Enhancing Cycling Stability and Specific Capacitance of Vanadium Nitride Electrodes by Tuning Electrolyte Composition

In this study, the tuning of the KOH electrolyte composition is proposed as a strategy to drastically limit the capacitance fade of vanadium nitride (VN) electrode. We demonstrate that the use of a V⁵⁺ (as VO₄³⁻ vanadates anions) containing KOH electrolyte enhances the cycling stability of VN thin film electrode: a loss of 59% of the capacitance is observed for the electrode tested in KOH over 3000 consecutive cycles. After V⁵⁺ addition in the electrolyte, the capacitance fade is decreased to 23%. Furthermore, the presence of V⁵⁺ species in the solution leads to VN capacitance enhancement from 379 mF cm⁻² for V⁵⁺ ions free electrolyte up to 577 mF cm⁻² at 5 mV s⁻¹ for V⁵⁺-containing KOH solution. The enhanced cycling stability is attributed to the stabilization of an oxide/oxynitride layer at the VN surface, instead of its dissolution, thanks to the chemical equilibrium shift of the VN dissolution reaction. This simple and innovative strategy consisting in tuning the electrolyte composition opens new pathways for other systems that suffer from electrode dissolution in the electrolyte while being electrochemically cycled.