The State Key Lab of
High Performance Ceramics and Superfine Microstructure
Shanghai Institute of Ceramics, Chinese Academy of Sciences
中 国 科 学 院 上 海 硅 酸 盐 研 究 所 高 性 能 陶 瓷 和 超 微 结 构 国 家 重 点 实 验 室
Microscopic Insights into Conductivity and Stability of Solid Electrolyte Interfaces
Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Despite their different chemistries, novel energy-storage systems, e.g., Li- air, Li-S, all-solid-state Li batteries, etc., share the same concept of using solid electrolyte materials to enable the use of lithium metal. An ideal solid electrolyte material must be highly ionically conductive and exhibit desirable stability with metallic lithium. Over the past several decades, new solid electrolyte materials were developed that demonstrated high conductivity, which is comparable to that of organic liquid electrolytes. However, unexpectedly high resistivity from grain boundaries and electrolyte-lithium interfaces is often observed and is the major limitation in realizing the practical application of these materials. Due to spatial confinement and structural and chemical complications, experimentally probing these interfaces is challenging. Thus, the exact origins of the interfacial resistivity are unclear. Here, in situ and atomic-resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) are used to study these interfaces. Oxide solid electrolytes, including Li0.33La0.55TiO3 (LLTO) and Al-Li7La3Zr2O12 (LLZO), and LIPON, are used as prototype materials. The atomic-scale origin of the high grain boundary resistivity in polycrystalline LLTO was revealed to be due to the formation of a TiOx binary oxide layer with a thickness of 2-3 unit cells. This layer is deficient in Li ions and does not contain adequate vacancy sites for Li+ transport, significantly lowering the overall ionic conductivity in LLTO. At the LLZO-Li interface, an ultra-thin, self-limiting interfacial layer was discovered by utilizing in situ STEM, serving as a passivation layer that stabilizes the interface. In addition to chemical and structural transformations, interfacial polarization could also significantly influence mass transport and charge transfer behavior at ionic interfaces. A direct experimental approach to measure ion conduction behavior of Li ions at local interfaces will also be introduced.