Future Battery for the Electric Car

Future Battery for the Electric Car Future Battery for the Electric Car Future Battery for the Electric CarThe price tag notwithstanding, theres one reason that drivers arent lining up to purchase a Tesla Model S, or a Chevrolet Volt, or a ZAP Alias, or a Fisker Karma for that matter. The hurdle is the very thing that puts those cars on the road in the first place the battery. In a cell phone, lithium ion batteries seem pretty small and nifty. In a car, theyre massive and will only get you so far. Thats not likely to change soon. GMs chief technology officer,Jon Lauckner, has said recently that increased and more efficient manufacturing is not likely to reduce the price or increase the capacity of lithium ion batteries. To see a change, well need a sea change. Thats likely to come in the form of the lithium sulfur battery. This chemistry has long been poised to vanquish the lithium ion battery. With a pure lithium anode rather than graphite, these batteries can store as much as five and half times the energy that a lithium ion battery can hold. And sulfur is cheap and plentiful. The small downside is that the battery dies after 50 or so cycles. Short Life Span For some time now researchers have thought they understood why lithium sulfur batteries had such short life spans. During use, crystalline sulfur particles would form higher order polysulfides. As these sulfides are all soluble, they would dissolve into the electrolyte, and go anywhere the electrolyte can goincluding the anode side of the battery where they would interact directly with he lithium metal. Working with scientists at SLAC and Stanford University, Johanna Nelson uses powerful X-ray imaging to study lithium sulfur batteries. Image Slac.stanford.edu The misconception arose thanks to a flaw in how sulfur batteries were examined. The usual M.O. welches to first cycle the battery until it was useless, or almost so, then take it apart and examine it with an electron microscope. To prepare the disass embled battery for examination, they had to first wash the elements. Once under the microscope, it appeared that polysfulfides had entirely fled the cathode to ruin the battery elsewhere. In fact, the researchers themselves had inadvertently removed polysulfides from the cathode during their preparations. Johanna Nelson, a researcher at Stanfords SLAC National Accelerator Laboratory, had a better microscope. The labs X-ray microscope allowed Nelson and her colleagues to look inside a battery while it was in use. They were able to zero in on sulfur particles and monitor their behavior as the battery was discharged. What we found is that a tiny bit of these polysfulfides went into the electrolyte, says Nelson. This tiny amount produces large capacity loss. Hardly any polysfulfides had left the cathode. Imaging Results The result flew so hard in the face of what the battery establishment assumed that Nelson and her colleagues doubted what they were seeing. When we first got the imaging results, we actually thought they were wrongthey were so opposite of what we expected, says Nelson. We said, OK this is wrong, lets repeat it. Convincing ourselves was one of the hardest things. With the new knowledge in hand, electric car and battery manufacturers (who have indeed been calling Nelsons lab) need only find a way to trap those polysuflites on the cathode. One possibility is a yoke-like sheath that can stretch to allow the sulfur to expand. These mere technical challenges mean the higher capacity lithium sulfur batteryand a farther driving carare soon to hit the streets. Talking to industry, it sounds like at most ten years, unless something better comes along, says Nelson. Pretty much if youve solved this problem, youve solved it. Michael Abrams is an independent writer.When we first got the imaging results, we actually thought they were wrong.Johanna Nelson, researcher, Stanford