MIT Cracks The Concrete Capacitor

It’s a story we’ve heard so many times over the years: breathless reporting of a new scientific breakthrough that will deliver limitless power, energy storage, or whichever other of humanity’s problems needs solving today. Sadly, they so often fail to make the jump into our daily lives because the reporting glosses over some exotic material that costs a fortune or because there’s a huge issue elsewhere in their makeup. There’s a story from MIT that might just be the real thing, though, as a team from that university claim to have made a viable supercapacitor from materials as simple as cement, carbon black, and a salt solution.

Supercapacitors use plate materials with a huge surface area on which to store charge. Conventional supercapacitors often use an electrochemical construction, and activated charcoal is a frequent electrode material. The cement capacitor uses the property of cement curing, which creates a dense branching network of openings in the material as the water reacts with the cement. By introducing electrically conductive carbon black to the mix and using potassium chloride solution instead of water, they turn the huge surface area of the resulting structure into a conductive electrode suffused with charged ions. This can be used as a plate of a supercapacitor, separated from another similar one by a membrane.

The suggestion is that, in the future, the foundation of a house or other structure might be cast in this cement to provide in-situ energy storage for rooftop solar generation. There’s an environmental question over the carbon footprint of cement manufacturing. Still, since the materials and techniques appear neither exotic nor expensive, we hope this is the one energy storage miracle discovery that makes it.

We’ve gone into more detail on supercaps in the past.

Header image: Michael Coghlan, CC BY-SA 2.0.

60 thoughts on “MIT Cracks The Concrete Capacitor

  1. And how does one prevent leakage current from sapping all of the energy stored within the concrete? It’d need to be insulated somehow.

    Simply driving a bolt through the wrong part of the material could short circuit the whole device. And how would such a device assembled within the concrete structure of a building ever be maintained or replaced if it failed? It doesn’t seem very practical.

      1. As long as the energy release doesn’t outright vaporize the capacitor.

        The issue with using capacitors as bulk energy storage is, beyond a certain scale they become electrostatic bombs.

        1. Would be a pretty impressive amount of joules needed to vaporize a concrete pad. A rocket engine on full-blast won’t do that. Anybody want to do some back-of-the-envelope math? If somebody is storing that much energy at home, they ought to be nervous.
          The system described seems to inherently involve some pretty massive reservoirs for heat; I think what would happen is the self-healing phenomenon, or perhaps it would simply obliterate whatever caused the short in the first place.

          1. Depends on how the transfer of energy happens. With the rocket launch pad, you have energy blowing around everywhere and mostly elsewhere and crucially the rate of release is much slower, whereas with the concrete capacitor the energy is concentrated across a micrometers thick separator membrane that takes very little time to fail.

            Gasoline contains about 42 Megajoules per kg, but it can’t react with itself and as such is completely inert. Gunpowder contains about 3 MJ/kg but it CAN react with itself in a self-accelerating manner, even detonate given a sufficient shock. When you start to approach kilowatt-hours (3.6 MJ) per kg energy densities such as batteries do, but capacitors thankfully don’t, you approach the properties of gunpowder.

          2. warning, i used GPT4 to do this math.

            Total Energy (Q) = Mass (m) * (Specific Heat (c) * Temperature Change (Delta T) + Latent Heat of Fusion (Lf) + Latent Heat of Vaporization (Lv))

            Assuming a concrete cube of 3.5 meters across, with a density of 2400 kg/m³, the mass is 102,900 kg. With a specific heat of 0.84 kJ/kg·K, and approximating a temperature change of 2000 K to reach vaporization, alongside rough estimates for latent heats of fusion and vaporization similar to quartz (2230 kJ/kg and 23300 kJ/kg respectively), the energy required to vaporize the cube is about 2.475 TJ. Comparatively, a 10 kWh battery holds only 36 MJ. Hence, the battery holds a minuscule fraction of the energy required to vaporize the concrete structure.

        2. Though I don’t think the energy density of a concrete capacitor would be very great. Something like milliJoules per kg – and on the same token it would be completely inconsequential for energy storage.

    1. I agree it seems implausible to just pour concrete wherever and use it as a capacitor. It would be more like, you buy a capacitor from a factory and it happens to be a huge concrete object.
      But there are lots of realistic construction uses for big chunks of prefab concrete. Stairs and foundation pads, for example; and in steel-framed buildings the floors are typically big prefab concrete slabs. With elements like that, you don’t generally drill into the concrete once it’s installed; service conduits and mechanical fixtures would be cast at the factory.
      And there are much more ambitious prefab designs out there, which could become economically attractive if the energy storage thing was real.
      That said, this application does sound very speculative and would need a lot of work.

      1. Cracks in SMT capacitors very often lead to short circuits, which is quite logical. The cracks are caused by mechanical stress, and the parts move relative to each other when it cracks and causes the shorts between the layers which should be of “opposite polarity”.

      2. In a case where a foundation cracks and settles, it could offset the boundary layer a bit lower on one side, bringing it in contact with the opposite pole. Would make for an interesting night

  2. Every insulator is a capacitor if the potential is high enough
    I’m curious if relatively low voltages like 12V or maybe even upto 48V can be used with these cement capacitors

  3. Supercapacitors are called that because they store much more charge than regular capacitors _for the same volume_. Capacitors can easily be made to store large charges, they just get very large (and hazardous to play with, natch). I haven’t seen density numbers so I regard “supercap” claims on this tech as wild and rather uninformed speculation.

    The shtick seems rather to be that it’s easier and cheaper to scale up, rather than more charge per volume. Note that for the particular application, even a lower charge density could well be acceptable, if the lower cost gains are worth the extra expense to stick the bulk somewhere out-of-the-way.

