High-resolution isotopic analysis of lithium by micro laser-induced breakdown self-reversal isotopic spectrometry (LIBRIS) for isotopic labelling of lithium in solid-state electrolyte of lithium batteries

In order to improve the safety of Li-ion batteries, solid-state electrolytes have been studied for many years. However, lithium is known to have lower diffusion coefficients in these materials. Various methods can be used to investigate lithium transport mechanisms; one of them relies on isotopic tracing. This method often used in environmental sciences, medicine and biology has been developed since 2011 by Lu et al. in the battery field. In addition to the techniques commonly used for isotopic analysis of lithium in battery materials, such as nuclear magnetic resonance (NMR) and mass spectrometry techniques, a new complementary method for determining the spatial distribution of the lithium isotopic ratio in solid electrolytes has been developed: laser induced self-reversal isotopic spectrometry (LIBRIS) proposed by Touchet et al. in 2020. In this paper, a proof of concept of LIBRIS analysis of a solid electrolyte composed of poly(ethylene oxide) (POE) containing 6Li enriched lithium bis(trifluoromethylsulphonyl)imide (LiTFSI) was first achieved. Then, the lateral resolution of LIBRIS measurements was improved from 250 μm down to 7 μm. Such lateral resolution is well adapted to future studies of lithium transport mechanisms in a solid electrolyte composed of a dispersion of ceramic microparticles in a polymer matrix. This material design is used as a trade-off to improve Li diffusion compared to polymer-based electrolytes. The sources of signal fluctuations were discussed, and a calibration curve of the 6Li isotopic abundance in POE/LiTFSI samples was finally obtained, with a relative uncertainty of 25%. The results demonstrate the feasibility of high resolution isotopic analysis by the LIBRIS technique and could be applied in the future to the characterization of the lithium mobility in battery materials.