FeSe@C Microrods as a Superior Long-Life and High-Rate Anode for Sodium Ion Batteries.

Transition-metal selenides have emerged as promising anode materials for sodium ion batteries (SIBs). Nevertheless, they suffer from volume expansion, polyselenide dissolution, and sluggish kinetics, which lead to inadequate conversion reaction toward sodium and poor reversibility during the desodiation process. Therefore, the transition-metal selenides are far from long cycling stability, outstanding rate performance, and high initial Coulombic efficiency, which are the major challenges for practical application in SIBs. Here, an efficient anode material including an FeSe core and N-doped carbon shell with inner void space as well as high conductivity is developed for outstanding rate performance and long cycle life SIBs. In the ingeniously designed FeSe@NC microrods, the N-doped carbon shell can facilitate mass transport/electron transfer, protect the FeSe core from the electrolyte, and accommodate volume variation of FeSe with the help of the inner void of the core. Thus, the FeSe@NC microrods can maintain strong structural integrity upon long cycling and ensure a good reversible conversion reaction of FeSe during the discharge/charge process. As a result, the as-prepared FeSe@NC microrods exhibit excellent sodium storage performance and ultrahigh stability, achieving an excellent rate capability (411 mAh g at 10.0 A g) and a long-term cycle performance (401.3 mAh g after 2000 cycles at 5.0 A g).