(435e) Scalable, Economical and Sustainable Manufacture of Porous-Silicon for Li-Ion Battery Anodes

Silicon has one of the highest specific capacities of all the potential lithium-ion battery anode materials, being able to store almost 10x more charge than the presently used graphite. Despite its huge volumetric expansion, extensive research in the field have shown that damage caused by this expansion can be limited or avoided by using porous silicon (p-Si). Producing p-Si in bulk can be achieved via the magnesiothermic reduction (MgTR), however, it requires high temperatures (³650^oC) to attain meaningful yields [J. Mater. Chem. A, 2018, 6, 18344]. Operating MgTR at such temperatures causes loss of porosity due to sintering, while also requiring uneconomical amounts of energy [J. Mater. Chem. A, 2020, 8, 4938].

We have discovered a process that can remove these limits and showed that p-Si can be produced at as low as 380°C [RSC Adv., 2021, 11, 35182]. This ultra-low temperature (ULT) method achieved yields of silicon up to 83 mol% with initial capacity of 1822 mAh/g, stabilising to 1000 mAh/g after 100 cycles. The electrochemical performance of p-Si obtained from ULT method exceeded that of those produced at ≥650°C. We have also investigated the scale-up of p-Si production, and by understanding the formation pathways of MgTR reaction, we have scaled-up and optimised the process to demonstrate its scalability. Further, extensive technoeconomic analysis showed that p-Si produced from our method will cost ~25% of current market price of silicon. Taken together, these results strongly suggesting that UTL process has the potential to enable the economic bulk production of silicon.