Lithium Storage Properties Of Organics/Graphene Composites Fabricated By Mechanochemical Methods

The demand for energy in today’s society is increasing constantly,however,the massive application of fossil fuels has led to increasingly serious problems of environmental pollution.To effectively solve these problems,fossil energy should be gradually replaced by green energy.However,compared with traditional fossil fuels,the instability of green energy limits its large-scale application.Therefore,it is necessary to convert green energy into electrical energy and store it.As a novel energy storage device with high energy density,low self-discharge rate,long cycle life and environmental friendliness,lithium-ion batteries（LIBs）are widely used in portable electronic equipment,electric vehicles and other fields.However,conventional inorganic electrode has two major problems:low theoretical capacity and serious environmental pollution during the preparation process.In contrast,organic electrode with multi-electron reactions has the advantages of high theoretical capacity,controlled structure,low cost and environmental friendliness,which make it received widespread attention.However,the intrinsic poor conductivity of organic materials and the dissolution of organic small molecules limit the application of organic electrode.The electrical conductivity can be significantly improved by addition of graphene,and theπ-πinteraction between graphene and organic small molecules inhibits the dissolution of organic small molecules during the charging and discharging processes.In addition,the synthesis of traditional organic composites is generally based on hydrothermal and solvothermal reactions.The mechanochemical method can avoid large use of organic solvents and greatly shorten the reaction time,which is more in line with the concept of"green chemistry".Graphene prepared by mechanical ball-milling exfoliation method has the advantages of low cost,few defects and easy large-scale preparation.The main work of this paper includes the following three aspects:（1）A series of VG8@Gr composites were prepared by one-step ball milling method using graphite as raw material and carbonyl-rich organic small molecule-Vat Green 8（VG8）as intercalation agent.The exfoliation of graphite and the in-situ combination of VG8 and graphene were achieved by mechanical ball milling.Graphene with a thickness of about 4 layers and VG8 is uniformly loaded on the surface of graphene were achieved by adjusting the ball milling time and graphene content.Using VG8@Gr composites as the cathode of LIBs,the specific capacity was 100.3 m Ah g^-1 after 150 cycles at a current density of 0.1 A g^-1,which was significantly higher than that of the pure VG8 electrode(19.0 m Ah g^-1).That may due to the fact that the graphene formed by graphite exfoliation can improve the conductivity of the composites and inhibite the dissolution of organic small molecules.（2）Using graphite as raw material and cyclohexanehexone（C₆O₆）as intercalation agent,series of C₆O₆@Gr composites were prepared through mechanical ball milling and subsequent dehydration process.The electrochemical properties of C₆O₆@Gr composites were optimized by adjusting the ball milling speed and the graphene content.It was found that using C₆O₆@Gr as the cathode of the LIBs,the specific capacity was 227.2 m Ah g^-1 after 200 cycles at a current density of 50 m A g^-1.（3）Using graphite as raw material and terephthalaldehyde as intercalation agent,preparation of Schiff base@graphene（PSB@Gr）composites with nanoarray structure by mechanochemical polymerization with p-phenylenediamine.The formation of the array structure increases the specific surface area of composites electrode,which is beneficial to the exposure of electrochemistry active sites,the infiltration of electrolytes,the transport of electrons and the diffusion of ions.The electrochemical performance of PSB@Gr composites was optimized.The results show that the specific capacity is 712.6 m Ah g^-1 after 170 cycles at 100 m A g^-1.