Preparation And Sodium Storage Properties Of Petroleum Coke And Asphalt-based Soft And Hard Carbon Anode Materials

With the rapid development of electric vehicles and energy storage,lithium-ion batteries（LIBs）have been widely used.Followed by the shortage of lithium resources.In order to solve the crisis of lithium resource shortage in the future,it is increasingly important to develop new energy storage technologies.Compared with lithium,sodium has more abundant reserves,more uniform distribution,similar chemical properties,lower cost,and sodium ion batteries（SIBs）have the same working principle as LIBs.Therefore,SIBs are considered to be one of the ideal candidate batteries for LIBs.However,the development of SIBs anode materials is relatively lagging behind,which limits the large-scale commercial application of SIBs.Studies have shown that carbon-based materials are ideal anode materials for SIBs.Although graphite has been successfully applied to LIBs,a large number of studies have shown that it is not suitable for SIBs.Therefore,the development of new carbon-based anode materials is a problem that SIBs need to solve.In this thesis,a series of soft-hard carbon composites were prepared by using low-cost petroleum coke and asphalt-based as soft carbon precursors.The factors affecting the electrochemical properties of the prepared samples were investigated,which provided theoretical support and practical basis for the application of soft-hard carbon composites in the field of SIBs.The main research contents of this thesis are as follows:（1）Using petroleum coke as carbon source,a series of petroleum coke-based anode materials were prepared by acid washing and carbonization temperature regulation.The effect of carbonization temperature on the structure of petroleum coke-based anode materials was investigated,and its sodium storage mechanism was analyzed in SIBs.Furthermore,the PCGLU-800 prepared by combining the petroleum coke-based soft carbon with the hard carbon derived from glucose pyrolysis was used as the anode of SIBs.After 100 cycles at a current density of 25 m A g^-1,the capacity was maintained at 255.2 m Ah g^-1.Even after 1000cycles at 500 m A g^-1,it can still maintain 170.7 m Ah g^-1,which is much higher than the capacity of hard carbon and soft carbon.PCGLU-800 has excellent electrochemical performance,which is attributed to the fact that PCGLU-800 carbon surface has no large accumulation,moderate interlayer spacing and excellent conductivity of soft carbon,which accelerates electron transfer and improves Na⁺storage.（2）Asphalt-doped nitrogen-rich graphite g-C₃N₄ materials were prepared by carbonization and ball milling using asphalt-derived soft carbon as carbon source and melamine as nitrogen source.The physical characterization and electrochemical performance test of the prepared materials were carried out.It was found that the carbon material of NAP-0.5 had excellent electrochemical performance when used as the anode of SIBs.The capacity is 268.8 m Ah g^-1 after 100 cycles at a current density of 25 m A g^-1,and the capacity can still be maintained at 142.3 m Ah g^-1 after 1000 cycles at a high current density of 500 m A g^-1.This is because the nitrogen contained in NAP-0.5 can increase the defects on the surface of the material and increase the chemical reaction active sites;the developed pore size and moderate carbon layer spacing（～0.344 nm）are beneficial to the diffusion of electrolyte and the insertion and extraction of Na⁺during charge and discharge cycles,thus improving the electrochemical performance of NAP-0.5 electrode materials.（3）A series of soft-hard carbon composites were prepared by organic solvent dissolution,drying and carbonization using asphalt as soft carbon precursor and biomass-based pine pollen as hard carbon precursor.Through material characterization and electrochemical performance tests,it was found that when APHC-1000 was used as the anode material for SIBs,the capacity remained at 318.9 m Ah g^-1 after 100 cycles at a current density of 25 m A g^-1,which was much higher than that of soft carbon and hard carbon.The excellent electrochemical performance of APHC-1000 is attributed to the superior conductivity of soft carbon and the stable structure and high capacity of hard carbon.