Preparation Of Nitrogen-doped Graphene Based Composites And Lithium Storage Properties

In recent years,with the problems of energy and environmental getting worse,the rapid development of the electric vehicle market has been driven.Lithium-ion batteries are considered as energy storage devices with great development prospects due to numerious advantages such as high energy density and high power density,and long cycle life.However,as anode electrode material for commercial lithium-ion batteries,graphite has a low theoretical capacity of 372 mA h g-1,which greatly limits the realization of lithium-ion batteries for wider applications.In contrast,graphene,which is also a member of the carbon family,has a unique two-dimensional structure and excellent electrical conductivity.Therefore,it has quickly become one of the potential anode materials for lithium-ion batteries.In this paper,we choose graphene as raw material,finally prepared nitrogen-doped graphene-based composites by in-situ growth and hydrothermal treatments,and explore their electrochemical performance as anode materials in lithium-ion batteries.The specific research content is as follows:(1)The ZIF-8/GO composite was prepared by the induced effect of abundant oxygen-containing functional groups of graphene oxide surface,and finally the nitrogen-doped porous graphene nanosheets(known as N-PGNS for short)composite was obtained after one-step pyrolysis.After research,it is found that the composite material has ultra-thin 2D nanosheet structure,high nitrogen doping rate,rich hierarchical porous structure and a large specific surface area.Therefore the composite possess high electrical conductivity;rich pore structure;large specific surface;smaller transmission resistance and stable structure.The N-PGNS composite as anode material for lithium-ion batteries were performed.The results show that N-PGNS has a high reversible capacity.The reversible capacity remains at 467.5 mA h g-1 after 100 cycles at 0.5 A g-1.And N-PGNS possess superior cycle stability,the reversible capacity remains at 335.7 mA h g-1 after 1000 cycles at 5 A g-1,the capacity retention ratio is 90.4%.Furthermore,the N-PGNS possess high Coulomb efficiency and outstanding rate performance.The electrochemical performance of N-PGNS is obvious superior to N-PC.(2)Using PAM to functionalize the GO,the PAM-GO was obtained.Then,the FL-MoS2/N-G was prepared by hydrothermal treatment and pyrolysis.The special structure of FL-MoS2/N-G has many advantages:nitrogen-doped graphene as a conductive framework can improve the conductivity of electrode materials;the MoS2 coated by GO not only can prevent the agglomeration of MoS2,but also can enhance the stability and transmission of FL-MoS2/N-G;the flower-like MoS2 with a wide interlayer distance is beneficial for the rapid lithium ion and electron diffusion;the strong combination of MoS2 and nitrogen-doped graphene can avoid structural collapse during the cycling,overcome the originally poor cycle stability of MoS2.As a lithium-ion battery anode material,the results show that the FL-MoS2/N-G composite has a high reversible capacity.The reversible capacity remains at 1144.3 mA h g-1 after 100 cycles at 0.5 A g-1.And FL-MoS2/N-G possess superior cycle stability,the reversible capacity remains at 832.8 mA h g-1 after 900 cycles at 2 A g-1.In addition,the FL-MoS2/N-G possesses rate outstanding performance.(3)The mechanism of charge storage of FL-MoS2/N-G composites during the cyclic process was investigated,and the results showed that the surface capacitance control process is the main control process when FL-MoS2/N-G composites are used as the anode material of lithium ion battery.This result further proves that FL-MoS2/N-G composite material has a fast charge transfer rate when used as the anode material of lithium ion battery and is a promising electrode material.