Enhancing the Lithium-Ion Battery Performance of Commercial Micron-sized Silicon Particles using Graphene

Abstract

Silicon is known to be one of the most promising anode material for future-generation lithium-ion batteries, thanks to its theoretical specific capacity of approximately 3579 mAh/g. Nonetheless, the use of silicon anodes is hampered in practical devices owing to their large volume expansion during lithiation, the instability of the solid electrolyte interface, capacity decay, and poor rechargeability. Specifically, micron-sized commercial-grade silicon particles exhibit drastic pulverization, along with the loss of electrical contact, during the cycling process. This thesis attempts to improve the electrochemical properties of commercial micron-sized silicon materials by thick graphene coating. A comprehensive strategy included the size reduction of the materials via ball mill processing, the introduction of functional groups through APTES silanization, the deposition of graphene oxide, and finally, chemical reduction of the resultant material on the surface of the silicon materials to create a graphene layer. The optimized ball-milled, uniformly graphene-coated silicon electrodes revealed a remarkably high discharge capacity of about 3400 mAhg-1. Significantly improved stability was also observed, retaining a discharge capacity of 1600-1800 mAhg-1 after 25 cycles in a designed half-cell. However, the unmodified silicon electrodes, along with the non-uniformly modified samples, suffered from a sharp decrease in discharge capacities below the 500 mAhg-1mark. These findings prove the effectiveness of homogeneous graphitic coatings, together with size reduction, in reducing the volume expansion of silicon and preserving electrical connections. This work presents a feasible, affordable method to enhance the performance of commercial, micron-sized Si anode materials, filling the technological gap between the lab scale and commercial Li-ion batteries (LIB).