Spatially-resolved nanoscale detection and quantification of lithium in emerging materials are critical for such key technology application areas as renewable energy, transportation, aerospace, organic synthesis and pharmacy. Li is the lightest element that can generate characteristic X-rays by electron interaction, but >99% of Li X-ray photons are expected to be absorbed in a 0.3 µm thick polymer window [1, 2]. Windowless silicon drift (SDD) energy-dispersive X-ray (EDX) detectors with

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... e electronics and more efficient geometry designed to collect X-rays under low-kV conditions down to 20 eV have advanced ultra-soft X-ray light element analysis by eliminating the absorption of Li Ka and other soft X-rays. Although lithium detection in Li metal foils by SDD EDXS was demonstrated recently [1, 2], detection challenges remain [2, 3] . Li and its compounds are often highly reactive and, upon being exposed to air, readily react with it. The escape depth of Li is less than 20 nm and, as the surface accumulates the oxidation products, the Li Ka X-rays are increasingly absorbed in the oxidized layer. Additionally, the transition from the Li Ll to K shells is not allowed by the selection rule. Unless bonding interaction causes the Ll electron to take on more L2,3 characteristics, Li X-ray generation therefore cannot occur [1, 3] .