Department of Materials Science and Engineering, ‡Department of Mechanical Sciences and Engineering, §Frederick Seitz Materials Research Laboratory, ⊥Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
ACS Nano. 2015 Feb 24;9(2):1985-94. doi: 10.1021/nn507003z. Epub 2015 Feb 4.
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(-1) (∼750 mAh cm(-3)), 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. In situ 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.
稳定性和高能量密度是新兴电池电极的基本要求。由于其高比容量，硅被认为是一种很有前途的阳极候选材料。然而，在锂化和脱锂过程中几倍的体积变化会导致裂缝和不稳定的固体电解质界面（SEI）层的连续形成，从而导致容量迅速衰减。在这里，我们提出了一种碳-硅-碳（C@Si@C）纳米管三明治结构，解决了与 Si 阳极相关的机械和化学稳定性问题。C@Si@C 纳米管阵列的容量约为 2200 mAh g(-1)（约 750 mAh cm(-3)），显著超过商业石墨阳极的容量，并且在 60 次循环中库仑效率接近 98%。此外，与没有碳涂层的 Si 纳米管、ZnO@C@Si@C 纳米棒、Ni 泡沫上的 Si 薄膜以及 C@Si 和 Si@C 纳米管相比，C@Si@C 纳米管阵列具有更好的容量和结构稳定性。循环过程中的原位 SEM 显示，管在锂化时向内和向外膨胀，同时伸长，然后在脱锂后恢复到初始尺寸和形状，表明在体积变化过程中的稳定性。力学模型表明，纳米管中的整体塑性应变远小于纳米棒中的应变，这可能会显著降低低周疲劳。三明治结构的纳米管设计非常通用，可为许多新兴的阳极和阴极系统提供指导。
