1. Department of Advanced Manufacturing and Robotics, College of Engineering, Peking University, Beijing100871, P. R. China
2. Energy Storage and Distributed Resources Division, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
3. School of Mechanical Engineering and Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing210096, P. R. China
4. Applied Science and Technology Graduate Group, University of California, Berkeley, California94720, United States
5. The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
6. George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia30332, United States
7. Department of Mechanical Engineering, University of California, Berkeley, California94720, United States