Vacancy-Free Prussian Blue Nanocrystals with High Capacity and Superior Cyclability for Aqueous Sodium-Ion Batteries

Aqueous Na-ion batteries have the competitive advantages of being low costing and possessing inherent safety, and they are particularly suitable for large-scale energy-storage applications. However, the development of this new battery system is hindered by the lack of suitable Na hosts with sufficiently high capacity and cycle life. Herein, we report vacancy-free Na2CoFe(CN)(6) nanocubes synthesized by a controlled crystallization reaction and reveal their use as a new aqueous cathode with reversible Na-storage behavior. Owing to its perfect lattice framework with two redox-active sites, this material exhibits a high reversible capacity of 130 mA hg(-1), a strong rate capability at 20 C, and superior cyclability with 90% capacity retention over 800 cycles, all of which indicate that this material may possibly serve as a high-performance and long-life cathode for aqueous Na-ion batteries. Also, the synthetic strategy described in this work may be extended to a wide range of Prussian blue compounds for the fabrication of well-shaped nanocubes with few defects for energy storage, catalysis, and other applications.