>"Of all the materials that one might use in an anode, lithium has the greatest potential. Some call it the Holy Grail," said Yi Cui, a Stanford professor of materials science and engineering and leader of the research team. "It is very lightweight and it has the highest energy density. You get more power per volume and weight, leading to lighter, smaller batteries with more power."<p>while it is theoretically true, the lithium is only part of the whole weight. The metals of the same group - potassium or sodium (though sodium seems to have more issues than potassium) anode looks order of magnitude easier (on the order of Al anodes while still being rechargeable) and provide almost the close to lithium perf/weight when whole battery is considered.