FeFe(CN)₆ Nanocubes as a Bipolar Electrode Material in Aqueous Symmetric Sodium-Ion Batteries

Bipolar materials, which work as both the cathode and anode material in aqueous sodium-ion batteries, have advantages over aqueous electrolytes such as the low cost of sodium and high convenience of the material processing. However, the available materials are greatly limited. Herein, Prussian blue FeFe(CN)₆ nanocubes were successfully synthesized by using a modified co-precipitation method. Owing to the well-separated redox reactions, fair cycling stability and rate capability of FeFe(CN)₆ , it could be developed as a bipolar material in an aqueous sodium-ion battery. The as-obtained full battery exhibits good cycling stability and rate capability. It was able to deliver a capacity of 32 mA h g^-1 at 20 C, 76 % of the capacity at 2 C. After 200 cycles at 2 C, 97 % of the initial capacity was maintained for this battery, which suggests good cycling stability.