Electrochemical sodium storage of copper hexacyanoferrate with a well-defined open framework for sodium ion batteries

Sodium ion batteries are considered to be a promising low-cost alternative to common lithium batteries. The exploration of new electrode materials is extremely important for developing sodium ion batteries. In this work, copper hexacyanoferrate (CuHCF), a kind of Prussian blue analogue, was synthesized by a chemical co-precipitation method and the feasibility of the electrochemical sodium ion storage reaction in CuHCF nano-particles in aqueous solution was investigated. All the results demonstrate that the sodium ions can be reversibly inserted/extracted into/from CuHCF nano-particles in aqueous solution, and a specific capacity of 46 mA h g (-1) is obtained at the current density of 20 mA g (-1). The sodium ion insertion and extraction behaviors are controlled by the solid phase diffusion process in the CuHCF electrode. The well-defined open framework of CuHCF ensures it has good cycle stability. The good performance indicates that CuHCF will be a promising candidate for the cathode materials of sodium ion batteries.