石墨烯/尖晶石LiMn2O4纳米复合材料制备及电化学性能

采用溶胶凝胶法和还原氧化石墨法制备尖晶石LiMn2O4纳米晶和石墨烯纳米片,并采用冷冻干燥法制备了石墨烯/尖晶石LiMn2O4纳米复合材料,利用XRD、SEM、AFM等对其结构及表面形貌进行表征;利用CV、充放电、EIS研究纳米复合材料的电化学性能和电极过程动力学特征。结果表明:纳米LiMn2O4电极材料及其石墨烯掺杂纳米复合材料的放电比容量分别为107.16 mAh.g-1,124.30 mAh.g-1,循环100周后,对应容量保持率为74.31%和96.66%,石墨烯可显著改善尖晶石LiMn2O4电极材料的电化学性能,归结于其良好的导电性。纳米复合材料EIS上感抗的产生与半导体尖晶石LiMn2O4不均匀地分布在石墨烯膜表面所造成局域浓差有关,并提出了感抗产生的模型。

Synthesis and Electrochemical Performance of Graphene Modified Nano-Spinel LiMn2O4 Cathode Materials

Nano-LiMn₂O₄ and graphene nanosheets were synthesized by sol-gel route and reduction of exfoliated graphite oxides method respectively. Graphene modified spinel LiMn₂O₄ cathode nanocomposites were synthesized by freeze-drying method. The structure, morphology and electrochemical performance of the synthesized materials were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge techniques. The graphene modified spinel LiMn₂O₄ nanocomposites exhibited a high discharge capacity of 124.30 mAh·g^-1 at 0.1C, while spinel LiMn₂O₄ only delivered 107.16 mAh·g^-1 at the same rate. Compared with pure LiMn₂O₄, the graphene modified LiMn₂O₄ exhibited excellent cycle ability, with a capacity retention of 96.66% after 100 cycles versus about 74% for pure LiMn₂O₄. The improved electrochemical performance was attributed to the excellent conductivity of graphene nanosheets. The inductive loop observed in the impedance spectra of the graphene modified LiMn₂O₄ electrode was attributed to the formation of nano-LiMn₂O₄ local concentration cell from which current flows in opposition to Li de-intercalation into cathode, consistent with the conditions for the generation of an inductive loop. Consequently a model was proposed to explain the inductive loop response of composites electrode for lithium ion batteries.