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Elucidating the role of dopants in the critical current density for dendrite formation in garnet electrolytes

Garnet-type solid electrolytes have attracted great interest in solid state battery research thanks to their high ionic conductivity at room temperature (10 −3 S cm −1 ) and their electrochemical stability against lithium metal anodes. However, the formation of lithium dendrites following charge/dis...

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Bibliographic Details
Published in:Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2018, Vol.6 (40), p.19817-19827
Main Authors: Pesci, Federico M., Brugge, Rowena H., Hekselman, A. K. Ola, Cavallaro, Andrea, Chater, Richard J., Aguadero, Ainara
Format: Article
Language:English
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Summary:Garnet-type solid electrolytes have attracted great interest in solid state battery research thanks to their high ionic conductivity at room temperature (10 −3 S cm −1 ) and their electrochemical stability against lithium metal anodes. However, the formation of lithium dendrites following charge/discharge limits their applicability and commercialisation. Although widely investigated, no clear explanation of dendrite formation has been previously reported. In this work, we employ cubic Al- and Ga-doped Li 7 La 3 Zr 2 O 12 , which represent two of the solid electrolytes with higher technological importance, to investigate the formation and chemical composition of dendrites. For the first time, this study elucidates the role that the dopants play in determining the critical current density for dendrite formation and highlights the importance of controlling the dopant distribution in the garnet structure. We use a combination of techniques including Secondary Electron Microscopy and Secondary Ion Mass Spectrometry in order to analyse the microstructure and chemical composition of dendrites in Li 7 La 3 Zr 2 O 12 . We show that, following electrochemical cycling, Li 6.55 Ga 0.15 La 3 Zr 2 O 12 systematically displays a critical current density 60% higher than Li 6.55 Al 0.15 La 3 Zr 2 O 12 . Chemical analysis revealed that in Li 6.55 Al 0.15 La 3 Zr 2 O 12 the dendritic features are composed of a mixture of Al and Li species, whereas in Li 6.55 Ga 0.15 La 3 Zr 2 O 12 they are uniquely composed of Li. We also show that only in pristine Li 6.55 Al 0.15 La 3 Zr 2 O 12 , the dopant segregates at the grain boundaries suggesting that local chemical inhomogeneity can have a fundamental role in the nucleation and propagation of dendrites.
ISSN:2050-7488
2050-7496
DOI:10.1039/C8TA08366E