Hydrophobic Lattice Engineering of Prussian Blue Analogs with Accelerated Redox Kinetics for High-Areal-Capacity Sodium-Ion Battery Electrodes

Abstract

Sodium-ion batteries (SIBs) are considered a promising solution for large-scale energy storage owing to their high safety and economic advantages. Fe-based Prussian blue analogs (PBAs) have attracted significant attention due to their open-framework structure, low cost, and high theoretical capacity (170 mAh g^-1). However, huge lattice distortion, moisture sensitivity of high-spin Fe (Fe^HS), and sluggish electron transport induced by strong Fe···Fe electronic coupling of Fe-based PBAs impede their industrial application. Herein, trace Zn incorporation is employed as a hydrophobic lattice engineering strategy to precisely regulate the coordination environment of Fe^HS-N octahedra without compromising their geometric integrity. This strategy integrates lattice modulation, coordination structure, and electronic regulation to synergistically alleviate structural distortion, enhance air stability, and facilitate the transportation charge and Na⁺ ions, especially in high-loading electrodes. As a result, the optimized Fe-based PBAs electrode achieves a capacity retention of over 84% after 200 cycles, even at a high mass loading (22 mg cm^-2). Moreover, after 1 month of exposure to a humid environment, a high reversible capacity of 144 mAh g^-1 was maintained. This study presents a coordination-chemistry-guided approach for the rational design of stable PBAs, thereby narrowing the gap between fundamental research and industrial-scale applications of PBA-based SIBs.