posted on 2021-09-16, 19:08authored bySubhayan Roychoudhury, Zengqing Zhuo, Ruimin Qiao, Liwen Wan, Yufeng Liang, Feng Pan, Yi-de Chuang, David Prendergast, Wanli Yang
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.