功能化咪唑碘盐的导电机理研究

According to the Grotthuss charge exchange mechanism, alkyl-substituted imidazolium iodides can exhibit extraordinarily high ionic conductivity only when they are mixed with high concentration iodine. However, we recently find that addition of a propargyl group to the imidazolium ring results in exceptionally high conductivity in the absence of iodine, which cannot be explained by the Grotthuss mechanism. To figure out the essential reason why the propargyl-substituted imidazolium iodide possesses extraordinarily high conductivity, a series of functionalized imidazolium iodides will be designed and synthesized through addition of various functional groups to the imidazolium ring, and their single crystal structures will be determined. The molecular geometries will be fully optimized with dispersion corrected density functional theory using the initial geometries extracted from the crystallographic information files. Accurate descriptions of the non-covalent interactions existing in the crystal obtained from the optimized geometries will help to study the influencing rules of functional groups on the crystal structures. The electronic structures will be systematically discussed for the monomers and the aggregates of imidazolium iodides. In a word, to clarify the conductive mechanism, it is essential to reveal the relationship between the crystal structure and conductivity as well as the role of the functional group in the ionic conductivity. This project is of important theoretical and scientific significance for the development of highly conductive solid-state electrolytes based on the functionalized imidazolium iodides.

根据Grotthuss导电机理，烷基取代咪唑碘盐只有当与高浓度碘混合后，才产生超高的离子电导率。然而，最近我们研究发现，炔丙基取代咪唑碘盐无需与碘混合就可以产生超高的电导率，无法用Grotthuss机理解释。为了解释炔丙基取代咪唑碘盐具有超高电导率的本质原因，本课题拟在咪唑环上引入不同的功能基团，设计合成一系列功能化咪唑碘盐，确定它们的单晶结构。通过色散力校正密度泛函理论，优化功能化咪唑碘盐的几何结构，准确描述分子之间的非共价键相互作用，探究功能基团对晶体结构的影响规律。系统讨论咪唑碘盐的单体和聚集体的电子结构，揭示晶体结构与电导率的关系规律，剖析功能基团对电导的作用，阐明导电机理。本项目研究对于发展高电导率的咪唑碘盐固态电解质具有重要的理论和科学意义。

将苯基、联苯基、萘基、2-噻吩基、3-噻吩基、酯基、炔丙基等功能基团连接到咪唑环上，合成了一些列功能化咪唑碘盐基离子导体。培养了部分离子导体的单晶，解析了单晶结构，研究了离子导体晶体结构与电导率之间的关系规律。研究发现，咪唑环上的功能化基团对离子导体晶体的堆积结构、层间距、相邻碘离子之间的距离、HOMO-LUMO能级差、结合能、电子云分布等具有明显的影响，从而对电导率产生了显著影响。我们将功能化咪唑碘盐应用于染料敏化太阳能电池和钙钛矿太阳能电池，可以获得较高的能量转化效率和较好的长效稳定性。利用联苯基取代的双咪唑离子导体，制作准固态染料敏化太阳能电池，获得了8.89%的能量转换效率，开路光电压高达820 mV。利用羧基功能化咪唑碘盐自组装到导电玻璃上，可以制备无电子传输层的高效钙钛矿太阳能电池，降低了制作成本，改善了长效稳定性。实验结果表明，咪唑碘盐的电导率可以通过引入合适的功能化基团来调节。通过理论计算发现，电导率与HOMO-LUMO带隙具有明显的相关性；HOMO-LUMO带隙越小，电导率越大。当咪唑环上引入炔丙基，具有明显的π-π堆积，HOMO-LUMO带隙很小，因此具有很高的电导率。本课题的研究结果对于进一步提高离子导体的电导率具有理论指导意义，同时对于发展染料敏化太阳能电池的高效固态电解质具有重要的科学意义。