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 FeSe2 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 FeSe2@NC microrods, the N-doped carbon shell can facilitate mass transport/electron transfer, protect the FeSe2 core from the electrolyte, and accommodate volume variation of FeSe2 with the help of the inner void of the core. Thus, the FeSe2@NC microrods can maintain strong structural integrity upon long cycling and ensure a good reversible conversion reaction of FeSe2 during the discharge/charge process. As a result, the as-prepared FeSe2@NC microrods exhibit excellent sodium storage performance and ultrahigh stability, achieving an excellent rate capability (411 mAh g-1 at 10.0 A g-1) and a long-term cycle performance (401.3 mAh g-1 after 2000 cycles at 5.0 A g-1).
Keywords: anode materials; hollow structure; microrods; sodium ion batteries; ultralong cycle life.