Solid state batteries are the long-promised Holy Grail of battery technology. They’re smaller and better than existing Lithium Ion batteries. They charge more quickly and last much longer. What’s not to like? Trouble is, no-one’s managed to mass produce one at any useful scale yet. Turns out it’s quite tricky to make them reliable! Now though, two major Japanese companies are finally firing up their full production lines. So will 2021 be the year?