Ni-MH电池正极活性材料改性研究

发布时间：2018-06-23 09:42

本文选题：超声波辅助共沉淀法 + 多元掺杂α-Ni(OH)_2　；参考：《广东工业大学》2015年硕士论文

【摘要】：氢氧化镍是二次碱性电池的正极储能材料,如镍氢、镍镉、镍锌、镍铁电池等。由于安全性能好、性价比高、耐过充能力强等优点,被广泛应用于民用电器和新能源汽车等领域。但是,目前商用Ni-MH电池使用的正极材料是β-Ni(OH)2,理论比容量仅为289mAh·g-1,提升空间比较小；而Ni(OH)2的另一种晶型α-Ni(OH)2的理论比容量可高达482mAh·g-1,且其较大的层间距对提高材料的高倍率性能有着重要的影响,但其堆积密度较低且在碱液中结构不稳定,易转化为β-Ni(OH)2,使其迄今还没有得到应用。此外,较差的导电性Ni(OH)2也是制约其性能的重要因素。因此,如何解决α-Ni(OH)2的稳定性差问题并提高其堆积密度和改善Ni(OH)2(半导体材料)的导电性,对于提高镍氢电池的市场竞争力和应用前景有着重要的意义。本文针对α-Ni(OH)2结构稳定性差的技术瓶颈,通过多元掺杂的方法制备出稳定性较高的纳米α-Ni(OH)2,并系统地研究了掺杂离子种类与掺杂比例、掺杂离子间的协同作用、层间阴离子以及晶体结构对于样品物理化学性能的影响。同时,通过一元掺杂制备出Sn掺杂α-Ni(OH)2和Ca掺杂α/β-Ni(OH)2,并研究了掺杂元素离子、层间阴离子、颗粒大小以及晶体结构等因素对于物理化学性能的影响。本文工作主要分为以下三个方面：1.采用超声波辅助共沉淀法以Na2CO3为缓冲剂分别制备了一元、二元、三元掺杂样品。实验结果表明,未掺杂样品为β-Ni(OH)2晶体结构,而掺杂的样品为α-Ni(OH)2晶体结构；随着掺杂离子种类和比例的增加,样品的结构稳定性随之增强,电化学性能逐步提高。Al-Mn-Yb三元掺杂样品在电解液中浸泡30天后,其晶体结构仍为α-Ni(OH)2晶相结构;同时三元掺杂样品制备的复合电极具有较高的质子扩散系数、较小的电化学极化作用和最大的放电比容量(309.0mAh/g)。这是由于掺杂离子对晶体内部晶体场、层间阴离子含量等因素的影响以及掺杂离子间的协同作用所致。因此,选取合适的掺杂比例与元素种类是提高α-Ni(OH)2电化学性能的有效方法。2.采用上述方法(Na2CO3为缓冲剂)制备了不同掺杂比例的单元Sn取代α-Ni(OH)2,其掺杂比例对样品的形貌、晶体结晶度、颗粒大小以及电化学性能均产生重要的影响。结果表明,随着掺杂离子含量的增加,层间距逐渐变大,二次颗粒粒径先减小后增大,晶体结晶度先提高后变差,当Sn掺杂比例达到15 mo1%时,样品具有最好的结晶度。通过恒流充放电、循环伏安、交流阻抗谱电化学性能测试表明,Sn掺杂量为15mol%的样品制备的电极具有最小的电荷转移电阻(Rct)、最大的质子扩散系数、最佳的循环稳定性以及最高的放电比容量(303.6mAh/g)。这说明掺杂离子的含量对于晶体的结晶度、粒度及形貌均有着重要的作用,进而影响其电化学性能。3.采用上述方法并添加Na3PO4为沉淀剂制备出了Ca单一掺杂的α/β-Ni(OH)2样品。结果表明,在Ca2+掺杂量相同情况下,无Na3PO4沉淀剂添加时,不能生成α晶相的Ni(OH)2,添加摩尔比Ni2+:PO43-=1:0.066的Na3PO4后,生成了α/β混合相结构的Ni(OH)2。无掺杂样品为纯β-Ni(OH)2结构。通过电化学性能测试发现,与纯β-Ni(OH)2相比,α/β-Ni(OH)2混合相样品具有较高的电化学活性、较好的电化学可逆性和充电效率、较高的放电平台和循环稳定性。含混合相样品的复合电极在0.2C和0.5C倍率下经过80个循环后,其放电比容量仍能保持在271.7 mAh/g和238 mAh/g,这说明Ca单一掺杂的α/β-Ni(OH)2具有优异的电化学性能。
[Abstract]:Nickel hydroxide is the positive energy storage material of the two alkaline battery, such as nickel hydrogen, nickel cadmium, nickel zinc, nickel iron battery and so on. Due to the advantages of good safety, high performance price ratio, high ability to overcharge and so on, it is widely used in the fields of civil electrical appliances and new energy vehicles. However, the positive material used for commercial Ni-MH batteries is beta -Ni (OH) 2, and the theoretical specific capacity is only only For 289mAh g-1, the lifting space is relatively small; while the theoretical specific capacity of another crystalline alpha -Ni (OH) 2 of Ni (OH) 2 can be as high as 482mAh g-1, and its larger interlayer spacing has an important influence on improving the high performance of the material, but its accumulation density is low and the structure is unstable in the alkali solution, and it is easily converted to beta -Ni (OH) 2, so far it has not been obtained. In addition, the poor conductivity of Ni (OH) 2 is also an important factor restricting its performance. Therefore, how to solve the problem of the poor stability of alpha -Ni (OH) 2 and improve the bulk density and improve the conductivity of Ni (OH) 2 (semiconductor material) is of great significance for improving the market competitiveness and application prospects of Ni MH batteries. This paper is aimed at alpha -Ni (OH). 