1. Advanced Li-ion Battery Engineering Laboratory, CAS Engineering Laboratory for Graphene, Key Laboratory of Graphene Technologies and Applications of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering (NIMTE), Chinese Academy of Sciences, Ningbo 31520, P. R. China
2. College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences (UCAS), Beijing 100049, P. R. China