Potentials in Li-Ion Batteries Probed by Operando Ambient Pressure Photoelectron Spectroscopy

Development of hard X-ray photoelectron spectroscopy in liquid cells using optimized microfabricated silicon nitride membranes

We present first hard X-ray photoelectron spectroscopy (HAXPES) results of aqueous salt solutions and dispersions of gold nanoparticles in liquid cells equipped with specially designed microfabricated thin silicon nitride membranes, with thickness in the 15-25 nm range, mounted in a high-vacuum-compatible environment. The experiments have been performed at the HAXPES endstation of the GALAXIES beamline at the SOLEIL synchrotron radiation facility. The low-stress membranes are fabricated from 100 mm silicon wafers using standard lithography techniques. Platinum alignment marks are added to the chips hosting the membranes to facilitate the positioning of the X-ray beam on the membrane by detecting the corresponding photoemission lines. Two types of liquid cells have been used, a static one built on an Omicron-type sample holder with the liquid confined in the cell container, and a circulating liquid cell, in which the liquid can flow in order to mitigate the effects due to beam damage. We demonstrate that the membranes are mechanically robust and able to withstand 1 bar pressure difference between the liquid inside the cell and vacuum, and the intense synchrotron radiation beam during data acquisition. This opens up new opportunities for spectroscopic studies of liquids.

Toward Operando Characterization of Interphases in Batteries

Electrode/electrolyte interfaces are the most important and least understood components of Li-ion and next-generation batteries. An improved understanding of interphases in batteries will undoubtedly lead to breakthroughs in the field. Traditionally, evaluating those interphases involves using ex situ surface sensitive and/or imaging techniques. Due to their very dynamic and reactive nature, ex situ sample manipulation is undesirable. From this point of view, operando surface sensitive techniques represent a major opportunity to push boundaries in battery development. While numerous bulk spectroscopic, scattering, and imaging techniques are well established and widely used, surface sensitive operando techniques remain challenging and, to a larger extent, restricted to the model systems. Here, we give a perspective on techniques with the potential to characterize solid/liquid interfaces in both model and realistic battery configurations. The focus is on techniques that provide chemical and structural information at length and time scales relevant for the solid electrolyte interphase (SEI) formation and evolution, while also probing representative electrode areas. We highlight the following techniques: vibrational spectroscopy, X-ray photoelectron spectroscopy (XPS), neutron and X-ray reflectometry, and grazing incidence scattering techniques. Comprehensive overviews, as well as promises and challenges, of these techniques when used operando on battery interphases are discussed in detail.

Dip-and-pull ambient pressure photoelectron spectroscopy as a spectroelectrochemistry tool for probing molecular redox processes

Ambient pressure x-ray photoelectron spectroscopy (APXPS) can provide a compelling platform for studying an analyte's oxidation and reduction reactions in solutions. This paper presents proof-of-principle operando measurements of a model organometallic complex, iron hexacyanide, in an aqueous solution using the dip-and-pull technique. The data demonstrates that the electrochemically active liquid meniscuses on the working electrodes can undergo controlled redox reactions which were observed using APXPS. A detailed discussion of several critical experimental considerations is included as guidance for anyone undertaking comparable experiments.