【作者】 李超群；

【导师】 李新海；

【作者基本信息】 中南大学 ， 冶金工程， 2013， 博士

【摘要】 集流材料是组成电池的重要部件。本文选取冲孔钢带为研究对象,通过减薄、表面粗糙化、镍沉积和热处理工艺改善冲孔镀镍钢带的性能。首次应用电解加工方法同步实现了冲孔钢带的减薄和表面粗糙化。减小冲孔钢带(钢带)的厚度,能更好地解决极板的卷绕性能,提高单位体积内活性物质的载量,增大电池的容量；加大冲孔钢带表面粗糙度,从而增大其比表面积,能改善沉积层与冲孔钢带结合强度,增强与活性材料的粘结性,减小接触电阻和电化学极化,提高电池的电化学性能。对于0.045mm冲孔钢带在最优电解加工条件下,厚度减小了16.56μm；电解加工后表面粗糙度由0.23μm增加到0.491μm,表面残余应力由102.5Mpa降至24.87Mpa。利用氧化还原反应原理和E-pH图,通过加入抗坏血酸,增强了电解加工溶液的稳定性,详细分析了抗坏血酸还原Fe3+离子的反应机理,推导出动力学方程,计算出二级反应速率常数是5.5688(mol/L)-1.min-1。抗坏血酸可重复使用,无毒、对环境友好。利用柠檬酸钠较高的缓冲容量和配位性质,结合镍-柠檬酸钠体系电位-pH图,成功地实现了用柠檬酸钠取代硼酸用作镍沉积溶液的缓冲剂,消除了硼酸对人类和环境造成极大的危害。在pH=3-5范围内,硼酸和柠檬酸钠镀镍溶液的缓冲容量分别是0.01lmol/L和0.025mol/L,实验结果表明：柠檬酸钠是一种优良、实用和对环境友好的硼酸替代品,柠檬酸钠镀液是具有电流效率高、缓冲容量大、分散能力好、电导率高和极化度大的性能良好的电解液。首次用电化学阻抗技术研究了柠檬酸钠镀镍溶液中镍的电沉积行为,沉积过程分两步得到两个电子,其中第一个得电子转移步骤是速度控制步骤,反应中生成了一价镍离子的吸附态的电活性中间产物Ni(OH)ads,而且吸附态的中间产物是以电感的形式影响电极反应的阻抗。从理论上推导了电极反应速度的动力学方程,通过实验验证,得出了动力学参数为：阴极过程Tafel斜率为0.142V,表观传递系数α=0.49,交换电流密度是7.56×10-6A/cm2,反应级数为ZNi2+＝1,在pH=2-5的缓冲溶液中,OH-浓度对电极反应速度影响不大,Ni(OH)ads覆盖率0不能忽略,表观活化能平均值为50.3kJ/mol.首次采用循环伏安法和计时电流法研究了柠檬酸钠镀镍溶液中镍电结晶规律。在低过电位下(-0.9～-1.0V),Ni初期电结晶成核／生长过程遵循三维连续成核机制；高过电位下(-1.1～-1.5V),镍的初期电结晶成核/生长方式遵循瞬时成核机制。在两种模式下分别计算出镍离子的扩散系数D为(1.63±0.48)×10-7cm2·s-1和(1.074±0.093)×10-6cm2.s-1.柠檬酸钠对镍垂直于基体表面方向的生长速率有妨碍作用,而硫酸镍有一定的促进作用。检测了冲孔镀镍钢带的性能,硬度、结合强度、孔隙率和腐蚀试样评级都符合《可充电电池用冲孔镀镍钢带》标准要求。在优化条件下得到的表面粗糙度是0.41μm。用浸泡法、动电位扫描极化曲线和电化学阻抗谱对冲孔镀镍钢带的抗腐蚀性能进行研究,结果表明：冲孔镀镍钢带极化电阻大,腐蚀电流小,电荷转移阻抗高,腐蚀速度小,抗腐蚀性强,从镍-柠檬酸钠溶液中得到的冲孔镀镍钢带改善了抗腐蚀性能。粗糙腐蚀是引起腐蚀速度加快的原因之一。用动电位极化曲线和XPS证实冲孔镀镍钢带在5%NaCl溶液腐蚀介质中有钝化膜形成,认为冲孔镀镍钢带具有较好的耐蚀性能原因是：镍沉积层的包覆隔离作用,阻止了冲孔钢带基体与腐蚀介质的直接接触；而钝化膜形成,在试样表面产生较致密的钝化保护,降低了腐蚀反应的电流密度。采用EDS分析方法,测量了镀镍钢带热处理后的Fe和Ni浓度分布曲线,通过应用玻尔磁曼-俣野法计算出不同温度和浓度下的铁镍互扩散系数,计算出不同铁浓度时的频率因子、扩散活化能。应用动电位扫描极化曲线和电化学阻抗谱方法测试了镀镍钢带不同热处理工艺后的防腐性能,热处理工艺改善了镀镍钢带的耐腐蚀性和抗溶液渗透性,当表面露铁率超过30%,抗腐蚀性显著下降。图179幅,表68个,参考文献295篇。更多还原

【Abstract】 The collecting materials is an important component of cell. In this thesis, the hole-punched steel strip has been studied and its mechanical and electrochemical performance are improved by reducing the thickness, roughening the surface, Ni electrodeposition and heat treatment.For the first time, the reduction of thickness and surface-roughing of hole-punched steel strip are accomplished by electrochemical machining method. By reducing the thicknesses of hole-punched steel strip, and thus the volume occupied by such non-reactive elements are reduced, the winding performance of batteries electrode plate can be improved. The fraction of the battery devoted to holding electrochemically active material therein is increased, with corresponding increase in the capacity of the battery. By roughing of surface, the hole-punched steel strip has a high surface roughness, which result in the increase of the specific surface area, provides the desired improvement in adhesive bonding of the nickel plated layer to the base steel strip, enhances the amount of physical and electrical contact and the better adhesion between the active material and Nickel plated punched steel strip so as to reduce the contact resistance and the electrochemical polarization to increase the battery electrical performance. Under the optimal conditions of electrochemical machining, the thickness of hole-punched steel strip can be reduced to28.44μm(theoretical value:25.63μm), the surface roughness increases from0.23μm to0.49μm. The original deformation layer is partially or completely removed and the metallographic structure of the hole-punched steel strip is not changed. The residual stress decreases from102.5Mpa to24.87Mpa.According to the redox reaction principle and E-pH diagram, ascorbic acid is added to the Fe-riched chloride electrolyte to slow down the oxidation of Fe2+in the baths. In the presence of ascorbic