高容量镍氢电池正极合成与性能研究

发布时间：2018-05-20 16:57

本文选题：氢氧化镍 + 正极材料　；参考：《北京有色金属研究总院》2014年硕士论文

【摘要】：镍氢电池是一种被广泛使用的二次电池,已经成为二次电池市场的主流产品,其具有高容量、低记忆效应、环境友好、工艺成熟和造价低廉等诸多优点。但随着电池技术的发展,镍氢电池的容量成为阻碍其进一步发展的瓶颈,尤其是近年来电动汽车(EV)对于电池容量的要求日益迫切,而镍氢电池目前尚难以满足。因此高容量将成为镍氢电池下一步发展过程中的关键技术。镍氢电池的容量由正极和负极中容量较低的短板来决定,而目前负极容量已经远远超过正极容量,提高镍氢电池容量的瓶颈即为正极材料容量。因此研发具有高容量的正极材料具有重要的意义。传统的镍氢电池正极为β-氢氧化镍,经过多年研究和改良,其放电容量逐渐迫近理论容量289mAh/g,进一步提升的空间有限,而α-氢氧化镍由于电子转移数较高,其理论容量高达479mAh/g,因此日益受到研究者的关注。但是其在碱性环境下结构不稳定,会自发转变为β-氢氧化镍,循环稳定性不佳,限制了其进一步应用。本工作在总结了相关研究的基础上,以锰掺杂为手段,设计和合成了一种具有混合相结构的氢氧化镍,以β相为基体提供结构稳定性,α相为增强相提高容量,综合α相和β相的优缺点实现互补,以期得到具有优良综合性能的氢氧化镍正极材料。本工作首先系统的研究了混合相氢氧化镍的合成条件,简要讨论了共沉积合成的化学环境以及后处理过程对于产物的影响,同时通过正交试验和均匀设计试验两种不同的实验设计方法,对于锰掺杂量、搅拌电机频率、pH值这三项对于产物影响最大的因素进行了详细的分析。试验结果表明,锰掺杂量宜保持在10%-15%之间,过低的锰掺杂量无法有效地提高样品的放电容量,而过高的锰掺杂量则有可能导致氢氧化镍结构损伤,劣化电极性能。搅拌电机频率宜保持在30Hz左右,过低的搅拌电机频率不利于Mn2+离子的氧化,从而导致α相含量偏低；过高的搅拌电机频率则不利于金属离子的共沉积,导致结晶状况劣化。pH值则在试验范围内越高越有利于放电容量的提高,原因在于高pH值条件下的沉积有利于晶体缺陷的生成,从而提高氢氧化镍的充放电效率。为了进一步研究锰掺杂混合相氢氧化镍的形成机制和实际使用性能,本工作通过合成不同锰掺杂含量的氢氧化镍并对其进行物理化学表征,详细探究了锰掺杂量对氢氧化镍样品的影响。结果显示,随着锰掺杂量的不断提高,氢氧化镍的晶体结构由β相逐渐转变为α相,在这一转变过程中出现了符合本实验设计的混合相氢氧化镍结构。同时随着锰掺杂量的提高,嵌入氢氧化镍层间的阴离子和水分子的数量也显著增多,这些嵌入粒子一方面通过扩大层间间距诱导了α相的生成,另一方面扩大的层间间距又反过来使得更多的粒子可以嵌入层间。因此层间间距的扩大与嵌入粒子的数量增多互相作用,共同诱导了氢氧化镍的相转变行为。通过对合成样品的形貌分析可以看到,样品在扫描电子显微镜下具有独特的蜂窝状微观形貌,其有利于提高氢氧化镍样品的充放电效率。合成样品的电化学性能测试表明,符合本实验设计结构的混合相氢氧化镍在0.2C充放电速率下不仅放电容量达到了330mAh/g,相比普通商用p-氢氧化镍提高约16%,同时在充放电循环中保持了良好的结构稳定性,50次循环后容量没有出现衰减现象。为了满足电动汽车大功率动力电池的需要,本工作进一步对合成的混合相氢氧化镍做了覆钴处理,结果显示包覆钻氧化物样品的粉末电阻明显降低,电性能测试显示尽管在0.2C下放电容量有一定衰减,但是在1C大电流充放电时相比未覆钴样品容量有较为明显提升,因此其有望作为一种大功率高容量正极材料得到应用。
[Abstract]:Ni MH battery is a widely used two battery. It has become the mainstream product in the two battery market. It has many advantages, such as high capacity, low memory effect, friendly environment, mature technology and low cost. But with the development of battery technology, the capacity of Ni MH battery has become a bottleneck that hinders its further development, especially in recent years. Electric vehicle (EV) is becoming more and more urgent for battery capacity, and Ni MH battery is still difficult to meet at present. Therefore, high capacity will be the key technology in the next development process of Ni MH battery. The bottleneck of the capacity of high nickel hydrogen battery is the capacity of cathode material. Therefore, developing high capacity cathode materials is of great significance.
The traditional nickel hydrogen battery positive electrode is beta - nickel hydroxide. After years of research and improvement, the discharge capacity is gradually approaching the theoretical capacity of 289mAh/g, and the space for further upgrading is limited, while the theoretical capacity of the alpha hydroxide nickel hydroxide is up to 479mAh/g because of the high electron transfer number, so it is increasingly concerned by the researchers. But the structure is in the alkaline environment. Instability will change spontaneously into beta nickel hydroxide, and its poor stability will limit its further application.
On the basis of the related research, a kind of nickel hydroxide with mixed phase structure is designed and synthesized with manganese doping as a method. The structure stability is provided with beta phase as the matrix, the alpha phase is enhanced to enhance the capacity and the advantages and disadvantages of the synthesis of alpha and beta phase are complementation, in order to obtain good comprehensive properties of nickel hydroxide. Material Science.
