Researchers have built a cement-based supercapacitor with 3D-printed electrodes, creating an energy-storage device that can bear loads comparable to ordinary structural concrete.
As renewable energy becomes more available, researchers are looking for ways to store electricity closer to where it is generated and used. Home batteries are increasingly common, but could the building itself become part of the energy-storage system? One candidate is cement, among the world’s most widely used construction materials.
A recent study in ACS Nano describes what its authors call an “all-cement-based” supercapacitor, made with 3D-printed electrodes. Supercapacitors hold less energy than batteries; their strengths are fast charging and discharging over many thousands of cycles.
Building Blocks
Many cement supercapacitors are built like a sandwich: two electrodes with a layer of cement between them. The cement layer holds water and dissolved ions that move between the electrodes as the device charges and discharges. Because the ions travel through the device’s thickness, making it thicker to bear more load lengthens their path and weakens performance.
To get around this, the team developed a printable electrode “ink” containing cement, two forms of conductive carbon (carbon nanotubes and carbon black), and a clay that helps the ink hold its shape. Using a 3D printer, they laid down the electrodes side by side in a pattern resembling interlocking fingers, then filled the gaps with cement mortar. After the device is soaked in a salt solution, the mortar’s network of tiny pores carries ions between neighboring electrodes.
Because ions cross only the short gap between prongs, and more electrode surface touches the mortar, thicker electrodes didn’t suffer the drop in efficiency typical of sandwich designs. The electrodes also sit inside the mortar as one continuous piece, which the authors say eliminates the risk of layers separating.
Putting Cement to the Test
As a proof of concept, a single printed supercapacitor lit 10 LED bulbs for about 30 seconds. The device also retained 95% of its starting capacitance across 10,000 charge–discharge cycles.
On its own, the printed electrode material measured only about 2 megapascals (MPa) in compression tests. Encased in mortar, the full device reached about 23 MPa (roughly 3,300 pounds per square inch), in the same range as ordinary concrete grades used for beams, floor slabs, and stairs. The mortar and interlocking design bear the load, shielding the weaker electrode inside.
The electrode’s position within a beam also affected bending strength. A bending beam is squeezed along its top and stretched along its bottom; beams reached about 8 MPa with the electrode near the top but about 6 MPa with it near the bottom, where the electrode–mortar boundary became a starting point for cracks.
In short-term tests at 5 °C and 40 °C (41 °F and 104 °F), the device kept at least 92% of its room-temperature capacitance. At −18 °C (0 °F), however, that figure fell to about 8%, most likely because the liquid in its pores partially froze.
Not Quite Set in Stone
The authors describe the results as preliminary, lab-scale work. Per gram of carbon, the device stores less charge than standard high-performance supercapacitors, as well as some earlier cement-based designs. Adding carbon black, which improves conductivity, also lowered compressive strength by about 29%. Future work will focus on electrolytes that resist freezing and drying out, along with long-term durability testing.
As Jing Zhong, one of the study’s corresponding authors, notes in a recent press release, “If building materials could not only support structures but also store energy, sense their surroundings, and even interact with people, buildings would become more than passive shelters. They could become truly smart environments.”
Browse Related Articles in ACS Journals
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