Direct Experimental Observation of the Interfacial Instability of the Fast Ionic Conductor Li10GeP2S12 at the Lithium Metal Anode

Thursday, 23 June 2016
Riverside Center (Hyatt Regency)
S. Wenzel (Justus-Liebig-University Giessen), W. G. Zeier (Justus-Liebig-Universität Giessen, Germany), and J. Janek (Justus-Liebig-Universität Giessen)
High capacity and low potential anode materials like lithium metal are preferred for high energy densities in all solid-state batteries. Due to the highly reducing potential of lithium metal, the electrochemical and thermodynamic stability of a solid ion conductor at the interface plays a crucial role for the performance of all solid-state batteries.

When a solid electrolyte is in contact with lithium metal, three different types of interfaces may occur:1 (I) A stable interface may form with electrolytes that are thermodynamically stable against Li contact. (II) A reaction occurs and a mixed ionic-electronic conducting (MCI) new interphase forms,2 which rapidly growths due to the electronic percolation pathways. (III) A reaction occurs and a solid electrolyte interphase (SEI) forms,3 which only conducts ions. While (I) may be preferred and (II) is exclusively detrimental, due to a proceeding reaction front, the impact of (III) on the battery performance depends on the type of forming SEI.

Here we will shortly introduce the types of possible interphases/interfaces and discuss the expected effects on the overall resistance and performance of an all-solid-state battery. Using time-resolved impedance spectroscopy and time-resolved cyclic voltammetry we introduce a guideline to characterize solid electrolytes for their stability against metal interfaces. The solid electrolyte Li10GeP2S12 will be shown as an example of an instability,4 as has been theoretically predicted.5,6 SEI formation occurs, affecting the overall cell resistance detrimentally.

Using a novel in situ X-ray photoelectron technique we study the resulting interphase formation when Li10GeP2S12 is in contact with Li. Using the observed chemical species, in combination with time-resolved electrochemical measurements, we suggest a reaction mechanism for the interphase formation as well as provide an understanding of the growth kinetics.

1Wenzel S., Leichtweiss T., Krüger D., Sann J., Janek J. Solid State Ion. 2015, 278, 98-105

2Hartmann P., Leichtweiss T., Busche M., Schneider M., Reich M., Sann J., Adelhelm P., Janek J. J. Phys. Chem. C 2013, 117, 21064-21074

3 Wenzel S., Weber D., Leichtweiss T., Busche M., Sann J., Janek J. Solid State Ion. 2016, 286, 24-33

4Wenzel S., Randau S., Leichtweiss T., Weber D., Sann J., Zeier W.G., Janek J. submitted

5Zhu Y., He X., Mo Y. ACS Appl. Mater. Int. 2015, 7, 23685-23693

6Zhu Y., He X., Mo Y. J. Mater. Chem A 2016 DOI: 10.1039/C5TA08574H.