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

Manganese-based oxide cathodes for sodium-ion batteries face irreversible degradation from Mn³⁺ Jahn-Teller distortion and Mn²⁺ dissolution, compounded by cyclic strain during (de)sodiation. To address this, a P2-K_0.7Mn_0.8Ni_0.1Ti_0.1O₂ (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 Mn²⁺ formation, establishing a new paradigm for stable Mn-rich cathodes.