Polymer-Derived SiOC for Energy Applications

This thesis investigates polymer-derived silicon oxycarbide (SiOC) materials for advanced thermal insulation and lithium-ion battery applications. The work is organized into two parts. First, hybrid preceramic and inorganic SiOC aerogels were prepared via sol–gel processing of silicon alkoxides, followed by supercritical CO₂ drying, to achieve ultralow thermal conductivity and high optical transparency. Second, composite anodes were fabricated by embedding nanosilicon in a polymer-derived SiOC matrix, and their electrochemical performance was evaluated in Li-ion cells. In the first part, crack-free aerogel monoliths were successfully synthesized. The hybrid aerogels, designed for transparent building insulation, exhibited extremely low thermal conductivity, on the order of ~15 mW m⁻¹ K⁻¹, consistent with the bestreported values for silica-based aerogels. In addition, the inorganic SiOC ceramic aerogels, obtained via pyrolysis in an Ar-H₂ atmosphere at 800 °C, exhibited thermal conductivities similar to those of hybrid aerogels and retained high optical transmittance. The combination of ultralow thermal conductivity, optical transparency, thermal stability, and high IR absorption underscores their potential for energy-efficient solar thermal insulation applications. In the second part, silicon nanoparticles/silicon oxycarbide (SiNPs/SiOC) composite anodes were synthesized and electrochemically evaluated. Electrochemical cycling tests demonstrated higher reversible capacity and improved cycling stability compared to the neat SiOC ceramic. The SiNPs/SiOC electrodes maintained structural integrity over extended cycling, showing that the amorphous SiOC network plays a dual role, both contributing to lithium storage and serving as a mechanically resilient and electronically conductive host capable of accommodating the large volume changes of silicon during lithiation and delithiation.