| Nowadays,lithium ion batteries(LIBs)have been widely used.However its energy density is so low that unable to meet the growing needs of people,so the development of new anode materials is particularly critical.Lithium-oxygen(Li-O2)batteries have become a research hotspot due to its ultra-high theoretical specific energy density.But its high over-potential leads to low energy efficiency and poor cycle stability,which limits its practical application.Therefore,it is urgent to develop some efficient cathode catalysts.In this paper,three kinds of graphitic carbon nitride(g-C3N4)derived composites were prepared.Their composition and microstructure were analyzed by many characterization methods,and they were tested as cathode catalysts for Li-O2 batteries and anode materiales for LIBs.The specific research contents are as follows:(1)The thermal polymerization method was improved by divided into two steps to prepare g-C3N4 with larger specific surface area and higher porosity.Pd nanoparticles was obtained by reduction and loaded onto g-C3N4 to prepare Pd-CN composite,which was researched as cathode catalyst for Li-O2 battery.It was found that the Pd-CN2 composite exhibited best battery performance.It showed initial discharge specific capacity of 26614 mAh g-1 at the current density of 100 mA g-1.It also cycled 70 times at the current density of 100 mA g-1 and constant capacity of 1000 mAh g-1.g-C3N4 with large specific surface area and excellent pore structure was benefit to the infiltration of electrolyte as well as the transport of ions and electrons,and provided sufficient storage space for discharge products.In addition,Pd nanoparticles improved electrical conductivity and provided a large number of catalytic active sites,which resulted in the excellent electrocatalytic performance of Pd-CN composite.(2)The hierarchical structure was designed to solve the agglomeration of rGO layers by inserting g-C3N4 between.The improved two-step thermal polymerization method was used to prepare g-C3N4 to increase the specific surface area,and hydrothermal synthesis was used to reduce graphene oxide and combine two materials.The obtained CN-rGO composite was researched as the anode material for LIBs.The results showed that CN4-rGO-2 composite exhibited the best lithium storage performance.At the current density of 100 mA g-',the reversible capacity was 710 mAh g-1 after 100 cycles.When the current density was 1A g-1,the reversible capacity was 655 mAh g-1,and cycled stable for 500 turns.The large surface area provided by the hierarchical structure increased the storage space for Li+ and provided transport channels.The high nitrogen content brought by g-C3N4 provided abundant N active sites and the electrical conductivity of the composite was optimized by rGO.Therefore,CN-rGO composites showed excellent lithium storage performance(3)Using bulk-C3N4 as carbon and nitrogen source,a three-dimensional nitrogen doped carbon nanotubes with Ni nanoparticles coated composites(Ni@CNT-N)was prepared by impregnation of Ni ions and high temperature calcination.It was researched as anode materials for LIBs.At the current density of 100 mA g-1,the reversible capacity of Ni@CNT-N-750 composite was 705 mAh g-1 after 50 cycles However,under the continuous high current the reversibility and stability were poor due to the damage of the network structure.The three-dimensional network formed by carbon nanotubes provided abundant channels for infiltration of electrolyte as well as the transport of ions and electrons.The doped N elements provided Li+ store activity sites.Ni nanoparticles used as catalyst to promote the electrochemical reaction,it can not only improve the electrical conductivity of composites,but also play an important role to support structure in the process of charging and discharging,so that the lithium storage performance of composites was improved. |
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