First-Principles Study of EMIM-FAFSA Molecule Adsorption on a Li(100) Surface as a Model for Li-Ion Battery Electrodes

作者：Valencia Hubert^*; Kohyama Masanori; Tanaka Shingo; Matsumoto Hajime

来源：Journal of Physical Chemistry C, 2012, 116(15): 8493-8509.

DOI：10.1021/jp2109797

The atomic and electronic structures of 1-ethyl-3-methyl imidazolium [C6H11N2](+) (EMIM) fluoroalkyl-fluorosulfonyl amid (FAFSA) molecule adsorption on a Li(100) surface were examined using periodic density functional theory calculations, as a model for a room-temperature ionic-liquid (RTIL) electrolyte/Li-anode interface in a Li-ion battery. First, we examined the nature of isolated FAFSA anions and EMIM-FAFSA pairs for bis(fluorosulfonyl) amid [(F - SO2)(2)N](-) (FSA), fluorosulfonyl(trifluoromethylsulfonyl) amide [(F3C-SO2)N(SO2-F)](-) (FTA), bis(trifluoromethylsulfonyl) amid [(F3C-SO2)(2)N](-) (TFSA), and 1,2,3-dithiazolidine-4,4,5,5-tetrafluoro-1,1,3,3-tetracadde [-((F2C-SO2)N(SO2-CF2))-](-) (CTFSA). These FAFSA(-) molecules except for CTFSA(-) with a ring structure have both trans and cis conformers. Free EMIM-FAFSA pairs prefer to form trans conformers, while cis conformers become more stable when the pairs are adsorbed on a Li(100) surface. The ion-pair adsorption on a Li(100) surface generally reveals the following features, essentially similar to the EMIM-BF4/Li case in our previous studies: the surface Li atoms under the FAFSA anion are remarkably attracted toward the anion, leading to O-Li or F-Li bond formation, while valence electrons around the Li atoms are transferred to the EMIM cation, leading to substantial reduction of EMIM+. The EMIM-FSA, EMIM-FTA, and EMIM-TFSA systems show similar features with systematic variations depending on the fluoralkyl substituent, while the EMIM-CTFSA pair shows somewhat different features. We discussed the relation between the present theoretical results and the experimental electric transport properties at RTIL/electrode interfaces.

• 出版日期2012-4-19