Are there any alternatives to chemical batteries in development?

I read a post earlier about how Li-ion batteries haven't changed that much in 20 years and it got me pretty worried. They still seem so limited, especially when you start moving up to higher capacities like what you'd find in electric vehicles. There doesn't seem to be a way, for example, of effectively storing excess renewable energy that doesn't involve building a dam.

Hydrogen looks good on paper but AFAIK the process of producing and recombining it is really inefficient.