【作者】 李扬；

【导师】 雷永泉；

【作者基本信息】 浙江大学 ， 材料学， 2007， 硕士

【摘要】 在对国内外稀土系非AB₅型贮氢合金的研究进展进行全面综述的基础上，本文确定以La-Mg-Ni系AB₃型贮氢电极合金作为研究对象，采用XRD分析及恒电流充放电、线性极化及恒电位阶跃放电等电化学测试技术系统地研究了Ni含量及化学计量比对La₂MgNi_x（x=8．7-9．9）合金和La₂Mg(Ni_0．85Co_0．15)_x（x=9．0-10．5）合金的相结构、电化学性能的影响规律与机制，并从中筛选出一种综合性能较好的AB_3．2型合金。在此基础上，通过采用6种合金元素部分替代La₂MgNi_9.6合金中的Ni，进一步研究了La₂Mg(Ni_0．90M_0．10)_9．6（M=Co，Mn，Fe，Cu，Al，Sn）系列AB_3．2型合金的相结构和电化学性能，考查了上述合金元素替代的影响规律，力求进一步提高合金的综合电化学性能。对于La₂MgNi_x（x=8．7-9．9）三元合金，本文系统的研究了合金的Ni含量及化学计量比x对合金相结构和电化学性能的影响。结果表明，上述合金均由一种具有PuNi₃型结构的（La，Mg）Ni₃主相及少量杂相（LaNi₅，MgNi₂）组成。随x值的增大，合金主相的晶胞体积及吸氢体积膨胀率（△V／V）均而有所降低（△V／V值由x=8．7时的24．4％降低到x=9．9时的22．3 %），合金的放氢平台压力逐渐升高。随着x值的增加，合金的最大放电容量增大，并在x=9．0时达到最大值（411．5mAh／g），然后又随x值的增大而逐渐减小。随x值的增大，合金电极的高倍率放电性能（HRD）得到明显改善，其HRD₈₀₀从38．8％（x=8．7）提高到84．4％（x=9．9）。研究发现，合金HRD的提高主要是由于合金电极的电催化活性及氢在合金中的扩散速率均随x值的增加而增大所致。经100次充放电循环后，上述合金的容量保持率(S₁₀₀)为54．1-63．4％，循环稳定性随x值增大而有所改善。在所研究的合金中，以x=9．6的La₂MgNi_9．6的AB_3．2型合金的综合性能较好，其C_max=396．8mAh／g，HRD₈₀₀=74．5％，S₁₀₀=63．4％，合金的高倍率放电性能及循环稳定性有待进一步改善。对La₂Mg(Ni_0.85Co_0．15)_x（x=9．0-10．5）合金的研究表明，上述四元合金均由一种具有PuNi₃型结构的（La,Mg）Ni₃主相及少量LaNi₅及La₂Ni₇等杂相组成，但x值的增大会导致杂相的含量明显增多。随着x值的增大，合金主相的晶胞体积及吸氢体积膨胀率（△V／V）均有所降低（△V／V值从x=9．0时的23．2％降低到x=10．5时的20．2％）。随着x值的增加，合金的最大放电容量略有增大，并在x=9．3时出现最大值（405mAh／g），然后又随x值的增大而有所降低。随着x值的增加，合金的高倍率放电性能（HRD）有显著改善(HRD₈₀₀可由x=9．0时的85．7％提高到x=10．5时的94．8％)，其原因主要是由于合金电极的电催化活性及氢在合金中的扩散速率均随x值的增加而增大所致。上述合金的循环稳定性(S₁₀₀)随着x的增加而有所降低，其S₁₀₀由x=9．0时的69．5％降低到x=10．5时38．5％。研究认为，随x值的增加，由于合金中出现有较多的LaNi₅及La₂Ni₇相，因主相和杂相吸氢体积膨胀率的不同加剧了合金纷化及腐蚀可能是导致其循环稳定性降低的重要原因。在所研究的合金中，以x=9．6时的La₂Mg(Ni_{0.85Co0．159．6}合金(AB_3．2)的综合性能较好。其C_max=390．5mAh／g，HRD₈₀₀=91．4％，S₁₀₀=66．0％，合金的循环稳定性有待进一步改善。对La₂Mg(Ni_{0．9M0．19．6}（M=Co,Mn，Fe，Cu,Al，Sn）AB_3．2型合金的研究表明，上述合金的主相基本保持PuNi₃型结构（含Al合金出现有部分氢致非晶化的现象）。M元素对Ni的部分替代使合金的晶胞体积有所增大，但可使合金的吸氢体积膨胀率有不同程度降低。上述M元素替代均使合金的放电容量有所降低(M=Mn、Fe、Cu、Al、Sn合金的C_max=195-305mAh／g)。除Sn替代的合金外，其它合金的高倍率放电性能（HRD）均较La₂MgNi_9．6合金有明显降低，但上述合金元素对Ni的部分的替代均可使合金的循环稳定性得到不同程度的改善。在所研究的合金中，以La₂Mg(Ni_0．90Co_0．10)_9．6的综合性能较好，其C_max=380mAh／g，HRD₈₀₀=43．3％，S₁₀₀=66．8％，合金的高倍率放电性能及循环稳定性有待进一步改善。更多还原

