Selenium vacancy-rich and carbon-free VSe2nanosheets for high-performance lithium storage

VSe(2)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 VSe(2)nanomaterial for electrochemical applications has been seriously impeded by the practical difficulty of synthesizing phase-pure VSe2. In this work, Se vacancy-rich VSe(2)nanosheets were synthesized by a one-step solvothermal method with suitable reactants. Benefiting from the strong reduction ability of hydrazine hydrate, V(4+)was partly reduced into V3+, resulting in abundant Se vacancies being generatedin situin the as-obtained VSe(2)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 VSe(2)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 VSe(2)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.