Methods–Temperature-Dependent Gassing Analysis by On-Line Electrochemical Mass Spectrometry of Lithium-Ion Battery Cells with Commercial Electrolytes

Abstract

The evolution of gases is often associated with the decomposition of the electrolyte or active materials. Thus, its detection can be powerful for understanding degradation mechanisms in Li-ion batteries (LIBs). Here, we present an evaluation method for gas detection and quantification by on-line electrochemical mass spectrometry (OEMS) when using volatile electrolytes (e.g., electrolytes with linear alkyl carbonates) and a new OEMS cell design for improved leak tightness. With a significant fraction of the gases in the cell head-space being electrolyte vapor, we observe a pressure/time-dependency of the electrolyte background in the mass spectrometer, for which we here developed a correction method. We apply this method for the temperature-dependent gas analysis of a graphite/NCM831205 full-cell with an LP57 (1 M LiPF6 in EC:EMC 3:7 wt:wt) electrolyte. We conclude that the activation energy of the gas evolution associated with the formation of the solid-electrolyte interphase (SEI) is ∼15–20 kJ mol−1. Furthermore, we identify a significant temperature dependence of the lithium alkoxide triggered trans-esterification of EMC with an activation energy of ∼70 kJ mol−1. Lastly, the temperature-dependent analysis reveals the relation between the evolution of hydrogen related to water and HF impurities during the initial SEI formation and in situ generated protons.