Degradation rate at the Solid–Solid interface of sulfide-based solid Electrolyte–Cathode active material

Degradation Analysis by X-ray Absorption Spectroscopy for LiNbO3 Coating of Sulfide-Based All-Solid-State Battery Cathode

“…The EDS mapping images imply the following: (1) the mapping after floating indicated the obvious presence of O in the SE region in contrast to the before sample; (2) the Nb element derived from LiNbO 3 coating had remained at the interface of SE/NCM523 even after the floating test. The result of (1) is in good agreement with our previous reports, and it corresponds that the oxidized decomposition reaction of the sulfide SE had occurred into phosphates (PO x ) and sulfates (SO x ) components observed by using ToF-SIMS and XPS. , However, as with the report by Kobayashi et al, no clear trace of O release from the cathode active material with LiNbO 3 coating was also confirmed by TEM/EELS in our previous study . Veith et al also reported much better stability of high-voltage-cycled NMC622 with a SE than with an ordinary liquid electrolyte .…”

“…Based on the analyses of TEM/EDS and XAS, the typical chemical equations are described below: the decomposition side reactions of LiNbO 3 coating and the release of Li and O, which is estimated to be electrochemically triggered by the charged state, higher-delithiated state, of the NCM523: LiNbO 3 → Li 1 − 2 x NbO 3 − x + x Li 2 normalO Li 2 normalO → 0.5 normalO 2 + 2 Li + + 2 normale − P−S compounds , sulfur + Li 2 normalO , normalO 2 → PO x nobreak0em0.25em⁡ and nobreak0em0.25em⁡ SO x nobreak0em0.25em⁡ compounds The above equations were expected from our previous analysis of XPS Nb 3d spectra . In this study, we succeeded in more directly confirming the state change by analyzing the XAS spectra of Nb K-edge and L 3 -edge.…”

“…The sample preparation, the ASSB cell fabrication, and the durability test have been explained in detail in a previous paper ,,, and will only be briefly described here.…”

“…Therefore, all-solid-state battery (ASSB) using solid electrolyte (SE) is a promising candidate of the next-generation energy devices. They can replace ordinary liquid-type LIBs in terms of their higher rate capability, safety, and durability. − There are various types of SEs: polymers and molecular crystals as organics, and halides, oxides, and sulfides as inorganics. ,,− Among them, sulfide-based SEs have high ionic conductivity of 10 –3 –10 –2 S cm –1 comparable to liquid-type electrolyte , and thermoplasticity. , These advantages lead to the ASSBs using sulfide-based SEs being studied intensively.…”

“…We have also conducted several studies on ASSB using sulfide-based SE, especially focusing on cathode of argyrodite-structured Li 6 PS 5 Cl/LiNbO 3 -coated LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) system, with investigation of the range of operation temperature and cathode potential. ,,, In durability tests, the discharge capacity retention rate was >99% after continuous charging (floating) at 4.25 V vs Li/Li + and 60 °C for about 1 month, which showed extremely high durability of ASSB cathode . Although the retention rate had an excellent value of ∼80% even after floating in a harsh condition at higher potential of 4.55 V vs Li/Li + and 60 °C for about 1 month, the oxidization decomposition of sulfide SE into phosphates (PO x ) and sulfates (SO x ) components was clearly observed by using time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). , To confirm the origin of the oxidization, NCM523 in obviously degraded cell at 4.55 V vs Li/Li + was analyzed by X-ray diffraction (XRD) and transmission electron microscope/electron energy loss spectroscopy (TEM/EELS). However, the NCM523 region has not changed before and after floating at all, which means that the oxidation was not derived from the NCM523.…”