A Survey of In Situ Gas Evolution during High Voltage Formation in Li-Ion Pouch Cells

Li-ion pouch cells were made to study the factors that influence gas evolution during formation (first charge). Electrode materials, electrolyte additives and temperature were varied. Measurements were made using the Archimedes' In Situ Gas Analyzer at Dalhousie University. When cells are charged to high voltages (>4.2 V) there is gas evolution, presumed to be from reactions on the surface of the positive electrode. This is separate from the gas evolution known to happen at lower voltage (<3.5 V) caused by reactions on the negative electrode. Both evolutions were characterized by the magnitude of volume changes and their onset voltages. Gas volumes appear to increase and onset voltages decrease, respectively, with increasing temperature. Use of the additive prop-1-ene-1,3-sultone at 2% by weight in Li[Ni0.42Mn0.42Co0.16]O2/graphite cells yields smaller volume and higher onset voltage of gas evolution at all temperatures, compared to other additives tested. Certain cathode materials, namely some coated LiCoO2 samples, can be charged to high voltages (≤4.7 V) without producing gas at high voltage.