铁掺杂ε-MnO2纳米片的制备与电化学性能

Preparation and Electrochemical Properties of Fe Doped ε-MnO2 Nanosheets

摘要:

二氧化锰因资源丰富、价廉、无污染等特点，有望成为下一代锂电池正极材料。由于二氧化锰结晶形态的多样性，因此可以通过结构状态优化电极材料的制备方法，制备出具有优良的锂嵌入脱出性能的电极。然而，二氧化锰在循环过程中体积的变化及本征电导率低的原因，导致材料的容量衰减十分迅速。为了改善上述问题，可采用多种策略，如制备纳米结构的MnO₂、掺入其他元素稳定结构、与高导电的碳材料复合等，改善二氧化锰的电化学性能。以高锰酸钾(KMnO₄)和十八水合硫酸亚铁(FeSO₄·18H₂O)为原料，通过水热反应在碳布上(CC)生长Fe掺杂的ε-MnO₂纳米片，同时为了提高纳米片正极的导电性和稳定性，将导电炭黑(Super P)和海藻酸钠(SA)的混合物涂敷在电极表面。通过X射线衍射仪(XRD)、场发射扫描电子显微镜(SEM)和拉曼光谱，分别对MnO₂纳米片正极样品的形貌和结构进行了表征；使用循环伏安法(CV)、恒流充放电等方法，研究MnO₂纳米片正极样品的电化学性能。结果表明，Fe掺杂后的ε-MnO₂晶体尺寸减小，同时电荷转移电阻(R_ct)变小，纳米片正极的电化学性能得到提高。在电极上涂覆Super P和SA后，电极的锂离子扩散系数提高，长循环性能与倍率性能进一步提高，在0.5 C电流密度下，循环100圈后，电极的放电比容量为151.8 mA?h?g^-1，比相同条件下制备的纯MnO₂的放电比容量提高了83.4 mA?h?g^-1；在2 C大电流密度下循环120圈后，MnO₂纳米片电极的比容量为133.4 mA?h?g^-1。

Abstract:

Manganese dioxide is a promising candidate for the next generation lithium battery cathode materials owing to its abundant resources， low cost and environmentally friendly nature.. The diversity of manganese dioxide crystal provides an opportunity to optimize electrode material preparations and structural configurations， thereby enabling the fabrication of electrodes with excellent lithium intercalation/deintercalation properties. However， significant volume changes and low intrinsic conductivity of manganese dioxide during cycling process lead to rapid capacity decay. To address these challenges， it is possible to construct nanostructured MnO₂， incorporate other elements for structural stabilization， and form composites with highly conductive carbon materials. In order to improve the electrochemical properties of manganese dioxide， potassium permanganate （KMnO₄） and ferrous sulfate octadetahydrate （FeSO₄·18H₂O） were used as raw materials to grow Fe-doped manganese dioxide （MnO₂） nanosheets on carbon cloth （CC）. A mixture of conductive carbon black （Super P） and sodium alginate （SA） was applied to the electrode surface in order to improve the conductivity and stability of the nanosheet cathode. The morphology and structure of the samples were characterized by X-ray diffraction （XRD）， field emission scanning electron microscopy （SEM） and Raman spectroscopy. Electrochemical properties of the samples were studied by cyclic voltammetry （CV） and constant current charge-discharge methods. The results show that Fe doping effectively reduced particle size and charge transfer resistance （R_ct）， consequently improving electrochemical performance. After further coating the electrode with Super P and SA， the lithium-ion diffusion coefficient of the electrode was increased， and the long-cycle performance and rate performance were further improved. The discharge specific capacity of the material was 151.8 mA?h?g^-1 after 100 cycles at a current density of 0.5 C， which was 83.4 mA?h?g^-1 higher than that of pure MnO₂ prepared under the same conditions At the current density of C， the specific capacity of the nanosheet electrode is 133.4 mA?h?g^-1 after 120 cycles.