The material Li₂(OH)Cl is experimentally found to exist in two phases, a poor Li-ion conducting orthorhombic phase (T<312K) and a fast Li-ion conducting disordered cubic phase (T>312K). Recently experiments report the high temperature phase cycled in a symmetric cell with lithium electrodes with the apparent creation of a stabilizing solid electrolyte interphase layer[1]. Li₂(OH)Cl is related to a variety of other materials that have been studied for their Li-ion electrolyte properties, Li_2+x(OH_1-x)Cl, Li₂(OH)Br, and Li₂(OH)_1-xF_xCl.[2][3]

We report the results of a combined computational and experimental study of the structural and ion migration properties of this material as a function of temperature. Using first principles methods to calculate the idealized static structures together with estimations of the phonon free energies in the quasi-harmonic approximation, the simulations predict several phases at low temperature including tetragonal and orthorhombic structures. The predicted orthorhombic phases are similar to experimental X-ray analysis performed at temperatures 15 K < T < 300 K as well as with literature reports,[1][2] while the tetragonal phase may be difficult to experimentally realize. Additionally, the disordered cubic phase was investigated using first-principles molecular dynamics to determine the lithium tracer diffusion and several order parameters in the temperature range of ~350-650 K.

[1] Hood, Z. D., Wang, H., Pandian , A. S., Keum, J. K. and Liang, C. J. Am. Chem. Soc. 138 1768-1771 (2016).

[2] Schwering G., Hönnerscheid, A., van Wüllen, L., and Jansen, M., CHEMPHYSCHEM, 4, 343-348 (2003).

[3] Li, Y., Zhou, W., Xin, S., Li, S., Zhu, J., Lü, X., Cui, Z., Jia, Q., Zhou, J., Zhao, Y., Goodenough, J.B.,. Angewandte Chemie International Edition, 9965–9968 (2016).

Acknowledgements:

Jason Howard was supported by NSF grant DMR-1507942. Computations were performed on
the Wake Forest University DEAC cluster, a centrally managed resource with support provided in part by the University. A portion of this research was supported by the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory, which is a U.S. Department of Energy (DOE) Office of Science User Facility. Zachary Hood was supported by a Graduate Research Fellowship award from the National Science Foundation (DGE-1148903) and the Georgia Tech-ORNL Fellowship.