A novel phase splitter, namely, sulfolane, was proposed to advance the traditional monoethanolamine (MEA) absorption technology for CO2 capture by simultaneously promoting the absorption rate and lowering heat duty. The phase-splitting phenomenon was observed after the CO2 loading level had exceeded 0.73 mol CO2/L, thereby generating a CO2-rich MEA upper layer and a lower layer containing sulfolane. Sulfolane facilitated CO2 absorption because of its strong affinity with acid gases, which resulted in an absorption rate 2.7 times higher than that of the conventional MEA process. The process simulation using Aspen Plus indicated that the regeneration heat with the MEA/sulfolane mixture as a solvent substantially decreased to 2.67 GJ/t-CO2, which was 31% lower than that of the conventional MEA process (3.85 GJ/t-CO2). Moreover, the sensible heat and vaporization heat of MEA/sulfolane were markedly decreased by 62.4% and 47.9%, which could be ascribed to the decreased stripping volume and relatively high CO2 partial pressure caused by liquid-liquid phase separation. The proposed system is proved to be a promising candidate for the advancement of CO2 capture techniques with high CO2 absorption capacity, rapid absorption rate, and low-energy penalty.