MIT's carbon-cement supercapacitor now stores ten times more energy, in the lab

Oct. 1, 2025 — MIT researchers say optimized electrolytes and a new way of mixing them in have raised the energy storage of their carbon-cement supercapacitors by about ten times. Here's what happened, what it cost, and what went wrong.

Cost and outcome (as of Oct. 1, 2025)

Outcome: In 2023, about 45 cubic metres of ec³ would have been needed to store a typical home's daily energy needs; with the new electrolyte it's about 5, the volume of a basement wall, MIT says. (MIT News, Oct. 1, 2025)
Cost: Not reported.
Status: Lab prototypes: a 12-volt stack and a small load-bearing arch. (MIT News, Oct. 1, 2025)

What changed

ec³, pronounced "e-c-cubed," combines cement, water, ultra-fine carbon black and electrolytes into a conductive "nanonetwork" that could let walls, sidewalks and bridges store and release electricity, MIT News says. The team reports its latest results in PNAS. Masic, who co-directs MIT's EC³ Hub, framed it as "multifunctional concrete": "Concrete is already the world's most-used construction material, so why not take advantage of that scale to create other benefits?" (MIT News, Oct. 1, 2025; PNAS paper, DOI 10.1073/pnas.2511912122)

Using FIB-SEM tomography, which removes thin slices with an ion beam and images each one, the team reconstructed the network at its highest resolution yet and found a fractal-like web around the pores. The researchers then added electrolyte directly into the mixing water instead of soaking cured electrodes, which let them cast thicker electrodes that store more energy. (MIT News, Oct. 1, 2025)

The best results came with organic electrolytes combining quaternary ammonium salts with acetonitrile: a cubic metre of that ec³, about the size of a refrigerator, can store over 2 kilowatt-hours, about enough to run a refrigerator for a day, MIT says. First author Damian Stefaniuk said viable electrolytes even include seawater, which could suit offshore wind supports. (MIT News, Oct. 1, 2025)

The prototypes

A 12-volt prototype, made by stacking ec³ electrodes between electrolyte-soaked separators, powered a 12-volt computer fan and a 5-volt video game console over USB. A miniature 9-volt arch supported its own weight and additional load while powering an LED, and the light flickered as load increased. Lead author Admir Masic said that "may be a kind of self-monitoring capacity." (MIT News, Oct. 1, 2025)

MIT says ec³ has already been used to heat sidewalk slabs in Sapporo, Japan, as an alternative to salting. The team is working toward parking spaces and roads that charge electric vehicles, and homes that run off the grid. "We believe that ec³ is a viable substitute" for batteries, said co-director Franz-Josef Ulm. Stefaniuk said one motivation was the renewable transition: solar "can only generate power when there's enough sunlight." Co-author James Weaver of Cornell University, a former EC³ Hub researcher, said the team had shown that a material "as ancient as concrete" can "do something entirely new." (MIT News, Oct. 1, 2025)

What went wrong

Batteries still win on density. MIT News acknowledges that batteries maintain a higher energy density; ec³'s pitch is that it can be built into slabs, walls and vaults and last as long as the structure. (MIT News, Oct. 1, 2025)
Best result isn't seawater. The top performance came with an acetonitrile-based organic electrolyte, which MIT describes as a liquid often used in industry, rather than the seawater the team also flags. (MIT News, Oct. 1, 2025)
No cost or field data. Neither MIT nor its quotes give a cost per kilowatt-hour or results from a full-size structure.
What we don't know yet: how ec³ holds up over years of charging in a real building, and whether the flicker can be calibrated into a reliable stress signal.

Our follow-up question for The MIT EC³ Hub

What would ec³ storage cost per kilowatt-hour at building scale, and when will a full-size structure be tested?

Sources

MIT News (Andrew Paul Laurent, MIT Concrete Sustainability Hub), “Concrete 'battery' developed at MIT now packs 10 times the power,” Oct. 1, 2025. news.mit.edu
Stefaniuk, D., et al. (lead author Admir Masic), “High energy density carbon–cement supercapacitors for architectural energy storage,” PNAS (as cited by MIT News). doi.org

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