New designs for solid-state electrolytes may soon revolutionize the battery industry

A pressing concern with current commercial batteries 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 advancing solid-state battery technology. As the world gears up to regulate internal combustion engine vehicles and expand the use of electric vehicles in the ongoing global shift toward sustainable transportation, research into the core components of secondary batteries, particularly solid-state batteries, has gained significant momentum.

To make solid-state batteries practical for everyday use, it is crucial to develop materials with high ionic conductivity, robust chemical and electrochemical stability, and mechanical flexibility. While previous research successfully led to sulfide and oxide-based solid electrolytes with high ionic conductivity, none of these materials fully met all these essential requirements.

In the past, scientists have also explored chloride-based solid electrolytes, known for their superior ionic conductivity, mechanical flexibility, and stability at high voltages. These properties led some to speculate that chloride-based batteries are the most likely candidates for solid-state batteries. However, these hopes quickly died out, as the chloride batteries were considered impractical due to their heavy reliance on expensive rare earth metals, including yttrium, scandium, and lanthanide elements, as secondary components.

To address these concerns, the IBS research team looked at the distribution of metal ions in chloride electrolytes. They believed the reason trigonal chloride electrolytes can achieve low ionic conductivity is based on the variation of metal ion arrangements within the structure.

They first tested this theory on lithium yttrium chloride, a common lithium metal chloride compound. When the metal ions were positioned near the pathway of lithium ions, electrostatic forces caused obstruction in their movement. Conversely, if the metal ion occupancy was too low, the path for lithium ions became too narrow, impeding their mobility.

Building on these insights, the research team introduced strategies to design electrolytes in a way that mitigates these conflicting factors, ultimately leading to the successful development of a solid electrolyte with high ionic conductivity. The group went further to successfully demonstrate this strategy by creating a lithium-metal-chloride solid-state battery based on zirconium, which is far cheaper than the variants that employ rare earth metals. This was the first instance where the significance of the metal ions arrangement on a material's ionic conductivity was demonstrated.

This research brings to light the often-overlooked role of metal ion distribution in the ionic conductivity of chloride-based solid electrolytes. It is expected that the IBS Center's research will pave the way for the development of various chloride-based solid electrolytes and further drive the commercialization of solid-state batteries, promising improved affordability and safety in energy storage.

Corresponding author KANG Kisuk states, "This newly discovered chloride-based solid electrolyte is poised to transcend the limitations of conventional sulfide and oxide-based solid electrolytes, bringing us one step closer to the widespread adoption of solid-state batteries."