In situ imaging analysis of the inhibition effect of functional coating on the volume expansion of silicon anodes

Abstract As a hopeful anode material for lithium ion batteries, the silicon (Si) is faced with the main problems of huge volume expansion and poor conductivity. Reasonable coating design on silicon surface is a key to restrict its volume expansion. Herein, a novel hybrid coating of amorphous titanium dioxide (TiO2) and graphene on Si nanoparticles (named Si@aTiO2@G) are designed. The amorphous TiO2 and graphene are bonded by C-O, which mitigates the volume change of nano Si, and endows nano Si with high ionic and electronic conductivity. The electrochemical tests reveal that Si@aTiO2@G delivers high specific capacity of 2970 mA h g-1 after 50 cycles at 0.1 A g-1 and great rate capability of 2200 mA h g-1 after 5 cycles at 1 A g-1. Additionally, real time on-line imaging analysis shows that Si@aTiO2@G electrode produces only 53% of maximum volume expansion compared with bare Si electrode of 338%. In other words, the functional coatings of amorphous TiO2/graphene can reduce the volume expansion rate of nano silicon by 285%. This work provides a new idea to reduce volume expansion and improve conductivity by designing the special functional coating on nano silicon materials, and shows a feasible approach to quantitatively analyze the dynamic evolution of electrode during charging/discharging process.