Nano-Structured Silicon Derived from Silica Precursors as Anode Material for Lithium Ion Batteries

Silicon is valuable as a high energy density anode material for Li-ion battery applications. However, the high lithium storage capacity leads to extreme volume expansion during lithiation and delithiation that can lead to mechanical deterioration and poor cycle life. To improve cyclability, nano-structured materials can be used to facilitate the volume change without deterioration. By using structured SiO₂ precursors, the goal is to reduce SiO₂ to Si while maintaining the structure and porosity of SiO₂ and thus, mitigating degradation effects during cycling.

Nanostructured Si has been synthesized by Mg vapor reduction from SiO₂ precursors [1] (e.g. SiO₂ microspheres from 3M, SiO₂ aerogel, and mesoporous SiO₂ [2]). Following the reduction to Si, the materials were chemically treated in HCl and HF to remove remaining MgO and SiO₂ respectively. Figures 1 and 2 confirm the presence of Si in reduced samples and successful removal of MgO and SiO₂. TGA/DSC has been used to optimize the reduction time and temperature.  

CV data (Figure 3) and cyclability tests (Figure 4) demonstrate a specific capacity of up to 2065 mAh/g with a low charge transfer resistance (Figure 3, inset).

SEM, TEM, BET, EDS, XRD, and Raman spectroscopy data will be presented for SiO₂ and reduced Si to describe chemical composition and morphology. Structure dependent electrochemical properties such as impedance spectroscopy, cyclic voltammetry, galvanostatic discharge, and cycle stability will be presented and discussed.

References:

[1] R. Cook, M. Schrandt, P. Kolla, W. Rhine, R. Koodali, A. Smirnova, MRS Online Proceedings Library,1643 (2014).

[2] D. Zhao, A. Rodriguez, N. M. Dimitrijevic, T. Rajh and R. T. Koodali, J. Physical Chemistry C, 114, 15728 (2010)