Ion conduction and structural chemistry of phosphidosilicates

• Applicant: Professor Dr. Dirk Johrendt
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 543298761

Ion-conducting solid electrolytes as key components of solid-state batteries are being inten-sively researched worldwide. Among many properties that solid electrolytes must meet for use in batteries, an ionic conductivity around 1 mS/cm is especially crucial. Many of the best solid ionic conductors known today are sulfides with too low chemical stability for battery ap-plications. Whether more stable metal halides are more suitable is still unclear because of the high cost of transition- and rare-earth metals. Ion-conducting phosphides were poorly studied for a long time. In 2015, we discovered the novel phosphidosilicate LiSi2P3, where Li ions move in interspaces of a diamond-like network of large supertetrahedra. Although lithium is "diluted" between the Li-free supertetrahedra, the ionic conductivity of LiSi2P3 is as high as that of Li8SiP4, which contains five times more lithium. We were subsequently able to show that the ionic conductivity increases with the size of the supertetrahedra, and have extended this concept to sodium and potassium ionic conductors. Our project aims to increase the ionic conductivity in ASi2P3 (A = Li, Na, K) by chemical substitution, and to discover other potentially ion-conducting phosphidosilicates with novel structural motifs. Our preliminary work shows that this can be accomplished by combinations of alkali metals with alkaline earth metals. We also prepare the analogous rubidium and cesium compounds, which are model systems that provide important information for a better understanding of ionic motion between supertetra-hedra. The additional introduction of alkaline earth metals is a preparative challenge that we are addressing with mechanochemical synthesis methods to discover previously unknown quaternary phosphidosilicates.

• DFG Programme: Research Grants