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 AI 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 roust important factor responsible for the improvement of the cycling stability of the La-Mg-Ni-Mn-Co-Al type alloy electrodes.     

Effects of Mm(NiCoAlMn)_5 hydrogen storage alloy coated with Ni-Co-P alloy by electroless plating on electrochemical properties of hydride electrodes

1　INTRODUCTIONNickel metalhydride (MH Ni)rechargeablebatterieswithhydrogenstoragealloysasthenegativeelectrodematerialhaveattractedincreasingattentionsbecauseofseveralinherentadvantages[16 ] .Sofar ,manymulti component,mischmetal based ,hydro gen storagealloyshavebeendevelopedtomeetthere quirementofhighcyclinglife ;theseincludesubstitu tionofthenickelbyMn ,CoandAl[7] .Thecomposi tionofthealloyisimportant ,andtheeffectsofsur facecompositionandmorphologyarealsosignificant.Micro encapsulat…     

La0.7Mg0.3Ni2.55-xCo0.45Alx(x=0～0.4)贮氢合金的循环稳定性

为了提高La-Mg-Ni系贮氢合金的循环稳定性,以Al部分替代Ni,采铸造及快淬工艺制备了La0.7Mg0.3Ni2.55-xCo0.45Alx(x=0,0.1,0.2,0.3,0.4)电极合金,研究了Al替代量及快淬工艺对合金微观结构及电化学循环稳定性的影响。X射线衍射分析结果表明:铸态及快淬态合金具有多相结构,包括(La,Mg)Ni3相、LaNi5相和一定量的LaNi2相;Al替代使铸态合金中LaNi2相的量显著增加,但对快淬态合金中LaNi2相的相丰度影响不显著。电化学测试结果表明:随Al替代量的增加,合金的循环寿命大幅度提高;快淬处理可以提高合金的循环寿命,但随Al替代量的增加,淬速对循环寿命的影响减小。     

Structure and electrochemical properties of La-Mg-Ni system hydrogen storage alloys with different Co contents

1 INTRODUCTIONTo increase the discharge capacity of nickel/metal-hydride ( Ni/ MH) batteries , new types ofhydrogen storage alloys with higher energy densityhave been paid considerable attention by research-ers . Particularly , recent investigations on theR-Mg-Ni (R=rare earth or Ca element) systemhydrogen storage alloys have led to a newseries ofternary alloys with a high hydrogen storage capaci-ty[1 3]. Kohno et al[4]found that the maxi mumdis-charge capacity of the La0 .7Mg0 .3Ni2 …     

Microstructure and electrochemical properties of low-temperature hydrogen storage alloy used in Ni/MH batteries

AB5 hydrogen storage alloys La0.54Ce0.28Pr0.18Ni4-xCo0.6Mno35Alx （x=0.1, 0.2, 0.3） were prepared by arc melting method under an Ar atmosphere. The results show that the contents of Ni and Al have obvious influences on the microstructure and electrochemical properties of the alloys. Both the lattice parameters and the cell volumes decrease with decreasing x value. Moreover, the discharge capacity at different temperatures, the high rate discharge property, and the cycling life of the alloy electrode are also in close relationship with the x value. When x value increases from 0.1 to 0.3, the discharge capacities with a discharge current density of 60 mA/g slightly decreases at 25℃, but evidently deteriorates at -40℃, the high-rate property gravely decreases, and the cycle life of the alloy electrode is improved in some extent. Therefore, it is meaningful to control Al content for the AB5 hydrogen storage alloys used in Ni/MH batteries.     

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, M Cr 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, M Cr 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.     

Effects of compaction pressure on the electrochemical properties of Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 metal hydride electrodes

In this work, the negative electrodes of the nickel-metal hydride rechargeable batteries were prepared at different compaction pressures. The maximum discharge capacities and cycle stabilities of the electrodes were measured by means of electrochemical method. The crystal structures and surface morphologies of the alloys were intensively studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS), respectively. Based on these observations, the effects of compaction pressure on the electrochemical properties of the electrodes were systematically investigated. The results showed that the electrode prepared at a compaction pressure of 25 MPa exhibited the best discharge capacity and better cycle stability.     

