Most electric cars, from the Tesla Model S to the Nissan Leaf, run on rechargeable lithium-ion batteries a pricey technology that accounts for more than half of the vehicle's total cost. One promising alternative is the lithium-sulfur battery, which can theoretically store five times more energy at a much lower cost.
But lithium-sulfur technology has a major drawback: After a few dozen cycles of charging and discharging, the battery stops working.
"The cycle life of lithium-sulfur batteries is very short," said Johanna Nelson, a postdoctoral scholar at the SLAC National Accelerator Laboratory at Stanford University. "Typically, after a few tens of cycles the battery will die, so it isn't viable for electric vehicles, which require many thousands of cycles over a 10- or 20-year lifetime."
A typical lithium-sulfur battery consists of two electrodes a lithium metal anode and a sulfur-carbon cathode surrounded by a conductive fluid, or electrolyte. Several studies have attributed the battery's short cycle life to chemical reactions that deplete the cathode of sulfur.
But a recent study by Nelson and her colleagues is raising doubts about the validity of previous experiments. Using high-power X-ray imaging of an actual working battery, the Stanford-SLAC team discovered that sulfur particles in the cathode largely remain intact during discharge. Their results, published in the Journal of the American Chemical Society (JACS), could help scientists find new ways to develop commercially viable lithium-sulfur batteries for electric vehicles.
"Based on previous experiments, we expected sulfur particles to completely disappear from the cathode when the battery discharges," said Nelson, the lead author of the JACS study. "Instead, we saw only negligible changes in the size of the particles, the exact opposite of what earlier studies found."
Nelson and her co-workers conducted their experiments at SLAC using
|Contact: Mark Shwartz|