New insights into the kinetics of metal|electrolyte interphase growth in solid-state-batteries via an operando XPS analysis - part I: experiments

Abstract

To harness all the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals make them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quantitative information about the interphase chemical composition and rate of formation are challenging to obtain because the reaction occurs at a buried interface. In this study, a thin layer of Na metal (Na0) is plated on the surface of a SE of the NaSICON family (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a commercial XPS system whilst continuously analysing the composition of the interphase operando. We identify the existence of an interphase at the Na0|NZSP interface, and more importantly, we demonstrate for the first time that this protocol can be used to study the kinetics of interphase formation. A second important outcome of this article is that the surface chemistry of NZSP samples can be tuned to improve their stability against Na0. It is demonstrated by XPS and time-resolved electrochemical impedance spectroscopy (EIS) that a native Na3PO4 layer present on the surface of as-sintered NZSP samples protects their surface against decomposition.

Operando characterization and theoretical modelling of metal|electrolyte interphase growth kinetics in solid-state-batteries - Part II: Modelling

“…XPS spectra is taken from ref. 11 This second part focuses on understanding how the kinetics of SEI formation and Na 0 electroplating are interrelated in the operando XPS experiment. More specifically, the coupled ion-electron transfer (CIET) model is adapted to describe how Na 0 plating on a NZSP surface is affected when a blocking SEI layer is formed at the Na 0 |NZSP interface.…”

“…The simulated model is employed to fit XPS data from ref. 11 The adapted CIET model is able to accurately describe the evolution of the XPS peak areas and peak shifts as a function of plating time (Figure 2), where The change in photoelectron binding energy is correlated with the coverage of a given interface on the NZSP surface, while the integrated area of the Na 0 peak is correlated with the total amount of Na 0 plated. This second part of the study provides information about the kinetics of SEI formation and demonstrates the depth of information which can be extracted from a single XPS experiment to study the stability of a metal|SE interface.…”