Where are those promising solid-state batteries?

Abstract

In recent years there have been regular reports about a new generation of batteries in which the liquid electrolyte is replaced by a solid material: the solid-state batteries. With a higher energy density and a better safety than current batteries, solid-state batteries potentially would boost electric mobility by enhancing the driving distance of e-cars and prevent extreme battery fires. Why are they not yet implemented in the latest generation of e-cars?.