Preparation And Properties Of Ultra-regular Graphite/graphene Anode Materials

As energy shortages and environmental problems become more prominent,countries around the world begin to develop a series of new energy sources,including wind energy,solar energy,and tidal energy.And these new energy sources need conversion systems to convert into stable energy sources and store them.Lithium-ion batteries are used as the storage and output links for these new energy sources,and have been widely studied because of their series of advantages.Among them,the anode material is an important component that determines the performance of lithium ion batteries.Graphite is one of the widely used anode materials,it has the advantages of mass production in industrial production and low cost.However,graphite as a negative electrode material for lithium ion batteries will still have some defects,such as the formation of SEI film during charging and discharging,which consumes some lithium ions and causes capacity loss.The actual specific capacity is lower than the theoretical value,which cannot meet human needs for lithium ion batteries with high energy density.In terms of aspect,the interlayer distance of graphite is 0.34 nm,which is smaller than the interlayer distance of lithium-graphite compound 0.37 nm,so during repeated deintercalation of lithium ions,graphite layer peeling may occur,thereby reducing the service life of the battery.Because graphite has the above shortcomings,its performance is optimized to meet the actual application requirements.The laboratory prepared large flake graphite with a purity of 99.9%.Compared with commercially available graphite,its crystal structure is regular and its defects are low.It is suitable for battery active electrode materials.On this basis,the modification of large flake graphite,the main research contents are as follows:1.Large scale flake graphite is oxidized to obtain expandable graphite with increased lamellar distance,and then use ultrasonic supercritical fluid method to insert supercritical CO2 molecules into the expandable graphite.When the pressure is released,using a strong impact to open the graphite sheet layer structure to obtain fewer layers of graphite and graphene sheet molecules,that is,to prepare super-regular graphite/graphene composite materials(sr-GG),and then characterize the morphology of the composite materials by SEM and TEM.Characterize the crystal structure of the composite by XRD,XPS and FTIR.Raman,AFM are also used to characterize the graphene in the composite.2.At the same time,when the sr-GG composite material is applied to the negative electrode material of a lithium-ion battery,the reversible specific capacity is 537.1 mAh·g-1 and the coulomb efficiency is 99.5%when it is cycled to 500 cycles at a current density of 100 mA·g-1.During the magnification performance test,first circulate 340 cycles,and then at 100 mA·g-1 current density,the average reversible specific capacity is 536.51 mAh·g-1,when the current density returns to 100 mA·g-1 again,the average reversible specific capacity is 531.71 mAh·g-1.Compared with the previous period,the reversible specific capacity does not change much,indicating that the prepared sr-GG has better cycle performance and rate performance.Compared to using graphite alone as lithium,even if the negative electrode material of the ion battery is compared with the theoretical specific capacity of 372 mAh·g-1,the specific charge and discharge capacity is still increased by 159.71 mAh·g-1.3.Doping modification and performance testing of graphite/graphene composite materials.Add conductive carbon black Super-P to sr-GG to prepare graphite/graphene/Super-P composite material(sr-GG/S).The sheet-shaped sr-GG and the granular Super-P achieve the face-to-point contact effect,reduce the contact resistance inside the battery,and improve the reversible specific capacity of the composite material.The morphology of sr-GG/S was characterized by FE-SEM,and the structure of the composite material after doping with Super-P was analyzed by XRD.At the same time,the effect of the amount of Super-P added on sr-GG was studied.The experimental results show that when the amount of Super-P added is 10%,the reversible specific capacity of sr-GG is most significant.Under the condition of current density of 100 mA·g-1,the reversible specific capacity is 752.41 mAh·g-1 after 500 cycles,which is increased by 215.31 mAh.g-1 compared with that before unmodification.The results prove that Super-P doping can effectively improve the electrochemical performance of the composite.