Four‐Coordinate Boron in Transition Metal Layer Suppresses Lattice Oxygen Evolution for Stable Sodium Layered Cathodes

Layered metal oxide materials are considered promising cathode candidates for sodium‐ion batteries (SIBs) owing to their high specific capacity and favorable scalability. However, they suffer from severe surface structure degradation, which is closely related to oxygen evolution, particularly at high charge voltages. Herein, boron (B) is incorporated into interstitial sites of transition‐metal (TM) layers for NaLi 0.1 Ni 0.3 Fe 0.1 Mn 0.4 Ti 0.1 B 0.02 O 2 (B‐LTNFM) via a secondary annealing process to modulate the local electronic structure. It preferentially occupies tetrahedral sites due to its small atomic size to form strong covalent tetrahedron [BO 4 ] 5− , and donates additional electrons to its neighboring oxygen. This suppresses oxygen redox activity at deep charge states to prevent surface structure degradation of cathode and alleviate electrolyte decomposition induced by reactive oxygen species. These enable a high specific capacity of 158 mAh g −1 and outstanding cycling stability with 93% capacity retention after 200 cycles. This work provides insights into electronic structure modulation to enhance lattice oxygen stability of high energy density layered cathodes of SIBs and beyond.