AN EPOXY-SILANE APPROACH TO PREPARE ANODE MATERIALS FOR RECHARGEABLE LITHIUM ION BATTERIES

A series of carbonaceous materials containing silicon and oxygen have been synthesized via pyrolysis of epoxy-silane composites prepared from hardened mixtures of epoxy novolac resin and epoxy-functional silane. Chemical composition of the pyrolyzed materials has been determined to be C1-y-zSizOy by a combination thermogravimetric analysis, Auger electron spectroscopy, carbon, hydrogen, and nitrogen analyses, and wet chemical analyses. Pyrolysis of the epoxy novolac resin gives pure carbon made up predominantly of single graphene sheets having lateral dimension of about 20 Angstrom which are stacked like a ''house of cards.'' Pyrolysis of the pure epoxy-functional silane gives C0.50Si0.19O0.31 with a glassy structure. X-ray diffraction and electrochemical tests show that pyrolyzed materials prepared from mixtures initially containing less than 50% (by weight) silane are mixtures of the carbon Single-layer phase and the glassy phase, while those initially with greater than 50% silane show predominantly the glassy phase. The reversible specific capacity of these materials increases from about 500 mAh/g for the pure disordered carbon up to about 770 mAh/g in the material which contains the most silicon and oxygen. However, the voltage profile develops hysteresis of about 1 V and the irreversible capacity associated with the first reaction with lithium increases as the silicon and oxygen contents are increased. Further work is needed to eliminate these drawbacks.