UC Riverside

Silicon-based nanostructures were synthesized and characterized with the ultimate aim of creating a high performance, environmentally benign, and highly scalable material technology for next-generation Li-ion battery (LIB) anodes. Herein, four distinct silicon-based nanomaterials were synthesized and thoroughly characterized including silicon nanowires (SiNWs), silicon dioxide nanotubes (SiO2 NTs), nano-silicon from beach sand (nano-Si), and silicon nanofibers (SiNFs). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), cyclic voltammetry (CV), potentiostatic electrochemical impedance spectroscopy (PEIS), and galvanostatic cycling are all notable techniques used to characterize these various materials

Metal assisted chemical etching (MACE) of crystalline silicon wafers is investigated as a means of synthesizing high aspect ratio SiNWs and characterized in the half-cell configuration. Electron beam evaporated gold thin films are used as an etching assistant using in situ synthesized anodic aluminum oxide (AAO) templates. A discussion on the attempted fabrication of silicon nanotubes (SiNTs) is also included using argon sputter redeposition (ASR).

Silicon dioxide is discussed and analyzed as a potential next-generation LIB material in the form of SiO2 NTs synthesized via chemical vapor deposition (CVD) of polydimethylsiloxane (PMDS) elastomer on anodic aluminum oxide (AAO) templates. SiO2 NTs produce a highly stable specific capacity of 1266 mAh g-1 after 100 cycles with Coulombic efficiencies (CEs) in excess of 98.5%.

Magnesiothermic reduction (MTR) is used to synthesize nano-Si from naturally occurring sand and to fabricate SiNFs from electrospun SiO2 nanofibers (SiO2 NFs). Nano-Si delivers a reversible capacity of 1024 mAh g-1 after a staggering 1000 cycles at a current density of 2 A g-1 with CEs in excess of 99%. The nano-Si technology demonstrates scalability, performance, and environmental benignity rarely reported in literature or industry.

Electrospun SiNFs demonstrate the highest performance of all the structures synthesized herein with a reversible capacity of 802 mAh g-1 after 659 cycles while still offering a relatively scalable, non-toxic, and environmentally friendly approach to LIB material synthesis. Elimination of copper current collectors and inactive polymer binders make this technology a candidate for producing a potential leap in LIB performance in lieu of the incremental improvements seen year after year.