Preparation and physical properties of lithium phosphide lithium chloride, a solid electrolyte for solid state lithium batteries

Solid electrolytes with high ionic conductivity and thermodynamic stability are required for high energy density lithium batteries. In this work we prepared a series of composite electrolytes made of lithium phosphide and lithium chloride which are thermodynamically stable in contact with a lithium electrode and which have ionic conductivity significantly higher than other known lithium ion conductors. These composites were made through solid state reactions between lithium phosphide and lithium chloride. The structure of the composites were analyzed using X-ray diffraction. Thermal analysis of the composites showed only a narrow range of miscibility between LiCl and Li3P. The phase diagram of lithium phosphide-lithium chloride was constructed. Formation of a simple eutectic at 9Li(3)P + LiCl concentration was observed. The ionic conductivity of lithium phosphide chloride at various mole ratios of LiCl to Li3P was examined from ambient temperature to 500 degrees C. In most cases a low activation energy for lithium transport was observed.