In Situ Reduction in Carbon Disorder during Electrochemical Cycling of Silicon–Carbon Composite Electrodes

In lithium-ion batteries (LIBs) with silicon (Si) electrodes, Si's enormous volume change (>300%) causes pulverization and rapid capacity deterioration. Strategies such as embedding Si into carbon matrices with optimized porosity and conductivity have been explored to improve capacity retention and cycling stability. Here, we report a viable two-step emulsion polymerization and carbonization technique to transform biomass into a porous amorphous carbon cloud with commercial Si nanoparticles embedded within it, referred to as Si@CC. Two types of Si@CC with similar Si contents were prepared: Si@CC1 (carbon source: Kraft lignin) and Si@CC2 (carbon source: Kraft lignin and precarbonized soyhulls). A thorough electrochemical analysis of Si@CC2 revealed an anomalous electrochemical behavior─a constant decrease of internal resistance and a downward shift in the charging plateau with cycling. Raman spectroscopy and X-ray diffraction studies revealed an in situ disorder reduction in the amorphous carbon cloud. A greater disorder reduction was observed for Si@CC2, which is attributed to the higher proportion of mesopores (2 nm < pore sizes < 50 nm). The in situ disorder reduction (first report for LIBs) originates from the interplay of Si's volume fluctuations, the low compressibility of the liquid electrolyte, and the load transfer between the liquid electrolyte, Si nanoparticles, and the carbon cloud. This phenomenon contributes to the superior capacity retention of Si@CC2 (81% after 500 cycles at 0.42 A g-1) compared to pristine Si and Si@CC1. In situ disorder reduction in amorphous carbon cloud during cycling holds promise for developing stable, long-lasting, and energy-dense Si-anode LIBs.