二维磷酸铁锂纳米片的制备及其电化学性能的研究

发布时间：2018-05-31 00:40

本文选题：磷酸铁锂 + 水　；参考：《太原理工大学》2017年硕士论文

【摘要】：能源是当今社会发展的主要动力,经济的高速发展离不开能源的推进作用。目前普遍适用的传统能源来自于非可持续再生的煤、石油等,日益不断的开采,将面临此类非可持续资源逐步匮乏的问题,与此同时,传统非可再生能源的利用过程中,还将面临严重的环境问题,诸如温室气体的排放等等。新型可再生清洁能源的开发利用是目前亟待解决的主要问题。其中,风能、太阳能、潮汐能等新型可再生清洁能源的开发将为能源领域注入新的活力,将成为替代传统能源的主要候选之一。然此类能源均属于非连续型能源,找寻合适的储能装置是推动此类能源应用发展的关键。锂离子电池是目前为止最有潜力的电源系统,因其可以提供高的工作电压及能量密度,而有望用做大规模能量存储及电动汽车和插电式混合动力汽车的车载能量存储的电池。目前商用锂离子电池正极材料主要为LiCoO_2,但这种材料的缺陷较多,例如成本昂贵、安全性能差等。相比于LiCoO_2,LiFePO_4因其原材料价格低廉、理论容量高、循环寿命长且环境友好等优势,成为目前热门的正极材料之一。但由于本身晶体结构的限制,其电子电导率和离子传导率较差,成为阻碍LiFePO_4材料被广泛应用于动力及储能领域的主要因素。本论文采用溶剂热合成法,以FeSO_4·7H_2O、H_3PO_4、和LiOH·H_2O为原料合成磷酸铁锂,应用XRD、SEM对材料的结构及形貌进行表征,利用恒电流充放电方法、循环伏安法及交流阻抗研究所合成磷酸铁锂的电化学性能,综合考察了合成条件中不同水含量对磷酸铁锂形貌和电化学性能的影响。同时通过添加石墨烯,考察不同含量石墨烯对磷酸铁锂电化学性能的改善。研究表明:合成条件中不同水含量对所形成的磷酸铁锂产物的形貌有很大影响,不同水含量合成条件下,最终形成不同粒子尺寸的磷酸铁锂纳米片。另外加入不同含量的石墨烯对磷酸铁锂正极材料的电化学性能有不同程度的优化,其中,添加磷酸铁锂活性质量2%的石墨烯条件下样品的性能为最佳,通过电化学性能测试分析,5 mlH_2O条件下加入石墨烯量为磷酸铁锂质量2%所合成的材料,在充放电倍率为0.2 C时,达到165 mAh·g~（-1）的首次放电容量,倍率方面,在30 C充电条件下,仍可保持118.6 mAh·g~（-1）的高比容量,并在5 C电流密度下,循环100次后比容量仍能得到很好的保持,不会发生衰减。
[Abstract]:Energy is the main driving force of social development, and the rapid development of economy can not be separated from the role of energy. At present, the traditional energy sources that are generally applicable come from the non-sustainable renewable coal, oil and so on. With the increasing exploitation of such non-sustainable resources, they will face the problem of the gradual scarcity of such non-sustainable resources. At the same time, in the process of using traditional non-renewable energy, Will also face serious environmental problems, such as greenhouse gas emissions and so on. The development and utilization of new renewable clean energy is the main problem to be solved. Among them, the development of new renewable clean energy, such as wind energy, solar energy, tidal energy and so on, will inject new vitality into the energy field, and will become one of the main candidates for replacing traditional energy. However, these kinds of energy are discontinuous energy sources, and finding suitable energy storage devices is the key to promote the development of such energy applications. Li-ion battery is the most potential power system by far, because it can provide high working voltage and energy density, it is expected to be used as a battery for large-scale energy storage and on-board energy storage for electric vehicles and plug-in hybrid vehicles. At present, LiCoO2is the main cathode material for commercial lithium-ion batteries, but there are many defects in this material, such as high cost, poor safety performance and so on. Compared with LiCoO2LiFePO4, it has become one of the most popular cathode materials due to its advantages of low raw material price, high theoretical capacity, long cycle life and environmental friendliness. However, due to the limitation of its crystal structure, its electronic conductivity and ionic conductivity are poor, which is the main factor that hinders the wide application of LiFePO_4 materials in the field of power and energy storage. In this paper, lithium iron phosphate was synthesized by solvothermal synthesis from FeSO_4 7H _ 2OH _ 2O _ 3PO _ 4 and LiOH _ H _ 2O as raw materials. The structure and morphology of the material were characterized by XRD-SEM, and the constant current charge-discharge method was used. The electrochemical properties of lithium iron phosphate synthesized by cyclic voltammetry and impedance spectroscopy were investigated. The effects of water content on the morphology and electrochemical properties of lithium iron phosphate were investigated. At the same time, the improvement of electrochemical performance of lithium iron phosphate with different content of graphene was investigated by adding graphene. The results show that different water content has great influence on the morphology of the synthesized lithium ferric phosphate products. Finally, different particle sizes of lithium iron phosphate nanoparticles are formed under different water content synthesis conditions. In addition, the electrochemical properties of lithium ferric phosphate cathode materials were optimized by adding different contents of graphene, and the best performance of the samples was obtained when the active mass of lithium iron phosphate was 2% of graphene. The first discharge capacity of the material prepared by adding 2% graphene to lithium ferric phosphate at a charge / discharge rate of 0.2C reached 165 mAh / g ~ (-1) at 30 C charging condition was analyzed by electrochemical performance test. The high specific capacity of 118.6 mAh / g ~ (-1) can still be maintained at 5 C current density, and the specific capacity can still be maintained very well after 100th cycle without decay.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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