Defect nucleation and their effect on ion spatial distribution in operando sodium ion batteries*

Recently, layered transition metal (TM) oxide materials for cathodes have attracted attention in sodium ion batteries (SIBs). Despite appeal of SIBs for large-scale energy storage due to the relative abundance of sodium, its lower toxicity, and ease of production, the SIBs are yet to demonstrate sufficient cycle life.Understanding and imaging defect nucleation and evolution of strain in the layered cathode materials during the battery operation is crucial to overcome the SIB problems and improve material design. We extended operando Bragg coherent diffractive imaging to observe in 3D structural changes within nanoparticles of sodium ion battery cathode. We observe nucleation of defects perpendicular to the layers during the charging of the battery in layered SIB cathode materials. We also observe the differences in interlayer distance within the nanocrystal, implying difference in ionic diffusion. Operando observation of the defect formation and interaction opens ways to understanding and rational design of durable functional layered oxide materials.