Characterising lithium-ion electrolytes via operando Raman microspectroscopy

Abstract

Knowledge of electrolyte transport and thermodynamic properties in Li-ion and beyond Li-ion technologies is vital for their continued development and success. Here, we present a method for fully characterising electrolyte systems. By measuring the electrolyte concentration gradient over time via operando Raman microspectroscopy, in tandem with potentiostatic electrochemical impedance spectroscopy, the Fickian “apparent” diffusion coefficient, transference number, thermodynamic factor, ionic conductivity and resistance of charge-transfer were quantified within a single experimental setup. Using lithium bis(fluorosulfonyl)imide (LiFSI) in tetraglyme (G4) as a model system, our study provides a visualisation of the electrolyte concentration gradient; a method for determining key electrolyte properties, and a necessary technique for correlating bulk intermolecular electrolyte structure with the described transport and thermodynamic properties.

Parameterising continuum level Li-ion battery models & the LiionDB database

“…One can measure V e and V 0 readily with densitometry, as discussed in section 5.2.5. Recent spectroscopic techniques have also allowed for the probing of solvent concentrations [192,193].…”

“…These profiles are used to validate [211] or inversely fit relevant transport properties [192,200,212]. Raman spectroscopy and X-ray scattering has also been used to measure salt concentration profiles [193,208]. Transport parameters obtained from inverse fitting are therefore highly dependent on the formulation of the models used to fit composition gradients.…”

“…The electrolyte density can easily be attained by comparing the mass and volume of a particular solution. It is commonly measured with commercial densitometers, that operate based on the oscillating U-tube principle [170,173,178,192,193]. By vibrating a container filled with solution, the frequency is then linked to the mass per unit volume.…”

Accelerating Battery Characterization Using Neutron and Synchrotron Techniques: Toward a Multi‐Modal and Multi‐Scale Standardized Experimental Workflow

“…Lab‐scale techniques are being constantly developed to measure structural, morphological, and chemical changes at nm, µm, or mm scales during battery cycling, for example, operando transmission electron microscopy, [ 3 ] nuclear magnetic resonance (NMR), [ 4 ] Fourier transform infra‐red, [ 5 ] Raman, [ 6 ] and more. To complement lab‐scale studies, cutting‐edge experiments at large scale facilities (LSF) have been increasingly developed.…”

Insights into the Transport and Thermodynamic Properties of a Bis(fluorosulfonyl)imide-Based Ionic Liquid Electrolyte for Battery Applications

“…Concentration gradients were visualized using operando Raman microspectroscopy ( Figure 1 ), specifically, a time-series of one-dimensional (1D) Raman scans across a custom-built optical Li|Li symmetric cell while current is passed. 22 Importantly, the cell was placed vertically on the stage, with stripping occurring at the bottom and plating at the top, to avoid natural convection from density differences of the bulk concentration. The line-scan was performed every 4 h for 36 h. Electrolyte solutions were prepared gravimetrically (molal) to increase reliability and accuracy of preparation (for density measurements and molarity equivalents, see Supporting Methods ).…”