A Comprehensive Capacity Fade Model and Analysis for Li-Ion Batteries

Abstract

A physics-based side-reaction coupled electrochemical model for capacity fade of a graphite/LiMn2O4 cell is developed by including the key degradation mechanisms in both anode and cathode. The side reactions considered in this study include 1) solid electrolyte interphase (SEI) growth and manganese deposition on the anode and 2) manganese dissolution, electrolyte oxidation and salt decomposition on the cathode. Our study reveals three stages of capacity fade upon long term cycling: acceleration, stabilization, and saturation. In the acceleration stage, capacity fade is due mainly to the cyclable lithium loss induced by the anode SEI growth. In the stabilization stage, the anode SEI growth slows down as it gets thicker, the cathode Mn dissolution-induced capacity loss outpaces cyclable lithium loss, and the cathode becomes more intercalated at the end of discharge. In the saturation stage, cathode capacity degrades further and becomes the limiting factor, the cyclable lithium is shifted to the anode and the cathode reaches end-of-discharge saturation due to the severe cathode capacity fade. This study shows that the cyclable lithium loss and the cathode capacity loss are the two major contributors to the cell capacity fade, and the interaction between them determines the cell capacity.