Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy

Julia Maibach,Hans Siegbahn,Håkan Rensmo,Ida Källquist,Maria Hahlin,Kristina Edström,Margit Andersson,Samuli Urpelainen

doi:10.1038/s41467-019-10803-y

Abstract

Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy. Here, we present the ambient pressure photoelectron spectroscopy characterization of a model electrolyte based on 1M bis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. For the first time, we show ambient pressure photoelectron spectroscopy data of propylene carbonate in the liquid phase by using solvent vapor as the stabilizing environment. This enables us to separate effects from salt and solvent, and to characterize changes in electrolyte composition as a function of probing depth. While the bulk electrolyte meets the expected composition, clear accumulation of ionic species is found at the electrolyte surface. Our results show that it is possible to measure directly complex liquids such as battery electrolytes, which is an important accomplishment towards true operando studies.

Highlights

Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy
Ambient pressure photoelectron spectroscopy (APPES) measurements were performed on two samples: a solvent drop, consisting of pure propylene carbonate (PC) on Li metal and a liquid electrolyte drop, consisting of 1M LiTFSI in PC on Li metal
This is in contrast to measurements obtained in 2 mbar ambient pressure of Ar gas, which resulted in the instantaneous evaporation of the PC drop and a continuous evaporation of PC from the electrolyte drop

Summary

Introduction

Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy. We show ambient pressure photoelectron spectroscopy data of propylene carbonate in the liquid phase by using solvent vapor as the stabilizing environment This enables us to separate effects from salt and solvent, and to characterize changes in electrolyte composition as a function of probing depth. Investigations of the SEI commonly use scanning electron microscopy (SEM)[3,4,5], transmission electron microscopy (TEM)[6,7], photoelectron spectroscopy (PES)[4,5,8], and Fourier transform infrared spectroscopy (FTIR)[5,6], along with diffraction[4,7] and electrochemical methods[3,6,7] These diverse methods yield complementary information about the structure, composition, functional groups, and resistivity of the SEI, the full characteristics of its formation remain unclear. The high brilliance radiation gives additional advantages, such as, high resolution and a tunable photon energy ranging from soft to hard X-rays[11] that permits for depth profiling

Methods

Results

Conclusion