    This is cool tech _IFF_ it scales as they calculated. But we don’t know that yet. They have so far produced button-sized cells. Beyond that, this is still massively oversold breathless hype, like usual. Maybe there’s something in it, the idea sounds compelling, but I’ll believe it when I see it. Build that “three and a half metre cube” thing and tell us how it goes. Then I’d like to know self-discharge rates, actual costs per kWh stored, longevity numbers, and so on. They haven’t done that yet. Any of that. Thus, at least the article is mostly hot air and speculation.

    It’s still a massive block to have in your backyard, so you’ll want to bury it, and that’s going to be spendy, take construction permits, and so on. It could well be worth it, it looks promising, but it’s also really oversold for what they’ve actually done so far. As usual.

      1. In many homes, the problem is that the concrete foundations are perpetually wet from moisture wicking up from the ground. That’s why so-called “false foundation” homes tend to rot away in a few years because they’re just concrete slabs poured directly on the ground without any seams to provide breaks for the wicking effect. Busy builders also have a habit of not letting the concrete set for long enough before they build a house on top, which gives you moisture problems from day one.

        Having a built-in heater would make it possible to dry the slab quicker, but there’s a caveat: if the slab gets too hot – and the chemical reaction already heats it up – it will crack.

    1. Don’t pre-stress about it. On aggregate these results provide a solid base upon which to build their research, which should cement their reputation amongst their piers.

      1. It remains to be seen if this technology is ready-mix for prime-time. Scalability issues could surface-finish, thereby rebarring its future use. In that case they’d have no choice but to throw in the trowel.

    2. No need to be so hard headed. It’s obvious they’re chipping away at basic scientific principles that had been long set in stone. They’re rocking the boat and will eventually persevere.

  4. You will find potentially revolutionary discoveries like this on a daily basis on or the Science X Newsletter. Some small percentage of them might actually pan out. Most are going to be too costly, not practical, not reliable, etc.

    1. I remember there’s one forum with a thread that keeps track of battery technology announcements, with something like 10,000 posts over the past 10 years with new “breakthroughs” that never materialized into commercial products.

  5. There’s a very telling paragraph near the end of the original article…

    ‘“So, it’s really a multifunctional material,” he adds. Besides its ability to store energy in the form of supercapacitors, the same kind of concrete mixture can be used as a heating system, by simply applying electricity to the carbon-laced concrete.’

    If it’s heating up that much it suggetsts any capacitor is going to have terrible ESR and so be hoplessly inefficient for grid storage. The fact that they have only powered an LED with no series resistor in sight supports this idea.

    All in all this looks like a solution in search of a research grant rather than a problem.

    1. Not true at all. If you were to stick a contact on either side of one pole sheet inside a traditional capacitor and run a current across it you’d be able to create heat. Additionally it would still work as a capacitor as the other pole is still isolated.

      Not that I think this idea will pan out in any signifigant way, just pointing out how the article is not fibbing with it’s claims to that extent.

    1. It would go around the foundation through the grounding rod, same as normal.. Your house is already far too much of a capacitor when it comes to a bolt of lightning, so it should come pre-shorted. If it’s not, better plan a trip to the hardware store.

  6. Did some digging in the source article and lol, lmao even:
    >20–220 Wh/m3
    For reference, that converts to:
    >0.02-0.22 Wh/L
    In comparison to ordinary lead-acid batteries (truly the pinnacle of efficiency), which get:
    >60-90 Wh/L

    This is meme science. Cement is for buildings.

    1. A comparison to chemical battery probably isn’t fair. As this being concrete it would probably be a permanent part of the structure, and being a capacitor aught to last vastly longer than a battery – in theory plausible it just works as long as the building stands…

      Obviously some significant testing is required to see how well this composite survives all the challenges that will get thrown at it in the real world, but it isn’t a terrible idea if it will last in the real world pulling double duty as electrical store and structural element. You needed the structure anyway presumably…

      I do agree though it doesn’t sound very ‘supercap’ to me…

    2. Still adds up. Of course it’s not going to equal the energy density of a car battery, but it’ll be a LOT cheaper and (hopefully) require less maintenance. That second part would be the thing that makes or breaks this concept; does it reliably last 30 years or more?

      Assuming the answer was yes and all our dang parking garages all over the place in every city were made of this stuff, it would be significant grid storage

  7. Imagine a large wind turbine with a commensurate (primarily non structural) massive concrete base utilised as a low intensity capacitor for times of excess power storage and even power release between gusts. Again consider a turbine incorporated in a tidal lagoon constructed from mass concrete in the main and capable of power storage between tides. – makes you think of the potential when storage is a secondary use for the concrete needed in the construction anyway. Or prioritising concrete roads over bitumen based construction. Must be research worth funding. If the concrete strength loss can be compensated for in a higher cement ratio or by using larger structural elements then that brings far more multistorey buildings and public infrastructure into consideration.Modern Cement is becoming far less carbon intensive over time.

    1. > Imagine a large wind turbine with a commensurate (primarily non structural) massive concrete base utilised as a low intensity capacitor for times of excess power storage and even power release between gusts

      This is the first decent application in this thread. As everyone else has pointed out, it’s not the right scale for a domestic house but *maybe* for other, bigger structures there *may* be enough benefit…

  8. Brilliant you only need 100,000 dollars worth of carbon fiber to act as electrodes as every single other material will corrode by being in contact with a corrosive material and eventually have incredibly high contact resistance. Not to mention this material always has resistance with whatever metal you connect to it that will also oxidize as the whole thing needs to be kept wet and incredibly high internal resistance through the current collectors. Your house will also reek of mildew. I’m surrounded by fucking morons.

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