氮掺杂多孔炭片的模板法制备及其储锂性能研究

Template-Assisted Preparation and Lithium Storage Performance of Nitrogen Doped Porous Carbon Sheets

以氧化镁/三聚氰胺/聚乙二醇混合物为初始原料,通过模板辅助的方法成功地制备了高储锂性能的氮掺杂多孔炭片(NPCSs).采用红外光谱(FTIR)、X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、扫描电镜(SEM)、透射电镜(TEM)、循环伏安(CV)、恒流充放电(GCD)和交流阻抗(EIS)对样品进行了详细地表征和分析.结果显示:NPCSs为交错连接的多孔炭片网络,并显示出较高的比表面积(370.8 m^2·g^(-1))、多级的孔道和高的氮含量(8.5 at%).这种连续多孔的结构,有利于电子在三维方向的传输,缩短了锂离子扩散的距离,扩大了锂离子与电极的接触面积,也为锂离子的储存提供了有利场所.此外,高的氮掺杂水平为锂离子的嵌入和脱出提供了大量的活性位点,增强了材料的导电性.基于此独特的结构,NPCSs电极显示了高的首次可逆比容量(电流密度为100 m A·g^(-1)时,扣除乙炔黑贡献后的比容量为914m Ah·g^(-1))和较好的循环稳定性(电流密度为1000 m A·g^(-1),循环至300圈,仍保留523 m Ah·g^(-1)的比容量).而且,该材料显示出较高的倍率性能,在电流密度为3000 m A·g^(-1)时的可逆比容量达到355 m Ah·g^(-1).因此,所获得的NPCSs有望成为锂离子电池负极材料.

Nitrogen doped porous carbon sheets （NPCSs） having high lithium storage performance were successfully pre- pared by a template-assisted approach using magnesium oxide/melamine/polyethylene glycol （MgO/melamine/PEG） as raw materials. In a typical procedure, the precursor, which consisted of MgO, melamine and PEG in a mass ratio of 7 ： 3 ： 10, was carbonized at 700 ℃ for 3 h in a temperature-programmed tubular furnace under N2 flow with a heating rate of 5 ℃ · min-1. The intermediate was immersed into 3 mol·L^-1 HC1 solution for several times to remove MgO. Subsequently, the sam- ple was rinsed with water and ethanol until a neutral pH was obtained, and then dried at 80 ℃ in a vacuum oven. The sam- ple was systematically characterized and analyzed by Fourier transform infrared spectrometer （FTIR）, X-ray powder diffrac- tometer （XRD）, X-ray photoelectron spectrometer （XPS）, scanning electron microscope （SEM）, transmission electron micro- scope （TEM）, cyclic voltammetry （CV）, galvanostatic charge/discharge （GCD） and electrochemical impedance spectroscopy （EIS）. The results indicated that NPCSs showed an interconnected porous carbon sheet networks, showing relatively high specific surface area （370.8 m2·g^-1）, hierarchical pore channels, and high nitrogen content （8.5 at%）. Such a continuous po- rous structure could enhance the electron transport on three-dimensional direction, shorten the diffusion distance of lithium ions, enlarge the interface area between lithium ion and electrolyte, and provide the place for the accommodation of lithium ions. Additionally, high N-doping level in NPCSs could provide numerous activated sites for the intercalation and deinterca- lation of lithium ions, and enhance the electronic conductivity. Based on the unique structure, NPCSs electrode could exhibit high initial reversible specific capacities （after excluding the contribution of acetylene black, 914 rnAh·g^-1 at 100 mA·g^-1） and good cycling stability （still remaining a specific capacity of 523 mAh·g^-1 at 1000 mA·g^-1 up to 300 cycles）. Moreover, NPCSs displayed high rate capability with a reversible capacity of 355 mAh·g^-1 at a current density of 3000 mA·g^-1. There- fore, the NPCSs obtained are expectable to be widely used as anode material in lithium-ion batteries.