Preparation And Electrochemical Properties Of Doped Biomass Carbon Materials

With the development of industry and increasingly serious environmental problems,energy supply and environmental protection have increasingly become the focus of researchers.Lithium-sulfur batteries have attracted more attention due to their high energy density,and the sulfur is rich-reserved in the earth’s crust,non-toxic and environmentally friendly,which has attracted extensive attention and intensive research by researchers.Many biomass materials presented in nature can be efficiently converted into porous carbon materials.Biomass carbon materials and sulfur constitute a lithium-sulfur battery cathode composite,which also exhibits good electrochemical performance.Therefore,porous carbon materials prepared from different biomass precursors and were modified to prepare modified biomass porous carbon materials improving their electrochemical performance and cycle stability.Firstly,with flowers tea and oatmeal as biomass precursor materials,a series of biomass porous carbon materials were prepared by high temperature activated carbonization.It can be obtained by SEM and TEM that the MLPC-4 material has a structure in which a three-stage pore is nested and a graphene-like thin layer is formed.The MLPC-4/S composite cathode material has a first discharge specific capacity of up to 1554 mA-h/g,After 100 cycles,the capacity is 521 mA·h/g,while the capacity is 349 mA·h/g after 500 cycles,and the Coulomb efficiency is stable at around 85%.MLPC-4 material not only provides a good conductive network,but also has a graphene-like thin layer fold structure which can be a good carrier of sulfur,increasing the electrochemical reaction contact area,improving the effective utilization of sulfur.Secondly,nitrogen-doped biomass porous carbon material(N-PC)was prepared by doping modification of biomass porous carbon material by post-treatment method using CON2H4 as nitrogen source.The XPS results show that the nitrogen content of the 2N-PC material is 3.23 at%,and the doping form of the nitrogen atom is mainly presented as "pyridinic N " and"pyrrolic N".From the Raman test,the ID/IG value of 2N-PC was increased by 0.004 compared with PC,indicating that the degree of defects of 2N-PC material increased,which provided more reactive sites.The capacity of the first discharge ratio of the composites is 1065 mA·h/g,the capacity retention rate is about 40%after 100 cycles,and the cycle performance is good.In addition,the CV curve indicates that the nitrogen atom doping does not affect the battery charging and discharging platform.Finally,oxygen-doped biomass porous carbon material(O-PC)series materials were successfully synthesized by impregnation and acidification of biomass porous carbon with solution of nitric acid as oxygen source by solution impregnation method.The oxygen content of the 80-PC material is 10.86 at%,and the O atom is mainly classified into three forms of"C=O","C-OH" and "C-O-C".The composite material has superior electrochemical performance,in which the first discharge specific capacity can reach 1506 mA·h/g,and the capacity after 100 cycles is 470 mA·h/g,which may be the doping of oxygen atoms into the carbon material.The oxygen-containing functional group enhances the structural stability of the carbon material,and has a certain chemisorption effect on the reaction intermediate of the lithium-sulfur battery.After charging and discharging at 0.1-1 C different rate,the discharge specific capacity is 600 mA·h/g when the magnification is 0.1 C.This may be due to the presence of oxygen-containing functional groups,which increases the mechanical strength of the material and can withstand large-rate charge and discharge tests.