Molecular Dynamics Study On Microstructures Of Ionic Liquids In Mica Nanopores

The supercapacitor is a new type of energy storage devices and has great values in the power balance and energy recovery of electric vehicles.Studying microstructures inside nanopores will be an important way of device design optimization and macroscopic performance enhancement.Room temperature ionic liquids（ILs）,which have the advantages of wide voltage window,low vapor pressure and chemical inertness,contribute to improve the performance of energy and security in supercapacitors.In this study,molecular dynamics simulations have been used to study the microstructures of ionic liquids in mica nanopores and the effect of adding solvents on microstructures.The primary contents of this thesis are described below.（1）In order to investigate the structural forms of ionic liquids within nanopores,the microstructures of the ionic liquid bis（trifluoromethanesulfonyl）azanide([C₁₀mim][TFSA])within nanopores with different spacing and different surface charges are studied.It is shown that[C₁₀mim][TFSA]presents a bilayer structure within nanopores.The imidazole rings of the cations in each set of bilayers are mainly distributed on the outer side and the carbon chains show a tilted distribution on the inner side.The study demonstrates that the microstructures of ionic liquids within nanopores change with pore conditions,which provides a theoretical basis for the improvement of device performances by tuning ionic liquid structures.（2）Based on the research of[C₁₀mim][TFSA],this thesis studies the microstructures within nanopores of dicationic ionic liquid 1-decyl-dimethylimidazolium bis（trifluoromethanesulfonyl）azanide([C₁₀（mim）₂]（TFSA）₂)which has two positive charge centers.The results show that[C₁₀（mim）₂]（TFSA）₂ has a relatively uniform density and orientation distribution in the region outside the first adsorption layer and no longer exhibits bilayer structures.It is revealed that the types of ionic liquids show a large influence on microstructures within nanopores.（3）In addition to the studies of ionic liquid structures along the perpendicular direction to the surface,this thesis also examines the two-dimensional in-plane structures parallel to the mica surface.The results show that the in-plane structure of the ionic liquid is gradually ordered with the increase of potassium ion adsorption and is mainly related to the surface positions of potassium ions and mica.The study reveals that the relationship between the structures of charged surfaces and the structural order of ionic liquids,providing a theoretical basis for the screening of electrode materials.（4）To address the problem of large viscosity of ionic liquids,the structural changes of the mixed solutions with different proportions of dimethyl sulfoxide（DMSO）solvents and ionic liquids are investigated.The addition of DMSO does not change the bilayer structures of ionic liquids.The diffusion coefficients of all components in the ionic liquid solutions increase with the proportion of solvents,indicating that the addition of solvents is an effective way to improve the dynamic properties of ionic liquids.