Influence of ultrashort-pulse laser-induced melt formation on the electrochemical performance of garnet-type solid electrolytes for solid-state batteries

Solid-state batteries promise higher safety and energy density than conventional lithium-ion batteries, positioning them as a key technology for next-generation energy storage systems. The garnet-type solid electrolyte lithium lanthanum zirconium oxide (LLZO) is among the most promising electrolytes for solid-state batteries. However, long-term operation requires a stable interface between the LLZO and the active materials, motivating targeted interfacial engineering. Ultrashort-pulsed laser ablation enables precise and flexible surface modification. However, it can also induce localized melting, increasing the risk of lithium loss and decomposition of the cubic LLZO phase, which is essential for high ionic conductivity. In this study, laser processing parameters were systematically varied to induce different regimes of melt formation on the LLZO surface, and the resulting effects on structure, interfacial stability, and mechanical integrity were investigated. Raman spectroscopy revealed that even pronounced laser-induced melting did not result in detectable phase changes within the bulk material. In symmetric lithium metal cells, an improved interfacial contact was observed for all laser-treated samples, while a pronounced increase in the critical current density occurred only for moderate melt residues compared to untreated reference samples. In contrast, excessive melting resulted in a reduced critical current density and diminished mechanical stability of the solid electrolyte. These findings highlight the existence of a processing regime in which controlled melt formation enhances the interfacial stability without compromising the structural integrity of the LLZO.