Suppressed Voltage Decay by Local Structure Tuning for High-stability Sodium Layered Oxide Cathodes

P2-type Fe/Mn-based layered oxides have emerged as promising cathode materials for sodium-ion batteries (SIBs) due to their high capacity and cost-effectiveness. However, the irreversible lattice distortion caused by Fe⁴⁺ and Mn³⁺ Jahn-Teller (J-T) effect during electrochemical cycling leads to severe voltage hysteresis, continuous voltage decay, and structural degradation upon extensive cycling, thereby compromising energy efficiency and life-span. In this work, trace amounts of scandium are introduced into the transition-metal layers to modulate the local electronic structure and coordination environment. The strong Sc-O ionic bonding enhances TM-O covalency, reduces the geometric symmetry of the ligand field, and eliminates the 3d orbital degeneracy of Fe and Mn ions, thereby suppressing the J-T distortions of Fe⁴⁺O₆ and Mn³⁺O₆ octahedra. Benefitting from the stable structure, the resultant Na_0.67Fe_0.49Mn_0.5Sc_0.01O₂ (NFMO-Sc) exhibits small voltage hysteresis and voltage decay, as well as remarkable long-cycling stability. This work highlights the potential of trace-element-enabled local structural tuning as a practical strategy to alleviate J-T distortion and enhance voltage stability, offering valuable insights into the design of high-stability layered oxide cathodes for advanced SIBs.