Direct imaging of lithium ions using aberration-corrected annular-bright-field scanning transmission electron microscopy and Associated contrast Mechanisms

The vast potential and fast development of implementing lithium-based batteries as an alternative power source to replace the existing lowefficiency and environmental-hazardous materials have urged an ever expediting pace for investigation of the corresponding characterization methods, in particular to observe lithium ions at atomic scale. Here we demonstrate a feasible annular-brightfield (ABF) imaging method based on aberrationcorrected scanning transmission electron microscopy to observe lithium ions directly at atomic resolution using LiFePO₄, a positive electrode material routinely used, for a case study. In addition, we performed extensive image simulations, including the influences from specimen thickness, high tension, illumination angle, collection angle, material vacancy and lattice distortion, to compare and interpret explicitly the displayed image contrast and the attainable optimum operation conditions.