Operando Structural Characterization of the Lithium-Substituted Layered Sodium-Ion Cathode Material P2-Na0.85Li0.17Ni0.21Mn0.64O2 by X-ray Absorption Spectroscopy.

Layered sodium-ion cathode material P2-Na_0.85Li_0.17Ni_0.21Mn_0.64O₂ was investigated using operandoXASto 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 ⁶Li 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. [ABSTRACT FROM AUTHOR]