Two of humanity's most ancient materials unlock bulk energy storage solution

"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.”

Supercapacitors, also known as ultracapacitors, are energy storage devices that store and release energy much faster than traditional batteries. 

Unlike regular batteries, which rely on chemical reactions, supercapacitors store energy in an electric field between two closely spaced electrodes. 

This unique mechanism allows them to charge and discharge rapidly, making them ideal for applications requiring quick power bursts. The power capacity of a capacitor depends on its conductive plate surface area.

The MIT team's innovative yet simple supercapacitors are achieved through a unique method involving a cement-based material with an exceptionally high internal surface area.

By adding conductive carbon black to a cement mixture and allowing it to cure, a dense, interconnected network of conductive material forms within the volume.

As the cement reacts with water, a branching network of openings develops, with carbon migrating into these spaces, creating wire-like structures with a fractal-like pattern, resulting in a vast surface area within a small volume.

To complete the supercapacitor, the material is soaked in a standard electrolyte like potassium chloride, providing charged particles that accumulate on the carbon structures.

Two electrodes made from this material, separated by a thin space or insulating layer, form a powerful supercapacitor akin to rechargeable battery poles.

When connected to an electricity source, energy is stored in the plates, and upon connecting to a load, the electrical current flows back out to provide power.

EV-charging roads

Concrete, a common component of our built environment, provides ample opportunities for scaling the technology to meet various bulk energy storage needs. The versatility of the material enables applications in both residential and commercial settings.

Could this mean roads that can charge electric vehicles as they drive, shelters that generate their own power, or even storing energy from wind and tidal turbines for use during cloudy or calm days? According to the researchers, yes.

If successfully implemented, they believe this composite material could play a pivotal role in making renewable energy more reliable and accessible.

The study opens up new frontiers in renewable energy storage, offering hope for a future where clean and sustainable energy sources power our lives. 

The full study was published in PNAS on July 31st.

Study abstract:

The large-scale implementation of renewable energy systems necessitates the development of energy storage solutions to effectively manage imbalances between energy supply and demand. Herein, we investigate such a scalable material solution for energy storage in supercapacitors constructed from readily available material precursors that can be locally sourced from virtually anywhere on the planet, namely cement, water, and carbon black. We characterize our carbon-cement electrodes by combining correlative EDS–Raman spectroscopy with capacitance measurements derived from cyclic voltammetry and galvanostatic charge-discharge experiments using integer and fractional derivatives to correct for rate and current intensity effects. Texture analysis reveals that the hydration reactions of cement in the presence of carbon generate a fractal-like electron-conducting carbon network that permeates the load-bearing cement-based matrix. The energy storage capacity of this space-filling carbon black network of the high specific surface area accessible to charge storage is shown to be an intensive quantity, whereas the high-rate capability of the carbon-cement electrodes exhibits self-similarity due to the hydration porosity available for charge transport. This intensive and self-similar nature of energy storage and rate capability represents an opportunity for mass scaling from electrode to structural scales. The availability, versatility, and scalability of these carbon-cement supercapacitors opens a horizon for the design of multifunctional structures that leverage high energy storage capacity, high-rate charge/discharge capabilities, and structural strength for sustainable residential and industrial applications ranging from energy autarkic shelters and self-charging roads for electric vehicles, to intermittent energy storage for wind turbines and tidal power stations.