| In recent years,ionic liquids have been widely used in the field of electrochemistry as a green solvent.In modern industry,aluminum is produced by electrolysis of cryolite-alumina melts.The process is high-energy-consuming because of the high temperature.However,the application of ionic liquids as the electrolyte has opened a window new direction for low-temperature aluminum electrolysis process.On the other hand,aluminum is inexpensive and has excellent stability in air,and it can exchange three electrons in an electrochemical reaction.So the aluminum ion battery has received much attention in energy storage.However,due to the shortcomings of its electrolytes that are sensitive to water and have strong corrosivity,the development of aluminum ion batteries is limited.Furthermore,in the study of room temperature ionic liquid electrodeposition of aluminum,there is also the problem that the electrolyte is sensitive to water.Therefore,finding a new type of electrolyte is a problem worth studying in the field of electrodeposited aluminum and aluminum ion batteries.TF2N-(bistrifluoromethanesulfonimide)is a representative of anions in second-generation ionic liquids.The ionic liquid formed by combining with cations such as imidazole and pyridine is stable to water and oxygen and has a weak corrosivity,a wide electrochemical window and a good thermal stability.Those make it a potential electrolyte for aluminum ion battery and electrodepositing aluminum.In the present study,AlCl3-[EMIM][TF2N]-additive(with 5%molar fraction of LiCl,EC(ethylene carbonate),nicotinamide)ionic liquid system was used as electrolyte for electrodepositing aluminum process and aluminum ion batteries.Fixed conductivity cell constant technique,linear voltammetry and Raman spectroscopy were used to study the electrical conductivity,electrochemical window and ionic structure of ionic liquid systems,respectively.The electrochemical behaviors of aluminum reduction behavior were studied by cyclic voltammetry and potentiostatic electrolysis.Morphology and phase composition of the electrodeposited products were studied by SEM and XRD,respectively.The electrochemical performance of aluminum ion batteries was studied by constant current charge and discharge method.The results showed that the conductivity decreased with the increase of the molar ratio of AlCl3 to[EMIM][TF2N]in the AlCl3-[EMIM][TF2N]-additive ionic liquid system.Meanwhile,it was increased with the addition of LiCl,but decreased with the addition of EC and nicotinamide.The molar ratio and additives had little effect on the electrochemical window.There were two ion complexes of Al2Cl7-and AlCl4-in the ionic liquid system.The relative content of Al2Cl7-increased with the increase of molar ratio,and the addition of additives decreased the relative content of Al2Cl7-obviously.When AlCl3-[EMIM][TF2N]ionic liquid system was used as the electrolyte of electrodepositing aluminum,the larger the molar ratio of AlCl3 to[EMIM][TF2N],the coarser the particles obtained by constant potential deposition.With the addition of additives in the electrolyte,the grain of the electrodeposited product was refined and the coating was more uniform.When an ionic liquid system with AlCl3 and[EMIM][TF2N]molar ratio of 1.7 was used as an electrolyte for aluminum ion battery,its discharge specific capacity was 75 mAh/g and coulomb efficiency was 98%,and it had a good cycle stability.With LiCl adding to the electrolyte,the battery discharge specific capacity decreased to 30 mAh/g,the coulomb efficiency was 98%,and the cycle performance became poor.With the addition of EC to the electrolyte,the battery discharge specific capacity was 51 mAh/g,the coulomb efficiency was 96%,and it showed a good cycle stability. |
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