| Since lithium-ion batteries have been commercial used,it has broad application prospects in the fields of intelligent machines,mobile devices and electric vehicles.Among those applications,graphite is the most mature and popular anode material of lithium-ion batteries for commercial applications.And its theoretical specific capacity is 372 m Ah g-1which still needs to be improved.The development of new anode materials with safe,non-toxic,cycle stability and high energy density to replace graphite has become the focus of research.While the pseudocapacitive process of TiO2(B)anode material makes it excellent in electrochemical performance due to its abundant reserves and stable electrochemical performance.However,low conductivity and theoretical specific capacity are still the challenges.The nano-sheet structure has a large specific surface area,while can effectively shorten the ion transport path and improve the battery cycle performance of the material.Moreover,because Co3O4has the high specific capacity but low capacity retention rate during long-term circulation,combining those two materials into nano-base composite structure is an efficient way to enhances its capacity while improve the cycle stability.In this paper,TiO2(B)nanosheets were prepared and annealed to improve the cycle properties of the materials.The TiO2(B)-Co3O4 composite nanosheets were designed and prepared.The advantages of the two materials were utilized and the metal particles were used to improve the conductivity,in order to obtain composite materials with high cycle stability and high capacity.The main research work and results are as follows:1.TiO2(B)nanosheets were first prepared by solvothermal method,and annealed at350°C,then photoposited Ag nanoparticles,and solvothermal grown Co3O4,at last the composite structure of TiO2-Ag-Co3O4 was achieved.The effects of the deposition amount of Ag nanoparticles and the mass ratio of Co(Ac)2·4H2O to TiO2 during solvothermal reaction on the cycle performance of the electrode material was investigated.The results show that annealing significantly improve the performance of TiO2 electrode.Deposition a small amount of Ag particles promotes the cycle performance of the composite.The mass ratio of Ag to TiO2 was maintained at 1/8 during photodeposition,the amount of Co3O4 in the composite was controlled by changing the mass ratio of Co(Ac)2·4H2O to TiO2 during hydrothermal reaction,and the optimum mass ratio was 3/8.The prepared TiO2-Ag-Co3O4composite structure has a stable lithium ion transport capacity and stable cycle performance,the capacity was 398 m Ah g-1 after 100 cycles at a current rate of 1 C.2.TiO2(B)nanosheets were prepared by solvothermal method and treated at different annealing temperatures.The effects of annealing temperature on the crystal formation,morphology,specific surface area,pore size and electrode cycle properties of titanium dioxide were investigated.It has been found that annealing at temperatures above 250°C will change the TiO2(B)phase into anatase phase,and the nanosheets will begin to smash and agglomerate.The proper temperature annealing of TiO2(B)can effectively improve the lithium storage performance of TiO2(B)nanosheets.Ti-200 sample annealed at 200°C for 1 h can maintain the appearance and crystal formation,while the lithium ion transport channel was dredged and the reversibility of lithium was increased,the cycle performance of TiO2(B)nanosheets is maximized.3.The cycle performance of TiO2(B)-Co3O4 composites was studied.The optimal amount and photodeposition time of Au,as well as the optimum mass ratio of Co(Ac)2·4H2O to TiO2(B)were investigated.The results show that the optimum amount Au deposited is100?L(0.01 g m L-1)of chloroauric acid per 100 mg of TiO2(B).And the best illumination time is 10 min.The optimal mass ratio of Co(Ac)2·4H2O to TiO2(B)is 5/9 in the second solvothermal reaction.The composite structure prepared under this condition has the best battery cycle performance.After circulating 1000 cycles at a high rate of 5 C,the specific capacity exceeds 400 m Ah g-1,showed the potential to adapt into fast charge. |
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