Exploring the Disparities in Capacity and Cycling Stability of NH4V4O10 Cathodes in ZnSO4 and Zn(OTf)2 Electrolytes

This investigation delves into the critical role of electrolyte selection in determining the capacity and cycling stability of NH4V4O10 (NVO) cathodes within aqueous zinc-ion batteries. As a commonly used electrolyte, ZnSO4 electrolyte, while economical, exhibits suboptimal performance due to earlier byproduct formation and the presence of less soluble byproducts compared to Zn(OTf)2 electrolyte. This leads to slower electrochemical kinetics, increased impedance, and ultimately, lower capacity. Furthermore, the original NVO cathode undergoes partial transformation into a lower capacity cathode of Zn3(OH)2V2O7·2H2O (ZVO) after multiple cycles in ZnSO4 electrolyte, contributing to further degradation in cycling stability. In stark contrast, the use of Zn(OTf)2 electrolyte demonstrates superior cyclability, characterized by the absence of ZVO formation and the reversible generation/disappearance of byproduct ZBS, thereby delivering enhanced cycling stability. These observations are corroborated by kinetic analyses employing electrochemical impedance spectroscopy (EIS), galvanostatic intermittent titration technique (GITT), and in situ pH measurements. This study provides valuable insights into the intricate interplay between electrolyte choice, byproduct formation, and battery performance, offering valuable guidance for optimizing electrolyte selection in aqueous zinc-ion batteries.