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

ABSTRACT 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 Fe ⁴⁺ and Mn ³⁺ 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 Fe ⁴⁺ O ₆ and Mn ³⁺ O ₆ octahedra. Benefitting from the stable structure, the resultant Na _0.67 Fe _0.49 Mn _0.5 Sc _0.01 O ₂ (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.