Defect and interlayer spacing engineering of vanadium selenide for boosting sodium-ion storage

Abstract

Vanadium selenide (VSe_2−x) is a promising anode material for grid-scale energy storage due to its high conductivity, large interlayer spacing, and distinctive multielectron transport. However, the electrochemical performances are restricted by sluggish redox kinetics, which deteriorate the cycling stability and specific capacity. Here we propose a synergistic strategy to boost sodium-ion storage by introducing Se vacancies and tuning the interlayer spacing of VSe_2−x. The V–Se bond energy is decreased by the vacancy, which promotes sodium-ion adsorption/conversion, and in parallel, the expanded interlayer spacing accelerates sodium-ion transport. The obtained VSe_2−x/nitrogen-doped carbon (VSe_2−x/NC) exhibits ultrahigh specific capacity (584.4 mA h g⁻¹ at 0.5 A g⁻¹), high rate performance, and excellent cycling stability. In particular, a sodium-ion full cell composed of the VSe_2−x/NC anode and a Na₃V₂(PO₄)₃ cathode delivers unexpected stability with the cycle number exceeding 2400. The sodium-ion storage mechanism is clarified by theoretical calculations and in situ experimental characterization. This work provides a new paradigm to boost sodium-ion battery performances by combining defect and structure engineering.