Development of Sustainable Rapid Microwave Assisted Process for Extracting Nanoporous Si from Earth Abundant Agricultural Residues and Their Carbon-based Nanohybrids for Lithium Energy Storage

Bamboo culm (BC), rice husk (RH), and sugarcane bagasse (SB) are the most earth abundant, low cost, and eco-friendly agricultural residues that contain a substantial amount of biogenic silica (SiO2) in the form of amorphous hydrated silica grains. In this study, we successfully extracted SiO2 from various agricultural residues such as BC, RH, and SB via rapid microwave assisted solid-state ashing (MW,SS), followed by microwave assisted magnesiothermic reduction (MW-MR) of SiO2 into crystalline silicon (Si) at <650 degrees C for 30 min without the need for a reducing gas atmosphere. The MW-MR process further supports the development of an interconnected three- dimensional porous Si network with pore diameter of 50-80 nm and wall thickness of similar to 23 nm. The obtained Si is further decorated with dimensionally modulated carbon-based materials such as carbon (C), graphene nanosheets (GNS), and multiwall carbon nanotubes (MWCNT), which can offer higher delithiation capacities (1997, 1290, and 1166 MAh g(-1) respectively) compared to pristine Si (956 mAh g(-1)) extracted from RH at C/5 rate after 200 cycles. These results suggest that the earth abundant BC, RH, and SB could be sustainable resources for large-scale production of nanoporous crystalline Si, which has been extracted via an energy efficient, low-cost microwave assisted sustainable process for lithium ion battery anodes.