A team at the University of Science and Technology of China (USTC) reports a new method for the synthesis of polycrystalline silicon nanoparticles for use as anode materials in Li-ion batteries in a paper in the journal Angewandte Chemie. As an anode for rechargeable Li-ion batteries, the as-prepared Si delivers the reversible capacity of 3083 mAh g−1 at 1.2 A g−1 after 50 cycles, and 1180 mAh g−1 at 3 A g−1 over 500 cycles.
To prepare the nanoparticles, the team reduced SiCl4 with metallic magnesium in a molten salt of AlCl3 at 200 ˚C inside a stainless steel autoclave.
The resulting silicon nanoparticles range in size from several 10s of nanometers to ~100 nm. The method, wit its relatively mild reaction conditions, is high yielding (more than 80%).
AlCl3 not only acts as molten salt, but also participates in the reaction. The related experiments confirm that metallic Mg reduces AlCl3 to create nascent Al which could immediately reduce SiCl4 to Si, and the by-product MgCl2 would combine with AlCl3 forming a complex of MgAl2Cl8.—Lin et al.
Lin, N., Han, Y., Wang, L., Zhou, J., Zhou, J., Zhu, Y. and Qian, Y. (2015) “Preparation of Nanocrystalline Silicon from SiCl4 at 200 °C in Molten Salt for High-Performance Anodes for Lithium Ion Batteries,” Angew. Chem. Int. Ed.. doi: 10.1002/anie.201411830