Defect Electrochemistry in Stabilizing Corrugated Layered NaMnO₂

Lattice defects in layered metal oxides critically influence the structural stability and electrode reversibility in rechargeable batteries. However, the role of these defects remains poorly understood. Corrugated-layered β-NaMnO₂ provides an ideal model system because stacking fault (SF) formation plays a key role in its thermodynamic stability. Controlling the SF distribution thus offers a unique opportunity to elucidate the interplay between defects and electrochemical performance. Herein, we show that the partial substitution of Mn with Cu or Zn effectively modulates SF formation in β-NaMnO₂. Synchrotron X-ray diffraction, scanning transmission electron microscopy, and Raman spectroscopy revealed distinct defect structures: the pristine material exhibited ordered SF domains, Cu-substitution stabilized defect-free zigzag stacking, and Zn-substitution introduced randomly distributed SFs. Both doped materials exhibited improved capacity retention, reflecting suppressed evolution of the α-phase defects during cycling. These findings establish a direct link between SF distribution and electrochemical reversibility, highlighting defect engineering as a strategy for designing durable battery materials.