In an effort to develop high-temperature CO2 adsorbents, we report on the improvement of CO2 capture performance of our previously developed potassium-promoted CaO double salts (K-Ca) through metal doping with iron and indium. The morphological, chemical, and structural characteristics of K-Ca doped metals were systematically evaluated while their CO2 capture behavior was investigated at 500-700 °C. Our initial screening tests identified the optimum loading for Fe and In to be 3 wt % with Fe3/K-Ca and In3/K-Ca displaying CO2 adsorption capacities of 14.65 and 14.24 mmol/g at 650 °C, respectively, and achieving 90% of their capacities ∼10 min faster than that of bare K-Ca. Moreover, our results revealed that metal doping not only enhances capture capacity but also the kinetics of both CO2 adsorption and desorption relative to bare K-Ca double salt and that roughly all the adsorbed CO2 desorbed from both adsorbents. However, the cyclic tests revealed a dramatic loss in CO2 uptake for both bare and metal-doped materials at 650 °C, whereas at 375 °C, high stability for both doped-metal adsorbents was noted. In situ X-ray diffraction experiments also revealed the reversible nature of crystalline phase alterations during adsorption and desorption, whereas our kinetic analysis showed that the CO2 uptake rate is controlled by both surface reaction and diffusion. Our findings highlight the necessity of addressing performance-stability trade-off at high temperatures for K-Ca double salts.