Sodium titanium hexacyanoferrate as an environmentally friendly and low-cost cathode material for sodium-ion batteries

A new type of Prussian blue analog, sodium titanium hexacyanoferrate, has been synthesized with good electrochemical performance using an environmentally friendly, solution precipitation method. Because of the hydrolysis reaction of titanium, it has been proved that the synthetic reaction is sensitive to heat, and the best reaction temperature is 60 °C. The resulting particles belong to a well-defined open framework with cubic structure. Because of the two sodium storage sites provided by the low-spin [Fe(CN)₆]^4-/3- couple and high-spin Ti^3+/4+ couple, sodium titanium hexacyanoferrate exhibits a high specific capacity over 90 mAh g^-1, and two pairs of clear charge/discharge platforms at 3.0 V/2.6 V and 3.4 V/3.2 V, respectively. The results show that this material can be applied as a low-cost cathode electrode with good electrochemical performance for sodium ion batteries.