| AVS 65th International Symposium & Exhibition | |
| Thin Films Division | Monday Sessions |
| Session TF2-MoM |
| Session: | IoT Session: Thin Film Processes for Energy Storage |
| Presenter: | Giorgio Nava, University of California, Riverside |
| Authors: | G. Nava, University of California, Riverside J. Schwan, University of California, Riverside L. Mangolini, University of California, Riverside |
| Correspondent: | Click to Email |
Over the last decade, the research community engaged in significant efforts to investigate novel anode materials for Li-ion batteries with the goal of increasing the storage capacity of these devices. Among several candidates, silicon-carbon nanocomposites represent one of the most promising choices, featuring the highest theoretical gravimetric storage capacity. The small size of the silicon -Si- structures tackles the volume expansion undergone by the semiconductor upon lithiation, which causes pulverization of bulk Si electrodes, and promotes a robust cycling. The carbonaceous coatings, on the other hand, improve the electrical conductivity of the composite and prevent the direct interaction of Si with the electrolyte which in turn enhances the stability of the solid electrolyte interphase. Although a wide range of different Si-C nanocomposites have been investigated, these structures are often produced with methods characterized by questionable scalability, hence hindering the immediate introduction of these materials into actual manufacturing. In this contribution, we describe a facile and scalable-by-design approach for the fabrication of Si-core graphite-shell nanoparticles -NPs. Commercial Si NPs with an average size of 100 nm are introduced into a hot-wall furnace with an alumina combustion boat. The NPs are wrapped with a conformal coating of amorphous carbon resulting from the dissociation of acetylene - C2H2 - at 650 °C. After removing C2H2 from the reaction zone, the furnace is ramped up to 1000°C in Argon -Ar- yielding a controlled graphitization of the C-shell, as highlighted by Raman and TEM analysis, with no detectable presence of silicon-carbide. The as-produced composites are introduced into a slurry with no addition of conductive additives, coated onto a copper substrate and studied as pure anode material in Li-ion battery half-cell assemblies. The amorphous-C-coated Si NPs exhibit a high first cycle coulombic efficiency – CE – in the order of 87% and a capacity of 1800 mAh g-1 which rapidly decays below 1000 mAh g-1 during the first 40 cycles. The graphitization of the C-shell, achieved through the high-temperature step in Ar, significantly improves the cycling stability of the material showing a capacity above 1500 mAh g-1 over more than 100 cycles. Finally, the silicon-graphite composite is tested as a simple drop-in additive in graphite anodes. The addition of small amount of the Si-based active material (10% in wt) enables the fabrication of electrodes with a gravimetric capacity 30% higher than the one of the pure graphite electrodes used in commercial batteries, a first cycle CE of 90% and stable cycling over 100 cycles.