• Permien, S.; Indris, S.; Neubueser, G.; Fiedler, A.; Kienle, L.; Zander, S.; Doyle, S.; Richter, B.; Bensch, W.: The Role of Reduced Graphite Oxide in Transition Metal Oxide Nanocomposites Used as Li Anode Material: An Operando Study on CoFe2O4/rGO. Chemistry - A European Journal 22 (2016), p. 16927-16936

10.1002/chem.201603160

Abstract:
A composite consisting of CoFe2O4 spinel nanoparticles and reduced graphite oxide (rGO) is studied as an anode material during Li uptake and release by applying synchrotron operando X-ray diffraction (XRD) and operando X-ray absorption spectroscopy (XAS), yielding a comprehensive picture of the reaction mechanisms. In the early stages of Li uptake, a monoxide is formed as an intermediate phase containing Fe2+ and Co2+ ions; this observation is in contrast to reaction pathways proposed in the literature. In the fully discharged state, metallic Co and Fe nanoparticles are embedded in an amorphous Li2O matrix. During charge, metallic Co and Fe are oxidized simultaneously to Co2+ and Fe3+, respectively, thus enabling a high and stable capacity to be achieved. Here, evidence is presented that the rGO acts as a support for the nanoparticles and prevents the particles from contact loss. The operando investigations are complemented by TEM, Raman spectroscopy, galvanostatic cycling, and cyclic voltametry.