Seems like solid state batteries are just around the corner now. Never really thought of a dry capacitor as a solid state battery until this came up.
"The company claims that its newly developed lithium-ion ultracapacitors boast the advantages of capacitors—high energy density, quick charge and discharge, and low degradation—but also larger storage capacities, comparable to that of a battery. At a commercialized, EV-ready scale, this technology could decrease charge times, have a longer service life than a traditional lithium-ion battery, resist overheating during heavy charge or discharge, and be capable of greater energy output."