Investigation of Li metal and ionic compounds through experimental and theoretical spectroscopy has been of tremendous interest due to their prospective applications in Li–metal and Li-ion batteries. Li K-edge soft X-ray absorption spectroscopy (sXAS) provides the most direct spectroscopic characterization; unfortunately, due to the low core-level energy and the highly reactive surface, Li–K sXAS of Li metal has been extremely challenging, as evidenced by many controversial reports. Here, through controlled and ultra-high energy resolution experiments of two kinds of in situ prepared samples, we report the intrinsic Li–K sXAS of Li–metal that displays a prominent leading peak that has not been revealed before. Furthermore, theoretical simulations show that, due to the low number of valence electrons in Li, the Li–K sXAS is strongly affected by the response of the valence electrons to the core hole. We successfully reproduce the Li–K sXAS by state-of-the-art calculations with considerations of a number of relevant parameters such as temperature, energy resolution, and, especially, contributions from transitions which are forbidden in the single-particle treatment. Such a comparative experimental and theoretical investigation is further extended to a series of Li ionic compounds, which highlight the importance of considering the total and single-particle energies for obtaining an accurate alignment of the spectra. Our work provides the first reliable Li–K sXAS of the Li metal surface with advanced theoretical calculations. The experimental and theoretical results provide a critical benchmark for studying Li chemistry in both metallic and ionic states.

中文翻译：

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锂金属和锂盐吸收光谱的控制实验和优化理论

由于锂金属和锂离子电池的潜在应用，通过实验和理论光谱研究锂金属和离子化合物引起了极大的兴趣。Li K-edge软X射线吸收光谱（sXAS）提供最直接的光谱表征；不幸的是，由于低核能级和高反应性表面，锂金属的 Li-K sXAS 一直极具挑战性，许多有争议的报道都证明了这一点。在这里，通过两种原位的受控和超高能量分辨率实验制备的样品，我们报告了锂金属的固有 Li-K sXAS，它显示了以前未发现的显着领先峰。此外，理论模拟表明，由于 Li 中的价电子数较少，Li-K sXAS 受到价电子对核孔响应的强烈影响。我们通过最先进的计算成功地再现了 Li-K sXAS，并考虑了许多相关参数，例如温度、能量分辨率，尤其是单粒子处理中禁止的跃迁的贡献。这种比较实验和理论研究进一步扩展到一系列锂离子化合物，这突出了考虑总能量和单粒子能量以获得准确的光谱对齐的重要性。我们的工作通过先进的理论计算提供了第一个可靠的锂金属表面的 Li-K sXAS。实验和理论结果为研究金属态和离子态的锂化学提供了关键基准。