[P2-63] Molecular dynamics screening for developing compounds of electrolytes with high performance in lithium ion batteries
Recently, there is great interest in development of electric vehicles, so it demands improvement in performance of Lithium-ion Battery (LIB). For higher performance, it is important to develop new substances used for electrolyte or electrode. In particular, electrolyte is an important chemical factor for moving lithium ions between positive and negative electrodes in the battery. When the amount of ions moving is enhanced, the performance of the battery will be effectively improved. But there are hundreds of thousands of compounds as candidates for electrolytes, so we need to screen and choose ones from these many compounds. In this research, we perform atomistic evaluation about various characteristics of possible compounds of electrolyte (such as viscosity, ionic conductivity, degree of dissociation and diffusion coefficient) by mainly using molecular dynamics (MD) simulations. In evaluating at a molecular level, we can understand how the molecular level structure and properties affect the behavior of electrolyte. Molecule models we are using are ethylene carbonate (EC), fluoro ethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL), γ-valerolactone (GVL), dimethyl carbonate (DMC), ethyl-methyl carbonate (EMC), diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6). An electrolytes system in which 1 mol of LiPF6 is mixed per 1 L of single solvent (solvent + 1M-LiPF6) is simulated. The results suggest that we can determine a criterion for the screening of superior compounds based on information about molecular structures and properties of electrolyte. It is found that the smaller solvent molecules that easily diffuse contribute to the higher ionic conductivity of electrolytes. This is because diffusion coefficient of Li cation is greatly affected by that of solvent molecules. It is also found that solvation structure and size around Li cation take large effect on its diffusivity.