Se vacancies-rich VSe2 nanosheets with carbon-free 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, the further research of the VSe2 nanomaterial for electrochemical applications has been seriously impeded by the practical difficulty of synthesizing phase-pure VSe2. In this work, Se vacancies-rich VSe2 nanosheets were synthesized by one-step solvothermal method with suitable reactants. Benefitting from the strong reduction ability of hydrazine hydrate, V4+ was partly reduced into V3+, thus resulting in abundant Se vacancies generating in-situ in the as-obtained VSe2 nanosheets. Positron annihilation lifetime spectroscopy (PALS), X-ray absorption spectroscopy (XAS) and photoluminescence (PL) spectroscopy all confirmed the existence of the 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 the lithium-ion diffusion rate and increase the number of the electrochemical active sites, and these two factors are responsible for the good lithium storage performance. This work may provide an alternative light for rationally designing other high-performance electrode materials for LIBs to satisfy the demand for future sustainable development.