title: Engineering the electrochemical capacitive properties of graphene sheets in ionic-liquid electrolytes by correct selection of anions.
abstract: Graphene sheet (GS)-ionic liquid (IL) supercapacitors are receiving intense interest because their specific energy density far exceeds that of GS-aqueous electrolytes supercapacitors. The electrochemical properties of ILs mainly depend on their diverse ions, especially anions. Therefore, identifying suitable IL electrolytes for GSs is currently one of the most important tasks. The electrochemical behavior of GSs in a series of ILs composed of 1-ethyl-3-methylimidazolium cation (EMIM(+)) with different anions is systematically studied. Combined with the formula derivation and building models, it is shown that the viscosity, ion size, and molecular weight of ILs affect the electrical conductivity of ILs, and thus, determine the electrochemical performances of GSs. Because the EMIM-dicyanamide IL has the lowest viscosity, ion size, and molecular weight, GSs in it exhibit the highest specific capacitance, smallest resistance, and best rate capability. In addition, because the tetrafluoroborate anion (BF4(-)) has the best electrochemical stability, the GS-[EMIM][BF4] supercapacitor has the widest potential window, and thus, displays the largest energy density. These results may provide valuable information for selecting appropriate ILs and designing high-performance GS-IL supercapacitors to meet different needs.
authors.affiliation: Laboratory of Clean Energy Chemistry and Materials, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, 730000 Lanzhou (PR China); State Key Laboratory of Gansu Advanced Non-ferrous Metal Materials, Department of Material Science and Engineering, Lanzhou University of Technology, 730000 Lanzhou (PR China).
authors.forename: Minjie
authors.initials: M
authors.lastname: Shi
authors.forename: Shengzhong
authors.initials: S
authors.lastname: Kou
authors.forename: Xingbin
authors.initials: X
authors.lastname: Yan
mesh_terms: D025802:Electric Capacitance; D004566:Electrodes; D004573:Electrolytes / Q000737:chemistry; D006108:Graphite / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D007093:Imidazoles; D052578:Ionic Liquids; D006108:Graphite
keywords: anions; graphene; ionic liquids; reaction mechanisms; supercapacitors