Synthesis Of Graphene Based Composites And Their Applications In Lithium Rechargeable Batteries

In recent years, more and more researches are focused on the synthesis of graphene composites. Graphene composites can meet the requirement of high efficiency on energy transferring in energy storage materials. Graphene composites can effectively improve the electrochemical performance of Lithium rechargeable batteries, thus show more attractive prospects. A series of graphene composites including metal compound/graphene and sulfur/graphene are synthesized by hydrothermal method and studied in this paper. Crystal structure, morphology, specific surface area and electrochemical performance in lithium rechargeable batteries of these composites are characterized and analyzed by SEM, TEM, XRD, BET and battery tests. The main contents of the paper are presented as follows:1. ZnO/graphene (ZnO/GN) composite is successfully synthesized using graphene oxide as precursor by a one-step hydrothermal method. The ZnO/GN composite shows good electrochemical performance when using as anode in lithium ion batteries. ZnO/GN exhibits an irreversible discharge capacity of 849 mAh g-1 at 0.2 A g-1 after the formation of SEI film. After 100 cycles, the ZnO/GN electrode still has a discharge capacity of 547 mAh g-1. The rate of capacity increased is 35.4% when compare with pure ZnO electrode.2. MoS2/graphene (MoS2/GN) composite is successfully synthesized using graphene oxide as precursor by a one-step hydrothermal method. The MoS2/GN composite shows good electrochemical performance when using as anode in lithium ion batteries. MoS2/GN exhibits an irreversible discharge capacity of 1260 mAh g-1 at 0.1 A g-1 after the formation of SEI film. After 80 cycles, the MoS2/GN electrode still has a discharge capacity of 970 mAh g-1. The rate of capacity increased is 83.7% when compare with pure MoS2 electrode.3. A novel sulfur/graphene/carbon nanotube (S/GN/CNT) aero-gel composite is successfully prepared by a facile hydrothermal co-assembling route. When used as cathode for lithium sulfur battery, the S/GN/CNT composite can be pressed directly onto nickel foam without binder and conductive additive, thereby simplifying the manufacturing process. S/GN/CNT exhibits an irreversible prime discharge capacity of 1070 mAh g-1 at 0.2 C. After 100 cycles, the S/GN/CNT electrode still has a discharge capacity of 759 mAh g-1. The rate of capacity increased is 94.6% when compare with S/GN aero-gel composite.4. Graphene/MnO2/sulfur (GN/MnO2/S) composite is successfully synthesized using graphene oxide as precursor through hydrothermal method followed by infusion and heat treatment. S and MnO2 nanoparticles are homogeneously distributed over the conductive matrix of graphene sheets. When using as cathode in lithium sulfur batteries, the GN/MnO2/S composite shows good electrochemical performance. GN/MnO2/S exhibits an irreversible prime discharge capacity of 1116 mAh g-1 at 0.2 C. After 100 cycles, the GN/MnO2/S electrode still has a discharge capacity of 825 mAh g-1. The rates of capacity increased are 24.5%,47.1% and 931.3% when compare with GN/S, MnO2/S and pure S electrodes, respectively.5. A novel self-assembled LiFePO4/graphene (LiFePO4/GN) composite is successfully prepared through a facile template-free hydrothermal approach followed by sintering. The aqueous rechargeable lithium batteries are developed by using LiFePO4/GN as cathode, zinc as anode and the solution of LiCH3COO and Zn(CH3COO)2 as electrolyte. The LiFePO4/GN composite shows good electrochemical performance in aqueous rechargeable lithium batteries. It exhibits an irreversible discharge capacity of 81 mAh g-1 at 5 C. After 400 cycles, the GN/MnO2/S electrode still has a discharge capacity of 63 mAh g-1.The rate of capacity increased is 57.5% when compare with pure LiFePO4 electrode.