Probing the Interfacial Parasitic Reactions Kinetics in Lithium-Ion Battery

Abstract

The global R&D effort has been driven by the growing application of high energy-density lithium-ion batteries to electrify the transportation system and achieve significant reduction on non-renewable fuels consumption and greenhouse gas emission. However, high initial energy-density is still generally obtained with the price of a reduction on battery safety and life, which are fundamentally connected to the parasitic reactions in the cell at various temperatures. The practical high energy-density lithium-ion chemistry needs to be carefully balanced between energy-density and safety/lifetime of the chosen chemistry. The electrochemical validation of the effectiveness of those approaches for improving battery life is practically trivial, but extremely time-consuming, especially for those chemistries that have already been demonstrated capable of being charged/discharged for more than thousand cycles. Therefore, the fundamental understanding/measurement of parasitic reactions not only helps to select a proper life improving strategy, but also substantially shortens the lengthy electrochemical validating process. In this work, a home-built high-precision leakage current measuring system was deployed to investigate the parasitic reaction kinetics between lithium transition metal oxide cathode (LiNi0.6Mn0.2Co0.2O2) and conventional carbonate electrolyte (1.0 M LiPF6 EC/EMC 3:7). The working electrode was held at a specific potential using the source meter, presuming that the state of the charge or the lithium concentration in the working electrode will reach an equilibrium state after the constant-voltage charge/discharge. During this process, the electron obtained from the environment by oxidizing the solvent, will be electrochemically monitored by the external circuit. The kinetic study revealed a strong dependence of parasitic reactions on the practical upper cutoff potential in terms of both the reaction mechanism and the reaction rate. The kinetic data also indicated a significant change of reaction mode at ~4.5 V vs. Li+/Li. The study implies that a different strategy might be needed for effective mitigation of the parasitic reactions for materials targeted for operation at a potential higher than 4.5 V vs. Li+/Li. It demonstrated that the kinetic study could be crucial in developing advanced electrode materials with a fundamental balance between energy density and battery life. Figure 1