Characterisation of mesocarbon microbeads (MCMB) as active electrode material in lithium and sodium cells

Mesocarbon microbeads (MCMB) derived from petroleum residua and heat treated under different experimental conditions were characterised by X-ray and electron diffraction, proton magnetic resonance (PMR), Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The presence of two different forms of hydrogen is retained after heating to 750 degrees C under vacuum. Graphitisation to 3000 degrees C leads to graphite ribbon-like particles surrounding microbeads of a few microns in size. The crystalline graphite monodomains are with a small band gap or are semimetallic as observed by EPR. Heat treatment even at 3000 degrees C does not eliminate completely the localised paramagnetic defects in the microbeads. These properties condition the aptitude of these materials toward their use in lithium and sodium electrochemical cells. The samples prepared at 750 degrees C have a reversible intercalation behaviour, while samples prepared at 3000 degrees C evidence solvent decomposition resulting in a non-reversible extended discharge plateau when using sodium perchlorate electrolyte dissolved in pure propylene carbonate (PC). (C) 2000 Elsevier Science Ltd. All rights reserved.