Insight into the Lithiation of SiO2 As a New Energy Storage Anode Material for Li-Ion Batteries

Silica (SiO₂) has been considered as a promising anode material of lithium ion batteries (LIBs) due to its similar advantages of storing a large quantity of lithium and low discharge potentials of Silicon (Si) electrodes. Besides, Atomic layer deposition of SiO₂is a predominant coting material to mitigate the chemo-mechanical degradation of Si nanostructures anode. Si anodes coated with native oxide layer can sustain more than 6000 cycles with little capacity fade. Therefore, it is vital to determine the effect of the oxide layers on the volume expansion, lithium insertion and the morphology changes of Si anodes in LIBs. While the lithiation of Silicon (Si) has been extensively studied from both experimental and theoretical point of view, the underlying mechanism of lithium insertion in the silicon oxide has not yet been recognized well.

To better understand the lithiation behavior in SiO₂ at the atomistic level we herein performed a series of reactive molecular dynamics simulation combining with the grand canonical montecarlo (GCMC) to demonstrate the lithiation behavior of SiO₂. In addition, the Li transports throughout both crystalline and amorphous silica have been investigated. ReaxFF parameters are improved to account for the interaction of Li with Si and O atoms. We performed density functional theory calculations to examine the structural evolution, bonding mechanism, and voltage profile of lithiated c-SiO₂ and a-SiO₂. Both ReaxFF and DFT results indicate anisotropic long range Li-diffusion throughout the a-Quartz lattice. More specifically, Li should overcome 0.12 eV barrier heights when it transports along the c-axis of α-Quartz crystal, whereas the barrier of diffusion for Li moving perpendicular to the c-axis is calculated around 0.9 eV. Li transport throughout a-SiO₂ bulk is also investigated and the results are compared with barriers obtained from DFT simulations.