acid, there is a tendency to decrease pH of solution and to reduce ferric to ferrous. The mechanism of the reduction of Fe3+ion by ascorbic acid is analyzed in details and the kinetic equation is derived. The second order reaction rate constant is5.5688(mol/L)-1.min-1. Ascorbic acid is a non-toxic and environmental friendly ingredient, it can be used repeatedly.Using higher buffering capacity and coordination properties of sodium citrate, combined with Ni-citrate system E-pH diagram, a new electrolytes for nickel electrodeposition, which contains sodium citrate instead of boric acid as the butter has been developed. Owing to high toxicity of boron compound, it causes serious pollution to the environment if the direct discharge of wastewaters without treatment. The citrate bath exhibits excellent buttering capacity (0.025mol/L) for bath pH3-5, which are comparable with those of the watts bath (0.011mol/L). The results show that a citrate bath offers an excellent, practical, and more environmentally friendly substitute for boric acid in a Watts bath. The electrolytes provide good electrochemical performance, such as high current efficiency, good butter properties, high values of the throwing power, the electrical conductivity and cathodic polarization.For the first time, the electrodeposition mechanism of Nickel from citrate bath is investigated by means of electrochemical impendence spectroscopy (EIS) method. The influence of the deposition potential, electrolyte composition and technological conditions on the charge transfer resistance and capacitance are systematically investigated during the Nickel electrodeposition. By analyzing the EIS spectroscopy, it can be concluded that the mechanism of Ni electrodeposition as follows:in the acidic citrate bath, it involves two consecutive one-electron charge transfers, the first involving the participation of an anion(assumed to be OH") with formation of an adsorbed complex Ni(OH)ads followed by subsequent reduction to Ni. The rate-determining step is the first electron transfer reaction. The low frequency inductive loop is ascribed to the relaxation of the electrode coverage by an adsorbed intermediate NiOHads, the kinetic equation of electrode reaction can be derivated from the theoretical views and verified by experiment. The results indicate as follows:the Tafel slope of the cathodic process is0.142V decade-1, the apparent transfer coefficient a is0.49, the exchange current density is 7.56×10-6A/cm2, the order of the reaction is1with respect to Ni2+. When the electrolyte pH varies between2-5, no dependence of cathodic rate constants on pH can be found. The coverage of intermediate Ni(OH)ads can not be ignored, the average value of the apparent activation energy of electrochemical reaction is50.3kJ/mol.For the first time, the mechanism of electrocrystalline of nickel on vitreous carbon from citrate bath is investigated by cyclic voltammetry and chronoamperometry methods. Electrochemical tests show that nickel electrodeposition may begin at applied potential-0.9V or so. Under lower overpotential (applied potential:-0.9～-1.0V), the electrocrystalline process of Ni from citrate bath in the initial stage follows the mechanism of Scharitker-Hill three dimensional progressive nucleation and growth manner. Under higher overpotential (applied potential:-1.1～-1.5V), the deposition nucleation of Ni in the initial stage follows the instantaneous nucleation and growth of Scharitker-Hill mechanism with three-dimensional. The nucleation time of Ni-citrate solution system may gradually be shortened with the increase of overpotential. By analyzing of the potentiostatic transients, the diffusion