Abstract:

A carbon film (Fe₂C /N-C) co-doped with Fe₂C and nitrogen was prepared by the directional freezing-carbonization method as an integrated electrode for lithium-sulfur batteries. Due to its regular conductive networks and well-connected ion diffusion channels, it can effectively alleviate the poor conductivity of the active substance sulfur and the final discharge products, meanwhile, the microporous structure can effectively buffer the volume expansion effect during the charging/discharging process. This membrane structure is conducive to electron transfer and lithium ion diffusion, coupled with the addition of Fe₂C which can provide the adsorption of lithium polysulfides (LiPSs) and the catalytic conversion of LiPSs to the final discharge products, the synergistic effect can effectively inhibit the “shuttle effect”, increase the sulfur utilization rate, and significantly improve the comprehensive performances and cycling stability of the batteries. Therefore, the Li-S batteries with Fe₂C/N-C/S as cathodes exhibit a high specific capacity of 833.0 mA·h·g^-1 at 1.0 C after 100 cycles with the coulombic efficiency of 99.3% and an extended cycling stability of 0.02% per cycle capacity decay at sulfur loading of 1.1 mg·cm^-2, even at a higher sulfur loading of 3.8 mg·cm^-2, the specific capacity of 714.3 mA·h·g^-1 can be obtained at 0.2 C after 100 cycles.

Key words: directional freezing, metal carbide, membranes, nanomaterials, shuttle effect, lithium-sulfur batteries

摘要：

利用定向冷冻-碳化法制备了Fe₂C、氮共掺杂的碳膜（Fe₂C/N-C）作为一体化电极用于锂硫电池。由于其兼具规则的导电网络和连通的离子扩散通道，可有效缓解活性物质硫及放电终端产物导电性差的问题，且孔道结构亦可有效缓冲充放电过程活性物质的体积膨胀效应。该膜结构有利于电子传递和锂离子扩散，掺杂的Fe₂C纳米颗粒对多硫化锂具有较强的吸附作用以及向放电终端产物转化的催化作用，有效抑制了多硫化物的“穿梭效应”，提高硫利用率，显著提升电池的综合性能和循环稳定性。Fe₂C/N-C电极在载流量1.1 mg·cm^-2、1.0 C电流密度下循环100圈后得到833.0 mA·h·g^-1的比容量、99.3%的库仑效率、每圈容量衰减率低至0.02%，在较高载硫量3.8 mg·cm^-2时，0.2 C下循环100圈仍能取得714.3 mA·h·g^-1的比容量。

关键词: 定向冷冻法, 金属碳化物, 膜, 纳米材料, 穿梭效应, 锂硫电池