Investigation of Microscopic Structure and Ion Dynamics in Liquid Li(Na, K)EutecticCl Systems by Molecular Dynamics Simulation

Jie Wu,Jia Wang,Jianguo Yu,Haiou Ni,Guimin Lu

doi:10.3390/app8101874

Jie Wu, Jia Wang + Show 3 more

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https://doi.org/10.3390/app8101874

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Abstract

Molten chloride salts are the main components in liquid metal batteries, high-temperature heat storage materials, heat transfer mediums, and metal electrolytes. In this paper, interest is centered on the influence of the LiCl component and temperature on the local structure and transport properties of the molten LiCl-NaCl-KCl system over the temperature range of 900 K to 1200 K. The liquid structure and properties have been studied across the full composition range by molecular dynamics (MD) simulation of a sufficient length to collect reliable values, such as the partial radial distribution function, angular distribution functions, coordination numbers distribution, density, self-diffusion coefficient, ionic conductivity, and shear viscosity. Densities obtained from simulations were underestimated by an average 5.7% of the experimental values. Shear viscosities and ionic conductivity were in good agreement with the experimental data. The association of all ion pairs (except for Li-Li and Cl-Cl) was weakened by an increasing LiCl concentration. Ion clusters were formed in liquids with increasing temperatures. The self-diffusion coefficients and ionic conductivity showed positive dependences on both LiCl concentration and temperature, however, the shear viscosity was the opposite. By analyzing the hydrodynamic radii of each ion and the coordination stability of cation-anion pairs, it was speculated that ion clusters could be the cation-anion coordinated structure and affected the macro properties.

Highlights

Molten chloride salts have been widely used in liquid metal batteries [1,2,3], high-temperature heat storage materials, heat transfer mediums [4], and metal electrolytes, owing to their favorable characteristics, such as wide operating temperature range, low vapor pressure, moderate heat capacity, low cost, and high thermal stability [5]
Molecular dynamics simulations have been carried out on ternary systems composed of LiCl and (NaCl-KCl)eutectic in the temperature range from 900 to 1200 K
Shear viscosities calculated by the reverse non-equilibrium molecular dynamics (RNEMD) method, as well as the ionic conductivity, were in good agreement with experimental data

Summary

Introduction

Molten chloride salts have been widely used in liquid metal batteries [1,2,3], high-temperature heat storage materials, heat transfer mediums [4], and metal electrolytes, owing to their favorable characteristics, such as wide operating temperature range, low vapor pressure, moderate heat capacity, low cost, and high thermal stability [5]. Both the structure and properties of molten chloride salts are hard to measure due to the extreme high-temperature, corrosive, and volatile conditions, needless to consider the accuracy of testing.

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