Theoretical Study On The Influence Mechanism Of Additives On Ionic Liquid Electrodeposition Of Aluminum

At present,the Hall-Heroult process is widely used in industrial aluminium production,which has a series of problems,such as high energy consumption s and serious corrosion to equipment.The existence of ionic liquid makes it possible to electrodeposit aluminium in an environmentally friendly and energy-saving way.However,there are some problems in pure ionic liquid electrodeposition of aluminum,such as the viscosity is higher,the conductivity is lower,and the deposited layer has severe dendrite phenomenon.Adding additives to ionic liquid is one of the effective methods to solve the above problems.But it is unclear how the addit ive affects the microstructure and physicochemical properties of the system,and which functional groups are beneficial to the electrodeposition of aluminum.In this thesis,the structural characteristics,active sites of additives and ionic liquids,and the effects of additives on the microstructure and physicochemical properties of ionic liquid systems and the effects of aluminum electrodeposition processes were investigated,which further reveals the mode of action of additives in aluminum electrodeposition,it also provides theoretical guidance for the selection of additives.The effect of benzene?C₆H₆?and methylene chloride?DCM?on the structure,activity and interaction energy of triethylamine hydrochloride chloroaluminate ionic liquid were investigated by quantum chemistry.When DCM was added,the hydrogen bond is formed with the cat ions and anions of ionic liquid,increasing the distance between anions and cations and reducing the interaction energy,while C₆H₆ only interacts strongly with cations.Molecular dynamics simulation was used to study the effects of C₆H₆ and DCM on the microstructure of the inter-ion radial distribution function,coordination number,spatial distribution function and density,viscosity,conductivity and ion diffusion capacity of the system.The results of density,viscosity and conductivity of the system are in good agreement with the experiment al values.The radial spatial distribution function s and the spatial distribution function s clearly indicate that DCM tends to be located between the anions and cations to weaken the interaction and let the aluminum complex ions mainly exist in the form of Al₂Cl₇^-,reduces ion diffusion capacity,and improve the viscosity and increases the conductivity.It is found that both DCM and C ₆H₆ have strong diffusion ability,but the promotion effect of DCM on the electrochemical properties of the system is stronger than C₆H₆,which is consistent with the experimental results.The effects of DCM and toluene?C ₇H₈?on 1-butyl-3-methylimidazolium trichloride?[BMIM]Cl/Al Cl₃?ionic liquid electrodeposition aluminum system were investigated by quantum chemistry.It was found that DCM forms hydrogen bonds with anions and cations.Adding DCM not only increases the distance but also reduces the interaction energy of anions and cations,but C₇H₈ only interacts strongly with cations.Molecular dynamics simulation was used to study the effects of DCM and C ₇H₈ on the system.As the DCM increases,the peak value of the radial distribution functions between the anions and cations increase,the interaction weakens,resulting in the enhancement of ion diffusion ability,the decrease of viscosity and the increase of conductivity,and indicating that the aluminum complex ions mainly exist in the form of Al₂Cl₇^-.When x=0.7,DCM significantly increases the content of Al ₂Cl₇^-and the ion diffusion rate.Therefore,DCM makes the viscosity decrease and the conductivity increase also significantly.In addition,DCM has the largest diffusion capacity,and can reach the electrode surface preferentially and reduce the effective surface area of the electrode,which is beneficial to obtain fine aluminum deposition layer.Therefore,the halogenated alkane DCM is more favorable for electrodeposition of aluminum than the aromatic hydrocarbon C₇H₈,which is consistent with the experimental results.The influence of acetic acid?Ac OH?,methyl acetate?MAC?and methyl carbamate?MC?on 1-ethyl-3-methylimidazolium trichloride ionic liquid electrodeposition aluminum system was studied by quantum chemistry.When MC and Ac OH was added,the hydrogen bond is formed with the cat ions and anions of ionic liquid,MAC only has a strong interaction with cations.MAC obviously increases the spacing between anions and cations.Molecular dynamics simulation was used to study the effects of three additives on the system.The radial distribution functions and spatial distribution function of Ac OH,MC and MAC with a mole fraction of 0.005 around the anion and cation are consistent with the quantitative results.It can be clearly found that M AC is prefer positioned around the cation to weaken the interaction between ions,and promote migration of ions in the system.thereby making the aluminum complex ions existed in the form of Al₂Cl₇^-.In addition,the strongest diffusion ability of M AC not only accelerates the rate of ion movement,but also has the most obvious effect on t he decrease of viscosity and the increase of conductivity,and it is easy to reach the electrode surface preferentially and reduce the effective surface area of the electrode.By studying the effects of dimethyl carbonate?DMC?,DCM and C ₇H₈ on the electrodeposition of[BMIM]Cl/Al Cl₃ ionic liquid.It was found that DCM easily forms hydrogen bonds with anions and cations,and it increases the spacing between anions and cations significantly,while C ₇H₈ and DMC only interact strongly with cations.Molecular dynamics simulation was used to study the effects of three additives on the system.The radial distribution function and the spatial distribution function indicate that DCM is more likely to be distributed between anions and cations,thus weaken its interaction.C₇H₈ and DMC are mainly distributed around the cation,and have a certain dilution effect.DCM significantly weakens the interaction between anions and cations in the system and it has the strongest diffusion,which makes the viscosity of the system lower and the conductivity increase is the best.And it can reach the electrode surface preferentially and reduce the effective surface area of the electrode,C ₇H₈followed,DMC was the worst,which is consistent with the experimental results.