Electrochemical Properties of Ball-Milled Zinc Hexacyanoferrate Cathode Material for Calcium Ion Batteries

In this study, ball-milled zinc hexacyanoferrate (ZnHCF) active materials, a Prussian blue analogues (PBAs), were applied in the aqueous rechargeable calcium-ion battery (ARCIB) system. X-ray diffraction (XRD) analysis confirmed that there was no structural destruction of the ZnHCF active materials upon ball milling. A comparison of the pristine and ball-milled ZnHCF active materials by scanning electron microscopy (SEM) confirmed that the ball-milled ZnHCF active material particles were smaller than those of the pristine material. The highest initial charge/discharge capacity was observed on the electrode based on the ZnHCF active material that was ball-milled for 9 h. As the time of the ball mill process was reduced, the initial charge/discharge capacity of the electrodes gradually decreased. XRD and SEM confirmed the eventual collapse of the electrode structure, which explained why the increased capacity of the ARCIB system was not sustained.