Monolithic 3D-Printed Interdigitated Cement-Based Supercapacitors for Structural Energy Storage

Multifunctional building materials that can simultaneously bear load and store electrical energy could expand the role of civil infrastructure, yet the scalable fabrication of architected cement-based energy-storage devices remains challenging. The poor mechanical properties at the interface between the electrode and the separator, as well as the inefficient ion transport due to the long path in the thickness direction, remain challenging. Here, monolithic interdigitated cement-based supercapacitors were fabricated by direct ink writing using a cement-based separator and printable cement-based nanocarbon electrode inks. This design effectively avoids the electrochemical performance degradation typically associated with increased thickness by reconfiguring the ion-transport pathways. The monolithic structure seamlessly embeds the cement-based electrodes within a cement mortar separator, eliminating interfacial delamination risks. More importantly, the interdigitated pattern transforms the long through-thickness ion path into a much shorter in-plane pathway between adjacent electrodes, while simultaneously increasing the active electrode-electrolyte contact area. The optimized device delivered an areal capacitance of 162.14 mF cm-2 at 0.46 mA cm-2, an areal energy density of 22.52 μWh cm-2, and a power density of 0.49 mW cm-2 over a 1.0 V operating window. The cement-based device also maintained a compressive strength of 23.00 MPa, demonstrating simultaneous electrochemical and structural functionality. Short-term temperature tests showed stable operation under moderate heating and cooling, whereas performance decreased sharply at -18 °C, indicating that electrolyte freezing and moisture management remain key challenges. These findings demonstrate the feasibility of integrating electrochemical energy storage with load-bearing cementitious components.