High-Entropy Prussian Blue Analogues as Cathodes for High-Performance Aqueous Al-Ion Batteries

Prussian blue analogues (PBAs) are promising cathodes for aqueous aluminum-ion batteries (AAIBs) due to their 3D open frameworks, which potentially facilitate fast Al³⁺ transportation. However, their practical applications are severely hindered by poor electronic conductivity, suboptimal Al³⁺ diffusion kinetics, and structural degradation. This study proposes a high-entropy Prussian blue analogue (HE-HCF) cathode through synergistic incorporation of multiple transition metals (Mn, Fe, Ni, Cu, and Zn) to enhance aqueous Al³⁺ storage. This approach alters the local coordination environment, inducing the reduction of [Fe(CN)₆] groups and thus enhancing their reactivity. Moreover, density functional theory (DFT) calculations reveal improved electronic conductivity and decreased Al³⁺ diffusion barrier. When coupled with a polyvinylidene fluoride-coated Zn-Al alloy (Zn-Al(P)) anode, the assembled HE-HCF//Zn-Al(P) full cell delivers a high capacity of 110 mAh g^-1 at 0.1 A g^-1 and a high energy density of 163.8 Wh kg^-1. Additionally, the full cell achieves a long lifespan of 1600 cycles at 1.0 A g^-1, which is attributed to the low fluctuation of lattice parameters brought from strengthened metal-cyanide bonds within HE-HCF. This work provides new insights into the design of multivalent ion batteries employing high-entropy engineering.