Synthesis of core-shell silicon-carbon nanocomposites via in-situ molten salt-based reduction of rice husks: A promising approach for the manufacture of lithium-ion battery anodes

Abstract

Silicon (Si) has gained substantial interest as a potential component of lithium-ion battery (LIB) anodes due to its high theoretical specific capacity. However, conventional methods for producing Si for anodes involve expensive metal reductants and stringent reducing environments. This paper describes the development of a calcium hydride (CaH₂)-aluminum chloride (AlCl₃) reduction system that was used for the in-situ low-temperature synthesis of a core-shell structured silicon-carbon (Si-C) material from rice husks (RHs), and the material was denoted RHs-Si@C. Moreover, as an LIB anode, RHs-Si@C exhibited exceptional cycling performance, exemplified by 90.63 % capacity retention at 5 A g^-1 over 2000 cycles. Furthermore, the CaH₂-AlCl₃ reduction system was employed to produce Si nanoparticles (Si NPs) from RHs (R-SiO₂, where SiO₂ is silica) and from commercial silica (C-SiO₂). The R-SiO₂-derived Si NPs exhibited a higher residual silicon oxides (SiO_x) content than the C-SiO₂-derived Si NPs. This was advantageous, as there was sufficient SiO_x in the R-SiO₂-derived Si NPs to mitigate the volumetric expansion typically associated with Si NPs, resulting in enhanced cycling performance. Impressively, Si NPs were fabricated on a kilogram scale from C-SiO₂ in a yield of 82 %, underscoring the scalability of the low-temperature reduction technique.

Keywords: Core–shell structure; Lithium-ion batteries; Molten salts; Rice husk; Silicon anode.