Structural supercapacitor electrolytes based on cementitious composites containing recycled steel slag and waste glass powders

Incorporating solid wastes into cement-based materials is beneficial for the waste disposal and the conservation of natural resources. In this study, cement-based electrolyte incorporated with recycled steel slag powder (SSP) and waste glass powder (GP) was proposed as a potential candidate for assembling structural supercapacitor cells (SSCs) with multi-functionality. Compared with pure cement devices, the 28-day conductivity and areal capacitance of the SSCs containing SSP and GP increased by up to 112% and 84%, respectively, at a current density of 0.1 mA cm−2. On the one hand, the addition of SSP and GP increased the pore volume in the cement-based electrolyte, which in turn resulted in more paths for ion transport. On the other hand, the presence of SSP and GP increased the concentration of major ions, such as Na+ and OH−, in pore solution. Both the increased ion transport paths and the improved ion concentration contributed substantially to the enhancement of the energy storage performances of the SSCs. At 28 days, an additional incorporation of 10% GP made up for the strength loss caused by SSP as an appropriate amount of GP with high pozzolanic activity resulted in an increased amount of C-S-H product, a reduction of porosity, and a denser microstructure. The proposed SSCs containing the cement-based electrolyte with cement partially replaced by 20% SSP and 10% GP is competitive for the development of green building energy storage devices.