1. College of Chemistry and Chemical Engineering of Inner Mongolia University, Hohhot 010021, P. R. China
2. School of Materials Science and Engineering and Inner Mongolia Key Laboratory of Graphite and Graphene for Energy Storage and Coating, Inner Mongolia University of Technology, Hohhot 010051, P. R. China
3. Institute of Applied Nanotechnology, Jiaxing, Zhejiang 314031, P. R. China
4. Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 101400, P. R. China
5. School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
6. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States