A Molecular Dynamics Study Of The Effect Of Electrolytes On The Energy Storage Properties Of Supercapacitors

Driven by the demand for renewable green energy,electrochemical energy storage devices have always been the focus of attention in the energy field.As an emerging green energy storage device,supercapacitors can form a nanometer-thick electrode/electrolyte electric double layer solid-liquid interface through ion transport to achieve energy storage.Due to a series of advantages such as high power density,supercapacitors have received more and more attention in the field of energy storage.The performance of supercapacitors is affected by the electrolyte material.This paper mainly simulates the performance of capacitors in water system,ionic liquid system and ionic liquid-organic solvent system by molecular dynamics method.The main work of this paper is as follows:1.The aqueous electrolyte has high conductivity,and the ions conduct in the electrolyte at high speed,showing excellent power density in the supercapacitor.At the same time,it has many advantages,such as high safety,easy assembly,low price,etc.Therefore,water electrolyte has great application value in high power density supercapacitors.In this paper,the performance of 1M Li Cl,Na Cl and KCl of three water electrolyte double-layer supercapacitors was calculated by molecular dynamics simulation method.It is found that the capacitance performance is independent of the radius of alkali metal cations.When potassium citrate aqueous solution is used as electrolyte,it can guarantee the working voltage and provide high capacitance at the same time.It is a promising material in water system electrolyte.2.Ionic liquids have become new electrolytes in the field of supercapacitors due to its wide electrochemical window and excellent thermal stability,which provids a way to realize high energy density and long life.However,the development of capacitors based on ionic liquids has been largely limited due to the high viscosity and low ionic conductivity of ionic liquids.Bis-trifluoromethane sulfonimide(TFSI)ionic liquid is widely used in energy storage devices for its good electrochemical performance.In order to further improve the performance of supercapacitors,the molecular dynamics simulation method was used to adjust the structure of TFSI anion,and the ion transport properties of the modified electrolyte were improved by 2 times.The double electric layer structure of the modified sulfonyl fluoride ionic liquid was studied,and the influence of the microstructure of the double electric layer on the working performance of the supercapacitor was explored from the molecular scale.It provides a theoretical basis and optimization scheme for the practical application of ionic liquid supercapacitors.3.Choline amino acid ionic liquids have attracted much attention in recent years because of their simple extraction process,abundant sources,and easy degradation.Due to the high viscosity of this type of ionic liquid,the addition of organic solvents can adjust the transport performance of ionic liquids.This paper discusses the different solvents(methanol,ethanol)and the effect of different temperatures on the diffusion properties and conductivity of ionic liquids.The results show that as the temperature increases,the conductivity increases linearly.The addition of organic solvents can improve the conductivity of ionic liquids,and the addition of methanol solvents has a higher compatibility with choline amino acid ionic liquids.The conductivity of methanol mixed with choline glycine was 5 times higher than that before mixing.