Effect of starch addition on thermochemical energy storage in CaCO₃/kaolin composites

Thermochemical energy storage (TCES) has attracted widespread attention due to its high theoretical energy storage density and abundant raw material sources. However, traditional Calcium-based materials suffer from complex fabrication processes and rapid degradation of reactivity and energy storage performance during repeated high-temperature carbonation/calcination cycles, severely restricting their engineering deployment. To address these challenges, this study proposes a synergistic design strategy. We combine structural regulation with inert framework stabilization in composite CaO-based materials. We systematically investigated their reaction behavior, energy storage performance, and cycling stability. Multiscale material characterization techniques were used to reveal the evolution of phase composition and microstructure and their impact on reaction kinetics. The results indicate that, compared to pure CaO, the composite materials effectively suppress grain sintering and pore occlusion under high-temperature cycling. By maintaining an open, interconnected pore network, the materials reduce CO₂ mass-transfer resistance and delay kinetic attenuation. The optimized sample maintained stable reaction rates and energy storage density throughout the cycling tests. After 30 cycles, the energy storage density was approximately twice that of pure CaO, while the output heat flow remained consistently high and stable; notably, the maximum output heat flow reached 22.28 kW·kg⁻¹ of composite even in the 30th cycle. Furthermore, the volumetric energy storage density and cycling stability significantly outperformed the control samples, reaching 1.07 GJ·m⁻³ and 0.87 GJ·m⁻³ at the 1st and 30th cycles, respectively. This study provides new insights and a material foundation for the development of highly stable TCES materials through the synergistic regulation of structural stability and reaction kinetics.