A lot of shaky stuff in here that has a long way to go before it makes it out of the lab.

3.5 cubic meters of material ought to be enough to make quite a comfy house

OP, a 3.5 m-wide cube is not 3.5 cubic meters. That’s the size of a decently large shed… Of solid concrete.

would have enough capacity to store about 10 kilowatt-hours of energy, which is considered the average daily electricity usage for a household

No mention in the article about round trip efficiency, self-discharge rates / storage duration, etc.

Storing 10 kWh doesn’t mean much if it loses much of that to internal losses, leakage into the environment, etc., before you can use it.

Capacitors generally tend to be designed to store very little energy but can charge/discharge repeatedly at a high rate. Is this designed to discharge quickly? If so, what happens if someone touches the giant Borg cube in your yard?

Concrete is also prone to cracking, which last I checked, is not good for electronics.

That said, this is an interesting concept, and if it can perform at a useful level / scale, I could see industrial uses for large systems with high peak loads / energy recovery / regenerative braking, as a cost effective way to smooth grid loads, but probably wouldn’t expect to see it in use at people’s homes for a loooong time.

Less “you can make a super capacitor at home”, more “innovative material uses may one day make super capacitors more cost effective for certain applications, if it can be scaled out of a lab”