An alternative to batteries that could provide cheap and scalable energy storage for renewable energy sources.

At their core, capacitors are basic devices, composed of two conductive plates submerged in an electrolyte and separated by a layer.

When the capacitor is powered, the electrolyte’s positive ions gather on the negatively charged panel, and the negatively charged ions amass on the positively charged panel. The interposing layer prevents ion transfer, resulting in an electric field and consequently, the charging of the capacitor.

These panels can store this dual charge for an extended period and release it swiftly when required. Supercapacitors, a variety of capacitors, have the ability to store particularly large charges. The power a capacitor can retain is influenced by the total surface area of its conductive panels.

An article titled “MIT engineers create an energy-storing supercapacitor from ancient materials” reveals an innovative way to store renewable energy.

According to the article, a new study from MIT researchers shows how Cement and carbon black, two of the most prevalent historical materials known to humankind, could serve as the foundation for a unique, cost-effective energy storage system.

This technology may enable the consistent use of renewable energy sources like solar, wind, and tidal power by ensuring energy networks remain stable despite the variable supply of renewable energy.

The researchers discovered that combining these materials with water could produce a supercapacitor—an alternative to traditional batteries—capable of electrical energy storage. The creators of the system at MIT propose that their supercapacitor could be integrated into a house’s concrete foundation, storing a full day’s worth of energy while adding little to no extra cost to the foundation’s price and still providing the required structural integrity. They also envision a concrete road that could wirelessly recharge electric cars as they traverse it.

This innovative yet straightforward technology is discussed in an upcoming paper in the PNAS journal by MIT professors Franz-Josef Ulm, Admir Masic, Yang-Shao Horn, and four others at MIT and the Wyss Institute.

The breakthrough in the newly developed supercapacitors by this team lies in a method of generating a cement-based substance with a highly dense internal surface area due to a rich, interconnected network of conductive material throughout its volume.

This was achieved by mixing carbon black — a highly conductive material — with cement powder and water, and allowing it to set. When soaked in an electrolyte like potassium chloride, charged particles gather on the carbon structures, forming a powerful supercapacitor.

How do supercapacitors store energy?

The plates of the capacitor work in a similar manner to a rechargeable battery of the same voltage. When connected to an electricity source, energy is stored in the plates. This energy is then released to provide power when connected to a load.

Masic calls the material intriguing, as it combines the most-used manmade material, cement, with carbon black, a historically significant material. As the mix sets and cures, the carbon black self-assembles into a conductive wire. This process is not only easy to replicate but also uses inexpensive materials available worldwide.

“The material is fascinating,” Masic explains, “because you have the most-used manmade material in the world, cement, that is combined with carbon black, that is a well-known historical material — the Dead Sea Scrolls were written with it. You have these at least two-millennia-old materials that when you combine them in a specific manner you come up with a conductive nanocomposite, and that’s when things get really interesting.”

As the mixture sets and cures, he adds, “The water is systematically consumed through cement hydration reactions, and this hydration fundamentally affects nanoparticles of carbon because they are hydrophobic (water repelling).”

As the mix evolves, “the carbon black is self-assembling into a connected conductive wire,” he says.

The procedure is simple to duplicate, and the components are affordable and easily accessible anywhere in the world. To create a percolated carbon network, just a very tiny quantity of carbon is required—as little as 3% of the mix’s volume, according to Masic.

The team estimates that a 45 cubic meter block of nanocarbon-black-infused concrete could store about 10 kilowatt-hours of energy, equivalent to a household’s average daily electricity usage. Since the concrete would maintain its strength, a house with a foundation made of this material could store a day’s worth of energy generated by solar panels or wind turbines. Additionally, supercapacitors can charge and discharge faster than batteries.

After conducting tests to determine the optimal ratios of cement, carbon black, and water, the team successfully created small supercapacitors. They now plan to build larger versions, starting with the size of a typical car battery, and gradually increase to a 45 cubic meter version.

There is a balance between the storage capacity and the structural strength of the material. While adding more carbon black can increase energy storage, it slightly weakens the concrete. This could be beneficial in scenarios where the concrete does not play a structural role or where the full strength-potential of concrete is not necessary.

Another possible use of carbon-cement supercapacitors is in the construction of concrete roadways that could store energy generated by roadside solar panels and wirelessly deliver this energy to electric cars.

This technology might initially be used for remote homes or buildings, which could be powered by solar panels connected to cement supercapacitors.

“You can go from 1-millimeter-thick electrodes to 1-meter-thick electrodes, and by doing so basically you can scale the energy storage capacity from lighting an LED for a few seconds, to powering a whole house,” he adds.

The system could be adapted for specific applications by adjusting the mixture. For instance, a road that charges vehicles would require a very fast charge and discharge rate, while a home could utilize slower-charging material.

“So, it’s really a multifunctional material,” he comments.

In addition to energy storage, the same kind of concrete mixture could serve as a heating system by applying electricity to the carbon-infused concrete.

Ulm views this as “a new way of looking toward the future of concrete as part of the energy transition.”

Source: 10.1073/pnas.2304318120 

Image Credit: Franz-Josef Ulm, Admir Masic, and Yang-Shao Horn