Dual-Coated Si Anode with Soft and Hard Carbon: A Strategy for Enhanced Electrochemical Performance

Abstract

Silicon (Si) has garnered significant attention as a next-generation anode material for lithium-ion batteries due to its high theoretical capacity (~4200 mAh g⁻¹), and low operating potential (~0.37 V vs. Li/Li⁺). However, substantial volume expansion (~300%) during charge/discharge cycles leads to structural degradation and detachment from the current collector, resulting in rapid capacity fading. To address these challenges, we synthesized silicon anodes with a dual-layer carbon coating comprising hard carbon and soft carbon, using sucrose and pitch as precursors. We also investigated the impact of a caramelization process on carbon layer formation. The dual-layer carbon coating prevents direct contact between silicon and the electrolyte, reducing continuous electrolyte decomposition. It combines the excellent mechanical strength of hard carbon with the flexibility and superior electrical conductivity of soft carbon, effectively mitigating silicon’s volume expansion during cycling and enhancing its electrical conductivity. This synergy improves both the physical and electrochemical performance of the anodes. Various physical analyses (FE-SEM, TGA, BET/BJH, RAMAN) and electrochemical analyses (GCD, EIS, CV) validated these findings. Notably, the Si@pit/suc_cm sample with dual-layer carbon coating exhibited a 4.01% improvement in initial Coulombic efficiency at a 0.1 C-rate and a 27.38% enhancement in cycle life at a 1 C-rate over 100 cycles compared to bare Si. These results confirm the superior electrical conductivity and volume expansion suppression effect of the dual carbon coating.