Phase change absorbents had great potential to achieve low energy-consuming CO₂ capture. In this work, a novel four-component phase change absorbent system, N,N-diethylethanolamine (DEEA)/N-(2-aminoethyl) ethanolamine (AEEA)/1-butyl-3-methyl imidazolium tetrafluoroborate ([Bmim][BF₄])/H₂O blends, was designed. AEEA and DEEA were used as the main absorption component and the phase separation component, respectively. As one of the most conventional ionic liquids, [Bmim][BF₄] was introduced as a promoter to improve the phase separation capability and the absorption/desorption performance. The species distribution was determined by ¹³C NMR analysis, and it was found that [Bmim][BF₄] was located in the lower phase. Quantum chemical calculations unveiled that the main reason for phase separation was the difference in polarity and hydrogen bond interactions. The introduction of the [Bmim][BF₄] not only promoted CO₂ absorption through chemical and physical intensification effects but also enhanced the desorption rate through hydrogen bond formation. Moreover, the [Bmim][BF₄] addition significantly reduced regeneration energy consumption due to its lower heat capacity and less water evaporation. The energy consumption of this absorbent could be reduced to 2.06 GJ∙t⁻¹ CO₂, which was 45.8% less than 30 wt% MEA.