PORE CREATION IN SILICON OXYCARBIDES BY RINSING IN DILUTE HYDROFLUORIC-ACID

We have prepared silicon oxycarbides by the pyrolysis of siloxane poly mers at a maximum temperature of 1000 degrees C. The resulting silicon oxycarbides are networked glasses which we believe also contain some graphene sheets. After washing in a dilute solution of hydrofluoric ac id for times between 2 min and 24 h, these materials lost, at most, 40 % of their mass. Powder X-ray diffraction (XRD), small-angle scatterin g (SAX), BET surface area measurements, elemental analysis, and silico n K-edge X-ray absorption spectroscopy (XAS) were used to determine th e physical structure of the bulk material and the local chemical envir onments of the Si atoms. It was found that a microscopic pore network was created in the material upon HF washing. The number of pores, but not their size, increased with HF washing time. The HF etching reveale d a passivating layer, which we believe consists mainly of silicon and carbon, that prevented further etching of the material. The electroch emical behavior of these materials in Li batteries was not affected by the radical changes in surface chemistry.