Conductor−Insulator Interfaces in Solid Electrolytes: A Design Strategy to Enhance Li-Ion Dynamics in Nanoconfined LiBH4/Al2O3

Roman Zettl; Katharina Hogrefe; Bernhard Gadermaier; Ilie Hanzu; Peter Ngene; Petra E. De Jongh; H. Martin R. Wilkening

doi:10.1021/acs.jpcc.1c03789

Conductor−Insulator Interfaces in Solid Electrolytes: A Design Strategy to Enhance Li-Ion Dynamics in Nanoconfined LiBH₄/Al₂O₃

Roman Zettl, Katharina Hogrefe, Bernhard Gadermaier, Ilie Hanzu, Peter Ngene, Petra E. De Jongh, H. Martin R. Wilkening^*

^*Corresponding author for this work

Institute for Chemistry and Technology of Materials (6380)

Research output: Contribution to journal › Article › peer-review

Abstract

Synthesizing Li-ion-conducting solid electrolytes
with application-relevant properties for new energy storage devices
is a challenging task that relies on a few design principles to tune
ionic conductivity. When starting with originally poor ionic
compounds, in many cases, a combination of several strategies,
such as doping or substitution, is needed to achieve sufficiently
high ionic conductivities. For nanostructured materials, the
introduction of conductor−insulator interfacial regions represents
another important design strategy. Unfortunately, for most of the
two-phase nanostructured ceramics studied so far, the lower
limiting conductivity values needed for applications could not be
reached. Here, we show that in nanoconfined LiBH4/Al2O3prepared by melt infiltration, a percolating network of fast
conductor−insulator Li+ diffusion pathways could be realized. These heterocontacts provide regions with extremely rapid 7Li
NMR spin fluctuations giving direct evidence for very fast Li+ jump processes in both nanoconfined LiBH4/Al2O3 and LiBH4-LiI/
Al2O3. Compared to the nanocrystalline, Al2O3-free reference system LiBH4-LiI, nanoconfinement leads to a strongly enhanced
recovery of the 7Li NMR longitudinal magnetization. The fact that almost no difference is seen between LiBH4-LiI/Al2O3 and
LiBH4/Al2O3 unequivocally reveals that the overall 7Li NMR spin-lattice relaxation rates are solely controlled by the spin
fluctuations near or in the conductor−insulator interfacial regions. Thus, the conductor−insulator nanoeffect, which in the ideal case
relies on a percolation network of space charge regions, is independent of the choice of the bulk crystal structure of LiBH4, either
being orthorhombic (LiBH4/Al2O3) or hexagonal (LiBH4-LiI/Al2O3). 7Li (and 1H) NMR shows that rapid local interfacial Li-ion
dynamics is corroborated by rather small activation energies on the order of only 0.1 eV. In addition, the LiI-stabilized layer-
structured form of LiBH4 guarantees fast two-dimensional (2D) bulk ion dynamics and contributes to facilitating fast long-range ion
transport.

Original language	English
Pages (from-to)	15052−15060
Number of pages	9
Journal	The Journal of Physical Chemistry C
Volume	125
Issue number	27
DOIs	https://doi.org/10.1021/acs.jpcc.1c03789
Publication status	Published - 15 Jul 2021

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
General Energy
Surfaces, Coatings and Films
Physical and Theoretical Chemistry

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Cite this

@article{8c4b801f88e5441e849ed95e2e5d3d0e,

title = "Conductor−Insulator Interfaces in Solid Electrolytes: A Design Strategy to Enhance Li-Ion Dynamics in Nanoconfined LiBH4/Al2O3",

abstract = "Synthesizing Li-ion-conducting solid electrolyteswith application-relevant properties for new energy storage devicesis a challenging task that relies on a few design principles to tuneionic conductivity. When starting with originally poor ioniccompounds, in many cases, a combination of several strategies,such as doping or substitution, is needed to achieve sufficientlyhigh ionic conductivities. For nanostructured materials, theintroduction of conductor−insulator interfacial regions representsanother important design strategy. Unfortunately, for most of thetwo-phase nanostructured ceramics studied so far, the lowerlimiting conductivity values needed for applications could not bereached. Here, we show that in nanoconfined LiBH4/Al2O3prepared by melt infiltration, a percolating network of fastconductor−insulator Li+ diffusion pathways could be realized. These heterocontacts provide regions with extremely rapid 7LiNMR spin fluctuations giving direct evidence for very fast Li+ jump processes in both nanoconfined LiBH4/Al2O3 and LiBH4-LiI/Al2O3. Compared to the nanocrystalline, Al2O3-free reference system LiBH4-LiI, nanoconfinement leads to a strongly enhancedrecovery of the 7Li NMR longitudinal magnetization. The fact that almost no difference is seen between LiBH4-LiI/Al2O3 andLiBH4/Al2O3 unequivocally reveals that the overall 7Li NMR spin-lattice relaxation rates are solely controlled by the spinfluctuations near or in the conductor−insulator interfacial regions. Thus, the conductor−insulator nanoeffect, which in the ideal caserelies on a percolation network of space charge regions, is independent of the choice of the bulk crystal structure of LiBH4, eitherbeing orthorhombic (LiBH4/Al2O3) or hexagonal (LiBH4-LiI/Al2O3). 7Li (and 1H) NMR shows that rapid local interfacial Li-iondynamics is corroborated by rather small activation energies on the order of only 0.1 eV. In addition, the LiI-stabilized layer-structured form of LiBH4 guarantees fast two-dimensional (2D) bulk ion dynamics and contributes to facilitating fast long-range iontransport.",

author = "Roman Zettl and Katharina Hogrefe and Bernhard Gadermaier and Ilie Hanzu and Peter Ngene and {De Jongh}, {Petra E.} and Wilkening, {H. Martin R.}",

year = "2021",

month = jul,

day = "15",

doi = "10.1021/acs.jpcc.1c03789",

language = "English",

volume = "125",

pages = "15052−15060",

journal = "The Journal of Physical Chemistry C",

issn = "1932-7447",

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T1 - Conductor−Insulator Interfaces in Solid Electrolytes: A Design Strategy to Enhance Li-Ion Dynamics in Nanoconfined LiBH4/Al2O3

