Extended Data Fig. 1: Structure and orientation of LCO particles, and comparison of iSCAT and SEM images.

a, Crystal structure of LiCoO₂. Top left, view down the c axis, showing edge-sharing CoO₆ octahedra. Right, angled view showing alternate layers of cobalt-centred and lithium-centred octahedra. Four unit cells are displayed (two repeats in the a and b directions). Lithium transport occurs in the a–b plane. b, X-ray diffraction patterns of the pristine LCO powder (black trace) and the self-standing electrode film (blue trace). The comparatively high intensities of the (00l) reflections indicate that the LCO particles display a preferred orientation within the electrode film, with the [001] direction (that is, the c direction) normal to the electrode film. The peak marked * originates from the conductive carbon. c, Mass-weighted diameter distribution for LCO particles (based on 681 particles). d, SEM image of a dilute working electrode, showing two particles of LCO dispersed in a conductive matrix. Scale bar, 10 μm. e, iSCAT image of a single active LCO particle in the electrode (250 μs exposure time). Intensity values are normalized to a linear scale between 0 (black) and 1 (white). Scale bar, 5 μm. f–i, Left, iSCAT intensity image of an LCO particle, normalized between 0 (black) and 1 (white). Right, corresponding SEM image of the same LCO particle. The white dashed line represents the outline of the bright region in the iSCAT image. All scale bars, 2 μm. Comparisons of iSCAT and SEM images confirm that the bright regions observed by iSCAT correspond to relatively flat areas on the particle surface. The curved sides of each particle are out of focus, and do not contribute substantially to the iSCAT image (Supplementary Information section 2). The flat surfaces imply that, for these particles, the direction of observation is along the c axis of the crystal. This particle orientation is ideally suited to investigate the in-plane ion transport within the layered host lattice.