1. Advanced Energy Storage Materials and Devices Lab, School of Physics and Electronic-Electrical Engineering, Ningxia University, Yinchuan 750021, P. R. China
2. Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore
3. National University of Singapore (Suzhou) Research Institute, 377 Lin Quan Street, Suzhou Industrial Park, Suzhou, Jiangsu 215123, P. R. China
4. Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore
5. Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, 117603 Singapore
6. Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai
New City, Fuzhou 350207, P. R. China