Survey of Gas Expansion in Li-Ion NMC Pouch Cells

This preliminary study investigates initial gas formation in Li[Ni0.4Mn0.4Co0.2]O2 (NMC442) pouch cells with three different electrolytes: 3:7 ethylene carbonate : ethyl methyl carbonate (EC:EMC) w/ 1 M LiPF6 as the control, control + 2% prop-1-ene-1,3-sultone (PES) and control + 2% vinylene carbonate (VC). In situ volume measurements reveal three main features of gas evolution, an initial gas step, gas absorption, and a second gas step at higher voltage. Gas chromatography-mass spectrometry is employed to identify the gaseous compounds. This work illustrates the strong dependence of volume change due to gas evolution on additives, charging rate and temperature.