A Novel Hydrated Iron Vanadate Cathode Material for Advanced Aqueous Nickel‐Ion Batteries

Abstract Aqueous nickel‐ion batteries (ANIBs) as an emerging energy storage device attracted much attention owing to their multielectron redox reaction and dendrite‐free Ni anode, yet their development is hindered by the divalent properties of Ni 2+ and the lack of suitable cathode materials. Herein, a hydrated iron vanadate (Fe 2 V 3 O 10.5 ∙1.5H 2 O, FOH) with a preferred orientation along the (200) plane is innovatively proposed and used as cathode material for ANIBs. The FOH cathode exhibits a remarkable capacity of 129.3 mAh g −1 at 50 mA g −1 and a super‐high capacity retention of 95% at 500 mA g −1 after 700 cycles. The desirable Ni 2+ storage capacity of FOH can be attributed to the preferentially oriented and tunnel structures, which offer abundant reaction active planes and a broad Ni 2+ diffusion path, the abundant vacancies and high specific surface area further increase ion storage sites and accelerate ion diffusion in the FOH lattice. Furthermore, the Ni 2+ storage mechanism and structural evolution in the FOH cathode are explored through ex situ XRD, ex situ Raman, ex situ XPS and other ex situ characteristics. This work opens a new way for designing novel cathode materials to promote the development of ANIBs.