Molecular Dynamics Study On The Ion Diffusion Of Electrolytes In Electrochemical Devices

Fossil energy,such as coal,oil and natural gas,has experienced a series of problems,such as the continuous reduction of the total fossil energy content and the environmental and ecological problems caused by the use of fossil fuels in the development of human society.Therefore,the development and utilization of renewable energy is the main mean to solve this problem,but the non-renewable energy can't be used directly,it needs to be converted and stored with the corresponding energy storage equipment.Therefore,the development and the improvement of energy storage equipment is the main direction of the current study.In this paper,the behavior of the diffusion of electrolyte ions in electrochemical devices was studied by molecular dynamics simulation.There are many advantages with Br₂ and HBr as positive electrolyte solution,many of the batteries select Br₂/Br as positive electrolyte solution.However,there are some problems with Br₂/Br as electrolyte solution at the same time,the most critical problem is that bromine can easily pass through the Nafion membrane,which causes electrolyte cross-contamination and affect the battery performance.Therefore,mastering the molecular movement of the crossover of bromine,which will solve the problem of the crossover of bromine will be of great significance on the battery performance.In this paper,the diffusion of bromine in Nafion films was studied by molecular dynamics method.The results show that the diffusion of electrolyte ions into the Nafion film is mainly through the water channel formed by the sulfonic acid groups in the Nafion chain and water.Br^-exists in the water channel,but it distributes relatively far from the sulfonate.Br₂ can't be determined in the Nafion membrane position,its location has nothing to do with the water channel and the distribution is of no obvious law.The diffusion coefficient of Br^-increases with the constantly increasing of Br^-concentration,Br₂ concentration,water content and temperature.The diffusion of Br₂ is only affected by the concentration of Br₂,which increases with the increase of Br₂ concentration.Then,the polyphosphazene membrane was modeled and the diffusion of water and hydronium ions was studied by modifying the polyphosphazene side chains.It was found that the growth of the side chains in the same modification resulted in the decrease of diffusion of water.When the modified fluorocarbon chains on both sides of the polyphosphazene are 7,the proton diffusion coefficient is the highest,and the proton transfer ability is the highest,which most suit for the modified polyphosphazene membrane.Finally,the diffusion of electrolyte ions in the graphene layer was studied.The influence of the graphene interlayer distance and the graphene doping concentration on the diffusion of the electrolyte were studied by molecular dynamics method.The results shows,when the electrolyte flows between graphene layers,the distance between pure graphene layers should be at least 28.5?,and with the doping concentration increased,the intercalation distance of doped graphene decreases.With high doping concentration,the diffusion is hardly influenced even when the interlayer distance is only 22.3?.