A Power-Law Decrease in Interfacial Resistance between Li₇La₃Zr₂O₁₂and Lithium Metal after Removing Stack Pressure

The high interfacial resistance between solid electrolytes and lithium metal is a hurdle to developing all solid-state batteries. External pressure applied on the lithium and solid electrolyte interface prior to electrochemical cycling is known to effectively lower the interfacial resistance. Here we report that the interfacial resistance between Li6.4La3Zr1.4Ta0.6O12 (LLZTO) and lithium metal decreases over time even after removing the external pressure. The irreversible decrease of interfacial resistance can be understood by a gradual reduction of the total energy of the system, including strain energy and interfacial energy. Under external pressure exceeding ∼25 MPa, however, lithium can be squeezed into LLZTO, fracturing the ceramic solid electrolyte. These observations can help improve the understanding of lithium metal creep and the interactions between garnet-type solid electrolytes and lithium metal.