Yes, last time I checked, they had about the same energy density as lithium batteries, but the problem is their "effective series resistance," which at least was pretty high, I haven't checked in recent years.
ESR made it difficult to get energy out of the supercap quickly, and you paid a high price in efficiency for charging and discharging.
The good thing about them is that they charge much faster than lithium batteries.
I think some Bluetooth earpieces use supercaps instead of batteries, but I'm not sure.
It would seem that Super Caps might have orders of magnitude greater recharging cycles than most rechargeable battery technologies, but I don’t know.
You might appreciate this, or, maybe not. Maybe it’s too advanced and engagement in nuclear physics at the level of the atom with consideration of the ‘force balance’ between proton and electron is not a subject you’re familiar with, nor wish to be:
https://www.youtube.com/watch?v=8dCzVUnnL00