低热固相反应法制备水合磷酸铁正极材料及其充放电性能研究
发布时间：2019-02-26 09:35
【摘要】：FePO4作为LiFePO4的脱锂化合物,其作为正极材料具有电压适中、比容量高及热稳定性好等优点,因而有希望运用在锂离子电池中。目前制备FePO4的方法大都是液相沉淀和水热法,其制备过程繁杂且难以得到纯相的磷酸铁。另外FePO4作为正极材料,由于本身晶体结构的限制(电导率低和锂离子扩散性能差),从而导致其实际比容量不高且大电流放电性能差。本文针对以上问题做了以下三个方面的研究： 1.低热固相反应具有能耗低、污染少、选择性高及不需要溶剂等优点,在无机纳米材料制备领域占有重要地位。本文采用低热固相反应合成法,以FeCl3·6H2O作为铁源,探究了Na3PO4·12H2O、Na2HPO4·12H2O及NaH2POa-2H20作为磷源制备磷酸铁类材料的可行性。XRD结果表明当P/Fe为1时,只有选用Na2HPO4·12H2O作为P源,才能得到纯相的具有晶型结构的FePO4·2H2O。电化学测试同时表明该法制备的FePO·2H20无需任何处理就具有优异的充放电循环性能,且效果优于失去结晶水的FePO4。 2.以FeCl3·6H2O为铁源,Na2HPO4·12H2O为磷源,系统研究了不同P/Fe比、不同陈化温度、不同陈化时间、表面活性剂的添加对低热固相反应法制备FePO4·2H2O材料结构、形貌及充放电性能的影响。XRD结果表明陈化时间对产物晶型结构无显著影响；而适当增加P/Fe比和降低温度,样品趋向无定形化。表面活性剂的加入对样品形貌影响很大。SEM测试表明加入PEG-6000后可制得球状的FePO4·2H2O,该样品整体放电比容量不高,但倍率性能优异。 3.以二水合磷酸二氢钠(NaH2POa·2H20)、六水合三氯化铁(FeCl3·6H2O)及多壁碳纳米管(MWNTs)为原料通过均相沉淀法合成FePO4·2H2O/MWNTs复合物。采用TG-DTA、XRD及IR分析了复合物的组成。TEM测试表明FePO4·2H2O粒径在20 nm左右,并均匀的负载在MWNTs表面。充放电测试结果表明FePO4·2H2O/MWNTs复合物充放电性能远高于纯相的FePO4·2H2O。以0.1 C充放电,首次放电比容量达到129.9 mAh·g-1,经20次循环以后的容量仍保持在114.3 mAh·g-1,容量保持率接近90%。如此优异的充放电性能归因于FePO4·2H2O较小的粒径缩短了Li+的扩散路程,MWNTs的存在提高了FePO4·2H2O的导电性,同时,MWNTs之间相互交错形成的三维导电网络结构有利于电解液的渗透。
[Abstract]:As a delithium compound of LiFePO4, FePO4, as a cathode material, has the advantages of moderate voltage, high specific capacity and good thermal stability, so it is promising to be used in lithium ion batteries. At present, most of the methods for preparing FePO4 are liquid phase precipitation and hydrothermal method. The preparation process is complicated and it is difficult to obtain pure phase iron phosphate. In addition, as a cathode material, due to the limitations of its crystal structure (low conductivity and poor lithium ion diffusion), the actual specific capacity of FePO4 is not high and the discharge performance of high current is poor. In this paper, the following three aspects of research on the above problems have been done: 1. Low-thermal solid-state reaction has the advantages of low energy consumption, less pollution, high selectivity and no need of solvent, so it plays an important role in the preparation of inorganic nano-materials. In this paper, using FeCl3 路6H2O as Tie Yuan, the feasibility of using Na3PO4 路12H2O, Na2HPO4 路12H2O and NaH2POa-2H20 as phosphorus sources to prepare iron phosphate materials was studied by low-temperature solid-state reaction method. The results show that when P/Fe is 1, The pure FePO4 路2H2O with crystal structure can be obtained only by using Na2HPO4 路12H2O as P source. Electrochemical measurements also show that the FePO 路2H20 prepared by this method has excellent charge / discharge cycle performance without any treatment, and the effect is better than that of FePO4. without crystal water. 2. Using FeCl3 路6H2O as Tie Yuan and Na2HPO4 路12H2O as phosphorus source, the structure of FePO4 路2H2O was systematically studied with different P/Fe ratio, different aging temperature, different aging time, and the addition of surfactant to low heat solid state reaction method. The results of XRD show that the aging time has no significant effect on the crystal structure of the product. However, when the P/Fe ratio is increased and the temperature is lowered, the sample tends to be amorphous. SEM results show that spherical FePO4 路2H2O can be prepared by addition of PEG-6000. The specific discharge capacity of the sample is not high, but the performance of the sample is excellent. 3. The FePO4 路2H2O / MWNTs composite was synthesized by homogeneous precipitation using sodium dihydrogen phosphate dihydrate (NaH2POa 路2H20), ferric chloride hexahydrate (FeCl3 路6H2O) and multi-walled carbon nanotubes (MWNTs) as raw materials. Tem test showed that the particle size of FePO4 路2H2O was about 20 nm and loaded uniformly on the surface of MWNTs. The composition of the composite was analyzed by TG-DTA,XRD and IR. The results of charge-discharge test show that the charge-discharge performance of FePO4 路2H2O / MWNTs composite is much higher than that of pure FePO4 路2H2O. At 0.1C, the initial discharge specific capacity reached 129.9 mAh 路g-1, and the capacity remained at 114.3 mAh 路g-1 after 20 cycles. The capacity retention rate was close to 90%. The excellent charge-discharge performance is due to the fact that the small particle size of FePO4 路2H2O shortens the diffusion path of Li, and the existence of MWNTs improves the conductivity of FePO4 路2H2O. At the same time, the structure of three-dimensional conductive network interlaced between MWNTs is beneficial to the permeation of electrolyte.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：TM912
