Eco-friendly synthesis of SiO2 nanoparticles confined in hard carbon: A promising material with unexpected mechanism for Li-ion batteries
Résumé
A fast, simple and environmentally friendly one-pot route to obtain carbon/SiO 2 hybrid materials is reported in this work. This consists in simple mixture of carbon and silica precursors, followed by thermal annealing at different temperatures. An interpenetrating hybrid network composed of hard carbon and amorphous SiO 2 nanoparticles (2e5 nm) homogeneously distributed was achieved. Increasing the annealing temperature from 600 C up to 1200 C, the material porosity and oxygen functional groups are gradually removed, while the amorphous nature of SiO 2 is conserved. This allows to diminish the irreversible capacity during the first charge-discharge cycle and to increase the reversible capacity. An excellent cycling capability, with a reversible capacity up to 535 mA hg-1 at C/5 constant current rate was obtained for C/SiO 2 materials used as anodes for Li-ion batteries. An atypical increase of the capacity during the first 50 cycles followed by a stable plateau up to 250 cycles was observed and related to electrolyte wettability limitation through the materials, particularly for those annealed at high temperatures which are more hydrophobic, less porous and the SiO 2 nanoparticles less accessible. The SiO 2 lithiation mechanism was evaluated by XRD, TEM and XPS post-mortem analyses and revealed the formation of reversible lithium silicate phases.
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