【作者】 郭蕊；

【导师】 雷永泉；

【作者基本信息】 浙江大学 ， 材料学， 2002， 硕士

【摘要】 本文首先对国内外V基固溶体型贮氢电极合金的研究进展进行了全面综述。在此基础上，本文确定了以Ti-V-Ni三元贮氢电极合金为起点，逐步优化拓展到多组元V基固溶体型合金的研究思路，通过XRD、SEM、EDS以及电化学测试等手段，比较系统地研究了不同合金组元及退火处理对合金相结构和电化学性能的影响规律，力求优化合金的相结构并提高合金的综合性能。 对于TiV_2.1Ni_x（x=0.1～0.9）三元合金，本文首先研究了Ni含量的变化对铸态合金的相结构及电化学性能的影响。结果表明，铸态合金均由V基固溶体主相和TiNi基第二相组成，第二相随合金含Ni量的增加（x≥0.3）而显著增多，并沿晶界形成三维的网状结构。电化学测试表明，较低的Ni含量（x=0.3）对合金的活化性能有利，而进一步提高Ni含量则有利于改善合金的高倍率放电性能和循环稳定性。经退火处理后，除在x≤0.5的合金中出现少量的Ti₂Ni基相之外，合金的相结构与铸态合金大体相同。主相的点阵常数及摩尔分数较铸态合金有所增大。退火处理对活化性能无显著影响，可提高合金的低倍率放电容量，但使合金的高倍率放电性能和循环稳定性下降。在所研究的合金中，铸态TiV_2.1Ni_0.5合金电极的活化性能、放电容量及循环稳定性相对较好，其活化次数为5次，在放电电流密度为25mA/g的条件下，该合金的放电容量可达400mAh/g，经30次充放电循环后的容量保持率为70.60％，但该合金电极的高倍率放电性能较差，在500mA/g下的放电容量仅为73.28mAh/g。 在对三元合金筛选的基础上，本文研究了添加不同量的Hf对TiV_2.1Ni_0.5合金相结构及电化学性能的影响。在铸态TiV_2.1Ni_0.5Hf_x（x=0～0.25）合金中，当x≥0.05时，合金的第二相由三元合金中的TiNi基相转变成六方结构的C14型Laves相，该第二相仍沿晶界呈三维网状结构分布，且其摩尔分数随着Hf含量的增加而增大。电化学测试表明，Hf含量较低（x≤0.05）时，合金的活化性能及高倍率放电性能均随合金含Hf量的增加而得到改善；Hf含量增大到x=0.12时，合金的高倍率放电性能最好，但活化性能略有下降，且最大放电容量明显降低；进一步增加Hf含量，合金的活化性能无明显变化，但高倍率放电性能显著下降。Hf的加入使合金电极的循环稳定性恶化。经退火处理后，x=0.025的合金中也出现了少量的C14型Laves相。退火态合金中主相的晶胞体积有所减小，而第二相的晶胞体积有所增大，第二相的摩尔分数略有增加。退火处理可提高x=0.025合金电极的活化性能及低倍率放电容量，还可不同程度地改善x≥0.05合金电极的高倍率放电性能（x=0.12的合金除外），但退火处理使合金的循环稳定性均较铸态时有所下降。在所研究的合金中，铸态TiV_2.1Ni_0.5Hf_0.05合金电极的放电容量最高，在第一次循环即可达444mAh/g（放电电流为25mA/g）。但该合金电极在放电电流为400mA/g时的高倍率放电性能(HRD₄₀₀=C₄₀₀/C₂₅×100％)仅为 浙 江 大 学 硕 士 学 位 蛤 文 26．5％，合金电极的循环稳定性也比较差，经30次充放电循环后的容量保持率 仅为 30石3％。 在优选出的 TIV川＊们Hfo。。四元合金的基础上，针对该合金循环稳定性差的 特点，本文又进一步研究了Co、Cr、Nb和Ta等添加元素在合金中的作用。合 金相结构的研究表明，在卫 川NiNHfo叮合金中添加少量的 Co、Cr或Nb和 Ta 后，合金仍由 V基固溶体主相和 CI4型 Laves相第 h相形成的H维网络结构所 组成，但合金中的第二相有不同程度的增加。退火后，合金中主相和第二相的 数量也有所变化。其中，在添加了C。或＊r的合金中，主相的摩尔分数增大： 在添加了 Nb和 Ta的合金中，主相的摩尔分数保持不变或有所增加。电化学测 试表明，Co和 Cr可以改善合金电极的高倍率放电性能和循环稳定性，如铸态 TIV。；NI。。Hfo。。CO。；。。和TIV。；NI。。Hfo0。Cio；。。合金电极的H RDRD尽口口可提高至so．15一 刀斗0％，经3o次充放电循环后的容量保持率可达78．86－87．32％。但同时也使合 金电极的活化次数增多，最大放电容量显著下降O29上 卜退火处理使 含 C。合金的高倍率放电性能进一步有所改善（退火态n 川NiuHfo叮CO川Q的 HRD。。。提高到67．41％），可提高含Cr合金的低倍率放电容量，并在一定程度上 改善其高倍率放电性能。另一方面，Nb和Ta的加人不会影响合金的活化性能， 使合金的低倍率放电容量有所下降O403 X 但可使合金的高倍率放电 性能和循环稳定性得到改善。其中，铸态TIV川NiMHG们Nb。们，的Hm川。为 64．18O，铸态 TIV。；Ni。；HG。。Nb。。。山。。，的容量保持率（30次循环后）达至 71石5％，相对较好。退火处理后，上述合金的活化性能未发生变化，低倍率放 电容量得以提高＊ ＊ 卜 但合金的高倍率放电性能及循环稳定性均较 铸态时明显下降，退火态TIV川Ni。；HG。爿b。m，的更多还原

