An Electronic-Geometric Descriptor for Predicting High-Voltage Prussian Blue Analogue Cathodes.

Abstract

Prussian blue analogues (PBAs) are promising sodium-ion battery cathodes owing to their open frameworks, compositional tunability, and high operating voltages. However, the rational design of high-voltage PBAs is hindered by the lack of physically interpretable descriptors connecting atomic-scale properties with voltage behavior. Here, we develop an electronic-geometric coupled descriptor for correlating and predicting voltage plateaus in PBAs. The descriptor combines the p-band center of the cyano-ligand N atom, which characterizes the electronic contribution to Na-N interactions, with a lattice-response term that describes framework confinement during sodiation. Density functional theory calculations on ordered binary PBAs show that the coupled descriptor improves the correlations with both high- and low-voltage plateaus relative to the electronic descriptor alone, and the predicted trends are consistent with available experimental reports for representative systems. We further apply this descriptor to screen 78 PBA compositions, including ordered binary, multielement-doped Fe-based, and high-entropy PBAs. Eight compositions are predicted to exhibit both high- and low-voltage plateaus above 3.8 V, among which Cu[Fe(CN)6], Ni[Fe(CN)6], and Zn2Cu2[Fe(CN)6]4 agree with reported experimental trends, while Zn[Zn(CN)6], Zn[Fe(CN)6], Cu[Mn(CN)6], Cu[Zn(CN)6], and Ni3Zn[Fe(CN)6]4 are proposed as candidates for further experimental validation. This study offers a descriptor-guided strategy for the discovery of high-voltage PBA cathodes.