Modifying the Properties of Fast Lithium-Ion ConductorsThe\nLithium Phosphidotetrelates Li₁₄SiP₆, Li₁₄GeP₆, and Li₁₄SnP₆

Abstract

A broad\nrepertoire of potential solid-state electrolytes is a prerequisite\nfor the development and optimization of high-energy-density all-solid-state\nbatteries. An isovalent substitution of suitable elements is a very\nsuccessful tool to get access to new materials with improved properties,\nwhich allow for a detailed investigation of structure–property\nrelationships. Here, we present the two new lithium phosphidotetrelates\nLi₁₄GeP₆ and Li₁₄SnP₆ with\nionic conductivities of σ ∼ 1 mS cm^–1 at room temperature. To evaluate the rules for the structure–property\nrelationships, all experimental data of lithium phosphidogermanate\nLi₁₄GeP₆ and lithium phosphidostannate Li₁₄SnP₆ are compared to the recently reported lithium\nphosphidosilicate Li₁₄SiP₆. The isotypic compounds\nLi₁₄<i>Tt</i>P₆ (<i>Tt</i> = Si, Ge, Sn) are accessible via a straightforward and simple synthesis,\nstarting from ball milling of the elements, followed by annealing\nof the obtained mixtures. Because of the high Li and low <i>Tt</i> content, all of these compounds are considered as lightweight materials\nwith a density of 1.644–2.025 g cm^–3. The\nmaterials were analyzed applying powder X-ray diffraction, differential\nscanning calorimetry, ⁶Li, ³¹P, and ¹¹⁹Sn solid-state magic angle spinning NMR as well as temperature-dependent ⁷Li NMR experiments, and electrochemical impedance spectroscopy.