Nitrogen and fluorine co-doped 3D carbon framework embedded VSe2 nanosheets as high-performance sodium-ion battery anode materials

With the shortage of lithium resources caused by the development of lithium-ion batteries, sodium-ion batteries have attracted research interest. Vanadium diselenide (VSe2), a transition metal disulfide compound with large layer spacing, is very promising to be utilized in sodium-ion batteries. However, the material suffers from great volume changes and disordered stacking agglomeration during battery charging and discharging, which brings bad effects on its electrochemical performance. For this reason, the nitrogen-fluorine co-doped three-dimensional carbon framework embedded VSe2 nanosheet (VSe2@3D-CNF) material was prepared by high-energy ball milling method. The three-dimensional carbon framework structure can well alleviate the volume expansion caused by charging and discharging, while avoiding the problem of no stacking of VSe2 during charging and discharging, which is beneficial to improve the stability of the electrode material, and the N and F double doping can increase the active sites and improve the electron transfer rate. The results show that the reversible capacity of VSe2@3D-CNF composite after 200 cycles at a current density of 200 mA g(-1) is 447.3 mAh g(-1), and the Coulomb efficiency is 99.32%. The rate capacities are 522.4, 465, 433.9, 403.4, 367.7, and 283.6 mAh g(-1) at current densities of 0.1, 0.2, 0.3, 0.5, 1, and 2 A g(-1), and the long cycle performance was 335.5 mAh g(-1) after 500 cycles at a high current density of 1 A g(-1). The above results indicate that VSe2@3D-CNF composites are very promising for application in anode materials for SIBs.