Ever worry that your cell phone will fade when you need it most? Or that the same thing will happen when driving your electric car? Lightweight lithium-sulfur batteries could be the answer, holding two times the energy of those on store shelves, but they often fade and won't hold a charge for long. Through the Joint Center for Energy Storage Research (JCESR), scientists at DOE's Pacific Northwest National Laboratory identified one of the reasons behind this problem.They found that salts used in the liquid in the batteries make a big difference. When a salt called LiTFSI is packed in the liquid, a test battery can hold most of its charge for more than 200 uses. The LiTFSI helps bind up lithium atoms and sulfur on the electrode but quickly releases them. In contrast, a similar liquid ties up the lithium and sulfur but doesn't release it. The result is an electrode that quickly degrades; the battery fades after a few dozen uses.