Porosity Engineering of Si Nanoparticle-Based Electrodes by Carbon Nanostructures

Abstract

Silicon (Si) has been considered as a next-generation anode material due to natural abundance, low operating potential (<0.5 V vs. Li/Li+), and high theoretical specific capacity of 4200 mAh g-1.1 However, the electrochemical alloying reaction of Si involves large volume changes of 400% during lithiation and delithiation, causing cracking and pulverization of Si.1 In addition, solid electrolyte interface (SEI) of Si anode experiences constant changes due to unstable SEI reactivity.2 Considerable efforts have been made to design nanostructured Si materials to address the issues because nanostructuring can relieve the mechanical strain.3 However, when compared to micrometer-sized active materials having sufficient electrolyte pathway through interparticle space, the nanoparticle (NP)-based electrodes tend to be densely packed. As mass loading is higher and electrode is thicker, ion transport issue can become more severe in the densely packed electrodes.4 In this work, we will present studies on engineered porosity impacts performance in Si NP electrodes by altering porosity with carbon nanostructures. We explore the extreme limit of effectively non-porous electrodes using quasi-spherical, 6 nm diameter Si NPs produced via plasma-enhanced chemical vapor deposition (PECVD), which result in densely packed electrodes when slurry is prepared with conventional carbon black. We engineer porosity using carbon nanostructures including single-walled carbon nanotubes and carbon nanorods in place of conventional carbon black to create pore structure in Si NP-based electrodes. These experiments provide a correlation between mass loading, porosity and silicon utilization in Si NP-based electrodes.