锂电池电解质溶液中离子溶剂化的热力学和谱学研究

The standard partial molar volumes and viscosity B-coefficients of lithium salts (LiClO4, LiPF6, LiBF4 and LiBr) in propylene carbonate (PC), ethylece carbonate(EC), g-butyrolacton (BL)-based solvent mixtures have been determined systematically, in this project, under the background of development and optimization of lithium battery electrolyte solutions. These data were used to calculate the standard partial molar volumes and viscosity B-coefficients for Li+ and associated anions by the extrapolation method suggested by Conway and co-worker. It is shown that these parameters of Li+ in the most of the systems studied are independent of the nature of the solvents and the composition of the solvent mixtures. The further IR, Raman and NMR results suggested that this phenomenon is resulted from the strong attractive interaction of Li+ with PC, EC, BL and the related co-solvents. And this interaction occurs mainly on the C=O, C-O, -CN or -SO2 groups of the organic molecules. The sovation number of Li+ is found to be dependent on the nature of the solvent and the concentration of the lithium salts. These values are generally in the range of 1-4 in the studied systems. The preferential solvation of Li+ in the solvent mixtures are determined by the difference in the donor number of the solvent and the co-solvent. The power of ion association for lithium salts follows the order: LiBF4"LiClO4>LiCF3SO3>LiPF6. In the solvent with high dielectric constant, lithium salts exist in the form of free ions and solvent separated ion pairs. However, contact ion pairs is also detected in the low dielectric solvents. Quantum chemistry calculation was carried out to study the geometries of ion pairs. It is found that the bidentate structure for Li+ClO4- and Li+BF4- and the tridenate structure for Li+PF6- and Li+AsF6- are preferable.Based on the above experimental and theoretical results, the dielectric friction theory for viscosity B-coefficient of the electrolytes was examined, and the new issues for the improvements of this theory are explored. The effect of Li+ solvation on the cycling behavior of intercalating carbon electrodes, and that of ion solvation and ion association on the performance of lithium battery electrolyte solutions were explained. This provides part of the base for the development of new systems of electrolyte solutions for lithium battery.

拟用红外、拉曼、核磁、体积和粘度等技术研究锂电池电解质溶液中与离子相互作用的溶剂分子基团、离子溶剂化层的结构、离子的存在状态及溶剂对离子体积和粘度B系数影响的分釉颍煅楹头⒄估胱拥藓先芤豪砺郏教諰i溶剂化对嵌入电极循环行为影响的可能机理鲜独胱尤芗粱屠胱拥藓隙缘绯匦阅艿挠跋旎恚⑿滦偷缫禾逑堤峁├砺垡谰荨?..