Atomically Well-Ordered Structure at Solid Electrolyte and Electrode Interface Reduces the Interfacial Resistance

Using synchrotron surface X-ray diffraction, we investigated the atomic structures of the interfaces of a solid electrolyte (Li 3 PO 4 ) and electrode (LiCoO 2 ). We prepared two types of interfaces with high and low interface resistances; the low-resistance interface exhibited a flat and well-ordered atomic arrangement at the electrode surface, whereas the high-resistance interface showed a disordered interface. These results indicate that the crystallinity of LiCoO 2 at the interface has a significant impact on interface resistance. Furthermore, we reveal that the migration of Li ions along the interface and into grain boundaries and antiphase domain boundaries is a critical factor reducing interface resistance.