Preparation and characterization of lithium-boron alloys: electrochemical studies as anodes in molten salt media, and comparison with pure lithium-involving systems

Abstract

Because of its low melting point (180.5°C), lithium cannot be used as a negative electrode in high current density generators (particularly thermally activated batteries). The lithium-boron alloy, first discovered in 1978, presents advantageous properties: it remains solid and stable up to 650°C and its electrochemical behaviour is very close to that of pure lithium. Conditions of synthesis of a metal lithium-rich alloy have been analysed; the multiphase material consisted of a porous refractory matrix filled with pure metal lithium, it was studied by nuclear magnetic resonance and its matrix examined by electron microscopy and porosimetry. Lithium-boron alloy electrochemical properties were analysed in LiCl-KCl media. In a flooded electrolyte, the behaviour of LiB is similar to that observed in non-aqueous media, particularly in dioxolane (DOL)-1.5 m LiAsF₆. In the case of single cell discharges (starved electrolyte), some problems arose from the nature of the electrolyte used (LiCl-KCl+SiO₂), which were solved by the substitution of SiO₂ by MgO in the electrolyte. Discharge curves were then identical to those obtained in flooded electrolytes and were characterized by two plateaux corresponding to the discharge of metallic lithium, and ionic lithium from the matrix, respectively.