Graczyk-Zajac, Magdalena ; Vrankovic, Dragoljub ; Waleska, Philipp ; Hess, Christian ; Vallachira Sasikumar, Pradeep ; Lauterbach, Stefan ; Kleebe, Hans-Joachim ; Soraru, Gian Domenico (2018)
The Li-storage Capacity of SiOC Glasses with and without Mixed Silicon Oxycarbide Bonds.
In: Journal of Materials Chemistry A, 6 (1)
doi: 10.1039/C7TA09236A
Artikel, Bibliographie

Kurzbeschreibung (Abstract)

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 the pyrolysis in Ar flow, while in the second case, the glass is synthesized under CO2 flow. The microstructural characterization of the glasses unambiguously demonstrates that the Ar-pyrolyzed material (SiOC-Ar) is a SiOC/Cfree nanocomposite with mixed SiCxO4-x 0≤x≤4 units, whereas the CO2-pyrolyzed sample (SiOC-CO2) is a SiO2/Cfree 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 SiCxO4-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 bonds- containing sample is more disordered/defective than the one dispersed into 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 mAhg-1, respectively). We rationalize this difference in terms of the enhanced Li-ion storage in the more disordered free carbon phase of SiOC-Ar, while this disorder is induced by the presence of the mixed-bonds units.

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