Optimal microstructural design of pitch-derived soft carbon shell in yolk-shell silicon/carbon composite for superior lithium storage

Highlights: • The facile and cost-effective preparation process of yolk-shell Si/C composites and modification methods with high scalability. • The designed pore channel structures endowing the optimal lithium storage capacity and volume change tolerance. • The high crystallinity ensures the outstanding electronic conductivity and robust carbon shell. • The optimal Si/C composite with a well matching microstructure of carbon shell exhibits excellent cycling performance and rate capacity (55% retention at 300th cycle, 743 mAh g⁻¹ at 2 A g⁻¹). • Correlation between microstructural feature (crystallinity and pores) of the carbon shell and the electrochemical behaviors of the Si/C electrodes is established. -- Abstract: Silicon-carbon composites have proved to be effective in addressing the issues of silicon anodes, however, few works focus on understanding the effect of the microstructure of the carbon component on their electrochemical performance. Herein, we prepare a series of yolk-shell structured silicon-carbon nanocomposites with adequate voids through a facile and scalable process. By deliberately selecting the pitch species and delicately adjusting the heat treatment temperature, the microcrystal texture and pore structure of the soft carbon can be easily tuned. Finally, a well matching of the crystalline and pore structure ensure the rapid charge transport and the good structural robustness, further endowing the optimal lithium storage, cycle performance and rate capability of the electrodes. The Si/C composite with an optimized carbon shell delivers a reliable cycle stability with a capacity retention ratio of 55% after 300 cycles at 0.2 A g⁻¹ and a remained capacity of 743 mAh g⁻¹ at a high current density of 2.0 A g⁻¹. Importantly, the correlation between the lithium storage of the Si/C composites and the microstructure features (crystallinity and pores) of the carbon shell has been established, which may provide an effective guidance for optimizing the microstructure design of the promising Si/C anode materials.