Silicate-Mediated Electrolytic Silicon Nanotube from Silica in Molten Salts

Electrochemical preparation/processing of functional silicon from abundant silica is an ideal protocol to promote sustainability of energy sectors. Such an imperative task is challenged by poor electrical conductivity of Si/SiO₂ and inadequate mass diffusion of bulk silicon. Herein, a template-free and one-step preparation of silicon nanotubes (Si-NT) from electrochemical reduction of silica in molten salts is reported. An in situ oriented growth of silicate nanorods (NRs) from silica is clarified as the key step to direct a self-template evolution of Si-NT from silica. The silicate-mediated construction of Si-based NT is versatile and successfully extended to prepare Si-NT/graphite and Ti_x Si_y -NT. Benefitting from fast longitudinal motorways for fast transport of electrons and ions along/inside NTs, an energy consumption 30% lower than industrial silicon production is achieved. When evaluated as anode of lithium ion battery, the Si-NT-based electrodes show outstanding initial Coulombic efficiency and high reversible capacity. The silicate-mediated construction of Si-based NT integrates straightforward preparation and intriguing functionality of Si-based materials, bridging a closed-loop Si-based energy infrastructure.