Concrete Capacitors: The Future of Energy Storage

Storing Energy In Concrete Capacitors

When it comes to energy storage, all the attention is concentrated on batteries. While for a time it was mostly on ever-improving lithium-ion technology, now sodium-ion, solid-state, and other types of alternative battery chemistries are also being developed or reaching the commercial stage.

In all cases, these batteries store electricity in a chemical form, usually using metallic ions to carry the electric charge change.

Source: Let’s Talk Science

This is, however, not the only way you can store electricity. Another option is using a supercapacitor.

Contrary to batteries storing the electric charge in a mass of metallic ions, supercapacitors and ultracapacitors hold the electric charge on the surface of a conductive material.

Source: Sinovoltaics

This fundamental difference in the energy storage concept changes how capacitors work compared to batteries. Because the energy is available at the surface of the material, it can be mobilized very quickly, allowing for ultra-fast charge and discharge cycles, while batteries are slowed down by the speed of the required chemical reactions.

Capacitors so far have been mostly a niche product, as they hold less charge than batteries, and are often more expensive, as they require more expensive materials.

This might be changing, with the development of concrete-based capacitors by four researchers at the Massachusetts Institute of Technology (MIT), which could ultimately be used to turn buildings and roads into giant batteries.

They published their latest design in the prestigious scientific journal Proceedings of the National Academy of Sciences (PNAS) under the title “High energy density carbon–cement supercapacitors for architectural energy storage”.

Capacitors’ Applications

Capacitors’ low charge compared to batteries has so far hindered their usage for large or long-term energy storage, despite their remarkable durability.

However, their ability to handle very quick changes in electric charge and much higher voltage, without suffering any damage, makes them useful for applications where a lot of energy is produced or needed at once.

For example, supercapacitors are used in automobiles, trains, cranes, and elevators, for short-term energy storage, regenerative braking, or burst-mode power delivery.

While the total energy is not necessarily that high, the intensity and speed are.

For power grids and energy storage applications, supercapacitors are most effective in bridging power gaps that last from a few seconds to a few minutes and can be quickly recharged.

Improving Concrete-Based Capacitors

Making Concrete Stores Energy

For batteries, the energy differential between the different electrochemical reactions and the amount of reactive metal available usually limits capacity.

For capacitors, the main limitation is the total surface of the material. So generally, the most porous materials will carry a lot more charge.

For this reason, heterogeneous materials (made of multiple elements) are often best, as well as any material that is the result of the polymerization of simpler materials, with many pores and alveoli inside.

Already in 2023, the MIT researchers had explored the potential of concrete, a material with a complex microscopic structure that could, in theory, be turned into a capacitor.

This was achieved using cement, water, ultra-fine carbon black (with nanoscale particles), and electrolytes. Together, they created the so-called electron-conducting carbon concrete (ec³, pronounced “e-c-cubed”).

ec³ contains a “carbon nanonetwork” inside the concrete that can store and conduct electricity.

Concrete Abundance

Cement and concrete are by far the most produced materials on Earth, reaching total volumes and mass of 1.7 billion cubic meters and 4.1 billion tons, higher than any other material, including sand and steel.

Source: Visual Capitalist

As a result, this means that even turning a very small fraction of the world’s concrete into energy storage could radically change how we store energy in our homes, offices, and cities.

“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?”

Admir Masic – Associate professor of civil and environmental engineering (CEE) at MIT.

Improving ec³ Performances

Boosting Energy Density

The original 2023 prototype was energy-dense enough so that 45 cubic meters of ec³, roughly the amount of concrete used in a typical basement, was enough to meet the daily needs of the average home.

While interesting, questions of costs and practicality made this number not really commercially usable.

The researchers’ new versions of the product can store the same amount of energy in 1/9^th the volume, or only 5 cubic meters (176 cubic feet).
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In-Depth Analysis

This higher performance was achieved through using a focused ion beam to remove sequentially thin layers of the ec³ material. These layers were then analyzed with a scanning electron microscope (FIB-SEM tomography).

This allowed the researchers to reconstruct a high-resolution image of the conductive nanonetwork. They discovered it forms a “fractal-like web” that surrounds ec³ pores, which is what allows the electrolyte to infiltrate and for current to flow through the system.

With this superior analytical tool, the research team went on to experiment with different electrolytes and their concentrations to see how they impacted energy storage density.

“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.”

Damian Stefaniuk – EC³ Hub research scientist

They measured that organic electrolytes, especially those that combined quaternary ammonium salts found in everyday products like disinfectants, performed best when mixed with acetonitrile, a clear, conductive liquid often used in industry.

Better Manufacturing Of Concrete Batteries

Previously, the method used had to cure the ec³ electrodes and then soak them in electrolyte. Instead, they discovered they could add the electrolyte directly to the mixing water.

This was essential in casting thicker electrodes that stored more energy.

As a demonstration of this technology, the team built a miniature ec³ concrete arch to show how structural form and energy storage can work together.

Operating at 9 volts, the arch supported its own weight and additional load while powering an LED light.

Automatic Monitoring Of Structural Integrity

A surprising phenomenon occurred when they increased the charge on the test arch. At some point, the light started to flicker, reflecting the concrete starting to damage and the electricity storage failing.

This makes apparent structural damage despite no visible cracks. Such a capacity could come very handy in real-life buildings.

“There may be a kind of self-monitoring capacity here. If we think of an ec³ arch at architectural scale, its output may fluctuate when it’s 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.”

Admir Masic – Associate professor of civil and environmental engineering (CEE) at MIT.

Self-Warming Concrete

This concrete design not only can store power, but also has higher thermal conductivity. As a result, it can help melt ice deposited on it, and has already been used for that purpose in Sapporo, Japan, representing a potential alternative to salting.

Energy stored and then realized in the form of heat could also be used to melt ice on roads, sidewalks, and walking paths.

The Future of Concrete Batteries and Energy Storage

So far, utility-scale batteries have been mostly imagined as heat batteries, hydrogen storage, or batteries using low-cost materials like sodium, iron, or aluminum, to replace the more expensive lithium/cobalt/nickel of lithium-ion batteries.

However, if we are to scale up battery storage to fully power industrialized civilization with solar energy, a more ubiquitous material like concrete could be ideal.

First, it uses even less rare materials, as even alternative chemistry batteries still require a lot of copper, for example.

Secondly, it could also be more seamlessly incorporated into everyday urban landscapes and constructions.

The team is already working toward applications like parking spaces and roads that could charge electric vehicles, as well as homes that can operate fully off the grid.

As the resulting concrete has the same structural integrity as normal concrete, it could make sense to just use it instead, and entirely bypass the need for extra space and construction procedure of battery parks.

“By combining modern nanoscience with an ancient building block of civilization, we’re opening a door to infrastructure that doesn’t just support our lives, it powers them.”

Admir Masic – Associate professor of civil and environmental engineering (CEE) at MIT.

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