离子液体电解质种类对活性炭电极超级电容器电化学性能的影响

Engineering the Electrochemical Capacitive Properties of Activated Carbons by Correct Selection of Ionic-Liquid Electrolytes

本文将经水蒸气二次活化的椰壳活性炭(W-AC)作为电极材料,选择1-乙基-3甲基咪唑四氟硼酸盐([EMIM]BF4)作为电解质,结果表明W-AC电极的比电容量远高于未活化的椰壳活性炭(R-AC).使用循环伏安、恒电流充放电、交流阻抗等方法研究了不同种类离子液体电解质对超级电容器电化学性能的影响.不同阴阳离子组成的离子液体作为电解质,直接影响着超级电容器的电化学性能.研究表明,由EMIM+和BMIM+阳离子与BF4-、TFSI-阴离子构成的离子液体电解质较适用于W-AC电极.其中,在[EMIM]BF4电解质中,单片电极的比电容量可高达153 F·g^(-1);在1-丁基-3-甲基-咪唑四氟硼酸盐([BMIM]BF4)电解质中电位窗可达3.5 V,能量密度高达57Wh·kg^(-1).本研究对于构筑高性能超级电容器离子液体的选择提供参考,以期满足不同应用领域需求.

In order to improve the electrochemical capacitive properties and to apply coconut shell activated carbon（AC） serving as electrode materials in ionic liquid（IL）-based supercapacitor（SC）,the coconut shell AC material was re-activated using a steam as an activating agent in this work,forming a secondary AC（W-AC）.The results showed that the specific capacitance of the W-AC electrode was much larger than that of the raw activated carbon electrode（R-AC） in 1-ethyl-3-methylimidazolium tetrafluoroborate（[EMIM]BF4）.The electrochemical techniques including cyclic voltammetry（CV）,galvanostatic charge/discharge（GCD） measurement,and electrochemical impedance spectroscopy（EIS） were used to systematically study the capacitive properties of W-AC electrode in a series of ILs composed of different cations and anions.The electrochemical performances of the W-AC electrode using different ILs as electrolytes varied because of the different ion diameters,liquid viscosities and ionic conductivities for various ILs.Among them,the IL electrolytes composed of EMIM＋,BMIM＋and BF4-,TFSI-were found to be most suitable for W-AC electrode.The specific capacitance of W-AC electrode reached 153 F·g-1 in [EMIM]BF4 IL electrolyte,and the as-assembled SCs could achieve a high energy density of 57 Wh·kg-1 with a potential window of 3.5 V in [BMIM]BF4.These results may provide valuable information for selecting appropriate ionic liquids and designing high-performance supercapacitors to meet different needs.