【作者】 李拴魁；

【导师】 闫鹏勋；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2014， 博士

【摘要】 锡基材料由于较高的理论容量成为极具发展潜力和应用前景的新型离子电池负极材料。但其在充放电过程中产生的巨大的体积膨胀以及较大的首次不可逆容量限制了锡基负极材料在商业化生产中的应用。将锡基材料纳米纳米化及与碳基材料复合能有效改善其作为锂离子电池负极材料的性能,并有望代替碳作为成为下一代锂离子负极材料。本论文以SnS及SnO2为研究目标,主要针对其作为锂离子电池的负极材料的性能的改善,进行了两方面的努力：①对SnS纳米材料的可控制备。通过简单的溶剂热法制备了SnS复杂纳米结构,在研究了形成机理的基础之上对其形貌进行了调控,探索了纳米结构对其作为锂离子负极材料的性能的影响。②通过与碳基材料,包括MWCNTs、GO、非晶碳的复合,制备了一系列碳SnS、SnO2复合材料,改善其性能。本论文主要做了如下几方面的工作：采用溶剂热法在乙二醇溶剂中,成功制备了SnS纳米片构成的空心纳米花,其形成机理主要是奥氏熟化。在深入的研究了其形成机理的基础上,通过引入柠檬酸或柠檬酸钠来影响反应前期乙二醇与Sn2+的配位反应,成功达到了对SnS纳米结构进行调控的目的。电化学测试表明,由鳞片状SnS超薄纳米片组装而成的SnS多孔球相比于其他结构的SnS纳米花具有明显的性能优势,在100mA/g的电流密度下,其可逆容量达到了762mAh/g,这主要是由于其超薄的纳米片厚度和独特的多孔结构造成的。上述研究不仅有助于设计和制备各种特殊形貌的SnS纳米结构,而且对于纳米结构与其性能之间的联系具有重要意义。为了改善SnS作为锂离子电池的负极材料的性能,我们首次制备了SnS/MWCNTs复合纳米结构。并且,对复合材料的纳米结构进行调控,研究了结构对其性能的影响。相对于纯的SnS纳米结构,MWCNTs的加入改善了电极材料的导电性,同时有效地提高了充放电过程中电荷转移的速率,从而使得复合纳米结构具有较好的循环性能和倍率充放电性能。同时,SnS NSs/MWCNTs相对于SnS NPs/MWCNTs复合纳米结构在性能方面具有明显的改善,这主要是由于其特殊的结构所造成的。相对于纳米颗粒,SnS超薄纳米片更利于锂离子的进入和传输。另外,SnS纳米片具有了极大的比表面积,这些开放的边缘可以使锂离子在活性材料中更快地扩散,较大的比表面积也能让锂离子更易结合到活性物质当中,从而提高其容量及循环稳定性。本文的研究结果为其它高性能碳纳米管复合电极材料的设计和制备提供了依据。采用溶剂热法设计制备出SnS纳米片/石墨烯复合材料。探讨了这种特殊的复合纳米结构的形成机理及电化学性能。结果表明,SnS-GO纳米复合材料作为锂离子电池负极材料的性能得到了明显提高,这主要是由于SnS-GO的特殊的结构所造成的。超薄SnS纳米片更利于锂离子的进入和传输,并且较高SnS的含量保证了其高的可逆容量。超薄的SnS纳米片平铺在氧化石墨烯的表面的独特结构可以尽可能的增大石墨烯与SnS的接触面积,有利于电荷的快速运动,而且可以防止SnS的粉化及从石墨烯表面脱落有效的缓解体积膨胀,从而使得复合纳米结构具有较好的循环性能和倍率充放电性能。这对石墨烯基复合电极材料的设计和制备具有指导意义。在上面研究的基础上,以C@SnS多孔球为原料在葡萄糖的水溶液中制备了多孔非晶碳骨架负载SnO2纳米颗粒的复合纳米结构。这种复杂的复合纳米结构的形成主要是由于非晶碳层的模板作用和葡萄糖相关的氧化过程的共同作用的结果。电化学测试表明,我们制备的C/SnO2复合纳米材料作为锂离子电池的负极材料表现出高的可逆容量、优异的循环稳定性及倍率性能,这主要是由于其独特的结构决定的。该方法有望在其他新型复合电极材料的设计制备中得到应用。更多还原

