Research on solid state batteries has been ongoing since then. E.g. Quantumscape founded in 2010. and is planning to start small scale production next year. We'll see how successful they are of course. You are right that it takes quite long to take technology into production. But the counter argument is that there are a few decades behind us with stuff that is now slowly trickling into the market.

Double the energy sounds amazing. Until you ask the question "double of what". Double of what's available in the market right now (450 wh/kg, Amprius sells these in low volumes) would be 900 wh/kg. That's perhaps not what they mean. The article is infuriatingly hand wavy on what is being compared to what. Or maybe they do. Hard to tell.