New solid-state electrolyte designs could revolutionize the battery industry
Researchers are making significant progress in solid-state electrolytes from lithium metal and lithium chloride.
The researchers, led by Professor Kang Keesuk from the Center for Nanoparticle Research within the Institute for Basic Science (IBS), have announced a major advance in the next generation of solid-state batteries. They have discovered a new chloride-based solid electrolyte with exceptional ionic conductivity, which is expected to enable the development of more efficient batteries.
Need for solid electrolytes
A pressing concern with current commercial batteries is their reliance on liquid electrolytes, which leads to flammability and explosion risks. Therefore, the development of non-combustible solid electrolytes is of paramount importance for the development of solid-state battery technology. As the world prepares to regulate internal combustion engine vehicles and expand the use of electric vehicles in the ongoing global shift toward sustainable transportation, research into the basic components of secondary batteries, especially solid-state batteries, has gained significant momentum.
To make solid-state batteries practical for daily use, it is necessary to develop materials with high ionic conductivity, strong chemical and electrochemical stability, and mechanical flexibility. While previous research has successfully led to the production of sulfide and oxide-based solid electrolytes with high ionic conductivity, none of these materials have fully met all of these basic requirements.
Advances in chloride-based solid electrolytes
In the past, scientists have also discovered chloride-based solid electrolytes, known for their superior ionic conductivity, mechanical flexibility, and stability at high voltages. These characteristics have led some to speculate that chloride-based batteries are the most likely candidates for solid-state batteries. However, these hopes were soon dashed, as chloride batteries were considered impractical due to their heavy reliance on expensive rare earth metals, including the elements yttrium, scandium, and lanthanide, as secondary components.
To address these concerns, the IBS research team looked at the distribution of metal ions in chloride electrolytes. They believed that the reason why triple chloride electrolytes could achieve such low ionic conductivity depended on the different arrangements of the metal ions within the structure.
They first tested this theory on lithium yttrium chloride, a common compound of lithium metal chloride. When metal ions were placed close to the path of lithium ions, electrostatic forces inhibited their movement. Conversely, if the occupancy of the metal ions is too low, the path of the lithium ions becomes too narrow, hindering their movement.
Based on these insights, the research team presented strategies to design electrolytes in a way that mitigates these conflicting factors, ultimately leading to the successful development of solid electrolytes with high ionic conductivity. The group went further to successfully demonstrate this strategy by creating a zirconium-based lithium chloride solid-state battery, which is much cheaper than alternatives that use rare earth metals. This was the first time that the importance of the arrangement of metal ions on the ionic conductivity of a material was demonstrated.
Effect of metal ion distribution
This research highlights the often overlooked role of metal ion distribution in the ionic conductivity of chloride-based solid electrolytes. The IBS Center’s research is expected to pave the way for the development of several chloride-based solid electrolytes and further advance the commercialization of solid-state batteries, which promise improved affordability and safety in energy storage.
“This newly discovered chloride-based solid electrolyte is poised to surpass the limitations of traditional sulfides and oxide-based solid electrolytes, bringing us one step closer to the widespread adoption of solid-state batteries,” says corresponding author Kang Keesuk.
Reference: “Design of a triple-halide superionic conductor by regulating the order disorder of cations” by Sungju Yoo, Joohyun Noh, Byunghoon Kim, Jun Hyuk Song, Kyungbae Oh, Jakyun Yoo, Sunyoung Lee, Sung Oh Park, Wonjo Kim, Byungwook Kang Dongyun Kil and Kiseok Kang, November 2, 2023, Sciences.
The study was funded by the Institute for Basic Sciences.