1. State Key Laboratory of Silicon Materials; Department of Materials Science and Engineering; Zhejiang University; Hangzhou 310027 People's Republic of China
2. Key Laboratory of Advanced Materials and Applications for Batteries of Zhejiang Province; Zhejiang University; Hangzhou 310027 People's Republic of China
3. Department of Physics and Astronomy; Clemson University; Clemson SC 29634-0978 USA