Precursor‐Regulated Stacking Faults Enable High‐Voltage Stability for P2‐Type Layered‐Oxide Sodium‐Ion Cathodes

ABSTRACT Layered‐oxide cathodes for sodium‐ion batteries suffer from rapid capacity fading at high voltage due to structural instability and irreversible oxygen redox. Here, precursor chemistry is shown to provide an effective route to regulate stacking disorder and thereby stabilize high‐voltage electrochemical behavior of Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode. Cathodes derived from carbonate precursors form a P2 structure containing intermittently distributed O3‐type stacking faults. Structural analysis indicates that the origin of such planar defects is the overlap between Na + insertion and the solid‐solution phase transformation during calcination. More importantly, the stacking faults serve as intrinsic strain buffers, suppressing c ‐axis contraction and mitigating oxygen release during cycling. As a result, the prepared cathodes exhibit highly reversible lattice evolution, weakened ligand‐to‐metal charge transfer and more stable Ni‐O coordination, revealing enhanced reversibility of oxygen redox. In contrast, the cathodes synthesized from hydroxide precursors exhibit a conventional and highly ordered structure through a P3‐P2 phase transition during calcination, which promotes pronounced P2‐O2 phase transitions at high voltages and accelerates structural degradation. Consequently, the carbonate‐precursor‐synthesized cathode achieves a capacity retention of 83.7% after 200 cycles at 2.0–4.3 V. This work highlights precursor chemistry as a powerful tool for engineering stacking disorder and enabling stable high‐voltage operation in layered sodium‐ion cathodes.