Structure Control And Electrochemical Performance Of TiO₂/Graphene Aerogels

As the unique two-dimensional structure, graphene possesses many superior physical and chemical properties, such as excellent electrical conductivity and a large specific surface area. All of these characteristics justifies graphene as a potential anode material for lithium-ion batteries. But a lot of research have shown that when single graphene acted as the anode material of lithium-ion batteries, it contained some shortcomings such as low cycle efficiency and poor circulation stability. So graphene aerogels were prepared by hydrothermal method to enhance the diffusion of lithium ions or improve electons migrating rate through graphene sheet. In addition, TiO2/graphene aerogels nanocomposite were prepared to enhanced lithium-ion insertion/extraction by using the high theoretical capacity of TiO2. The innovation of these work was that ultradispersed TiO2 single nanocrystals were prepared via a one-step hydrothermal process which can be in-situ loading onto the graphene sheet with nanoparticle size ranging from 4-10 nm. The main work were like this:1) The influence of preparation conditions towards structure and electrochemical performance of graphene aerogels was discussed; 2) The structural characteristics and electrochemical performance of TiO2/graphene aerogels under different preparation conditions were analysised,which were prepared by one-step hydrothermal method. The major conclusions are summarized as follows.(1) The surface area, pore volume and average pore size of graphene aerogels were 128 m2/g,0.545 cm3/g,3 nm, when the concentration of oxide graphene was 2 mg/ml, hydrothermal temperature was 180℃, hydrothermal reaction time was 12 h.(2) The surface area, pore volume and average pore size of graphene aerogels were 188 m2/g,0.381 cm3/g,4 nm, when the concentration of oxide grapheme was 2 mg/ml, titanyl sulfate was 120 mg, urea was 60 mg, hydrothermal temperature was 180℃ and the reaction time was 12 h. The size of ultradispersed TiO2 nanoparticles ranged from 4 to 10 nm, which was distributed equally on the surface of grapheme sheet.(3) When the TiO2/graphene aerogels were acted as the anode of lithium-ion batteries, the first discharge capacity was 609 mAh/g at a current rate of 100 mAh/g and the first cycle efficiency (49.1%) was higher than graphene aerogels (37.8%). After 100 cycles, the discharge capacity could be stabilized at 187.7 mAh/g. At the same time coulomb efficiency could grow up to 92.3% which were higher than graphene aerogels (85.1%); Discharge capacities were 377,245,207,169,138,114 mAh/g under 40,100,200,400,1000 and 2000 mA/g current density. All of these anodes were exhibited excellent high circulation stability.