| Lithium-oxygen batteries are one of the most promising candidates for energy storage and conversion in the future,because their theoretical energy density is higher than that of lithium-ion batteries.The previous researches found that electrolyte decomposition is one of the reasons for the poor cyclic performance of lithium-oxygen batteries.Recently,researchers have found that the use of ionic liquids can effectively improve the cycle stability of lithium-oxygen batteries.In this paper,the ionic liquid?IL?was used as an electrolyte additive to improve performance of lithium-oxygen batteries.The main research contents were as follows:Three kinds of ionic liquids,1-butyl-3-methylimidazolium tetrafluoroborate?[BMIM]BF4?,1-butyl-3-methylimidazolium bromide?[BMIM]Br?and benzyl triethylammonium chloride?TEBA?were prepared by double decomposition,nucleophilic addition and quaternization reaction,respectively.The preparation process parameters were optimized,and the yields were increased to 94.4%,93.2%,97.6%respectively.Then,The results of lithium ion conductivity test showd that[BMIM]BF4 had the highest ionic conductivity of 5.2×10-5 S cm-1.Finally,The test results of the viscosity and ionic conductivity of DMSO/[BMIM]BF4 mix electrolyte with LiTFSI and LiBF4 as lithium salts showed that with the increased of lithium concentration and ionic liquid content,the viscosity gradually increased,and the ionic conductivity first increased and then decreased.When the concentration of lithium salt was 0.5 mol L-1,the maximum ionic conductivity was 17.5 S cm-1,18.16 S cm-1,respectively.And when the volume ratio of DMSO/[BMIM]BF4 was 3,the maximum ionic conductivity was 14.2 S cm-1 and 16.07 S cm-1,respectively.The electrochemical performance of DMSO/[BMIM]BF4 mix electrolyte with LiTFSI and Li BF4 as lithium salt and DMSO/[BMIM]BF4 as solvent was tested by CV,LSV and RRDE,and the stability of the mixed electrolyte to lithium peroxide and potassium peroxide was tested by FTIR.The CV test results indicated that the current density is the highest when the concentration of lithium salt is 0.5 mol L-1 and the volume ratio of DMSO/[BMIM]BF4 was 3,which is 1.01 m A cm-2,0.77 mA cm-2and 1.01 mA cm-2,0.92 mA cm-2,respectively.Compared with DMSO/LiTFSI and DMSO/LiBF4,LSV test results show that the electrochemical window of DMSO/[BMIM]BF4/LiTFSI and DMSO/[BMIM]BF4/LiBF4 increases from 3.4 V and 3.9V to 4.3 V and 4.2 V,respectively.And results of RRDE demonstrated that the concentration of discharge products was low and the oxygen reduction ability was strong after adding ionic liquid and DMSO/[BMIM]BF4 mixed electrolyte showed high limiting diffusion current density,wide electrochemical window and good stability.DMSO/[BMIM]BF4/LiTFSI and DMSO/[BMIM]BF4/Li BF4 were applied as electrolyte for lithium oxygen battery.And it was found that the cycle performance and discharge capacity of the batteries were greatly improved.Compared with the DMSO/LiTFSI and DMSO/LiBF4,the capacities of DMSO/[BMIM]BF4/LiTFSI and DMSO/[BMIM]BF4/LiBF4 were increased from 3200 mA h g-1 and 3500 mA h g-1 to 27000 m A h g-1 and 31000 mA h g-1,and the cycle number was increased from33 and 79 to 242 and 286,respectively.And the analysis of anode and cathode with SEM and XRD showed that the electrolyte of this system was helpful to alleviate the lithium corrosion and lithium dendrite,and the cathode passivation caused by the accumulation of LiOH. |
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