Silicon/Mesoporous Carbon (Si/MC) Derived from Phenolic Resin for High Energy Anode Materials for Li-ion Batteries: Role of HF Etching and Vinylene Carbonate (VC) Additive

Silicon/mesoporous carbon (Si/MC) composites with optimum Si content, in which the volumetric energy density would be maximized, while volume changes would be minimized, have been developed. The composites were prepared by dispersing Si nanoparticles in a phenolic resin as a carbon source, subsequent carbonization, and etching with hydrofluoric acid (HF). Special attention was paid to understanding the role of HF etching as post-treatment to provide additional void spaces in the composites. The etching process was shown to reduce the SiO2 native layer on the Si nanoparticles, resulting in increased porosity in comparison to the non-etched composite material. For cell optimization, vinylene carbonate (VC) was employed as an electrolyte additive to build a stable solid electrolyte interphase (SEI) layer on the electrode. The composition of the SEI layer on Si/MC electrodes, cycled with and without VC-containing electrolytes for several cycles, was then comprehensively investigated by using ex-situ XPS. The SEI layers on the electrodes working with VC-containing electrolyte were more stable than those in configurations without VC
this explains why our sample with VC exhibits lower irreversible capacity losses after several cycles. The optimized Si/MC composites exhibit a reversible capacity of ~800 mAhg&minus
1 with an average coulombic efficiency of ~99 % over 400 cycles at C/10.