Environmental Sustainability of Liquid-Based Chemical Synthesis of Si Nanotube as Anode for Lithium-Ion Batteries

Si nanotubes (NTs) have been widely studied as a promising anode material for next-generation lithium-ion batteries (LIBs). The potential environmental impacts of their fabrication are significant due to the involved toxic chemicals and process emissions. In this study, a scalable liquid-based synthetic method of Si NT was developed via fabrication of SiO2 NTs followed by chemical reduction in magnesium vapor to produce Si NTs. The Si NTs were then used as the anode in LIB and obtained a specific capacity of 1061 mAh/g after five cycles. The environmental emissions from the synthetic process were investigated through a series of techniques with a process-based approach. Throughout the whole synthetic process, 51.59% of Si was recovered. To synthesize 1.00 g of Si NTs, 60.09 g of C6H12, 43.66 g of Brij 58, 1.01 g of NiCl2, 2.39 g of N2H4·H2O, 3.63 g of C4H11N, 14.38 g of TEOS, 145.49 g of IPA, and 9.36 g of Mg were needed. The wastes could be categorized into three groups: gases, particles, and liquids. A small portion of chemicals were released in the form of gases, such as C6H12, N2H4, C4H11N, NH3, CO2, and NO2. About 3.5 × 1010 # particles composed of C and O were emitted into the atmosphere. Diameters of the particles were within 10 μm. Concentrations of Ni, C, N, and Mg in the aqueous wastes were 0.458, 98.1, 0.786, and 3.52 g, respectively, indicating significant discharge of metals and organic components. The results reported in this study can be useful for supporting sustainable manufacturing and life cycle assessment of Si NT-based LIBs in the future.