Simultaneous Purification and Perforation of Low-Grade Si Sources for Lithium-Ion Battery Anode.

Silicon is regarded as one of the most promising candidates for lithium-ion battery anodes because of its abundance and high theoretical capacity. Various silicon nanostructures have been heavily investigated to improve electrochemical performance by addressing issues related to structure fracture and unstable solid-electrolyte interphase (SEI). However, to further enable widespread applications, scalable and cost-effective processes need to be developed to produce these nanostructures at large quantity with finely controlled structures and morphologies. In this study, we develop a scalable and low cost process to produce porous silicon directly from low grade silicon through ball-milling and modified metal-assisted chemical etching. The morphology of porous silicon can be drastically changed from porous-network to nanowire-array by adjusting the component in reaction solutions. Meanwhile, this perforation process can also effectively remove the impurities and, therefore, increase Si purity (up to 99.4%) significantly from low-grade and low-cost ferrosilicon (purity of 83.4%) sources. The electrochemical examinations indicate that these porous silicon structures with carbon treatment can deliver a stable capacity of 1287 mAh g(-1) over 100 cycles at a current density of 2 A g(-1). This type of purified porous silicon with finely controlled morphology, produced by a scalable and cost-effective fabrication process, can also serve as promising candidates for many other energy applications, such as thermoelectrics and solar energy conversion devices.