【作者】 王丹丹；

【导师】 赵敏寿；

【作者基本信息】 燕山大学 ， 环境工程， 2010， 硕士

【摘要】 本文采用溶胶-凝胶法制备锂离子电池正极材料Li₃V₂（PO₄）₃/C,并通过金属离子掺杂和金属氧化物包覆技术对Li₃V₂（PO₄）₃/C进行改性研究,以期改善材料的电化学性能。根据Li₃V₂（PO₄）₃/C前驱体的TG-DTA分析确定制备样品的温度范围。利用XRD和恒电流充放电测试等方法研究Mn2+和Y3+离子掺杂对Li₃V₂（PO₄）₃/C材料的结构和电化学性能的影响。结果表明,掺杂少量Mn2+和Y3+离子不影响材料的晶体结构,适量的Mn2+和Y3+离子掺杂均改善磷酸钒锂材料的循环稳定性能和倍率性能。采用FE-SEM、XPS和EIS对Li3V1.94Mn0.09（PO4）3/C材料的形貌特征和电化学性能进行研究。结果表明,掺杂Mn2+离子可以细化材料颗粒。XPS分析表明,Li3V1.94Mn0.09（PO4）3/C中的V和Mn分别以+3和+2价存在。EIS分析表明,Li3V1.94Mn0.09（PO4）3/C的电荷转移电阻明显小于Li₃V₂（PO₄）₃/C。采用XRD和SEM对金属氧化物包覆的Li₃V₂（PO₄）₃/C材料的微观结构和形貌进行分析。研究发现,包覆少量金属氧化物不影响Li₃V₂（PO₄）₃/C材料的晶体结构,包覆后材料的粒径进一步增大。通过恒电流充放电测试技术对经包覆处理后的锂离子电池正极材料的最大放电容量,循环稳定性和倍率性能进行研究。结果表明,适量的Al2O3包覆和MgO包覆均可以改善Li₃V₂（PO₄）₃/C材料的循环稳定性和倍率性能,其中MgO包覆还显著提高材料的最大放电容量,降低极化度,进一步改善材料的电化学性能。当包覆量为4.5 mol%时,包覆效果最佳,大幅提高了材料的高倍率充放电性能。在0.2 C电流密度下,放电容量达195 mAh/g,已非常接近磷酸钒锂的理论容量197 mAh/g,当电流密度分别增加到0.5 C和1 C时,放电容量仍高达174 mAh/g和149 mAh/g。更多还原

【Abstract】 The cathode material Li₃V₂（PO₄）₃/C for lithium-ion battery is prepared by sol-gel method in this paper, and modified by ion doping and metal oxide coating.The temperature for synthesization is determined according to TG-DTA curves of Li₃V₂（PO₄）₃/C precursor. The effect of Mn2+ and Y3+ doped on the structure and electrochemical performances of Li₃V₂（PO₄）₃/C is investigated by XRD and galvanostatic charge-discharge. The results show that doping small amount of Mn2+ and Y3+ ion does not affect the monoclinic structure of the material Li₃V₂（PO₄）₃/C, and doping the proper amount Mn2+ and Y3+ ion can improve cyclic stability and high-rate dischargeability of Li₃V₂（PO₄）₃/C.Li3V1.94Mn0.09（PO4）3/C is investigated by FE-SEM、XPS and electro -chemical impedance spectroscopy （EIS）. The results show that the particles of Mn-doped sample are smaller than those of un-doped sample. XPS analysis shows that oxidation valences state of V and Mn in Li3V1.94Mn0.09（PO4）3/C is +3 and +2, respectively. EIS measurement indicates that doping Mn reduces the charge transfer resistance.Metal oxide coated Li₃V₂（PO₄）₃/C is investigated by XRD and FE-SEM. The results show that coating with a small amount of metal oxide does not affect the monoclinic structure of the material and the particles of metal oxide coated samples become bigger than those of non-coated sample.Effect of metal oxide coated on the electrochemical property of Li₃V₂（PO₄）₃/C is studied. For example, the maximum discharge capacity, cyclic stability and high-rate dischargeability of resultant materials are measured by galvanostatic charge-discharge. The results show that coating with proper amount of Al2O3 and MgO can improve cyclic stability and high-rate dischargeability of Li₃V₂（PO₄）₃/C. MgO-coating enhances the discharge capacity significantly and reduces the polarization of material and improves electrochemical properties of Li₃V₂（PO₄）₃/C material. The sample of coating amount of 4.5 mol% exhibits excellent electrochemical properties, and can deliver a reversible capacity as high as 195 mAh/g at a discharging rate 0.2C, which is close to its theoretical capacity of 197 mAh/g, and it is able to deliver a capacity of 174 mAh/g and 149 mAh/g at 0.5 C and 1 C, respectively.更多还原