Encapsulating Selenium into Biomass-Derived Nitrogen-Doped Porous Carbon As the Cathode for Sodium–Selenium and Potassium–Selenium Batteries

Developing a host that enhances active selenium utilization and mitigates the polyselenide shuttle effect is crucial for both sodium–selenium (Na–Se) and potassium–selenium (K–Se) storage systems. Herein, a biomass-derived three-dimensional nitrogen-doped cross-linked porous carbon (3D-N-CPC) is designed as a Se host. The high specific surface area of 3D-N-CPC ensures the efficient utilization of Se/Na2Se/K2Se. The abundant micromesoporous structures can not only serve as physical barriers for storing small selenium molecules and confining polyselenides but also effectively alleviate the volume expansion during cycling. In addition, in situ biomass-derived N-doped active sites can improve the electrical conductivity and accelerate the polyselenide conversion kinetics. By combining these advantages, the 3D-N-CPC/Se electrode exhibits a high reversible capacity of 393 mA h g–1 after 2000 cycles at 2C and a superior rate performance of 328 mA h g–1 at 10C for Na–Se batteries. Moreover, the 3D-N-CPC/Se electrode demonstrates performance in Na–Se batteries across a wide temperature range (−10 to 50 °C). In K–Se batteries, the 3D-N-CPC/Se electrode maintains a capacity of 476 mA h g–1 after 200 cycles at 0.2C. This work could pave the way for the development of a biomass-derived conductive carbon matrix with porous structure in advanced selenium-based battery systems.