Dual-functional porous Si@C composites from ferrosilicon: Toward high-capacity LIB anodes and high-performance supercapacitors

Silicon is regarded as the most important anode material for lithium-ion batteries (LIBs) due to its low working potential (<0.5 V) and high theoretical specific capacity (3579 mAh g⁻¹). However, Si-based anodes experience internal mechanical strain, pulverization of silicon particles during charging and discharging, and poor electrical conductivity (6.7 × 10⁻⁴ S cm⁻¹). The effectiveness of various nanostructured architectures in resolving the problems with high-capacity Si anodes has been established. In this study, industrial ferrosilicon was used as a low-cost Si source, and a scalable method was introduced to construct a porous Si@C composite anode using two-step leaching–ball milling followed by heat treatment, through which porous Si nanoparticles are wrapped with multilayer carbon sheets derived from polyacrylonitrile (PAN). By encapsulating porous silicon nanoparticles with multiple layers of carbon sheets, creating a dependable framework for conductivity was made possible, ensuring fast transport of electrons, that also mitigated the changes in volume of silicon. This technique was both scalable and straightforward, utilizing cost-effective industrial ferrosilicon as a source of silicon. The nano-sized porous Si/C anode therefore achieves a steady cycling with 887.1 mAh g⁻¹ more than 200 cycles at 1 A g⁻¹ and a rate capability of 657.2 mAh g⁻¹ at 5 A g⁻¹. Also, the resulting porous Si@C powders were evaluated for their electrochemical performance as supercapacitor electrodes. The specific capacitance of the porous Si@C powders was found to be 1494 F g⁻¹ at 1 A g⁻¹, decreasing to 894 F g⁻¹ at 10 A g⁻¹. Additionally, a hybrid capacitor comprising of the porous Si@C powders and activated carbon was tested, which exhibited comparable electrochemical energy storage performance. The energy density of this hybrid capacitor was measured to be 37.2 W h kg⁻¹ at a power density of 694 W kg⁻¹. These findings demonstrate the potential of using Si-based electrodes in supercapacitors, particularly porous Si@C powders, to improve their performance.