【作者】 李书存；

【导师】 赵敏寿；

【作者基本信息】 燕山大学 ， 应用化学， 2009， 博士

【摘要】 贮氢合金是镍-金属氢化物电池的核心材料,其综合性能的改善是提高镍-金属氢化物电池性能的关键。本研究以探索镍-金属氢化物电池新型负极材料为目的,以V基固溶体型贮氢合金为研究对象。本文以Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33合金为参比合金,以添加或取代的方法加入B、Mo、Cr、Si以及稀土La、Ce、Pr、Nd、Gd等元素,采用XRD、FESEM-EDS及TEM等方法研究了该类电极合金微观结构;针对V基固溶体合金电极吸放氢动力学性能较差及容量衰减严重等问题,采用EIS、恒电位放电及ICP-MS等分析技术对合金电极的吸放氢动力学性能及合金腐蚀情况进行表征,以期改善合金电极的吸放氢动力学性能和电化学性能。结果表明,所有合金均有V基固溶体相和C14型Laves相两相组成。添加Mo和B可提高Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33合金的放电容量,Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33B0.1合金电极在60 mA·g-1电流放电时的放电容量达到476.7 mAh·g-1。添加Si、Mo和Cr部分取代V对合金电极的循环稳定性改善明显;而Si、Mo、B和Cr的添加或取代却不同程度地降低了合金的高倍率放电性能,使合金电极表面上电化学反应的电荷转移电阻（Rct）显著增加,交换电流密度（I0）显著降低。添加B和Mo可显著改善Ti_0.26Zr_0.08V_0.24Mn_0.1Ni_0.33合金电极的高温放电性能,Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33Mo0.075合金电极在343 K高温下其放电容量仍达到633 mAh·g-1。研究了添加La、Ce、Pr、Nd和Gd五种稀土元素对Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33合金的微观结构和电化学性能的影响。结果表明,Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33和Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33RE0.01（RE = La, Ce, Pr, Nd, Gd）合金均由体心立方结构的V基固溶体主相和少量六方结构的C14型Laves相组成;在合金中加入稀土元素,会使合金中两相的晶胞体积同时增大。添加五种稀土元素都可以改善合金电极的活化性能,而对合金电极其它性能的影响则各有不同,其中添加Ce和Pr可以提高合金电极的最大放电容量,而添加Nd和Gd能改善合金电极的循环稳定性。工作温度对合金电极的放电容量影响较大,温度超过343 K时使其循环容量衰减加剧;而含稀土元素的合金电极在333 K温度下放电容量达到最大值。稀土对合金电极的荷电保持率产生一定影响;La、Ce、Pr稀土元素的添加能够改善合金电极的倍率放电性能。采用稀土元素Ce、Nd、Gd部分取代V元素,研究了Ti0.26Zr0.07V0.23Mn0.1Ni0.33RE0.01 （RE = Ce, Nd, Gd）电极合金微观结构和电化学性能。Nd元素可以有效改善合金的动力学性能,使合金电极表面上电化学反应的电荷转移电阻（Rct）显著降低,交换电流密度（I0）和氢的扩散系数显著增加;稀土元素Ce可以提高合金电极的放电容量,其最大放电容量在放电电流密度为60 mA·g-1可达403.9 mAh·g-1。研究机械球磨对Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33钒基固溶体材料的结构和电化学性能的影响。经机械球磨处理的Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33固溶体合金仍具有V基固溶体相和C14型Laves相结构;机械球磨可以明显改善Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33合金材料的放电循环稳定性,40周后的容量保持率从46.3%（t=30 min）提高到78.3%（t=180 min）;电化学阻抗和恒电位放电研究表明,球磨处理使合金电极的动力学性能提高。采用FESEM-EDS、EIS及ICP-MS技术对Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33合金电极的容量衰减机制进行研究,该合金的容量衰减涉及到以下三方面:随循环次数的增加,合金电极表面的裂纹明显加宽、加深,存在氧化现象,这既增加电极的内阻,又阻碍氢在合金内的扩散;电荷转移电阻增加,交换电流密度减小,这些动力学因素的变化使得氢化物电极的放电容量逐渐减小;合金组分元素V、Ti和Zr的腐蚀溶解明显,这是合金电极容量衰减的主要原因之一。更多还原

