Electrochemical modeling, Li plating onsets and performance analysis of thick graphite electrodes considering the solid electrolyte interface formed from the first cycle

Abstract

Based on a crack dominated solid electrolyte interface (SEI) resistance, an electrochemical model considering the SEI formed from the first cycle is established to investigate the comprehensive influence of electrode thickness, solid volume fraction and C-rate on the performance of thick graphite electrodes. Reasonable agreement is obtained for the simulated and measured charge and discharge profiles of Li/graphite cells including the first cycle. The periodic evolution of SEI film resistance during the cycles can be well interpreted by the mechanism based on the growth of SEI crack. The potential drop over SEI is found to contribute little to the polarization during Li inter- and deintercalation, and the electrode porosity reduction caused by SEI growth has larger effect for thick electrode than traditional thin electrode. The cell voltages, total potential drop of the electrode, state of charge and ratio of SEI capacity to the total capacity at the onsets of Li plating are analyzed. A linear relationship is developed for the Li plating onset voltages with the increasing of electrode thicknesses, solid volume fractions and C-rates. Finally, the performance of Li/graphite cells with electrode thicknesses (δ) ranging from 100 μm to 500 μm, solid volume fractions (εs) ranging from 0.35 to 0.6 and C-rates ranging from 0.05C to 0.5C is simulated and compared. The ionic migration limitation is aggravated by the growth of SEI for electrodes thicker than 300 μm as the solid volume fraction increases. The maximal areal capacity appears around δ = 500 μm and εs = 0.4, with a rate performance of 13.8 mAh cm−2, 13.6 mAh cm−2 and 13.1 mAh cm−2 at 0.1C, 0.2C and 0.5C, respectively.