Copyright SlashGear
Humans began mixing crushed limestone with water to make cement over 2,000 years ago, and the material is still in use today as the main ingredient in concrete. Concrete is the second-most used substance on earth behind water, and the Aquia Appia aqueduct in Rome built of concrete in 312 BCE is still standing. Since then the mixture has been in continual use and continues to evolve;one interesting recent development in concrete came from scientists at Massachusetts Institute of Technology. Four researchers from the university's Department of Civil and Environmental Engineering published a paper in the Proceedings of the National Academy of Sciences in September 2025 outlining the utility of electron-conducting carbon concrete, or ec3. This advancement promises to take concrete beyond building material and into the realm of energy storage. The technology has been in the works for years and uses ultra-fine carbon black (a nearly pure carbon powder) with an electrolyte material. Together they allow ec3 to store and release energy, effectively turning any concrete structure into a battery. Carbon black is a byproduct of petroleum combustion that is used to make tires, and gives most modern tires their black color. MIT's engineers have tried an array of electrolytic solutions and construction techniques and used what they learned to increase the energy density of ec3 ninefold sine 2023. A press release noted that the latest version of ec3 can pack enough energy to power an average home into about 5 cubic meters (~176 cubic feet); that's roughly what goes into a single basement wall. While powering homes and office buildings is an obvious use for ec3, its developers envision a world where nearly entire cities function as giant batteries. This is hardly the only surprising energy storage innovation in play; abandoned mines can also be used to store and retrieve energy. Ec3 depends on a few basic components to perform its wizardry. The electrolyte-rich cement provides a structural and functional base, and its formula can be adjusted based on the application. The carbon black particles form a microscopic network along the concrete's natural pores, acting as electrical wiring inside the hardened concrete. When researchers switched from adding the electrolyte to cured ec3 to including it in the mixing water for the concrete, the electrolyte penetrated better and made the material even more potent. The choice of electrolyte also has an effect on the material's performance; organic electrolytes performed best with a particular combination of quaternary ammonium salts and acetonitrile being particularly effective. The former is commonly found in sanitizer sprays and the latter is a solvent used to make everything from pharmaceuticals to batteries. As is sometimes the case with these things, the scientists at MIT discovered that the material worked without being 100% sure how. Using a high-resolution scanning technique called focused ion beam scanning electron microscopy, they discovered that the web of carbon allowed current to move so freely and efficiently within ec3 it had essentially become a supercapacitor. These materials are capable of very dense energy storage; in 2021 a team of European scientists made a 1.6-volt supercapacitor battery smaller than a speck of dust. MIT says that about 2 kilowatts of electricity can be stored in a cubic meter of ec3 (~35 cubic feet); that's enough to run a household refrigerator for about a day. For illustration, a cubic meter is roughly the space taken up by about 40% of a hot tub, 200 bowling balls, or 1,500 20-ounce beverages. Ec3 has already broken free from the bounds of academia into real-world applications. In Japan, sections of heated sidewalk slabs made from ec3 are being tested as a potential alternative to salting in winter. But MIT researchers hope that this is just the tip of the iceberg, and everything from park plazas to bridges could someday act as massive batteries. The MIT team expects the capacitive and conductive elements of ec3 to last as long as the concrete, making it a good long-term investment. In addition to acting as an energy reservoir, ec3 can also be a diagnostic tool providing real-time data on a structure's health. This was discovered almost accidentally when researchers built a self-supporting miniature arch that powered a single LED. When additional weight was applied as a test of the arch's integrity the LED began flickering, suggesting that the fractal network of carbon black could react to stress or damage within a structure. Looking ahead, the research team envisions parking lots that charge electric cars, foundations and patios able to power off-grid homes, and bridges that can monitor their own aging. The scientists at MIT freely admit that the energy density of ec3 is far below that of lithium-ion batteries, but with 33 billion tons of concrete used annually it could still revolutionize how the world is powered.
