| In the field of portable electronic devices,Li-ion batteries have attracted widespread attention as the most promising new energy.Among them,the anode plays a decisive role in the electrochemical performance of the Li-ion battery.The low theoretical capacity?372m Ah/g?of the most common graphite anode has limited its application in the high energy density field.Therefore,it is urgent to develop a kind of high energy density anode for practical use.Graphene aerogel?GA?have become hot topic due to its good electron conductivity,large specific surface area and porous structure,while transition metal oxides?TMOs?own higher theoretical specific capacity.In this thesis,the advantages of GA and TMOs will be combined to prepare a GA-based composite electrode,so as to achieve a relatively high LIBs performance.The main research contents are listed as follows:?1?Firstly,nitrogen doped graphene?NG-X?was synthesized through a simple hydrothermal method with urea using as the nitrogen source.We investigated the influence of urea adding amounts on the morphology,structure and electrochemical performance of the obtained composite.Results showed that a reversible specific capacity of 780 m Ah/g was achieved in the NG-40 anode sample after 100 times of charge/discharge cycles under thea current density of 0.1 A/g under a current density of0.1 A/g after 100 times constant current charge and discharge cycle.The improved electrochemical performance could be attributed to the enhanced conductivity of graphene after doping with nitrogen,as well as the improved wettability between electrode and electrolyte.?2?On the basis of the research on the graphene anode,GA was constructed as the anode.At the same time,GA/Mn O2 nanocomposites were prepared by combining hydrothermal method and freeze-drying method.We also investigated the influence of KMn O4 adding amounts and p H value on the morphology,structure and electrochemical performance of the obtained composite.The results showed that when the p H value was 2 and the addition amount of KMn O4 were 160mg,Lithium storage performance of the anode reached the maximum value,leading to reversible specific capacities of 1701.9m Ah/g?at low current density?and 210.5 m Ah/g?at high current density?,respectively.In addition,according to the CV curves test under different sweep speeds,it can be found that the larger specific surface area of the GA/?-Mn O2composite contributes more capacitive capacity,and can be calculated to be approximately 76.56%through formulation.That it to say,the optimization of experimental parameters is conducive to obtain the best electrochemical performance of the GA/?-Mn O2 anodes.?3?GA/Sn O2 nanocomposites were prepared by one-step hydrothermal method.We also investigated the influence of Sn Cl4·5H2O adding amounts on the morphology,structure and electrochemical performance of the obtained composite.Results showed that the maximum reversible specific capacity of 1144.9 m Ah/g was achieved after 33charges/discharge cycles and under a current density of 0.1 A/g.The reversible specific capacity of GA/Sn O2-150 was much higher than the samples with other components.The enhanced performance is mainly attributed to a fact that GA could provide a large specific surface area to enhance the electrical conductivity of Sn O2,leading to more rapid ion and electron transfer in the composite anodes.Besides,the doping of GA could also alleviate the volume changes of Sn O2 during the charge/discharge cycling processes.There are 48 figures,4 tables and 119 references in this thesis. |
PDF Full Text Request