Improvement of Ambient Stability and Conductivity of Amorphous Li–La–Zr–O–F Solid Electrolyte through Diversified Utilization of LiF

Abstract

The primary challenge in the development of solid-state electrolytes (SSEs) lies in achieving competitive ionic conductivity with liquid-based electrolytes, while retaining their inherent advantages. Among various SSEs, garnet-type oxide Li7La3Zr2O12(LLZO) stands out due to its high ionic conductivity (∼10–4S/cm) and chemical/electrochemical stability against Li metal, making it a promising candidate. However, polycrystalline cubic-LLZO, possessing a large grain-boundary volume, easily suffers from the fatal flaws of Li-dendrite penetration and battery short circuits. Furthermore, conventional high-temperature sintering conditions (>1000 °C) lead to lithium loss, which often requires a material-wasting approach, such as using a sacrificial mother powder batch, to compensate. Importantly, LLZO is sensitive to H2O and CO2in ambient conditions, which leads to the thickening of Li2CO3, increasing interfacial resistance between the electrode and LLZO. Here, we propose an amorphous Li–La–Zr–O–F thin film to tackle these two issues of Li loss and Li2CO3formation. Significantly, LiF serves multiple roles: it provides supplemental Li, acts as an F dopant after post-annealing, and functions as a protective layer against Li2CO3submersion inside LLZO. Our perspective offers an innovative strategy to address the issues of Li2CO3formation and Li loss while simultaneously achieving a significant improvement in ionic conductivity, which can be extended to other oxide-based SSEs.