A Design Strategy of Carbon Coatings on Silicon Nanoparticles as Anodes of High-Performance Lithium-Ion Batteries

Carbon coatings are commonly used to improve the performance of silicon anodes by providing a conductive shell that discourages the formation of excess solid/electrolyte interphase (SEI). Lack of understanding on the links between the properties of carbon components, such as mechanical properties and conductivity, and the electrochemical properties limits the advances in development of high-performance silicon-carbon nanocomposites. Herein, uniform carbon coatings with different degrees of graphitization were formed on the surface of silicon nanoparticles using bitumen as a carbon precursor. Analysis of electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) shows that the carbon coating of higher elasticity and high Li+ diffusion coefficient through the control of carbonizing bitumen coatings on silicon nanoparticles greatly enhanced the electrochemical performance of carbon-coated silicon anodes. The high elasticity provides stable contacts between silicon and carbon coatings and maintains a stable electrode/electrolyte interface (without excessive SEI growth) during long-term cycling. Compared with electronic conductivity, the efficiency of ion diffusion in the carbon coating is found to play an important role in the rate capability of the electrode. This work provides a design strategy to further optimize the performance of the silicon-based anodes.