Check out the article below, a new technology has acheived a 40% - 60% in crease in lithium-ion battery energy density:-
New tech produces lighter, long-lasting batteries from silicon | Business Standard News
There are several new battery technologies in the works at many universities. It would seem that nanotube silicon is the path that a few of them are working on. Imagine a battery that has four to five times the Kwh output of todays best Lithium ion, at 2/3 of the weight, and several thousand life cycles! Come on battery builders, we are ready and waiting!