1. School of Electrical Engineering, Guangxi University, Nanning 530004, China
2. Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, China
3. School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
4. Energy Storage and Electrotechnics Department, China Electric Power Research Institute, Beijing 100192, China