I saw a video a few weeks back where someone took an experimental Solid-State cell, hooked it up to a lamp to show when the cell was functioning properly, and then cut a chunk out of the cell with tin-snips. There was minimal smoke and sparking as the cell was cut into and while it was being shorted by the metal blade of the snips the cell stopped working - but as soon as the snips were removed the cell continued to work. Also no large fires etc when a nail was driven through another cell.
Amazing leaps forwards in terms of the safety side - Now all they've got to do is match the performance of the Li-ion cells that are around.
I'm eager to see proven technologies being implemented widely that address many of the concerns folk have (i.e. avoiding conflict minerals such as Cobalt, more recycling at end-of-life and/or just longer outright life). Energy Density is important, but with current Li cells it's good enough - just would be better if the cost would be driven lower!