镁基非晶电极合金的容量衰减机制探讨

Capacity Fading Mechanism for Mg-Based Amorphous Electrode Alloys

采用熔体快淬法制备了(Mg70.6Ni29.4)100-xNdx(x=2,5,10,15)电极合金带,用恒流充放电的方法在三电极电池测试仪上测定其电化学循环性能。用X射线衍射仪、场发射扫描电镜和高分辨电镜对合金在充放电循环过程中的组织结构变化进行了动态检测。结果表明:(Mg70.6Ni29.4)90Nd10非晶电极合金拥有最高的放电容量(580.5 mAh·g-1),经过20个循环以后,合金表面存在严重的氧化(含氧量为26.7%)和开裂粉化现象;在充放电循环过程中,合金内部逐渐形核长大,形核的初生相NdMg2Ni9最终转化为Mg2Ni,α-Mg和Nd2H5相;非晶态Mg-Ni-Nd电极合金在充放电循环过程中放电容量的衰减来自于内外两个方面的综合效应:合金表面碱液的氧化腐蚀和开裂粉化以及非晶合金的晶化导致其贮氢机制失效,反应动力学性能下降,从而引起放电容量的衰减。

Amorphous and nanocrystalline （ Mg70.6Ni29.4 ） 100-xNdx （x - 2, 5, 10, 15 ） alloys were prepared by rapid solidification. The electrochemical cycling performance was measured by three-electrode cell tester. The phase structures of the ribbons before and af- ter charge/discharge cycling were characterized by high-resolution transmission electron microscopy （HRTEM）, X-ray diffraction （XRD） and field emission scanning electron microscope（SEM）, respectively. It was found that the amorphous （Mg70.6Ni29.4）90Nd10 alloy had the highest discharge capacity （580.5 mAh.g-1 ）, after 20 cycles, there was a serious oxidation （oxygen content of 26. 7% ） and cracking of the chalking phenomenon in the alloy surface and the NdMg2 Ni9 phase formed at beginning gradually decomposed into Mg2 Ni, α-Mg and Nd2 H5 phases as hydrogenation/dehydrogenation proceeds. The discharge capacity decayed for amorphous Mg-Ni-Nd electrode alloys in the charge-discharge cycle process came from both internal and external aspects ： the oxidation of the alloy surface lye corrosion and cracking of the powder, as well as the crystallization of the amorphous alloy, which led to the attenuation of the discharge capacity.