真空状态下合成磷酸铁锂正极材料及性能研究

发布时间：2018-05-09 20:40

  本文选题：锂离子电池 + 真空烧结法　； 参考：《昆明理工大学》2017年硕士论文

【摘要】：锂离子电池不仅在各相关领域中得到广泛应用,在商业上也获得了巨大的成功。本文采用真空烧结法合成LiFePO4/C正极材料,采用XRD、SEM以及室温恒流充放电和交流阻抗等测试方法进行表征,对比了不同的反应条件对合成LiFePO4/C正极材料的形貌特征和电化学性能的影响。本文用碳酸锂(Li2CO3)、草酸亚铁(FeC2O4 2H2O)、磷酸二氢铵(NH4H2PO4)为原料,蔗糖作为碳源,经过高能机械球磨,在氩气和真空状态的不同组合方式下,采用两段式高温固相烧结法,首先对比了合成LiFePO4/C复合正极材料的区别;然后通过改变碳源加入方式,预烧结时间,以及不同碳源包覆等因素,探讨了合成LiFePO4/C的最佳条件。实验结果表明:两段烧结均在真空状态下合成的LiFePO4/C正极材料比氩气气氛保护下合成的LiFePO4/C正极材料形貌规则颗粒细小,倍率和循环性能更好,并且减少了保护气的消耗,降低生产成本。采用真空状态下两段固相烧结法,在前驱体中加入蔗糖作为碳源,经350℃烧结5 h,再升温到650℃烧结6 h合成的LiFePO4/C材料电化学性能最佳。该材料在0.2 C放电倍率下放电比容量为156.2 mAh g-1，，在1 C放电倍率下循环100次后有98.9%的容量保持率。为了进一步减小能耗,采用真空状态下一段高温固相烧结法合成了 LiFePO4/C正极材料,分别讨论烧结温度,烧结时间以及碳包覆量对合成材料性能的影响。实验结果表明:在真空状态下用碳含量为7 wt%的前驱体,经过650℃烧结6h合成的LiFePO4/C材料电化学性能最好,0.2 C放电倍率下放电比容量为154.5 mAh g-1,即使在1 C放电倍率下放电比容量为123.6 mAh g-1,且循环100次后具有98.3%的容量保持率。真空高温烧结法合成正极材料的过程含氧量很少,可以避免材料表面氧化问题。真空烧结法也具有烧结温度低,烧结时间短,耗气少等诸多优点,使之成为合成电极材料的有效方法。
[Abstract]:Lithium ion batteries have not only been widely used in various fields, but also achieved great commercial success. LiFePO4/C cathode materials were synthesized by vacuum sintering and characterized by room temperature constant current charge-discharge and AC impedance measurements. The effects of different reaction conditions on the morphology and electrochemical properties of synthesized LiFePO4/C cathode materials were compared. In this paper, lithium carbonate Li _ 2CO _ 3, FeC _ 2O _ 4 H _ 2O _ 4 H _ 2O _ 4, NH _ 4H _ 2PO _ 4) were used as raw materials, sucrose as carbon source, high energy mechanical ball milling, two-stage high temperature solid-state sintering method in argon and vacuum state. The differences of LiFePO4/C composite cathode materials were compared at first, and then the optimum conditions of LiFePO4/C synthesis were discussed by changing the carbon source addition mode, pre-sintering time, and different carbon source coating. The experimental results show that the LiFePO4/C cathode materials synthesized in vacuum state by two-stage sintering are smaller in shape, smaller in size and better in cycling performance than those synthesized in argon atmosphere, and the consumption of protective gas is reduced. Reduce production costs. The best electrochemical properties of LiFePO4/C were obtained by two-stage solid-state sintering in vacuum state, adding sucrose to the precursor as carbon source, sintering at 350 鈩

本文编号：1867344