Spectroscopy and quantification of lithium by x-ray microanalysis – SQLX

Lithium is an increasingly important element because of its applications for energy in particular: the demand for lithium batteries is increasing with the development of electric vehicles. It is crucial to be able to quantify it, determine its concentration, reliably and with an easy-to-access and easy-to-use laboratory instrument, in minerals that can be used as ore, in devices such as batteries and even in materials to be recycled. The Li K emission is a highly sensitive emission band for the chemical state of lithium and conventional quantification models, based on measuring the intensity of a characteristic X emission, cannot be applied as such. To obtain a reliable quantification, we propose a research project divided into three tasks.

First, we will equip the spectrometer of an electron microprobe with a periodic multilayer designed for the Li K spectral range. This multilayer has already been manufactured and partially characterized. The results are promising and show that this dispersive element is suitable for spectroscopy around 50 eV. Pending the start of the next task, this first step will allow the project partners to become familiar with this particular spectral range by analyzing reference samples with a spectral resolution of the order of 3 eV.

The second task will be to install a spectrometer with high spectral resolution on an electron microprobe. The dispersive element of this apparatus, which is commercially available, is a reflective Fresnel zone, operating in an analogous manner to a variable line spacing grating. It will allow the K-spectrum of lithium to be obtained with a resolution of 0.7 eV, i.e. the shape of the emission band will be sensitive to the chemical state of the lithium atom. The samples of the first task will in turn be analyzed and will be complemented by measurements on minerals.

The third task, carried out partly in parallel with tasks 2 and 3, will consist in developing an original model for the quantification of lithium in solids, based on the measurement of the intensity of its emission band. Since quantification cannot be based on an intensity measurement at a single energy and on a single X-ray attenuation coefficient, emission and absorption spectra will be calculated. For this purpose, ab initio calculations of occupied and unoccupied densities will be necessary as well as a critical evaluation of the fundamental parameters existing in the literature, attenuation coefficients and fluorescence yields. Taking into account the integrated intensity of the emission band as well as the optimized choice of attenuation coefficients will lead to an elementary quantification model which will be tested first on reference samples and then validated on minerals. Finally, in the final part of the project, the model will be used for geological applications, in particular the quantification and distribution of lithium in natural deposits in the Alps.

The consortium consists of five institutions and eleven partners. It brings together specialists in X-ray instrumentation, the implementation of electron microprobes, the development of elementary quantification models, ab initio calculations of occupied and empty state densities, evaluation of fundamental parameters, geological applications, etc. One PhD student will join the project at the beginning of its second year and will actively participate in tasks 2 and 3. This will bring together all the scientific skills needed to complete the SQLX project.