A Freestanding and Long‐Life Sodium–Selenium Cathode by Encapsulation of Selenium into Microporous Multichannel Carbon Nanofibers

Abstract Selenium cathode has attracted more and more attention because of its comparable volumetric capacity but much higher electrical conductivity than sulfur cathode. Compared to Li–Se batteries, Na–Se batteries show many advantages, including the low cost of sodium resources and high volumetric capacity. However, Na–Se batteries still suffer from the shuttle effect of polyselenides and high volumetric expansion, resulting in the poor electrochemical performance. Herein, Se is impregnated into microporous multichannel carbon nanofibers (Se@MCNFs) thin film with high flexibility as a binder‐free cathode material for Na–Se batteries. The fibrous unique structure of the Se@MCNFs is beneficial to alleviate the volume change of Se during cycling, improve the utilization of active material, and suppress the dissolution of polyselenides into electrolyte. The freestanding Se@MCNF thin‐film electrode exhibits high discharge capacity (596 mA h g −1 at the 100th cycle at 0.1 A g −1 ) and excellent rate capability (379 mA h g −1 at 2 A g −1 ) for Na–Se batteries. In addition, it also shows long cycle life with a negligible capacity decay of 0.067% per cycle over 300 cycles at 0.5 A g −1 . This work demonstrates the possibility to develop high performance Na–Se batteries and flexible energy storage devices.