Traces of species in batteries are known to impact battery performance. The effects of gas species, although often reported in the electrolyte and evolving during operation, have not been systematically studied to date and are therefore barely understood. This study reveals and compares the effects of different gases on the charge-discharge characteristics, cycling stability and impedances of lithium-ion batteries. All investigated gases have been previously reported in lithium-ion batteries and are thus worth investigating: Ar, CO 2 , CO, C 2 H 4 , C 2 H 2 , H 2 , CH 4 and O 2 . Gas-electrolyte composition has a significant influence on formation, coulombic and energy efficiencies, C-rate capability, and aging. Particularly, CO 2 and O 2 showed a higher C-rate capability and a decrease in irreversible capacity loss during the first cycle compared to Ar. Similar discharge capacities and aging behaviors are observed for CO, C 2 H 4 and CH 4 . Acetylene showed a large decrease in performance and cycle stability. Furthermore, electrochemical impedance spectroscopy revealed that the gases mainly contribute to changes in charge transfer processes, whereas the effects on resistance and solid electrolyte interphase performance were minor. Compared to all other gas-electrolyte mixtures, the use of CO 2 saturated electrolyte showed a remarkable increase in all performance parameters including lifetime.