1. Laboratory of Electrochemical Power Sources, Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang, Sichuan 621000, P. R. China
2. College of Chemistry and Materials Engineering, Anhui Science and Technology University, Bengbu 233000, P. R. China
3. School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710126, P. R. China