Boosting the Lithium-Ion Conductivity in Li7TaP4 by Aliovalent Li versus Ta Substitution by Three Orders of Magnitude

High Resolution Image Download MS PowerPoint Slide Lithium-ion conductors are one of the key features of all-solid-state lithium-ion batteries. To modify their properties and enable their implementation in high-performance devices, an understanding of the relationship between the crystal structure and the transport properties of the mobile species is important. Lithium phosphidotetrelates and -trielates are classes of lithium-ion conductors reaching ionic conductivities of up to 4.5 × 10 –3 cm –1 at room temperature for ω-Li 9 GaP 4 . Here, we present the new lithium phosphidotantalate Li 7 TaP 4, and the aliovalent substitution of Ta by Li atoms, which leads to a partial filling of octahedral voids in the structure of Li 7 TaP 4 . As a result, the lithium-ion conductivity of Li 7 TaP 4 (1.3 × 10 –7 S cm –1 ) increases by 3 orders of magnitude to 3.7 × 10 –4 S cm –1 in Li 9.5 Ta 0.5 P 4 . Li 7 TaP 4 and Li 9.5 Ta 0.5 P 4 crystallizing in the cubic space groups Pa 3̅ and Fm 3̅ m, respectively, show a close structural relationship. The structure-property relationship is highlighted and compared with the isotypic tetrel element analogues.