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 (NH 4 + ) host material that possesses high capacity and prolonged cycle life. Herein, we explore the potential of layered V 10 O 24 ·nH 2 O, synthesized via electrodeposition method, for use in high-capacity aqueous NH 4 + storage. Our investigation, supported by both experimental observations and first-principles theoretical computations, has demonstrated that the layered V 10 O 24 ·nH 2 O exhibits commendable electrochemical performance for aqueous NH 4 + 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 NH 4 + in the V 10 O 24 ·nH 2 O 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 V 10 O 24 ·nH 2 O electrodes for sustainable energy storage applications and offers some insights for high-performance hybrid capacitors with non-metallic NH 4 + as the charge carrier.