本文编号：2430654
[Abstract]:As a delithium compound of LiFePO4, FePO4, as a cathode material, has the advantages of moderate voltage, high specific capacity and good thermal stability, so it is promising to be used in lithium ion batteries. At present, most of the methods for preparing FePO4 are liquid phase precipitation and hydrothermal method. The preparation process is complicated and it is difficult to obtain pure phase iron phosphate. In addition, as a cathode material, due to the limitations of its crystal structure (low conductivity and poor lithium ion diffusion), the actual specific capacity of FePO4 is not high and the discharge performance of high current is poor. In this paper, the following three aspects of research on the above problems have been done: 1. Low-thermal solid-state reaction has the advantages of low energy consumption, less pollution, high selectivity and no need of solvent, so it plays an important role in the preparation of inorganic nano-materials. In this paper, using FeCl3 路6H2O as Tie Yuan, the feasibility of using Na3PO4 路12H2O, Na2HPO4 路12H2O and NaH2POa-2H20 as phosphorus sources to prepare iron phosphate materials was studied by low-temperature solid-state reaction method. The results show that when P/Fe is 1, The pure FePO4 路2H2O with crystal structure can be obtained only by using Na2HPO4 路12H2O as P source. Electrochemical measurements also show that the FePO 路2H20 prepared by this method has excellent charge / discharge cycle performance without any treatment, and the effect is better than that of FePO4. without crystal water. 2. Using FeCl3 路6H2O as Tie Yuan and Na2HPO4 路12H2O as phosphorus source, the structure of FePO4 路2H2O was systematically studied with different P/Fe ratio, different aging temperature, different aging time, and the addition of surfactant to low heat solid state reaction method. The results of XRD show that the aging time has no significant effect on the crystal structure of the product. However, when the P/Fe ratio is increased and the temperature is lowered, the sample tends to be amorphous. SEM results show that spherical FePO4 路2H2O can be prepared by addition of PEG-6000. The specific discharge capacity of the sample is not high, but the performance of the sample is excellent. 3. The FePO4 路2H2O / MWNTs composite was synthesized by homogeneous precipitation using sodium dihydrogen phosphate dihydrate (NaH2POa 路2H20), ferric chloride hexahydrate (FeCl3 路6H2O) and multi-walled carbon nanotubes (MWNTs) as raw materials. Tem test showed that the particle size of FePO4 路2H2O was about 20 nm and loaded uniformly on the surface of MWNTs. The composition of the composite was analyzed by TG-DTA,XRD and IR. The results of charge-discharge test show that the charge-discharge performance of FePO4 路2H2O / MWNTs composite is much higher than that of pure FePO4 路2H2O. At 0.1C, the initial discharge specific capacity reached 129.9 mAh 路g-1, and the capacity remained at 114.3 mAh 路g-1 after 20 cycles. The capacity retention rate was close to 90%. The excellent charge-discharge performance is due to the fact that the small particle size of FePO4 路2H2O shortens the diffusion path of Li, and the existence of MWNTs improves the conductivity of FePO4 路2H2O. At the same time, the structure of three-dimensional conductive network interlaced between MWNTs is beneficial to the permeation of electrolyte.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：TM912
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