Hubert Valencia - Ab initio study of EMIM-BF4 molecule adsorption on Li surfaces as a model for ionic liquid/Li interfaces in Li-ion batteries

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  Hubert Valencia, Masanori Kohyama, Shingo Tanaka, and Hajime   Matsumoto, Phys. Rev. B 78, 205402   (2008)


  The adsorption of 1-ethyl-3-methyl imidazolium tetrafluoroborate   (EMIM-BF4)  molecules onto Li (100), (110), and (111) surfaces is   investigated by means of periodic density-functional theory   calculations as a model for room-temperature ionic   liquid/Li-metal anode interfaces in a Li-ion battery. We examined   the atomic and electronic structures of isolated EMIM+  and BF4  molecules, a pair of [EMIM]+[BF4],   and Li bulk and surfaces, which are in good agreement with   previous theoretical and experimental results. We observed that   the EMIM-BF4  adsorption generally induces significant changes on the Li   surfaces. One or two Li-surface atoms are greatly attracted to   the BF4  anion, resulting in electronic density depletion at the attracted   Li atoms while the electrons are attracted toward the EMIM   cation, regardless of the coordination mode of adsorption or the   kinds of Li surfaces. These features represent the tendency of   easy ionization of Li and Lix-BF4-cluster   formation, coupled with reduction in EMIM+,   which is in contrast to the EMIM-BF4  adsorption on a Au (100) surface without any displacements of Au   atoms or any specific electronic behavior to reduce EMIM+.

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