1. Beijing Institute of Nanoenergy and NanosystemsChinese Academy of Sciences Beijing 100083 P. R. China
2. Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education)Jilin University Changchun 130012 P. R. China
3. Department of Materials Science and EngineeringNational Tsing Hua University Hsinchu 30013 Taiwan P. R. China
4. School of Nanoscience and TechnologyUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China
5. Center on Nanoenergy ResearchSchool of Physical Science and TechnologyGuangxi University Nanning Guangxi 530004 P. R. China