Structure and electrochemical hydrogen storage characteristics of the as-cast and annealed La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 （x=0-0.4） alloys

In order to ameliorate the electrochemical cycle stability of the RE-Mg-Ni based A2B7-type electrode alloys, the Mg content in the alloy was reduced and La in the alloy was partially substituted by Sm. The La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4) elec-trode alloys were fabricated by casting and annealing. The microstructures of the as-cast and annealed alloys were characterized by XRD and SEM. The electrochemical hydrogen storage characteristics of the as-cast and annealed alloys were measured. The results revealed that all of the experimental alloys mainly consisted of two phases: (La,Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure. As Sm content grew from 0 to 0.4, the discharge capacity and the high rate discharge ability (HRD) first in-creased and then decreased for the as-cast and annealed alloys, whereas the capacity retaining rate (S100) after 100 cycles increased continuously.     

Effect of annealing temperature on microstructure and electrochemical performance of La0.75Mg0.25Ni3.5Co0.2 hydrogen storage electrode alloy

To improve the cyclic stability of La-Mg-Ni system alloy, as-cast La0.75Mg0.25Ni3.5Co0.2 alloy was annealed at 1123, 1223, and 1323 K for 10 h in 0.3 MPa argon. The microstructure and electrochemical performance of different annealed alloys were investigated systematically by X-Ray Diffraction （XRD）, Scanning Electron Microscopy （SEM）, X-Ray Photoelectron Spectroscopy （XPS）, and electrochemical experiments. The results obtained by XRD and SEM showed that the as-cast and annealed （1123 K） alloys had multiphase structure containing LaNis, （La, Mg）2（Ni, Co）7 and few LaNi2 phases. When annealing temperatures approached 1223 and 1323 K, LaNi2 phase disappeared. The annealed alloys at 1223 and 1323 K were composed of LaNi5, （La, Mg）2（Ni, Co）7 and （La, Mg）（Ni, Co）3 phases. With increasing annealing temperature, the maximum discharge capacity of the alloy decreased monotonously, but the cyclic stability was improved owing to structure homogeneity and grain growth after annealing, as well as the enhancement of anti-oxidation/corrosion ability and the suppression of pulverization during cycling in KOH electrolyte.     

Structure and electrochemical hydrogen storage characteristics of Ce-Mg-Ni-based alloys synthesized by mechanical milling

The substituting Mg with Ni and milling as-cast alloy with Ni were adopted to obtain nanocrystalline/amorphous CeMgnNi+x wt.%Ni(x=100,200) alloys and promote the electrochemical hydrogen storage performances of CeMg_(12)-type alloys.Analyzing the structural features of the alloys provided a mechanism for ameliorating the electrochemical hydrogen storage properties.The electrochemical tests demonstrated that all the alloys just needed one cycle to be activated.Rising Ni proportion had an obvious role on charge-discharge reaction.The discharge capacities of the as-milled(60 h) alloys increased sharply from 182.0 mAh/gfor x=100 alloy to 1010.2 mAh/gfor x=200 alloy at current density of 60 mAh/g.Furthermore,milling time largely determined the performances of electrochemical reaction.The discharge capacity continued to grow along with prolonging milling time,while the cycle stability obviously decreased for x=100 alloy,and first declined and then augmented for the x=200 alloy with milling time extending.In addition,there was an optimal value with milling time varying for the high rate discharge abilities(HRD),which was 80.3%for x=100 alloys and 86.73%for x=200,respectively.     

Influence of rapid quenching on cyclic stability of La-Mg-Ni system （AB3-type） electrode alloys

Aiming at the improvement of the cyclic stability of La-Mg-Ni system （PuNi3-type） hydrogen storage alloy, Ni in the alloy was partly substituted by Fe. The electrode alloys of La0.7Mg0.3Co0.45Ni255-xFex （x=0, 0.1, 0.2, 0.3, 0.4） were prepared by casting and rapid quenching. The influence of the quenching on cyclic stability as well as structure of the alloys was investigated in detail. The results of electrochemical measurement indicated that rapid quenching significantly improved cyclic stability. When the quenching rate rose from 0 （As-cast was defined as a quenching rate of 0 m/s） to 30 m/s, the cyclic life of Fe-free alloy （x=-0） increased from 81 to 105 cycles, and for alloy containing Fe（x=0.4）, it grew from 106 to 166 cycles at a current density of 600 mA/g. The results obtained by XRD, TEM and SEM revealed that the as-cast and quenched alloys had multiphase structures, including two major phases （La, Mg）Ni3 and LaNi5 as well as an imptLrity phase LaNi2. Rapid quenching helped the formation of an amorphous-like structure in Fe containing alloys.     