Effect of surface modification of metal hydride electrode on performance of MH/Ni batteries

A novel method was applied to the surface modification of the metal hydride(MH)electrode of MH/Ni batteries.Both sides of the electrode were plated with a thin silver film about 0.1μm thick using vacuum evaporation plating technology,and the effect of the electrode on the performance of MH/Ni batteries was examined.It is found that the surface modification can enhance the electrode conductivity and decrease the battery ohimic resistance.After surface modification,the discharge capacity at 5C(7.5A)is increased by 212 mA.h and the discharge voltage is increased by 0.11 V,the resistance of the batteries is also decreased by 32%.The batteries with modified electrode exhibit satisfactory durability.The remaining capacity of the modified batteries is 89%of the initial capacity even after 500 cycles.The inner pressure of the batteries during overcharging is lowered and the charging efficiency of the batteries is improved.     

Rare earth-Mg-Ni-based hydrogen storage alloys as negative electrode materials for Ni/MH batteries

This review is devoted to new rare earth-Mg-Ni-based (R-Mg-Ni-based) hydrogen storage alloys that have been developed over the last decade as the most promising next generation negative electrode materials for high energy and high power Ni/MH batteries. Preparation techniques, structural characteristics, gas-solid reactions and electrochemical performances of this system alloy are systematically summarized and discussed. The improvement in electrochemical properties and their degradation mechanisms are covered in detail. Optimized alloy compositions with high discharge capacities, good electrochemical kinetics and reasonable cycle lives are described as well. For their practical applications in Ni/MH batteries, however, it is essential to develop an industrial-scale homogeneous preparation technique, and a low-cost R-Mg-Ni-based electrode alloy (low-Co or Co-free) with high discharge capacity, long cycle life and good kinetics.     

无钴LaNi4.1Al0.3Mn0.4Si0.2Fex (x=0~0.4)储氢合金性能

采用电弧熔炼制备LaNi4.1Al0.3Mn0.4Si0.2Fex(x=0~0.4)储氢合金,借助XRD、SEM等分析LaNi4.1Al0.3Mn0.4Si0.2Fex合金的晶体结构和相组成,并研究合金的电化学性能。结果表明:合金主要由LaNi5单相组成,当x≥0.1时,在LaNi5主相上分布着些许灰色的第二相。随着LaNi4.1Al0.3Mn0.4Si0.2Fex(x=0~0.4)合金中Fe的加入量增加,合金最大放电容量由295.4mAh/g(x=0)降低到278.2mAh/g(x=0.4),活化次数也由10次增加到18次。同时合金200次循环后的容量保持率却由66.85%(x=0)提高到93.33%(x=0.4)。     

Electrochemical investigation on hydride electrode with tungsten carbide additive

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化学镀Ni-Co-P合金对贮氢电极电化学性能的影响

研究了化学镀Ni Co P镀层对贮氢合金电极性能的影响。研究表明 ,引入 1 .74%Co的Ni Co P合金镀层可有效地提高负极贮氢合金活性物质的利用率 ,MH电极的活化性能得到明显改善 ,初次放电容量即达到 2 0 8mA·h/g、最大放电容量达 2 95.8mA·h/g ;同时循环寿命亦有所提高 ,化学镀Ni Co P合金的贮氢电极在进行 1 0 0次循环充放后 ,电容量的保持率为 88% ,而未镀贮氢电极电容量衰减至 62 %。镀Ni Co P合金电极容量的增加 ,主要是由于Co氧化电流和微电流集流效率改善双重作用的结果。化学镀后贮氢合金的抗粉化和抗氧化能力得以改善 ,使得MH电极在自放电性能上有较大改进 ,不可逆部分的容量损失由 2 3.2mA·h/g降到了 3.6mA·h/g。借助于SEM和XRD分析了化学镀Ni Co P合金对MH电极性能改善的影响机理。     

Structure and electrochemical properties of low-cobalt La1- xLixNi3.2Co0.3Al0.3(0≤x≤0.2) hydrogen storage electrode alloys

The structure and electrochemical properties of a new low cobalt hydrogen storage electrode alloys La1-xLixNi3.2Co0.3Al0.3(0≤ x ≤0.2) were investigated with a different additions of Li in replacement of La. With the increase of Li contents the maximum discharge capacity increases from 240 mAh·g -1 ( x =0) to 328.4 mAh·g -1(x=0.1) and the cycle stability is improved correspondingly. The capacity decay can remaiN28.6% ( x =0.2) after 230 charge/discharge cycles. The high rate discharge(HRD) ability of the alloys( x≤0.1) is improved and the best HRD is 34.1%( x =0.1) under the discharge current density 1200 mA·g -1 . It is found that the prepared alloys are basically composed of LaNi5 as matrix phase and LaNi3 as second phase( x ≤0.1). But the abundance of LaNi3 phase dramatically decreases with increasing x . When x =0.2, a new phase Al(NiCo)3 is formed.     