coefficient D of the depositing nickel ions is (1.63±0.48)×10-7cm2·s-1under the progressive nucleation and growth mechanism, and (1.074±0.093)×10-6cm2·s-1under the instantaneous nucleation and growth mechanism respectively. Sodium citrate may causes an inhibition of outward growth rate of Ni deposits, and nickel sulfate may accelerate both nucleation and crystal growth.The performances of nickel plated punched steel strip are tested, such as microhardness, adhesion, porosity, surface roughness and rating of test specimens subjected to corrosion tests, and so on. The results show that products meet the requirements of "nickel plated punched steel strip for rechargeable battery" standard. Under the optimal electrodeposition conditions, the surface roughness of the as-deposited Ni is0.41μm when the thickness of the deposit layer is about6μm, smaller than that of base steel strip processed by electrochemical machining.The influence of electrolyte compositions and technological conditions on electrochemical corrosion behavior of the nickel plated punched steel strips in5%NaCl corrosion media is characterized by immersion corrosion tests, potentiodynamic polarization tests and electrochemical impedance spectroscopy methods. The results reveal that the Ni deposited from citrate bath has higher polarization resistance, smaller corrosion current, higher charge transfer resistance and smaller corrosion rate, compared with that from Watts bath. It exhibits superior corrosion resistance, and the results calculated from potentiodynamic polarization tests are in good agreement with those obtained from impedance measurements. The magnitude of corrosion rate of the Ni deposits decreases with increasing of sodium citrate concentration. The Ni deposits with rough surfaces may accelerate the corrosion reaction rate in5%NaCl solution. All the nickel samples exhibits active-passive potentiodynamic polarization behavior. The results shows that passive film formed on the Ni deposits, and confirmed by X-ray photoelectron spectroscopy (XPS) surface analysis. The XPS analysis indicates that the passive film is composed of stable, continuous Ni hydroxide and NiO. The improved corrosion resistance of Ni in NaCl solution can be explained as follows:Ni prevent the punching steel strip from direct imposing in the corrosion media and passive film formation seems to be another dominant factor, because Ni is a metal that can be passivated easily. The insoluble Ni(OH)2and NiO cover the surface of the corroded samples and create the passivation region so as to reduce the corrosion rate.The concentration distribution profiles in the neighborhood of interface after heat-treatment are measured by EDS. The interdiffusion coefficients at different temperature and concentration of Fe are calculated by Boltzmann-Matano analysis. Within the range of about600℃to750℃for a soaking time of2hours, the diffusion frequency factor, and activation energy of diffusion are estimated.The anti-corrosion properties of nickel plated punched steel strip in5%NaCl solution are measured by potentiodynamic polarization tests and electrochemical impedance spectroscopy methods after various heat-treatment process. The results show that the corrosion resistance and resistance to penetration of aqueous medium are far better than those of as-deposited Ni. However, in this heat-treatment, the thickness of a Fe-Ni diffusion layer should be controlled so that the Fe/Ni ratio is within the range of30%or less on the surface of the nickel plated punched steel strip. When the Fe/Ni ratio exceeds30%, the corrosion resistance substantially decreases as the exposure rate of iron increases.更多还原