Layered V10O24•nH2O as a new ammonium ion host material for aqueous and quasi-solid-state ammonium-ion hybrid capacitors

Aqueous ammonium-ion hybrid capacitors (AIHCs) emerge as a promising candidate for efficient and sustainable charge storage. Yet, a pivotal challenge lies in the development of an ammonium ion (NH4+) host material that possesses high capacity and prolonged cycle life. Herein, we explore the potential of layered V10O24 center dot nH2O, synthesized via electrodeposition method, for use in high-capacity aqueous NH4+ storage. Our investigation, supported by both experimental observations and first-principles theoretical computations, has demonstrated that the layered V10O24 center dot nH2O exhibits commendable electrochemical performance for aqueous NH4+ storage, which is attributed to the presence of certain amount of crystal water and unique nanowire network structure. This allows for a high specific capacity of 203.1 mAh g- 1 at 0.3 A g- 1 , and the capacity retention is 97.6 % after 20,000 cycles. Ex-situ characterizations uncovered that the insertion and extraction of NH4+ in the V10O24 center dot nH2O layers are reversible processes, accompanied by changes in the oxidation states of vanadium and the reversible contraction and expansion of the interlayer spacing. Furthermore, the as-assembled AIHCs device not only exhibits a voltage window of 1.8 V, surpassing other types of hybrid capacitors, but also retains 82.8 % capacitance after 10,000 cycles, showcasing its good flexibility and potential for series-parallel combinations. The study highlights the potential of layered V10O24 center dot nH2O electrodes for sustainable energy storage applications and offers some insights for high-performance hybrid capacitors with non-metallic NH4+ as the charge carrier.