Preparation Of Carbon Nanosheets And Their Application In Lithium Storage

The widespread application of lithium ion batteries?LIBs?have changed our lives dramatically,while there are increasingly strict requirements of battery performance from the emerging modern electric devices.However,graphite-based LIBs can't meet the requirement of various electric devices in terms of energy density due to its relative low theoretical specific capacity(372 mA h g^-1).In addition to excellent electricity conductivity and stability,carbon nanosheets also possess many advantages such as the open surface,high specific surface area,and abundant active sites,indicating the enormous potential in anode materials with high energy density.This thesis has developed hierarchically porous carbon nanosheets with both high graphitization degree and large specific surface area,as well as flower-like assembly of carbon nanosheets embedded with hollow Co₃O₄ nanospheres.The major research contents and results are presented as follows:Hierarchical porous carbon nanosheets were prepared via hydrothermal combined with carbonization-activation method with waste resin,FeCl3·6H2O and ZnCl2 as the starting materials.The as-prepared carbon nanosheets achieved the incorporation of high graphitization degree?Raman Spectra,ID/IG=0.48?and large surface area(2109 m2 g^-1).It was revealed that the catalytic activity of iron contributed to the high graphitization of the carbon nanosheets,while the activation effect of ZnCl2 played a significant role in enhancing surface area of the materials.Used as the anode material of LIBs,the porous carbon nanosheets maintained a high capacity of 1100 mA h g^-1 at 500 mA g^-1 after 150 cycles.Even cycled at a high current density of 2000 mA g^-1,the capacity of this materials still stabilized at about 400 mA h g^-1 after 300 cycles.This work successfully converted waste resin into high-performance carbon nanosheets,demonstrating a new pathway for the high value-added utilization of spent resins.In spite of a high theoretical specific capacity(890 m A h g^-1)as the anode material for LIBs,it remains a great challenge to achieve the practical application of Co₃O₄ due to its inferior mechanical stability and electricity conductivity.Herein,we synthesized a flower-like assembly consisting of carbon nanosheets decorated with hollow Co₃O₄ nanospheres.The as-synthesized assembly realized an ultrahigh loading mass?83 wt%?of Co₃O₄.Acting as the anode active material,this flower-like assembly maintained high specific capacities of about 750 mA h g^-1 at 500 mA g^-1 and 700 mA h g^-1 at 1000 mA g^-1 after 400 cycles.This outstanding electrochemical performance was attributed to the synergistic effect between the 0D hollow Co₃O₄ nanospheres,2D carbon nanosheets,and 3D porous structure.This work demonstrates that the incorporation of hierarchical structure possesses great potential for the synthesis of high-performance anode materials.