Investigation of the soft carbon microstructure in silicon/carbon anodes for superior lithium storage

Abstract

It is essential to consider the controllable microstructure of soft carbon and its enhancement effect on the electrochemical performance of silicon (Si) active materials. In this study, a series of Si@mesocarbon microbead (Si@MCMB) composites were prepared using mesophase pitch as the soft carbon source to coat nano-Si. The results showed that the ordered carbon layer stacking of soft carbon increased slightly with increasing heat treatment temperature in the range of 800–1400 °C. The Si@MCMB composites at higher temperature had a turbostratic carbon layer texture with rich porosity and smaller specific surface area, and had good cycle stability and high rate performance. These results highlighted that the co-existing structure of turbostratic carbon arrays with abundant porosity from soft carbon, provided the electron/ion transfer channels, underwent Si alloy volume change and enhanced the mechanical stability. Importantly, the relationship between the capacity retention rate of the Si@MCMB anodes and the microstructural characteristics (carbon layer and porosity) of soft carbon was established, which provided effective guidance for the design of high-performance silicon/carbon (Si/C) anode materials.