Surface Lattice-Matched Engineering Based on In Situ Spinel Interfacial Reconstruction for Stable Heterostructured Sodium Layered Oxide Cathodes

Layered transition metal oxide (NaxTMO2), being one of the most promising cathode candidates for sodium-ion batteries (SIBs), have attracted intensive interest because of their nontoxicity, high theoretical capacities, and easy manufacturability. However, their physical and electrochemical properties of water sensitivity, sluggish Na+ transport kinetics, and irreversible multiple-phase translations hinder the practical application. Here, a concept of surface lattice-matched engineering is proposed based on in situ spinel interfacial reconstruction to design a spinel coating P2/P3 heterostructure cathode material with enhanced air stability, rate, and cycle performance. The novel structure and its formation process are verified by transmission electron microscopy and in situ high-temperature X-ray diffraction. The electrode exhibits an excellent rate performance with the highly reversible phase transformation demonstrated by in situ charging/discharging X-ray diffraction. Additionally, even after a rigorous water sensitivity test, the electrode materials still retain almost the same superior electrochemical performance as the fresh sample. The results show that the surface spinel phase can play a vital role in preventing the ingress of water molecules, improving transport kinetics, and enhancing structural integrity for NaxTMO2 cathodes. The concept of surface lattice-matched engineering based on in situ spinel interfacial reconstruction will be helpful for designing new ultra-stable cathode materials for high-performance SIBs.