Light fraction of pitch realizes robust coating on silicon anodes: The inhibition of volume expansion by self-delithiation

Extreme volume expansion upon lithiation remains a key challenge for Silicon (Si)-based anode materials, which commonly results in electrochemi-mechanical degradation and subsequent fast capacity fading. Pitch-derived carbon coating is an efficient strategy to alleviate the expansion of Si. However, clarifying the relationship between the microstructures of pitch-derived carbon and its expansion confinements properties is still difficult due to the complexity of pitch composition. Herein, we develop core-shell Si@C anode materials with robust protective pitch-derived carbon coating by pitch fraction separation and confirm the expansion confinements properties is connected to molecular structure and weight of pitch fractions. Small and disordered microcrystalline units of light fractions confer high resilience to the derived carbon coating which is less prone to rupture. The compressive stress from resilience coating leads to the transformation of lithium-silicon alloys to amorphous silicon during the early stages of lithiation, which allows for reduction in the expansion of Si. The composites of light fractions derived carbon with Si exhibits the best cycling stability. This work provides new insights into the understanding of expansion confinements in silicon-carbon anode materials.