Atomic-Scale Observations of Oxygen Release Degradation in Sulfide-Based All-Solid-State Batteries with Layered Oxide Cathodes

All-solid-state batteries exhibit considerable potential for applications in electric vehicles. Understanding and controlling the oxygen release from the layered cathode active material are essential in achieving long-term operation of all-solid-state batteries because the oxygen release degrades the cathode material and the solid electrolyte, triggering capacity degradation. In this study, we verified the specific interface where the oxygen release is accelerated by atomic-scale scanning transmission electron microscopy and electron energy loss spectroscopy analyses. Oxygen release is suppressed at the interface where the LiNbO₃ coating layer is sufficiently formed. Decomposition products on the solid electrolyte and the antisite defect layers on the cathode surface are formed by oxygen release at the interface where the Li₂S-P₂S₅ solid electrolyte and Li(Ni_1/3Mn_1/3Ni_1/3)O₂ cathode are in direct contact. These irreversible passivation layers lead to capacity degradation. In addition, we found that exfoliation of the LiNbO₃ coating from the cathode not only physically breaks the Li conduction path but also results in oxygen release and the deterioration of the cathode. These atomic-scale insights can further advance the development of all-solid-state batteries by suppressing oxygen release.