Aqueous nickel-ion battery with Na2V6O16·2H2O nanowire as high-capacity and zero-strain host material

Abstract Aqueous multivalent metal-ion rechargeable batteries have attracted particular interest as the safe and sustainable storage systems for renewable energies. Herein, a new charge carrier of Ni2+ is reported, which can shuttle between the chosen Na2V6O16·2H2O host material and Ni foam in the Ni(CF3SO3)2-based aqueous electrolyte. The proposed Na2V6O16·2H2O delivers a specific capacity of 164.9 mA h g−1 at the current density of 50 mA g−1 and high Coulombic efficiency of nearly 100%. Ex-situ XRD suggests Na2V6O16·2H2O undergoes a negligible volume change of 0.19% owing to the smaller ionic radius of Ni2+. Moreover, a combination of spectroscopic measurements and theoretical simulations not only confirm the rocking-chair mechanism in the designed Ni-ion battery but also good electrochemical reversibility as well as fast Ni2+ diffusion.