Characterization and Electrochemical Modeling of Advanced SiO Anode Material for Li-Ion Batteries

Abstract

Silicon monoxide (SiO) anodes have recently received much attention for their high energy density and improved cyclability, and this technology is being currently commercialized. Although numerous studies have focused on the electrochemical properties of SiO anodes, experimental observations of the key features such as the volume expansion upon lithiation, the open circuit potential (OCP) and its related hysteresis are still poorly understood. In this regard, we investigated the electrochemical properties of SiO anodes by combing experimental characterization and high fidelity modeling. In this study, we performed experimental studies by comparing electrochemical properties between SiO and Si anodes. The OCP of each anode was measured by using Galvanostatic Intermittent Titration Technique (GITT) in Fig. 1. The differential capacity (dQ/dV) of SiO anode, which was recorded at C/20 rate, showed similarity to the Si anode (see, Fig. 2). However, Scanning Electron Microscopy (SEM) analysis revealed that SiO particles experienced 118% volume expansion during cycling, which is much less than that of Si particles (c.a. 280% [1]). In addition, the diffusion coefficient of Li-ions in SiO particles was calculated by GITT data, which ranges from 10-8 to 10-12 cm2/s, as shown in Fig. 3. We adopted the experimental data as parameters for a high-fidelity electrochemical model, which was developed for predicting the performance of SiO anodes and gaining a deeper understanding of the physical phenomena that determine the electrochemical behavior. The model stems from the Enhanced Single Particle Model (ESPM) [2]; however it includes a prediction of the volume change effects on the solid/liquid diffusion and electrode porosity. Unlike other existing electrochemical models for silicon-based anodes where the convective flux induced by particle expansion/contraction during lithiation and delithiation is neglected in the solid diffusion [3, 4], such convective flux is considered here. The resulting solid diffusion equation with moving boundary is converted to a traditional fixed boundary problem using Landau Transformation [5]. An expression for volume change is derived based on the work by Obrovac et al. [1]. Porosity changes in the SiO electrode region due to particle volume changes are also included in the model. An extra convective term arises in the liquid diffusion equation as a consequence of porosity changes. The resulting model will be calibrated and validated with experimental data from rate capability tests. Model-based analyses will be performed to investigate the effect of cell design parameters on the cell performance.