Hydrogen Sodium Vanadium Oxide Hydrate with Oxygen Vacancy: A New Layered Cathode Material for Sodium-Ion Battery

The layered HNaV6O16·4H2O (hydrogen sodium vanadium oxide hydrate) with large interlayer spacing and interlayer H+ has been used as a cathode for the zinc-ion battery. However, it is rarely applied in sodium-ion batteries, and only a report tests its initial discharge capacity of ∼23 mAh g–1 at 50 mAh g–1. In this regard, we first develop HNaxV6O16–y·nH2O with an abundant oxygen vacancy (Vo) by a hydrothermal method and then realize the double modification of Co2+ preintercalation and further Ti3C2Tx coating (Vo-CHNVOT) by an in situ preintercalating and electrostatic self-assembly method, respectively. Benefiting from the synergistic effect of Vo, Co2+, and Ti3C2Tx, Co2+ preintercalation and further Ti3C2Tx coating improve the Na+ diffusion kinetics, reinforce the lattice stability, weaken the electrochemical polarization, elevate the charge and discharge stability, and enhance the reaction activity at high voltage. The Vo-CHNVOT cathode shows excellent Na+ storage properties with discharge capacities of 85.5 and 82.5 mAh g–1 after 100 cycles at 165 and 660 mA g–1, where the capacity retention rates reach 75.2% and 78.6%, respectively.