AU - Zettl, Roman

AU - Hogrefe, Katharina

AU - Gadermaier, Bernhard

AU - Hanzu, Ilie

AU - Ngene, Peter

AU - De Jongh, Petra E.

AU - Wilkening, H. Martin R.

PY - 2021/7/15

Y1 - 2021/7/15

N2 - Synthesizing Li-ion-conducting solid electrolyteswith application-relevant properties for new energy storage devicesis a challenging task that relies on a few design principles to tuneionic conductivity. When starting with originally poor ioniccompounds, in many cases, a combination of several strategies,such as doping or substitution, is needed to achieve sufficientlyhigh ionic conductivities. For nanostructured materials, theintroduction of conductor−insulator interfacial regions representsanother important design strategy. Unfortunately, for most of thetwo-phase nanostructured ceramics studied so far, the lowerlimiting conductivity values needed for applications could not bereached. Here, we show that in nanoconfined LiBH4/Al2O3prepared by melt infiltration, a percolating network of fastconductor−insulator Li+ diffusion pathways could be realized. These heterocontacts provide regions with extremely rapid 7LiNMR spin fluctuations giving direct evidence for very fast Li+ jump processes in both nanoconfined LiBH4/Al2O3 and LiBH4-LiI/Al2O3. Compared to the nanocrystalline, Al2O3-free reference system LiBH4-LiI, nanoconfinement leads to a strongly enhancedrecovery of the 7Li NMR longitudinal magnetization. The fact that almost no difference is seen between LiBH4-LiI/Al2O3 andLiBH4/Al2O3 unequivocally reveals that the overall 7Li NMR spin-lattice relaxation rates are solely controlled by the spinfluctuations near or in the conductor−insulator interfacial regions. Thus, the conductor−insulator nanoeffect, which in the ideal caserelies on a percolation network of space charge regions, is independent of the choice of the bulk crystal structure of LiBH4, eitherbeing orthorhombic (LiBH4/Al2O3) or hexagonal (LiBH4-LiI/Al2O3). 7Li (and 1H) NMR shows that rapid local interfacial Li-iondynamics is corroborated by rather small activation energies on the order of only 0.1 eV. In addition, the LiI-stabilized layer-structured form of LiBH4 guarantees fast two-dimensional (2D) bulk ion dynamics and contributes to facilitating fast long-range iontransport.

AB - Synthesizing Li-ion-conducting solid electrolyteswith application-relevant properties for new energy storage devicesis a challenging task that relies on a few design principles to tuneionic conductivity. When starting with originally poor ioniccompounds, in many cases, a combination of several strategies,such as doping or substitution, is needed to achieve sufficientlyhigh ionic conductivities. For nanostructured materials, theintroduction of conductor−insulator interfacial regions representsanother important design strategy. Unfortunately, for most of thetwo-phase nanostructured ceramics studied so far, the lowerlimiting conductivity values needed for applications could not bereached. Here, we show that in nanoconfined LiBH4/Al2O3prepared by melt infiltration, a percolating network of fastconductor−insulator Li+ diffusion pathways could be realized. These heterocontacts provide regions with extremely rapid 7LiNMR spin fluctuations giving direct evidence for very fast Li+ jump processes in both nanoconfined LiBH4/Al2O3 and LiBH4-LiI/Al2O3. Compared to the nanocrystalline, Al2O3-free reference system LiBH4-LiI, nanoconfinement leads to a strongly enhancedrecovery of the 7Li NMR longitudinal magnetization. The fact that almost no difference is seen between LiBH4-LiI/Al2O3 andLiBH4/Al2O3 unequivocally reveals that the overall 7Li NMR spin-lattice relaxation rates are solely controlled by the spinfluctuations near or in the conductor−insulator interfacial regions. Thus, the conductor−insulator nanoeffect, which in the ideal caserelies on a percolation network of space charge regions, is independent of the choice of the bulk crystal structure of LiBH4, eitherbeing orthorhombic (LiBH4/Al2O3) or hexagonal (LiBH4-LiI/Al2O3). 7Li (and 1H) NMR shows that rapid local interfacial Li-iondynamics is corroborated by rather small activation energies on the order of only 0.1 eV. In addition, the LiI-stabilized layer-structured form of LiBH4 guarantees fast two-dimensional (2D) bulk ion dynamics and contributes to facilitating fast long-range iontransport.

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U2 - 10.1021/acs.jpcc.1c03789

DO - 10.1021/acs.jpcc.1c03789

M3 - Article

SN - 1932-7447

VL - 125

SP - 15052−15060

JO - The Journal of Physical Chemistry C

JF - The Journal of Physical Chemistry C

IS - 27

ER -

Conductor−Insulator Interfaces in Solid Electrolytes: A Design Strategy to Enhance Li-Ion Dynamics in Nanoconfined LiBH₄/Al₂O₃

Abstract

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