Effect of Li super(+)/H super(+) exchange in water treated Ta-doped Li sub(7)La sub(3)Zr sub(2)O sub(12)

While aliovalently doped Li sub(7)La sub(3)Zr sub(2)O sub(12) (LLZ) is stable against metallic lithium, lithium ions can be exchanged by protons under air humidity or immersion in water, which poses a concern for applications of solid electrolyte. In this work, the chemical stability as well as the...

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Bibliographic Details
Published in:Solid state ionics 2016-09, Vol.292, p.122-129
Main Authors: Yow, Zhen Feng, Oh, Yuan Liang, Gu, Wenyi, Rao, Rayavarapu Prasada, Adams, Stefan
Format: Article
Language:English
Subjects:
Exchange
Immersion
Ion exchange
Lithium
Molecular dynamics
Simulation
Solid electrolytes
Tantalum
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Summary:While aliovalently doped Li sub(7)La sub(3)Zr sub(2)O sub(12) (LLZ) is stable against metallic lithium, lithium ions can be exchanged by protons under air humidity or immersion in water, which poses a concern for applications of solid electrolyte. In this work, the chemical stability as well as the ionic conductivity of Ta-doped Li sub(6.6)La sub(3)Zr sub(1.6)Ta sub(0.4)O sub(12) pellet and powder samples after immersion in water were thoroughly studied. The percentage of Li super(+)/H super(+) exchange in LLZ is assessed from thermogravimetric analysis. In the powder samples the compositions quickly approaches Li sub(3)H sub(3.6)La sub(3)Zr sub(1.6)Ta sub(0 .4)O sub(12), while for the pelletized sample only the surface layer exhibits a similarly pronounced proton exchange. Lattice parameters of Ta-doped LLZ were found to increase after water treatment in accordance to literature data and our molecular dynamics (MD) simulations of LLZ. MD simulations clarify the proton distribution and suggest that for minor levels of proton exchange as in Li sub(6.5)H sub(0.5)La sub(3)Zr sub(2)O sub(12 ) the hardly affected lithium ion mobility dominates over the proton mobility, while for compositions Li sub(3)H sub(4)La sub(3)Zr sub(2)O sub(12) corresponding to the equilibrated powder samples the material becomes essentially a proton conductor with higher activation energy and lower room temperature than for Li super(+) ion conductivity in H super(+)-free cubic LLZ. A reduced extent and retarded kinetics of the Li super(+)/H super(+) exchange is demonstrated by immersion in LiOH solutions. Hence, despite the ion exchange, doped LLZ solid electrolytes appear to be suitable as anode-protecting membranes in Li-air batteries with sufficiently basic catholytes.
ISSN:0167-2738
DOI:10.1016/j.ssi.2016.05.016