Thermochemical Core-Shell Architecturing of Si-SWCNT Composites for High-Performance Li-Ion Battery Anodes

Silicon (Si) is a promising anode for next-generation lithium-ion batteries (LIBs) because of its ultrahigh theoretical capacity, yet its practical application is hindered by severe volume expansion, unstable interfaces, and sluggish reaction kinetics. Here, we report a thermochemically engineered core-shell Si architecture integrating alloy stabilization, nanoporous strain buffering, and chemically anchored conductive networks. Starting from a SWCNT-coated Mg₂Si precursor, a CH₄-assisted thermochemical treatment induces localized exothermic Mg oxidation, followed by selective MgO etching to construct a SiC-anchored SWCNT conductive network and a nanoporous Si shell surrounding a robust Mg-containing Si core. Reactive molecular dynamics simulations reveal that localized hot-atom generation during Mg oxidation activates CH₄ molecules, providing atomistic insight into the low-temperature formation of the SiC interfacial layer. The resulting architecture decouples mechanical strain from charge transport, enabling an initial reversible capacity of 1890 mAh g^-1 with 74% capacity retention after 100 cycles. Graphite composite electrodes containing 20 wt.% Si deliver 640 mAh g^-1 and retain 78% capacity after 200 cycles, substantially exceeding the Si content used in commercial electrodes. Pouch-type full cells paired with Li[Ni_0.6Co_0.2Mn_0.2]O₂ cathodes achieve an energy density of 275 Wh kg^-1 with 75% capacity retention after 1000 cycles, demonstrating a scalable strategy for high-energy-density LIBs.