2 -Ni (OH) 2 with high stability was prepared by multiple doping method. The effects of doping ions and doping ratio, synergistic action between doped ions, interlayer anions and crystal structure on the physical and chemical properties of the samples were systematically studied. Sn doped alpha -Ni (OH) 2 and Ca doped alpha / beta -Ni (OH) 2, and the effects of doping elements ions, interlayer anions, particle size and crystal structure on physical and chemical properties. This work is mainly divided into three aspects: 1. using ultrasonic assisted coprecipitation method to prepare one yuan, two yuan, three yuan respectively with Na2CO3 as a buffer. The experimental results show that the undoped sample is the crystal structure of beta -Ni (OH) 2 and the doped sample is the crystal structure of alpha -Ni (OH) 2. With the increase of the type and proportion of doping ions, the structure stability of the sample increases and the electrochemical properties gradually increase the crystal structure of the.Al-Mn-Yb three element doped sample in the electrolyte for 30 days. It is still a phase structure of alpha -Ni (OH) 2 crystal. At the same time, the composite electrodes prepared by three element doped samples have higher proton diffusion coefficient, smaller electrochemical polarization and maximum discharge specific capacity (309.0mAh/g). This is due to the influence of doping ions on the crystal field in the crystal, the content of interlayer anion and the synergistic interaction between the doped ions. Therefore, the selection of appropriate doping ratio and element species is an effective method to improve the electrochemical properties of alpha -Ni (OH) 2.2. by using the above method (Na2CO3 as a buffer) to prepare a unit Sn replacing alpha -Ni (OH) 2 with different doping proportions. The ratio of doping to the sample's morphology, crystal crystallinity, particle size and electrochemical properties all produce weight. The results show that with the increase of doping ion content, the interlayer spacing gradually becomes larger, the two particle size decreases first and then increases, the crystallinity of the crystal increases first and then becomes worse. When the proportion of Sn doping reaches 15 mo1%, the sample has the best crystallinity. The electrochemical performance test of the AC impedance spectroscopy shows that Sn by constant current charge discharge, cyclic voltammetry, and AC impedance spectroscopy. The electrode doped with 15mol% has the minimum charge transfer resistance (Rct), the maximum proton diffusion coefficient, the optimal cycle stability and the highest discharge specific capacity (303.6mAh/g). This indicates that the content of doped ions plays an important role in the crystallinity, particle size and morphology of the crystal, and then affects its electrochemical properties. A single doped Ca / beta -Ni (OH) 2 sample with Ca doping was prepared by using the above method and adding Na3PO4 as precipitant. The results showed that, when the Ca2+ doping amount was the same, the Ni (OH) 2 of the crystalline phase could not be generated without Na3PO4 precipitator, and the addition of mole ratio Ni2+: PO43-=1:0.066 Na3PO4, 2. adulteration of alpha / beta mixed phase structure was generated. The sample is a pure beta -Ni (OH) 2 structure. Through the electrochemical performance test, it is found that the samples of the mixed phase of alpha / beta -Ni (OH) 2 have higher electrochemical activity compared with pure beta -Ni (OH) 2, better electrochemical reversibility and charging efficiency, higher discharge platform and cyclic stability. The composite electrode of the mixed phase sample has 80 evidence-based at 0.2C and 0.5C ratio. After discharge, the discharge specific capacity can still be maintained at 271.7 mAh/g and 238 mAh/g, indicating that Ca single doped alpha / beta -Ni (OH) 2 has excellent electrochemical properties.
【学位授予单位】：广东工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM911.14

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