Decoding the mechanism of self-discharge and optimal electrolyte reconfiguration for advanced vanadium-based aqueous zinc batteries

The self-discharge of aqueous zinc batteries during idle periods remains elusive, and warranting adequate voltage and sufficient capacity is not trivial, due to the components of the battery system and the reciprocal influence among them. To investigate the origin of self-discharge, herein we construct a Zn||V₂O₅·nH₂O system with sulfate- and sulfonate-based electrolytes. Diagnosing self-discharge at various electrolyte concentrations and pH values and under different test conditions such as time and temperature provides valuable insights into the underlying mystery. Subsequently, the addition of dimethyl sulfoxide (DMSO) or ethylene glycol (EG) into the electrolyte, combined with polyacrylamide (PAM), forms a consummate tactic. This tactic triggers a double coupling network and an interactive synergistic effect, successfully mitigating the reversible and irreversible self-discharge while safeguarding the open-circuit voltage. It results in remarkable anti-self-discharge performance, with the ZnSO₄-PAM-40%DMSO or ZnSO₄-PAM-70%EG gel electrolyte exhibiting ∼80% capacity retention after 24 hours of self-discharge, superior to 61.1% for the initial ZnSO₄ electrolyte. Moreover, the open-circuit voltage of the cell is also effectively elevated. This work represents a substantial achievement in addressing the self-discharge issue, paving the way for further development of aqueous zinc batteries for large-scale energy storage.