From the Synchrotron to the Laboratory: Recent Advancements in X-Ray Instrumentation for Electrochemical Energy Storage and Conversion
Authors: Gelb Jeff , Lewis Sylvia , Seshadri Srivatsan , Stripe Benjamin , Yang Xiaolin , Vine David , Yun Wenbing 
Published: February 2020

X-ray probes have grown in popularity in recent years for understanding and characterizing lithium-ion batteries. Owing to the high penetrating power of X-rays, the non-destructive nature of their interactions with matter, and the range of information they can provide, X-ray instrumentation has been demonstrated to be a powerful, flexible solution for characterization. Crystal structure and bulk composition can be analyzed through X-ray diffraction (XRD), localized composition with fluorescence (XRF), 3D microstructure with computed tomography (XCT), and oxidation states with absorption spectroscopy (XAS), all while preserving the specimen for future analysis (such as destructive and/or electrochemical testing).

While X-ray techniques are undoubtedly powerful, access to them is often limited to synchrotron facilities. The instrumentation at these facilities is world-class, but the facilities tend to be significantly oversubscribed, severely limiting access for a large population of researchers. Many X-ray instruments are available in a laboratory format, but are subject to various limitations. Laboratory XRF, in particular, is often limited in spatial resolution to the 100s of micrometers, with chemical sensitivity in the parts-per-million (ppm) range. XAS and XCT techniques often are limited in throughput, requiring integration times in the tens of hours or longer. These techniques are widely used at synchrotrons, but have yet to become popular in general electrochemical characterization laboratories due to the various practical limitations encountered.

In our work, we have developed a unique suite of laboratory instrumentation, capable of providing access to a variety of synchrotron X-ray techniques in stand-alone packages. We began with redesigning the conventional laboratory X-ray source in a unique way, enabling high throughput imaging with access to a variety of X-ray energies / wavelengths. This source concept was subsequently paired with an assortment of X-ray lenses, such as parabolic capillary condensers, crystal analyzers, and/or Fresnel zone plates, to enable a variety of characterization platforms. Through this design concept, we have developed a laboratory micro-XRF system capable of providing single-micron spatial resolutions with chemical sensitivity in the parts-per-billion (ppb) range, as well as a laboratory XAS configuration that provides sub-eV energy resolution, short data collection times, and spatial resolutions in the 10s of micrometers. Further, by coupling a Fresnel zone plate objective to a capillary condenser, nano-scale XCT is now possible with spatial resolutions down to 40 nm, delivering a 3D map of battery microstructure and equally applicable to studies of electrodes, separators, and other integral components of electrochemical devices.

Here, we will present the design concepts of this novel characterization platform and demonstrate the application of each technique to studying Li-ion battery materials. The trace element content is mapped with microXRF, while the 3D microstructure is revealed using nano-scale XCT. Oxidation state information is mapped using XAS, thus providing a rich suite of data to aid in the understanding of battery structure, composition, and redox dynamics. We will review the types of studies that have been performed at synchrotron facilities and discuss the path forward, to increase the availability of the techniques and enhance the understanding of energy storage and conversion devices.