Local Structure and Ionic Conduction at Interfaces of Electrode and Solid Electrolytes

Abstract

All solid state batteries are attracting interests as next generation energy storage devices. However, little is known on interfaces between active materials and solid electrolytes, which may affect performance of the devices. In this study, interfacial phenomena between electrodes and solid electrolytes of all solid state batteries were investigated by using nano-composites of Li2SiO3-TiO2, Li2SiO3-LiTiO2, and Li2SiO3-FePO4. Studies on ionic conductivity of these composites revealed lithium ion transfer across the interfaces without electric field, which depended on electrode potentials. For Li2SiO3-TiO2, conductivity of the composites was enhanced by addition of TiO2 and well explained by space charge layer model. With LiTiO2 which shows lower electrode potential, the conductivity was deteriorated due to decrease in vacancies in Li2SiO3. At the interface of Li2SiO3-FePO4, a lot of Li ions in Li2SiO3 are trapped at the interface or maybe are inserted into FePO4, resulting in many vacancies in Li2SiO3 and lattice distortion. The results show the ionic conduction at the interface is strongly affected by the electrode potential and the importance of design of interfaces of all solid state batteries is pointed out.