Operando structural characterization of the lithium-substituted layered sodium-ion cathode material P2-Na_0.85Li_0.17Ni _0.21Mn_0.64O₂ 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 Ni2-3/4+ 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.