Factors Influencing Gas Evolution from High-Nickel Layered Oxide Cathodes in Lithium-Based Batteries

Gas evolution from high-nickel layered oxide cathodes (>90% Ni) remains a major issue for their practical application. Gaseous species, such as CO2, O-2, and CO, that are evolved at high states of charge (SOC) worsen the overall safety of batteries, as pressure build-up within the cell may lead to cell rupture. Since these gasses are produced during cathode degradation, tracking the formation of gasses is also important in diagnosing cathode failure. Online electrochemical mass spectrometry (OEMS) is a powerful in situ technique to study gas evolution from the cathode during high-voltage charge. However, the differences in the OEMS experimental setups between different groups make it challenging to compare results between groups. In this perspective, the various factors that influence gas evolution based on the OEMS results collected in this group are presented. The focus is on the conditions that lead to gas release, with a particular emphasis on reactive oxygen formation and subsequent chemical reactions with the electrolyte. Promising strategies, such as electrolytes, compositional tuning, and surface coatings that are effective at suppressing gas evolution from the cathode are highlighted. Critical insights into mitigating cathode degradation and gas evolution are provided to guide the development of safer, high-energy batteries.