Utilization of Coal Fly-Ash derived Silicon (Si) as Capacity Enhancer of Li-Ion Batteries Anode Material

¹ Chemical Engineering Department, Vocational School, Universitas Sebelas Maret, Jl. Kolonel Sutarto 150 K, Surakarta 57126
² Centre of Excellence for Electrical Energy Storage Technology, Universitas Sebelas Maret, Jl. Slamet Riyadi 435, Surakarta 57146
³ Chemical Engineering Department, Faculty of Engineering, Universitas Sebelas Maret, Jl. Ir. Sutami 36A, Surakarta 57126

^* Corresponding author: corneliussyudha@staff.uns.ac.id

Abstract

The increasing demand for energy has caused a rise in coal usage, resulting in high fly ash generation. The high SiO₂, Al₂O₃, and Fe₂O₃ content in fly ashes (FAs) allow them to be processed in electrical energy storage technology, such as lithium-ion-based secondary batteries. The research aims to develop silicon from FAs for Li-ion battery applications. The fabrication of silicon materials employed in this study are (i) extraction of SiO₂ from FA, (ii) gelation of SiO₂, (iii) magnesiothermic reduction of SiO₂ to Si under N₂ flow, (iv) purification of silicon, (v) the solid-state composite fabrication of Si/C. The as-prepared Si was characterized. XRD test showed the presence of silicon phase and minor impurities in Mg. SEM analysis of the Si showed that the material has a polymorph shape with a rough surface of micron-sized secondary particles. EDX test showed the presence of impurities in the form of O and Mg atoms; meanwhile, the EDX mapping confirmed the dominant distribution of Si in the sample. Galvanostatic charge-discharge analysis of a battery with 5%Si/C anode and LiNi_0.8Co_0.1Mn_0.1O₂ or NCM811 cathode resulted in a specific charge and discharge capacity of 600 mAh/g and 473.6 mAh/g, respectively, which is greater than the graphite theoretical capacity of 372 mAh/g.