Relevant influence of alkali carbonate doping on the thermochemical energy storage of Ca-based natural minerals during CaO/CaCO₃ cycles

The calcium-Looping process is an advantageous candidate for thermochemical energy storage in Concentrated Solar Power plants. Achieving fast thermal energy storage at a moderate temperature would be highly beneficial for the heat storage process. In this study, commercially available alkali carbonates (Li₂CO₃, Na₂CO₃, K₂CO₃) were used as dopants for limestone/dolomite to improve their decarbonation rates and cycling stability. Results show that alkali carbonate doping reduces the decarbonation temperature of limestone and dolomite by accelerating the ion diffusion during decomposition. However, the doping of alkali carbonate also enhanced the sintering of limestone-based CaO so that the alkali carbonate doped limestones fail to maintain their heat storage capacity after multiple cycles. In contrast, the Li₂CO₃ doped dolomite still maintains excellent cyclic stability, attributed to the inhibition effect of the MgO skeleton on sintering. From these results, we then derived the effect scheme of Li₂CO₃ on the decarbonation and carbonation of limestone or dolomite. This study presents a simple yet effective method of reducing the heat storage temperature of Ca-based mineral materials and maintaining their cycling stability, simultaneously, with promising potential for industrial use.