Atomically Intimate Solid Electrolyte/Electrode Contact Capable of Surviving Long-Term Cycling with Repeated Phase Transitions

Atomic-Resolution Electron Microscopy Unravelling the Role of Unusual Asymmetric Twin Boundaries in the Electron-Beam-Sensitive NASICON-Type Solid Electrolyte

An atomic-scale understanding of the role of nonperiodic features is essential to the rational design of highly Li-ion-conductive solid electrolytes. Unfortunately, most solid electrolytes are easily damaged by the intense electron beam needed for atomic-resolution electron microscopy observation, so the reported in-depth atomic-scale studies are limited to Li0.33La0.56TiO3- and Li7La3Zr2O12-based materials. Here, we observe on an atomic scale a third type of solid electrolyte, Li1.3Al0.3Ti1.7(PO4)3 (LATP), through minimization of damage induced by specimen preparation. With this capability, LATP is found to contain large amounts of twin boundaries with an unusual asymmetric atomic configuration. On the basis of the experimentally determined structure, the theoretical calculations suggest that such asymmetric twin boundaries may considerably promote Li-ion transport. This discovery identifies a new entry point for optimizing ionic conductivity, and the method presented here will also greatly benefit the mechanistic study of solid electrolytes.

Li3TiCl6 as ionic conductive and compressible positive electrode active material for all-solid-state lithium-based batteries

The development of energy-dense all-solid-state Li-based batteries requires positive electrode active materials that are ionic conductive and compressible at room temperature. Indeed, these material properties could contribute to a sensible reduction of the amount of the solid-state electrolyte in the composite electrode, thus, enabling higher mass loading of active materials. Here, we propose the synthesis and use of lithium titanium chloride (Li₃TiCl₆) as room-temperature ionic conductive (i.e., 1.04 mS cm^-1 at 25 °C) and compressible active materials for all-solid-state Li-based batteries. When a composite positive electrode comprising 95 wt.% of Li₃TiCl₆ is tested in combination with a Li-In alloy negative electrode and Li₆PS₅Cl/Li₂ZrCl₆ solid-state electrolytes, an initial discharge capacity of about 90 mAh g^-1 and an average cell discharge voltage of about 2.53 V are obtained. Furthermore, a capacity retention of more than 62% is attainable after 2500 cycles at 92.5 mA g^-1 and 25 °C with an applied external pressure of 1.5 tons. We also report the assembly and testing of a "single Li₃TiCl₆" cell where this chloride material is used as the solid electrolyte, negative electrode and positive electrode.