【摘要】 高容量材料对于实现锂离子电池高能量密度至关重要.本文通过一种新颖、简便的冷冻干燥与原位镁热还原相结合的方法,以二氧化硅和氧化石墨烯为原料制备了一种高度分散的三维石墨烯包裹多孔纳米硅复合负极材料(P-Si@rGO).该材料具有许多吸引人的特性:高度分散和被单独包覆的硅颗粒,硅和石墨烯之间紧密的Si–O–C相互作用,硅结构的多孔设计以及高孔隙率.这些优点显著增强了电极的反应动力学,赋予了复合材料更大的电接触面积和足够的缓冲空间以应对硅在锂化/脱锂过程中的体积变化,最终使P-Si@rGO获得优异的循环稳定性.本文研究了复合材料的相组成和微观结构对其电化学性能的影响,分析了电极在循环后期容量增加的原因,为硅基负极的功能化演变提供了新的思路.更多还原

【Abstract】 The use of high-capacity materials in lithium-ion batteries（LIBs） is critical for achieving higher energy density. In this paper, a highly-dispersed three-dimensional（3D） graphene-wrapped porous nano-silicon composite（P-Si@rGO, where rGO is reduced graphene oxide） is synthesized from SiO₂ and graphene oxide through a novel and facile approach that consists of freeze-drying and in-situ magnesium-thermal reduction. The composite is then utilized as a high-capacity anode for LIBs. A number of attractive properties are evident in this new silicon-based composite and include qualities such as individually encapsulated and highly dispersed silicon particles, close Si–O–C interactions between silicon and graphene, a porous design for the silicon structure,and a bulky porosity. These merits significantly enhance the reaction kinetics of the electrode and endow the composite with both a large electrical contact area and a sufficient buffer space to cope with the volume change during the lithiation/delithiation process. Ultimately, the P-Si@rGO sample demonstrates an excellent cycling stability, boasting a capacity of 1123 mAh g^-1at 1000 mA g^-1over 500 cycles. In this paper,materials with different morphologies are prepared by changing the magnesium-thermal reaction time, so as to study the effects of phase composition and microstructure of the composites on their electrochemical performances. Importantly,the reasons for the capacity increase seen in later stages of the cycling process are also investigated. In brief, these findings provide new insights into the future functional evolution of silicon-based anode materials.更多还原