Green Strategy for Li₂CO₃ Regulation in Garnet-Type Solid-State Electrolytes via Acoustic Cavitation

Garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZTO) holds significant potential as a solid-state electrolyte (SSE) comprising promising features such as high Li+ conductivity, wide electrochemical stability window, and compatibility with Li-metal. However, air exposure forms a thick Li2CO3 passivation layer (∼50 nm), which hinders storage, handling, and interfacial performance, especially for LLZTO nanoparticles (NPs) with a high surface area. This study introduces a scalable, green sonication-assisted method to control the Li2CO3 layer thickness (<10 nm), which enhances air stability without compromising ionic conduction. In-situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) further reveals the carbonate formation mechanism under atmospheric conditions. Electrochemical tests in ceramic-in-polymer (CIP) and polymer-in-ceramic (PIC) composite polymer electrolytes (CPEs) confirm that regulated Li2CO3 does not degrade the performance of passivated-LLZTO. The chemical-free, green approach suggested in this work maintains electrochemical properties, which enables scalable use of LLZTO-based SSEs for next-generation Li-metal batteries.