title: Morphology Effect of Vertical Graphene on the High Performance of Supercapacitor Electrode.
abstract: Graphene and its composites are widely investigated as supercapacitor electrodes due to their large specific surface area. However, the severe aggregation and disordered alignment of graphene sheets hamper the maximum utilization of its surface area. Here we report an optimized structure for supercapacitor electrode, i.e., the vertical graphene sheets, which have a vertical structure and open architecture for ion transport pathway. The effect of morphology and orientation of vertical graphene on the performance of supercapacitor is examined using a combination of model calculation and experimental study. Both results consistently demonstrate that the vertical graphene electrode has a much superior performance than that of lateral graphene electrode. Typically, the areal capacitances of a vertical graphene electrode reach 8.4 mF/cm(2) at scan rate of 100 mV/s; this is about 38% higher than that of a lateral graphene electrode and about 6 times higher than that of graphite paper. To further improve its performance, a MnO2 nanoflake layer is coated on the surface of graphene to provide a high pseudocapacitive contribution to the overall areal capacitance which increases to 500 mF/cm(2) at scan rate of 5 mV/s. The reasons for these significant improvements are studied in detail and are attributed to the fast ion diffusion and enhanced charge storage capacity. The microscopic manipulation of graphene electrode configuration could greatly improve its specific capacitance, and furthermore, boost the energy density of supercapacitor. Our results demonstrate that the vertical graphene electrode is more efficient and practical for the high performance energy storage device with high power and energy densities.
authors.affiliation: State Key Laboratory of Optoelectronic Materials and Technologies, and Guangdong Province Key Laboratory of Display Material and Technology, School of Microelectronics, Sun Yat-Sen University , Guangzhou, 510275, People's Republic of China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Optoelectronic Materials and Technologies, and Guangdong Province Key Laboratory of Display Material and Technology, School of Microelectronics, Sun Yat-Sen University , Guangzhou, 510275, People's Republic of China.
authors.forename: Qionghui
authors.initials: Q
authors.lastname: Zou
authors.affiliation: Deptartment of Electrical Engineering and Computer Science, Vanderbilt University , Nashville, Tennessee 37212, United States.
authors.forename: Hua Shao
authors.initials: HS
authors.lastname: Hsu
authors.affiliation: Deptartment of Electrical Engineering and Computer Science, Vanderbilt University , Nashville, Tennessee 37212, United States.
authors.forename: Supil
authors.initials: S
authors.lastname: Raina
authors.affiliation: Department of Macromolecular Science, Fudan University , Shanghai, 200433, China.
authors.forename: Yuxi
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Deptartment of Electrical Engineering and Computer Science, Vanderbilt University , Nashville, Tennessee 37212, United States.
authors.forename: Joyce B
authors.initials: JB
authors.lastname: Kang
authors.affiliation: State Key Laboratory of Optoelectronic Materials and Technologies, and Guangdong Province Key Laboratory of Display Material and Technology, School of Microelectronics, Sun Yat-Sen University , Guangzhou, 510275, People's Republic of China.
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Optoelectronic Materials and Technologies, and Guangdong Province Key Laboratory of Display Material and Technology, School of Microelectronics, Sun Yat-Sen University , Guangzhou, 510275, People's Republic of China.
authors.forename: Shaozhi
authors.initials: S
authors.lastname: Deng
authors.affiliation: State Key Laboratory of Optoelectronic Materials and Technologies, and Guangdong Province Key Laboratory of Display Material and Technology, School of Microelectronics, Sun Yat-Sen University , Guangzhou, 510275, People's Republic of China.
authors.forename: Ningsheng
authors.initials: N
authors.lastname: Xu
authors.affiliation: Deptartment of Electrical Engineering and Computer Science, Vanderbilt University , Nashville, Tennessee 37212, United States.
authors.forename: Weng P
authors.initials: WP
authors.lastname: Kang
keywords: ion diffusion; morphology; orientation; supercapacitor; surface area; vertical graphene