Augment your battery research with non-ambient in-operando XRD – Q&A

by Zhaohui Bao, Thursday, 15th September 2022

Non-ambient in-operando XRD measurements on batteries provide key results allowing us to understand the dynamics of the battery materials at the atomic level. During our webinar event on the 17th of August 2022, we introduced two new specialized battery research stages for our popular Empyrean XRD platform. These two stages with heating and cooling features allow temperature-dependent measurements between -10°C and 70°C. The VTEC is an electrochemical cell including a beryllium window for reflection studies. The VTEC-trans provides a pouch cell stage for transmission studies.

If you did not join the live webinar on your desk but are interested here you can find the recording of the session. We’d like also to share some of the asked questions.

Will the XRD data be having high fluorescent background when the battery contains element identical to the tube anode material?

First of all, let’s understand the mechanism of X-ray fluorescence. The X-ray fluorescence is manifested by the emission of secondary X-rays from the elements that are excited by incident X-rays. The secondary X-ray photons have lower energy than the incident X-rays photons. In X-ray diffraction, the X-ray fluorescence contributes to an elevated background that appears across the entire 2theta range. To improve the XRD data from the impact of fluorescence, two methods are commonly used. The first method uses a diffracted beam monochromator or high-energy resolution detector (such as 1Der) to separate the fluorescent photon by energy. The second method uses an incident monochromatic beam (such as Bragg-Brentano HD) so that the higher energy photons that can cause fluorescence are removed before irradiating on the sample. When the battery contains the same element as the X-ray tube anode material such as Co, or Cu. In those cases, the fluorescent photons have identical energy to the characteristic X-rays of the anode material. This makes the monochromator or high energy resolution detector ineffective. The only method is using an incident beam monochromator. The graph below shows the effectiveness of the Bragg-Brentano HD in removing the fluorescence of the Cu element compared to a classic slit optic.

A measurement with slit optics and a beta filter (red) on a Cu-rich sample shows a very high background due to fluorescent radiation from the sample. With Bragg-Brentano HD (blue), this fluorescent background is completely absent. The insert shows a detailed view of the background.

However, the practical solution combining both the incident beam monochromator and the high-energy resolution detector gives a complete solution that can work with any elements. Malvern Panalytical’s BBHD/iCore optic with 1Der detector fulfills this solution perfectly and provides the best data quality to the XRD measurements independent of the elements of the materials.

Data collected on a mixture of Cr2CuO4 +Cr2O3 + CrCuO2. (Blue) a classic slit optic with a standard detector. (Green) a classic slit optic with 1Der the high-energy resolution detector. (Red), the iCore with 1Der detector which show the lowest background level amongst all solutions.

What is the influence of the temperature on the crystallite size?

As shown in the example data, the LiFePO4 crystallite size has a clear dependence on the temperature. The crystallite size is reduced at a lower temperature after going through the same charging-discharging condition at different temperatures. During the same duration, the crystallite does not grow as fast as at high temperatures due to the reduced electrochemical reaction rate at lower temperatures.

At the given temperature, the effect of the crystallite on the performance of the battery can be investigated across a series of the battery. We are looking forward to seeing your results studied with VTEC or VTEC-trans.

Can the VTEC-trans be used to study solid-state batteries and which X-ray tube should be used?

In an XRD measurement, the X-ray beam is attenuated by the battery. The intensity should be sufficient to reveal the diffraction peaks of the battery materials within the given data collection duration. To improve the diffraction signal, hard radiation and an efficient detector should be used. Ag or Mo radiation has higher penetration power and the GaliPIX^3D with CdTe sensor detects more effectively the hard X-ray photons with ~ 100% quantum efficiency. Therefore, if the batteries’ dimension and attenuation are compatible with the selected X-rays, it’s possible to investigate them with VTEC-trans. However, the solid-state battery requires a stack pressure load that the VTEC-trans is not designed for.

I have a potentiostat. Can it be used with VTEC or VTEC-trans?

We have a fully integrated solution with the BioLogic potentiostat. We also have off-the-shelf robust solutions for potentiostat brands such as Maccor, Ivium, Lanhe. But any potentiostat can be used with VTEC or VTEC-trans stages when the integrated control is not a must. If you are interested in an integrated solution with a specific type of potentiostat, please reach out to us for a customized solution.

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