Different Behaviors of Metal Penetration in Na and Li Solid Electrolytes.

Solid-state batteries with alkali metals (Li, Na, etc.) as anodes have the potential to achieve high energy density. However, the Li penetration through the garnet occurs without preindication during electrochemical cycling, leading to sudden short circuit and safety concerns. Various improvement strategies are developed but such a problem still exists when the current density exceeds the critical value. In contrast, the electrochemical Na plating/stripping on the β″-alumina ceramic electrolyte (BASE) has been explored with improved interfacial contacts by introducing an Au intermediate layer. When being cycled around the critical current density, the polarization potential of the Na/Au/BASE symmetric cells increases progressively until it stabilizes at a certain value without the sudden short circuit. It is revealed that the increasing polarization originates from a gradual Na penetration into the BASE ceramics from the interface and the subsequent stable cycles correlate with the formation of a sustainable Na/Au/BASE interface. These results disclose the difference in a growth model of metal filaments through Li and Na solid electrolytes, shedding new light on understanding of the metal penetration in solid electrolytes.