Influence of Ni impurity ions in electrolyte on the performance of vanadium redox flow battery

The impurity ions have negative effects on the thermal stability and electrochemical performance of the electrolyte, limiting the cycling stability of vanadium redox flow battery (VRFB). Since the Ni ions are considered as one of the most common impurity ions in the electrolyte of VRFB, this study focuses on the effect of Ni ions on various aspects of battery performance. The results showed that Ni ions above 10 mg/L observably accelerated the precipitation of the V(V) electrolyte and deteriorated the reversibility of the V²⁺/V³⁺ couple. In addition, the Ni ions above 10 mg/L have greatly negative influences on the diffusion coefficient of vanadium ions, the coulombic efficiency, and energy efficiency of the battery. It was found that such unfavorable effects were mainly due to the Ni ions in the electrolyte masking the active sites of graphite felt for vanadium redox reaction.