【Abstract】 In this thesis, previous research work on V-based hydrogen storage electrode alloys were exhaustively reviewed first. On this basis, the research scheme for improving the phase structures and electrochemical performance of the ternary Ti-V-Ni alloys by means of multi-component alloying and anneal treatment was chosen and the method of step-by-step optimization was adopted. XRD analyses, SEM/EDS investigations and electrochemical measurements were used in this research.For ternary TiV21Nix (x=0.1-0.9) electrode alloys, the effects of Ni content on the phase structure and electrochemical properties were systemically investigated. It was found that all the as-cast alloys composed of a V-based solid solution main phase and a TiNi-based secondary phase. As the Ni content (x>0.3) increased, the amount of the secondary phase significantly increased and a three-dimensional network formed along the grain boundaries of the main phase. The electrochemical measurements showed that a little Ni content (x=0.3) was helpful to the activation property, and increasing the Ni content further can improve the high-rate dischargeability and the cycle stability of the alloys. After anneal treatment, there were little changes in the phase structure but a little Ti2Ni-based phase appeared in the alloys with Ni content x<0.5. Comparing with the as-cast alloys, the volume of unit cell and molar fraction of the main phase increased. It was found that anneal treatment can lead to an increase in discharge capacity but a decrease in high-rate dischargeability. The TiV2.1Ni0.5 alloy had a better activation property, a larger discharge capacity and a higher cycle stability. This alloy can be activated in 5 cycles and had a discharge capacity of 400mAh/g at a discharge current of 25mA/g. Furthermore, the TiV2..1Ni0.5 alloy showed a capacity retention rate of 70.60% after 30 charging-discharging cycles. However, its discharge capacity was only 73.28mAh/g at a higher discharge current of 500mA/g.On the basis of the above work, the quarternary alloys TiV2 ,NiOJHfx (x=0~0.25) was studied. It was found that the secondary phase changed from the TiNi-based phase to a C14 Laves phase after adding proper Hf (x>0.05) to the as-cast TiV2.1Ni0.5 alloy. The C14 Laves phase increased with the increase of Hf content and still precipitated as a three-dimensional network along the boundaries of the main phase. For the alloys with x < 0.05, both the activation property and high-rate dischargeability were improved with the increasing Hf content; And when the Hf content reached to 0.12, the alloy had the highest high-rate dischargeability but a worse activation property and a smaller discharge capacity; further increasing thecontent of Hf, the high-rate dischargeability decreased significantly. Additionally, adding Hf always led to a degradation in cycle stability of the alloys. After anneal treatment, some C14 laves phases also appeared in the alloy with x=0.025. Comparing with the as-cast alloys, the volume of the unit cell of the main phase contracted but that of the secondary phase expanded for the annealed alloys. At the same time, the amount of the secondary phase increased. As for the electrochemical performance, anneal treatment resulted in an increase in activation property and discharge capacity as x=0.025, and an improvement in high-rate dischargeability to some extension as x >0.05 (except the alloy with x=0.12). Among the alloys studied above, the as-cast TiV2 ,Ni0.5Hf0.05 alloy showed the highest discharge capacity of 444mAh/g (at 25mA/g) at the first cycle, but its high-rate dischargeability HRD400 was only 26.50% and its capacity retention was only 30.63% after 30 cycles.To improve the cycle stability of the. TiV2 ,Ni0.5Hf0.05 alloy, we chose Co, Cr, Nb and Ta as the adding elements and the TiV2 ,Ni0.5Hf0.05Mx (M=Co, Cr, Nb and Ta; x=0~0.192) were studied. It was found that the addition of Co or Cr or Nb and Ta gave rise to a decrease of the amount of the main phase and an increase of the amount of the secondary phase without change in t更多还原