Silicon nanoparticles with a graphene shell as anodes for Lithium Ion Batteries: study of the role of graphene to silicon ratio

Summary:

Silicon is a promising material in lithium-ion battery technology. As a negative electrode, it exhibits more than 3800 mAh/g of theoretical specific capacity which is way higher compared to the 370 mAh/g of graphite’s theoretical specific capacity. Furthermore, silicon is the second richest material in the earth’s crust, it is non-toxic and environmentally friendly. However, silicon undergoes volume changes during lithiation and delithiation process, up to 300%, which results in cracking and pulverization leading to a short cycling life. Another problem that appears due to the volume changes is the continuous formation of solid electrolyte interphase (SEI) after each cycle and the fast decomposition of the electrolyte. Various methods have been proposed to solve this issue such as creating special coatings, reducing the size of silicon to nanoparticles, or creating nanostructures with hollow or void space for the silicon to be able to expand. Graphene is a fine candidate to be used as a coating for silicon due to its mechanical strength and high conductivity. Silicon in nanoparticle form has more space to expand during lithiation process thus pulverization is avoided, whereas, graphene enwraps silicon nanoparticles, protecting them from direct SEI formation and increasing the electrical conductivity of the electrode. SEI is formed mostly on graphene instead of silicon which decreases the fast decomposition of the electrolyte.
In this work, silicon nanoparticles will be mixed with graphene through ball milling. The resulting material will be a sphere-like structure with a graphene shell around silicon. The study will examine the electrochemical behavior of the material in comparison to its size. Prepared electrodes demonstrated gravimetric specific capacity of 600 mAh/g, areal capacity of 1.4 mAh/cm2, and was able to perform more than 280 cycles, whereas bare silicon nanoparticles electrodes usually can achieve no more than 40 – 60 cycles, with a gravimetric capacity of 2000 mAh/g.