Selenium vacancy-rich and carbon-free VSe₂ nanosheets for high-performance lithium storage

VSe₂ is a typical transition metal dichalcogenide with metallic conductivity, which makes it a potentially promising electrode material for lithium-ion batteries (LIBs). However, further research into the VSe₂ nanomaterial for electrochemical applications has been seriously impeded by the practical difficulty of synthesizing phase-pure VSe₂. In this work, Se vacancy-rich VSe₂ nanosheets were synthesized by a one-step solvothermal method with suitable reactants. Benefiting from the strong reduction ability of hydrazine hydrate, V⁴⁺ was partly reduced into V³⁺, resulting in abundant Se vacancies being generated in situ in the as-obtained VSe₂ nanosheets. Positron annihilation lifetime spectroscopy, X-ray absorption spectroscopy and photoluminescence spectroscopy all confirmed the existence of Se vacancies. When applied as the anode material for LIBs, the VSe₂ nanosheets can deliver a remarkable reversible capacity of 1020 mA h g^-1 at 0.1 A g^-1 after 100 cycles, and even at 2 A g^-1 a high specific capacity of 430 mA h g^-1 is reached. Electrochemical characterizations further reveal that the Se vacancies in the VSe₂ nanosheets can significantly enhance lithium-ion diffusion kinetics and increase the number of electrochemical active sites, which are responsible for the good lithium-storage performance. This work may provide an alternative approach for rational design of other high-performance electrode materials for LIBs to satisfy demand for future sustainable development.