Editors\u27 Choice—Understanding Chemical Stability Issues between Different Solid Electrolytes in All-Solid-State Batteries

Sulfide-based solid electrolytes (SE) are quite attractive for application in all-solid-state batteries (ASSB) due to their high ionic conductivities and low grain boundary resistance. However, limited chemical and electrochemical stability demands for protection on both cathode and anode side. One promising concept to prevent unwanted reactions and simultaneously improve interfacial contacting at the anode side consists in applying a thin polymer film as interlayer between Li metal and the SE. In the present study, we investigated the combination of polyethylene oxide (PEO) based polymer films with the sulfide-based SE Li10SnP2S12 (LSPS). We analyzed their compatibility using both electrochemical and chemical techniques. A steady increase in the cell resistance during calendar aging indicated decomposition reactions at the interfaces. By means of X-ray photoelectron spectroscopy and further analytical methods, the formation of polysulfides, P–[S]n–P like bridged PS43− units and sulfite, SO32−, was demonstrated. We critically discuss potential reasons and propose a plausible mechanism for the degradation of LSPS with PEO. The main objective of this paper is to highlight the importance of understanding interfaces in ASSBs not only from an electrochemical perspective, but also from a chemical point of view

Slurry-Based Processing of Solid Electrolytes: A Comparative Binder Study

Limited energy density of today\u27s Li-ion battery technologies demands for novel cell technologies, such as the all-solid-state battery (ASSB). In order to achieve high energy densities and enable large-scale processing, thin and flexible solid electrolyte (SE) layers have to be implemented. This study focuses on slurry-based processing of the sulfidic solid electrolyte Li$_{10}$SnP$_{2}$S$_{12}$ (LSPS). Various polymers were investigated concerning their suitability as binders for thin and freestanding SE sheets. We conducted a parameter study in order to optimize e.g. LSPS-to-binder ratio, solids content and porosity. Significant differences were found with regard to the minimum amount of binder required for mechanically stable sheets as well as the homogeneity, density and flexibility of the resulting SE layers. The impacts of binder type and weight fraction on ionic conductivity were examined through lithium diffusion measurements. Impedance analysis was conducted in comparison, proving sufficiently high ionic conductivity for potential application of the SE sheets in ASSB. This work highlights the important role of the polymeric binder in slurry-based processing of SEs and gives an impression how important a well-considered selection of parameters is to achieve good processing properties as well as desirable features for the final SE sheet