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Establishing Ultralow Activation Energies for Lithium Transport in Garnet Electrolytes.

Accepted version
Peer-reviewed

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Authors

Pesci, Federico M 
Bertei, Antonio 
Brugge, Rowena H 
Emge, Steffen P 
Hekselman, AK Ola 

Abstract

Garnet-type structured lithium ion conducting ceramics represent a promising alternative to liquid-based electrolytes for all-solid-state batteries. However, their performance is limited by their polycrystalline nature and inherent inhomogeneous current distribution due to different ion dynamics at grains, grain boundaries, and interfaces. In this study, we use a combination of electrochemical impedance spectroscopy, distribution of relaxation time analysis, and solid-state nuclear magnetic resonance (NMR), in order to understand the role that bulk, grain boundary, and interfacial processes play in the ionic transport and electrochemical performance of garnet-based cells. Variable temperature impedance analysis reveals the lowest activation energy for Li transport in the bulk of the garnet electrolyte (0.15 eV), consistent with pulsed field gradient NMR spectroscopy measurements (0.14 eV). We also show a decrease in grain boundary activation energy at temperatures below 0 °C, that is followed by the total conductivity, suggesting that the bottleneck to ionic transport resides in the grain boundaries. We reveal that the grain boundary activation energy is heavily affected by its composition that, in turn, is mainly affected by the segregation of dopants and Li. We suggest that by controlling the grain boundary composition, it would be possible to pave the way toward targeted engineering of garnet-type electrolytes and ameliorate their electrochemical performance in order to enable their use in commercial devices.

Description

Keywords

LLZO, activation energy, electrochemical impedance spectroscopy, garnet electrolytes, grain boundary, solid-state batteries, ssNMR

Journal Title

ACS Applied Materials and Interfaces

Conference Name

Journal ISSN

1944-8244
1944-8252

Volume Title

12

Publisher

American Chemical Society

Rights

All rights reserved
Sponsorship
Engineering and Physical Sciences Research Council (EP/P003532/1)
Engineering and Physical Sciences Research Council (1834544)
Engineering and Physical Sciences Research Council (EP/N032888/1)
Engineering and Physical Sciences Research Council (EP/S019367/1)
Engineering and Physical Sciences Research Council (EP/R00661X/1)