Preparation Of Nitrogen-doped Porous Graphene Aerogel Materials And Its Electrochemical Performance Study

The development of wearable and portable electronic devices as well as new energy vehicles has greatly stimulated the development of electrochemical devices.Especially in the booming field of new energy vehicles,longer mileage,higher charge efficiency,and durable service life require an electrochemical device with better storage and conversion efficiency.Given that electrode materials are the key link of energy storage devices,the design of novel and superior electrode materials has always been of interest to researchers.The stacking of pristine graphene sheets severely weakens its excellent characteristics of good electrical conductivity,chemical and thermal stability as well as ultra-high theoretical surface area,which greatly affects its researches and applications.In this paper,hydrothermal method was used to integrate graphene oxide into a three-dimensional holey graphene aerogel,and the heteroatom is uniformly introduced into the graphene sheet layer by using water-soluble reagents to improve the electrochemical performance.1.Nitrogen-doped graphene hydrogel was prepared by hydrothermal method using formamide solution as nitrogen-doping reagent,and then aerogels(NGAs)were obtained by carbonization after freeze-drying.The volume ratio of the formamide to GO aqueous solution was changed to obtain aerogels with different nitrogen level and pore structure.Using NGAs as the active material to assemble a lithium-ion negative half-cell and explore its performance by various means.Analyses show that NGAs-2 has a higher specific capacity(the initial discharge specific capacity reached to 1653.5 mAh g-1 at 0.1 A g'1 and its reversible specific capacity could still retain 534.8 mAh g-1 even after 100 cycles),outstanding rate performance(144.4 mAh g-1 at 5.0 A g-1)and excellent cycling performance(114.0%capacity retention at 5.0 A g-1 even after 5,000 cycles).In order to study the performance of its water-based capacitors,NGAs were used as electrode materials for symmetrical supercapacitors.Analysis shows that NGAs-1 has a higher specific capacity(239.8 F g-1 at 0.1 A g-1).In addition,NGAs-1 has a superior rate performance(the specific capacity is still 90.0F g-1 at 10.0 A g-1)and a longer cycle life(the capacity retention at 10.0 A g-1 after 5,000 cycles is 83.7%).2.Using ammonium fluoroborate as a dopant,ternary-doped graphene hydrogels of nitrogen,fluorine and boron were prepared by hydrothermal method,and aerogels(TGAs)were prepared by carbonization after freeze-drying.The mass ratio of ammonium fluoroborate to graphene oxide was adjusted to obtain materials with different doping types,doping level,and pore structure.Using TGAs as the active material to assemble a lithium-ion negative half-cell and explore its performance by various means.The experimental results show that TGAs-15 exhibits a higher initial specific capacity(1100.0 mAh g-1 at 0.1 A g-1)and retained 511.7 mAh g-1 after 200 cycles.The rate test shows that the specific capacity is still 200.0 mAh g-1 at 5.0 A g-1.Cycling tests show that its specific capacity increases continuously.After 3000 cycles at 5.0 A g-1,it reaches to 419.8 mAh g-1,which is an increase of 218.0%compared to the initial capacity.