Mechanical Damping at the P2/O3 Heterostructure in Fe/Mn-Based Cathodes: A Shock-Absorber Mechanism for Superior Sodium Storage

Abstract The economical nature of Fe/Mn-based cathodes establishes their strong competitiveness in sodium-ion batteries (SIBs). Intrinsically sluggish kinetics and poor ambient stability pose major barriers to the commercial viability of these materials. Featuring Mg/B codoping, the P2/O3-Na0.67Fe0.5Mn0.40Mg0.10B0.02O2 (NFM-MB2) cathode demonstrates outstanding stability for sodium storage. The relevant mechanisms are also elucidated in depth. A key insight from our analysis identified the biphasic interface as a damping region. This region stabilized the structure at high voltages through the dissipation of lattice stress and elimination of desodiation-induced distortions. In this way, Mg/B codoping has overcome the structural instability caused by phase transition and lattice strain: it demonstrated how to precisely control the P2/O3 interface to construct a damping zone, converting local lattice distortion into highly reversible structural evolution behavior, thereby maintaining its integrity and electrochemical reversibility. As a result, the NFM-MB2 cathode demonstrated considerable properties, including a high specific capacity (167.6 mAh g–1, 0.1 C), stable cycling (84.7%, 100 cycles), a rate capability of 82.8%, and an energy density of 346.6 Wh kg–1. This work advanced the comprehension of how the structure evolved. The research clarified that the P2/O3 interface damping region could convert the harmful lattice strain and distortion from deep desaturation into reversible microscopic deformation behaviors, thereby ensuring electrochemical reversibility. This discovery epitomized a paradigm shift regarding the biphasic collaborative mechanism, while simultaneously establishing novel guidelines for high-voltage Fe/Mn-based cathode materials.