title: Functionalized graphene for high performance lithium ion capacitors.
abstract: Lithium ion capacitors (LICs) have recently drawn considerable attention because they utilize the advantages of supercapacitors (high power) and lithium ion batteries (high energy). However, the energy densities of conventional LICs, which consist of a pair of graphite and activated carbon electrodes, are limited by the small capacities of the activated carbon cathodes. To overcome this limitation, we have engaged urea-reduced graphene oxide. The amide functional groups generated during the urea reduction facilitate the enolization processes for reversible Li binding, which improves the specific capacity by 37 % compared to those of conventional systems such as activated carbon and hydrazine-reduced graphene oxide. Utilizing the increased Li binding capability, when evaluated based on the mass of the active materials on both sides, the LICs based on urea-reduced graphene oxide deliver a specific energy density of approximately 106 Wh kg(total) (-1) and a specific power density of approximately 4200 W kg(total) (-1) with perfect capacity retention up to 1000 cycles. These values are far superior to those of previously reported LICs and supercapacitors, which suggests that appropriately treated graphene can be a promising electrode material for LICs.
authors.affiliation: Graduate School of EEWS (WCU), Korea Advanced Institute of Science and Technology, 373-1 Guseong Dong, Yuseong Gu, Daejon 305-701, Korea.
authors.forename: Ji Hoon
authors.initials: JH
authors.lastname: Lee
authors.forename: Weon Ho
authors.initials: WH
authors.lastname: Shin
authors.forename: Myung-Hyun
authors.initials: MH
authors.lastname: Ryou
authors.forename: Jae Kyu
authors.initials: JK
authors.lastname: Jin
authors.forename: Junhyung
authors.initials: J
authors.lastname: Kim
authors.forename: Jang Wook
authors.initials: JW
authors.lastname: Choi
mesh_terms: D011211:Electric Power Supplies; D004566:Electrodes; D004867:Equipment Design; D006108:Graphite / Q000737:chemistry*; D007477:Ions; D008094:Lithium / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D056951:Photoelectron Spectroscopy; D013499:Surface Properties
chemical_list: D007477:Ions; D006108:Graphite; D008094:Lithium