【Abstract】 In order to compete favorably with other advanced secondary batteries, the overall properties of hydrogen storage alloys used as negative materials in Ni/MH batteries should be substantially improved. The research and development of novel hydrogen storage alloys with high capacity, high rate dischargeability and high temperature dischargeability have obvious significance in both theoretical and practical application aspects.In this work, B, Mo, Cr, Si and rare earth elements La, Ce, Pr, Nd and Gd have been used as additive element to Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33 alloy to improve the electrocatalytic activity and the kinetic performance of the alloy electrode. The microstructure and electrochemical properties of the alloy have been investigated by XRD, FESEM-EDS, TEM, EIS, potentiostatic discharge technique and ICP-MS measurements.The results show that all alloys are composed of V-based solid solution with body-centered-cube （BCC） structure and C14 Laves phase with hexagonal structure. The addition of B and Mo increases the discharge capacity of Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33 alloy electrode and Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33B0.1 alloy delivers the discharge capacity of 476.7 mAh·g-1at discharge current of 60 mA·g-1. It is found that a small addition of Si, Mo and substitution of Cr for V greatly improve the cycle life of Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33 alloy electrode. But addition of Si、Mo、B or substitution of Cr for V decreases the high-rate discharge ability of the alloy electrode in some extent. EIS indicates that addition of Si, Mo and B or the substitution of Cr for V decreases the dynamic performance, which makes the charge transfer resistance （Rct） increases and the exchange current density （I0） decreases markedly. Considerable improvement in the high-temperature dischargeability is observed by addition of B and Mo, and the discharge capacity is up to 633 mAh·g-1 at 343 K for Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33Mo0.075 alloy electrode.The effects of five kinds of rare earth element addition on microstructure and electrochemical properties of Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33 alloys are studied in this paper. It is found that these alloys all consist of V-based solid solution with bcc structure as main phase and C14 Laves phase with hexagonal structure. The cell volumes of two phases are swelled after rare earth elements are added to the alloy. In the alloy, a new phase is found, which comprises of Ce and some other elements. Various kinds of rare earth elements can improve the activation characteristics of the electrodes alloy. However, the effect on the other performance of electrode alloy is different each other with the different rare earth elements addition. Cerium and praseodymium addition can enhance the maximum discharge capacity of electrode alloy, and neodymium and gadolinium addition improve the cycle stability of the electrode alloy. The discharge capacity of the alloys is quite sensitive to temperature, and the excessively high temperature makes the discharge capacity of the electrode alloys to degrade. The discharge capacity of the electrode alloys which contains of rare earth element is up to maximum at 333 K. The rare earth element has certain influence on the charge retention of the electrode alloy, and the addition with rare earth elements La, Ce, Pr can improve the high-rate dischargeability of the electrode alloy, respectively.Effects of rare earth elements Ce, Nd, Gd partial substitution for V on the microstructure and electrochemical properties of Ti0.26Zr0.07V0.23Mn0.1Ni0.33RE0.01 （RE = Ce, Nd, Gd） hydrogen storage alloy have been investigated. The partial substitution of Nd for V is beneficial for Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33 alloy to improve the kinetic performance, which makes the charge transfer resistance （Rct） decreases and the exchange current density （I0） and the hydrogen diffusion coefficient （D） increase markedly. The partial substitution of rare earth element Ce for V can improve the discharge capacity of the electrode alloy, and its maximum discharge capacity can reach 403.9 mAh·g-1 with discharge current density of 60 mA·g-1.In present study, high-energy ball milling （HEBM） is used to improve the cyclic stability and other electrochemical properties of Ti0.26Zr0.07Mn0.1Ni0.33V0.24 alloy. The effect of the milling time on crystallographic and electrochemical characteristics of the alloy has been investigated systematically. Electrochemical studies show that the cyclic stability of the ball-milled alloys is noticeably improved. The capacity retention rate C40/Cmax after 40 cycles increases from 46.3% （t=30 min） to 78.3% （t=180 min）, although the maximum discharge capacity of the ball-milled alloys decreases moderately. Both electrochemical impedance spectra and Potentiostatic discharge studies indicate that the electrochemical kinetics of the ball-milled alloys is improved with increasing the ball-milling time.The performances degradation of Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33 alloy electrode has been investigated. The decrease of hydrogen diffusion coefficient （D）, the increase of charge transfer resistances （Rct）, and the dissolution of V and Zr elements to KOH solution with charge/discharge cycling would be responsible for the performances degradation of the alloy electrode.更多还原