Researchers from the Technical University of Munich (TUM), in Germany, and the Massachusetts Institute of Technology (MIT), in the United States, have used above-bandgap light to decrease the grain boundary resistance in solid ionic conductors and improve ion mobility in lithium-ion batteries and fuel cells.
“Our research shows that illumination of ceramic materials for fuel cells, and possibly for batteries in the future, can significantly increase ion mobility,” said TUM scientist Jennifer L M Rupp, noting that the novel technology was initially used to improve ion mobility at ceramic grain boundaries.
The removal of the barriers that prevent the mobility of ions should be achieved at lower temperatures than those required in the production of solid-oxide fuel cells, which usually are of up to 700 degrees Celsius. “Our dream was to see if we could overcome the barriers using something that doesn’t require heat. Could we get the same conductivities with another tool?” said lead author Thomas Defferriere. “This tool turned out to be light, which had never been investigated in this context before.”
According to the research group, the grain boundary conductance of gadolinium-doped cerium oxide, which is a ceramic used as a solid-state electrolyte in fuel cells, can be improved by a factor of approximately 3.5 at 250 degrees Celsius, by applying the proposed light technique. They also found that the activation energy needed to trigger this process can be lowered from 1.12 to 0.68eV.
“This newly discovered ‘opto-ionic effect' could find a wide range of applications in the future,” the academics affirmed. “For example, it could improve the performance of solid-state electrolytes in tomorrow's lithium-ion batteries and thus facilitate higher charging speeds, or could pave the way to the development of new electrochemical storage and conversion technologies that work at lower temperatures and achieve higher efficiency levels.”
Their findings were introduced in the paper “Photo-enhanced ionic conductivity across grain boundaries in polycrystalline ceramics,” published in nature materials.
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