Phase structure and electrochemical characteristics of high-pressure sintered La-Mg-Ni-based hydrogen storage alloys

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• 作者：Jingjing Liu ; Shumin Han ; Yuan Li ; Yifei Lv ; Shuqin Yang ; Junling Zhang ; Jinding Wang
• 关键词：La&ndash ; Mg&ndash ; Ni-based alloy ; High pressure sintering ; Phase structure ; Electrochemical characteristics ; Electrochemical kinetic property
• 刊名：Electrochimica Acta
• 出版年：30 November, 2013
• 年：2013
• 卷：111
• 期：Complete
• 页码：18-24
• 全文大小：1772 K

文摘

A novel method high-pressure sintering was applied to prepare La_0.25Mg_0.75Ni_3.5 alloy as negative electrode material for nickel/metal hydride battery. The phase structures, electrochemical performance and electrochemical kinetics of the alloys sintered with various pressures have been investigated. When sintered within 1.5-2.5 GPa, the alloys have Ce₂Ni₇-type and Pr₅Co₁₉-type main phases and LaNi₅ minor phase. Pressurizing promotes the formation of Ce₂Ni₇-type phase with higher crystalline density. But when the sintering pressure reaches 4 GPa, the atomic diffusion is hindered, leading to the rise of LaNi₅ phase, appearance of MgNi₂ phase, and decrease of Ce₂Ni₇-type and Pr₅Co₁₉-type phases. Electrochemical measurements show that when the sintering pressure changes from 1.5 to 4 GPa, the maximum discharge capacity first increases then decreases. The alloy electrode sintered at 2 GPa shows superior high rate dischargeability and the gentlest capacity decrease with increasing discharge current density. Furthermore, kinetic study demonstrates that the reaction of alloy electrodes is controlled by charge-transfer step. Cycling stability is deteriorated as the sintering pressure increases due to higher expansion ratio of the cell volume and denser structures of the alloy.