Dual Strategy in Manganese‐Based Cathodes with K Expansion and Ni/Ti Compression for Stable Sodium Storage

Abstract Manganese‐based oxide cathodes for sodium‐ion batteries face irreversible degradation from Mn ³⁺ Jahn–Teller distortion and Mn ²⁺ dissolution, compounded by cyclic strain during (de)sodiation. To address this, a P2‐K _0.7 Mn _0.8 Ni _0.1 Ti _0.1 O ₂ (KMNT) cathode via dual‐regulation is developed: K ⁺ pillars expand alkali ‐ metal layers enabling fast Na⁺ diffusion, while Ni/Ti co‐doping compresses transition‐metal layers to suppress Mn migration and Jahn–Teller effect. Besides, the K ⁺ pillars in discharged KMNT enhance Mn─O interactions via electrostatic effects, elevating Mn redox potentials and enabling a high average discharge voltage of ≈2.6 V (vs. Na ⁺ /Na). Even at a low potential cut‐off of 1.5 V, the KMNT cathode demonstrates a reversible specific capacity of 124 mAh g ⁻¹ at 1 C with 98% capacity retention after 200 cycles and retains 83% after 900 cycles at a large current density of 10 C, significantly outperforming conventional Mn‐based cathodes. Electrochemical and operando tests confirm the dynamic K ⁺ /Na ⁺ exchange mechanism and absence of Mn ²⁺ formation, establishing a new paradigm for stable Mn‐rich cathodes.