We report here a method to convert RHs directly into Si nanoparticles,
and demonstrate their high performance as Li-ion battery
anodes. As shown in the flow chart and optical images in Fig. 1c–g,
raw RHs were first converted to nano-SiO2 by thermally decomposing
the organic matter, followed by magnesiothermic reduction to
produce nano-Si. Compared with the reported methods of producing
nano-Si (Fig. 1a), our method has several advantages: (i) the recovered
silicon inherits the intrinsic and unique nanostructure of the
silica in RHs, which allows for excellent battery performance by
mitigating pulverization; (ii) RHs are an abundant and sustainable
materials source with a supply that far exceeds the demand for LIB
anode materials; (iii) the overall method is simple, energy-efficient,
and easy to scale-up; and (iv) the overall process does not use expensive
Si precursors or reagents. Mg metal, one of the most commonly
used structural metals, is produced by electrolytic process or Pidgeon
process with a relatively low cost compared to other nano-Si precursors.
And Mg can be regenerated from the MgCl2 byproduct by
electrolysis as shown in Fig. 1c. Thus, the whole process only consumes
HCl and converts it to Cl2 after the electrolysis. The overall
process is green.