Optimized electrolytes and manufacturing processes increase the energy storage capacity of the latest electron-conducting carbon-cement-based materials (EC³) supercapacitors significantly, according to a study by the Massachusetts Institute of Technology (MIT).

EC³ supercapacitors are energy storage devices made from concrete. These devices can power electronics, store energy from renewable sources, and offer real-time structural health monitoring for buildings and roads.

The study, published on PNAS, states that storing energy adequate to meet an average home’s daily requirements would have needed approximately 43 m³ of EC³ in 2023.

However, after the recent discovery, approximately 5 m³ of concrete can achieve the same task.

Admir Masic, Co-director at MIT Electron-Conducting Carbon-Cement-Based Materials Hub (EC³ Hub), Associate Professor of Civil and Environmental Engineering at the institution, and the lead author of the new study, said, “A key to the sustainability of concrete is the development of ‘multifunctional concrete,’ which integrates functionalities like this energy storage, self-healing, and carbon sequestration. Concrete is already the world’s most-used construction material, so why not take advantage of that scale to create other benefits?”

MIT stated that a deeper understanding of the functioning of the nanocarbon black network inside the E³ and its interaction with electrolytes helped improve the supercapacitors’ energy density.

Researchers used focused beams to remove thin layers of EC³ material sequentially. They then conducted each slice’s high-resolution imaging with a scanning electron microscope (a technique called FIB-SEM tomography). The team from across the EC³ Hub and the MIT Concrete Sustainability Hub was then able to reconstruct the conductive nanonetwork at the highest resolution to date via these steps.

Through this approach, the team discovered that the nanocarbon network is a fractal-like “web” surrounding  E³ pores, allowing the electrolyte to infiltrate the system and the current to flow through it.

Masic added that understanding how such materials assemble themselves at the nanoscale is critical to achieving their new functionalities.

Based on this understanding, researchers experimented with different electrolytes and their concentrations to check their impact on energy storage density.

Damian Stefaniuk, First Author and Research Scientist at the EC³ Hub, stated, “We found that there is a wide range of electrolytes that could be viable candidates for EC³. This even includes seawater, which could make this a good material for use in coastal and marine applications, perhaps as support structures for offshore wind farms.”

The team at MIT team also streamlined the method of adding electrolytes to the mix. Instead of curing EC³ electrodes before soaking them in electrolyte, the team added electrolyte directly into the mixing water.

The MIT explained that since electrolyte penetration was no longer a limitation, researchers could cast thicker electrodes that stored more energy.

During the experiments, researchers achieved the highest performance after switching to organic electrolytes, specifically those combining quaternary ammonium salts (found in everyday products like disinfectants) with acetonitrile, a clear, conductive liquid often used in industry applications.

MIT stated that 1 m³ of this version of EC³ can store more than 2 kWh of energy. It added that while batteries can maintain a higher energy density, E³ can, in principle, be incorporated in a range of architectural elements, including slabs, walls, domes, and vaults. It can last as long as the structures it is integrated into.

The researchers drew inspiration from Roman architecture to build a miniature EC3 arch, demonstrating how energy storage can work together with structural form. The arch, operating at 9 V, supported its own weight as well as additional load while powering an LED light.

However, the LED light flickered when the load on the arch was increased. According to MIT, this is a result of the way in which stress impacts electrical contacts and the distribution of charges.

“There may be a kind of self-monitoring capacity here. If we consider an EC3 arch at architectural scale, its output may fluctuate when impacted by a stressor like high winds. We may be able to use this as a signal of when and to what extent a structure is stressed, or monitor its overall health in real time,” said Masic.

Developments in EC³ technology are already used to heat sidewalk slabs in places such as Sapporo, Japan, due to its thermally conductive properties.

A joint study by MIT and the Norwegian University of Science and Technology suggests that liquid air energy storage (LAES) could be a cost-effective long-term energy storage solution. The study stated that LAES can provide a reliable method for storing and releasing electricity as needed.