Earlier this year, a relatively unknown startup from Finland made a startling announcement : It had finally solved solid-state batteries. Not only that, but Donut Lab, a spinoff of Verge Motorcycles, said that its solid-state battery — long considered the “Holy Grail of batteries” for their high-density, durable, fast-charging abilities — would go into production later this year. Battery experts were understandably skeptical. After all, solid-state batteries are one of those technologies, along