Research On The Construction Of Three-dimensional Graphene Composites Based On Template Method And Their Electrochemical Lithium Storage Performance

The three-dimensional?3D?graphene structure has been widely concerned by researchers due to its advantages of large specific surface area,low density,high mechanical strength and good electrical conductivity.Commercialized melamine sponges are inexpensive,rich in micro-network structure,and high nitrogen content.Therefore,several strategies have been used to construct 3D graphene and 3D graphene-based composite materials by assembly of graphene oxide using melamine as a template.These materials have been applied to lithium ion batteries?LIBs?and lithium sulfur batteries to obtain excellent electrochemical performance.1.The 3D nitrogen-doped carbon tube?NCT?@graphene composites have been synthesized by dipping-freeze-drying and heat treatment method using melamine sponges?MS?and graphene oxide?GO?as raw materials.The MS coated by GO via an assembly process was used as a carbon template and nitrogen source to prepare NCT through one-step pyrolysis.The 3D connected tubular network structure provides a shorter transmission path for ions and electrons.The well connection between NCT and reduced graphene oxide improves the electrical conductivity of the composite.The nitrogen doping of carbon tube provides more active sites and increases the lithium storage capacity of the material.As an anode electrode for LIBs,the initial discharge specific capacity was 1204.6 mAh g^-1,and it still had the reversible discharge specific capacity of526.9 mAh g^-11 after 300 cycles at the current density of 0.2 A g^-1.2.Using metal zinc as the source of zinc and MS@GO composites as the precursor,a 3D nitrogen-doped graphene microbelts?NGMB?@ZnO composites were prepared by one-step chemical vapor deposition.At high temperature,zinc atoms vapor captures the oxygen atoms in GO to simultaneously prepare the reduced graphene oxide?RGO?and generate ultra-small ZnO nanoparticles?NPs?on the surface of RGO.So that,the ZnO and graphene can be tightly combined to improve the stability of ZnO NPs.The 3D graphene structures can not only inhibit ZnO volume expansion but also improve the conductivity of ZnO NPs.The NGMB@ZnO has excellent electrochemical lithium storage performance.At the current density of 0.2 A g^-1,the initial discharge specific capacity is 986.6 mAh g^-1,and the reversible discharge specific capacity can reach 728.4mAh g^-11 after 250 cycles.3.A 3D nitrogen-doped graphene sponge?N-RGOS?was successfully prepared by a combination of hydrothermal method and heat treatment method using a commercial melamine sponge as a template for the assembly of graphene oxide and nitrogen source.A N-RGOS@S composite was prepared by combining it with elemental sulfur.As cathode for Li-S batteries,it has good cycle performance and rate performance.At 0.1 C current density,the first discharge specific capacity is 1023.4 mAh g^-1,the coulombic efficiency is about 99.7%,and after circulating 100 cycles,it still maintains 549.8 mAh g^-1reversible discharge specific capacity,when the current of the rate performance test reaches 2 C,still has a discharge specific capacity of 495.5 mAh g^-1.The rich network structure of the sponge assists graphene to form a three-dimensional network structure,which provides sufficient expansion volume for sulfur.Nitrogen-doped graphene has excellent electrical conductivity and enhanced ability to capture polysulfide,which is beneficial for improving the electrochemical properties of the composite.