LITHIUM INSERTION IN PYROLYZED SILOXANE POLYMERS

We study the thermal pyrolysis of the siloxane polymers, polymethylphenylsiloxane (PMPS) and polyphenylsesquisiloxane (PPSSO) in inert gas using thermal gravimetric analysis and mass spectrometry. As the polymers decompose near 600-degrees-C, they predominantly evolve benzene and hydrogen. Chemical analysis and weight loss measurements show that the black pyrolyzed products have approximate compositions C2.9SiOH(y) and C3.9SiO1.5H(y) with y=0.5+/-0.5 for materials made from PMPS and PPSSO respectively at 1000-degrees-C. The materials are amorphous, as seen by powder X-ray diffraction. Lithium can be reversibly inserted into these amorphous pyrolysis products with a specific capacity near 600 mAh/g, with most of the capacity below 1.0 V versus metallic lithium. It is possible that such materials may prove to be useful alternatives to pure carbon for the anodes of lithium-ion cells.