Carbon-Rich Silicon Oxycarbide (SiOC) and Silicon Oxycarbide/Element (SiOC/X, X= Si, Sn) Nano-Composites as New Anode Materials for Li-Ion Battery Application
Carbon-rich silicon oxycarbide (SiOC) and silicon oxycarbide/element nano-composites (SiOC/X, X=Si, Sn) are prepared via thermal conversion of polyorganosiloxanes and studied as potential anode material for Li-ion battery application. The obtained materials are characterized by various chemical, structural, electrochemical and electro-analytical methods. The chemical composition and microstructure of the samples is analyzed and correlated with their electrochemical properties and performance. For carbon-rich SiOC, the lithium ion storage process, including the transport and mobility of lithium ions within the material, is investigated.
The electrochemical properties of carbon-rich SiOC strongly correlate with the ceramic microstructure and phase composition, which in turn correlate with the final temperature of pyrolysis. Both, an increasing organization of free carbon within the microstructure and the gradual degradation of the amorphous Si-O-C network lead to reduced capacities and changing voltage profiles. According to electro-analytical studies by PITT, GITT and EIS, the diffusion coefficient of Li-ions within SiOC prepared at 1100°C is in a similar order of magnitude as reported for disordered carbons, but faster than for graphite.
In the case of SiOC/X (X=Si, Sn) nano-composites, an additional Li-alloy forming phase is embedded within the SiOC matrix. For the synthesis of SiOC/Sn, a new innovative single-source precursor approach is introduced, which enables the in-situ precipitation of metallic Sn phase upon the thermal conversion of tin-modified polysiloxanes. Due to this microstructural design, the Li-ion storage capacity of the composite is enhanced, compared to pure SiOC. In addition, the embedding of Si and Sn alloy forming phases within stabilizing SiOC matrices strongly increases their cycling stability upon continuous lithiation and delithiation
