锂在共轭双键高分子中的电化学嵌入反应——Ⅱ.锂在聚吡咯中嵌入反应的量子化学研究

The Electrochemical Intercalation Reaction of Lithium in Polymer with Conjugated Double Bondes——Ⅱ. Quantum Chemical Calculation for Electrochemical Intercalation of Li into Polypyrrole

本文用量子化学CNDO/2方案计算,取文献中吡咯骨架原子的结构参数,再优化锂嵌入聚吡咯的几何参数。结果表明不管是Li^+离子还是中性Li原子,嵌入单个吡咯上还是嵌入两个吡咯之间,它与吡咯环四个碳原子平面的距离都为0.210到0.216nm。且锂与碳原子键合,形成多中心键,锂嵌入聚吡咯后,固有的C_α—C_β双键的键级和键能明显减弱。这与前一报中发现IR谱的15600m^(-1)吸收峰消失相一致。锂正离子嵌入聚吡咯后,使吡咯的前沿π~*矿空轨道的能量由正变为负值,而成为电子接受体(正极),遍及全部聚吡咯的π~*LUMO和HOMO使得聚吡咯呈现导电性能。

Quantum chemistry CNDO/2 program calculation has been used in this paper. In order to optimize the geometric parameters of Li intercalation into polypyrrole, the geometric parameters of pyrrole framework were taken from literature. The results show that either Li atom or Li ion intercalated into the sole ring or between the rings of pyrrole, the distance between Li and pyrrole ranges from 0.210 to 0.216nm. The intercalated lithium forms polycenters bond with the carbon atoms. The bond order and bond energy of C=C in pyrrole were obviously decreased after intercalation. This is consistent with the previously observed fact that the IR absorption bond disappeared at 1560 cm^(-1). When Li^+ was intercalated into polypyrrole electrode (positive electrode), the front unoccupied orbital energy of pyrrole turns from positive to negative, i. e. from higher energy level to lower energy level so as to become electron acceptor capable of accepting electrons from Li electrode of the cell. As the π LUMO and π HOMO of the intercalation compounds exhibit delocalization all over polypyrrole, this renders polypyrrole to have better conductivity.