In this work we investigate the electrochemical behaviour of two silicon oxycarbide (SiOC) glasses synthesized from the same starting precursor. In one case we perform pyrolysis in an Ar flow, while in the second case, the glass is synthesized under a CO₂ flow. The microstructural characterization of the glasses unambiguously demonstrates that the Ar-pyrolyzed material (SiOC–Ar) is a SiOC/C_free nanocomposite with mixed SiC_xO_4−x 0 ≤ x ≤ 4 units, whereas the CO₂-pyrolyzed sample (SiOC–CO₂) is a SiO₂/C_free nanocomposite with exclusively SiO₄ units forming the amorphous network. Therefore, in this study we investigate two model systems, addressing the question as to whether the mixed SiC_xO_4−x units in the SiOC glass play an essential role regarding electrochemical performance. The UV-Raman analysis reveals that the sp² carbon present in the mixed bond-containing sample is more disordered/has more defects than the one dispersed in the SiO₂ matrix. Apart from the above dissimilarities, the materials present comparable microstructures and a similar amount of free carbon. Nevertheless, SiOC–Ar recovers almost twice higher reversible Li-ion storage capacity than SiOC–CO₂ (325 vs. 165 mA h g⁻¹, respectively). We rationalize this difference in terms of the enhanced Li-ion storage in the more disorder free carbon phase of SiOC–Ar, while this disorder is induced by the presence of the mixed-bond units.

We report new polysiloxane and polycarbosilane aerogels, which have been obtained by crosslinking Si–H-containing polymers with a CC-containing crosslinker via hydrosilylation reactions. The crosslinking reaction has been carried out in a highly diluted solution using up to 97 vol% of solvent. The obtained aerogels have a colloidal structure with meso- and macropores. Density as low as 0.17 g cm⁻³ has been reached, which implies a porosity of ca. 84 vol%.

Within this work we define structural properties of the silicon carbonitride (SiCN) and silicon oxycarbide (SiOC) ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.