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Li-ion site disorder driven superionic conductivity in solid electrolytes: a first-principles investigation of β-Li3PS4

Journal Article · · Journal of Materials Chemistry. A
DOI:https://doi.org/10.1039/c6ta07713g· OSTI ID:1408640

The attractive safety and long-term stability of all solid-state batteries has added a new impetus to the discovery and development of solid electrolytes for lithium batteries. Recently several superionic lithium conducting solid electrolytes have been discovered. All the superionic lithium containing compounds (β-Li3PS4 and Li10GeP2S12 and oxides, predominantly in the garnet phase) have partially occupied sites. This naturally begs the question of understanding the role of partial site occupancies (or site disorder) in optimizing ionic conductivity in these family of solids. In this paper, we find that for a given topology of the host lattice, maximizing the number of sites with similar Li-ion adsorption energies, which gives partial site occupancy, is a natural way to increase the configurational entropy of the system and optimize the conductivity. For a given topology and density of Li-ion adsorption sites, the ionic conductivity is maximal when the number of mobile Li-ions are equal to the number of mobile vacancies, also the very condition for achieving maximal configurational entropy. We demonstrate applicability of this principle by elucidating the role of Li-ion site disorder and the local chemical environment in the high ionic conductivity of β-Li3PS4. In addition, for β-Li3PS4 we find that a significant density of vacancies in the Li-ion sub-lattice (~25%) leads to sub-lattice melting at (~600 K) leading to a molten form for the Li-ions in an otherwise solid anionic host. This gives a lithium site occupancy that is similar to what is measured experimentally. We further show that quenching this disorder can improve conductivity at lower temperatures. As a consequence, we discover that (a) one can optimize ionic conductivity in a given topology by choosing a chemistry/composition that maximizes the number of mobile-carriers i.e. maximizing both mobile Li-ions and vacancies, and (b) when the concentration of vacancies becomes significant in the Li-ion sub-lattice, it becomes energetically as well as entropically favorable for it to remain molten well below the bulk decomposition temperature of the solid. Finally, this principle may already apply to several known superionic conducting solids.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC); ORNL Laboratory Directed Research and Development (LDRD) Program
Grant/Contract Number:
AC05-00OR22725; AC02-05CH11231
OSTI ID:
1408640
Journal Information:
Journal of Materials Chemistry. A, Journal Name: Journal of Materials Chemistry. A Journal Issue: 3 Vol. 5; ISSN 2050-7488
Publisher:
Royal Society of ChemistryCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (11)

Borohydride-Scaffolded Li/Na/Mg Fast Ionic Conductors for Promising Solid-State Electrolytes journal October 2018
Sulfide Solid Electrolytes for Lithium Battery Applications journal August 2018
Advanced sulfide solid electrolyte by core-shell structural design journal October 2018
Niobium tungsten oxides for high-rate lithium-ion energy storage journal July 2018
Superionic conduction in β-eucryptite: inelastic neutron scattering and computational studies journal January 2017
Ab initio molecular dynamics study of 1-D superionic conduction and phase transition in β-eucryptite journal January 2018
The effects of mechanical constriction on the operation of sulfide based solid-state batteries journal January 2019
Lithium diffusion in L i 2 X ( X = O , S, and Se): Ab initio simulations and inelastic neutron scattering measurements journal June 2019
Reorientational motion and Li + -ion transport in Li 2 B 12 H 12 system: Molecular dynamics study journal July 2019
Electrodiffusion of alkali ions in alkali niobophosphate glasses and glass-forming melts journal August 2018
Niobium tungsten oxides for high-rate lithium-ion energy storage. text January 2018

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