In recent years, the primary concern in the electric vehicle (EV) market has been the short driving range and long charging times associated with single charges. However, the market is now facing another bottleneck due to safety issues. Lithium-ion batteries (LIBs) utilizing organic liquid electrolytes pose significant safety risks due to their low thermal stability and high fire hazard. To address this fundamental issue, there is a push to replace liquid electrolytes in current LIBs with solid-state electrolytes (SSEs). Among the materials used as electrolytes in solid-state batteries, oxide-based SSEs offer a wider potential window of 5 V or more compared to organic liquid electrolytes (<4.5 V). Their high elastic modulus and ion conductivity enable them to suppress the growth of lithium dendrites, allowing for the use of high-capacity lithium metal as the anode material. Additionally, oxide-based SSEs possess advantages such as high stability in air, high mechanical strength, and high oxidation voltage. However, they also exhibit higher interfacial resistance and lower lithium ion conductivity than sulfide-based SSEs, typically reported in the range of 10⁻³ ~ 10⁻⁴ S/cm.This study focused on enhancing the grain-boundary resistance of Li7La3Zr2O12 (LLZO) by coating its surface with Li2CO3. LLZO pellets were coated with Li2CO3 through a solution process and then sintered to form a solid-state electrolyte. X-ray diffraction (XRD) was utilized to analyze the crystal structure of the sintered LLZO pellets, while scanning electron microscopy (SEM) was used to evaluate the density of constituent elements and the surface structure. Electrochemical impedance spectroscopy (EIS) was employed to observe changes in lithium ion conductivity due to grain-boundary properties. The results demonstrated that Li2CO3-coated LLZO pellets exhibited lower grain-boundary resistance and higher lithium ion conductivity compared to uncoated LLZO pellets. Finally, all-solid-state batteries (ASSBs) were fabricated using the sintered Li2CO3-coated LLZO pellets, and their electrochemical properties were evaluated to predict improvements in battery performance due to grain-boundary properties. The findings of this study suggest that coating LLZO with Li2CO3 can significantly enhance the grain-boundary resistance and performance of all-solid-state batteries.
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