Mechanistic Study of Parasitic Reactions on Cathodes of Lithium-Ion Batteries

The side reactions between the change electrode materials, delithiated cathodes or lithiated anodes, significantly contributes to the continuous and irreversible consumption of accessible lithium during the normal charge/discharge cycling, leading to a degradation on electrochemical performance of lithium-ion batteries. Understanding these side reactions, parasitic reactions, is crucial for the development of robust algorithm for predicting the remaining life of a specific battery and for the development of functional materials for long-life lithium-ion batteries. Figure 1a shows a home-built high precision electrochemical testing system used to study the kinetics of parasitic reactions on LiNi 0.6 Mn 0.2 Co 0.2 O 2 . Figure 1b schematically shows the principle of the measurement. The working electrode was held at a specific potential using the source meter, maintaining a constant state-of-the-charge (SOC) for the working electrode. During this process, the electron obtained from the environment by the oxidation of the solvent, will be electrochemically collected by the external circuit. The measured leakage current is proportional to the reaction rate of parasitic (side) reactions between the working electrode and the electrolyte. Hence, the static leakage current can be used as a quantitative indicator for the reaction rate of the side reactions. Figure 1c shows a typical current relaxation curve collected, an exponential decay function was used to extract the static current (y 0 in Figure 1C), and to (1) minimize the impact of the high frequency noise, and (2) to get rid of the potential impact of slow intercalation/deintercalation reaction. In this work, the reaction mechanisms between delithiated cathodes and the non-aqueous electrolyte will be discussed. Figure 1