Solid-state electrolytes have the potential to improve the safety properties of lithium-ion batteries. Many different materials have been proposed over the years. However, especially at lower temperatures (at or near room temperature), most solid-state electrolytes display lithium ion conductivities lower than the one of conventional organic liquid electrolytes (about 3-5 mS cm^-1 at room temperature). Several sulfides are among the only compounds reported so far displaying lithium ion conductivities in or above this range. However, issues regarding costs and/or electrochemical stability of sulfide electrolytes still remain.
Here we report on several complex hydrides that display, for the first time, lithium ion conductivities near room temperature comparable to liquid organic electrolytes, adding a second class of materials to the group of highly conductive solid-state electrolytes and paving the way for high-power lithium solid-state batteries. An in depth study was carried out to understand the lithium transport mechanism of these materials. Density functional theory calculations combined with molecular dynamics simulations support a new anion assisted lithium hopping mechanism. We also show excellent stability of our solid-state electrolytes via long-term cycling in half-cell battery configuration.