Insights into Solid-Electrolyte Interphase Induced Li-Ion Degradation from in Situ Auger Electron Spectroscopy

Surface reactions occurring on LiMn2O4, LiCoO2, LiNiO2, [Ni1/3Mn1/3Co1/3]O-2, and LiFePO4 during charging and overcharging are studied by in situ and ex situ Auger electron spectroscopy. Carbon surface stability at the cathode solid electrolyte interphase (SEI), associated with carbonate formation, decomposition, and CO/CO2 evolution, on different electrodes during cycling correlates with their cycle life. To understand how associated CO and CO2 evolution affects cycle stability, LiMn2O4 is cycled in flowing gas. Flowing Ar enhances cycle life by a factor of 2, while flowing Ar with 1% CO2 reduces cycle life by a factor of 2. CO2 is proposed to degrade cycle life by trapping Li and metal ions as carbonate in the anode SEI.