An ultra-fast strategy for restoring garnet oxide electrolytes

Garnet-type solid-state electrolytes represent one of the most promising candidates for solid-state lithium-metal batteries, owing to their high ionic conductivity and excellent stability against lithium metal. However, their practical application is hindered by poor stability in ambient air, which leads to the formation of lithium carbonate (Li₂CO₃) on the surface and interior area. The resulting lithium deficiency within the electrolyte structure causes a significant decline in ionic conductivity and an increase in interfacial resistance, thereby severely impairing electrochemical performance. Conventional regeneration approaches, such as mechanical polishing and thermal annealing, face many limitations. The former often fails to achieve complete removal of Li₂CO₃, while the latter, especially under prolonged high-temperature conditions, aggravates lithium loss and compromises densification. These issues collectively lead to inferior ionic transport and poor interfacial properties. Thus, it is imperative to develop a safe, efficient, and economically feasible processing technique capable of thoroughly eliminating Li₂CO₃ while preserving the structural and electrochemical integrity of garnet electrolytes.

Recently, a team led by Wei Liu from Shanghaitech University, China first reported the rapid rejuvenation process which combined the immersion of LiOH solution and the ultra-fast high-temperature sintering (UHS) process towards the instability issue of LLZTO. This work not only shows the improved electrochemical properties after the rapid rejuvenation process, but also clarify the role of LiOH and the annealing of UHS.

The team published their work in Journal of Advanced Ceramics on November 11, 2025.

“In our work, we report a rapid method for restoring the stored Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) solid electrolytes through pre-immersing into LiOH solution followed by UHS. After long-time storage, the formation of Li₂CO₃ at surface and interior due to Li⁺/H⁺ ion exchange could lead to severe Li loss and high interface impedance between LLZTO and electrode. However, the pre-immersed LiOH could melt and evaporate into the surface and interior of the LLZTO uniformly, achieving rapid compensation for lithium loss and rapid improvement on grain size, which serves as sintering aids and supplemental source of lithium.” said Wei Liu, professor at Shanghaitech University, (China) an expert whose research direction includes all-solid-state batteries, electrochromic devices and ionic membranes.

In this work, the author describes the role of LiOH explicitly, together with the Li₂CO₃ layer at surfaces of LLZTO. “First, the Li₂CO₃ layer at surfaces of LLZTO could react with protonated LLZTO under high temperature; second, the addition of LiOH or Li₂CO₃ can serve as sintering aids and supplemental source of lithium. Specifically, the addition of LiOH or Li₂CO₃ can eliminate the residual pores through the formation of glassy like phases along the grain boundary of LLZTO after the decomposition into Li₂O as sintering aids; moreover, they can help suppress the transition from LLZO garnet phase to La₂Zr₂O₇ phase due to Li losses during the annealing process, as well as the promotion of reaction between different Li salts and protonated LLZO.” said Wei Liu.

Recovered-LLZTO exhibits a higher ionic conductivity of 4.08×10^-4 S cm^-1, compared with stored-LLZTO of 0.32×10^-4 S cm^-1. After the rapid restoration process, longer cycling life of over 360 hours and higher CCD of 0.52 mA cm^-2 is achieved for Li symmetric cells with recovered LLZTO. In addition, Li|LLZTO|NCM half cells demonstrated a higher specific capacity of 180 mAh g^-1 at 0.1 C and 130 mAh g^-1 at 1 C than stored ones, together with its highest capacity and capacity retention during long cycle test for half cells with recovered LLZTO pellets

“As a result, Li₂CO₃ at surface and in the interior of stored-LLZTO pellets were eliminated and the process of grain growth is promoted at the same time which could improve ionic conductivity, reduce electronic conductivity and restrain lithium dendrite penetration in LLZTO. Recovered-LLZTO exhibits a higher ionic conductivity of 4.08×10^-4 S cm^-1, compared with stored-LLZTO of 0.32×10^-4 S cm^-1. After the rapid restoration process, longer cycling life of over 360 hours and higher CCD of 0.52 mA cm^-2 is achieved. In addition, Li|LLZTO|NCM half cells demonstrated a higher specific capacity of 180 mAh g^-1 at 0.1 C and 130 mAh g^-1 at 1 C than stored ones, together with its highest capacity with the value of 180 mAh g^-1 and capacity retention with the number of 95.6% during long cycle test for 100 cycles of Li|NCM half cells with recovered LLZTO pellets. “The rapid restoration method was an effective way to recover garnet electrolytes after long-time storage for solid-state lithium-metal batteries.” said Wei Liu.

However, further works are still in need to figure out the best recipe of rapid rejuvenation process. In this regard, Wei Liu als put forward three issues to be considered in future works including the ratio of lithium salts to LLZTO pellets, the reaction rate of lithium salts into LiOH or Li₂O and the parameters of UHS process.                                                                                 

Other contributors include Chang Zhang, Tianyi Gao, Jinjiang Liang, Jiameng Yu, and Luyao Wang. from Shanghaitech University in Shanghai, China.

This work was supported by the National Natural Science Foundation of China (92472119, 52222311), the Natural Science Foundation of Shanghai (24ZR1451200), and Development Fund for Schools of ShanghaiTech University. The authors would like to thank for the microscopy experiments supported by the Center for High-resolution Electron Microscopy (CћEM) at ShanghaiTech University.

About Author

Dr. Wei Liu is a professor in Shanghaitech University. She received her PhD degree in Material Science and Engineering from Tsinghua University in 2013. She conducted her postdoctoral research at Professor Yi Cui’s group in Standford University. Her work explores the applications of solid-state ionic conductors, nanomaterials, and ceramic composites in energy storage and environmental fields, with specific interests in all-solid-state batteries, electrochromic devices, ionic membranes, and flexible materials.

Mr Jiahao Feng is a master’s student in Shanghaitech University. His research focuses on developing and improving garnet oxide electrolytes.

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2024 IF is 16.6, ranking in Top 1 (1/33, Q1) among all journals in “Materials Science, Ceramics” category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508