Stoichiometric irreversibility of aged garnet electrolytes

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 (similar to 10(-3) S cm(-2)) at room temperature and high stability with Li metal anode. However, the storage of doped LLZO in the ambient condition suffers the aging effect, including the structural transition (i.e. lowtemperature cubic form) and the stoichiometric changes (i.e. Li2CO3). These changes are detrimental to 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 an insitu synchrotron-based high-energy X-ray diffraction technique, our experiments revealed that the LLZO powders became a low-temperature cubic phase when exposed to the ambient condition for an extended period of time. A high temperature cubic form can be restored after a thermal treatment of the aged LLZO powder, regardless of the type of dopant. However, the restoration of the stoichiometry remained a challenge, and the degree of the restoration showed a clear dependence on the dopant chemistry. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Solid-state lithium batteries with solid-state electrolytes and lithium metal anodes offer higher energy density and safety. The aging effect of doped LLZO in ambient conditions affects its ionic conductivity and interfacial stability. Thermal treatment can restore the high-temperature cubic form of LLZO, but the restoration of stoichiometry depends on the dopant chemistry.