Emulsion-templated silicon/carbon anodes with reduced graphene oxide

Silicon is an attractive material for anodes in energy storage devices, because it has ten times the theoretical capacity of its state-of-the-art carbonaceous counterpart. Silicon anodes can be used both in traditional lithium-ion batteries and in more recent Li-O2 and Li-S batteries as a replacement for the dendrite-forming lithium metal anodes. The main challenges associated with silicon anodes are structural degradation and instability of the solid-electrolyte interphase caused by the large volume change (∼300%) during cycling, the occurrence of side reactions with the electrolyte, and the low volumetric capacity when the material size is reduced to a nanometre scale. The simple fabrication technique of emulsion-templated direct assembly, which was reported by Chen et al. (2014) is further developed, by using reduced Graphene Oxide (r-GO) to increase the conductivity and increase the silicon-carbon ratio (Si/C ratio). In this method, Si nanoparticles are confined in the oil phase of an oil-in-water emulsion stabilized by carbon black (CB). These CB nanoparticles are both oil- and water-wettable. The hydrophilic/hydrophobic balance for the CB nanoparticles also causes them to form a network in the continuous aqueous phase. Upon drying this emulsion on a current collector, the CB particles located at the surfaces of the emulsion droplets form mesoporous cages that loosely encapsulate the Si particles that were in the oil. The CB particles that were in the aqueous phase form a conducting network connected to the CB cages. The space within the cages allows for Si particle expansion without transmitting stresses to the surrounding carbon network. Half-cell experiments using this Si/CB anode architecture show a specific capacity of ∼1000 mAh/g Si + C and a Coulombic efficiency of 99.5% after 50 cycles. This corresponds to a increase to the previous work of over 30%. Emulsion-templating is a simple, inexpensive processing strategy that directs Si and conducts CB particles to desired spatial locations for superior performance of anodes in lithium ion batteries