1. Henan Joint International Research Laboratory of New Energy Storage Technology, Xinyang Normal University, Xinyang 464000, P. R. China
2. College of Physics and Electronic Engineering, Nanyang Normal University, Nanyang 473061, P. R. China
3. Department of Physics, Department of Materials Science & Engineering, and Department of Biomedical Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China