熔融盐体系下二维纳米硅/碳复合材料形态结构演化机制及储锂性能研究

Silicon, with high theoretical capacity, low voltage profile and abundant reserves, is an ideal candidate of anode materials for the development of Li ion batteries with high energy density. However, practical application of silicon anode is currently hindered by multiple challenges including its low electrical conductivity and enormous volume change during lithiation/delithiation processes. To address these issues from the viewpoint of material/surface and interface in mesoscale, a molten-salt route for magnesium-thermic synthesis of nano-silicon/carbon composites will be developed, in which only single organosilicon containing both silicon and carbon elements are used as the precursor. Nanostructured silicon can address problems caused by volume effect including particle pulverization and formation of unstable SEI layer. Combining nanostructured silicon with carbon material can also improve the electrical conductivity of silicon semiconductor. In this project, we will systematically study and clarify the coupling principles between chemical reaction and matter migration in molten-salt, identifying mechanism of morphology and structure transformation in mesoscale from organosilicon molecules to inorganic 2D nano-silicon/carbon composites. We will also systematically study and clarify the rules for electrochemical reaction of Li storage and charge (Li ion and electron) transport kinetics, identifying mechanism of electrode process and structure-activity relationship for this novel anode material. This project will offer new thinking and support for the rational design and synthesis of silicon anode material.

硅的理论比容量高，放电平台较低且储量丰富，是发展高比能锂离子电池的理想负极材料。然而，纯硅负极材料导电性差，且在锂化/脱锂过程中具有显著的体积效应，限制了其实际应用。为了解决这些问题，本项目拟从材料/表界面结构介尺度出发，建立以含硅和碳元素的单一有机硅源为前驱体，利用熔融盐体系下的镁热反应制备二维纳米硅/碳复合材料的新方法。硅的纳米化可以有效地缓解因体积效应而导致的材料粉化，难以形成稳定SEI膜等问题；纳米硅与碳材料复合可以显著地提高半导体硅的导电性。本项目将通过系统研究揭示熔融盐体系下的化学反应与物质迁移的耦合规律，阐明从有机硅源分子到无机二维纳米硅/碳复合材料的介尺度形态结构演化机制。通过系统研究揭示二维纳米硅/碳复合材料电化学储锂反应与电荷（锂离子和电子）传输动力学规律，阐明该新型负极材料的电极过程机理及构效关系。本项目将为硅基负极材料理性设计与合成提供新的思路和支持。

硅基负极材料具有高的理论比容量及较低的放电平台且储量丰富，是实现高比能锂离子电池的理想负极材料之一。但是硅在锂化/脱锂过程中显著的体积效应以及导电性差的特点限制了其实际应用。为了解决这些问题，本项目成功建立了以含硅和碳元素的单一有机硅源为前驱体，利用熔融盐体系下的镁热反应制备纳米硅/碳复合材料的合成方法。在此基础上进一步利用还原气氛替代镁金属作为还原剂，建立了基于熔融盐体系下制备纳米硅氧化物/碳复合材料的合成方法。该方法所得产物为典型的二维碳纳米片负载的纳米硅或硅氧化物复合材料。熔融盐反应环境为二维碳纳米片的形成提供了条件，分子动力学模拟也证实了碳原子在熔融盐中有重组为二维碳纳米片的演变趋势。该方法所制备的硅基复合材料展示出优异的储锂性能，在1A g-1的电流密度下500圈循环后容量能够保持在1250 mAh g-1，循环500圈的容量保持率为60%，相较于商业纳米硅循环有较大提升。本项目提供了一种从有机硅源分子到无机二维纳米硅/碳复合材料的演变途径，并发展了基于分子动力学模拟研究新型熔融盐反应环境下材料形貌演变的方法。本项目可以为硅基负极材料理性设计与合成提供新的思路和支持。