Kirkendall‐Effect‐Mediated Hollow Bimetallic Hexacyanoferrates for Aqueous Zn‐Ion Batteries: Suppressing Jahn–Teller Distortions and Enhancing Ion Transport and Cyclability

ABSTRACT The rational design of Prussian blue analogs (PBAs) with tailored architectures is essential for advancing aqueous zinc‐ion batteries (AZIBs). Here, a hollow bimetallic Ni–Mn hexacyanoferrate (H‐NiMnHCF) cathode is synthesized through a Kirkendall‐effect‐mediated route, in which the Ni content is systematically tuned to optimize shell thickness, structural uniformity, and electrochemical functionality. Ni incorporation induces controlled void formation and homogeneous Mn–Ni alloying, while enhancing electronic conductivity and suppressing Jahn–Teller (JT) distortions associated with Mn³⁺. Density‐functional theory (DFT) calculations reveal a reduction in axis‐selective bond anisotropy (ΔL₁ from ≈12.4% to ≈7.3%) and a narrowed bandgap with increased electronic states near the Fermi level, consistent with the experimentally observed low charge‐transfer resistance. The Kirkendall‐derived hollow morphology further increases the active surface and shortens Zn²⁺ diffusion pathways, enabling rapid ion transport and reversible redox kinetics. The optimized 1/2 Ni electrode delivers high capacity, low interfacial resistance, and excellent cycling retention (87.6% after 1000 cycles). Moreover, gel‐electrolyte pouch cells exhibit stable performance under bending, cutting, and puncturing, demonstrating mechanical robustness and safety. This study presents a morphology–composition co‐optimization strategy and offers mechanistic insights for designing structurally stable, high‐rate PBA cathodes for next‐generation AZIBs.