Carbon nanotubes filled with iron oxide nanoparticles
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Because of the extensive application in portable electronic devices, electric vehicles and hybrid electric vehicles, lithium-ion batteries have become the mainstream of research in the field of new energy materials and devices. Although lithium-ion batteries have the highest energy densities of today's commercial secondary batteries, their performance is still insufficient to meet evolving application requirements. Therefore, it is of great significance to develop a novel lithium ion battery electrode material with high energy density and high power density. Transition metal oxides based on the transition mechanism exhibit excellent lithium storage properties, such as iron oxide (Fe2O3) with specific capacity of up to 1007 mA h g-1, low cost, abundant reserves, and environmental friendliness, which led to the researchers Of the wide attention. However, the intrinsic conductivity of Fe2O3 is low, and its volumetric change is significant during the process of deintercalation of lithium, which makes the capacity of Fe2O3 rapidly decay. (CNT) as a unique nano-reactor, the Fe3 O3 nanoparticles were controlled in CNTs, and CNTs-limited Fe2O3 (superscript 3 +) - Fe2O3 nanoparticles were prepared in the CNTs. The electrochemical properties of the composite electrode materials were investigated. The in-situ transmission electron microscopy (TEM) was used to study the structure evolution of CNT-filled Fe2O3 particles during charging and discharging, and to reveal the mechanism of lithium storage.

CNTs are distinguished from other carbon nanomaterials in that they are one-dimensional tubular structures curled by graphene sheets and have a one-dimensional nano-cavity with diameters from less than 1 nm to 100 nm. On the one hand, CNT hollow tube can be used as nano-reactor for the synthesis of high-capacity lithium-ion battery composite electrode material; on the other hand, CNT can be used as nano-tubes to be filled electrode material electrochemical lithium storage mechanism. This is of great significance for the design and preparation of high performance lithium ion battery electrode materials. For this purpose, the team prepared an open-ended CNT with anodic aluminum oxide template and controlled the filling of Fe2O3 nanoparticles in its lumen, resulting in a iron oxide(Fe2O3) nanoparticle / CNT composite electrode material. When used as a negative electrode for Li-ion batteries, Fe2O3 in the CNTs in the confinement region exhibited a specific capacity of up to 2071 mA h g-1. Lithium ion batteries were fabricated by transmission electron microscopy (TEM). The process and mechanisms of lithium storage were studied in situ. It was found that the size of iron oxide nanoclusters with iron nuclei in the CNT lumen was much smaller than that on the CNTs surface during the charging process, indicating that the CNT nano-confinement Effect can significantly suppress the volume change of the active material. The results show that the high lithium capacity of Fe2O3 is mainly due to the interfacial intercalation of lithium in the CNT nanofibers, the reversible reaction of LiOH to LiH and the transformation of the mesophase in solid electrolyte, and the excellent electrical contact between Fe2O3 and CNT.

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