A strategy for improving CO2 capture by imidazolium ionic liquids (ILs) through a reduction in the formation of carbene CO2 complex was reported. The carbene CO2 complex content in CO2 capture by imidazolium ILs was determined by a quantitative NMR method, and the carbene CO2 complex formation was decreased through a reduction in the basicity of the anion and an enlargement in the steric hindrance of the cation. Thus, both enhanced absorption capacity and improved desorption were achieved, where an ideal IL, [Ipmim] [Triz], exhibited a very high capacity of 0.21 g of CO2/g of IL and excellent reversibility.