1. Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education); College of Chemistry; Collaborative Innovation Center of Chemical Science and Engineering (Tianjin); Nankai University; Tianjin 300071 P. R. China
2. Beijing National Laboratory for Condensed Matter Physics; Institute of Physics; Chinese Academy of Sciences; Beijing 100190 P. R. China
3. School of Materials Science and Engineering; Nanyang Technological University; 50 Nanyang Avenue Singapore 639798