Interfacial Strain Modulation in Core–Shell Manganese-Based Prussian Blue Cathodes Suppresses Jahn–Teller Distortion for High-Performance Sodium-Ion Batteries

Manganese-based Prussian blue analogues attract significant interest as cathodes for sodium-ion batteries due to their high theoretical capacity. However, the Jahn–Teller distortion causes rapid capacity degradation and a poor rate capability. In this work, core–shell Prussian blue analogues are fabricated comprising manganese hexacyanoferrate (MnPB) cores and nickel hexacyanoferrate (NiPB) shells, where interfacial stress is precisely modulated through controlled Ni/Mn ratios by tailoring the NiPB shell proportion. Validation through in situ XRD/EIS and finite element analysis confirms that the optimized NiMnPB 3-2 structure suppresses Jahn–Teller distortion, relieves internal stress, blocks Mn dissolution, and enhances charge transfer kinetics along with maintaining structural integrity. The cathode delivers exceptional performances, including outstanding rate capability (reversible capacity of 118.2 mA h g–1 at 50 mA g–1 and 50.1 mA h g–1 at 3200 mA g–1) and superior long-cycle stability (86.9% capacity retention after 1000 cycles at 800 mA g–1). The core–shell structures with tunable strain represent a promising approach to realizing high-performance Mn-based hexacyanoferrate as cathodes for sodium-ion batteries.