VSe2 ultrathin nanosheets embedded in a three-dimensional N-doped carbon framework with enhanced cycling performance for sodium-ion battery

Vanadium diselenide (VSe 2 ), with large interlayer spacing, is a promising anode material for sodium-ion batteries (SIBs). However, due to the existence of a conversion reaction, VSe 2 will encounter a huge volume change during charging/discharging, resulting in electrode pulverization. On the other hand, VSe 2 nanosheets are prone to disordered stacking during the deintercalation of sodium ions, affecting the next intercalation. Therefore, VSe 2 embedded into a three-dimensional N-doped carbon framework (VSe 2 @3D-CN), was constructed to solve the above problems. Firstly, the three-dimensional carbon framework, with void spaces, can maintain the structural integrity of the electrode during charging/discharging, improving cycle performance. Secondly, the structure that VSe 2 nanosheets are embedded in a three-dimensional carbon framework can avoid disordered stacking for VSe 2 , which can maintain an open insertion channel of sodium ions. Thirdly, nitrogen doping can increase the active sites, enhancing the absorption of sodium ions in the carbon layer and thus obtaining superior rate performance. Based on the synergistic effect of the above modification strategies, outstanding electrochemical performance was obtained. After charging and discharging 150 times at a current density of 200 mA/g, the specific capacity of VSe 2 @3D-CN is up to 465 mAh/g. Besides, the sodium storage model of VSe 2 @3D-CN has been built via ex situ XPS and ex situ HRTEM tests, which provides an important reference for improving cycle performance.