Synthesis And Sodium Storage Performance Of Three-dimensional Graphene-based Carbon Materials

Sodium ion batteries?SIBs?,owning to natural abundance,wide distribution and low cost of sodium and especially similar chemical properties with lithium,are regarded as a promising candidate to LIBs.However,the ionic radius of sodium is larger than that of lithium,leading to the sluggish kinetic process of sodium storage for the materials,which results in lower capability.Therefore,finding suitable electrodes are the key to the development of SIBs.Carbon materials,common and stable electrode material with diversity of structure and species,and stable physical and chemical properties,are widely used as anodes of sodium ion battery.However,the rapid charging and discharging ability of carbon materials is poor and the problem is urgent to be solved.The kinetics of adsorption energy storage on the surface of carbon materials is fast and the fast surface electrochemical reactions can be carried out,rapidly storing energy,which is an effective way to improve the fast charging/discharging capacity of carbon materials.In this work,we take highly conductive graphene as the main object,and constructe the three-dimensional?3D?framwork structure,compound with carbon materials with more active sites and create pores in the graphene sheets to increase the active sodium storage sites,enhancing the fast charging/discharging capacity of graphene according to the weakness of two-dimensional graphene.And some structural characterization,such as XRD,Raman,BET,FTIR,TG-MS tests,and electrochemical tests were carried out to investigate the mechanism and contribution of functional groups and defects to the sodium storage.The conclusions are as follows:?1?The 3D graphene-based composites were successfully prepared through a hydrothermal self-assembly process.When the mass ratio of graphite crystals and oxide graphene was 1:1,the obtained samples expressed a 3D network structure and obtained optimal electrochemical performance.It is well proved that the 3D graphene framework can not only guarantee the excellent conductivity but also supply the fast transmission channels for Na⁺,accelerating the fast energy storage of ions.Furthermore,the 3D-CGC/G1 exhibits good rate performance.At 50 mA g^-1,it still obtained specific capacity of 254 mA h g^-1through 350 rate cycles,manifesting the structural stability of materials and the enhancement of sodium storage capacity for materials by the introduction of oxygen functional groups and defects sites.At a large sweep rate of 2.0 mV s^-1,the energy storage contribution of 3D-CGC/G1 can reach to 83.5%,indicating that the introduction of oxygen functional groups and defect sites made a great contribution to the rapid energy storage on the surface of the material.?2?The 3D porous graphene with different pore sizes were successfully synthesized with metal etching method.The results shows that the average pore sizes of Co-PG,Ni-PG,Fe-PG samples are 22 nm,35 nm,42 nm,respectively.And the specific surface area of porous graphene are larger than graphene,where Ni-PG sample shows the maximum specific surface area and the optimal electrochemical performance at large current density,indicating that the creation of pores and introduction of defect site on the graphene sheet can increase sodium storage capacity and enhance the rapid reaction on surface of materials.Furthermore,the regulation of pores improves the diffusion ability of materials,and Ni-PG samples have the fastest ion diffusion rate of 8.80×10^-9 cm² s^-1,suggesting that the creation of pores can shorten the transmission distance of Na⁺and accelerate the transmission of Na⁺across the plane region.