Reaction beyond intercalation and the utilization of
metal ions beyond
lithium-
ions are two promising approaches for developing the next generation of high capacity and low cost energy storage materials. Here, we use
graphene supported Co3O4 nanocubes and study their reaction with
lithium,
magnesium and
aluminum using in situ transmission electron microscopy. On lithiation, the Co3O4 nanocubes decompose to Co metal nanoparticles (2 to 3 nm) and embed in as-formed Li2O matrix; conversely, the
CoO nanoparticles form on the Co site accompanying the decomposition of Li2O in the delithiation process. The lithiation process is dominated by surface diffusion of Li(+), and
graphene sheets enhance the Li(+) diffusion. However, upon charge with
magnesium, the Mg(2+) diffusion is sluggish, and there is no sign of
conversion reaction between Mg and Co3O4 at room temperature. Instead, a thin film consisting of
metal Mg nanoparticles is formed on the surface of
graphene due to a process similar to
metal plating. The Al(3+) diffusion is even more sluggish and no reaction between Al and Co3O4 is observed. These findings provide insights to tackle the reaction mechanism of multivalent
ions with
electrode materials.