Electrochemical Characterization of the Lithium-Ion Cells Assembled with Ester-Based Electrolyte at Low Temperature

Lithium-ion batteries (LIBs) have become promising power sources in the field of electric vehicles (EVs) and energy storage systems (ESS) due to their high energy density and long cycle life. However, poor performance of LIBs at low temperature limits their applications, and it is thus essential to improve the low temperature cycling performance. The main requirements of liquid electrolyte for LIBs are high ion conductivity, low viscosity, wide potential window and wide liquid range. One of the most important factors for improving low temperature performance of LIBs is extension of liquid phase range, which can be affected by freezing point of organic solvent. However, it is well known that carbonate-based solvents commonly used in current LIBs exhibit poor ion conductivity and low diffusivity of lithium ion in the electrode at low temperature. A lot of approaches such as using additives to form stable SEI layer and introducing co-solvent to modify electrolyte properties have been adopted to improve cell performance at low temperature. In this study, we propose ester-based solvents to improve low temperature performance of LIBs, which exhibit stable and good cycle performance at low temperature. Analysis techniques such as electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) have been implemented to understand the improvement of low temperature performance of LIBs.