1. Department of Materials Science; Fudan University; Shanghai 200433 P. R. China
2. Shanghai Innovation Institute for Materials; Shanghai 200444 P. R. China
3. Department of Chemistry; Fudan University; Shanghai 200433 P. R. China
4. Institute of Physics; Chinese Academy of Sciences; Beijing 100190 P. R. China
5. Energy Technologies Area; Lawrence Berkeley National Laboratory; Berkeley CA 94720 USA