Constructing hierarchical Si/PPy/PANI anodes with dual carbon layers for enhanced cycling stability and rate capability

Abstract

Silicon (Si) is considered one of the most promising anode materials for next-generation lithium-ion batteries (LIBs) due to its exceptionally high theoretical capacity. However, the severe volume expansion during charge/discharge cycles leads to particle pulverization and poor cycling stability. To address these challenges, a novel dual carbon source strategy is proposed in this study. A hierarchical Si/PPy/PANI composite is constructed by sequentially coating silicon nanoparticles with polypyrrole (PPy) and polyaniline (PANI) via in situ polymerization, followed by high-temperature carbonization under an Ar/H₂ atmosphere. The resulting material features a double-layer N-doped carbon shell, where the inner PPy-derived carbon exhibits a high degree of graphitization, forming a dense and conductive network that enhances electronic conductivity and structural robustness. The outer PANI-derived carbon layer contains abundant nitrogen doping and porous structures, which not only offer extra lithium storage sites but also buffer volume expansion and promote fast lithium-ion diffusion. Nitrogen doping further modulates the electronic structure of the carbon matrix, increasing the local charge density and facilitating Li⁺ adsorption. Benefiting from this synergistic dual-shell design, the Si/PPy/PANI anode demonstrates outstanding electrochemical performance. At a current density of 1000 mA g⁻¹, it delivers a reversible capacity of 790.1 mA h g⁻¹ after 400 cycles with a high coulombic efficiency of 99.66%. Even at a high rate of 5000 mA g⁻¹, the capacity remains at 882.4 mA h g⁻¹, showing excellent rate capability. These results confirm the effectiveness of the dual carbon shell in enhancing both the cycling stability and rate performance of silicon-based anodes. This work provides a simple and scalable approach to designing high-performance Si/C composite anodes with robust structural stability and efficient charge transport. The dual carbon encapsulation strategy offers new insights into advanced electrode engineering for high-energy lithium-ion batteries.