Surface Engineering of Li _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂ via Poly(ethylene glycol) Functionalization for High-Performance Poly(ethylene oxide)-Based Composite Electrolytes in All-Solid-State Lithium

In solid-state lithium-ion batteries, composite polymer-ceramic electrolytes (CPEs) of poly(ethylene oxide) (PEO) and nanosized Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particles combine polymer-like flexibility and processability with significantly enhanced ionic conductivity and electrochemical stability from the ceramic filler, forming a promising electrolyte system. However, the poor interfacial compatibility between LLZTO and PEO leads to inhomogeneous filler distribution during electrolyte preparation, compromising both interfacial stability and discharge capacity in solid-state batteries. To address this, we developed an effective modification approach involving PEG-functionalized LLZTO through ultrasonic-assisted solution processing, followed by composite electrolyte fabrication with PEO. This method significantly improves LLZTO dispersion homogeneity within the polymer matrix. The optimized CPEs demonstrate superior electrochemical performance, including high ionic conductivity (∼1.0 × 10–4 S cm–1 at 25 °C), exceptional electrochemical stability (up to 5.24 V vs Li+/Li), and excellent interfacial compatibility with lithium metal anodes. Consequently, the assembled Li//CPE//LiFePO4 all-solid-state batteries deliver a high initial discharge capacity of 147.1 mAh g–1 and outstanding cycling stability with 99.0% capacity retention after 100 cycles at 0.5C (55 °C).