Operando Structural Characterization of the Lithium-Substituted Layered Sodium-Ion Cathode Material P2-Na0.85Li0.17Ni0.21Mn0.64O₂by X-ray Absorption Spectroscopy

Layered sodium-ion cathode material P2-Na 0.85 Li 0.17 Ni 0.21 Mn 0.64 O 2 was investigated using operando XAS to characterize structural changes occurring in the material during electrochemical sodiation/desodiation. Based on XANES data, the primary mode of charge compensation in this material is due to Ni 2–3/4+ redox activity, while the Mn remains in the +4 oxidation state, thereby providing stability to this material during extended cycling. Investigation of the initial state of the compound by high resolution synchrotron XRD and 6 Li MAS NMR revealed a significant amount of structural disorder due to integration of a small amount of monoclinic layered Li phase within the overall hexagonal layered Na-structure, which manifests as Li-induced stacking faults. High quality EXAFS data could be obtained using our cell construction and revealed the local structural evolution around the redox active Ni centers.