Synthesis And Sodium Ion Storage Of Metallocene Derived Graphitic Carbon Nanomaterials

At present,sodium ion batteries are considered to be the most potential energy storage equipment for lithium-ion batteries due to their abundant resources,low cost and high safety.However,the selection and rational design of electrode materials are the key to the large-scale application of sodium-ion batteries.At present,hard carbon is the most widely studied in sodium-ion batteries anode materials due to its larger carbon layer spacing and abundant active sites.However,hard carbon faces disadvantages such as poor conductivity,structural instability and low density,which largely limits its high rate performance,long cycle stability and volumetric energy density.Compared with hard carbon materials,graphite has higher conductivity,but due to the smaller interlayer spacing of graphite(0.3354 nm)and larger sheet size,it is difficult to match the larger radius of sodium ions.Based on the issues above,this work focuses on the design of graphitic carbon nanomaterials,and investigates their morphology and formation mechanism through a series of characterization methods,revealing the relationship between structural composition and electrochemical properties.It provides guiding significance for further designing carbon anode materials with novel structure and excellent sodium storage performance.(1)Quadrilateral carbon nanotubes with one end opening were prepared by an in situ pyrolysis using 1,2,4,5-tetramethylbenzene and ferrocene as raw materials.Quadrilateral carbon nanotubes consist of four walls that are perpendicular to each other,unlike conventional multi-wall nanotubes.Each wall has a herringbone-like graphene structure with the size of only 80 nm and an average length of ca.5 ?m.As anode materials for sodium-ion batteries,quadrilateral carbon nanotubes exhibit excellent electrochemical performance and low dependence on electrolytes.At a current density of 0.1 A g-1,the first reversible specific capacities in the ether-and ester-based electrolytes were 212 and 200 mAh g-1,respectively.In the ether-based electrolyte,the reversible specific capacity of 132 mAh g-1 can be maintained even at a current density of up to 5 A g-1.The excellent electrochemical performance of quadrilateral carbon nanotubes in two electrolytes is mainly related to its small graphitic size and herringbone-like graphitic walls structure:it can greatly shorten the diffusion paths of sodium ions and effectively improve the diffusion kinetics of sodium storage.(2)Carbon microspheres with a particle size of about 4.0 ?m were prepared by an in situ pyrolysis using mannocene as raw material.The carbon microsphere is a micro/nano structure assembled from nano-onion-like particles,which not only can effectively alleviate the volume change during sodium storage,but also shorten the diffusion paths of sodium ions,and the pressing density is 1.36 g cm-3.As anode materials for sodium-ion batteries,the first reversible gravimetric and volumetric specific capacity at 0.1 A g-1 can reach 275 mAh g-1 and 374 mAh cm-3,respectively.Even at 1,2 and 5 A g-1,the gravimetric specific capacities can be maintained at 195,165 and 115 mAh g-1,and the volumetric specific capacities can reach 265,224 and 156 mAh cm-3.