| Lithium ion battery has been widely used in notebook, mobile telephone and numeral camera with its merits of small bulk, high work voltage, no pollution and long using life. In order to meet the demand of advance energy and low carbon economy, the application of lithium ion battery is being extended to large vehicle battery and large power storage battery and such battery used in special condition. But the use of the large power lithium ion battery is limited by cathode material used in battery and the security of the electrolyte. LiMn2O4 and LiFePO4 are two cathode active materials with good use prospect . However, in practical use, the crystal lattice of LiMn2O4 is easy to fall down and the conductivity of LiFePO4 is low. Crystal system intermingling is a useful method. Meanwhile, ionic liquid which has negligible vapor pressure and is inflammable is being hoped to replace traditional organic carbonates and solve the safety problem of lithium ion battery completely.In this work, the study is mainly focused on doping research of lithium manganese oxide and lithium iron phosphate cathode materials. And the application of alkane / alkene substituted imidazolium ionic liquid electrolyte in lithium ion batteries has also been sdudyed. Al doped lithium manganese oxide and lithium iron phosphate are synthesized and investigated.It is found that the best synthesis conditions contain doping amount of X is 0.05, sintering temperature is 750℃for lithium manganese oxide and 650℃for lithium iron phosphate, sintering time is 24 h, Follow this process, two types of good cathode materials Li1.05Mn1.9Al0.05O4 and Li1.05Fe0.9Al0.05PO4/C were synthesized. 1,2-dimethyl-3-alkyl substituted imidazolium Bis(trifluoromethylsulfonyl) imide ionic liquid were synthesized and characterized. The charge and discharge cycle performance of Li/Li1.05 Mn1.9 Al0.0504 and Li/ Li1.05Fe0.9Al0.05PO4/ Cbatteries containing such ionic liquid electrolytes have been tested. And the influence of different alkyl chain length on 3 position of imidazolium to the electrolyte property has been researched too. It is found that with the growth of the three alkyl chains, the density of electrolyte decreased, the viscosity of electrolyte increased, the conductivity decreased. With this ionic liquid electrolyte, Li/Li1.05Mn1.9Al0.0504 and Li/Li1.05Fe0.9Al 0.05PO4/C battery charge-discharge cycle performance is in equality and much lower than the performance of battery with traditional carbonate electrolyte. The density, excess volume, viscosity, conductivity and electrochemical properties in the ionic liquid and dimethyl carbonate mixed system have also been studied. It is found that with [HDMIM][TFSI] molar percent increase, the density increases, the excess volume decreases first, then increases and reach a minimum value of 0.3, the viscosity increased, the conductivity first increases and then decreases. Charge-discharge cycle tests show that when [HDMIM][TFSI] at 40% mass fraction, Li/Li1.05Mn1.9Al0.05O4 andLi/Li1.05Fe0.9Al0.05PO4/C battery have shown a relatively better electrochemical performance. At 0.1C rate in 3-4.3 V voltage range, constant current charge-discharge test results show that the addition of VC can improve battery performance. Imidazolium cation ionic liquid substituted with alkenes exhibited lower viscosity and special film–formimg performance. But the rate charge and discharge performance of the battery containing such electrolyte is poor. The electrochemical impedance (EIS) is used to further analyze the impact on the battery cycle performance.It is found that battery with1,2-dimethyl-3-alkyl substituted imidazolium Bis (trifluoromethylsulfonyl)imide ionic liquid electrolyte has stable interface. Ionic liquid substituted with alkenes also has stable interface after form a special film.
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