The pursuit of optimal sodium ions prestoring in potassium-sodium-cobalt hexacyanoferrate: toward high discharge performance supercapacitors

Prestoring sodium, which introducing sodium element into the crystal structure of material in the process of synthesis, is a novel approach to enhance the performance of material. Besides, crystal structure is also an important factor that influences the capacity of Prussian blue analogues' energy storage. In this work, the crystal structures of potassium-sodium-cobalt hexacyanoferrates (KNHCFs) were tuned by prestoring various content of sodium element. It has been discovered that the supercapacitors with KNHCF-0.5 (K1.7Na0.27Co[Fe(CN)(6)](0.71)center dot 1.6H(2)O) material reached highest performance with rhombohedral structure, showed optimal energy density (60 Wh kg(-1)), power density (10.8 kW kg(-1)) and long cycling performance of 92.3% capacitance retention even after 2000 cycles.