Influencing factors and behavior mechanism of the initial coulombic efficiency of silicon/graphite composites in lithium-ion batteries

Highlights: : • Four types of Si/G composites with the same components and different combination ways are prepared by simple methods. • Four types of Si/G composites are prepared to study the internal factors affecting the initial coulombic efficiency. • The Si-G@C with large specific surface area still owns the highest initial coulombic efficiency. -- Abstract: : Investigating the internal factors that affect the initial coulombic efficiency (ICE) of silicon/graphite (Si/G) composites and improving ICE are critical to promote applications of Si/G composites in lithium-ion batteries. Here, four types of Si/G composites are prepared with different specific surface area, Si–G phase interface and charge transfer impedance (R_ct) to study the internal factors affecting the ICE of Si/G composites. The experimental results show that the influencing factors on ICE of Si/G composites are not only specific surface area, but also the Si–G phase interface and R_ct. During the first lithiation process of Si/G composites, there are some reversible phase (Li_xSi, Li_xC) and irreversible phase (Li₂O, Li₂SiO₄ and organolithium) formed, the ICE of Si/G composites is mainly determined by the irreversible phase. The specific surface area, R_ct and Si–G phase interface can affect the reaction kinetics of the materials and the ratio of reversible/irreversible phase content, which ultimately affect the ICE of Si/G composites. A smaller specific surface area and well Si–G phase interface with a low R_ct will bring a higher ICE of Si/G composites. This report may provide a new idea for the research of ICE of Si/G composites and promote their practical application.