烧结时间对La_(4)MgNi_(19)合金相结构及电化学性能的影响

Influences of sintering duration on phase structures and electrochemical properties of La_(4)MgNi_(19) alloys

粉末烧结制备了La_(4)MgNi_(19)合金,系统研究了烧结时间对合金相结构及电化学性能的影响。XRD数据表明,合金主要由LaNi_(5)相、LaNi_(2)相(CeNi_(2)型)和LaMg_(2)Ni_(9)相组成,烧结时间的增加,会加剧Mg元素的挥发,促进LaNi_(2)相与LaMg_(2)Ni_(9)相向LaNi_(5)相转变。电化学性能测试表明,合金最大放电容量(C_(max))由187.79 mAh/g(4 h)增加到279.48 mAh/g(16 h),这是因为高容量的LaNi_(5)相的相丰度的增加;而合金循环稳定性随之增加而降低,S_(100)由75.76%(4 h)下降到58.62%(16 h),研究认为,LaNi_(5)主相的晶胞体积的减少,不利于吸放氢,合金抗粉化性能下降;合金高倍率性能(HRD_(900))明显改善,由43.96%(4 h)提高到90.67%(16 h),这与LaNi_(5)的高催化活性相关,此外,合金高倍率性能主要受电极表面电催化活性影响。

La_(4)MgNi_(19)alloys were prepared by powder sintering,and influences of sintering duration on the phase structures and electrochemical properties were systematically investigated.XRD data show that the alloy is mainly composed of LaNi_(5) phase,LaNi_(2) phase(CeNi_(2)-type)and LaMg_(2) Ni_(9) phase.The increase of sintering duration will increase the volatilization of Mg element and promote LaNi_(2) phase and LaMg_(2) Ni_(9) phase to transform into LaNi_(5) phase.Electrochemical tests reveal that the maximum discharge capacity(C_(max))was increased from 187.79 mAh/g(4 h)to 279.48 mAh/g(16 h),which is due to the increased phase abundance of LaNi_(5) with higher capacity.While the cycling stability declines that S_(100)is decreased from 75.76%(4 h)to 58.62%(16 h),and it is considered that the declined cell volume of LaNi_(5) hindered the ab-desorption of hydrogen,as a consequence of which,the anti-pulverization property of alloy gets worse.It is also founded that the high rate dischargeability is greatly increased from 43.96%(4 h)to 90.67%(16 h),which is related with the catalytic activity of LaNi_(5) phase.The high rate dischargeability is mainly controlled by the electrocatalytic activity on the surface of alloy electrodes.