Steric Effect Enhancing Reversible Oxygen Redox and Minimizing Voltage Decay in Layered Sodium Cathodes

Abstract Layered oxide cathodes with lattice oxygen activity in sodium‐ion batteries often face poor oxygen redox reversibility and significant voltage decay, attributed to irreversible metal interlayer migration and oxygen loss, resulting in structure and energy degradation during cycling. Herein, a steric‐effect strategy is presented to suppress Li migration and stabilize Na‐O‐Li configurations by incorporating Zn into the conventional Na 0.78 Li 0.26 Mn 0.74 O 2 (NLM) framework, resulting in enhanced reversible lattice oxygen redox and mitigated voltage decay during cycling. In the engineered Na 0.65 Li 0.17 Zn 0.07 Mn 0.76 O 2 (NLZM), Zn simultaneously occupies both Na and transition metal (TM) sites, with Na‐layer Zn preferentially positioning beneath Li within the TM layers, suppressing Li migration into Na layers. This unique Zn configuration stabilizes Na layers through strong Zn─O bonding (ICOHP = −1.34 eV), effectively suppressing TM‐slab glide and mitigating lattice oxygen evolution. X‐ray diffraction and electron diffraction confirm effective mitigation of phase variations and preservation of the LiMn6 superstructure during desodiation/sodiation. Additionally, the NLZM demonstrates highly reversible lattice oxygen redox behavior and stable oxygen coordination (with no oxygen release). Consequently, thanks to the steric effect, NLZM achieves 95.8% voltage retention after 100 cycles, marking a significant improvement over NLM (71.6%) and highlighting the critical role of steric hindrance in stabilizing oxygen‐active cathodes.