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

Area of Science:

• Materials Science
• Electrochemistry
• Surface Chemistry

Background:

• Lithium-ion batteries (LIBs) are crucial for energy storage.
• Understanding cathode surface reactions is key to improving LIB performance and cycle life.
• The solid-electrolyte interphase (SEI) plays a critical role in battery stability.

Purpose of the Study:

• To investigate surface reactions on various LIB cathode materials during charging and overcharging.
• To correlate carbon surface stability and gas evolution (CO/CO2) with electrode cycle life.
• To elucidate the mechanism by which CO2 impacts LIB cycle stability.

Main Methods:

• In situ and ex situ Auger electron spectroscopy (AES) were employed to analyze cathode surfaces.
• LiMn2O4 was cycled in controlled flowing gas environments (Ar, Ar + 1% CO2).
• Analysis of carbonate formation, decomposition, and gas evolution was performed.

Main Results:

• Surface reactions on LiMn2O4, LiCoO2, LiNiO2, Li[Ni1/3Mn1/3Co1/3]O2, and LiFePO4 were characterized.
• Carbonate formation/decomposition and CO/CO2 evolution at the SEI were linked to cycle life.
• Flowing Ar enhanced LiMn2O4 cycle life twofold, while Ar + 1% CO2 reduced it twofold.
• CO2 was identified as a detrimental species affecting cycle stability.

Conclusions:

• CO2 degrades LIB cycle life by trapping lithium and metal ions as carbonates within the anode SEI.
• Controlling gas evolution, particularly CO2, is essential for enhancing LIB longevity.
• Auger electron spectroscopy is a powerful tool for studying surface phenomena in LIBs.