快速凝固过化学计量比无钴储氢合金的相结构及电化学性能研究

【作者】 焦高峰；

【导师】 康龙；

【作者基本信息】 兰州理工大学 ， 材料学， 2004， 硕士

【摘要】 本文以无钴过化学计量比稀土系储氢合金La（NiMnM）x（x=5.6～6.0，M=Cu、Al、Fe、Sn等）为研究对象，采用DTA、XRD、SEM／EDS以及电化学测试等手段，比较系统地研究了储氢合金的化学计量比以及退火处理和快速凝固等制备技术对上述储氢合金组织结构和电化学性能的影响，提高储氢合金的电化学性能。 La（NiMnM）_6.0（M=Cu、Q、Sn、Co）快速凝固（≥30m／s）合金以及低温退火（≤500℃）合金均为单一的CaCu₅型结构，高温退火合金中有第二相析出，主相保持CaCu₅型结构。电化学测试结果表明，快速凝固合金活化困难（7～12次），容量低，高倍率放电性能差，但循环稳定性好。退火后合金活化性能得到改善（1～3次），容量提高，高倍率放电性能提高，循环稳定性降低。快速凝固合金经过不同元素替代Ni后电化学性能表现也各不相同，高温（1000℃×24h）退火处理后Cu0.2合金容量提高到299mAh／g，循环稳定性降低S₁₀₀=86％；而Sn的替代降低了合金容量（216mAh／g），提高了循环稳定性(S₁₀₀=97％)。 快速凝固La（NiMnM）5.6（M=Cu，Al，Fe，Sn）合金以及低温退火合金均为单一的CaCu₅型结构。快凝合金成分均匀，晶粒为细小柱状晶；低温退火使合金的晶粒长大，快凝的组织形貌消失。电化学实验表明，快速凝固过化学计量比合金LaNi_4.68Mn_0.93的容量相对快凝AB_6.0合金有很大提高，但循环稳定性降低；Al、Fe元素替代的合金提高了最大放电容量，循环稳定性提高；Cu、Sn元素替代合金容量降低，循环稳定性提高；活化次数需要6次循环以上才能达到最大放电容量。低温退火La（NiMnM）_5.6（M=Cu，Al，Fe，Sn）合金的活化性能改善（1-6次），容量提高，但循环稳定性下降。Cu_0.2合金的高倍率放电性能在退火后改善，而Al_0.2和Fe_0.2合金在退火后高倍率放电性能降低。 对不同计量比和冷却速度的快速凝固合金的研究结果表明，冷却速度35m／s，成分为LaNi_4.48Mn_0.93Al_0.2经400℃×1h退火处理的合金具有较好的综合电化学性能，其活化次数为4次，最大放电容量C_max=311mAh／g，高倍率放电性能HRD₆₀₀=79.25％，100次循环后容量保持率S₁₀₀=89％。 由此可见，将过化学计量比的储氢合金通过元素替代进行快速凝固加低温退火处理可有效改善其电化学性能，从而达到降低钴含量的目的。更多还原

【Abstract】 In this paper, the La (NiMnM) x (x=5. 6~6. 0, M=Cu Al Fe, Sn) Co-free nonstoichiometric rare earth hydrogen storage alloys were studied. By means of DTA, XRD analysis, SEM/EDS investigation and electrochemical measurements, the effects of chemical composition, the composition and the preparation process such as annealing and rapidly quenching on the phase structures and electrochemical properties were studied systemically.La(NiMnM)6.0(M=Cu,Cr,Sn, Co) melt-spun alloys (>30m/s) and annealed alloys at lower temperature (<500C) consist of single LaNi5 phase with CaCu6 type crystal structure. Annealed at higher temperature, it changed to two phases. The electrochemical performance measurement shows that the melt-spun alloys have the more activation number (usually 7to 10 times), and lower discharge capacity, higher cycle stability. After annealing, the activation property is largely improved, and higher discharge capacity, lower cycle stability. After Ni replaced different elements by annealed high temperature , the alloy of CuO. 2 have hige discharge capacity (299mAh/g) and low cycle stability(Sioo= 86%) ;But the alloy of Sn have lower discharge capacity(2116mAh/g) and higher cycle stability(S100= 97%).La (NiMnM) 5.6 (M=Cu, Al, Fe, Sn) melt-spun alloys (>30m/s) and annealed alloys at lower temperature (400*C X lh) consist of single LaNi5 phase with CaCu5 type crystal structure. Melt-spun alloys remain fine and homogenous cellular and strip structure. After annealed at low temperature, crystal grains grow up, stucture pattern changed. The electrochemical performance measurement shows the discharge capacity of LaNi4.68Mn0.93 is higher than AB6.0, and lower cycle stability. After replaced Sn Cu Al Fe,melt-spun alloys of Al, Fe increase discharge capacity and cycle stability, Cu> Sn reduce discharge capacity and increase cycle stability. After annealing, improveing activation property, increasing discharge capacity and reducing cycle stability.Among all the melt-spun and melt-spun+annealed.alloy samples prepared, the one with LaNi4.48Mn0.93Al0.2, and annealed at 400C for lh has the best general performance: its activation number 4 times, the maximum discharge capacity Cmax=311mAh/g, high-rate discharge ability HRD600=79.25%, and capacity retention S100=89% after 100 cycles.It is seen therefore that nonstochiometric hydrogen storage alloys after melt-spun and low temperature annealing will have an improved electrochemical properties with decreased usage of cobalt metal.更多还原