Investigations on Silicon Composite Electrodes for Lithium-Ion Batteries

Abstract

A porous electrode model for silicon anodes was developed and used to understand its performance. The model includes the volume change in Si and the phase transformation during the first intercalation reaction in addition to the porous electrode effect, kinetic behavior of Li+ intercalation/de-intercalation in Si, thermodynamic relationships, and mass and charge transport of Li+ in solid and liquid phases. First, the simulations were performed on a very thin (10 μm) and highly porous (80%) electrode in order to estimate the solid-phase diffusion coefficient of Li+ ions in to the Si nanoparticles. This model and experiment based investigation predicts the value of Li+ diffusion in Si to be as low as 3.25x10-16 cm2/s. Good agreement was seen between the model predictions and experimental data. The effect of particle size on the performance of Si electrode and the conditions under which Li15Si4 formation occurs during intercalation are analyzed. Next, the model was used to analyze the performance of Si when the electrode capacity is matched to a NCA cathode of 80 µm thickness and 35% porosity with a loading of 3.6 mAh/cm2 loading. The matching of the anode to cathode was performed for various cycling capacities for the Si (1000, 2000, and 3000 mAh/g) and simulations were conducted to understand the effect of rate on the charging of the anode and the associated concentration and design effects.