Effect of Simultaneous Substitution of Alkali Earth Metals and Nb in Li7La3Zr2O12 on Lithium-Ion Conductivity

Abstract

All-solid-state lithium-ion batteries show considerable promise, due to their potential to exhibit both high capacity and high energy density. Additionally, they may be used safely at elevated temperatures, since solid-state electrolytes are incombustible and there is no hazard associated with liquid leakage. Various inorganic compounds may function as solid state electrolytes, including sulfide-based and oxide-based materials. Of these, the sulfides have attracted significant attention since they show elevated levels of lithium-ion conductivity, potentially reaching the room temperature conductivity levels over 10 −3 Scm −1 obtainable with liquid organic electrolytes. 1–3 Sulfides, however, must not only be protected from ambient humidity, but also require the application of an oxide coating to associated electrode active materials to prevent elemental diffusion between sulfur and oxygen. 4–9 In contrast, oxides are stable when in contact with both electrode active materials and atmospheric humidity since they do not undergo elemental diffusion with oxygen. The main deficit of oxides is that they exhibit lower lithium-ion conductivity than the sulfides. Thus, if the lithium conductivity of oxides can be improved, they have the potential to become ideal solid-state electrolytes, with the added advantage that no special precautions will be necessary during their handling in air. Garnet-like oxides meet many of the most important requirements for electrolytes; they offer chemical stability, wide potential windows and relatively high lithium-ion conductivity compared to other oxide-based electrolytes. 10 One such oxide with a garnet-like structure and high lithium-ion conductivity is Li7La3Zr2O12 (LLZ), first reported by Weppner’s group in 2007 and increasingly the subject of investigation. 10 The lithium-ion conductivity of these materials may