碳化芦苇叶直接制备高性能Si/C锂离子电池负极试验

Synthesis of Si/C composites derived from directly-carbonized reed plants as high-performance anode for lithium ion batteries

以可再生生物质芦苇叶为原料,通过热解碳化、CO2高温脱碳和镁热还原三步热处理制备Si/C复合材料。利用扫描电子显微镜、热重与差热分析、拉曼光谱、X射线衍射等手段对芦苇叶热解碳化产物、CO2高温脱碳产物和最终合成的Si/C复合材料的形貌、组成和结晶度进行表征,同时对Si/C复合材料的电池性能进行综合评估。结果表明:在1 000℃下CO2高温脱碳处理6 h制备得到最佳的镁热还原前驱体,前驱体里的无定型SiO2在镁热还原反应中基本都转化成晶体硅,最终的Si/C复合物拥有约9.1%的N掺杂碳含量和高结晶度的晶体硅,保留了原始芦苇叶的三维硅骨架结构;Si/C电极在电流密度100 mA/g下的充电比容量高达935.7 mAh/g,在电流密度1 000和2 000 mA/g下比容量分别为520.7和277.8 mAh/g,且循环过程中库伦效率均在95%以上,表现出优越的倍率性能和良好的循环性能。此外,该制备工艺简单,这种低成本、储量丰富的生物质硅源材料芦苇叶有望作为下一代高能量密度锂离子电池硅负极的生产原料,推动实现硅负极的规模化生产。

Silicon is a promising candidate for an anode of high?energy lithium ion batteries because of its high theoretical specific capacity(3 579 mAh/g for Li15Si4,ten times than commercial graphite),low discharge voltage(<0.5 V vs.Li/Li^+),environmental friendliness,and natural abundance.Unfortunately,the wide utilization of silicon is ham?pered by several major drawbacks such as its large volume change(400%)during lithium ion insertion/extraction processes,low electrical conductivity(10^-3 S/cm)and ionic conductivity(10^-14-10^-13 cm^2/s).A useful strategy is to combine nanostructure silicon with carbon materials for reducing the volume change of Si.Furthermore,it has found that silicon nanomaterials have potential application in a number of areas.In this work,the scalable synthesis of Si/C composites was directly derived from natural reed leaves by three steps,namely,pyrolysis carbonization,high?temperature CO2 decarburization and magnesiothermic reduction.Natural reed leaves provided both carbon and silicon sources.The synthesized Si/C composites had a uniform carbon dispersion among the silicon nanoparticles by the CO2 high?temperature decarburization treatment at the temperature of 1 000℃for 6 h and the N?doping carbon content was about 9.1%.The resultant porous Si/C architectures were prepared by the magnesiothermic reduction.During the magnesiothermic reduction process,amorphous SiO2 could be converted into silicon with high crystallinity.The obtained Si/C composite electrodes exhibited a large specific capacity of 935.7 mAh/g at a current density of 100 mA/g.At the higher current density of 1 000 mA/g,there was a capacity of 520.7 mAh/g and 277.8 mAh/g even at a rate of 2 000 mA/g,demonstrating good rate performance.In additon,coulonbic efficiency of each cycle was above 95%for the Si/C composite electrode.Moreover,the uniquely small size and porous nature of the obtained Si/C complex gave it superior performance as the Li?ion battery anode.The small size,high porosity and interconnectedness of the nano?Si derived from reed leaves were the reasons to achieve such high performance,which reduced the lithium ion diffusion path and improved the penetration of the electrolyte.The N?doping carbon in silicon nanoparticles could enhance the electrical conductivity and ease the volume change of Si during the charging and discharging processes.The unique morphology was inherited by the natural silica nanoparticles in reed leaves and the successful preservation of the nanostructure throughout the high?temperature CO2 decarburization process.Thus,the simplicity,effectiveness,and scalability of the fabrication process made the reed leaf?derived Si/C composite anode promising for next generation Li?ion batteries.