We've already seen some zinc-air batteries hit the market, and now it sounds like lithium-based cells will be the next type to use air as a cathode. The only problem? Those of you who were awake in 10th grade chemistry might remember that exposing lithium metal to water causes it to explode -- which is why a company called PolyPlus has partnered with the government to develop a unique waterproof lithium metal-air battery that keeps the boom-boom in but lets the buzzy-buzz out. The coating allows lithium ions to seep out while preventing water from getting in, and because the membrane protects the cell, the battery won't discharge in storage. If that sounds a little pie-in-the-sky, well, it is -- PolyPlus founder Steven Visco called lithium metal "the holy-grail battery material." Us, we're a little more skeptical, but we're loving the sounds of prototypes that deliver the juice of current laptop batteries at one-fifth the weight -- hook us up, boys.