二次锂电池用离子液体电解质研究

Study of Ionic Liquid Electrolytes for Secondary Lithium Batteries

合成了哌啶类离子液体N-甲基-N-丙(丁)基哌啶三氟甲基磺酰亚胺[PP13(4)-TFSI],并与现在常用的两种离子液体1-丁基-3-甲基-咪唑六氟磷酸(BMIPF6)及1-丁基-3-甲基-咪唑四氟硼酸(BMIBF4)进行了各种电化学性能的对比.PP13(4)-TFSI的电化学稳定窗口可以达到5.8V,明显大于BMIBF4(4.7V)以及BMIPF6(4.6V).而且PP13(4)-TFSI负极极限电位(-0.3Vvs.Li/Li+)明显低于BMIPF6(0.5V)和BMIBF4(0.7V),有望被使用在以锂金属作为负极的二次锂电池中.以LiTFSI/PP14-TFSI为电解质溶液测试了Li/LiCoO2纽扣电池的电化学性能,在0.05mA?cm-2的恒定电流充放电条件下,电池的比容量可以达到150mAh?g-1,初始循环以后库仑效率接近100%.交流阻抗测试表明,电池的阻抗特性稳定,不存在明显的界面钝化现象.

Abstract Two room temperature ionic liquids （RTIL） consisting of N-methyl-N-propyl（butyl）piperidinium [（PP13（4）] cation and bis（trifluoromethanesulfonyl）imide （TFSI） anion were newly synthesized, and their electrochemical properties were investigated in comparison with the other two RTIL, 1-butyl-3-methyl-imidazolium tetrafluoroborate （BMIBF4） and 1-butyl-3-methyl-imidazolium hexafluorophosphate （BMIPF6）. The electrochemical window of PP13（4）-TFSI （5.8 V） is wider than those of BMIBF4（4.7 V） and BMIPF6 （4.5 V）. The cathodic limit of the PP13（4）-TFSI is about -0.3 V vs. Li/Li^＋, against 0.5 V for BM/PF6 and 0.7 V for BMIBF4, so it may be used as the electrolyte for second lithium batteries based on lithium anode. A Li/LiCoO2 test cell using LiTFSI/PP14-TFSI as electrolyte exhibited very good cycle performance at constant current density of 0.05 mA·cm^-2. The capacity of the cell reached 150 mAh·g^-1 and the coulombic efficiency was close to 100% after the first several cycles. RC impedance measurement of the cell showed that the interfaces between electrode and electrolyte were stable with the time. It appeared that the interfacial passivation did not occur during the cell storage.