Fluid Structure of Molten LiCl-Li Solutions

Molten mixtures of lithium chloride and metallic lithium (LiCl-Li) play an essential role in the electrolytic reduction of various metal oxides. These mixtures possess unique high temperature physical and chemical properties that have been investigated for decades. However, due to their extreme chemical reactivity, no study to date has been capable of definitively proving the basic physical nature of Li dissolution in molten LiCl. In this study, the evolution of the structure of molten LiCl-Li is probed as metallic Li is electrochemically introduced into the melt in situ, using synchrotron radiation experiments based on high energy wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). The time-resolved scattering results indicate the formation of transient Cl^- ion cages surrounding low-density voids with a periodicity of ∼8.3 Å, which suggests the formation of metastable Li nanocluster. The structure of the LiCl-Li nanoclusters in the solution is modeled using ab initio molecular dynamics (AIMD) simulations. The simulation results are in agreement with the X-ray diffraction measurement and suggest the nanoclusters are predominantly Li₈, along with smaller clusters.