基于纳米硅/聚合物核壳结构的高循环稳定性固相储锂负极反应

Silicon has been considered as a promising alternative anode material for next-generation lithium ion batteries, but the commercial application of Si anodes is still hindered by the poor cyclability. The low cyclability of silicon mainly resulted from the huge volumetric changes during lithium insertion/extraction cycles. Such an enormous volume change brings about two severe problems for Li-ion battery. One is the degradation of the mechanical integrity of the Si anode, leading to the loss of electrical contact and the gradual deactivation of the active materials. The other is the continuous change in the structure and morphology of the solid electrolyte interphase (SEI) on the Si surface. The repeated construction and destruction of the SEI will seriously decrease the coulombic efficiency, and the continuous growth of electronically insulating SEI film can cause electric disconnection between the electrode collector and anode materials. Much research work has been devoted to the relaxation of the volume change of silicon. However, little work has been focused on both the volume change and SEI reconstruction. The improvement of the cyclability of silicon is still not acceptable. In this work, we propose a new strategy to enhance the long-term cyclability of Si anode by embedding nano-Si particles into a Li+ - conductive polymer to form a Si/polymer composite with core-shell structure. In this core-shell structure, the polymeric matrix serves not only as a strong buffer to accommodate the volume change, but also as a protection barrier to prevent the direct contact of Si surface with electrolyte, so as to maintain the mechanical integrity of Si anode and suppress the repeated destruction and construction of SEI on the Si surface. This work will focus on the choice of the polymer matrix, prereparation and characterization of the composite anode materials.

硅是一种极具应用前景的高比容量锂离子电池负极材料。然而，由于合金化储锂过程中伴随巨大的体积膨胀，硅负极的循环稳定性较差，制约了其商业化应用。体积膨胀给硅负极带来两方面的负面影响：一是材料颗粒的粉化；二是Si颗粒表面SEI膜的不断破坏和重建。SEI膜的重复生长不仅导致电极充放电库仑效率的降低，以及电解液和锂离子的快速耗竭，而且带来SEI膜的不断增厚，进而造成Si颗粒之间的电接触不良。但目前的研究大多集中在缓冲硅的体积变化方面， 对于SEI膜的持续生长问题目前仍缺乏有效的解决方案。在此，我们提出了一种发展高循环稳定性Si负极的新思路，即将纳米硅颗粒分散嵌埋到锂离子传导型导电聚合物基质中，形成具有核壳结构的Si/聚合物复合物。在此结构中，聚合物基质不仅可以作为缓冲层用来缓解硅的体积变化，而且可以作为保护层用来阻挡硅表面与电解液的直接接触。本工作将围绕聚合物基质的选择、复合物的制备与表征展开研究。

该项目工作针对锂离子电池单质硅负极材料在充放电循环过程中巨大的体积膨胀/收缩的引发的循环稳定性低的问题，采用具有锂离子导电特性的导电聚合物材料在纳米硅粒子表面包覆，形成核壳结构纳米硅/导电聚合物复合材料，实现缓冲硅电极充放电过程中体积膨胀以及抑制SEI膜破坏和重建双重作用。研究工作内容基本按照计划执行，对纳米硅/聚合物核壳结构材料的聚合物进行了优选，最终选用聚多巴胺、聚丙烯腈作为包覆材料；分别采用这两种聚合物制备了核壳机构纳米硅基负极材料，所制备的电极材料装配的电池表现出优良的循环稳定性和倍率性能，对其作用机制进行了解析。在此基础上，我们还结合实验过程中遇到的具体现象和问题，在原有计划中优选聚合物、设计纳米硅结构、组装电池获得优良电化学综合性能的基础上，合成了碳包覆和氧化亚铜包覆材料、设计了基于纳米阵列的双层电极结构、对聚合物进行了石墨烯复合，使所制备的电极材料装配的电池表现出了更加优良综合电化学性能。本项目的完成，对于大幅度提高锂离子电池的硅负极材料的循环稳定性，推动高能量密度锂离子电池的发展，应对电动汽车和储能电站等新能源领域的应用需求具有重要作用和意义。项目所提出的纳米硅/聚合物核壳结构以及拓展工作作为一种简单而有效地改善电极材料性能的途径，具有广泛的科学意义和应用背景。