Graphene Liquid Cell Electron Microscopy of Initial Lithiation in CoO Nanoparticles.

As it governs the overall performance of lithium-ion batteries, understanding the reaction pathway of lithiation is highly desired. For CoO nanoparticles as anode material, here, we report an initial conversion reaction pathway during lithiation. Using graphene liquid cell electron microscopy (GLC-EM), we reveal a CoO phase of the initial conversion product as well as morphological dynamics during CoO lithiation. In accordance with the in situ TEM observation, we confirmed that the CoO to CoO conversion is a thermodynamically favorable process by calculating the theoretical average voltage based on density functional theory. Our observation will provide a useful insight into the oxide electrode that undergoes conversion reaction.