【作者】 同艳维；

【导师】 高家诚；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2014， 博士

【摘要】 V基贮氢合金电极具有较高的放电容量，是作为Ni-MH电池负极的核心材料。然而，较高的成本和较低的循环稳定性能限制了其产业化发展。本文是在全面综述V基贮氢合金电极研究进展的基础上，从降低成本和改善合金电极循环稳定性能出发，选择较低V含量的VTiCrNi四元合金为基础合金，以添加或取代的方式加入Mo、Mn、Sn元素以及V2O5金属氧化物。采用XRD、SEM等研究了合金电极的微观结构；采用高倍率放电、电化学阻抗、线性极化以及恒电位放电对合金电极的电化学性能进行表征；采用ICP分析了合金电极充放电后在电解液中的腐蚀成分。最后，通过在电解液中添加ZnO，研究其对合金电极性能的影响。对V2Ti1-xNiCrx（x=0.1-0.7）合金电极的组织结构及电化学性能进行了研究。结果表明，合金均由BCC结构的V基固溶体主相和TiNi二次相组成，BCC结构的V基固溶体呈树枝状均匀分布，而TiNi二次相则以三维网状结构分布在V基固溶体主相的周围。合金电极的活化性能以及最大放电容量均随着Cr替代Ti含量的增加有所减低；而合金电极经过30次充放电后的容量保持率C30/Cmax先升高而后降低，在x=0.5时达到最大值，为91.3%；高倍率放电性能先增大而后减小，适量的Cr替代Ti有利于降低合金电极表面阻抗，提高氢的扩散系数。因此，合金电极的性能和Ti、Cr比例有关，当Cr替代Ti含量x=0.5时，合金电极具有最佳的电化学性能。通过对V2Ti0.5Cr0.5Ni1-xMx（M=Mo、Sn、Mn）体系合金电极组织结构和电化学性能研究发现，所有合金均具有两相结构，即BCC结构的V基固溶体主相和TiNi二次相，V基固溶体主相呈树枝状分布，TiNi二次相以三维网络状分布在V基固溶体相的周围。Mo和Sn替代Ni对合金电极的最大放电容量Cmax影响不是很大，而Mn替代Ni后，合金电极的最大放电容量明显增大，在x=0.2时，最大放电容量达到429.3mAh/g。所有合金电极的容量保持率随着充放电循环过程的进行均有所降低，尤其是含Mn合金电极的容量衰退最为严重，这主要是由于含过多的Mn的合金在充放电循环过程中，易造成Mn的偏析，合金严重粉化，导致合金电极的循环稳定性能变差。电化学动力学研究表明，含Mo的合金电极电化学动力学性能随Mo替代Ni含量的增加先得到改善，而后降低，在x=0.04时，合金电极的高倍率放电性能，交换电流密度和氢扩散系数均得到最佳值。而Sn和Mn替代Ni之后，合金电极的交换电流密度和高倍率放电性能都降低，不利于合金电极的电化学动力学性能。对V2-xTi0.5Cr0.5NiOx（x=0-0.35）合金电极的组织结构和电化学性能研究，结果表明，当x=0时，合金由BCC结构的V基固溶体相和呈三维网状结构分布在主相周围的TiNi相组成，随着x值增加，合金中出现了Ti4Ni2O新相。电化学测试结果表明，随着合金电极中V2O5替代V含量的增加，合金电极的最大放电容量降低，由x=0时的366.8mAh/g减小到x=0.35时的225.3mAh/g。而合金电极的循环稳定性能得到了改善，经过100次充放电循环后，合金电极的容量保持率由x=0时的69.9%增大到x=0.2时的83.7%。电化学测试结果表明，随着合金电极中V2O5替代V含量的增加，合金电极的高倍率放电性能、交换电流密度和氢的扩散系数先增大后减小，合金电极在x=0.05时综合电化学性能较好，其最大放电容量Cmax为352mAh/g，合金电极经过100次充放电循环后的容量保持率为73.7%，放电电流密度为400mA/g时的倍率放电性能（C400/C60）为70.3%，氢的扩散系数D为6.51×10-11cm2/s。通过分析V2Ti0.5Cr0.5Ni0.9Mn0.1和V2Ti0.5Cr0.5Ni0.8Mn0.2合金电极在充放电循环过程中的电极表面形貌、电化学性能以及合金元素在电解中的腐蚀溶解量得出：随着充放电过程的进行，合金电极表面裂纹明显加宽、加深，这既增加了合金电极内阻，又阻碍了氢在合金体内的扩散，从而导致电荷转移电阻增大，交换电流密度减小，这些因素使得合金电极的放电容量降低，而合金电极中V和Ti元素的腐蚀溶解严重。结果表明，贮氢合金的容量衰退主要是由于合金电极在充放电过程中，活性吸氢元素在电解液中的腐蚀溶解、合金颗粒的粉化、合金电极表面元素的氧化腐蚀以及不可逆氢化物的形成。通过在电解液中添加不同含量的ZnO，分析了在添加不同含量ZnO的电解液中合金电极的表面形貌及电化学性能，发现电解液中添加ZnO明显改善了合金电极的循环稳定性能，当50mL KOH电解液中ZnO添加量为1.2g时，合金电极经30次充放电循环后的容量保持率最大，为97.8%。而随着电解液中ZnO含量的增加，合金电极的放电平台变窄，而且倾斜，表明电解液中添加过量的ZnO对合金电极的放电性能产生不利作用。合金电极的交流阻抗值随着电解液中ZnO含量的增加先减小而后增大，而相应的交换电流密度先增大后减小，在50mL KOH电解液中添加0.8g ZnO时，合金电极的动力学性能相对较好。更多还原

