In order to achieve high quality in situ spectroscopic X-ray microscopy of complex systems far from equilibrium, such as lithium ion batteries under standard electrochemical cycling, careful consideration of the total number of energy points is required. Enough energy points are need to accurately determine the per pixel chemical information; however, total radiation dose needs to be limited to avoid damaging the system which would produce misleading results. Here we consider the number of energy points need to accurately reproduce the state of charge maps of a LiFePO2 electrode recorded during electrochemical cycling. We observe very good per pixel agreement using only 13 energy points. Additionally, we find the quality of the agreement is heavily dependent on the number of energy points used in the post edge fit during normalization of the spectra rather than the total number of energies used. Finally, we suggest a straightforward protocol for determining the minimum number of energy points needed prior to initiating any in situ spectroscopic X-ray microscopy experiment.
Ptychography is an emerging high resolution coherent imaging technique which can improve the resolution of current scanning transmission X-ray microscopy systems by over ten-fold. Development of this capability is underway at Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, to establish sub-5 nm resolution ptychographic imaging with spatially resolved near-edge X-ray absorption fine structure spectroscopy. This is being achieved via an upgrade of the current soft X-ray scanning transmission X-ray microscope at beamline 13-1, involving the installation of an area detector and an interferometer system for high precision sample motor control. The undulator source on beamline 13-1 provides the spatially and temporally coherent X-ray beam required for ptychographic imaging in the energy range 500 – 1200 eV. This energy range allows access to the oxygen chemistry and the valence states of 3d transition metals found in energy storage materials, making soft x-ray ptychography a particularly powerful tool to study the chemical states and structure of battery materials at relevant length scales. The implementation of ptychographic imaging can therefore provide a wealth of additional information on battery operation and failure. Here we describe the development of this ptychography capability, along with its application to the study of energy storage materials.
Combining the energy tunability provided by synchrotron X-ray sources with transmission X-ray microscopy, the
morphology of materials can be resolved in 3D at spatial resolution down to 30 nm with elemental/chemical
specification. In order to study the energy dependence of the absorption coefficient over the investigated volume, the
tomographic reconstruction and image registration (before and/or after the tomographic reconstruction) are critical. We
show in this paper the comparison of two different data processing strategies and conclude that the signal to noise ratio
(S/N) in the final result can be improved via performing tomographic reconstruction prior to the evaluation of energy
dependence. Our result echoes the dose fractionation theorem, and is particularly helpful when the element of interest
has low concentration.
Radiation damage is a topic typically sidestepped in formal discussions of characterization techniques utilizing ionizing
radiation. Nevertheless, such damage is critical to consider when planning and performing experiments requiring large
radiation doses or radiation sensitive samples. High resolution, in situ transmission X-ray microscopy of Li-ion batteries
involves both large X-ray doses and radiation sensitive samples. To successfully identify changes over time solely due to
an applied current, the effects of radiation damage must be identified and avoided. Although radiation damage is often
significantly sample and instrument dependent, the general procedure to identify and minimize damage is transferable.
Here we outline our method of determining and managing the radiation damage observed in lithium sulfur batteries
during in situ X-ray imaging on the transmission X-ray microscope at Stanford Synchrotron Radiation Lightsource.