Revealing solid electrolyte interphase formation through interface-sensitive Operando X-ray absorption spectroscopy

Abstract

The solid electrolyte interphase (SEI) that forms on Li-ion battery anodes is critical to their long-term performance, however observing SEI formation processes at the buried electrode-electrolyte interface is a significant challenge. Here we show that operando soft X-ray absorption spectroscopy in total electron yield mode can resolve the chemical evolution of the SEI during electrochemical formation in a Li-ion cell, with nm-scale interface sensitivity. O, F, and Si K-edge spectra, acquired as a function of potential, reveal when key reactions occur on high-capacity amorphous Si anodes cycled with and without fluoroethylene carbonate (FEC). The sequential formation of inorganic (LiF) and organic (-(C=O)O-) components is thereby revealed, and results in layering of the SEI. The addition of FEC leads to SEI formation at higher potentials which is implicated in the rapid healing of SEI defects and the improved cycling performance observed. Operando TEY-XAS offers new insights into the formation mechanisms of electrode-electrolyte interphases and their stability for a wide variety of electrode materials and electrolyte formulations.

Nano-FTIR Spectroscopy of the Solid Electrolyte Interphase Layer on a Thin-Film Silicon Li-Ion Anode

“…This would be consistent with the beneficial properties of the FEC additive, which deposits LiF at a higher potential on Si resulting in better passivation and higher coulombic efficiency. 68 The successful implementation and demonstration of these strategies hinges on having adequate characterization methods that allow for the chemistry of the organic layer and the nanoscale morphology of the inorganic layer to be confidently tied to its passivation performance.…”

How Beam Damage Can Skew Synchrotron Operando Studies of Batteries

“…Operando experiments in batteries have offered valuable insights into the mechanisms at play inside the devices and thus have been performed using a variety of probes, e.g. neutrons, photons (from visible light to X-rays), electrons, and acoustic or nuclear magnetic resonance. − In particular, synchrotron radiation techniques such as spectroscopy, imaging, or diffraction offer a good penetration depth, element selectivity, and a large sensitivity that enable fast acquisitions, taking advantage of the intense photon flux available. The downside of using a large incident photon flux is the increase of unwanted interactions of the X-rays with the sample under scrutiny.…”

Structural and Interphasial Stabilities of Sulfurized Polyacrylonitrile (SPAN) Cathode

“…The evolution of carbon species is revealed in the carbon K-edge sXAS spectra. In the pristine sample, the peaks arise from different antibonding orbitals associated with the pyridine CC, C–S, and CO bonds, , which are labeled in Figure . After cycling, the pyridine CC peak intensity decreased because of the CEI formation, and a vinyl CC peak at lower energy was observed.…”