Lithium-ion is 50% better than it used to be (in terms of energy/mass, it's done better than that for energy/volume). A problem is that lithium is more or less

Lithium-ion is 50% better than it used to be (in terms of energy/mass, it's done better than that for energy/volume). A problem is that lithium is more or less the best choice for materials, and we've been pouring resources into developing it.