Carbon-Driven Enhancement in Zinc Hexacyanoferrate Composites: A Ball-Milling Approach for High-Performance Zn-Ion Batteries

Transition to a sustainable energy future demands the development of alternative battery technologies beyond lithium-ion batteries, which are challenging for large-scale implementation due to inherent safety concerns and resource scarcity. Aqueous zinc-ion batteries (ZIBs) are a promising solution; however, improvement of the cathode is essential for their widespread adoption. This study investigates the structural modification of zinc hexacyanoferrate (ZnHCF) as cathode materials using ball-milling and the addition of carbon black (Vulcan XC-72R). The improved electroactivity is attributed to the phase transition from cubic to rhombohedral, the conversion of Prussian blue analogue to Prussian white analogue phases, and the synergistic effect produced by the presence of carbon material. These changes lead to the formation of [Fe(CN)₆] vacancies, which draw water molecules into interstitial sites. Carbon material plays a crucial role in preserving the crystalline structure of ZnHCF and enhancing the electrochemical performance. The sample milled in presence of carbon material (BM-ZnHCF@C sample) demonstrates superior results compared to the samples unmilled and milled samples without carbon material, achieving a capacity close to 100 mAh g⁻¹ at a current density of 0.5 A g⁻¹. However, after 50 cycles, the capacity decreases by 53.3%, but is restored by replacing the Zn anode while retaining the same cathode. The zinc anode is the primary factor hindering the long-term performance of the assembled battery, as demonstrated by the evolution of the electrode potential over time in the ZIB using a T-type electrochemical cell.