1. Department of Physics Dongguk University Seoul 04620 Korea
2. Shaanxi Key Laboratory of Chemical Additives for Industry Shaanxi University of Science and Technology Xi'an 710021 China
3. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology Wuhan 430070 China
4. College of Physics and Electronic Information Yan'an University Yan'an 716000 China
5. Center for Energy Storage Research Clean Energy Institute Korea Institute of Science and Technology (KIST) Seoul 02792 Korea