Synthesis,Properties And Applications As Electrolytes In Lithium-ion Batteries Of Low-viscosity Pyrazolium Ionic Liquids

Ionic liquis?ILs?which possess some appealing properties,such as negligible volatility,wide liquid range and low flammability etc.,has been considered as new electrolytes for lithium-ion batteries.Lowering the viscosity of ionic liquids may be beneficial for battery performance in lithium-ion battery as electrolytes.Eight low viscosity pyrazolium ionic liquids based on dicyanamide?DCA^-?anion and bis?fluorosulfonyl?imide?FSI^-?anion have been synthesized and characterized.Their physical and chemical properties have been tested.Moreover,these ILs are used as electrolytes for Lithium-ion batteries.Four DCA-based ether-functionalized pyrazolium ionic liquids have been synthesized,and they are all liquids at room temperature.At 25 ?,their viscosities are lower than 40 mPa s,and their conductivities are bigger than 7mS cm^-1.The electrochemical windows of these ILs are about 3.2V.In order to study the interfacial characteristics between electrolytes and lithium metal,ionic liquids with 0.6mol/kg LiDCA are used in symmetric lithium cells as electrolytes.The cycling tests of symmetric lithium cells indicate that only PZ2o1-1-DCA and PZ2o1-2-DCA are suitable as electrolytes for Li-ion batteries.At 25?,0.1C,the discharge capacities of Li/LiFePO₄ cells with PZ2o1-1-DCA and PZ2o1-2-DCA electrolytes are 138mAh g^-11 and 146 mAh g^-1 after 50 cycles,respectively.And their coulombic efficiency are all higher than 98%.The rate property of PZ2o1-2-DCA electrolyte is better than that of PZ2o1-1-DCA electrolyte at room temperature.The cycling performance of PZ2o1-2-DCA electrolyte is also better than that of PZ2o1-1-DCA electrolyte at low temperature.Four FSI-based ether-functionalized pyrazolium ionic liquids have been synthesized,and they are all liquids at room temperature.They have good thermal stability,and their decomposition temperature are about 270 ?.At25 ?,their viscosities are lower than 40 mPa s,and their conductivities are at the range of 5-6.3mS cm^-1.The electrochemical windows of these ILs are about 4.0V.Four FSI-based pyrazolium ionic liquids with 0.8mol/L LiFSI are used in Li/LiFePO₄ cells as electrolytes.These cells have stable capacities and their coulombic efficiency are all higher than 98%.Except PZ2o1-1-FSI,the initial discharge capacities of other ionic liquids are all about 161 mAh g^-1 at 25 ?,0.1C.The cycling performance and rate property of PZ2o2-2-FSI electrolyte is better than other ILs electrolyte at room temperature.