Thermal stability of solid electrolyte interphase of lithium-ion batteries

Solid electrolyte interphase (SEI) is an electronically insulating and Li+-conducting layer formed on electrodes. It is still the most mysterious part of lithium ion batteries (LIBs). Understanding the nature of SEI is vital to suppress capacity loss, increase cycle life and improve safety of LIBs during cycling. Herein, we employ atomic force microscopy (AFM) technology, X-ray photoelectron spectroscopy (XPS) and Electrochemical Impedance Spectroscopy (EIS) to comprehensively study the evolution and thermal stability of SEI formed on highly oriented pyrolytic graphite (HOPG) surface in three type of electrolytes containing 1 M LiPF6 dissolved in a mixture of DMC/EC (1:1, V: V). Morphology, mechanical properties, chemical composition and resistance changes of SEI were systematic studied as a function of temperature. Our results show that both fluoroethylene carbonate (FEC) and lithium oxalyldifluoroborate (LiDFOB) additives can improve the thermal stability of SEI. This combined approach enables us to further understand the effects of temperature on SEI which will be helpful for designing of LIBs with enhanced performance.