Synthesis And Electrochemical Performance Of Fe-Mn-Ti-C Anode Materials For Lithium-ion Batteries

As one of the green and efficient chemical power sources, lithium-ion batteries (LIBs) have been widely used in portable devices and electric vehicles (EVs), and promisingly used in large energy storage system such as smart grid. However, the commercial anode material of graphite delivers a low theoretical capacity of only 372 mAh/g, hardly meeting the need for high-performance LIBs with high-energy and high-power densities. Therefore, intensive research has been devoted to explore alternative high-performance anode materials. In this paper, transition metal oxides were parpared by a simple precipitation method and then coated with nitrogen-doped carbon. In addition, sulfur-containing carbon nanofibers with the graphene layers perpendicular to their length direction were prepared by a simple one-step route. The electrochemical performance of the as-prepared products as anode materials for LIBs was investigated. The main contents are summaried as follows:(1) Fe-Mn-O composite oxides with various Fe/Mn molar ratios were prepared by a simple coprecipitation method followed by coating with nitrogen-doped carbon using pyrrole as the carbon source. When used as anode materials for LIBs, the carbon-coated composite oxides exhibit better cycling performance than the individual oxides prepared under the same conditions, and the composite oxide with a molar ratio of 2:1 reveals the best electrochemical performance. The enhanced performance could be ascribed to the smaller particle size of Fe-Mn-O than the individuals and the mutual segregation of heterogeneous oxides during delithiation and heterogeneous elements during lithiation.(2) Porous nanostructures composed of anatase TiO2 nanoparticles were prepared via the hydrolysis of tetrabutyl titanate, and were simply coated and composited with N-doped carbon using acrylonitrile as the carbon source. The carbon-coated composite exhibits superior cycling stability and reversible capacity to the as-sintered TiO2. The cycling performance and rate capability of the composite carbonized at 550℃ are more excellent than those of the composite fabricated at 600 ℃. The synergistic effect of the combined coating and compositing with the N-doped carbon is responsible for the outstanding electrochemical performance.(3) Ti-Fe-O composite oxides with various Ti/Fe molar ratios were prepared by a simple coprecipitation method followed by coating with nitrogen-doped carbon using pyrrole as the carbon source. The electrochemical performance of the carbon-coated Ti-Fe-O composite is greatly associated with the amount of TiO2 in the composite, and the composite with a Ti/Fe molar ratio of 1:2 exhibits the best cycling performance and high-rate stability. The remarkable electrochemical performance could be attributed to the synergistic combination of the superior cycling performance from TiO2 with the high capacity from Fe3O4 in the carbon-coated Ti-Fe-O composites.(4) Sulfur-containing carbon materials were prepared by a simple reaction between sulfur and n-heptane. With increasing the addition of sulfur, the morphology of the raction product changes from microspheres to nanofibers with the graphene layers approximately perpendicular to their length direction. The formation of nanofibers with the unique structure is greatly associated with the promotion of sulfur on changing the morphology in the presence of stainless steel as the catalyst. When used as anode materials for LIBs, the sulfur-containing carbon nanofibers exhibit good cycling performance and rate capability.