Mediation of the electrochemical polarization for durable zinc anode

Abstract

Aqueous zinc ion batteries (AZIBs) own significant potential as a promising large-scale electrochemical energy storage technology. However, the application of AZIBs is hindered by challenges of poor cycling life led by severe side reactions and dendrite formation on the Zn anode. Here, we present a strategy for mediating the electrochemical polarization of the Zn anode by introducing a KSeCN additive into the ZnSO₄ electrolyte to achieve high-performance AZIBs. Specifically, the additive's SeCN⁻ ion undergoes automatic decomposition into CN⁻ ions to form Zn(CN)₄²⁻, which possesses a stronger attraction for Zn but entails a larger de-solvation activation energy. The Zn(CN)₄²⁻ mitigates concentration polarization within the electrolyte while increasing the electrochemical polarization of the Zn anode. Consequently, Zn plating occurs gradually and uniformly during the charge and discharge process, resulting in smoother plating with diminished side reactions. As expected, the average Zn plating/stripping coulombic efficiency (CE) reaches 99.78% at a current density of 2 mA cm⁻¹, and the long cycling life of the Zn anode exceeds 1300 hours at a current density of 5 mA cm⁻¹. In addition, the assembled Zn|V₂O₅ cell exhibits excellent capacity retention of 92.44% after 1200 cycles at 2 A g⁻¹. The pouch cell with a high capacity of cathode (25 mg cm⁻²) also demonstrates prominent cycling stability. The strategy of increasing the surface polarization of the Zn anode to achieve a stable performance offers new inspiration for the development of advanced AZIBs.