An innovative structural energy storage solution using fly ash-cement composites for net-zero energy buildings

The rapid advancement of renewable energy highlights the urgent need for safe, cost-effective, and scalable energy storage solutions, particularly for net-zero energy buildings. In this study, we introduce an innovative energy storage solution utilizing fly ash-cement composites (FCS) as multifunctional components. The FCS, incorporating fly ash as a mineral admixture, achieves a refined pore structure and homogeneous air void distribution during early hydration, leveraging the ball-bearing characteristics and pozzolanic effect of fly ash. The optimized FCS, containing 50 wt% fly ash, exhibited an impressive ionic conductivity of 25.6 mS cm −1 and a compressive strength of 5.5 MPa after just one day of curing. When integrated into structural energy storage systems, it delivers a high specific capacitance of 102.4 mAh g −1 at 0.1 A g −1 , an energy density of 73 Wh kg −1 , and a power density of 76.3 W kg −1 , maintaining 92.9 % capacitance retention over 2000 cycles. These results underscore the scalability, cost efficiency, and structural benefits of FCS, offering a promising pathway to integrate energy storage directly into buildings and infrastructure. Moreover, this strategy provides a sustainable, high-value application for large volumes of industrial solid waste while addressing energy challenges in extreme environments such as deep-sea, deep-earth, and extraterrestrial constructions.