Effect Of Air Oxidation On Structure Of Pitch Derived Carbons And Their Lithium/Sodium Storage Property

With the rapid development of new energy technology,the requirements for energy conversion and storage devices are increasingly deepened.Due to the limited spacing between carbon layers,traditional graphite materials cannot meet the needs of sodium ion battery cathode materials.As amorphous carbon,the disorder of hard carbon structure and larger interlamellar spacing for sodium ion storage to provide more active site and layer orientation,the particularity of the structure makes the hard carbon anode materials in lithium/sodium ion battery has attracted much attention in the research.Asphalt is the high quality precursor of carbon materials,petroleum asphalt and coal asphalt are the subsidiary products in the process of crude oil and coal processing,both of which have good chemical reactivity.Soft carbon sources are used to prepare hard carbon.The pretreatment process of asphalt is very important.Oxidation stabilization treatment affects the final carbonization behavior of asphalt by changing the primary structure of raw asphalt.Based on two different structure of asphalt as a raw material,through oxidative stabilization treatment and high temperature carbonization of hard carbon materials was prepared and studied different oxidation temperature(150~350 oC)on the influence of microstructure,composition of asphalt and the terminal temperature carbonization influence on hard carbon structure,composition,and compared the two kinds of bitumen in oxidative stabilization and carbonization stage structure evolution and the differences between the electrochemical storage sodium.The oxidation stabilization treatment introduced C=O oxygen-containing functional groups.With the gradual increase of temperature,the oxygen content gradually increased,among which the oxygen content of 350 oC oxidized petroleum asphalt(o-P-350)was 27.42%,and that of 350 ℃ oxidized coal asphalt(o-C-350)was 15.68%.The oxidation process reduces the microcrystalline size of the two kinds of bitumen.Higher oxidation temperature(t ≥ 250 oC)brought about by thermoplastic asphalt molecules in coking stage to the conversion of thermosetting,inhibition of asphalt in high temperature carbonization inherent tendency of graphitization,generates more defects.Compared with the direct carbonization material of petroleum asphalt(PDC-1400),petroleum asphalt oxidized at 350 oC and carbonized at 1400 oC(o-PDC-350-1400)increases the specific capacity from 99.7 m Ah/g to 276.8 m Ah/g at the current density of 100 m A/g.The first efficiency increased from 51.45% to 73.38%.Compared with coal asphalt material(CDC-1400)directly carbonized,coal asphalt oxidized at 350 oC and carbonized at 1400 oC(o-CDC-350-1400)increased specific capacity from 85.5 m Ah/g to 255.0 m Ah/g at 100 m A/g current density.First efficiency increased from 47.61% to 73.86%.After 200 cycles of 100 m A/g,the specific capacity of o-CDC-350-1400 is 141.0 m Ah/g,higher than that of o-PDC-350-1400(126.3 m Ah/g).To verify the adaptability of oxidation treatment to the structural construction of composite materials,through mechanical ball grinding mix oxidized asphalt and nanometer silicon,carbonization,silicon/carbon composite material was prepared(Si@C-P),silicon content was 19.89% in Si@C-P.At the current density of 100 m A/g,the specific capacity of the first charge of Si@C-P was 684.4 m Ah/g and the initial efficiency was 73.9%.At the high current density of 5 A/g,it still has a charging specific capacity of 306.0 m Ah/g.Compared with petroleum asphalt and nano-silicon carbonized materials(Si@C),the specific capacity was increased by 70.9%.Si@C has a capacity retention rate of 89.1%,after 100 cycles at a current density of 5 A/g.