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LiFePO4/C复合正极材料研究与Mn3O4粉体制备
索鎏敏
学位类型硕士
导师康雪雅
2009-06
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业材料物理与化学
关键词锂离子电池 正极材料 Lifepo4 碳热还原法 沉淀法 四氧化三锰
摘要

橄榄石型LiFePO4因其价廉、无毒、环境友好、安全性高等优点被认是有望取代昂贵、有毒的LiCoO2成为最具开发和应用潜力的新一代锂离子电池正极材料。但低的电子导电率和离子扩散速率限制着LiFePO4的大电流充放电性能,制约着LiFePO4的实际应用,同时规模化制备工艺也是制约LiFePO4工业化的一个因素。 本文以蔗糖为还原剂,三价铁源为原料,通过固相碳热还原反应成功制备了LiFePO4/C,并对其进行了物理表征和电化学性能测试。通过与单质态乙炔黑对比可知,化合态的蔗糖为还原剂,起到了降低烧结温度,细化晶粒的作用,同时具有更好的碳包覆效果,材料电化学性能优良。以蔗糖为还原剂制备LiFePO4,通过工艺优化确定了最佳的工艺条件;通过XRD、SEM、TEM和FTIR分析表明合成的材料具有完好的橄榄石结构,颗粒粒径范围300-600nm,颗粒由碳包覆均匀,碳包覆厚度范围20~50nm。采用恒流充放电、循环伏安(CV)测试其电化学性能。LiFePO4规整的晶体结构、良好的颗粒表面形貌和微观结构使得合成的材料具有较好的电化学性能。通过对其进行电化学性能测试,表明材料具有良好的充放电性能,未除碳含量的情况下,0.1C倍率放电容量为136.9mAh/g,且循环稳定性较好。该方法制备工艺路线简单,能耗低;蔗糖既起到还原剂的作用又起到碳包覆的作用;原料以三价铁为铁源,降低了原材料成本。锰氧化物是一种用途很广的工业基础原料,在高密度铁磁储存介质、催化剂、离子交换剂、电化学材料等诸多方面有很广泛的用途。而锰源质量对材料的性能影响较大,单就用于制备锂离子正极材料的锰源而言,锰氧化物的颗粒大小、形貌及纯度等等性能直接决定了材料电化学性能。此外本论文对制备Mn3O4纳米粉体进行了初步研究,实验中探索了合成条件对形成纳米级Mn3O4粉体及对团聚体的影响因素,对锂离子电池正极材料所用锰源进行初步摸索。具体内容如下:以硝酸锰、氢氧化钠、氨水为原料,采用水解氧化沉淀法制备纳米级Mn3O4粉体材料。通过正交试验优化反应条件得到尺寸分布均匀,团聚程度小,颗粒分散性好的纳米级Mn3O4粉体。研究了制备过程中pH值、反应温度、搅拌速度、反应物浓度等因素对产物组成、晶体结构、晶粒尺寸、形貌及颗粒团聚程度的影响。采用LPSA、XRD、SEM以及化学滴定实验对反应产物进行分析表征。实验结果表明:采用水解氧化沉淀法制粉时,可得到纯度较高的Mn3O4,当工艺参数为: pH值为10、温度为40℃、搅拌速度3000 r/min、反应物浓度:Mn(NO3)2 : NaOH : NH4·OH = 2.4 : 4.8 : 0.96 mol/ L时,材料二次颗粒团聚程度最弱,分散性最好,一次纳米颗粒尺寸最小。

其他摘要
Olivine-structured LiFePO4, due to its advantages such as low cost, nontoxicity, environmental friendliness and high safety, is considered as a promising cathode material for lithium-ion batteries in place of expensive and toxic LiCoO2. However, the commercialization of LiFePO4 as cathode material for lithium-ion batteries is limited by its low electronic conductivity and slow lithium-ion diffusion. In addition, another problem is large-scale synthesis technique suitable for industrialization. In this paper, LiFePO4/C composite cathode materials were synthesized by a carbon thermal reduction (CTR) method using sucrose(C12H22O11)as reducing agent. For the method using sucrose as reducing agent, the synthesis conditions were optimized through a series of experiments. The LiFePO4 prepared by this method exhibits ordered olivine-type structure, good powder morphology and micro-structure which were examined by XRD,SEM,TEM and FTIR. The Particle size distribution is 300~600nm and the carbon-coated thickness is about 20~50nm. The electrochemical performances have been evaluated by constant current charge-discharge and cyclic voltammetry (CV). Through tests of charge and discharge, the prepared LiFePO4/C could deliver specific capacity of 136.9mAh/g at 0.1C rate, which also shows good electrochemical performance. This method using sucrose as reducing agent has such advantages: the synthesis route is simple and economic in synthesis technique and suitable for large-scale industrialization; it is cheap to produce LiFePO4 with Fe3+ source as raw material. Manganese oxide (Mn3O4) is currently used in many industrial application domains as magnetism, catalysis, electrochemistry or air decontamination. manganese hydroxide is also used in electrochemistry as a precursor in the synthesis of Li-Mn-O electrode materials for rechargeable lithium batteries . Using manganese nitrate, sodium hydroxide and ammonia as reactants,the nanometer Mn3O4 had been successfully prepared via a Hydrolysis and Oxidation precipitation method in a self-assembly tank reactor. The preparation of manganese hydroxide was significantly dependant on synthetic condition, such as the reaction temperature, pH, stirring speed, concentration of reactants, etc, and the optimized condition by orthogonal experiment method resulted in manganese oxide which has uniform particle size distribution, low second agglomeration degree and good dispersivity. The relation was studied between synthetic condition and material properties such as crystal structure, grain size, morphology and total manganese content by scanning electronic microscopy (SEM), Laser Particle Size Analyzer (LPSA) , X-ray diffraction (XRD) and Chemistry titration. The results show that, by a Hydrolysis and Oxidation precipitation method, the optimum technological parameters were as follows: pH=10, the reaction temperature 40℃, stirring speed 3000 r/min, concentration of reactants ( Mn(NO3)2 : NaOH : NH4•OH = 2.4 : 4.8 : 0.96 mol/ L ), and in this condition, the nano-powder have low second agglomeration degree, good dispersivity and small nano-particle size.
文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/3571
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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索鎏敏. LiFePO4/C复合正极材料研究与Mn3O4粉体制备[D]. 北京. 中国科学院研究生院,2009.
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