低聚丙烯腈和乙烯碳酸酯分子间作用的量子化学研究

A quantitative chemical study on the intermolecular interaction of low PAN and EC

以低聚丙烯腈(PANX,X=1,2,4,6)作为聚丙烯腈模型物,采用量子化学从头算的HF/3-21G方法研究PANX和乙烯碳酸酯(EC)分子间的作用。研究表明,聚丙烯腈基体与增塑剂EC分子间存在相互作用,其中N原子和O原子是主要的作用原子,形成了C—H…N、C—H…O(=C)、C—H…O(—C)3类氢键,同时PANX与EC分子的几何参数发生了明显变化。PANX和EC分子的静电势分析表明,PANX—EC体系分子间作用存在静电力。本研究有助于合理选择增塑剂的种类及优化用量,提高聚合物锂离子电池的安全性;有助于了解锂离子在聚合物电解质中的输运机理,提高聚合物电解质的离子电导率。

The present paper intends to find the intermolecular interaction between PAN base and EC plasticizer in the lithium batteries. In the paper, we have applied PANx（X = 1, 2, 4, 6） to the PAN of the former. As is known, since the polyacrylonitrile （PAN）-based gel polymer electrolyte tends to have some well-secured properties and ethylene carbonate （EC） which can usually be used in the polymer electrolyte of the lithium batteries, the intermolecular interaction between PAN and EC can be studied at the level of the HF/3 - 21G theory, with a few of the optimal structures obtained for PANx-EC with X = 1, 2, 4 and 6. In so doing, comparing and analyzing the optimal structures with the lowest energy, we have discovered that three kinds of hydrogen-bond were expected to come about, that is, C--H…N, C-H…O（ = C） and C-H…O（-C）, in which atom O and atom N can be thought of as the chief active atoms. At this, the intermolecular interaction between PAN and EC can be clearly taken as the result of the rotating and bending activities of the C--C bonds in PANx, with the bond angles of C--C--C and the di- hedral angles concerned noticeably changed, which, however, may not have any effect on the bond length. At the same time, noticeable change may also take place with the geometrical parameters of EC and the plane structure of five-element-ring. From the structures of the electrostatic potential it can be deduced that N in PAN and O in EC were surrounded by negative charges, while others--mainly by positive ones. Such interactions may actually be going on between the particles with negative charges in PAN and those with positive ones in EC or the other way around. This clearly indicates that some electrostatic force might be existing between PANx and EC. Thus, it can be concluded that our research is helpful to choose the kinds of plasticizers and improve the safety of the polymer lithium ion batteries. It may also contribute to disclosing the transition mechanism of the lithium ion in the polymer electrolyte and promoting its ionic conductivity.