Short abstract: Lithiaton/de-lithiaition during the operation of Li-ion batteries in most cases is accompanied by microstructural variations of active materials in the electrodes. These microstructural changes, in turn, could have significant impact on cycle life of the batteries. Knowledge of the dynamics of such deformation processes would be valuable to the development of batteries of long cycle-life. Previous in-situ/in-operando techniques have been limited to monitoring dimensional variations. Recent in-operando microscopic analytical techniques, including in-operando transmission electron microscopy and X-ray microscopy (TXM) have offered the opportunities to directly probe the changes in interior microstructures of the active material particles. This talk presents three examples of TXM analysis on subjects pertaining to Li-ion battery applications, including microstructural deformation of Sn-based anodes, microstructural development of Li-excess metal oxide cathode particle subjected to high-temperature treatment, and polysulfide dissolution in Li-S battery.