Dominant role of M element on the stability and properties of Prussian blue analogues NaxMFe(CN)6 (M = 3d transition metal) as cathode material for the sodium-ion batteries

The Prussian blue analogues (PBA) NaxMFe(CN)6 (M = 3d transition metal) synthesized by conventional synthesis methods usually contain defects. This hinders our understanding of its intrinsic properties as a cathode material, and causes difficulties in designing composite electrodes with heterogeneous structures. In this work, we performed first-principles calculations to study the properties of NaxMFe(CN)6 (M = Fe, Cr, Mn, Sc, Zn, V, Ti, Co, Ni, Cu) compounds as cathode materials for sodium-ion batteries, focusing on their structural stability, thermal effects and electrical performance during charging and discharging. The results confirm the strong correlation between the M element and the intrinsic characteristics of NaxMFe(CN)6 in the process of inserting/extracting sodium ions, and revealed the thermodynamic mechanism of the apparent physical properties related to the sodium-ion concentration. Based on the intrinsic physicochemical properties of NaxMFe(CN)6 systems, it is promising to develop sodium-ion cathode materials with complex heterostructures.