Interphase formation and degradation of charge transfer kinetics between a lithium metal anode and highly crystalline Li7P3S11 solid electrolyte

Abstract The properties of the interface between solid electrolytes and electrode materials are of vital importance for the performance of all solid-state batteries (ASSB). Unwanted reactions between alkali metal electrodes and the solid electrolyte can lead to the formation of compounds that either facilitate or block the ion transfer kinetics. In particular for lithium solid electrolytes in the Li 2 S–P 2 S 5 system with very high lithium ion conductivity only little is known about interfacial reactions with lithium metal. Here we monitor the formation of an interphase between Li 7 P 3 S 11 and lithium metal by a combined analytical approach, comprising in situ photoelectron spectroscopy and time-dependent electrochemical impedance spectroscopy. Utilizing a self-developed XPS peak fit model for Li 7 P 3 S 11 , we identify the components of this interphase, discuss its properties and develop a qualitative model, which shows that the reaction between electrolyte and lithium metal, and hence, the interphase growth, is limited to a few nm. The solid electrolyte being used is a highly crystalline form of the superionic conductor Li 7 P 3 S 11 without any residual glassy phase, and the synthesis of this Li 7 P 3 S 11 phase is also reported.