining single-crystal X-ray diffraction (SCXRD), in situ variable-temperature Raman spectroscopy, and density functional theory (DFT) calculations, the researchers revealed the molecular mechanism of V(II) precipitation. They found that decreasing temperature enhances the dissociation of HSO4-, leading to the accumulation of SO42- ions in solution. These sulfate anions bridge adjacent [V(H2O)6]2+ complexes via hydrogen bonding interaction, promoting V(II) dimerization and the formation of ordered clusters that ultimately evolve into VSO4·xH2O precipitates.
Low-temperature instability of the negative electrolyte in VFBs and the corresponding suppression strategy (Image by ZHAN Chengbo and LI Tianyu)
To address this issue, the team developed a dual-site solvation engineering strategyby introducing acetonitrile (ACN) and HCl as co-additives to simultaneously regulate the first and second solvation shells of V(II) ions. This synergistic approach effectively suppresses ion aggregation and enhances electrolyte stability at low temperatures.
As a result, VFBs employing the modified electrolyte maintained an energy efficiency exceeding 80% over 500 cycles at −10 °C, demonstrating outstanding low-temperature electrochemical performance.
"Our study provides fundamental insights into the low-temperature behavior of vanadium electrolytes and offers a rational strategy for designing highly stable, wide-temperature-range electrolytes for flow batteries," said Prof. LI.