A Yolk-Shell-Structured FePO4 Cathode for High-Rate and Long-Cycling Sodium-Ion Batteries.

Amorphous iron phosphate (FePO4 ) has attracted enormous attention as a promising cathode material for sodium-ion batteries (SIBs) because of its high theoretical specific capacity and superior electrochemical reversibility. Nevertheless, the low rate performance and rapid capacity decline seriously hamper its implementation in SIBs. Herein, we demonstrate a sagacious multi-step templating approach to skillfully craft amorphous FePO4 yolk-shell nanospheres with mesoporous nanoyolks supported inside the robust porous outer nanoshells. Their unique architecture and large surface area enable these amorphous FePO4 yolk-shell nanospheres to manifest remarkable sodium storage properties with high reversible capacity, outstanding rate performance, and ultralong cycle life.