Identification of LiH and nanocrystalline LiF in the solid-electrolyte interphase of lithium metal anodes

A comprehensive understanding of the solid-electrolyte interphase (SEI) composition is crucial to developing high-energy batteries based on lithium metal anodes. A particularly contentious issue concerns the presence of LiH in the SEI. Here we report on the use of synchrotron-based X-ray diffraction and pair distribution function analysis to identify and differentiate two elusive components, LiH and LiF, in the SEI of lithium metal anodes. LiH is identified as a component of the SEI in high abundance, and the possibility of its misidentification as LiF in the literature is discussed. LiF in the SEI is found to have different structural features from LiF in the bulk phase, including a larger lattice parameter and a smaller grain size (<3 nm). These characteristics favour Li+ transport and explain why an ionic insulator, like LiF, has been found to be a favoured component for the SEI. Finally, pair distribution function analysis reveals key amorphous components in the SEI. X-ray diffraction and Rietveld refinement analysis confirm the presence of LiH in the solid-electrolyte interphase of lithium metal anodes.

Automated summary

A comprehensive understanding of the solid-electrolyte interphase (SEI) composition is crucial for developing high-energy batteries based on lithium metal anodes. This study used synchrotron-based X-ray diffraction and pair distribution function analysis to identify and differentiate two elusive components, LiH and LiF, in the SEI of lithium metal anodes. The presence of LiH in the SEI was confirmed, with discussion on the possibility of its misidentification as LiF in the literature. The study also found that LiF in the SEI has different structural features from LiF in the bulk phase, which favor Li+ transport and make it a favored component for the SEI.