1. Department of Physics; University of Science and Technology Beijing; Beijing 100083 P. R. China
2. BattFlex Technologies, Inc; Wuhan 430079 P. R. China
3. Institute for Applied Physics; University of Science and Technology Beijing; Beijing 100083 P. R. China
4. College of Chemistry; Chongqing Normal University; Chongqing 401311 P. R. China