Achieving Ultra-Long Cycling Stability in Sodium-Ion Batteries via Entropy-Stabilized Chromium-Doped Prussian Blue Analogue Cathodes

Prussian blue analogues (PBAs) are promising cathode materials for sodium-ion batteries (SIBs) but suffer from structural instability and poor cycling performance. Herein, a high-entropy Prussian blue analogue (Cr-HEPBA) coordinated with five transition metals (Cr, Mn, Fe, Ni, Zn) is synthesized via an entropy-driven strategy. Cr-HEPBA exhibits a "quasi-zero-strain" structure during Na⁺ insertion/extraction, enabling exceptional cycling stability (70% capacity retention after 18,000 cycles at 1500 mA g⁻¹) and superior rate capability (42.9 mAh g⁻¹ at 30 C). Density functional theory (DFT) calculations reveal that the multimetal synergy optimizes the electronic structure, narrowing the band gap for enhanced conductivity and providing low Na⁺ migration barriers (∼0.45 eV). This study demonstrates that the cooperative interaction of chromium doping and entropy stabilization effectively inhibits phase transition processes, accelerates Na⁺ diffusion (DNa⁺ ≈ 5 × 10⁻¹⁰ cm² s⁻¹), and activates multimetal redox centers (Cr/Mn/Fe/Ni). Remarkably, Cr-HEPBA maintains 80.4% of its initial capacity after six months of air exposure, demonstrating exceptional environmental stability. This work provides a paradigm for designing robust PBA cathodes for grid-scale energy storage.