Study On Properties Of Ionic Liquids Electrolyte For Lithum-air Batteries

Lithium-air batteries due to the high specific capacity, low cost and other advantages, which is expected to become a new generation of powered equipment. Using organic electrolyte as lithium battery’s electrolyte, that will generate some issues such as volatile, easily decomposed and the lithium anode protection. This paper intends to use ionic liquid which have the characteristics of low vapor pressure, high stability and non-flammable as lithium-air batteries electrolyte, investigated oxygen electrochemical reduction behavior in different ionic liquid, explored its possible redox mechanism of such batteries, and provide theoretical and experimental basis for the development of this batteries.In this paper, five ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI),1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide (OMITFSI),1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI),1-methyl-1-octylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR18TFSI) was synthesized using two-step method. Their conductivity and electrochemical window were determined, the results show that electrochemical window of imidazolium-based ionic liquid is about 4.5V and that of pyrrolidinium-based ionic liquid is about 5.4V. Their electrochemical properties were measured using cyclic voltammetry, chronoamperometry and electrochemical impedance spectra. The testing results shows that the shorter the chain length of the ring on the side chain, the better the electrochemical performance. Also, cyclic voltammetry shows that in imidazolium-based their have obvious ion-pair effect, while in pyrrolidinium-based ionic liquid do not find obvious ion-pair effect.On the basis of previous studies, we choose EMITFSI, BMITFSI, PYR14TFSI, PYR18TFSI and add lithium bis(trifluoromethanesulfonyl)imide to them as electrolyte for lithium-air battery. Under the condition of whether containing MnO2, the cathode oxygen reduction mechanism on glassy carbon electrode were investigated by cyclic voltammetry. The test results show that:in the absence of the catalyst, O2 is reduced with Li+generating superoxide, and a part of superoxide disproportionate to peroxides, then superoxide and peroxide in turn be re-oxidation. For the containing catalysts process, the reduction peak maybe due to generate superoxide, the oxidation peak is not easy to determine because the presence of MnO2, remains other adjunct to do further research.