Study On Preparation And Electrochemical Performance Of Xylem Fiber Carbon Embedded With Manganese Oxide Composite Material

Development of material materials has become the focus of contemporary research to building a resource-saving and environment-friendly society.xylem fiber widely present in biomass materials and has an abundant carbon source mainly consists of cellulose,hemicellulose and lignin.Pre-treatment of biomass materials to prepare xylem fiber carbon materials can eliminate the agglomeration phenomenon caused by direct pyrolysis of biomass,which were beneficial to the improvement of electrochemical performance.Therefore,xylem fiber carbon was constructed into a negative electrode material of lithium-ion battery with high specific surface area,plentiful pores and high conductivity were a good choice.However,xylem fiber carbon still faces various problems such as low energy density and low initial coulombic efficiency,which were difficult to meet market demand.Therefore,it is necessary to modify the xylem fiber carbon material to improve its electrochemical performance.Among them,manganese-based oxide doping not only can improve the conductivity of the carbon material,but also can increase the specific capacity of the carbon material.However,the manganese-based oxide was prone to volume expansion and fall off from the carbon material during repeated charging and discharging,which hinders the improvement of the electrochemical performance of the composite material after the manganese-based oxide embedded in the carbon material.Coating graphene with high conductivity and high ductility on the surface of the composite material forms a "sandwich"structure,which can alleviate the shedding and volume expansion effects of manganese-based oxides to improving the lithium storage performance.In this experiment,xylem fiber was used as the carbon source,MnO was grown in situ on the xylem fiber carbon material and coating with graphene(labeled as rGO after high temperature reduction)to prepared the composite anode material.The shape,morphology,structure and of the composite material was characterized by SEM,TEM,XRD,Raman,XPS and BET.The lithium storage performance was tested by an electrochemical workstation.The main research results are as follows:(1)Select bamboo,pine,paulownia and poplar wood as raw materials,and convert bamboo and wood into micron-sized xylem fibers through a simple delignification process in nitric acid,and then further convert these fibers into individual microtube xylem fiber carbon through pyrolysis.SEM and TEM results show that the four xylem fiber carbon materials retain the original morphology of xylem fiber carbon and have a hollow structure,show an amorphous carbon structure,and have a large interlayer distance(0.39-0.40 nm);BET results show that pine fiber carbon has the most abundant pore structure.(2)The initial discharge specific capacity of bamboo,pine,paulownia and poplar fiber carbon materials are similar(585.2-657.6 mA h g-1)at the current density is 50 mA g-1,and they all have excellent rate performance and stability cycle performance.When the pyrolysis temperature of the pine fiber carbon material is 800,1000,1200℃,the electrochemical performance shows that the initial coulombic efficiency of 1000℃ is the highest.(3)The pine carbon fiber with the most abundant pore structure as the research object,KMnO4 is the manganese source,MnO is grown in situ on the pine fiber carbon with a pyrolysis temperature of 1000℃ through hydrothermal reaction,SEM and TEM results show that MnO nanoparticles cover the surface of the pine fiber carbon anode material.Therefore,in this work we successfully prepared the PCF@MnO composite anode material.(4)When the mass ratio of the amount of MnO embedded to the pine carbon fiber is 2:1,the initial discharge specific capacity of the PCF@MnO composite anode material is 923 mAh g-1.The discharge specific display maximum capacity is 258 mAh g-1 at the current density is 2000 mA g-1,which has good rate performance.(5)Taking the preferred PCF@MnO composite material as the research object for further optimization,the graphene of different quality is coated on the composite material by hydrothermal method.SEM and TEM shows that the surface of the PCF@MnO composite material is wrapped with a layer of graphene,Therefore,the PCF@MnO@rGO composite anode material was prepared in this work.(6)Coating of rGO in the composite anode material can improves the electrochemical performance.When the mass ratio of the coating amount of graphene to PCF@MnO is 5%,the electrochemical performance of the PCF@MnO@rGO composite material is the best,the initial discharge specific capacity of the composite material is 1192 mAh g-1 at the current density of 50 mA g-1,the reversible specific capacity is 257.3 mA h g-1 of the composite material remains at the current density of 400 mA g-1 and has a high capacity retention rate after 400 cycles,the PCF@MnO@rGO composite material has a good cycle stability.Therefore,we give full play to the synergistic effect between xylem fiber carbon,MnO and graphene jointly promotes the improvement of the electrochemical performance for anode material in this work.