1. Institute for Advanced Materials and Technology University of Science and Technology Beijing Beijing 100083 P. R. China
2. Key Laboratory of Physics and Technology for Advanced Batteries Ministry of Education College of Physics Jilin University Changchun 130012 P. R. China
3. Department of Material Science and Engineering and Center for Functional Photonics (CFP) City University of Hong Kong Hong Kong SAR 999077 P. R. China