According to this abstract Alternative strategy for a safe rechargeable battery - Energy & Environmental Science (RSC Publishing) researchers at UT (including a 94-year old, John Goodenough!) think that this type of battery is denser than today's Li-ion types. Here is the story: Lithium-Ion Battery Inventor Introduces New Technology for Fast-Charging, Noncombustible Batteries Obviously, Na is a heckuva lot more prevalent than Li, albeit heavier. This technology is also supposed to work quite well in sub-zero temperatures. Is this feasible, or another one of those works-well-in-a-lab, but not so well in mass production and in common use designs?