Effect of Rapid Quenching on Microstructures and Electrochemical Performances of La2Mg（Ni0.85Co0.15）9M0.1 （M = B, Cr） Hydrogen Storage Alloys

The La-Mg-Ni-system （PuNi3-type） La2Mg （Ni0.85 Co0.15 ）9M0.1 （ M = B, Cr） hydrogen storage etectrode alloys were prepared by casting and rapid quenching. The electrochemical performances and microstructures of the as-cast and quenched alloys were determined and measured. The effects of rapid quenching on the microstructures and electrochemical properties of the alloys were investigated in detail. The obtained results show that the alloys are composed of the （La, Mg） Ni3 phase （PuNi3-type structure） and the LaNi5 phase, as well as the small amount of the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloy containing boron, and the Ni2B phase in the alloy nearly disappears after rapid quenching. The relative amount of each phase in the alloys depends on the quenching rate. The rapid quenching technique can greatly improve the electrochemical performance of the alloy, and the effect of rapid quenching on the activation performances of the alloys is minor. Rapid quenching enhances the cycle stability of the alloy, and the cycle life of the alloy increases with the increase of the quenching rate.     

Electrochemical properties of cobalt-free La0.80Mg0.20Ni2.85Al0.11M0.53 （M=Ni, Si, Cr, Cu, Fe） alloys

In order to investigate the effect of different B-site additions on phase structure and electrochemical properties of cobalt-free La-Mg-Ni based alloys, La0.80Mg0.20Ni2.85Al0.11M0.53 (M=Ni, Si, Cr, Cu, Fe) hydrogen storage alloys were prepared and studied systemati-cally. X-ray powder diffraction showed that the alloys consisted mainly of LaNi3 phase and LaNi5 phase except that Cr addition caused a minor Cr phase. Electrochemical testing indicated that alloys with additional Ni, Cr, Cu or Fe were activated within only 1-2 cycles, while that with Si addition needed 4 cycles. Adding Si, Cu and Fe increased cycling stability of La-Mg-Ni based alloys. However, maximum discharge capacity decreased from 362 mAh/g to 215 mAh/g in the order of Ni>Fe>Cu>Cr>Si. In addition, electrochemical kinetics of alloy electrodes was also researched by measuring high rate discharge ability (HRD), hydrogen diffusion coefficient (D) and limiting current density (IL).     

Effect of the partial substitution of samarium for lanthanum on the structure and electrochemical properties of La_(15)Fe_(77)B_8-type hydrogen storage alloys

La15Fe77B8 hydrogen storage alloys were prepared using a vacuum induction-quenching furnace. The results of X-ray diffraction(XRD) and scanning electron microscopy(SEM) suggested that La15–xSmxFe2Ni76Mn5B2(x=0, 2, 4, 6) alloys had multiphase structure including the main LaNi5 phase, La3Ni13B2 phase and(Fe, Ni) phase. With the increasing substitution of Sm for La, the main phase structure of alloys did not change, while the unit cell volumes decreased, the cycle stability was improved and the maximum discharge capacity decreased, but the low temperature maximum discharge capacity of the same substitution alloy was gradually approaching the maximum discharge capacity at room temperature, which showed that La15Fe77B8 hydrogen storage alloys of the partial substitution of Sm for La had better low-temperature dischargeability(LTD). For the same substitution alloys, self-discharge characteristics and cycle stability at low temperature were better than that at room temperature. Furthermore, the high-rate dischargeability(HRD) and the exchange current density I0 first increased and then decreased with the increasing of Sm content, whereas the hydrogen diffusion coefficient D in alloy bulk decreased gradually, which indicated that appropriate substitution of Sm for La improved the electrochemical kinetics properties of the alloys. The HRD was mainly dominated by the charge-transfer rate on the alloy surface.     

