Internal Buffering-External Reinforcement of Si@C Nanostructure-Based Anodes via Dual SWCNT Networks for Stable Lithium-Ion Batteries

Silicon–carbon (Si/C) composites are promising lithium-ion battery anodes attributed to silicon’s ultrahigh theoretical capacity (∼3579 mAh g–1), yet severe volume expansion during lithiation and consequent structural instability remain critical bottlenecks. A typical mitigation strategy is carbon coating to form Si@C core–shell structures, but such Si@C still suffers from shell fracture at high Si contents due to insufficient mechanical robustness and limited buffer space. To address these issues, we propose a cooperative “inside-out” structural strategy for Si@C composite anodes by integrating dual single-walled carbon nanotube (SWCNT) networks. On the one hand, an interwoven SWCNT network is introduced inside the carbon shell, tightly wrapping Si particles. Benefiting from SWCNTs’ exceptional strength and flexibility, the internal network buffers lithiation stress to protect the outer carbon shell and constructs continuous electron–ion transport pathways. On the other hand, an additional SWCNT layer coated outside the carbon shell serves as secondary reinforcement, synergistically suppressing expansion-induced stress and enhancing structural stability. This dual “internal buffering-external reinforcement” design enables excellent electrochemical performance even at high Si content (∼86%). The anode delivers 1676.5 mAh g–1 after 200 cycles at 1 A g–1 and 1230.6 mAh g–1 after 350 cycles at 2 A g–1. This work provides a practical paradigm for high-silicon Si/C anodes.