title: The Anion Effect on Li(+) Ion Coordination Structure in Ethylene Carbonate Solutions.
abstract: Rechargeable lithium ion batteries are an attractive alternative power source for a wide variety of applications. To optimize their performances, a complete description of the solvation properties of the ion in the electrolyte is crucial. A comprehensive understanding at the nanoscale of the solvation structure of lithium ions in nonaqueous carbonate electrolytes is, however, still unclear. We have measured by femtosecond vibrational spectroscopy the orientational correlation time of the CO stretching mode of Li(+)-bound and Li(+)-unbound ethylene carbonate molecules, in LiBF4, LiPF6, and LiClO4 ethylene carbonate solutions with different concentrations. Surprisingly, we have found that the coordination number of ethylene carbonate in the first solvation shell of Li(+) is only two, in all solutions with concentrations higher than 0.5 M. Density functional theory calculations indicate that the presence of anions in the first coordination shell modifies the generally accepted tetrahedral structure of the complex, allowing only two EC molecules to coordinate to Li(+) directly. Our results demonstrate for the first time, to the best of our knowledge, the anion influence on the overall structure of the first solvation shell of the Li(+) ion. The formation of such a cation/solvent/anion complex provides a rational explanation for the ionic conductivity drop of lithium/carbonate electrolyte solutions at high concentrations.
authors: State key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.|Department of Chemistry, Rice University , Houston, Texas 77005, United States.
authors: Bo
authors: B
authors: Jiang
authors: Université Grenoble Alpes, INAC-SYMMES; CNRS, INAC-SYMMES; and CEA, INAC-SYMMES, F-38000 Grenoble, France.|Universite Grenoble Alpes, LITEN-DEHT; and CEA, LITEN-DEHT, F-38000 Grenoble, France.
authors: Veerapandian
authors: V
authors: Ponnuchamy
authors: State key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.
authors: Yuneng
authors: Y
authors: Shen
authors: State key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.
authors: Xueming
authors: X
authors: Yang
authors: State key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.
authors: Kaijun
authors: K
authors: Yuan
authors: Universite Grenoble Alpes, LITEN-DEHT; and CEA, LITEN-DEHT, F-38000 Grenoble, France.
authors: Valentina
authors: V
authors: Vetere
authors: Université Grenoble Alpes, INAC-SYMMES; CNRS, INAC-SYMMES; and CEA, INAC-SYMMES, F-38000 Grenoble, France.
authors: Stefano
authors: S
authors: Mossa
authors: Université Grenoble Alpes, INAC-SYMMES; CNRS, INAC-SYMMES; and CEA, INAC-SYMMES, F-38000 Grenoble, France.
authors: Ioannis
authors: I
authors: Skarmoutsos
authors: Department of Chemistry, Rice University , Houston, Texas 77005, United States.
authors: Yufan
authors: Y
authors: Zhang
authors: State key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.|College of Chemistry and Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University , Beijing 100871, China.|Department of Chemistry, Rice University , Houston, Texas 77005, United States.
authors: Junrong
authors: J
authors: Zheng