On the chemical interaction of Li1+x(Ni,Mn)O2 with carbon and carbon precursors

The thermal stability of Li1+xNi0.5Mn0.5O2 cathode materials in contact with carbon and in the course of carbon coating by pyrolysis of various carbon precursors in argon is studied. XRD patterns of Li1+xNi0.5Mn0.5O2–carbon mixtures demonstrate the first traces of phase decomposition at 600 °C while corresponding TG curves show at the significant interaction between components at T>400 °C. Similar interaction of complex oxide with polyethylene glycol pyrolysis products causes the complete deterioration of the layered compound. The first stage of this deterioration is a systematic increase in cation disorder between A and B sublattices of the hexagonal ABO2 structure. However, the pyrolysis of polyvinyl alcohol at 350 °C results in the formation of nanostructured carbon film. The analysis of as-obtained Li1+xNi0.5Mn0.5O2–carbon composites by Raman spectroscopy shows that the linear structure of polyvinyl alcohol promotes the domination of sp2 forms of carbon in the pyrolysis products while the thermolysis products of cross-linked polymer contain mostly sp3-carbon.