This work first systematically studied the synthesis conditions of the mixed phase nickel hydroxide, briefly discussed the chemical environment of the co deposition and the effect of the post-treatment process on the product. At the same time, two different experimental design methods, through orthogonal test and uniform design test, were used for the three items of manganese mixing, stirring motor frequency, and pH value. The test results show that the amount of manganese doping should be kept between 10%-15% and the low manganese doping amount can not effectively improve the discharge capacity of the sample, while the excessive manganese doping may lead to the damage of the nickel hydroxide structure and the deterioration of the electric polarity. The frequency of the stirred motor should be kept around 30Hz. The low frequency of the stirred motor is not conducive to the oxidation of Mn2+ ions, which leads to the low content of the alpha phase, and the high frequency of stirred motor is not conducive to the co deposition of metal ions. The higher the crystallization condition, the higher the.PH value in the test range is beneficial to the increase of discharge capacity. The reason is that the deposition of high pH is beneficial to the lack of crystal. Thus, the charge and discharge efficiency of nickel hydroxide is improved.
In order to further study the formation mechanism and practical performance of Mn doped nickel hydroxide, the physical and chemical characterization of nickel hydroxide with different manganese content was synthesized and the effect of manganese doping on the sample of nickel hydroxide was investigated in detail. The crystal structure is gradually transformed from beta phase to alpha phase. In the process of this transformation, the structure of the mixed phase nickel hydroxide which is in accordance with the experimental design has appeared. With the increase of manganese doping, the number of anions and water molecules embedded in the layer of nickel hydroxide increased significantly. These embedded particles have induced the alpha phase by expanding the interlayer space. The expansion of interlayer space on the other hand, in turn, makes more particles embedded in the interlayer. Therefore, the expansion of the interlayer space and the number of embedded particles interact with each other, which co induces the phase transition behavior of nickel hydroxide. The unique honeycomb micro morphology is beneficial to improve the charge discharge efficiency of the nickel hydroxide sample. The electrochemical performance test of the synthesized sample shows that the discharge capacity of the mixed phase nickel hydroxide conforming to the design structure is 330mAh/g at the charge discharge rate of 0.2C, and is about 16% higher than that of the ordinary commercial p- nickel hydroxide. The discharge cycle keeps good structural stability, and the capacity does not decay after 50 cycles.
In order to meet the needs of the high-power power battery of the electric vehicle, the composite phase of the mixed phase nickel hydroxide was further treated with cobalt treatment. The results showed that the powder resistance of the coated oxide sample was obviously reduced. The electrical performance test showed that although the discharge capacity was attenuated under the 0.2C, it was compared with the 1C when the high current charge and discharge were not covered. The cobalt sample capacity has been significantly improved, so it is expected to be used as a high-power, high capacity cathode material.
【学位授予单位】：北京有色金属研究总院
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

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