【作者】 徐剑晖；

【导师】 李朝林；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2010， 硕士

【摘要】 随着移动电子设备的迅速发展,要求电池具有高比容量,这就促进了锂电池和锂离子电池的迅速发展。相对负极而言,作为锂离子电池锂源的正极材料研究较为滞后,成为制约锂离子电池整体性能进一步提高的关键因素。而目前研究最多的几种正极材料LiCoO2、LiNiO2、LiMn2O4等均存在着不同的缺点而难以满足动力电池的需要。橄榄石结构LiFePO4材料具有对环境友善、资源丰富、价格便宜和安全性能好等优点,被认为是非常具有发展前景的锂离子电池正极材料。磷酸铁锂的电导率低,高倍率充放电性能较差和批次稳定性较差是限制其商业化的瓶颈。本论文以制备高电导率,高倍率充放电性能和批次稳定的磷酸铁锂为主要目的,对LiFePO4材料的合成条件、形貌、金属掺杂、碳包覆、电性能等展开了深入系统的研究。本课题首次采用草酸铁作为铁源,以磷酸和氢氧化锂作为磷源和锂源,采用液相共结晶+机械合金化+高温烧结合成制备得到锂离子电池正极材料LiFePO4。利用X射线衍射仪、扫描电镜、能量分散谱仪、热重分析和电化学性能测试等方法对磷酸铁锂材料的物相结构、表面形貌、含碳量以及电性能进行分析研究。讨论了不同的烧结温度、不同的烧结时间、不同分散剂添加量和机械合金化对材料形貌的影响。实验确定的最佳合成工艺为:锂铁比为1:1,碳在前驱体中包覆量为3.2wt%,预烧结温度为350℃,烧结时间为5h,高能球磨料球比为1:50,转速580r/min,球磨时间3h,高温烧结温度为650℃,合成时间为8h,合成过程在惰性气氛下完成。在上述工艺条件下合成的LiFePO4材料,结晶性能良好、物相较纯,一次粒径在50~100nm之间,比表面积为28.9m2/g,一次颗粒球型度好,粒径分布均匀。以Mn、Ti、Mg为掺杂元素,按照摩尔比制得成品为Li0.99Mg0.01Fe0.99Mn0.006 Ti0.004PO4,在2.5~4.2V、0.1C倍率下的首次放电比容量为133.2mAh/g;1C倍率下的首次放电比容量为102.2mAh/g,循环50次容量保持率为99%。更多还原

【Abstract】 With the development of mobile electronic equipments, the demand to high capacity of lithium ion batteries increases. Comparing with the anode of lithium ion battery, the cathode material obviously lags. To improve the performance of the cathode is a key method for lithium ions batteries. So far,the conventional cathode materials such as LiCoO2, LiNiO2 and LiMn2O4 etc. are the mainstream materials and they have different short comings not to meet the demand of the power battery.Olivine-struetured LiFePO4 is considered as a promising cathode material for lithium-ion batteries due to its advantages such as environmentally friendliness, abundant raw materials, inexpensive price and high safety. However, it suffers from low conductivity, poor rate Performance and low batch stability, which prevents it from commercial use. To improve the conductivity, electrochemical performances and batch stability of LiFePO4 material, the synthesis condition, morphology, metal doping, carbon coating and electrochemieal behavior of LiFePO4 as cathode materials were studied in detail in this dissertation.The study introduce iron oxalate as iron source for the first time, phosphoric acid and lithium hydroxide as the phosphorus sources and lithium source respectively, and use co-crystallization + mechanical alloying + high-temperature sintering to prepare LiFePO4. The crystalline structure, morphology, carbon contents and electrochemical performances were investigated by XRD, SEM, EDS, thermogravimetric analysis and electrochemical tests. The effects of synthesis time, temperature, the different amount of dispersant and mechanical alloying on electrochemical performances of LiFePO4 material were discussed. In this experiment, the optimized synthesis condition was obtained, the ration of Li/Fe was 1, the amount of carbon in precursor was 3.2%, the pre-sintering temperature was 350℃, the time of sintering was 5h. In high-energy ball milling, the ration of material/ball was 1:50, the rotating speed was 580r/min, the time of ball milling was 3h, the sintering temperature was 650℃, the sintering time was 8h in inert atmosphere. LiFePO4 synthesized by the above-mentioned process has good and pure crystal, and the diameter is between 50~100nm, the specific surface area is 28.9m2/g, has good degree of spherical particles, uniform particle size distribution.LiFePO4 was doped by Mn, Ti and Mg, and the Doped LiFePO4 exhibited the initial discharge capacity of 133.2mAh/g in 2.5~4.2V and at 0.1C rate, 102.2mAh/g at 1C rate, and retaining 99% after 50 cycles.更多还原