Electrochemical Performances Of Iron Based Oxide With Zinc Doping

During the past few decades, with the increasing consumption of fossil fuels and the continuous deterioration of our daily environment, an increasingly demands of environmentally-friendly and commercialized energy storage devices have become a main issue by a lot of researchers. Among them, lithium ion batteries (LIBs) which are regarded as promising energy storage devices have been paid numerous attentions. Nowadays, the disadvantages of commercial graphite have already restricted its large-scale application in the ever-growing number of energy storage devices. The transition-metal oxides (TMOs) as anode materials have indeed been considered as promising alternative anode materials due to their high theoretical capacity and lower operating voltage. However, most of the transition-metal oxides serving as anodes for LIBs usually suffer from the large volume changes resulted in poor capacity retention and low energy efficiency during the lithiation/delithiation processes, which has hindered their applications in LIBs. Therefore, an increasing number of research attentions have been paid in searching high reversible capacity, high safety and long-term cycling electrode materials.To improve the cycling and rate performance of the TMOs, a variety of strategies have been adopted. As the nanostructured electrode materials could provide better relief of stress-strain as well as maintain the structural integrity of anode materials during the repeated lithium extraction/insertion approaches, and thereby improving the cycle stability of LIBs. So an effective approach is to design nanostructured materials. Another approach depends on the enhancement of electrode materials’ electrical conductivity. Doping with semiconductor components which is also beneficial to LIBs has been employed in several previous researches.The main research and results are as follows:(1) Zn2+-doped Fe3o4 nanorods with carbon coating have been prepared by reducing lab-made Fe2o3 nanorods and carbonizing pyrrole carbon precursor. The as-prepared Zn-Fe3O4@C nanocomposites were evaluated as anode materials for lithium-ion batteries (LIBs). The results show that the Zn-Fe3O4@C nanorods with 2.5 mol%Zn2+doping demonstrated a reversible capacity of 949.1 mAh g"1, compared to only 315.4 and 235.5 mAh g-1 for Fe2o3 and Fe3O4@C nanorods, respectively, after 60 cycles at a current density of 100 mA g"1(2) The Zn2+-doped BaFe12O19 nanoplates were synthesized through a facile hydrothermal route followed by a calcination process. The nanoplates with the thickness of ca.50 nm will shorten the pathway for Li-ion diffusion and provide more contact surface area between the active materials and electrolyte, and Zn2+doping will increase the electronic conductivity of BaFe12o19. Electrochemical tests demonstrated that the Zn2+-doped BaFe12O19 nanoplates with 2.7 mol%Zn2+doping delivered a higher reversible capacity of 665.5 mAh g-1 than that (441.5 mAh g-1) of BaFe12o19 nanoplates after 250 cycles at a current density of 100 mA g"1.(3) Zn2+-SrFe12o19 nanoplates were firstly prepared via a calcination approach of brown precipitates which were synthesized through a solvothermal route on basic of synthesizing pure, well-structured strontium hexaferrites. The nanoplates are ca. 40-60 nm in thickness which could offer more contact surface area between electrolyte and SrFe12O19 nanoplates and shorten the diffusion route of Li-ion. The electrochemical measurements illustrated that both the Zn2+-doped SrFe12O19 and SrFe12o19 nanoplates exhibited a high reversible capacity of 1015.8 mAh g-1 and 456.5 mAh g-1, respectively, after 270 cycles at a current density of 100 mA g-1. Moreover, both samples exhibit good high-rate cycling performances, especially the Zn2+-doped SrFe12O19 nanoplates delivered 457.6 mAh g-1 at a high current density of 500 mA g-1 after 700 cycles.