Dual-Doped Cubic Garnet Solid Electrolytes with Superior Air Stability

Ljalem Hadush Abrha; Tesfaye Teka Hagos; Yosef Nikodimos; Hailemariam Kassa Bezabh; Gebregziabher Brhane Berhe; Teklay Mezgebe Hagos; Chen-Jui Huang; Wodaje Addis Tegegne; Shi-Kai Jiang; Haile Hisho Weldeyohannes; She-Huang Wu; Wei-Nien Su; Bing Joe Hwang

doi:10.1021/acsami.0c01289

Dual-Doped Cubic Garnet Solid Electrolytes with Superior Air Stability

ACS Appl Mater Interfaces. 2020 Jun 10;12(23):25709-25717. doi: 10.1021/acsami.0c01289. Epub 2020 Jun 1.

Authors

Affiliations

¹ Nano-electrochemistry Laboratory, Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan.
² Nano-electrochemistry Laboratory, Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan.
³ Applied Research Center for Thin-Film Metallic Glass, National Taiwan University of Science and Technology, Taipei 106, Taiwan.
⁴ National Synchrotron Radiation Research Center (NSRRC), Hsin-Chu 30076, Taiwan.
⁵ Sustainable Energy Development Center, National Taiwan University of Science and Technology, Taipei 106, Taiwan.

PMID: 32407073
DOI: 10.1021/acsami.0c01289

Abstract

Li₇La₃Zr₂O₁₂ (LLZO) garnet is one kind of solid electrolyte drawing extensive attention due to its good ionic conductivity, safety, and stability toward lithium metal anodes. However, the stability problem during synthesis and storage results in high interfacial resistance and prevents it from practical applications. We synthesized air-stable dual-doped Li_6.05La₃Ga_0.3Zr_1.95Nb_0.05O₁₂ ((Ga, Nb)-LLZO) cubic-phase garnets with ionic conductivity of 9.28 × 10^-3 S cm^-1. The impurity-phase species formation on the garnet pellets after air exposure was investigated. LiOH and Li₂CO₃ can be observed on the garnet pellets by Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) once the garnets are exposed to humid air or come in contact with water. The (Ga, Nb)-LLZO garnet is found to form less LiOH and Li₂CO₃, which can be further reduced or removed after drying treatment. To confirm the stability of the garnet, an electrochemical test of the Li//Li symmetric cell was also performed in comparison with previously reported garnets (Li₇La_2.75Ca_0.25Zr_1.75Nb_0.25O₁₂, (Ca, Nb)-LLZO). The dual-doped (Ga, Nb)-LLZO showed less polarized and stable plating/stripping behavior than (Ca, Nb)-LLZO. Through Rietveld refinement of XRD patterns of prepared materials, dopant Ga was found to preferably occupy the Li site and Nb takes the Zr site, while dopant Ca mainly substituted La in the reference sample. The inherited properties of the dopants in (Ga, Nb)-LLZO and their structural synergy explain the greatly improved air stability and reduced interfacial resistance. This may open a new direction to realize garnet-based solid electrolytes with lower interfacial resistance and superior air stability.

Keywords: air stability; dual-doped cubic garnet; interfacial resistance; ionic conductivity; morphology; stable Li plating/stripping.