Defect Engineering Offers New Routes to Air-Stable Garnet LLZO Solid Electrolytes

Garnet-type LLZO solid electrolytes are widely regarded as key materials for high-energy-density all-solid-state lithium batteries, thanks to their high ionic conductivity, wide electrochemical stability window, and stability against lithium metal. Yet a persistent weakness has held back their practical deployment: when exposed to air, LLZO undergoes Li+/H+ exchange that generates a contaminant layer of LiOH and Li2CO3 on its surface. This layer raises interfacial impedance and degrades ion transport, severely constraining the material’s use in real devices.

A new review published in the journal Ionics takes stock of how researchers are tackling this air-stability bottleneck, and highlights a decisive shift in strategy. According to the review, the research perspective has moved away from the passive removal of surface contaminants after they form, toward the active modulation of the material’s intrinsic stability. In other words, rather than cleaning up the damage, scientists are now redesigning the material itself so the degradation reactions are less likely to occur in the first place.

The review, authored by Tingting Zhao, Yichuan Zhang, Yiwei Deng, Daoxin Wu, Xingli Xiao, Jia Chou, Yinjie Kuang, Liubin Song and Xue Wen, frames this progress through the lens of defect engineering. It organizes the field into two main routes. The first is surface delithiation modulation, in which acid treatment or thermal treatment is used to construct a lithium-depleted layer near the LLZO surface. By modulating the surface lithium chemical potential, this depleted layer helps suppress the regeneration of the degradation reactions that produce the LiOH/Li2CO3 contaminant layer.

The second route is bulk vacancy modulation, which works deeper in the material. Here, controllable lithium vacancies are introduced into the LLZO lattice through aliovalent cation doping, co-doping, and anion doping. The review states that this approach enhances the intrinsic air stability of the material at the thermodynamic level, addressing the problem within the crystal structure itself rather than only at the surface.

The authors also take a critical look at the limitations of these strategies. They analyze shortcomings in terms of protective depth, treatment conditions, and applicability to powders, acknowledging that current defect-engineering methods do not yet fully resolve the air-stability problem across all forms of the material. The review closes with an outlook on future research directions, aiming to offer theoretical reference and feasible pathways for overcoming the air stability bottleneck of LLZO. As a review article, the work summarizes and synthesizes existing research progress rather than presenting new experimental results, but its systematic framing of surface and bulk defect strategies provides a consolidated map of where the field stands and where it may go next.

Subject of Research: Defect engineering strategies for improving the air stability of garnet-type LLZO solid electrolytes

Article Title: Defect engineering for modulating the air stability of garnet-type LLZO solid electrolytes: Mechanisms and strategies

Article References: Zhao, T., Zhang, Y., Deng, Y., Wu, D., Xiao, X., Chou, J., Kuang, Y., Song, L., & Wen, X. (2026). Defect engineering for modulating the air stability of garnet-type LLZO solid electrolytes: Mechanisms and strategies. Ionics. https://doi.org/10.1007/s11581-026-07596-8

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07596-8

Keywords: LLZO, solid electrolytes, garnet, defect engineering, air stability, lithium vacancies, aliovalent doping, surface delithiation, all-solid-state lithium batteries, Li+/H+ exchange, interfacial impedance, review