Effects of Ti on the cycle life of amorphous MgNi-based alloy prepared by ball milling
Effects of Ti on the cycle life of amorphous MgNi-based alloy prepared by ball milling
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DOI：
10.1016/s0925-8388(00)00753-2
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发表时间：
2000-06
影响因子：
6.2
通讯作者：
Sang-Cheol Han;P. S. Lee;Jai-Young Lee;A. Züttel;L. Schlapbach
中科院分区：
文献类型：
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作者：
Sang-Cheol Han;P. S. Lee;Jai-Young Lee;A. Züttel;L. Schlapbach
非晶态MgNi合金作为Ni/MH二次电池的负极材料具有很高的容量，但存在循环性能差的问题。为了提高合金的循环寿命，抑制了非晶MgNi合金的退化机制。结果表明，MgNi合金表面的氧化镁层厚度增加，合金的放电容量降低，因此，MgNi合金的表面性质是提高循环寿命的关键因素。为了防止镁的进一步氧化，采用钛表面涂层和替代方法。钛替代被发现是非常有效的提高循环寿命，而钛表面涂层被证明是几乎没有效果。Mg 50 Ni 50合金中的镁被钛取代。钛的量（Mg 1-xTixNi1.0中的x）在0.1至0.3之间变化。当x=0.3（Mg0.7Ti0.3Ni1.0）时，合金具有最佳的循环寿命。为了解释这一现象，进行了电化学和唯象分析。电化学阻抗谱（EIS）分析表明，Mg0.7Ti0.3Ni1.0合金与电解液之间的电荷转移电阻（Rct）在充放电循环过程中没有增加。俄歇电子能谱（AES）分析还发现，Mg_（0.7）Ti_（0.3）Ni_（1.0）合金表面氧化层的厚度小于Mg Ni合金表面氧化层的厚度。同时，在Mg0.7Ti0.3Ni1.0合金表面发现了镍的富集层。X射线光电子能谱（XPS）也表明Mg 0.7Ti 0.3Ni 1.0合金中的镁以金属态存在，而钛形成氧化物层。这些结果表明，钛氧化物层不仅防止了镁的进一步氧化，而且在合金表面上诱导了镍富集层。
Amorphous MgNi alloys have a critical problem of poor cyclic behavior in spite of their high capacity for the negative electrode of a Ni/MH rechargeable battery. In order to improve the cycle life of the alloys, the degradation mechanism of amorphous MgNi alloy is suppressed. It is found that the surface property of the MgNi alloy is a critical factor for improvement of cycle life because an increase of the thickness of the magnesium oxide layer on the alloy surface results in a decrease of the discharge capacity of the alloy. To prevent further oxidation of magnesium, both titanium surface coating and substitution methods are adopted. Ti substitution is found to be very effective for improving the cycle life while Ti surface coating proves to be hardly effective. Magnesium in the Mg50Ni50alloy is replaced by titanium. The amount of titanium (x in Mg1−xTixNi1.0) is varied from 0.1 to 0.3. In the case of x=0.3 (Mg0.7Ti0.3Ni1.0), the alloy shows the best cycle life. To explain this phenomenon, both electrochemical and phenomenological analyses are conducted. Electrochemical impedance spectroscopy (EIS) analysis shows that the charge transfer resistance (Rct) between the Mg0.7Ti0.3Ni1.0alloy and the electrolyte does not increase during charge–discharge cycles. It is also found by auger electron spectroscopy (AES) that the thickness of the surface oxide layer on the Mg0.7Ti0.3Ni1.0alloy is thinner than that of the oxide layer on the MgNi alloy. At the same time, a nickel-enriched layer is found on the surface of the Mg0.7Ti0.3Ni1.0alloy. X-ray photoelectron spectroscopy (XPS) also shows that magnesium in the Mg0.7Ti0.3Ni1.0alloy exists in metallic state while titanium forms an oxide layer. These results indicate that the titanium oxide layer not only prevents further oxidation of magnesium, but also induces a nickel enriched layer on the alloy surface.