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Preparation And Electrochemical Performances Of Several Transition Metal Oxide Anode Materials For Lithium Ion Batteries

Posted on:2017-05-05Degree:MasterType:Thesis
Country:ChinaCandidate:P G ZhangFull Text:PDF
GTID:2271330485463793Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
Lithium ion batteries (LIBs) have been focus on energy storage because of the advantages of large specific capacity, less quality, high cycle life, comparing to the traditional batteries (lead acid battery, nickel cadmium battery etc.). As the development of the society, LIBs are in progress because of the improved requirment for LIBs performances. Graphite materials are the main commercial LIBs anode materials, but their prospects are limited due to the low specific capacity. Transition metal oxides have raised attention for the strengths of abundant resources, low cost and high specific capacity. But the cycling life of transition metal oxide anode materials is shorten, because the volume of materials get larger in the process of lithium extraction and insertion, leading the electrode broken, then electrode materials will separate from collector. In order to improve electrochemical performances of transition metal oxides, many methods are employed, including controlling morphology, compositing with carbon materials or doping nitrogen in carbon. The main contents and results of this thesis r are as follows:1. The as-prepared TiO2 precursors are calcined in Ar and NH3 atmospheres, then the different nanocomposites, TiO2/C and N-TiO2/C, will be obtained, respectively. The products are both spheres with the average-diameter of 160 nm, and the surfaceof TiO2/C is smooth but that of N-TiO2/C is rough because it is assemblied by many small nanoparticles. The reversible capacity of the N-TiO2/C composite is 277 mAh g"1 after 220 cycles at a current density of 0.6 C, and the reversible capacity of TiO2/C electrode material is only 228 mAh g-1, indicating that the N-TiO2/C composite exhibits higher specific capacity. The N-TiO2/C composite also has a good rate capability at different current densities, proving that electrode performances are improved by N-doping.2. Template-free method is used to facilely synthesize TiO2 hollow microspheres via one-step hydrothermal method. Interestingly, the TiO2 hollow microspheres have porous shell with thickness of about 450 nn. The formation mechanism of the hollow@porous TiO2 microspheres involves the formation and aggregation of TiO2 nanoparticles followed by oriented growth, etching of HF, and then Ostwald ripening and transformation process. The prepared TiO2 microspheres show a reversible capacity of ~170 mAhg-1 after 150 cycles at a current density of 0.6 C and also exhibit a good rate capability of 40.8 mAh g-1 at a current density of 24 C due to the unique hollow@porous structure, which can offer more sites for the storage and insertion of Li ions, and accelerate electrolyte diffusion and Li ions transport. The results also indicate that the as-prepared TiO2 material possesses excellent electrochemical performances, which may be an ideal anode material for lithium ion battery3. The Cu-MOF precursors are synthesized by coordinate transformation method under ultrasound according to the interaction of [Cu(NH3)4]2+ with benzenetricarboxylic acid. Then, Cu-MOFs are calcined at different temperatures to prepare electrode materials. The component of the product prepared at the calcination temperature of 250 ℃ is CuO/C, while that at 300 ℃,350 ℃ are CuO without carbon, respectively. The former exhibits hollow porous cube rod morphology, and the latter two display irregular shapes. The reversible capacity of CuO/C at 250 ℃, is 505 mAh g-1 after 200 cycles at a current density of 100 mAh g-1, which is much higher than that of CuO (250.1 mAh g-1 and 192.3 mAh g-1) obtained at 300 ℃ and 350 ℃, respectively. The rate capability of CuO/C nanocomposite is also better than that of CuO, illustrating the improvement of electrochemical performance owing to the hollow porous structure and carbon.
Keywords/Search Tags:transition metal oxides, titanium dioxide, cupric oxide, lithium ion batteries, anode
PDF Full Text Request
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