Publication date: 15th December 2025
This work investigates the liquid-phase-assisted densification and interfacial stabilization of Li6.6La3Zr1.6Ta0.4O12 (LLZTO) garnet electrolytes through borate glass modification. Borate glasses with tailored Li:B ratios are synthesized to achieve the Li3BO4 stoichiometry and mixed with LLZTO powders in various proportions. X-ray diffraction and microscopy reveal that molten borate glass extracts lithium from LLZTO at the initial sintering stage, forming La2Zr2O7, while prolonged heating promotes lithium re-incorporation and restores the cubic structure through a self-healing mechanism. The resulting composites achieve full densification at 950 °C—nearly 400 °C lower than conventional solid-state sintering. SEM observations confirm the presence of amorphous intergranular films that enhance particle rearrangement and suppress abnormal grain growth. High-temperature microscopy demonstrates a distinct shrinkage transition associated with glass softening, validating the liquid-phase densification mechanism. Electronic conductivity measurements show values in the 10-9–10-8 S cm⁻¹ range, confirming excellent electronic insulation. Electrochemical impedance and DRT analyses reveal reduced interfacial resistance and faster relaxation dynamics at the Li⁰ interface, indicating improved lithium wettability. Overall, borate-glass incorporation provides a controllable route to low-temperature sintering, microstructural reconstruction, and enhanced interfacial stability in garnet-type solid electrolytes.
The authors gratefully acknowledge financial support from the by the ELISA project (ref. CNS2023-145494), funded by MCIN/AEI/10.13039/501100011033 and by the European Union “NextGenerationEU”/PRTR. Additional support was provided by projects 2024ICT207, 20226AT009 and COOPB23103 of the CSIC. The authors also wish to thank Pamela Vargas, Sara Serena Palomares, Cristina Ruiz Santa Quiteria Gomez, and María José Velasco Manjón from ICV-CSIC, Spain, for their invaluable assistance with the XRD, HTM, and ICP-XRF measurements. Their technical expertise and support in operating the equipment were essential to the success of this research.
Xinhao Yang acknowledges financial support from the China Scholarship Council (CSC, Grant No. 202508390003).
The authors thank the Research Support Services of the University of Extremadura (SACSS-SAIUEx)
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