Mechanism of gas build-up in a Li-ion cell at elevated temperature

A study has been made of the swelling behaviour at 90 °C, due to gas evolution, of pouch-type Li-ion cells that contain LiCoO2 (LCO) or LiNi0.8Mn0.1Co0.1O2 (LNMCO) as the cathode and an artificial-graphite material as the anode. Swelling of the LCO cell is dominated by the reaction at the cathode at cell voltages above 4 V, but is dominated by the reaction at the anode below 4 V. Results of gas composition analyses and the voltage dependence of the swelling indicate that the swelling in the charged state might be due to oxidation of the electrolyte at the cathode, and that in the discharged state to reduction of the electrolyte at the anode by lithium from the lithiated graphite. By contrast, swelling of LNMCO-cathode cells, may be dominated by the cathode at cell voltages above 3.2 V since swelling of the LNMCO-cathode is far greater than that of the anode, even in the low-voltage region.