Dual-Doped Cubic Garnet Solid Electrolytes with Superior Air Stability

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 Li6.05La3Ga0.3Zr1.95Nb0.05O12 ((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 (Li7La2.75Ca0.25Zr1.75Nb0.25O12, (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.

Air‐stable inorganic solid‐state electrolytes for high energy density lithium batteries: Challenges, strategies, and prospects

“…Adams et al 84 4H). 87 Therefore, elemental doping is an effective strategy for garnet-based solid electrolytes to achieve impressive air stability and low interfacial resistance. 87 In addition to elemental doping, coating a protective layer is also a good choice.…”

“…87 Therefore, elemental doping is an effective strategy for garnet-based solid electrolytes to achieve impressive air stability and low interfacial resistance. 87 In addition to elemental doping, coating a protective layer is also a good choice. Guo et al 88 put forward a significant method in which contaminants (Li 2 CO 3 and LiOH) were consumed through a reaction with functional additives, forming a fluorinated nanocoating layer around the garnet particles.…”

“…86 Copyright 2020, Electrochemical Society) and (Ga, Nb) LLZO (H) (Reproduced with permission. 87 Copyright 2020, American Chemical Society) symmetric Li cell under a large current density of 1.0 mA cm À2 . 92 Adding additives is also an efficient way of inhibiting side reactions with air.…”

“…Copyright 2009, Elsevier); XRD pattern of some days for Al(0.2)/Mg(0.1) co‐doped LLZO sintered pellet (G) (Reproduced with permission 86 . Copyright 2020, Electrochemical Society) and (Ga, Nb) LLZO (H) (Reproduced with permission 87 . Copyright 2020, American Chemical Society)…”

The effect of two different substituted atoms in lithium positions on the structure of garnet-type solid electrolytes

“…It is reported in the literature that the existence of Al 3+ on the Li + sites helps to get a dense LLZO structure [10]. Furthermore, with different co-doped elements such as Ba-Ta [12], Y-Sb [13], Al-Mn [14], Ga-Nb [15], Al-Ga [16], it has been approved that although doping has a very important contribution to Li + ion dynamics, the interaction of different substituted atoms with each other have a great effect on the properties of the final product. Since the Ga doping provides a high conductivity, Ga was preferred in this study.…”