Boron and defects co-doped MXene enables high-performance Na-Se batteries.

Sodium selenium (Na-Se) batteries are considered promising candidates for next-generation energy storage devices due to their high volumetric energy density. However, the Se cathode still faces the problems of the shuttling effect and sluggish selenium reduction kinetics. Improving the surface adsorption and catalytic process of selenium cathode can greatly solve the above issues and achieve excellent performance to enhance the application of Na-Se batteries. Herein, experimental and theoretical simulation results indicate that the boron and defects co-doped MXene (BD-MXene) could initiate the redistribution of electrons and improve the surface polarity, promoting chemical adsorption, thus effectively suppressing the shuttle effect. More importantly, the BD-MXene can promote the conversion between polyselenide, accelerating the electrochemical reaction kinetics of Sodium polyselenide. As a result, the obtained Se@BD-MXene exhibits a high rate performance of 502 mAh g at 50 A g (calculated based on Se@BD-MXene) and excellent cycling stability with a decay per cycle of 0.001 % over 4500 at 10 A g. This work provides a viable strategy to design Se cathodes for Na-Se batteries with high-rate capability and long-term cycling.