Synthesis of silicon nanowire-graphite composites for Li-Sulfur batteries
Résumé
As the demand for high energy density storage increases, lithium-sulfur batteries (LSBs) are being considered as a promising solution. However, before commercialization, they must overcome several limitations, including instability of sulfur cathodes and lithium metal anodes. Considering this, silicon nanowires (SiNWs), with a high theoretical capacity and low discharge potential, represent an interesting alternative anode material capable of meeting this demand. Nonetheless, their synthesis requires a cost reduction to achieve industrial relevance. Our study introduces low-cost catalysts, tin sulfide/or oxide, that allow growing silicon nanowire directly on graphite, producing Si-rich anode composites (over 30%wt of Si). The non-uniform distribution of self-confined conductive silicon nanowires on the surface of graphite takes advantage of their matrix to effectively pad volume changes and significantly reduce the phenomenon of sputtering and capacity fading during lithium insertion and extraction, as well as maintaining the SiNWs' integrity.
Within the ERA-MIN3 project “2BoSS” (2boss.eu), we recently inquired how to improve this process towards a more sustainable material to be included in lithium-sulfur batteries. First we developed a post-synthesis treatment to remove the tin growth catalyst from the composite. Second, we turned to recycled graphite to include this material in a circular strategy in the battery sector. Third, we used porous carbon obtained from biowaste to synthesize composites with very high silicon content (over 40%wt).
We also optimized a formulation of electrolyte able both to stabilize the SEI of Si-rich anodes and the cycling of sulfur cathodes. Assembly of full cells is under way.