10.1021/nn507003z.s001 Jinyun Liu Jinyun Liu Nan Li Nan Li Matthew D. Goodman Matthew D. Goodman Hui Gang Zhang Hui Gang Zhang Eric S. Epstein Eric S. Epstein Bo Huang Bo Huang Zeng Pan Zeng Pan Jinwoo Kim Jinwoo Kim Jun Hee Choi Jun Hee Choi Xingjiu Huang Xingjiu Huang Jinhuai Liu Jinhuai Liu K. Jimmy Hsia K. Jimmy Hsia Shen J. Dillon Shen J. Dillon Paul V. Braun Paul V. Braun Mechanically and Chemically Robust Sandwich-Structured C@Si@C Nanotube Array Li-Ion Battery Anodes American Chemical Society 2015 chemical stability issues plastic strain energy densities Coulombic efficiency capacity decay structure stability battery electrodes Si anodes volume changes graphite anode anode candidate Si nanotubes Ni foam SEM SEI cathode systems 60 cycles carbon coatings 2015-02-24 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Mechanically_and_Chemically_Robust_Sandwich_Structured_C_Si_C_Nanotube_Array_Li_Ion_Battery_Anodes/2193598 Stability and high energy densities are essential qualities for emerging battery electrodes. Because of its high specific capacity, silicon has been considered a promising anode candidate. However, the several-fold volume changes during lithiation and delithiation leads to fractures and continuous formation of an unstable solid-electrolyte interphase (SEI) layer, resulting in rapid capacity decay. Here, we present a carbon–silicon–carbon (C@Si@C) nanotube sandwich structure that addresses the mechanical and chemical stability issues commonly associated with Si anodes. The C@Si@C nanotube array exhibits a capacity of ∼2200 mAh g<sup>–1</sup> (∼750 mAh cm<sup>–3</sup>), which significantly exceeds that of a commercial graphite anode, and a nearly constant Coulombic efficiency of ∼98% over 60 cycles. In addition, the C@Si@C nanotube array gives much better capacity and structure stability compared to the Si nanotubes without carbon coatings, the ZnO@C@Si@C nanorods, a Si thin film on Ni foam, and C@Si and Si@C nanotubes. <i>In situ</i> SEM during cycling shows that the tubes expand both inward and outward upon lithiation, as well as elongate, and then revert back to their initial size and shape after delithiation, suggesting stability during volume changes. The mechanical modeling indicates the overall plastic strain in a nanotube is much less than in a nanorod, which may significantly reduce low-cycle fatigue. The sandwich-structured nanotube design is quite general, and may serve as a guide for many emerging anode and cathode systems.