The Nanostructured Silicon From Rice Husks For High Performance Li-Ion Battery Anodes: Synthesis, Characterization And Electrochemical Properties

ABSTRACT

Nanostructured silicon has attracted considerable attention as a promising anode material for next generation Lithium-ion batteries for applications in portable electronic devices and hybrid electric vehicles. This interest is mainly due to its large theoretical specific charge capacity of 4,200 mAh g-1 that is ten times more than the theoretical specific charge capacity of conventional graphite anodes. This work exploits an alternative method of fabricating pure silicon nanoparticles (SiNPs) from rice husks (RHs), an abundant agricultural waste, produced at a rate of approximately 1.2 × 108 tons per year. The methods uses acid pre-treatment and subsequent combustion of RHs, followed by additional acid leaching of the rice husks ash obtained. To synthesize SiNPs, heat scavenger assisted magnesiothermic reduction of the rice husks originated silica was performed. The silica from rice husks (RHs) and the synthesized SiNPs were characterized by energy-dispersive X-ray (EDX) spectroscopy and FTIR spectroscopy, the morphology was determined using Scanning Electron Microscopy (SEM), while particle size and structure were probed by X-Ray Diffraction (XRD). Acid pre-treatment of RHs with 3M HCl for 12 hours followed by combustion at 600 oC for 5 hours yielded 22.50% ash of which 98.520 (±0.457) % was amorphous silica. Further acid-leaching of the silica with 2M HCl for 6 hours substantially decreased the level of metallic impurities present to achieve silica of high purity of approximately 99.046 (±0.451) %. Magnesiothermic reduction of this silica yielded SiNPs of high purity of approximately 98.794 (±0.335) % from EDX analysis. The recovered SiNPs used in fabricating Li-ion battery anodes in this study were highly crystalline with their XRD pattern readily indexed to that of pure silicon (JCPDS No. 27-1402). The crystallite size of 10 to 100 nm and porous nature of the recovered SiNPs exhibited superior electrochemical performance over commercially available graphite as Li-ion battery anodes, delivering a high reversible capacity of 2,732 mA hg-1 which is seven times greater than the theoretical capacity of graphite anodes (372 mA hg-1), with a high coulombic efficiency in first cycle and a long cycle life (97.20 % capacity retention over 16 cycles). Thus, the results obtained indicate that the prepared nanostructured silicon electrode is a promising anode material for high performance lithium-ion battery anode.