Characterization of lithium isotopes in innovative materials for energy-related applications using elemental mapping based on LIBS analysis
Abstract
Lithium is an element of interest in various fields such as geochemistry, archaeology, biochemistry and energy [1]. In this latter field, the increasing demand for lithium induces competition for imports between different countries due to its categorization as a critical raw material [2]. Moreover, its electrochemistry is still being studied to develop innovative materials for future generation batteries. As one of the most sensitive elements in optical spectrometry, lithium is well suited for characterization using LIBS-based techniques. In this work, we introduce the use of this technique to characterize Li-containing materials used for the two applications described below related to the energy field.
The first one is part of the research performed on new materials for lithium extraction from brines. In order to characterize the mechanisms and extraction efficiency of these materials, LIBS imaging can be successfully used. Particularly, localization of the selective adsorption sites of lithium in hierarchical materials by LIBS with a lateral resolution of 8 µm will be presented. The results will be compared with other ones obtained by time of flight secondary ion mass spectrometry (ToF-SIMS).
The second application focuses on lithium batteries, particularly on lithium isotopic labelling in hybrid electrolyte materials constituted by an ionic conductive ceramic in polymer matrix dedicated to solid-state batteries [3]. Thus, we aim at characterizing the mobility of lithium ions and at better understanding its behavior at interfaces in the electrochemical system. For that purpose, we developed Laser-Induced Breakdown Self-Reversal Isotopic Spectrometry (LIBRIS). Based on the same instrumentation as LIBS, the LIBRIS technique aims to overcome the low spectral shift between lines of 6Li and 7Li isotopes using the self reversal phenomenon. Self-reversal is an extreme case of self-absorption, i.e. absorption by the outer layers of the plasma of photons emitted by the plasma core, for which an absorption dip appears in the center of the emission line. The analytical method is based on the correlation between the wavelength of the absorption dip and the isotopic abundance. We will present experiments on LIBRIS analysis in model stack electrochemical systems (7Li electrode/electrolyte/6Li electrode). Lithium isotopes analysis is developed in depth-profiling mode, and by mapping the lithium isotopic abundance at high lateral resolution over a transverse section of the system. This characterization is performed on samples of variable complexity, from pristine material to hybrid materials used as solid-state electrolytes in Li-ion batteries. This approach aims at providing insight on transport mechanisms of lithium in such materials, with the objective of their optimization to enhance batteries performances.