电池正极材料球形Ni（OH）₂的制备条件与性能研究

【作者】 顾琳；

【导师】 郭玉忠； 王剑华；

【作者基本信息】 昆明理工大学 ， 材料物理与化学， 2010， 硕士

【摘要】 镍氢电池以其大功率、高容量、记忆效应小、安全性能良好、价格便宜、绿色环保无污染等优点具有广阔的发展空间。但是对于电池正极材料球形氢氧化镍来说一直存在着高活性和高密度不能兼顾的问题。本文综述了国内外镍氢电池的研究现状,指出了镍氢电池存在的问题。采用控制化学结晶法在自制连续搅拌反应器(CSTR)中制备电池正极材料球形氢氧化镍。利用材料热力学理论、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、电化学性能测试等研究手段系统深入研究了pH值、反应时间、镍离子浓度和氨镍比对球形氢氧化镍材料的表面形貌、晶体结构、堆积密度和电化学性能的影响。材料热力学理论计算表明,反应pH值控制在9.5-11.5之间时,氢氧化镍在氨碱水溶液体系中实现热力学动态平衡,达到完全沉淀,可以有效避免体系中镍离子或碱液过多生成胶体。SEM分析表明制备得氢氧化镍均为球形颗粒,颗粒粒径粗大,颗粒直径从几微米到二十微米均匀分布。XRD分析表明其晶型均为β-Ni(OH)2,晶胞结构完整,晶体结构有序。反应pH值是影响球形氢氧化镍结构和性能的的主要因素,在一定范围内,随着pH值的增大,球形氢氧化镍的堆积密度先增大后减小,粒径分布同样先增大后减小,pH值过大体系过饱和度高,结晶度差易形成胶体,微观形貌为片状,晶粒细化因此堆积密度降低。pH值在10.5-11.5之间都具有较高的堆积密度,粒径分布均匀,球形度较好。反应时间延长利于结晶。随着反应时间的延长氢氧化镍颗粒尺寸逐渐增大,从结构松散的细小团絮状,变成颗粒尺寸较大的团聚状类球形,最终成为结构致密的球形颗粒,粒径均匀分布在2-18μm之间。镍离子浓度过大过小时,材料的球形度差,堆积密度低,因此镍离子浓度适宜控制在0.1-0.12mol/L。随着氨镍比的增大堆积密度先增大后减小,氨镍比在1-1.2之间易得到高密度的电极材料。恒流充放电试验显示,粒径增大放电比容量降低,堆积密度增大放电比容量随之降低。pH值为10.5-11.5,镍离子浓度为0.1-0.12mol/L,氨镍比为1-1.2,反应时间>24h时,制备得氢氧化镍具有较高的放电比容量和稳定的放点平台。因此在pH值为11,镍离子浓度为0.12mol/L,氨镍比为1.2,反应时间≥24h时,制备的球形氢氧化镍颗粒球形度好,流动性好,同时具有良好的放电比容量和高堆积密度,是理想的高性能电池正极材料。更多还原

【Abstract】 With the deepening researched and developed of MH-Ni battery materials, the spherical nickel hydroxide cathode material is one of the materials first choice for the battery in the future, because of its advantages on higher power and capacity, smaller memory effects, excellent safety, lower cost, and much more environmentally friendly. However, it is still difficult for the spherical nickel hydroxide applied to cathode material battery, because the spherical nickel hydroxide cathode material would own a higher packing density, while a higher capacity. This problem would still be a challenge to the spherical nickel hydroxide cathode material.In this paper, the current conditions and existing problems in the research of MH-Ni battery was analyzed. The spherical nickel hydroxide particles were synthesized by the controlled chemical crystallization method in a continuous stirring tank reactor. The formation, structure, packing density and electrochemical properties of spherical nickel hydroxide were studied by means of thermodynamic analysis, SEM, XRD and electrochemical techniques analysis. The relationship between pH value, reaction time, nickel ions concentration, mole ratio of NH3/Ni and properties of spherical nickel hydroxide were discussed.The results of thermodynamic analysis showed that nickel hydroxide precipitated totally between pH=9.5 and pH=11.5, and attained an equilibrium conditions in the reaction system. In this case, the nickel ions could be completely precipitated as Ni(OH)2 while mixed with NH3·H2O. It was found from SEM analysis that the crystallinity degree of spherical nickel hydroxide was high. The size of particles distributes equably between a few microns and twenty microns or more. And it was found from XRD analysis that crystal cell becomes integrated gradually and crystal structure becomes more ordered ofβ-Ni(OH)2. The pH value of the reaction is the main factor which affects the structure and properties of spherical nickel hydroxide. Within the certain range of pH value, with the increase of pH value, the packing density and grain size of spherical nickel hydroxide increase at first and then decrease. Too high pH value was disadvantage to the saturation, because the packing density decreases when the pH value is enhanced. When nickel hydroxide precipitated totally between pH=10.5 and pH=11.5, it possesses a high packing density, uniform particle size and good distribution spherical degree. The reaction time was advantage to crystallization. With the increase of reaction time, grain size of spherical nickel hydroxide is increasing which distributes from 2 microns to 18 microns, and the crystalline form becomes from fine aggregate to spherical aggregate. Too low or too high nickel ions concentration was disadvantage to the spherical degree and packing density, and the nickel ions concentration was controlled in the range of 0.1～0.12 mol/L. With the increase of mole ratio of NH3/N1, the packing density of spherical nickel hydroxide increases firstly and then decreases. The mole ratio of NH3/Ni was controlled in the range of 1 to 1.2.Constant current charge-discharge tests showed that the electrochemical properties of the spherical nickel hydroxide electrode characterized with discharge capacity is generally lowered by increasing the size of crystallites and the packing density of the spherical nickel hydroxide particles. The spherical nickel hydroxide possessed a higher discharge capacity and platform potential when it has been precipitated between pH=10.5 and pH=11.5, while the nickel ions concentration was controlled in the range of 0.1-0.12 mol/L, mole ratio of NH3/Ni was from 1 to 1.2, and the reaction time is more than 24 hours.The results showed that the spherical nickel hydroxide with good flowability, high packing density and capacity was prepared when pH=11, the nickel ions concentration was controlled in 0.12mol/L, mole ratio of NH3/Ni is 1.2, and the reaction time is more than 24 hours.更多还原