Study on synergy effect of hydrated ionic radius and oxidation state for pre-intercalated cations towards highly reversible magnesium ions batteries

Magnesium ions batteries (MIBs) are promising in that Mg anode shows high theoretical volumetric capacity (3833 mAh cm−3) and is dendrite free deposition upon charging. However, the higher charge/radius ratio of Mg2+ with bivalent nature shows strong electrostatic interaction between Mg2+ and host anion lattice of VS4 in situ grown on N doped tubular graphene (VS4/N-TG), causing the sluggish reaction kinetics and poorer structural stability. Therefore, there is great need to develop strategy for modifying VS4/N-TG. Although interlayer pre-intercalation is an effective way to improve the overall cell performance, the systematic study about the various ionic radius and oxidation states of pre-intercalated cations on modulating electronic structure to enhance the electrochemical performance has not been focused. In this study, cations pre-intercalation engineering is achieved in VS4/N-TG for constructing M0.06VS4/N-TG cathode via electrochemical method. After the systematic study about the effect of hydrated ionic radius and oxidation state of various pre-intercalated cations on electrochemical performance of M0.06VS4/N-TG, pre-intercalated Mg2+ with moderate hydrated ionic radius and oxidation state would enlarge the interchain spacing for facilitating magnesium working ions transportation and maintaining structural stability, as well as change the oxidation states of V element as V2+ and V3+ to enhance the electrochemical reactivity. Therefore, Mg0.06VS4/N-TG deliver superior electrochemical properties, including the excellent cycling stability with nearly 100% capacity retention ratio after 1500 cycles, high specific capacity about 170 mAh/g at 50 mA g−1, superior rate capability (107 mAh/g at 1000 mA g−1) and high anti-self-discharge behavior. The highlighted synergic effect of the hydrated ionic radius and oxidation state would guide more energy storage devices design for obtaining the excellent electrochemical performance.