Strengthening Na−O interaction to stabilize sodium O3-layered cathodes by orbital hybridization regulation

Sodium-ion batteries (SIBs) are emerging as promising alternatives to lithium-ion technology for energy storage, driven by the cost-effectiveness and sustainability of sodium resources. However, a persistent challenge lies in developing layered oxide cathode materials that simultaneously exhibit high energy density and robust moisture stability. In this work, we demonstrate an orbital-hybridization regulation strategy to concurrently address these limitations by reinforcing Na−O bonds. This regulation is effectively achieved through the incorporation of Ti, Sn, and Li metals (without single d electrons) into the transition metal (TM) slabs. This reduces the hybridization between TM 3d and O 2p orbitals, thereby restricting the gliding of the TMO₂ slab and preventing spontaneous Na+ extraction from a model compound O3-Na_0.85Ni_0.40Mn_0.60O₂. Consequently, the phase evolution, previously observed as a complex sequence of O3 −O′3 −P3 − P′3 −P3′−O3′−O1, is simplified. Furthermore, the deleterious and spontaneous P-to-O phase transition, which typically occurs under deep desodiation conditions, is completely suppressed. As a result, the synthesized O3-Na_0.85Ni_0.40Mn_0.35Ti_0.2Sn_0.03Li_0.02O₂ cathode exhibits superior electrochemical performance and significantly enhanced air stability. This research provides valuable insights into an effective orbital-hybridization regulation approach for developing high-energy and highly stable cathode materials suitable for advanced rechargeable batteries.