Synergistic Suppression of Jahn–Teller Distortion in P2‐Type Li/Mn Cathodes by Fe Substitution and Increased Na Content

Promoting oxygen redox is an effective strategy to boost capacity in layered cathode materials for sodium-ion batteries. P-type Li- and Mn-based layered oxide cathodes are among the most promising candidates for triggering oxygen redox, but they face significant challenges, including low initial coulombic efficiency (due to sodium deficiency) and severe Jahn-Teller distortion when Mn⁴⁺ is reduced to Mn³⁺. In this work, Jahn-Teller distortion is effectively alleviated and initial coulombic efficiency is remarkably improved in a P2-type layered oxide cathode Na_0.75Li_0.2Mn_0.7Fe_0.1O₂ (LMF-75), through the synergy of Fe substitution and increased Na content. Fe substitution effectively suppresses MnO₆ octahedra distortion and promotes coupled redox between oxygen and transition metals, thereby improving oxygen redox reversibility. The increased Na content significantly improves the initial coulombic efficiency and regulates Mn redox, thus reducing Mn³⁺ formation and alleviating the associated Jahn-Teller distortion. As a result, the synergy of Fe substitution and increased Na content efficiently enhances structural stability and electrochemical performance. The LMF-75 cathode delivers a high reversible capacity of 196.7 mAh g^-1, an initial coulombic efficiency of 92.6%, and outstanding cycling stability of 96.2% capacity retention after 100 cycles. This synergistic strategy provides a promising approach for designing high-performance Li- and Mn-based cathode materials.