Studies On Ising Model Of Electric Double Layer Capacitor

Electrical double-layer capacitors(EDLC)is a research hotspot in the field of electric energy storage systems.The focus of theoretical and experimental research is how to improve the energy density of EDLC.EDLC stores charges by forming an electrical double layer(EDL)on the interface between liquid electrolyte and solid electrode.The total energy storage is positively correlated with the contact area of electrode /electrolyte,so porous electrode with high specific surface area is a good choice to improve the energy storage performance.Theoretically,EDLC based on sub nanoporous electrode can be simplified into one-dimensional system,which can be studied by one-dimensional Ising model.In order to study the influencing factors of EDLC energy storage density,this thesis uses the Kramers Wannier transfer matrix method of one-dimensional Ising model to solve several different types of EDLC models.1)In view of the shortcoming of oversimplifying solvent molecules in the existing theoretical research of aqueous electrolyte EDLC,a solution is proposed to treat solvent molecules as neutral hard spheres with electric dipoles.The problem of theoretical calculation is how to determine the orientation of the electric dipole moment of each solvent molecule in the one-dimensional electrode hole.In this thesis,the Kramers Wannier migration matrix method of one-dimensional Ising model is used to solve this problem successfully,and three kinds of aqueous electrolyte EDLC models are studied in depth: hydrophilic solvent molecular EDLC model,porous solvent molecular EDLC model and aqueous dimer cationic EDLC model.At the same time,the internal structure of cations is considered in the third model.Compared with the existing theoretical results,the results obtained in this thesis can better reflect the details of the real EDLC and have a wider scope of application.2)Aiming at the unreasonable model assumptions in the theoretical study of ionic liquids EDLC,a solution to modify the nearest neighbor interaction is proposed,which successfully solves the problem that the nearest neighbor interaction between ions is less than the next nearest neighbor interaction.The results show that the modified results can not only be restored to the existing theoretical results in the limit case,but also be applied to EDLC system in a wider range of conditions.It is found that for the aqueous electrolyte EDLC,the measures to improve the energy density include increasing the transfer free energy of solvent molecules and the dipole moment of solvent electricity,and increasing the counter-ions electricity price.For ionic liquid EDLC,the measures to improve the energy density include: reducing the size of counter-ions and co-ions,reducing the transfer free energy of counter-ions and increasing the transfer free energy of co-ions.In this thesis,the effects of electrode pore size,solvent electric dipole moment,the pore affinity and porosity of solvents and ions,and ion structure on the capacitance and energy storage behavior of sub nano electrode pore EDLC are systematically studied.The conclusion has theoretical significance for the design of EDLC electrode and the synthesis of working electrolyte.