The Preparation Of NC/Fe₃O₄ Nanocomposite For Anode Materials Of Li-ion Battery

With the rapid development of portable electronic products and electric vehicles, energy storage devices become more and more important. With the characteristics of high energy density, high power output and environmental friendliness, the lithium ion batteries?LIBs? have attracted much attention. Due to the low gravimetric capacity of conventional graphite anodes?372 mA hg-1?, great efforts were made to explore new alternatives. With the features of high theoretical capacities, low-cost, environment friendly and natural abundance, Fe₃O₄ became one of the most promising active materials for anode of LIBs. However, its practical application is still restricted by rapid capacity degradation, which resulted from dramatic volume change during lithiation/delithiation process. In this paper, in order to alleviate the dramatic volume change of the Fe₃O₄ nanoparticles, N-doped carbon/Fe₃O₄ nanocomposite were constructed by carbon coating for anode materials in the LIBs.1. Utilising the characteristics of self polymerization of dopamine in weak basic condition, polydopamine layer was deposited onto the surface of Fe₃O₄ nanoparticles?NPs?, then pyrolysised at high temperature, subsequently obtained the carbon coated Fe₃O₄. The battery performance tests showed that after 200 cycles at a current density of 200 mAg-1, its capacity was still as high as 823 m A hg-1, which was much higher than that of the bare Fe₃O₄?almost 0?. In the rate test, it still delivered a capacity of 254 mAhg-1 at the current density of 2 Ag-1.2. Based on the templating and anchoring function of the carboxyl group functionalized polystyrene latexes, hollow carbon nanosphere embedded with ultrafine Fe₃O₄ NPs?Fe₃O₄@HCNS? were fabricated. Besides, the performance as anode materials in LIBs were also studied. This chapter is mainly divided into following two parts:The first part is the preparation of magnetic polystyrene microspheres. With the help of the anchoring effect of carboxyl groups, the Fe₃O₄ NPs were loaded on the surface of the polystyrene latexes. The results showed that the Fe₃O₄ NPs were uniformly distributed on the polystyrene latexes. Moreover, other metal oxides, such as ZnO and Cu O, could also be loaded onto the polystyrene latexes. The results demonstrated the good universality of the carboxyl groups anchoring method.In the second part, Fe₃O₄@HCNS was synthesized by coating polydopamine on magnetic polystyrene microspheres and then removed the polystyrene template by annealing at high temperature in Ar. The results showed that the ultrafine Fe₃O₄ NPs with a diameter of 5 nm uniformly embedded in the inner wall of the HCNS. Battery performance tests showed that the reversible capacity of Fe₃O₄@HCNS increased with cycling and in the 200 th cycle, reached 1380 mA h/g, at a current density of 1000 mAg-1. Even at a high current density of 10 A/g, it still delivered a stable capacity of 290 mA h/g.