Electrochemical Conversion of Silica Nanoparticles to Silicon Nanotubes in Molten Salts: Implications for High-Performance Lithium-Ion Battery Anode

Understanding the material formation mechanism is critical to guide the material synthesis and exploitation. Herein, we reveal a different conversion mechanism of SiO2 particles to Si nanotubes (SNTs) in the molten salt electrolysis. Unlike conventional strategies employing templates and/or catalysts, the one-step electrochemical synthesis is template- and catalyst-free, which process involves lamination, exfoliation, and reduction. Specifically, SiO2 particles are first converted into layer-structured CaSiO3, from which CaO and O2- are subsequently extracted, causing the collapse of the layer structure and forming SiOx (0 < x < 2) layers. The newly formed SiOx layers are finally deeply reduced into SNTs. Besides, the morphology of silicon-based nanostructures can be controlled via altering the applied voltage between a SiO2 cathode and a graphite anode. In addition, the electrolytic SNTs show enhanced lithium-storage performances, such as a high specific capacity (2485 mAh g(-1) at 0.2 A g(-1)) and an excellent rate capability (1362 mAh g(-1) at 5 A g(-1)), which is benefited from the tube structure that can buffer the volume variation of Si. Overall, the revealed conversion mechanism will shed light on designing advanced Si-based nanomaterials for various applications.