Acoustic Cavitation Engineering of LLZTO-Coated Separators for Moisture-Resistant Lithium Metal Batteries

Abstract

Acoustic cavitation is an effective surface reconstruction strategy to overcome the intrinsic moisture sensitivity, carbonate contamination, and dispersion limitations of garnet-type LLZTO nanoparticles used in separator engineering for lithium-metal batteries. Through microbubble collapse-induced shock waves and microjets, cavitation partially removes the Li₂CO₃ shell to produce a thin, Li-deficient passivation layer while reducing particle agglomeration and enhancing surface charge. These physicochemical improvements enable the formation of a uniform, conformal LLZTO coating on polypropylene (PP) separators via a scalable, water-based process.The resulting PP-S-LLZTO separator exhibits markedly improved wettability, porosity, electrolyte uptake, and ionic transport and achieves an ionic conductivity of 1.43 mS cm^⁻1 , a widened electrochemical stability window of 5.6 V, and a Li⁺ transference number of 0.56. When implemented in Li∥Li symmetric cells, PP-S-LLZTO enables stable cycling for 800 h with suppressed polarization. By contrast, full cells exhibit high-rate capability and 92.7% capacity retention after 100 cycles at 1C. Mechanistic analysis reveals that the reconstructed LLZTO establishes homogeneous Li-ion flux pathways, mitigates interfacial impedance growth, and promotes uniform lithium nucleation. These results demonstrate that acoustic cavitation engineering provides a robust, scalable approach for separator modification and offers a practical route toward durable, high-performance lithium-metal batteries.