Egyptian blue: from pigment to battery electrodes

Herein we report on using Egyptian blue as an anode material for Li-ion batteries. A 1^st cycle lithiation capacity of 594 mA h g^-1 and reversible capacity of 210 mA h g^-1 at 20 mA g^-1, and at 500 mA g^-1 a reversible capacity of 120 mA h g^-1 (stable over 1000 cycles) were achieved with coulombic efficiency more than 99.5%. Using X-ray diffraction, and FTIR and X-ray absorption spectroscopies we found that the material goes through a conversion reaction during the 1^st cycle that results in the formation of amorphous mixed oxides with copper nanoclusters.