True, but looking at the trend in energy density improvements in Li ion batteries, it's linear and seems like it would take more than 2 years to achieve a 2x im

True, but looking at the trend in energy density improvements in Li ion batteries, it's linear and seems like it would take more than 2 years to achieve a 2x improvement: http://www.batteryuniversity.com/images/parttwo-55h.gif http://www.batteryuniversity.com/images/parttwo-55h.gif The problem with reducing the mass of the non-Li portion of the battery is that all of the practical candidates for the anode are metal oxides (e.g. Co, Fe, Mn oxides). Unless the whole metal oxide motif is replaced, you can't really achieve significant mass savings. There are research groups and startups working on alternate anode and cathode materials but there are tradeoffs in power density and safety. Also given that these approaches are still in the research phase, it'll take at least a couple of years before they reach commercial testing.