Preparation And Application Of Electrolyte For Aluminum Ion Battery Based On Deep Eutectic Solvent

Rechargeable aluminum ion batteries（AIBs）with aluminum（Al）as anode have high development potential due to its high safety,low cost,high theoretical specific capacity(8040m Ah cm^-3)and high power density.However,the dense oxide film on the surface of Al and its low deposition potential（-1.67 V）make the electrolyte hardly reach standard of AIBs.At present,imidazolyl chloroaluminate ionic liquids（ILs）have been used as AIBs electrolyte due to their wide stable electrochemical window and high conductivity.However,because of its high production cost and toxicity,ILs are greatly limited in both experimental research and commercial application.Based on the common problems of high cost and strong toxicity of conventional electrolytes,we developed and designed two new types of AIBs eutectic electrolytes,studied the deposition/stripping behavior of Al in the two electrolytes,and revealed the reaction mechanism in AIBs.This work provides experimental and theoretical guidance for the design and development of new electrolytes of AIBs.The specific research contents are as follows:（1）For the first time,high-performance AIBs have been constructed based on low-cost AlCl₃/AcAm deep eutectic electrolyte.The influence of AlCl₃/AcAm electrolytes with different molar ratios on the behavior of Al deposition and exfoliation was studied,and an AlCl₃/AcAm-1.3 electrolyte with stable performance was selected.Al-graphite AIBs constructed with AlCl₃/AcAm-1.3 electrolyte reached the level of electrochemical performance of devices constructed with commercial ILs electrolyte.The reversible discharge capacity of 89.1 m Ah g^-1at current density of 50 m A g^-1.Even at a high current density of 500m A g^-1,the capacity can still reach 66.8 m Ah g^-1.After 200 cycles at the current density of100 m A g^-1,the capacity is 80 m Ah g^-1,with the coulombic efficiency 90%,and the capacity retention rate is 71.8%.The energy storage mechanism of AIBs with AlCl₃/AcAm as electrolyte was elucidated through the characterization and analysis of ex-situ XPS,XRD and Raman spectra.（2）AlCl₃/Et₃NHCl deep eutectic solvents were prepared from industrial wastes Et₃NHCl as AIBs electrolyte.The deposition/exfoliation properties of Al in AlCl₃/Et₃NHCl electrolytes were studied.The optimal ratio of AlCl₃/Et₃NHCl was selected,which is AlCl₃/Et₃NHCl-1.6,and its electrochemical properties in AIBs were investigated.The average capacity of AIBs is160.9 m Ah g^-1at the current density of 50 m A g^-1.After 200 cycles at the current density of100 m A g^-1,the cathode capacity is～81 m Ah g^-1,the coulomb efficiency is more than 95%,and the capacity retention rate is 72.9%.The energy storage mechanism of AIBs with AlCl₃/Et₃NHCl-1.6 as electrolyte are as follows:During the charging process,AlCl₄^-anion is inserted into the graphite cathode to form graphite intercalation compound,and Al₂Cl₇^-anion is deposited on the surface of Al to form AlCl₄^-,and the opposite reaction occurs during the discharge process.（3）The factors affecting the electrochemical performance differences of AlCl₃/AcAm,AlCl₃/Et₃NHCl and commercial AlCl₃/EMIC ILs in AIBs are studied.Through experiments and calculations,it can be concluded that:the hydrogen bond network formed during the reaction of AlCl₃and AcAm and the electrolysis and the large size of[AlCl₂·（AcAm）₂]⁺ions in the solution is the main reason for its high viscosity.The formation mechanism of AlCl₃/Et₃NHCl is similar to that of commercial AlCl₃/EMIC electrolyte,and it shows higher viscosity than AlCl₃/EMIC because of the stronger interaction between anion and cation in AlCl₃/Et₃NHCl electrolyte.AlCl₃/Et₃NHCl electrolyte has higher electrochemical performance because of the optimal wettability with the graphite electrode.Due to the different species of cations in three electrolytes,the different interaction forces between cations and anions,the different wettability between electrolyte and electrode,the electrochemical reaction kinetics of three electrolytes are diversity.Finally,the three electrolytes show different electrochemical performance in the same AIBs system.