Elemental-sensitive Detection of the Chemistry in Batteries through Soft X-ray Absorption Spectroscopy and Resonant Inelastic X-ray Scattering

The overall goal of this protocol is to apply soft X-ray absorption spectroscopy and resonant inelastic X-ray scattering to battery material studies. This method is about utilizing soft X-ray spectroscopy, including X-ray absorption and resonant inelastic X-ray scattering, the so-called RIXS, as unique tools to answer the key questions in battery field. The main advantage of this technique is it can directly probe the chemical reactions in various battery material and develop this field beyond the conventional trial-and-error approach.

Though this method can provide insight into battery materials, it can also be applied to other systems, such as catalysts, solar cells, and semiconductors. Visual demonstration of this method is critical as synchrotron based soft X-ray spectroscopy is difficult to learn without it. This protocol provides a detailed visual example of a typical experiment.

To begin, cut the battery material samples to fit the sample holder, ensuring that each sample is larger than the beam spot. Fix the samples on the sample holder with double-sided conductive tape. For some powder samples, use indium foil to stick if necessary.

Then, vent the sample load lock with nitrogen gas. Use a sample grabber, such as large tweezers, to load the sample holder into the load lock. Close and evaluate the load lock.

Once the load lock pressure is sufficiently low, open the valve between the load lock and the main chamber. Using the transfer arm, transfer the sample holder to the main manipulator in the main chamber. Close the valve to the load lock, then open the valve between the main chamber and the beam line.

Locate the beam spot by observing visible light fluorescence on a reference sample or on a phosphor applied to the sample holder. Position a sample in the beam spot using the sample manipulator controls. Connect the X-ray beam flux monitor signal cables to the measurement computer.

Adjust the beam line monochromator slits to tune the energy resolution of the incident X-ray beam. Then, set the incident beam energy to the absorption edge of the element or elements of interest. Fix the monochromator mechanism in place.

Measure the beam flux intensity and identify the undulator gap value that provides the maximum possible beam flux. To begin the sXAS data collection process, ensure that the sample current signal used to measure the total electron yield is directed to the measurement computer. Turn on the power supplies and controllers of the electron multiplier or photo diode used to measure the total fluorescence yield.

Ensure that the signal is directed to the computer. Then, in the data acquisition software, select Single Motor Scan. Open the Scan Setup menu and set the incident X-ray photon scan range to span the sXAS edge of interest.

Click Start Scan to simultaneously record the total electron yield, total fluorescence yield, and the beam flux while scanning the incident X-ray photon energy. Follow the same beam alignment and data collection procedure to acquire sXAS data for additional samples. If a reference sample has been scanned, adjust the scan range accordingly for any shift observed in the sXAS values.

After collecting sXAS data, turn on the spectrometer for the sXES and RIXS system and cool down the soft X-ray detector, then open the motor controls. Set the spectrograph parameters to cover the energy range of the elements and edges of interest. Next, select CCD Instrument Scan and open the Scan Setup.

For sXES, set a single value about 20 to 30 electron volts above the calibrated sXAS absorption edge. For RIXS, set the scan range to span the sXAS absorption edge. Select Apply Cosmic Ray Filter so that cosmic ray signals will be removed from the raw RIXS 2D images after initial data collection.

Start the scan to collect fluorescent signals in 2D image form for each excitation energy. This RIXS image was collected from a lithium-ion battery material sample over the energy range of the Oxygen-K edge and the Manganese, Cobalt, and Nickel-L edges. A full range sXES covering all four edges simultaneously was collected in 10 seconds.

A RIXS map of the Nickel-L edge was generated from the raw RIXS image data. Analysis of this map showed that the Nickel-L RIXS features were dominated by d-d excitations. Transition metal redox states in sodium-ion and lithium-ion battery materials were analyzed by quantitative fitting of sXAS spectra.

The surface manganese valence distribution in layered sodium-manganese oxide electrodes at different electrochemical states was determined by quantitative fitting of sXAS spectra to a linear combination of Manganese II, III, and IV cation reference spectra. The redox process of a spinel lithium-nickel-manganese oxide electrode was identified as sequential single-electron transfers by a similar quantitative fitting approach using total fluorescence yield. Intermediate charge states of lithium-iron-phosphate electrodes were identified by quantitative fitting based on sXAS spectra of the electrodes at 0%and 100%charge.

We have been making efforts to utilize synchrotron-based soft X-ray spectroscopy to characterize battery materials with unprecedented results. After its development, the technique paved the way for the researchers in the field of battery materials. The researchers can use it to explore the fundamental mechanula of the battery material.

After watching this video, you should have a good understanding of how to perform soft X-ray spectroscopy at a synchrotron light source.