On the Formation of Clusters of Li8 in Molten Solutions of LiCl-Li

Abstract

Numerous base metals can be obtained via electrolytic reduction of their respective oxides in molten LiCl-Li2O electrolytes. In these processes, often times, Li+ is co-reduced to metallic Li. The formation of Li0 is undesirable and leads to a loss of current efficiency and therefore is of significant interest. In spite of its importance, molten mixtures of LiCl and Li are still poorly understood and previous research has demonstrated a variety of phenomena that are seemingly unexplainable. We have custom built a unique setup to conduct in-situ Raman spectroscopy of such molten mixtures. In this work, we show that a Raman active phase forms in the fused salt when Li is electrochemically reduced from Li2O in LiCl. The spectrum was comprised of three fundamental features at 285.5, 302.8, and 318.2 cm-1, with overtones of decreasing intensity at approximately integer multiples of these Raman shifts as Shown in Figure 1. This spectrum was found to be consistent with previously-reported characteristic spectrum of the lithium cluster Li8. The presence of a colloidal suspension of lithium clusters in the molten salt is hypothesized to be the reason behind anomalous physical behavior of LiCl-Li solutions. Acknowledgements: This work was performed under the auspices of the Department of Energy (DOE) through grant DE-NE0008262, and the US Nuclear Regulatory Commission (NRC) under contracts NRCHQ-11-G-38-0039, NRC-38-10-949 and NRC-HQ-13-G-38-0027. Mr. Kenny Osborne serves as the program manager for the DOE awards and Ms. Nancy Hebron-Isreal serves as the grants program officer for the NRC awards. Figure 1