From: DOE / Brookhaven National Laboratory
Published March 6, 2017 02:19 PM

Imaging the Inner Workings of a Sodium–Metal Sulfide Battery for First Time

Understanding how the structural and chemical makeup of the material changes during the charge/discharge process could help scientists advance battery design for future energy storage needs

Sometimes understanding how a problem arises in the first place is key to finding its solution. For a team of scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, taking this approach led them to the cause of degraded performance in an operating sodium-ion battery.

“We discovered that the loss in battery capacity is largely the result of sodium ions entering and leaving iron sulfide—the battery electrode material we studied—during the first charge/discharge cycle,” explained Brookhaven physicist Jun Wang, who led the research. “The electrochemical reactions involved cause irreversible changes in the microstructure and chemical composition of iron sulfide, which has a high theoretical energy density. By identifying the underlying mechanism limiting its performance, we seek to improve its real energy density.”

Read more at DOE / Brookhaven National Laboratory

Photo: Jun Wang (sitting), Christopher Eng (standing), Jiajun Wang (left, laptop screen), and Liguang Wang of Brookhaven National Laboratory used transmission x-ray microscopy combined with spectroscopy to produce the colored maps shown on the large screen. These maps reveal the structural expansion (and the resulting cracks/fractures) and chemical composition changes that occur as sodium ions (Fe, green) are added to and removed from iron sulfide (FeS, red) during the battery's first discharge/charge cycle. The pristine iron sulfide (box in upper left) does not return to its original state after this cycle, as some sodium ions remain trapped in the core (box in lower right). As a result, there is an initial loss in battery capacity.

Credit: Brookhaven National Laboratory

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