Revealing the cathode electrolyte interphase on Li- and Mn-rich materials by in-situ electrochemical atomic force microscopy

Solid electrolyte interphase (SEI) grown on electrode surfaces during charge-discharge processes plays a key role in the cycle performance of lithium-ion batteries. In-situ study of cathode electrolyte interphase (CEI) is challenging due to the complicated interfacial reactions on the cathode materials including gas formation and the formation of thin CEI film. Herein, we applied the electrochemical atomic force microscope (EC-AFM) to study the interfacial changes in high energy density Li- and Mn-rich (LMR) materials with an F-rich electrolyte (1 M LiPF6 FEC/FEMC/HFE). The study indicated that the electrolyte formed a uniform and dense passivation CEI film on the LMR material surface at high voltage. The CEI is composed of inorganic LiF substrate as confirmed by X-ray photoelectron spectroscopy (XPS). The assembled battery (LMR||Li) shows an excellent cycle performance and maintains capacity at 85.5% after 100 cycles, compared to the 13.7% retention rate of commercial carbonate electrolyte (1 M LiPF6 EC/EMC/DMC).