In operando observation of sodium ion diffusion in a layered sodium transition metal oxide cathode material, P2 NaxCo0.7Mn0.3O2

Abstract

In operando powder X-ray diffraction data reveals an unexpected structural evolution in a layered P2 type Na_xCo_0.7Mn_0.3O₂ material during cycling. The population of single crystallographic sites sometimes increases even though sodium ions are being extracted from the structure, implying a highly cooperative diffusion mechanism. The structural evolution is shown to proceed through a series of metastable structures that cannot be predicted by thermodynamics.