Preparation And Characterization Of Transitional Metal Anode Materials For Lithium-ion Batteries By Electrospinning

Lithium-ion batteries are green and clean storage devices. Lithium-ion batteries have attracted a lot of attention because of its high energy density, long cycle life, no memory effect, low cost, small self-discharge and no environmental harm. As the proportion of portable and smart devices increase in people's daily life, the requirements for the performance of lithium-ion batteries become more and more high. Among recent progress in electrochemistry, nanotechnology has led to the application of nanomaterials for high performance of lithium-ion batteries because of its unique morphologies and structures. Nanomaterials with large specific surface area and many active sites could provide more space and reaction sites for the intercalation/deintercalation reaction of lithium ions. Therefore, nanomaterials could be used to develop large ability for lithium ion storage and high energy of lithium-ion batteries with high performance.Based on the concept that nanomaterials could be used to develop high performance lithium-ion batteries, in this work, electrospinning technique was employed to prepare transitional metal nanofibers as anode materials for lithium-ion batteries. In this work, the method for preparing TiO₂ nanofibers and CoFe₂O₄ nanofibers prepared by electrospinning technique was described in details, and the crystal structure and morphologies of as-prepared samples were characterized by XRD, SEM, and TEM methods. The electrochemical performance of as-prepared materials was measured by charge/discharge measurement at constant current. The detail content of this work is as follows: 1. Different spinnable solution systems were prepared by dissolving tetrabutyl titanate and polyvinylpyrrolidone into different solvents, composite nanofibers were fabricated by electrospinning technique. The influence of different solvent systems on the morphologies of as-prepared composite nanofibers were discussed, the composite nanofibers had the most excellent morphology by electrospinning the solution in which anhydrous ethanol was used as solvent, based on the result of analysis. The composite nanofibers prepared from ethanol solvent system which were sintered at 500 oC, 600 oC and 700 oC for 3 h in air atmosphere, were characterized by SEM, TEM and XRD. The results revealed that all the samples were TiO₂ nanofibers with fibrous characteristic and anatase phase. The crystallinity and the grain size of TiO₂ nanoparticles composed of TiO₂ nanofibers increased with the increase of calcination temperature. The electrochemical performance of TiO₂ nanofibers as anode material for assembling the simulate batteries were measured. The results demonstrated that TiO₂ nanofibers obtained at 500 oC as anode material had the most excellent electrochemical performance. The first charge capacity reached 279 mAh/g at the discharge rate of 0.1 C, but its cycling property was quite bad, capacity reduced severely with the cycling. The capacities of the samples obtained at 600 oC and700 oC were also reduced severely. 2. The accounted amount of PAN and PVP according to 7:3 of the weight ratio of PAN and PVP was dissolved into DMF, the weighted amount of Co(NO3)2·6H2O and Fe(NO3)3·9H2O was also dissolved into the above solution according to Co(NO3)2·6H2O:Fe(NO3)3·9H2O=1:2 (molar ratio) and 30 wt% of polymer weight of the weight percentage of the two materials, then homogenous solution was prepared. Composite nanofibers were prepared by electrospinning method. The as-prepared composite nanofibers was sintered at different plans, the results showed that CoFe₂O₄ nanofibers with pure crystal phase were obtained only at the condition of 800 oC for 5 h in air. The electrochemical performance of CoFe₂O₄ nanofibers as anode material for assembling the simulate batteries were measured. The results revealed that as-prepared CoFe₂O₄ as anode material had very high specific capacity, which was much higher than the theoretical value of CoFe₂O₄. Though the efficiency of the obtained material reached more than 90 %, and its discharge capacity was only 134.19 mAh/g after 10 cycles, which indicated the capacity of the material reduced very fast and greatly. Cyclic voltammetry was employed to measure the charge/discharge mechanism of as-prepared sample, the results indicated that the great capacity reduction was due to the damage of the structure of the material.