Study On Fabrication And Potassium Storage Performance Of Fulvic Acid-based Carbon

Clean energy(wind energy,tidal energy,solar energy,etc.)has the problem of uneven distribution with time and space when replacing fossil energy,so energy storage and conversion play a crucial role in new energy promotion.Although lithium-ion batteries are widely used in commercial applications due to their low volume density and high energy density,the lack and uneven distribution of lithium resources lead to the problem of sustainability and cost,which limits the further development of lithium-ion batteries.Therefore,it is necessary to develop low-cost and superior performance energy storage devices to replace lithium-ion batteries.Because potassium and lithium are in the same primary group,they have similar chemical properties,and potassium has high reserves in the earth’s crust and low price,so potassium-ion battery is considered as a substitute for lithium-ion battery in the field of large-scale energy storage.The design and preparation of anode materials has become an important research direction to improve the performance of potassium-ion batteries.Non-graphite carbon materials are considered to the key material to promote the development of potassium-ion batteries because of their larger layer spacing,more pores and defects.However,there are still some problems restricting the development,such as volume expansion,low potassium-ion diffusion kinetics,low energy density and poor cycle stability.Based on this,a series of work has been carried out in the present thesis on the structure design and performance optimization of non-graphite carbon materials.The obtained results are as follows:Fulvic acid-based hard carbon materials were prepared by catalytic graphitization method using biochemical fulvic acid as hard carbon precursor.By comparing the samples prepared under different conditions(temperature,catalyst content),the effects of calcination temperature and catalyst addition on the morphology and potassium storage performance of the materials were investigated.It can be found that the effect of temperature is not obvious when the temperature reached 1000 ~oC,which can make the material graphitize.With the increase of catalyst content,the samples show better specific capacity and capacity retention.The maximum potassium storage capacity of the obtained hard carbon material is 402.3 m Ah g-1.After 500 cycles at a high current density of 1 A g-1,the capacity can reach 94.6 m Ah g-1,and the capacity retention rate is 67.5%,showing good rate and cycling performance.In order to further improve the electrochemical performance of the materials,fulvic acid-petroleum asphalt-based materials were prepared by soft and hard composite method combined with molten-salt template method.The obtained materials have the characteristics of large specific surface area,large interlayer spacing,rich pores and defeats,which not only alleviates the volume expansion to a certain extent,but also increases the potassium-ion transport kinetics and the potassium storage active sites,and improves the potassium storage performance of the materials.The obtained material show a specific capacity of 400.4 m Ah g-1.Even at a current density of 1A g-1 for 1000 cycles,the capacity remains at 128.4 m Ah g-1,and the capacity retention rate is 78%,which greatly improves the cycle stability.This work has already provided experimental data and theoretical analysis for the development of new anode materials for potassium-ion batteries.