Dynamics of Hydroxyl Anions Promotes Lithium Ion Conduction in Antiperovskite Li2OHCl

Published

October 13, 2020

Author(s)

Fei Wang, Hayden Evans, Kwangnam Kim, Liang Yin, Yiliang Li, Ping-Chun Tsai, Jue Liu, Saul H. Lapidus, Craig Brown, Donald J. Siegel, Yet-Ming Chiang

Abstract

Li₂OHCl is an exemplar of the anti-perovskite family of ionic conductors, for which high ionic conductivities have been reported, but in which the atomic-level mechanism of ion migration is unclear. The stable phase is highly defective, having 1/3 of the Li sites vacant, while the presence of the OH⁻ anion introduces the possibility of rotational disorder that may be coupled to cation migration. Here, complementary experimental and computational methods are applied to understand the relationship between the crystal chemistry and ionic conductivity in Li₂OHCl. X-ray and neutron experiments conducted over the temperature range 20 °C - 200 °C, including diffraction, quasi-elastic neutron scattering (QENS), maximum entropy method (MEM) analysis, as well as ab initio molecular dynamics (AIMD) simulations together show conclusively that the high lithium ion conductivity of cubic Li₂OHCl is correlated to "paddlewheel" rotation of the dynamic OH− anion. The present results suggest that in anti-perovskites and derivative structures, a high cation vacancy concentration combined with the presence of disordered molecular anions can lead to high cation mobility.

Citation

Chemistry of Materials

Volume

32

Issue

19

Pub Type

Journals

Keywords

Ion conductor, plastic crystals, Maximum entropy method, diffraction

Citation

Wang, F. , Evans, H. , Kim, K. , Yin, L. , Li, Y. , Tsai, P. , Liu, J. , Lapidus, S. , Brown, C. , Siegel, D. and Chiang, Y. (2020), Dynamics of Hydroxyl Anions Promotes Lithium Ion Conduction in Antiperovskite Li₂OHCl, Chemistry of Materials (Accessed October 10, 2024)