贮氢合金机械合金化制备的研究进展

机械合金化技术（MA）是一种制备材料的新兴工艺，用它可以制备一般方法难以制备的和性能优越的贮氢合金。本文详细概述了近几年来机械合金化技术在贮氢合金制备上的应用状况，并就今后机械合金化技术在贮氢合金制备上的应用研究提出了方向。     

快淬对低钻贮氢合金的电化学性能影响

为改善低钴贮氢合金的综合电化学性能，对其进行不同速度的快淬处理。结果表明：合适的快淬速度不仅可以大幅度的提高放电容量，而且明显的改善合金的循环稳定性和放电电压特性。18m／s快淬低钴合金具有较好的综合电化学性能。但快淬使得合金的活化性能有所降低。利用X射线衍射、扫描电镜对铸态及快淬合金进行微观分析，讨论了快淬对低钴贮氢合金电化学性能的影响机理。     

快淬对低钴贮氢合金的电化学性能影响

为改善低钴贮氢合金的综合电化学性能,对其进行不同速度的快淬处理。结果表明,合适的快淬速度不仅可以大幅度的提高放电容量,而且明显的改善合金的循环稳定性和放电电压特性。18 m/s快淬低钴合金具有较好的综合电化学性能,但快淬使合金的活化性能有所降低。利用X射线、扫描电镜对铸态及快淬合金进行微观分析。分析了快淬对低钴贮氢合金电化学性能的影响机理。     

镀镍对多元替代低钴贮氢合金的电化学性能影响

研究了化学镀镍对低钴贮氢合金粉末颗粒形态和电化学性能的影响.结果表明,镀镍能明显提高低钴贮氢合金的放电容量、1C高倍率放电性能及循环稳定性,对活化性能亦有改善.SEM分析表明,化学镀镍过程中伴有吸氢反应.分析了镀镍对低钴贮氢合金电化学性能的影响机理.     

退火对稀土系AB5低钴贮氢合金的影响

为提高多元替代低钴贮氢合金MlNi3.8 Al027 Mn0.36 Co0.24 Cu0.15 Cr0.1 Zn0.05 Fe0.05的电化学性能,研究了850℃与1050℃两种温度退火对合金的微观结构、组织以及电化学性能的影响.XRD分析表明,退火降低了合金的晶格应力和缺陷,同时使得合金的单胞体积增大.电化学测试结果表明,退火合金的放电容量明显提高,其中1050℃退火后合金的最大放电容量达到315mAh/g,比铸态合金提高26mAh/g.退火使得合金的高倍率放电性能略有降低,但仍达到96%,退火提高了合金的循环稳定性.     

贮氢合金V3TiNi0.56Mx耐腐蚀性能研究

钒基固溶体贮氢合金在KOH电解质溶液中容易腐蚀,导致合金的电化学循环稳定性差,限制了钒基固溶体贮氢合金在Ni/MH电池中的应用.通过测试贮氢合金V3TiNi0.56Mx(M=Al、Cr,x=0.1、0.3)在KOH溶液浸泡过程中组织结构变化和腐蚀电位、交流阻抗谱等,研究了钒基固溶体贮氢合金V3TiNi0.56Mx的耐碱液腐蚀性能.结果表明:钒基固溶体贮氢合金在碱液中的腐蚀原因是作为导电集流体的TiNi第二相在KOH溶液中的不断溶解;在合金V3TiNi0.56中添加Al和Cr元素,可阻止合金中分布于晶界的TiNi第二相的溶解,使合金的腐蚀电位提高,从而提高钒基固溶体贮氢合金的酎碱液腐蚀能力.     

热循环对20%SiC_w/6061Al复合材料尺寸稳定性的影响

通过测量 2 0 % (体积分数 )SiCw/6 0 6 1Al复合材料热循环 (2 5℃→ 30 0℃→ 2 5℃ )后的尺寸变化 ,研究了复合材料的热循环尺寸稳定性。结果表明 ,复合材料尺寸稳定性直接与晶须的取向方式有关。如果晶须取向为混乱分布 ,热循环后复合材料的尺寸变化不明显。当晶须取向为定向排列时 ,热循环可造成复合材料沿晶须方向的尺寸增大 ,同时垂直晶须方向尺寸减小