Long life and high-rate Berlin green FeFe(CN) 6 cathode material for a non-aqueous potassium-ion battery

A high-quality sized FeFe(CN)6 was synthesized as a cathode material for a non-aqueous potassium-ion battery. The electrode delivered a reversible capacity of 124 mA h g-1 at the current rate of 0.5C and still retained a reversible capacity of 93 mA h g-1 after 500 cycles at 5C with a columbic efficiency of 100%. Structural evolution and redox couples of low and high spin FeIII/FeII were investigated by ex situ X-ray diffraction, Mossbauer spectroscopy, and X-ray photoelectric spectroscopy. The negligible volume change during the electrochemical process should be responsible for the excellent cyclic stability.