具有微米纤维碳的硅/石墨/碳复合材料的制备及在锂离子电池中的应用

Preparation of silicon/graphite/carbon composites with fiber carbon and their application in lithium-ion batteries

  • 摘要: 以沥青为软碳原料,商业石墨的载体材料,通过高温热解法成功合成了硅/石墨/碳复合材料,同时原位生成了微米尺度的碳纤维.该硅/石墨/碳复合材料具有诸多优点,石墨片层堆叠之间的空隙为硅的体积膨胀提供了有效的空间,沥青热解碳材料的包覆能一定程度抑制硅基材料的体积效应和提高其电子电导率,同时微米级的碳纤维能提高材料的长程导电性和结构稳定性,从而极大的改善负极材料循环性能.通过电化学测试表明,硅/石墨/碳复合材料中硅/石墨/碳复合负极材料在200 mA·g-1电流密度下具有650 mA·h·g-1的可逆容量,在200 mA·g-1电流密度下经过500圈循环后容量保持率为92.8%,每圈的容量衰减率仅为0.014%,展现了优异的循环性能.

     

    Abstract: Lithium-ion batteries have been widely used in various industries because of their high energy density, long life cycle, and green ring. In recent years, with the rapid development of consumer electronics, mobile wearable devices, and especially electric vehicles, the energy density requirements of the lithium-ion battery have progressively increased, promoting the development of lithium-ion batteries of higher specific capacity and longer life cycle. The commonly used graphite negative electrodes have a low theoretical capacity of 372 mA·h·g-1, which does not meet the current requirements. Silicon is a very promising lithium-ion battery anode material because of its high theoretical specific capacity of 4200 mA·h·g-1, low price, and eco-friendliness. However, silicon experiences high volume expansion (~300%) during charging and discharging, leading to severe loss of electrical contact with conductive agents and current collectors along with capacity degradation. Thus, using pitch as a soft carbon raw material and nano-Si and commercial graphite as active materials, a silicon/graphite/carbon composite was successfully synthesized using the high-temperature pyrolysis method, and micron-scale carbon fiber was formed in situ. The silicon/graphite/carbon composite material has many advantages: the void between the graphite sheet provides an effective space for the volume expansion of silicon, the coating of the asphalt pyrolysis carbon material can inhibit the volume effect in the nano-Si and increase its electronic conductivity to a certain extent, and the micro-sized carbon fiber enhances the long-range conductivity and structural stability of the material, thus greatly improving the cycle performance of the negative electrode material. The electrochemical test show that the silicon/graphite/carbon composite anode material delivers a reversible capacity of 650 mA·h·g-1 at 200 mA·g-1 and a capacity retention rate of 92.8% after 500 cycles at a current density of 500 mA·g-1. The capacity decay rate per cycle was only 0.014%, indicating excellent cyclic performance.

     

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