Electrochemical and material analyses for sulfide-based solid electrolyte-cathode interface under high voltage

The active material coating of a cathode in all-solid-state lithium-ion batteries using sulfide-based solid electrolytes is known to be an essential technology. Electrochemical impedance spectroscopic measurements showed that two charge-transfer processes occurred at the interface between an argyrodite-type sulfide solid electrolyte and LiNi0.5Co0.2Mn0.3O2 both with and without a LiNbO3 coating. The process in the higher-frequency region was attributed to the solid electrolyte-coating and/or the coating itself, whereas that in the lower-frequency region was attributed to the lithiation/delithiation of the cathode active material. The two charge transfer resistances observed in the cell with a LiNbO3-coated cathode-after durability tests at various charging potentials-exhibited different trends. The charge transfer resistance was maintained at 4.55 V vs. Li/Li+, and only one at the higher frequency increased. The oxidation of sulfide at the solid electrolyte-coating interface was observed using time-of-flight secondary-ion mass spectrometry. However, the degradation at the active material surface was not observed using transmission electron microscope/electron energy loss spectroscopy. The results of the material analyses support the ascription of impedance spectra and their associated resistance trends in the durability test.

Automated summary

The research highlights the importance of the active material coating of a cathode in all-solid-state lithium-ion batteries for charge transfer. The study also shows that cathodes with a LiNbO3 coating exhibit different charge transfer resistance trends after durability tests at various charging potentials. In addition, oxidation of sulfide at the solid electrolyte-coating interface was observed using time-of-flight secondary-ion mass spectrometry.