Synergistic Dual-Pinning Engineering Enables Stable Mn-Based Layered Oxide Cathodes for High-Performance Sodium-Ion Batteries

Mn-based oxide cathodes for sodium-ion batteries (SIBs) often suffer from structural degradation caused by Jahn-Teller distortion and irreversible phase transitions. Here, we propose a dual-site stabilization strategy by Mo/Mg codoping, which not only drives the transformation of the tunnel-type Na_0.44MnO₂ into a P2-layered structure (Na_0.44Mn_0.97Mo_0.01Mg_0.02O₂, denoted as MoMg-12) by modulating the total energy to enhance capacity but also employs Mo and Mg ions substituting Mn sites to implement synergistic dual-pinning engineering to stabilize the structure. This dual-pinning mechanism concurrently suppresses Jahn-Teller distortion by stabilizing Mn redox activity and improves air stability by reducing Na⁺/H⁺ exchange while promoting a hydrophobic surface. The optimized MoMg-12 cathode delivers a high specific capacity of 189 mAh g^-1 within its stable P2-type layered structure coupled with superior rate capability and long-term cycling stability. In addition, its practical viability is demonstrated when paired with a Na₂C₂O₄ sodium compensation additive. This study highlights the effectiveness of the dual-pinning engineering in preserving structural integrity and offers a practical design example for high-energy-density and air-stable SIB cathodes.