新規LIB電解液用化合物のスクリーニングを目指した分子動力学シミュレーション

抄録

Lithium-ion Battery (LIB) is attracting a great deal of attention with the spread of electric vehicles and large storage batteries. Therefore, it is required that performance of LIB (safety, storage, cycle characteristics, electric power and so on) is more improved. In particular, electrolyte is important factor because it has an important role for the movement of ions between electrodes. We observed the relationship between molecular radius and physical properties of electrolytes mainly by using molecular dynamics simulations. In this research, we found that the smaller the molecule radius of solvent is, the more it contributes to enhancement in ionic conductivity. There are two reasons for the above. First, a smaller radius of solvent molecule makes it easy to diffuse. So some solvent molecules together tend to surround around- a lithium ion, and the diffusion coefficient of lithium ions becomes larger. Secondly, it is easier for small molecule of solvent to come close to ions. Thus, the size of solvent molecule affects degree of dissociation of salt. In this report, we clarify the relationship between molecular radius of solvent and coordination number of lithium ion via radial distribution function (RDF) analysis. As a results, a large peak of carbonyl oxygen appears around the separation 0.2 nm. Further, after the coordination number of lithium ion was calculated by numerically integrating RDF value in the range between 0 and 0.25 nm, we found that the coordination number of lithium ion is estimated at 2.8 ~ 4.4. This fact confirms the effectiveness of smaller solvent molecules.