【Abstract】 In this thesis, previous research works on RE-based non-AB₅ type hydrogenstorage alloys have been extensively reviewed. On this basis, the La-Mg-Ni basedAB₃-type hydrogen storage electrode alloys were selected as the subject of this study.By means of XRD analysis and the electrochemical test methods such as galvanostaticcharge-discharge, linear polarization, potentialstatic discharge etc., the phase structureand electrochemical properties of La₂MgNi_x（x=8.7-9.9） alloys andLa₂Mg(Ni_0.85Co_0.15)_x（x=9.0-10.5） alloys were studied systematically, and from whichthe AB_3.2-type alloy with a better overall electrode properties was selected for furtherstudy. Based on these works, the effect of the substitutions of Co, Mn, Fe, Cu, Al, Snon the phase structure and electrochemical properties of the AB_3.2-typeLa₂Mg(Ni_0.90M_0.10)_9.6 alloys were studied in order to improve the overallelectrochemical properties of the alloys.For the La₂MgNi_x（x=8.7-9.9） alloys, the effects of Ni content and stoichiometricratio（x） on the phase structure and electrochemical properties of all the alloys weresystemically investigated. It is found that all the alloys mainly consist of the（La,Mg）Ni₃ phase with the PuNi₃-type structure and a few impurity phases （LaNi₅ andLaNi₂） . But the increase of x value leads to a decrease in cell volume expansion rate（△V/V） on hydriding（24.4% as x=8.7 to 22.3% as x=9.9）. With increasing of x, thedesorption plateau pressure of the alloys increases noticeably, the discharge capacityof the alloys increases slightly and passes through a maximum of 411.5mAh/g atx=9.0 and then decreases with the further increase of x. The high-ratedischargeability（HRD） of the alloy electrodes improves greatly as x increases, theHRD₈₀₀ of the alloys increases from 38.8% （x=8.7） to 84.4% （x=9.9）. The increase ofhigh-rate dischargeability of the Ni-rich alloys is ascribed to the increase of both theelectrocatalytic activity of the alloy electrode and the diffusion rate of hydrogen in thealloy bulk. As x increases, the cycling stability (S₁₀₀) of the alloys increases slightly,increasing from 54.1% （x=8.7） to 63.4 （x=9.6）, Among the alloys studied, theLa₂MgNi_9.6(AB_3.2) alloy shows a relatively good overall properties with C_max=396.8mAh/g, HRD₈₀₀=74.5%and S₁₀₀=63.4%. The high-rate dischargeabilityand the cycling stability of the alloys are needed to be further improved.The study on La₂Mg(Ni_0.85Co_0.15)_x （x=9.0-10.5） alloys shows that all the alloysconsist of the （La,Mg）Ni₃ main phase with the PuNi₃-type structure and a fewimpurity phases（LaNi₅ and La₂Ni₇）, and the increase of x leads to noticeable increaseof the content of impurity phases. The increase of x leads to a decrease in both cellvolume and cell volume expansion rate （△V/V） on hydriding（23.2% as x=9.0 to 20.2%as x=10.5）. With increasing x value, the discharge capacity of the alloys increasesslightly and shows a maximum （405mAh/g at x=9.3） and then decreases with thefurther increase of x. The high-rate dischargeability（HRD） of the alloy electrodesincreases noticeably as x increases, the high-rate dischargeability of the alloyelectrodes(HRD₈₀₀) improves greatly from 85.7% as x=9.0 to 94.8% as x=10.5. Onthe other hand, the cycling stability(S₁₀₀) of the alloys decreases with the increase of x,decreasing from 69.5% as x=9.0 to 38.5 as x=10.5. The decrease in stability of thealloys is mainly attributed to that the alloys contain more impurity phases（LaNi₅,La₂Ni₇） as x increases and the difference between the main phase and impurity phasesin cell volume expansion rate would lead to a higher degree of pulverization andcorrosion of the alloys during cycling. Among the alloys studied, theLa₂Mg(Ni_0.85Co（0.15）)_9.6 alloy shows a relatively good overall properties withC_max=390.5mAh/g, HRD₈₀₀=91.4%and S₁₀₀=66.0%. The cycling stability of thealloys is needed to be further improved.For the AB_3.2 type La₂Mg(Ni_0.9M_0.1)_9.6（M=Co, Mn, Fe, Cu, Al, Sn） alloys, it isfound all the alloys still consist of the （La,Mg）Ni₃ main phase with the PuNi₃-typestructure and a few impurity phases （LaNi₅, LaNi and LaNiSn）, while a portion of theAl substituted alloy became amorphous on hydriding. The part substitution of Melement for Ni leads to an increase in cell volume of the alloys, but leads to somedecrease in cell volume expansion rate （△V/V） on hydriding. The substitution leads tosome decrease in the discharge capacity of the alloys (C_max=195-305mAh/g as M=Mn,Fe ,Cu, Al, Sn), and leads to a large reduction in high-rate dischargeability（HRD） ofthe alloys(HRD₈₀₀=33.9-58.8%) decrease greatly except the Sn substitution one. While the substitution improved the improvement in cycling stability (S₁₀₀) of thealloys to a different extent. Among the alloys studied, the La₂Mg(Ni_0.90Co（0.10）)_9.6 alloyshows a relatively good overall properties with C_max=380mAh/g, HRD₈₀₀=43.3%andS₁₀₀=66.8%. The high-rate dischargeability and the cycling stability of the alloys areneeded to be further improved.更多还原