Germanium as a donor dopant in garnet electrolytes
File(s)
Accepted version
Author(s)
Brugge, RH
Kilner, JA
Aguadero, A
Type
Journal Article
Abstract
Cubic Li 7 La 3 Zr 2 O 12 (LLZO) garnet electrolytes continue to be viewed as an enabler of all-solid-state lithium battery technologies, or as protective membranes for next-generation lithium battery systems. Supervalent dopants at the lithium sublattice are commonly used to stabilise the conductive cubic phase, through the creation of lithium vacancies. The use of germanium (Ge 4+ ) as a higher valent dopant substituting for Li + was studied here and shown to stabilise the cubic LLZO phase through substitution of x = 0.10 mol of Ge (at the tetrahedral 24d Li sites of the space group Ia-3d, based on the neutron powder diffraction result). This substitution preference follows that of Al 3+ (having a similar ionic radius and reported to reside at 24d sites), but with a lower critical concentration for cubic phase stabilisation, in agreement with charge neutrality arguments to obtain the required Li content (ca. 6.4–6.6 per formula unit) for optimum conductivity. The x = 0.10 composition gave the highest bulk Li ion conductivity of 2.8 × 10 −4 S cm −1 at 25 °C, on the order of reported values for Al-doped LLZO. Surface chemical analysis using time of flight secondary ion mass spectrometry showed Ge homogeneously distributed within the grains as well as some Li-, O- and Ge- enrichment along the grain boundaries. Cyclic voltammetry of the cells containing Ge-doped LLZO showed a redox stability up to +5 V.
Date Issued
2019-09-01
Date Acceptance
2019-04-22
Citation
Solid State Ionics, 2019, 337, pp.154-160
ISSN
0167-2738
Publisher
Elsevier
Start Page
154
End Page
160
Journal / Book Title
Solid State Ionics
Volume
337
Copyright Statement
© 2019 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/
Sponsor
Engineering & Physical Science Research Council (E
Grant Number
EP/R024006/1
Subjects
Energy
0204 Condensed Matter Physics
0306 Physical Chemistry (incl. Structural)
0912 Materials Engineering
Publication Status
Published
Date Publish Online
2019-05-01