The Synthesis Of Graphene/Oxide Composites And Application Mechanism In Cathode Materials Of Lithium Ion Battery

Lithium ion battery has a variety of applications due to its high energy density,no memory effect,high voltage,large capacity,long cycle life and other advantages.It can not only be used in portable electronic devices,but also be promising in electric vehicle and energy storage devices.In order to further improve the energy density and cycle life of lithium ion batteries,we need to further develop new anode materials.Graphene,a new two-dimensional nano-carbon material,have excellent electrical and mechanical properties,high surface area and chemical stability,so are promising in the applications of Lithium ion battery.Recently,constructed metal oxide with graphene to build composite structure,has been demonstrated as an efficient way to improve its electrochemical performances.Exploring effective preparation method to realize the efficient combination of graphene with other functional components is the key as well as the hotspot and difficult for the research of graphene composites.The loading of active electrode materials on graphene surface would effectively improve the conductivity of electrode materials,significantly enhance the rate capability,and improve the stability of electrode structure.The specific research works are as follows:?1?Buliding the strong interface between graphene and metal oxide in the 3D graphene composite structure.Fe₃O₄/GHs composites with different additive were synthesized by using hydrothermal method.The discharge capacity of Graphene/ Fe₃O₄ reach up to 1000 mAh g-1 after 300 cycles at 1C.The result endow that anionic surfactant with more functional group and short carbon chain can ensure larger contact area between material and electrolyte,shorter diffusion path for lithium ions transportation in the active material and larger buffering space for volume change during charging/discharging process.?2?The unique open structure at both ends and interlayer galleries that can be easily intercalated and adjusted,which effectively limits the volume expansion of Fe₃O₄ nanoparticles during the cycling process and shows great potential applications in energy storage.The discharge capacity of Fe₃O₄@GNS achieve 1620 mAh g-1 in the second cycle at 0.1 C and can remain 810 mAh g-1 after 100 cycles.For the NiO and Co₃O₄,the composites Co₃O₄@GNS and NiO@GNS can respectively remain 620 mAh g-1 and 800 mAh g-1 at current rate of 0.1C for 100 cycles.In the process of preparation of MO@GNS composite materials,the effect of the surfactant on morphology and electrochemical properties was studied in deatil.The use of additive with negetive charge in the aqueous solution enables better dispersion of MO particles and the functional groups allow each MO particle to be wrapped closer to GNSs and construct the strong interfacial interaction between MO particles and GNSs.Duing to its superior structure,the Fe₃O₄@GNS?SC?nanocomposite achieved a discharge capacity of 1800 mAh g-1 in the 10 st cycle,which is close to the twice of the theoretical capacity?924 mAh g-1?.The composite also displayed stable cycling behavior up to 550 cycles that the electrode can maintain its initial capacity of 1082 mAh g-1 at 1C.In order to prove this method for construct the strong interfacial interaction to improve the electrochemical performance of the MO@GNS composite,the Co₃O₄@GNS?SC?and NiO@GNS?SC?composite were also prepared,respectively.The results show that the performance was improved by adding SC during the Co₃O₄ and NiO composites preparation process.For the NiO and Co₃O₄,the composite display the same regulation and the discharge capacity of Co₃O₄@GNS?SC?and NiO@GNS?SC?can respectively remain 980 mAh g-1 and 1020 mAh g-1 which are better than composite without additive after 100 cycles.The results presented here may pave a way for obtaning new graphene based material for electrochemical energy storage applications.