Ultra-stable aqueous nickel-ion storage achieved by iron-ion pre-introduction assisted hydrated vanadium oxide cathode

Aqueous Nickel-ion batteries (ANIBs) are attractive prospects for next-generation energy storage devices, but their development is hindered by deficient satisfactory cathode materials and undefined reaction mechanisms. Herein, a novel layered vanadium oxide with Fe3+-ions pillars (Fe0.29V2O5·0.57H2O, FVO) is developed and innovatively used for effective Ni2+ ion storage. The large interlayer spacing and abundant oxide vacancies of FVO can provide broad ion migration channels and rich ion storage sites. The pre-intercalated Fe3+-ions can firmly support the integrity of the layered structure by Fe-O bonds to achieve excellent cyclic stability. RGO is further introduced to construct the FVO@G composite to improve the conductivity and stability of the FVO electrode. As a result, the FVO@G electrode exhibits exceptional Ni2+ storage performance of 169.8 mAh g−1 at 0.5C and ultrahigh capacity retention of 91.9% after 320 cycles at 10C. The Ni2+ storage mechanism in FVO@G is clarified by in-situ XRD and ex-situ Raman, ex-situ XPS techniques, the results show that FVO@G undergoes a phase transition accompanied by an expansion of the interlayer spacing upon the first charging, and the electrodes display a high degree of structural reversibility and a negligible volume expansion during the subsequent cycles. Furthermore, density functional theory (DFT) calculations show that FVO provides efficient diffusion paths along the b-axis with ultrafast transport kinetics. This work is a significant step in ANIBs research and provides valuable insights for the design of high-performance ANIBs cathode material.