Behaviour of highly crystalline graphites in lithium-ion cells with propylene carbonate containing electrolytes

Several TIMREX® synthetic and natural graphite negative electrode materials with different particle size distributions were tested with regard to their compatibility with propylene carbonate used as electrolyte component in lithium-ion cells. The first lithium insertion properties of these graphite materials were characterised in electrochemical lithium half-cells containing 1 M LiPF6 in ethylene carbonate/propylene carbonate as electrolyte system. Post mortem scanning electron microscopy was applied to study the exfoliation process observed for some of these graphite materials especially with coarser particle sizes. X-ray diffraction, Raman spectroscopy and nitrogen gas adsorption were used to characterise and correlate the material bulk and surface properties of the graphite materials with their electrochemical performance. Differential electrochemical mass spectrometry was applied to study the passivation process of the graphite material surface during the first electrochemical reduction. Non-exfoliating graphite materials indicate the formation of an efficient solid electrolyte interphase, which seems to be kinetically controlled by intrinsic properties of the graphite material bulk and surface.