Effects of rapid quenching on structure and cycle stability of La-Mg-Ni-Co type hydrogen storage alloy

In order to improve the cycle stability of La-Mg-Ni-Co type alloy electrode, rapid quenching technology was employed. The effects of rapid quenching on the microstructure and cycle stability of the alloy were investigated. The obtained results show that the La2Mg(Ni0.85Co0.15)9M0.1 (M=B, Cr) alloy electrodes are composed of (La, Mg)Ni3 phase, LaNi5 phase and a small amount of the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast MB alloy, and the Ni2B phase in the alloy nearly disappears after rapid quenching. Rapid quenching technology can slightly improve the cycling life of the alloy. When the quenching rate increases from 0 m·s-1 (As-cast is defined as quenching rate of 0 m·s-1) to 30 m·s-1, the cycle lives of the MB, MCr alloys enhance from 86 and 87 cycles to 106 and 119 cycles, respectively. On the other hand, the average capacity decay rates of the MB, MCr alloys decrease from 1.7172 and 1.7178 mAh·g-1·cycle-1 to 1.5751 and 1.3060 mAh·g-1·cycle-1 after 86 charge-discharges cycling, respectively.

Cycling stability of La-Mg-Ni-Co type hydride electrode with Al

The mechanism of the improvement of the cycling stability of the La-Mg-Ni-Co based hydrogen storage alloy electrode was systematically investigated. The results show that the cell volume expansion upon hydrogenation is obviously decreased after the partial substitution of Al for Ni. Therefore a decrease in the pulverization of the alloy particles is obtained, which leads to the decrease of the contact area of the fresh alloy surface with alkaline electrolyte and the increase of the charge/discharge efficiency. Moreover, the occurrence of Al in the alloy can create a dense Al oxide film on the surface of the alloy during charge/discharge cycling. This dense oxide film can prevent further oxidation of the active components in the alloy, which is believed to be the most important factor responsible for the improvement of the cycling stability of the La-Mg-Ni-Mn-Co-Al type alloy electrodes.

Cycling stability of La-Mg-Ni-Co type hydride electrode with Al

The mechanism of the improvement of the cycling stability of the La-Mg-Ni-Co based hydrogen storage alloy electrode was systematically investigated. The results show that the cell volume expansion upon hydrogenation is obviously decreased after the partial substitution of Al for Ni. Therefore a decrease in the pulverization of the alloy particles is obtained, which leads to the decrease of the contact area of the fresh alloy surface with alkaline electrolyte and the increase of the charge/discharge efficiency. Moreover, the occurrence of Al in the alloy can create a dense Al oxide film on the surface of the alloy during charge/discharge cycling. This dense oxide film can prevent further oxidation of the active components in the alloy, which is believed to be the most important factor responsible for the improvement of the cycling stability of the La-Mg-Ni-Mn-Co-Al type alloy electrodes.

退火对La0.75Mg0.25Ni3．5Co0.4贮氢合金电化学性能的影响

为了改善La-Mg-Ni-Co系合金电极的循环稳定性,对铸态合金La0.75Mg0.25Ni3.5Co0.4在0.3MPa压力氩气保护下进行不同温度的退火(1123,1223和1323K),保温时间均为10h。研究了退火温度对合金的电化学性能的影响。X射线衍射(XRD)分析结果表明,铸态及1123K温度退火后合金主要由LaNi5,(La,Mg)2(Ni,Co)7相以及少量LaNi2相组成;退火温度为1223和1323K时,合金中LaNi2相消失,合金主要由LaNi5,(La,Mg)2(Ni,Co)7及(La,Mg)(Ni,Co)3相组成。随退火温度升高,最大放电容量从341.2mAh/g增加365.8mAh/g;循环稳定性得到改善,100次充放电循环后容量保持率从铸态合金的58.63%提高到1323K时的72.91%。

化学计量比B／A对La0.75Mg0.25Ni2.5Mx(M=Ni,Co；x=0-1.0)电极合金微观结构及电化学性能的影响

为了探索化学计量比B／A（A和B分别为电极合金A侧和B侧元素的总和）以及Co替代Ni对ABx（x=2.5～3.5）型电极合金微观结构及电化学性能的影响，制备了电极合金La0.75Mg0.25Ni2.5Mx（M=Ni，Co；x=0，0.2，0.4，0.6，0.8，1.0）。系统地分析测试了合金的微观结构及电化学性能。结果表明，合金的微观结构与电化学性能与化学计量比B／A（相当于M含量x）密切相关。合金均具有多相结构，包括LaNi2，（La，Mg）Ni3和LaNi5相。随化学计量比B／A的增加，合金的主相由LaNi2转为（La，Mg）Ni3＋LaNi5相，并且合金的电化学性能，包括放电容量、高倍率放电能力（HRD）、放电电压特性等均显著改善。

Effect of cobalt content on electrochemical performance of La-Mg-Ni system (Ce_2Ni_7-type) electrode alloys

In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure of the alloys were investigated in detail. XRD results showed that the alloys had multiphase structure composed of （La, Mg）2Ni7, LaNi5 and small amount of LaNi2 phases. The discharge capacity of the alloys first increased and then decreased with increasing Co content. At a discharge current density of 900 mA/g, the HRD of the alloy electrodes increased from 81.3% （x=0） to 89.2 % （x=0.2）, and then reduced to 87.8 % （x=0.6）. After 60 charge/discharge cycles, the capacity retention rate of the alloys enhanced from 52.67% to 61.32%, and the capacity decay rate of the alloys decreased from 2.60 to 2.05 mAh/g per cycle with increasing Co content. The obtained results by XPS and XRD showed that the fundamental reasons for the capacity decay of the La-Mg-Ni system （Ce2Ni7-type） alloy electrodes were corrosion and oxidation as well as passivation of Mg and Lain alkaline solution.

A、B侧元素化学计量比对La-Mg-Ni-Co系四元储氢合金的电化学性能影响研究

采用共沉淀-还原扩散法制备了具有不同化学计量比的La-Mg-Ni-Co系储氢合金(AB3、AB3.3、AB3.5),重点考察B侧元素不同化学计量比对四元合金La-Mg-(Ni-Co)x(x=3.0,3.3,3.5)相结构和电化学性能的影响规律。结果表明,成分合金La0.67Mg0.33Ni2.5Co0.5(x=3.0)具有良好的综合电化学性能。同时采用3种电化学动力学实验分别对合金电极表面的电荷转移阻抗和电荷转移速率以及合金体相中氢的扩散速率进行了表征。证实合金元素化学计量是通过影响合金电极表面的电荷转移和合金体相中氢的扩散速率综合作用来改变其电化学动力学性能。

La-Mg-Ni系合金新型合成工艺及La_(0.67)Mg_(0.33)Ni_(3.0)合金微结构的研究(英文)

以含La、Mg、Ni元素的化学试剂为原料,先制得三元复合金属氧化物前驱体;再以优化后的实验参数,进行基于共沉淀及还原扩散法联用工艺制备La0.67Mg0.33Ni3.0合金及其微观结构的研究,并验证新型合成工艺的可行性。结果表明:以共沉淀和还原扩散法制得的合金均为多相结构,其组织和成分趋于均匀化,晶格畸变小;并且合金还原过程比较彻底,合金中含氧量极少,取得了预期的效果;La-Mg-Ni系合金新型合成工艺可行,但还需对该工艺进行再优化。