Interphase Formation of PEO 20 :LiTFSI-Li 6 PS 5 Cl Composite Electrolytes with Lithium Metal

• Published in: ACS applied materials & interfaces Vol. 12; no. 10; pp. 11713 - 11723
• Main Authors: Simon, Fabian J, Hanauer, Matthias, Richter, Felix H, Janek, Jürgen
• Format: Journal Article
• Language: English
• Published: United States 11-03-2020
• Subjects: composite polymer electrolyte; argyrodite; all-solid-state battery; lithium metal interface; solid polymer electrolyte
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.9b22968

Composite polymer electrolytes (CPEs), consisting of solid electrolyte particles embedded within a solid polymer electrolyte matrix, are promising materials for all-solid-state batteries because of their mechanical properties and scalable production processes. In this study, CPEs consisting of PEO
:LiTFSI blended with 1, 10, and 40 wt % (CPE40) of the Li
PS
Cl electrolyte filler are prepared by a slurry-based process. The incorporation of Li
PS
Cl improves the lithium-ion conductivity from 0.84 mS cm
(PEO
:LiTFSI) to 3.6 mS cm
(CPE40) at 80 °C. Surface-sensitive X-ray photoelectron spectroscopy (XPS) reveals LiF, polysulfides, and Li
PO
on the CPE surface, originating from decomposition reactions between PEO
:LiTFSI and Li
PS
Cl. The decomposition products influence the formation of the solid electrolyte interphase (SEI) at the lithium metal | CPE interface, resulting in a reduced SEI resistance of 3.3 Ω cm
(CPE40) compared to 5.8 Ω cm
(PEO
:LiTFSI) at 80 °C. The SEI growth follows a parabolic rate law and the growth rate declines from 1.2 Ω cm
h
(PEO
:LiTFSI) to 0.57 Ω cm
h
(CPE40) during thermal aging at 80 °C. By substituting CPEs for PEO
:LiTFSI in lithium plating and stripping experiments, the increase in SEI resistance was reduced by more than 75%. In order to get a deeper understanding of the SEI formation process, in situ XPS measurements were carried out where the lithium metal is successively deposited on the CPE sample and XPS is measured after each deposition step. On the basis of these measurements, a multistep decomposition mechanism is postulated, including the formation of LiF and Li
S as key components of the SEI.