X-ray photoemission studies of surface pre-treated graphite electrodes

Surface pre-treatment of graphitic electrode materials for lithium ion cells has recently been shown to significantly reduce the irreversible consumption of material and charge due to the formation of the so-called solid electrolyte interphase, during battery charging. In this paper we compare graphite powders and carbon fibres as model materials for studies of the effects of CO2 pre-treatments on solid electrolyte interphase (SEI) formation using X-ray photoemission spectroscopy (XPS). We observe significant modification in the surface elemental composition as a function of CO2 treatment temperature for carbon fibres, but no strong changes for graphite powders. We conclude that the predominance of the relatively unreactive basal plane in the surface area of the powders makes them far less suitable for detailed XPS studies than the fibres, where the more reactive prismatic planes predominate.