Optimising thermochemical energy storage: a comprehensive analysis of CaCO 3 composites with CaSiO 3 , CaTiO 3 , and CaZrO 3 .

With the increasing amount of renewable energy produced, many governments and industries are pushing for the installation of battery energy storage system (BESS) solutions. Thermal batteries are systems that store heat made from various energy sources, and can be used to produce electricity upon demand. These systems are easily scalable and can be installed in cities, homes and remote locations. Thermochemical energy storage (TCES) uses the enthalpy of a chemical reaction to store and release heat through endothermic and exothermic processes, respectively. CaCO 3 has been identified as an ideal TCES material as it is cheap and abundant, but maximising long-term cyclability is key to ensure battery longevity. This article investigates the addition of CaSiO 3 , CaTiO 3 and CaZrO 3 to CaCO 3 in a 1 : 1 ratio to ascertain the reaction properties and cyclic capacity over time. Cycling longevity and thermodynamic properties were determined using simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC-TGA) along with the Sieverts technique, and their reaction pathway studied by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The low cost of the CaCO 3 -CaSiO 3 material of $1.8 USD per kW h th suggests that if a suitable particle refinement agent were to be employed to ensure cycling longevity this material would be an excellent TCES material. Despite the CO 2 cycling capacity of the CaCO 3 -CaZrO 3 system only reducing by 16 wt% over 100 cycles, the cost of ZrO 2 brings the materials cost to $30.9 USD per kW h th , making this material currently unsuitable for application. The CaCO 3 -CaTiO 3 system showed only a 17% drop in total CO 2 uptake over 100 cycles, although the cost was $11.1 USD per kW h th .