Abstract:

Vanadium flow battery (VFB) is considered a promising energy storage technology for large-scale commercial application due to their easy scalability, environmental friendliness, and high safety. However, capacity fade during long-term cycling limits their widespread application in the energy storage field. This study deeply analyzed the changes in electrochemical characteristics of VFB before and after cycling, and combined with the results of potassium permanganate titration, identified electrolyte imbalance and electrode degradation leading to a reduction in anode active material and increased polarization as the main factors for capacity fade. Additionally, the specific discharge capacity of the electrolyte was restored to 92.7% of its initial capacity using oxalic acid reduction, and battery polarization was alleviated by swapping the anode and cathode, confirming that electrode exchange can effectively restore and stabilize the electrochemical activity of the electrodes. Finally, the oxalic acid residue issue was resolved using a constant-voltage charging method, and a process route for oxalic acid recovery of the electrolyte was established, successfully restoring the average oxidation state of the spent electrolyte from 3.580 to 3.508. This research comprehensively analyzed the underlying causes of VFB capacity fade, providing significant guidance for the recovery of the electrolyte. Meanwhile, it proposed a simple and effective technical solution for the residue issue during the oxalic acid recovery process, offering new possibilities for the recovery and reuse of the electrolyte.

Key words: vanadium flow battery, electrolyte recovery, oxalic acid reduction, chemical titration