Origin of O2 Generation in Sulfide‐Based All‐Solid‐State Batteries and its Impact on High Energy Density.

The cathode surface of sulfide‐based all‐solid‐state batteries (SBs) is commonly coated with amorphous‐LiNbO3 in order to stabilize charge–discharge reactions. However, high‐voltage charging diminishes the advantages, which is caused by problems with the amorphous‐LiNbO3 coating layer. This study has investigated the degradation of amorphous‐LiNbO3 coating layer directly during the high‐voltage charging of SBs. O2 generation via Li extraction from the amorphous‐LiNbO3 coating layer is observed using electrochemical gas analysis and electrochemical X‐ray photoelectron spectroscopy. This O2 leads to the formation of an oxidative solid electrolyte (SE) around the coating layer and degrades the battery performance. On the other hand, elemental substitution (i.e., amorphous‐LiNbxP1‐xO3) reduces O2 release, leading to stable high‐voltage charge–discharge reactions of SBs. The results have emphasized that the suppression of O2 generation is a key factor in improving the energy density of SBs. [ABSTRACT FROM AUTHOR]