Tripling the Energy Storage of Lithium-Ion Batteries

Scientists have synthesized a new cathode material from iron fluoride that surpasses the capacity limits of traditional lithium-ion batteries.

As the demand for smartphones, electric vehicles, and renewable energy continues to rise, scientists are searching for ways to improve lithium-ion batteries—the most common type of battery found in home electronics and a promising solution for grid-scale energy storage.  Increasing the energy density of lithium-ion batteries could facilitate the development of advanced technologies with long-lasting batteries, as well as the widespread use of wind and solar energy.  Now, researchers have made significant progress toward achieving that goal.

A collaboration led by scientists at the University of Maryland (UMD), the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, and the U.S. Army Research Lab have developed and studied a new cathode material that could triple the energy density of lithium-ion battery electrodes.  Their research was published on June 13 in Nature Communications.
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Scientists at UMD synthesized a new cathode material, a modified and engineered form of iron trifluoride (FeF3), which is composed of cost-effective and environmentally benign elements—iron and fluorine.  Researchers have been interested in using chemical compounds like FeF3 in lithium-ion batteries because they offer inherently higher capacities than traditional cathode materials.

“The materials normally used in lithium-ion batteries are based on intercalation chemistry,” said Enyuan Hu, a chemist at Brookhaven and one of the lead authors of the paper.  “This type of chemical reaction is very efficient; however, it only transfers a single electron, so the cathode capacity is limited.  Some compounds like FeF3 are capable of transferring multiple electrons through a more complex reaction mechanism, called a conversion reaction.”

Despite FeF3’s potential to increase cathode capacity, the compound has not historically worked well in lithium-ion batteries due to three complications with its conversion reaction:  poor energy efficiency (hysteresis), a slow reaction rate, and side reactions that can cause poor cycling life.  To overcome these challenges, the scientists added cobalt and oxygen atoms to FeF3 nanorods through a process called chemical substitution.  This allowed the scientists to manipulate the reaction pathway and make it more “reversible.”

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