Graphene-Coated Silicon Alloy with High Capacity and Good Cycling Stability for Lithium-Ion Batteries

The growing demand for high-performance energy storage devices for applications in portable electronic devices, electric vehicles and energy storage systems requires dramatic improvement in the energy density and cycle life. Silicon-based anode materials hold promise for these applications due to their high theoretical capacity and abundant availability for large-scale applications.  However, silicon anodes are known to have problems such as electrode pulverization due to its high volume expansion during repeated cycling and poor cycle life due to unstable solid-electrolyte interphase (SEI) layer. To solve these problems, many studies have been carried out in terms of thin film, nanostructure, alloy and composites. In this work, we synthesized Si-based alloy materials with high specific capacity. To improve their cycling stability, the silicon alloy materials were surface modified with reduced graphene oxide (rGO).  The rGO layer formed on the Si alloy played as a flexible confinement for accommodating volume changes during cycling.  And also, its high mechanical strength prevented the pulverization of the electrode.  In addition, its 2-dimensional structure enabled to electronically connect the individual Si alloy particles to the current collector. Their interfacial studies and cycling performances are investigated by electrochemical impedance spectroscopy, XPS, FE-SEM, HR-TEM and cycling test. Detailed characterization of the rGO-coated silicon alloy materials along with their electrochemical performance will be presented.