(a) Cycle performance and microstructure evolution of γ-Fe2O3@C/MWNT electrodes; (b) CV curves of γ-Fe2O3@C/MWNT electrodes after different cycles.

Recently, Qin Xiaoying's research team at the Institute of Solid State Physics, Chinese Academy of Sciences' Hefei Institute of Physical Science has made progress in the research of anode materials for lithium-ion batteries. The relevant results were published in the Journal of Materials Chemistry A (2015, 18, 9682-9688).

The negative electrode material is an important part of the lithium-ion battery. At present, the theoretical capacity of the commercial graphite material is low (372 mAh/g), which seriously restricts the development of the high energy density power battery. Therefore, the development of new anode materials with high charge and discharge capacity, safety and economy is one of the key areas in the field of battery materials research.

Fe2O3 as a lithium negative electrode material has the advantages of high theoretical capacity (-1000 mAh/g), low cost, and good environmental compatibility, and thus has received extensive attention. However, Fe2O3 itself has poor electrical conductivity, large volume change during charging and discharging, and is easily pulverized, which seriously impairs its electrochemical performance. The team led by Qin Xiaoying used vacuum carbonized metal-organic complex technology to prepare core-shell γ-Fe2O3@C nanoparticles and their composites with multi-walled carbon nanotubes (MWNT), and studied in detail. Its electrochemical performance and electrode activation process. At a current density of 100 mA/g, after 60 cycles, the capacity of the γ-Fe2O3@C/MWNT electrode is stable at 1139 mAh/g, which is higher than the theoretical capacity of the Fe2O3 material.

The study also found that at different current densities, the capacity showed a slowly increasing trend, corresponding to the slow activation of the electrode. Through cyclic voltammetry tests and microstructural characterization of the electrodes at different stages, it was found that γ-Fe2O3 particles gradually become porous vesicle-like structures during the cycling process, forming a large number of interfaces containing defects, and increasing the capacity through interfacial lithium storage. At the same time, the porous structure also promotes the rapid transport of Li+. On the other hand, the surface carbon shell effectively protects the Fe2O3 particles, inhibits their pulverization, and maintains the stability of the electrode structure. This work provides an important reference for the structural design of new negative electrode materials.

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