Controlled Experiments and Optimized Theory of Absorption Spectra of Li Metal and Salts

Investigations 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, 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, which displays a prominent leading peak that has never been revealed before, and a series of Li salts. Furthermore, theoretical simulations show that the Li-K sXAS is strongly affected by the response of the valence electrons to the core-hole. We consider a number of relevant parameters such as temperature, resolution, total and single-particle energies, and especially, contributions from transitions which are forbidden in the single-particle treatment.