Rechargeable batteries are power sources for many commercial and military tools and will be an essential energy source for many future automobiles. But the global supply of materials used in many rechargeable batteries is limited and shrinking quickly, to the point that the U.S. Army is working with researchers at the Georgia Institute of Technology to develop a new cathode and electrolyte system to replace expensive metals and traditional liquid electrolytes with lower-cost transition-metal fluorides and a solid polymer electrolyte. The ARO is part of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory (ARL).
One key to the novel batteries is a solid polymer electrolyte. “Electrodes made from transition metal fluorides have long shown stability problems and rapid failure, leading to significant skepticism about their ability to be used in next generation batteries,” said Gleb Yushin, a professor in Georgia Tech’s School of Materials Science and Engineering. “But we’ve shown that when used with a solid polymer electrolyte, the metal fluorides show remarkable stability—even at higher temperatures—which could eventually lead to safer, lighter, and cheaper lithium-ion batteries.”
The solid polymer electrolyte contrasts with the liquid electrolyte used in popular lithium-ion rechargeable batteries. It is used with iron fluoride cathodes to replace traditional cobalt- or nickel-based cathodes to form a smaller battery with more capacity and recharge cycles. “Professor Yushin has identified a novel approach to enable the use of iron fluoride cathodes and addresses issues with dimensional changes and parasitic side reactions to develop lithium batteries,” said Dr. Robert Mantz, division chief, electrochemistry, ARO. “Soldier-wearable technologies are expected to increase significantly, as will the need for power and energy sources to operate them. This research could make battery power more readily available to soldiers in a form that is safe and easily transportable.”
The researchers developed a process to infiltrate a solid polymer electrolyte into a prefabricated iron fluoride electrode. The combination was hot pressed to increase density and reduce voids. “Cathodes made from iron fluoride have enormous potential because of their high capacity, low material costs, and very broad availability of iron,” Yushin said. “But the volume changes during cycling as well as parasitic side reactions with liquid electrolytes and other degradation issues have limited their use previously. Using a solid electrolyte with elastic properties solves many of these problems.”