【Abstract】 V-based hydrogen storage alloys were used in Ni/MH due to their high dischargecapacity. Whereas, the high costs and poor cycling stability of this type of alloys preventthem from developing in industry. In this thesis, in order to reduce costs and improvethe cycling stability, based on an overall review of the research and development ofV-based hydrogen storage alloy electrodes, The elements of Mo, Mn, Sn and V2O5metal oxides have been used as the additional element to VTiCrNi alloy, which iscomposed of lower O content. The microstructure and electrochemical properties of thealloy electrodes have been investigated by SEM, XRD, EIS, liner polarization andpotential step and ICP measurements. Moreover, the addition of ZnO to the alkalineelectrolyte has been investigated.The structural and electrochemical properties of the V2Ti1-xNiCrx（x=0.1-0.7）alloy electrodes have been systematically studied. The results show that all of the alloysmainly consist of a V-based solid solution phase with a BCC structure and a TiNisecondary phase. With increasing the content of Cr substitution for Ti, theelectrochemical activity and maximum discharge capacity is decreased, while thecharge/discharge cycling stability first increased and then decreased, and geting its bestvalue （91.3%） at x=0.5. Electrochemical kinetic measurements show that withincreasing the content of Cr substitution for Ti, the high rate dischargeability （HRD）,the exchange current density I0and the hydrogen diffusion coefficient D in the alloyelectrodes are all first increased and then decreased. It is found that a moderate contentof Cr substitution for Ti is favorable for improving the electrochemical property of thealloy electrodes, and reaching a relatively good overall electrochemical properties atx=0.5.The effects of Mo, Sn and Mn element subsitution on microstructure andelectrochemical properties of V2Ti0.5Cr0.5Ni alloy electrodes are studied in this paper. Itis found that all of these alloys composed of V-based solid solution with BCC structureas main phase and TiNi secondary phase, and the TiNi phase precipitates along the grainboundary of the BCC main phase and forms a three-dimension network. Moreover, it isfound that an substitution of Mn for Ni can increase the maximum discharge capacity ofthe alloy electrodes obviously, and reach the maximum value429.3mAh/g at x=0.2, butdecrease the cycling stability at the same time. The electrochemical kinetic measurements show that a moderate content of Mo substitution for Ni can improve theHRD, exchange current density and hydrogen diffusion coefficient, and reach the bestperformance at x=0.04. With increasing the content of Mn and Sn subsitution for Ni, theHRD, exchange current density and hydrogen diffusion coefficient is decreased, so itnot benefit for improving the electrochemical properties of the alloy electrodes.The different content of V2O5substitution for V on the microstructure andelectrochemical properties of V2Ti0.5Cr0.5Ni alloy electrodes have been investigatedsystematically. It is found that the alloy V2Ti0.5Cr0.5Ni without V2O5consists of aV-based solid solution phase with BCC structure and TiNi secondary phase, withincreasing the content of V2O5substitution for V, a new phase Ti4Ni2O appears in thealloys. The electrochemical measurements show that with increasing the content ofV2O5the maximum discharge capacity of the alloy electrode decreases from366.8mAh/g （x=0） to225.3mAh/g （x=0.35）; The cycling stabiling improves remarkably,when x=0.2, the ratio of remaining capacity after100cycles is83.7%; The high ratedischargeability （HRD）, exchange current density and hydrogen diffusion coefficientfirst increased and then decreased. Among the alloys studied, the V1.95Ti0.5Cr0.5NiO0.05alloy electrode shows a relatively good overall electrochemical properties, of which theCmax, the C100/Cmax, the HRD400, the I0and D are352mAh/g，73.7%,70.3%,33.31mA/gand6.51×10-11cm2/s, respectively.In order to explain the cycling degradation mechanism of the V-based hydrogenstorage alloy electrode, V2Ti0.5Cr0.5Ni0.9Mn0.1and V2Ti0.5Cr0.5Ni0.8Mn0.2alloy electrodeshave been studied by means of XRD, SEM and EIS measurements. It is found that thedegradation of the discharge capacity is mainly caused by the pulverization alloyparticles and the oxidation/corrosion of the alloys during cycling in the KOH alkalineelectrolyte. The results of ICP analysis on the electrolyte indicate that the dissolutioncontent of main hydrogen absorbing elements V and Ti increasing with charge/dischargecycling, which is responsible for the cycling degradation mechanism of the alloyelectrode.The effects of introducing ZnO into electrolyte on the surface and electrochemicalproperties of alloy electrodes have been investigated. It is found that introducing ZnOinto electrolyte can improve the cycling stability and electrochemical kinetic propertiesof the alloy electrode. When1.2g ZnO is added into50mL KOH electrolyte, the ratio ofremaining capacity of the alloy electrode is97.8%after30cycles charge/discharge.With increasing the content of ZnO, the EIS decreases first and then increases, while the exchange current density first increased and then decreased. When0.8g ZnO is addedinto50mL KOH electrolyte, the alloy electrode shows a relatively good overallelectrochemical properties.更多还原