In this study, Li/Al hydrotalcite (HT) was treated with calcination and potassium hydroxyl-ethanol to form bcHT (basic-modified calcined hydrotalcite). This material was then polyethylenimine (PEI)-functionalized to create a new sorbent that has ultralow energy consumption. Various methods were applied to characterize the sorbent, including N2 adsorption–desorption, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. CO2 adsorption capacity, which was affected by PEI loadings and adsorption temperatures, was assessed with the CO2 adsorption isotherms and cyclic CO2 adsorption–desorption performance. Results showed that the optimal CO2 adsorption capacity of 1.723 mmol/g was reached when operating with temperature of 323 K and PEI loading of 40%. The Freundlich model was applied to provide optimal correlations with the experimental data, and the correlation coefficients reached 0.997. The average isosteric heat of CO2 adsorption was calculated to be 67.492 kJ/mol. The relatively low desorption energy consumption was calculated to be 63.20 kJ/mol with the Amenomiya equation. Four kinetic models were applied to analyze the kinetics of PEI-functionalized bcHT, and both the Avrami’s fractional order model and DEM model were well fitted to the experimental data. The activation energy of the bcHT-PEI-40% was 30.34 kJ/mol calculated by the Avrami’s fractional order model, which is obviously lower than the values of the CO2 adsorption with traditional amine solution.