Ionic Liquid Electrolytes For Aluminium Secondary Battery:Influence Of Organic Solvents

Rechargeable aluminum battery is a new promising green battery system It possesses advantages of high energy density,low cost,high safety and environment-amity.The gravimetric charge-storage capacity of aluminum metal is 2.98 Ah/g,which is next only to lithium in all metallic elements.The volumetric capacity of aluminum is 8.05 Ah/cm3,which is the highest in all metallic elements.In addition,aluminum is the most abundant metallic element in the earth's crust.These properties make aluminum-based batteries particularly attractive for stationary energy storage,the large scale of which requires the use of inexpensive raw materials.Ionic liquids comprising imidazolium salts and aluminum chloride have been widely used as the electrolytes of aluminium secondary battery.However,the high cost limits their further application.So it is necessary to develop suitable electrolyte systems,which are of low cost and good electrochemical performance.Aluminium chloride(AlCl3)/triethylamine hydrochloride(Et3NHCl)ionic liquids were used as the electrolytes.Organic solvents were tested as the additives to modify the physical properties and electrochemical performance of ionic liquid electrolytes.The aluminium secondary battery was constructed using aluminium foil as the negative electrode and sulfur-carbon cathodes as the positive electrode.The main research contents include the following three parts:(1)Et3NHCl/AlCl3 ionic liquids with different acidity were prepared and the changes of viscosity,density and conductivity varying with the acidity of ILs were studied.With the increase of acidity,the viscosity and conductivity increase and the density decreases.Cyclic voltammograms show that charges of the cathodic and anodic peak increase with the acidity.Considering the close relationship between the charges and the capacity of the battery,AlCl3(x=0.0667)/Et3NHCl(x is the mole fraction of AlCl3)is thought to be the better choice for the electrolyte.(2)Benzene,toluene,1,2-dichlorethane(DCE)and dichloromethane(DCM)were added to AlCl3(x=0.0667)/Et3NHCL The influence of organic solvents on the IL electrolyte was studied.It is found that DCM,DCE and benzene have a great effect on increasing the conductivity and decreasing the viscosity of IL.But benzene narrows the electrochemical potential window of IL electrolyte,so it can't be used as the additive.When the volume ratio(n)of DCM or DCE to IL comes to 0.2,the electrochemical properties of IL are greatly improved,while causing little influence on the thermal stability of IL.(3)Cyclic voltammograms of aluminium anodes and sulfur-carbon cathodes in the electrolytes were investigated.The results show that the dissolution of negative electrode itself is involved during the CV scans.And sulfur can be reversibly oxidized and reduced.AlCl3(x=0.0667)/Et3NHCl-DCM(n=0.2)was used as the electrolyte of the battery.The discharging capacity has the highest value of 131.67 mAh/g,and remains 104.69 mAh/g after 40 cycles.