Achieving Long‐Enduring High‐Voltage Oxygen Redox in P2‐Structured Layered Oxide Cathodes by Eliminating Nonlattice Oxygen Redox

Abstract Triggering reversible lattice oxygen redox (LOR) in oxide cathodes is a paradigmatic approach to overcome the capacity ceiling determined by orthodox transition‐metal (TM) redox. However, the LOR reactions in P2‐structured Na‐layered oxides are commonly accompanied by irreversible nonlattice oxygen redox (non‐LOR) and large local structural rearrangements, bringing about capacity/voltage fading and constantly evolving charge/discharge voltage curves. Herein, a novel Na_0.615Mg_0.154Ti_0.154Mn_0.615◻_0.077O₂ (◻ = TM vacancies) cathode with both NaOMg and NaO◻ local configurations is deliberately designed. Intriguingly, the activating of oxygen redox at middle‐voltage region (2.5–4.1 V) via NaO◻ configuration helps in maintaining the high‐voltage plateau from LOR (≈4.38 V) and stable charge/discharge voltage curves even after 100 cycles. Hard X‐ray absorption spectroscopy (hXAS), solid‐state NMR, and electron paramagnetic resonance studies demonstrate that both the involvement of non‐LOR at high‐voltage and the structural distortions originating from Jahn–Teller distorted Mn³⁺O₆ at low‐voltage are effectively restrained in Na_0.615Mg_0.154Ti_0.154Mn_0.615◻_0.077O₂. Resultantly, the P2 phase is well retained in a wide electrochemical window of 1.5–4.5 V (vs Na⁺/Na), resulting in an extraordinary capacity retention of 95.2% after 100 cycles. This work defines an effective approach to upgrade the lifespan of Na‐ion battery with reversible high‐voltage capacity provided by LOR.