Lawrence Berkeley National Laboratory

Advances in high-resolution transmission electron microscopy and exit-surface wave (ESW) reconstruction of the scattered electron wave push resolution to better than 0.1nm, providing opportunities to examine whether Li+ can be imaged and resolved in a transition metal oxide structure. From simulations of the ESW from structural models of LiCoO2, it was found that a microscope resolution of 1 Angstrom was needed to experimentally resolve individual lithium ions in the layered structure. The phase of the ESW is a function of the specimen potential. Our simulations show that the ESW phase of the lithium, cobalt and oxygen atom columns change almost linearly with specimen thickness. Comparison of simulated ESWs with experimental ESWs reconstructed from experimental focus-series of images obtained on a modified Philips CM300FEG/UT microscope with a native resolution of 1.7 Angstrom and a demonstrated reconstructed ESW resolution of 0.78 Angstrom showed that the intensity associated with the Li+ position in the experimental ESWs was the weakest in comparison to those of oxygen and cobalt. Simulation and experiment support the fact that Li+ was resolved atomically in LiCoO2.