An Entropically Stabilized Fast-Ion Conductor: Li3.25[Si0.25P0.75]S4

Laidong Zhou; Abdeljalil Assoud; Abhinandan Shyamsunder; Ashfia Huq; Qiang Zhang; Pascal Hartmann; Joern Kulisch; Linda F. Nazar

doi:10.1021/acs.chemmater.9b00657

An Entropically Stabilized Fast-Ion Conductor: Li_3.25[Si_0.25P_0.75]S₄

Laidong Zhou, Abdeljalil Assoud, Abhinandan Shyamsunder, Ashfia Huq, Qiang Zhang, Pascal Hartmann, Joern Kulisch, Linda F. Nazar

Powder Diffraction

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

64 Scopus citations

Abstract

We report on a family of lithium fast ion conductors, Li_3+x[Si_xP_1-x]S₄, that exhibit an entropically stabilized structure type in a solid solution regime (0.15 < x < 0.33) with superionic conductivity above 1 mS·cm^-1. Exploration of the influence of aliovalent substitution in the thermodynamically unstable β-Li₃PS₄ lattice using a combination of single crystal X-ray and powder neutron diffraction, the maximum entropy method, and impedance spectroscopy reveals that substitution induces structural splitting of the localized Li sites, effectively stabilizing bulk β-Li₃PS₄ at room temperature and delocalizing lithium ion density. The optimal material, Li_3.25[Si_0.25P_0.75]S₄, exhibits inherent entropic site disorder and a frustrated energy landscape, resulting in a high conductivity of 1.22 mS·cm^-1 that represents an increase of three orders of magnitude compared to bulk β-Li₃PS₄ and one order of magnitude higher than the nanoporous form. The enhanced ion conduction and lowered activation barrier with increasing site disorder as a result of aliovalent "tuning" reveals an important strategy toward the design of fast ion conductors that are vital as solid state electrolytes.

Original language	English
Pages (from-to)	7801-7811
Number of pages	11
Journal	Chemistry of Materials
Volume	31
Issue number	19
DOIs	https://doi.org/10.1021/acs.chemmater.9b00657
State	Published - Oct 8 2019

Funding

This research was supported by the BASF International Scientific Network for Electrochemistry and Batteries. L.F.N. also thanks NSERC for generous support via their Canada Research Chair and Discovery Grant programs. Neutron diffraction measurement at the POWGEN instrument at Oak Ridge National Laboratory, Spallation Neutron Source, was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. We would like to thank Dr. Melanie Kirkham for the neutron powder diffraction data collection. We would also like to thank Prof. Xiaoqi Sun from Northeastern University (China) for very helpful discussions.

Funders	Funder number
Office of Basic Energy Sciences
Scientific User Facilities Division
US Department of Energy
BASF
Oak Ridge National Laboratory

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10.1021/acs.chemmater.9b00657

Cite this

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title = "An Entropically Stabilized Fast-Ion Conductor: Li3.25[Si0.25P0.75]S4",

abstract = "We report on a family of lithium fast ion conductors, Li3+x[SixP1-x]S4, that exhibit an entropically stabilized structure type in a solid solution regime (0.15 < x < 0.33) with superionic conductivity above 1 mS·cm-1. Exploration of the influence of aliovalent substitution in the thermodynamically unstable β-Li3PS4 lattice using a combination of single crystal X-ray and powder neutron diffraction, the maximum entropy method, and impedance spectroscopy reveals that substitution induces structural splitting of the localized Li sites, effectively stabilizing bulk β-Li3PS4 at room temperature and delocalizing lithium ion density. The optimal material, Li3.25[Si0.25P0.75]S4, exhibits inherent entropic site disorder and a frustrated energy landscape, resulting in a high conductivity of 1.22 mS·cm-1 that represents an increase of three orders of magnitude compared to bulk β-Li3PS4 and one order of magnitude higher than the nanoporous form. The enhanced ion conduction and lowered activation barrier with increasing site disorder as a result of aliovalent {"}tuning{"} reveals an important strategy toward the design of fast ion conductors that are vital as solid state electrolytes.",

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