Rhombohedral (R-3) Prussian White as cathode material: An ab-initio study

Prussian whites (PW) have gained attention for their potential application as high energy density cathodes in Na-ion batteries. However, the rhombohedral phase of this compound still remains elusive. This study addresses the electronic and structural properties of the rhombohedral host material, as well as its ionic conductivity. Using periodic density functional theory calculations, we identified the critical factors that determine the sodium ion site preference and their ionic mobility. Specifically, the significant role of octahedral tilting and trigonal distortions of the structure have been highlighted. The study shows that the competition between coordination and bond length governs the Na site preference in the rhombohedral phase upon distortion. The results furthermore suggest that the redox activity is dominated by the transition metals. These findings provide insight into the fundamental mechanisms underlying ionic conductivity in solid hosts and could help enhance ion transport in battery electrodes.