Localized Overlimiting Ion Polarization Preceding Metal Penetration in Lithium-Ion Conducting Electrolytes

Next-generation high-energy batteries require rechargeable metal anodes, but hazardous dendrites tend to form during recharging, causing short-circuit risk and capacity loss, even with hard and stiff ceramic electrolytes, by mechanisms that still remain elusive. In this presentation, we will first demonstrate a rigorous analysis of the lithium dendrite formation in liquid electrolytes, through the intimate combination of operando experiments and transport models. Our results demonstrated the necessity to differentiate Li whiskers from Li dendrites, induced by different physical processes. Resolving the interfacial instability and metal whiskers led to an ideally smooth, non-porous, ingot-type Na metal plating, which enabled the anode-free Na metal full cells with a record-high retention rate of 99.93% per cycle at 3C charge and discharge. Novel electrochemical tests of garnet-type cubic Li_7-xLa₃Zr_2-xTa_xO₁₂ ceramic electrolytes confirmed a similar overlimiting ion polarization and dendrite initiation mechanism mainly through grain boundaries. Our theoretical and experimental discoveries suggest that both liquid and solid electrolytes follow a similar ion polarization process before the onset of localized metal penetration. The success of alkali metal batteries relies on the rational control of both the interfacial kinetics and the bulk ion transport.