  Amorphous polymer derived silicon oxycarbide (SiOC) is an attractive
candidate for Lithium ion battery anodes, as an alternative to graphite, which
is limited to a theoretical capacity of 372 mAh/g. However, SiOC tends to
exhibit poor transport properties and cycling performance as a result of
sparsely distributed carbon clusters and inefficient active sites. To overcome
these limitations, we designed and fabricated a layered graphene SiOC
heterostructure by solvent assisted infiltration of a polymeric precursor into
a modified three dimensional graphene aerogel skeleton. The use of a high
melting point solvent facilitated the precursors freeze drying, which following
pyrolysis yielded SiOC as a layer supported on the surface of nitrogen doped
reduced graphene oxide aerogels. The fabrication method employed here modifies
the composition and microstructure of the SiOC phase. Among the studied
materials, the highest levels of performance were obtained for a sample of
moderate SiOC content, in which the graphene network constituted 19.8 wt % of
the system. In these materials, a stable reversible charge capacity of 751
mAh/g was achieved at low charge rates. At high charge rates of 1480 mA/g, the
capacity retention was ca. 95% (352 mAh/g) after 1000 consecutive cycles. At
all rates, Coulombic efficiencies greater than 99% were maintained following
the first cycle. Performance across all indicators was majorly improved in the
graphene aerogel SiOC nanocomposites, compared with unsupported SiOC. The
performance was attributed to mechanisms across multiple length scales. The
presence of oxygen rich SiO4-xCx tetrahedral units and a continuous free carbon
network within the SiOC provides sites for reversible lithiation, while high
ionic and electronic transport is provided by the layered graphene SiOC
heterostructure.
