Nano-scaled Degradation Analysis of Sulfide Solid Electrolyte Around Cycled Cathode Material by STEM-EELS Technique

Using electron energy-loss spectroscopy in the scanning transmission electron microscope (STEM-EELS), the decomposition of a sulfide solid electrolyte (SSE) around a LiNbO3-coated Li(Ni0.8Co0.1Mn0.1)O2 cathode active material (CAM) in the charge/discharge cycle was clarified. In the initial cycle stage, Li3PS4 was directly assigned from an analysis of the S/P ratio by energy dispersive X-ray spectroscopy (EDX) and the EEL spectra of the P L-edge and S L-edge. In the cycled sample, an inhomogeneous decomposition was observed by the detection of POx species in the SSE around the CAM in the range of over approximately 100 nm. The Li K-edges observed in the initial cell and degraded cell showed that spectral changes had occurred, corresponding to the variation of the P L-edges.