The behavior of lithium oxide (Li2O) under an atmosphere of CO2 was studied using thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction techniques. Results show that Li2O can be used for CO2 retention. It is a better absorbent than other lithium ceramics. A chemisorption topochemical reaction is proposed to explain the sorption of CO2. The kinetic parameters were obtained. First, the CO2 sorption is controlled by a first-order reaction. Later, CO2 sorption depends on the diffusion of lithium through the formed shell of Li2CO3, with an extraordinary increase of the diffusion at 600 degrees C, due to an unusual increase of lithium mobility.