Prussian Blue Analogous Na2Ni0.33Co0.33[Fe(CN)6] Nanoparticles as Cathode Material for Non-Aqueous Na-Ion Batteries

We report on the electrochemical properties of 20 nm Na2Ni0.33Co0.33[Fe(CN)6] nanoparticles. Na2Ni0.33Co0.33[Fe(CN)6] nanoparticles overcome the poor electronic conductivity and deliver an initial charge capacity of 77 mAh g−1 at 0.1C rate and and 55 mAh g−1 after 320 cycles at 1C rate. At high current rate of 5C, they deliver 35 mAh g−1 and exhibit almost 100% columbic efficiency. The single redox sodium ion chemistry with 3 V makes the material suitable for non-aqueous sodium ion batteries. The redox couple Fe3+/Fe2+ is seen to be electrochemically active during the charge/discharge process, which is confirmed by ex situ X-ray photon spectroscopy.