Origin of O 2 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-LiNbO 3 in order to stabilize charge-discharge reactions. However, high-voltage charging diminishes the advantages, which is caused by problems with the amorphous-LiNbO 3 coating layer. This study has investigated the degradation of amorphous-LiNbO 3 coating layer directly during the high-voltage charging of SBs. O 2 generation via Li extraction from the amorphous-LiNbO 3 coating layer is observed using electrochemical gas analysis and electrochemical X-ray photoelectron spectroscopy. This O 2 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-LiNb x P 1- x O 3 ) reduces O 2 release, leading to stable high-voltage charge-discharge reactions of SBs. The results have emphasized that the suppression of O 2 generation is a key factor in improving the energy density of SBs.