Paper has been getting beat by electronics for years. But it may be about to stage a comeback. Researchers are reporting that they've made batteries and other energy-storage devices by printing layers of carbon nanotube–based ink atop standard photocopy paper. The result is a highly conductive sheet that can carry a charge and be easily incorporated into a flexible battery. Because of paper's low cost, that could help lower the price of batteries used in electric vehicles, wind farms, and other renewable sources. The idea of using paper to make a lightweight, flexible battery isn't new. Researchers led by Robert...