| As the environmental pollution, shortage of mineral resources has become more and more serious in the world wide. It is urgent for us to further excavate the surplus value of the industrial waste and develop circular economy. In this thesis, the byproduct of TiO2 industry was used as raw material to prepare LiFePO4 and α-Fe2O3 electrode materials for lithium ion batteries by hydrothermal or one-step solid-state method, and the electrochemical performance of as-prepared electrodes were also studied. The details are as follows:(1) The byproduct of TiO2 industry was used as the iron source to prepare LiFePO4 by hydrothermal method. As the byproduct contains a variety of metallic ions(Mg, Mn, Al, Ti et al.) and the total ion content is so high that it will reduce the electrochemical performance of LiFePO4. We blended it with FeSO4·7H2O(AR) in proportion to ease the contradiction based on the basis of dilution principle and then optimized the mixture ratio. At the best ratio, the electrochemical performance of the as-prepared sample is better than which prepared with Fe SO4·7H2O(AR) simply. After carbon coating, the multi-doped LiFePO4 can deliver a discharge capacity of 90 mAh g-1 at 10 C rate and a high capacity retention rate of 95.3% for 100 cycles at 1 C rate, showing a good electrochemical performance.(2) The byproduct of TiO2 industry was used as iron source to prepare nano-sized FePO4 by precipitation method. Based on the rule of solubility, pure nano-sized FePO4·2H2O can be prepared from the byproduct after the Ti, Al purification, oxidation and precipitation under pH control processes. The pH of purification, stirring time, amount of phosphate and reaction temperature were discussed according to the composition, morphology, particle size and P/Fe ratio of the products. Then, we prepared LiFePO4/C composite by one-step solid-state method with the synthesized FePO4·2H2O as iron source. The galvanostatic charge-discharge tests show that the LiFePO4/C composite cathode can deliver a discharge capacity of 101 mAh g-1 at 10 C rate and the high capacity retention rate of 97.4% after 100 cycles at 0.5 C rate.(3) The byproduct of TiO2 industry was also used as the iron source to prepare nano-sized α-Fe2O3 by hydrothermal method. The hydrothermal temperature, concentration of reactants, kind and dosage of morphology control agents were systematically investigated. By changing the reaction conditions, we had prepared a variety of nano-sized α-Fe2O3 with different morphology and particle sizes. Firstly, the as-synthesized α-Fe2O3 were used as iron source to prepare LiFePO4 by one-step solid-state method. The influence of morphology and particle size of α-Fe2O3 on LiFePO4 was also discussed. It turns out that: the particle size of α-Fe2O3 has more impact on the electrochemical performance of LiFePO4 than its morphology. The possible reasons are discussed. Secondly, we investigated the lithium storage properties of as-prepared nano-sized α-Fe2O3 by using them as anode materials for lithium ion batteries. The results show that the nano-sized α-Fe2O3 sphere has the best electrochemical performance among all the samples. It exhibits a high initial reversible discharge capacity of 1093 mAh g-1 at 0.1 C rate, but poor capacity retention rate of 47.3% after 50 cycles. Finally, in order to improve the cycle performance of α-Fe2O3 anode, a novel 3D α-Fe2O3/N-GNS/CNTs composite material was designed and prepared. The galvanostatic charge-discharge tests display that the composite electrode can deliver a high capacity retention rate of 97.3% at a current density of 0.1 A g-1 after 50 cycles, showing a great circulation property. |
PDF Full Text Request