Maybe because it's too dangerous?.....8^)
For one thing, Li-Ion batteries are such a promising technology that lots of people are working with them all around the world. It's not surprising that other folks make discoveries, too.
More to the point, if you've been following the FR threads on the topic (there have been many), you'd know that there is a lot of Li-Ion battery research in the US, including a large number of significant breakthroughs.
Maybe because it's too dangerous?.....8^)