Morphological change of Si-based electrode in charge-discharge reactions: Nondestructive measurements of as-grown SiO film

The effect of large volume changes caused by charge-discharge reactions in silicon-based negative electrodes on the morphological changes of active materials is evaluated by in-situ and ex-situ observations. As-grown SiO thin film is prepared as the electrode to observe changes in the condition of the active material and electrolyte. This electrode reversibly cycles charge-discharge reactions with a capacity of near 2000 mAh g -1 , without the use of conductivity aids or binders. After 50 charge-discharge cycles using Li metal as the counter electrode, the morphological changes are evaluated using phase-contrast X-ray CT and scanning electron microscopy. Numerous cracks are observed on the surface of the initially uniform SiO film, resulting in the formation of an 800 μm domain structure covering the surface. The film thickness increases to more than five times its initial value of 4 μm. The increased film thickness results in clear CT images. The cracks formed are less than 100 μm in width and are shown to be permeated by the electrolyte.