【Abstract】 Tin-based materials as a new type of anode material for lithium-ion batteries have tremendous development and application prospect because of its hight theoretical capacity. However, the large volume change and the huge initial irreversible capacity in the proeess of charging and disecharging limit the application of tin-based anode materials in commercial production to instead of carbon. Recent research indicated that the use of tin-based nanostructure and tin/carbon-based hybrids can avoid the above-mentioned problems, which is expected to replace carbon in lithium-ion battery as anode material to improve performance of battery.In this work, we reported our research achievements of nanomaterial (SnS、SnO2) synthesis, their growth mechanism, and the performance as an anode material for lithium-ion batteries. SnS/carbon-based materials hybrid is expected to show good performance as anode materials of lithium-ion batteries, since the synergy between the functions of the two materials, high capacity of SnS, good electronic conductivity and large surface area carbon-based materials such as amorphous carbon, MWCNT, Graphene, can be exploited in the SnS/C hybrids to yield high performance anodes in lithium-ion batteries.SnS hollow micro-flowers assembled from nanosheets have been successfully prepared by a citric acid assisted solvothermal method for the first time. It was found that the formation of the SnS hollow micro-flowers based on an inside-out Ostwald ripening mechanism. A series of SnS3D-hierarchical nanostructures with tunable morphology and sheet thickness have been synthesized by introducing additives to the solution. The electrochemical tests with the prepared SnS nanomaterials show that the SnS porous sphere built with scale-like ultrathin nanosheets exhibited the best performance and could retain a reversible capacity of762mAh/g at a current density of100mA/g. This performance is directly brought by faster ion diffusions and better stability owing to the ultrathin thicknesses as well as the unique porous structures.A hybrid of multi-walled carbon nanotubes (MWCNTs) anchored with SnS nanosheets is synthesized through a simple solvothermal method for the first time. Interestingly, SnS can be controllably deposited onto the MWCNTs backbone in the shape of nanosheets or nanoparticles to form two types of SnS/MWCNTs hybrids, SnS NSs/MWCNTs and SnS NPs/MWCNTs. When evaluated as an anode material for lithium-ion batteries, the hybrids exhibit higher lithium storage capacities and better cycling performance compared to pure SnS. The improved performance may be attributed to the ultrathin nanosheet subunits possess short distance for Li+ions diffusion and large electrode-electrolyte contact area for high Li+ions flux across the interface. It is believed that the structural design of electrodes demonstrated in this work will have important implications on the fabrication of high-performance electrode materials for lithium-ion batteries.A SnS nanosheet-graphene oxide nanosheet hybrid was synthesized by a facile one-step solvothermal route. Ultrathin SnS nanosheets with a lateral size of5-10nm are anchored on graphene nanosheets forming a unique sheet-on-sheet structure. The electrochemical tests showed that the nanohybrid exhibits a remarkably enhanced cycling stability and rate capability compared with bare SnS nanosheets. The excellent electrochemical properties of SnS/GO could be ascribed to the in situ introduced graphene matrix which offers two-dimensional conductive networks, disperses and immobilizes SnS nanosheet, buffers the volume changes during cycling, and directs the growth of SnS nanosheets with a favorable orientation.A novel hierarchical3D porous C/SnO2nanocomposite was synthesized by a facile, two-step hydrothermal growth method used porous C@SnS nanospheres as precursor. The SnO2interconnected nanoparticles10-20nm and homogeneously distributed on3D carbon framework. The formation of C/SnO2nanocomposites is mainly due to a cooperative process of an amorphous carbon layers template and glucose-related oxidation process. The cooperative effect of the high theoretical lithium storage capacities of SnO2and excellent electric conductivity of amorphous carbon framework make the as-synthesized3D composite as an excellent anode material for lithium-ion batteries with enhanced capacity and cycling property. Our results suggest that3D porous C/SnO2nanocomposite may serve as a promising anode material for high-power lithium-ion battery.更多还原