Construction Of Nitrogen And Phosphorus Co-doped Carbon Based Nanocomposites As High-Performance Anode Materials For Lithiumion Batteries

When the contradiction between the decrease of fossil energy and the increase of people's energy demand becomes prominent increasingly,it is very important to develop new green energy.In recent years,with the rise of lithium-ion battery industry,its anode materials have also been vigorously developed.The low theoretical specific capacity of graphite,a traditional anode material,has been unable to meet the application of lithium-ion batteries in the fields of kinetic energy vehicles and large-scale energy storage.Therefore,it has become a research hotspot to search for anode materials with high capacity and excellent cycle performance.In this paper,the construction and electrochemical properties of nitrogen and phosphorus co-doped carbon based nanocomposites as high-performance anode materials for lithium-ion batteries are studied.The research contents and results are as follows:?1?Study on nitrogen-phosphorus co-doped carbon-coated molybdenum oxycarbide composites.The nitrogen-doped carbon-coated molybdenum oxycarbide composites with one-dimensional nanofiber structure were synthesized by using ethylenediamine,pyridine and aniline as nitrogen and carbon sources respectively,with ammonium paramolybdate calcined at high temperature.And phosphorus doping of composite materials with sodium hypophosphite as phosphorus source.The effects of different types of nitrogen and phosphorus doping on the morphology,structure and electrochemical properties of the composites were studied.The experimental results show that the structural stability of aniline composites is better,and the complete one-dimensional nanofiber structure provides an excellent channel for ion and electron transport.Phosphorus-doped composites have better cycle properties,especially for improving the cyclic stability of electrode materials.Comparing comprehensively,nitrogen-phosphorus co-doped carbon-coated molybdenum oxycarbide?MoOC/N,P-C?composites prepared from aniline have more stable structure and excellent electrochemical properties.When the current density is200 mA g^-1,the first charge/discharge specific capacity of the material is 659.7/855.3 mA h g^-1,and the first Coulombic efficiency is 77.1%.After 800 cycles at high current 1 A,its specific capacity is still 566.9 mA h g^-1,showing excellent lithium storage performance.?2?Study on nitrogen-phosphorus co-doped carbon-coated cobalt phosphide composites.Nitrogen-phosphorus co-doped carbon-coated cobalt phosphide?CoP/N,P-C?particles with core-shell structure were synthesized by in-situ carbonization using a metal-organic framework as template by solvothermal method.The structure of one-dimensional nanofibers was maintained steadily by using glucose as an auxiliary carbon source.The experimental results show that the cyclic stability and capacity of glucose-assisted nitrogen-phosphorus co-doped carbon-coated cobalt phosphide?G-CoP/N,P-C?electrode materials are improved effectively after adding glucose.One-dimensional nanofibers can not only shorten the ion diffusion path in order to improve the ion diffusion kinetics and increase the conductivity in the direction of electron and ion transmission,but also alleviate the structural changes of active materials effectively during charging and discharging,which improves the electrochemical stability.In addition,this method can also prepare other transition metals phosphides such as Fe,Ni,etc.It is a green,efficient and general synthesis method.?3?Study on nitrogen-phosphorus co-doped graphene-loaded cobalt phosphide composites?CoP/N,P-RGO?.CoP/N,P-RGO composites were synthesized by hydrothermal-freeze drying method using graphene as carbon material with high specific surface area,excellent electronic conductivity,good chemical stability,high mechanical strength and flexibility.The experimental results show that the cycle performance of CoP/N,P-RGO under high current is better than that under low current.At current density of 1 A g^-1,the first discharge capacity of CoP/N,P-RGO is1642.7 mA h g^-1,and the coulombic efficiency is 74.9%.After 700 cycles,the discharge capacity is 589.7 mA h g^-1 and the coulombic efficiency is 99.6%.The cyclic stability of CoP/N,demonstrating excellent cyclic performance.