Stoichiometric Irreversibility of Aged Garnet Electrolytes

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Solid-state lithium batteries (SSLBs) have been regarded as one of the next-generation energy storage systems. With the adoption of solid-state electrolytes (SSEs) and lithium metal anodes, SSLBs enable higher energy density and more reliable safety than the state-of-the-art lithium-ion batteries. Among potential SSEs, the cation-doped Li7La3Zr2O12 (LLZO) is promising for its high ionic conductivity (~10-3 S cm-2) at room temperature and high stability with Li metal anode. However, the storage of doped LLZO under ambient condition suffers the severe aging effects, including the structural transition (i.e. low-temperature cubic form) and the stoichiometric changes (i.e. Li2CO3). These changes are detrimental for LLZO ionic conductivity and interfacial stability in SSLBs. To this end, we are motivated to investigate the structural and stoichiometric reversibility of aged LLZO during thermal treatment. With the help of in-situ synchrotron-based high-energy X-ray diffraction technique, our experiments revealed that the high temperature cubic form can be restored after a thermal treatment of the aged LLZO powder. However, the restoration of the stoichiometry remained a challenge, and the degree of the stoichiometric restoration showed a strong dependence on the dopant chemistry. This study provides a key understanding on the restoration of aged LLZO and aims to enhance the development of LLZO in solid-state lithium batteries. Figure 1