Study On Preparation And Electrochemical Performance Of LiMn₂O₄ Cathode Material For Lithium-ion Batteries

Among different kinds of lithium battery cathode materials, spinel Li Mn2O4 is considered to be an attractive cathode material because of its low cost, abundant resources,low toxicity and better safety and it has been studied for many years to replace LiCoO₂.However, it suffers capacity fading upon cycling which will become even severe at elevated temperature, resulting in a terrible long-term cycle stability. In order to improve the cyclic performance of LiMn₂O₄ electrode materials, we have synthesized LiMn₂O₄ cathode materials with different morphologies using different precursors and different synthesis methods. And the phase and morphology of the product were characterized, the cycling performance and the charge-discharge properties of the product were also systematically analyzed.In this paper, we firstly introduced the research background of Li ion battery, the component of lithium-ion battery and operation fundamentals of lithium-ion battery. And then, we gave a simple summary on the structure and application of typical cathode materials. What's more, for LiMn₂O₄, its shortcomings of structure, factors resulting in the poor performance as well as the corresponding improvement methods are still disscussed in detail.In order to analyze the influence of morphology and structure on the Li Mn2O4 cathode material, we synthesized precursor Mn O₂ with different morphologies by using hydrothermal and sol-gel method respectively. Then hydrothermal method and high temperature solid phase method were used to further synthesize the LiMn₂O₄. All the morphology of LiMn₂O₄ samples are the same as the precursor. The nanorod LiMn₂O₄ prepared by hydrothermal method shows an initial discharge capacity of 127.3m Ah/g at0.1C. After 200 cycles, it still retains a capacity of 101.8m Ah/g. The burr-like LiMn₂O₄ spheres with a uniform particle size prepared by high temperature solid-state method shows an initial discharge capacity of 135.4 m Ah/g. However, it only shows a capacity retention of 94.7 m Ah/g after 200 cycles. And when it was cycled at 1.0C, a more serious capacity fading happened during the circulation. Finally, the electrode exhibits a discharge capacity of 68.7m Ah/g after 200 cycles.Surface coating modification can effectively restrain the electrolyte corrosion on Li Mn2O4. The rod-like Mn OOH was first synthesized by solvent thermal method, then it was used as precursor to react with LiOH to synthesize LiMn₂O₄ cathode material by high temperature solid phase method. After that, the PANI coating was further carried out.Analyzed from SEM and TEM date, we are sure that PANI was successfully coated on thesurface of the LiMn₂O₄ nanorods. Although the specific capacity of the modified LiMn₂O₄ is inevitable decreased, it shows an outstanding cycling performance and rate behavior. It still retains 91% of its initial discharge capacity after 200 cycles at 0.1C rate.Finally, we also successfully synthesized the hollow Li Mn2O4 nanofibers with a porous structure using the electrospinning techniques and the subsequent thermal treatment.This unique structure can effectively both relife the structure expansion and provide more reaction sites as well as shorten the diffusion path for Li⁺. Electrochemical tests demonstrate that it delivered an initial discharge capacity of 125.9m Ah/g at 0.1C current density and 87.3% of its initial discharge capacity after 200 cycles. It is noted that there is only a decrease of 6m Ah/g from 100 to 200 cycles. Moreover, the capacity retention which cycled at 1.0C is only 8.1m Ah/g less than the 0.1C after 200 cycles. These results suggest that the LiMn₂O₄ fibers we synthesized exhibits outstanding cycling performance and rate behavior, which is entirely determined by its excellent structure.