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

Mesocarbon microbeads (MCMB) derived from petroleum residua and heat treate d under different experimental conditions were characterised by X-ray and e lectron diffraction, proton magnetic resonance (PMR), Fourier transform inf rared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The pr esence 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 semimetal lic as observed by EPR. Heat treatment even at 3000 degrees C does not elim inate completely the localised paramagnetic defects in the microbeads. Thes e properties condition the aptitude of these materials toward their use in lithium and sodium electrochemical cells. The samples prepared at 750 degre es C have a reversible intercalation behaviour, while samples prepared at 3 000 degrees C evidence solvent decomposition resulting in a non-reversible extended discharge plateau when using sodium perchlorate electrolyte dissol ved in pure propylene carbonate (PC). (C) 2000 Elsevier Science Ltd. All ri ghts reserved.