SiOx-Si/graphene/Si-SiOx锂离子电池负极材料的纳米结构构筑及其储锂行为

The main challenges for the practical implementation of Si anodes are the huge volume variation during lithiation and delithiation processes and low electronic conductivity, resulting in pulverization, low cycling efficiency and poor rate capability. Therefore, a novel 2-dimentional, sandwich-like and porous nanostructured SiOx-Si/graphene/Si-SiOx nanocomposite will be designed and synthesized for high energy density of lithium-ion batteries. The nanostructure and chemical characteristics of SiOx-Si/graphene/Si-SiOx nanocomposite will be controlled combined with the electrosorption of cetyltrimethylammonium bromide (CTAB) on the surface of graphene oxide, the molecular self-assemble mechanism of CTAB with tetraethoxysilane (TEOS), and the reduction/oxidation reaction mechanisms of Si with Mg and H2O. Moreover, the huge volume variation of Si during lithiation and delithiation processes will be solved by the flexible characteristics of 2-dimentional and porous nanostructures. Additionally, stable surface electrolyte interface (SEI)films can be formed on the surface of SiOx, which is beneficial to improve the cycling stability of Si anode. Importantly, the inartificial conductive network of graphene bonded with Si nanofilm with large contact area can cover the shortage of Si with low electronic conductivity. Meanwhile, the unique nanostructure of Si nanofilm with 2-dimentional and porous structure can slso assist a fast lithium diffusion and electron transport during the cycle charging-discharging processes, giving high rate capacities. Except for the controllable synthesis of SiOx-Si/graphene/Si-SiOx nanocomposite, the corresponding fundamental sciences will be elucidated, especially, the forming mechanism of sandwich-like nanostructure for Si/graphene/Si anode. And then the effect mechanism of nanostructures of SiOx-Si/graphene/Si-SiOx nanocomposite on its electrochemical performance will be explored.

针对Si在脱嵌锂过程中较大的体积变化率及低的电导率导致的超高容量不能有效利用和大电流倍率性能差的核心问题，本课题拟构筑一种"三明治"式二维多孔纳米结构的SiOx-Si/graphene/Si-SiOx负极材料加以解决。首先，基于分子间的电吸附和分子自组装原理以及Si与Mg、H2O之间的还原、氧化反应机理，控制该纳米复合材料的纳米结构和化学性质。其次，利用该材料二维纳米结构的柔性特性和丰富的纳米孔道以及SiOx能与电解液形成稳定SEI膜的特点，协同解决Si因在充放电过程中的粉化失效而导致的容量衰减问题；并利用石墨烯优异的导电性及其导电网络结构以及Si纳米膜超薄的二维多孔纳米结构，弥补Si电导率低的劣势以提高其大电流倍率性能。本课题拟在实现SiOx-Si/graphene/Si-SiOx材料可控制备的基础上，阐明该负极材料的"三明治"结构形成机理、纳米结构的控制机制及其储锂行为等基础科学问题。

针对 Si 在脱嵌锂过程中较大的体积变化率及低的电导率导致的超高容量不能有效利用和大电流倍率性能差的核心问题，可控制备一种二维“三明治”中孔结构的碳包覆Si-rGO-Si（C/Si-rGO-Si/C）新型锂离子电池负极材料。通过将“三明治”结构SiO2-rGO-SiO2镁热还原成Si-rGO-Si再包覆纳米碳层而制得。石墨烯及纳米碳层良好的导电性有效弥补了纳米硅电导率低的不足，而二维纳米结构和中孔结构又为纳米硅的体积膨胀提供了足够的缓冲空间并使得Li+具有较高的扩散速度。其中，C/Si-rGO-Si/C负极材料在1A.g-1电流密度下循环1000次后，可逆容量仍达894mAh.g-1。另外，以“三明治”结构SiO2-rGO-SiO2为模板，制得二维中孔结构的碳包覆SnO2-rGO-SnO2负极材料，其在1A.g-1的电流密度下循环1000次后可逆容量达667mAh.g-1。该课题实现了C/Si-rGO-Si/C的可控制备，阐明了该负极材料的“三明治”结构形成机理、纳米结构的控制机制及其容量提升机制等基础科学问题。.在此国家自然科学基金的支持下，在Journal of Materials Chemistry A、ACS Applied Materials & Interfaces等国际权威期刊发表SCI论文11篇。