Facet-Engineered Na2FeSiO4 Cathodes Realizing Zero-Strain Operation and Ultra-Stable Sodium Storage

초록

Designing polyanionic cathodes that simultaneously deliver structural stability and fast Na+ transport remains a key challenge for sodium-ion batteries. Here, we present a facet-directed lattice engineering strategy that enables controlled crystallographic orientation, defect chemistry, and ion-transport kinetics in Na2FeSiO4 (NFS). Solvent coordination coupled with thermodynamically guided calcination yields a cubic P213 phase with preferential exposure of the (210)/(211) facets. Structural analyses and density functional theory identify these planes as dominant Na+ migration highways with ultralow barriers (0.21–0.25 eV) and reversible elastic lattice breathing, supporting near-zero-strain operation during cycling. The optimized cathode delivers a high reversible capacity of 173.6 mAh g−1 at 0.2 C with 92.3% retention, minimal voltage hysteresis, and excellent rate capability. Beyond facet effects, the engineered lattice environment stabilizes the Fe2+/Fe3+ redox balance and an optimized oxygen-vacancy landscape, while the nanosheet architecture shortens diffusion lengths and buffers interfacial strain; concurrently, in situ–derived carbon forms a percolating conductive network that promotes electron transport and stabilizes the cathode–electrolyte interface (CEI). In pouch-cell configuration, the material retains >80% capacity with the lowest charge-transfer resistance among all variants, underscoring scalability and durability. This facet-governed design concept links atomic-scale crystal engineering with practical electrodes, offering a general route to high-rate, long-life sodium-ion batteries.

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