Mitigating Long Range Jahn-Teller Ordering to Stabilize Mn Redox Reaction in Biphasic Layered Sodium Oxide

To develop the next-generation commercial oxide cathodes for sodium-ion batteries, it is crucial to reduce the expensive Ni element content, and further regulate redox reaction of cheap transition metal elements such as Mn to elevate specific capacity. Nevertheless, the activation of Mn redox reaction (MRR) remains a challenge, and notably, MRR induces pronounced Jahn-Teller effect, resulting in severe structural distortion and fast performance decay. Herein, activated by Na vacancies and weakened hybridization of O (2p)-TM (3d-t_2g) orbital, a biphasic low-Ni Mn-based oxide P2/O3-Na_0.8Ni_0.23Fe_0.34Mn_0.43O₂ (P2/O3) exhibits reversible MRR, which performs the transition between Mn⁴⁺ and Mn³⁺ during charging and discharging. Due to the interlaced arrangement of P2-type and O3-type crystal domains in P2/O3, the long range Jahn-Teller ordering is restricted to mitigate the cooperative distortion of MnO6 octahedron induced by MRR and the Jahn-Teller effect is suppressed, ensuring sustained stable involvement of MRR in charge compensation. In addition, owing to the introduction of P2-type phase, there is a significant reduction of the migration barrier for sodium ions and no obvious capacity decline after air exposure, leading to a marked enhancement in dynamic performance and air stability of P2/O3, respectively. Consequently, P2/O3 exhibits excellent electrochemical and processing performance. © 2024 Wiley-VCH GmbH.