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

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 Ni²⁺ and the lack of suitable cathode materials. Herein, a hydrated iron vanadate (Fe₂V₃O_10.5∙1.5H₂O, 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 Ni²⁺ storage capacity of FOH can be attributed to the preferentially oriented and tunnel structures, which offer abundant reaction active planes and a broad Ni²⁺ 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 Ni²⁺ 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.