Unraveling the Ultrafast Phase Transition Pathways of Mn‐Based Layered Oxides

ABSTRACT Manganese‐rich layered oxides (MRLO) are promising cathodes for sodium‐ion batteries (SIBs) due to their high theoretical capacity and low cost, yet their practical application is severely hindered by structural instability, complex phase evolution, and sluggish Na ⁺ diffusion kinetics. Since the phase composition of MRLO critically determines their structural stability and sodium‐ion transport behavior, and neither a single O3 nor a single P2 phase can adequately fulfill both requirements, precise phase regulation is essential for enhancing electrochemical performance. Herein, a sequential two‐step thermal treatment combining conventional muffle furnace calcination with high‐temperature shock (HTS) is developed to regulate the phase composition of Na _0.75 Mn _0.6 Ni _0.2 Li _0.1 Ti _0.05 Fe _0.05 O ₂ (MNLTF). The resulting sample exhibits an O3‐dominated structure (95.7% O3 phase) with trace P2 phase. In situ high‐temperature synchrotron XRD reveals that the phase evolution pathways differ significantly under different synthesis conditions. The optimized cathode delivers improved rate capability (95.3 mAh g ⁻¹ at 10 C) and cycling stability (90.7% retention after 250 cycles at 1 C). These results demonstrate that this two‐step thermal treatment is an effective approach for phase regulation of layered oxide cathodes.