Comment by Animats | Hacker News Reader

Comment by Animats | Hacker News Reader

Energy density of 222 µWh cm−2

As a battery, this is not useful.

A standard brick is 2Kg, volume 1300 cm^2, or 0.0015 Kg/cm^2. So that's 148,000 uWh/Kg, or 0.148 Wh/Kg.

That's not much. A lead-acid battery is 30 to 50 watt-hours / Kg. Existing ultracapacitors have an energy density of 5 to 10 watt-hours / Kg. So this is about 1/200th the energy density of a lead-acid battery, or 1/33 of an ultracapacitor. Not bad for a first try. It may be possible to improve on the material. Get the surface to volume ratio up.

But as a capacitor, it's quite good. Use this technology to replace ordinary electrolytic capacitors in power supplies. Capacitors have been the weak point in power supplies for a century. As an ordinary capacitor, it's 1.60F/cm^2 at 1.2V. Farad, not uF. That's very good compared to ordinary electrolytics. The main problem is the low current - 0.5mA/cm^2. That has to be increased for this to be useful as a filter cap. That's mostly a connection problem - getting enough conductor near the capacitor component.

It looks like they claim about 20Wh in a reasonably-sized wall.

Not killowatt hours. Watt hours.

This is so far off from commercial densities that you are probably right, but it might be worth looking at some what-ifs for the next technology that starts out an order of magnitude or two higher.

Mass has its uses, and if we are looking at system efficiency we should look at cogeneration options for heavy solutions. In a home, thermal mass has its uses for efficient temperature regulation. A big clunky solution that sits in your basement and works as a heat storage device to dampen temperature cycling might still be practical, at least at some latitudes.

And cost-wise, the price of the used platinum foil and PEDOT electrolyte is also neglected but due to the low energy density a lot of that is needed as well. The article however emphasizes the cheap base material several times (bricks) and everyone has an idea of bricks. To me this publication can't hide that it has a PR smell to it. Also the peer review discussion is unexpectedly long and energy density wasnt initially considered to be included in the publication...

https://static-content.springer.com/esm/art%3A10.1038%2Fs414...

Edit: This article employs a clever (let's call it) reverse-bikeshedding trap by including a well known element with some easy to grasp attributes (cheap, abundant, easy to handle, nontoxic) in a complex environment (battery physics/chemistry) to spark a viral story where anyone can participate in.

The issue with using them in power supplies is the ESR (equivalent series resistance). Check out this Rohm data sheet for more info [1].

Aluminum polymer electrolytics already provide both large bulk capacitance and good ESR and ESL performance (although they’re a bit more expensive than more common chemistries).

Not to mention, you can reduce the capacitance necessary for your design by increasing the switching frequency so bulk capacitance isn’t nearly as important. You can also synthesize bulk capacitors with good ESR and ESL by using an aluminum electrolytic in parallel with, for instance, an MLCC ceramic capacitor or even niobium or tantalum. [2] Careful with tantalum though, not only is it a conflict material it tends to exhibit, uh, thermal runaway (they explode).

I didn’t see ESR performance in the write up but I suspect if it was low-ESR they would have led with that. Likely the 0.5mA/cm^2 limit is due to a sky-high ESR.

[1] http://rohmfs.rohm.com/en/products/databook/applinote/ic/pow...

[2] https://www.ti.com/lit/an/slyt639/slyt639.pdf

They aren't using a full standard brick, just slivers of them with these dimensions:

1 cm × 0.5 cm × 0.28 cm

Does your math change if you're basing it off these 0.25 gram slivers of brick?

No, the article normalizes for volume

Seems rather uncreative to just take a plain brick wall and coat it. Wouldn't adding perforations, divots, or slicing the brick into shards dramatically increase the capacity?

It’s also not a very good energy per unit cost, at about $600 per kWh (assuming $0.50 per brick, which is fairly typical for bulk brick orders). Meanwhile, Tesla is targeting a supercapacitor cost of $150/kWh.

Yeah but if you're building a house, you need the bricks anyway. Why not make your walls a battery while at it?

Are there still places where brick construction is common?

Any semi-modern building I've seen in my area is wood-frame with maybe a decorative brick facade on part of a wall.

I can't imagine the cost of building a brick house makes any financial sense when compared to more modern construction methods.

Am I wrong in this?

I'm no expert, but anecdotally in Australia I see lots of brand new brick houses.

As an Australia who grew up in a neighbourhood while under construction, they’re all just brick facades.

Many parts of the US prefer the aesthetics of brick. It isn't about the cost.

> Many parts of the US prefer the aesthetics of brick

At least around here, if you want the aesthetic, you go for wood frame with brick facade.

How does brick work for modern wiring, plumbing, insulation needs? Most of that stuff is traditionally routed at least partially through load bearing walls.

>How does brick work for modern wiring, plumbing, insulation needs? Most of that stuff is traditionally routed at least partially through load bearing walls.

it's not much different other than the addition of a masonry drill bit.

in the case of very large plumbing, sometimes whole bricks are left out and the area filled/finished with a conrete mixture and left to set around the pipe.

Yes. Modern brick buildings generally have load bearing frames and then brick in place of vinyl, but they're still called brick houses :)

External walls being load bearing is generally not a thing anymore since the "invention" of sensible construction methods and steel re-inforced cement / concrete.

I think it's very common in Germany, though I can't find any source to confirm my intuition.

In southern Ontario, Canada, the vast majority of houses are stick-built with complete brick facades on all sides of the house. This is even the case on "cheap" subdivision houses that are 4 feet apart.

They're targeting a battery cost of $100 / kWh per Elon some time ago.

> As a battery, this is not useful.

I disagree. The article also states that a brick can be fully charged in 15 seconds. If we go by your back-of-the-napkin math, this would mean the equivalent of a lead-acid battery would take a couple of minutes to fully charge.

Meanwhile, a lead-acid battery takes 12-16 hours to charge.

Depending on how these bricks handle load cycles, this technology seems absolutely brilliant for applications that involve energy storage/load balancing from renewable energy sources.

> volume 1300 cm^2

cm^2 is a unit of area, not volume. That said, I can't correct your numbers because I have no idea what the area of a brick means.

Not useful as a battery, artists could do a lot with it.

> volume 1300 cm^2

Discrepancy detected

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