Nishihara Hirotomo, Suzuki Takashi, Itoi Hiroyuki, An Bai-Gang, Iwamura Shinichiroh, Berenguer Raúl, Kyotani Takashi
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan.
Nanoscale. 2014 Sep 21;6(18):10574-83. doi: 10.1039/c4nr01687d. Epub 2014 Jun 27.
The precise design of Si-based materials at the nanometer scale is a quite complex issue but of utmost importance for their present and potential applications. This paper reports the first attempt to address the electrochemical reduction of SiO₂ at the nanometer scale. SiO₂ nanoparticles are first covered with a uniform carbon layer with controlled thickness at an accuracy of a few nanometers, by pressure-pulsed chemical vapor deposition. With appropriate thickness, the carbon layer plays significant roles as a current path and also as a physical barrier against Si-crystal growth, and the SiO₂ nanoparticles are successfully converted into extremely small Si nanocrystals (<20 nm) inside the shell-like carbon layer whose morphology is derived from the original SiO₂ nanoparticles. Thus, the proposed electroreduction method offers a new synthesis strategy of Si-C nanocomposites utilizing the morphology of SiO₂ nanomaterials, which are well known for a wide variety of defined and regular nanostructures. Owing to the volume difference of SiO₂ and the corresponding Si, nanopores are generated around the Si nanocrystals. It has been demonstrated that the nanopores around the Si nanocrystals are effective to improve cycle performance of Si as a negative electrode for lithium-ion batteries. The present method is in principle applicable to various SiO₂ nanomaterials, and thus, offers production of a variety of Si-C composites whose carbon nanostructures can be defined by their parent SiO₂ nanomaterials.
在纳米尺度上精确设计硅基材料是一个相当复杂的问题，但对于它们当前和潜在的应用来说至关重要。本文报道了首次在纳米尺度上解决二氧化硅电化学还原问题的尝试。首先通过压力脉冲化学气相沉积法，以几纳米的精度在二氧化硅纳米颗粒上覆盖一层厚度可控的均匀碳层。具有适当厚度时，碳层既作为电流路径发挥重要作用，又作为防止硅晶体生长的物理屏障，并且二氧化硅纳米颗粒在壳状碳层内成功转化为极小的硅纳米晶体（<20纳米），其形态源自原始的二氧化硅纳米颗粒。因此，所提出的电还原方法提供了一种利用二氧化硅纳米材料形态合成硅 - 碳纳米复合材料的新策略，二氧化硅纳米材料以其各种明确且规则的纳米结构而闻名。由于二氧化硅与相应硅的体积差异，在硅纳米晶体周围产生了纳米孔。已经证明，硅纳米晶体周围的纳米孔对于提高硅作为锂离子电池负极的循环性能是有效的。本方法原则上适用于各种二氧化硅纳米材料，因此能够生产出各种碳纳米结构可由其母体二氧化硅纳米材料定义的硅 - 碳复合材料。
