Mitigating P2 - P2' phase transition and lattice oxygen loss toward high-performance Fe/Mn-based Na-ion layered cathodes

P2-type Fe/Mn-based layered oxides are a compelling low-cost, high-capacity cathode for sodium-ion batteries (NIBs). However, the structural stability and electrochemical performance are severely constrained by Jahn-Teller-induced phase transitions and lattice oxygen loss at high voltage. Herein, a high-valence Sb⁵⁺-substitution strategy is proposed to effectively mitigate the Jahn-Teller distortion and stabilize the lattice oxygen during Na-ion extraction/insertion process. Upon the incorporation of strong SbO bonds, the NaO₂ interlayer spacing is moderately reduced, resulting in enhancing lattice stability. The P2 - P2' phase transition triggered by Jahn-Teller distortion is effectively inhibited upon Sb incorporation, as demonstrated by in situ XRD. Furthermore, the onset voltage of anionic redox is delayed, thereby mitigating lattice oxygen release, as confirmed by in situ DEMS. A stable and robust CEI layer is also formed in Sb-doped samples, leading to reduced interfacial resistance and improved Na-ion transport pathways, as evidenced by in situ EIS measurements. Consequently, Sb-doped cathodes exhibit excellent cycling stability (81.2% and 74.3% capacity retention after 50 and 100 cycles at 1C and 3C within 1.5-4.2 V, respectively) and outstanding rate capability. This work provides an effective approach to suppress Jahn-Teller-induced phase transitions and offers insights into the design of high-performance NIB cathodes.