Gas evolution in commercial Li-ion battery cells measured by on-line mass spectrometry - Effects of C-rate and cell voltage

: Ulriika Mattinen, Matilda Klett, Göran Lindbergh, Rakel Wreland Lindström

Publisher: ELSEVIER

: 2020

: Journal of Power Sources

: JOURNAL OF POWER SOURCES

: J POWER SOURCES

: ARTN 228968

: 477

: 12

: 0378-7753

: 1873-2755

DOI: https://doi.org/10.1016/j.jpowsour.2020.228968

Gas evolution in lithium ion batteries (LIB) caused by degradation of the battery cell components, is not only detrimental to cell performance, it is also a major safety risk. Understanding the connection between cell usage and gas evolution at different states of health of the battery is of utmost importance for the improvement of cell components as well as user protocols for LIBs. In this work, an electrochemical mass spectrometric in-operando cell house, capable of hosting a cylindrical 18650 cell, was developed and used to study the gas evolution at increasing cycle C-rates (from C/20 to 4C) between 2.6 V and 4.2 V and during stepwise increased/decreased cell voltages ranging from 2.2 V to 4.4 V. The cell under study was a commercial 1.5 Ah NMC-LMO/Graphite cell, pierced inside an Ar-filled glove box and mounted to the gas-tight cell house before being connected to the On-Line Electrochemical Mass Spectrometer (OEMS). The results show that the large capacity fade observed at high C-rate is associated to major evolution of ethylene gas. The voltage step experiments revealed that CO2 is the main gas evolving at high voltages (>4.15 V) and H-2 at low (<2.8 V). Despite significant gas evolution at these extreme voltages, the cell capacity remained stable.