急冷对Ti_(0.32)Cr_(0.345)V_(0.25)Fe_(0.03)Mn_(0.055)合金储氢性能的影响

为了研究急冷对储氢合金残余氢量的影响,利用真空电弧熔炼炉和铜模喷铸制备了Ti_(0.32)Cr_(0.345)V_(0.25)Fe_(0.03)Mn_(0.055)合金,采用XRD、PCT(压力-容量-温度)、TG/DTA等手段分析了急冷对储氢合金吸放氢性能的影响。结果表明,铸态合金和急冷合金均由BCC固溶体主相和Laves第二相组成;急冷对首次吸氢动力学行为影响较大,由铸态时的化学反应控制变为急冷时的新相晶核形成长大控制;急冷后,合金吸放氢平台压得到提高,且吸氢起始点左移,但吸放氢滞后性增大。TG/DTA曲线表明,急冷并没有改变合金的残余氢量,但氢化物放氢温度升高。     

Influence of magnesium content on structure and electrochemical properties of La_(1-x)Mg_xNi_(1.75)Co_(2.05) hydrogen storage alloys

La_(1-x)Mg_xNi_(1.75)Co_(2.05)(x=0.07, 0.08, 0.10, 0.13, 0.15) alloys were prepared by high-frequency inductive method, and then their structure and electrochemical properties were investigated systematically. The XRD analysis revealed that the alloys consisted of LaNi_5 phase and La_4MgNi_(19)(Ce_5Co_(19) + Pr_5Co_(19)) phase, and the introduction of Mg could promote the formation of La_4MgNi_(19) phase. The observation of microstructure showed that all the alloys processed dendritic structure, which was refined with the increase of x value. The electrochemical measurements showed that all the alloys could be activated within 2 cycles, and with increasing x, the maximum discharge capacity obviously increased from 254.00 m Ah/g(x=0.07) to 351.51 mAh/g(x=0.15), but the cycling stability(S_(80)) decreased somehow from 78.4% to 73.9%. Meanwhile, the appropriate addition of Mg could improve the high-rate discharge capacity(HRD) of the alloy electrodes, which was mainly controlled by the electrochemical reaction rate on the surface of the alloys.     

Effect of cobalt content on electrochemical performance of La-Mg-Ni system （Ce2Ni7-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.     

Effects of Strip Casting and Annealing on Electrochemical Properties of LPCNi3.55Co0.75Mn0.4Al0.3 Hydrogen Storage Alloys

The effect of thickness (1～10 mm) of the ingots on the electrochemical properties of as-cast and annealed strip cast LPCNi3.55Co0.75Mn0.4Al0.3 hydrogen storage alloys was investigated. It is found that the 0.2 C discharge capacity of as-cast LPCNi3.55Co0.75Mn0.4Al0.3 alloy increases with the increase of the thickness of the ingots. As-cast alloy with the thickness of 10 nun shows better activation property, higher 1C discharge capacity and better cyclic stability than others.It is mainly contributed to its larger unit cell volume and less internal stress. Annealed LPCNi3.55Co0.75Mn0.4Al0.3 alloywith the thickness of 3 mm shows much better comprehensive electrochemical properties than as-cast one; The cyclic stability of the alloy with the thickness of 6 mm and the activation properties of the alloys with the thickness of 3～6 mm are improved after annealing. It is mainly owing to the great release of intemal stress and the decrease fo the segregation of Mn in the alloys.     

Fatigue crack propagation in rapidly solidified aluminum alloys at 25 °C and 300 °C

The fatigue crack propagation performance of two rapidly solidified aluminum alloys was investigated in air at 25°C and 300°C. The results show that the crack propagation rates for continuous cycling tests of Al-8Fe-4Ce and Al-4.7-Fe-4.7Ni-0.2Cr alloys were similar at 25°C. Although the crack propagation rates of both alloys were increased at 300°C, the Al-Fe-Ce alloy exhibited the greater resistance to crack propagation. The inclusion of a tensile hold time in the fatigue loading cycle at 300°C produced an increase in the crack propagation rates for both alloys over the rates for continuous cycling. The fatigue crack propagation performance of the rapidly solidified alloys was not found to be superior when compared with the fatigue crack propagation performance of a wrought aluminum alloy tested under the same conditions. Transmission and scanning electron microscopy study of the tested specimens revealed that the crack propagation mode was primarily transgranular, with the metastable dispersoid particles providing impenetrable barriers to dislocation motion.     

Effect of annealing treatment on hydrogen storage properties of La-Ti-Mg-Ni-based alloy

The present study dealt with investigations on the effects of annealing on the hydrogen storage properties of La 1.6 Ti 0.4 MgNi 9 alloys.The experimental alloys were prepared by magnetic levitation melting followed by annealing treatment.For La 1.6 Ti 0.4 MgNi 9 alloys,LaNi 5,LaNi 3 and LaMg 2 Ni 9 were the main phases,Ti 2 Ni phase appeared at 900℃.Annealing not only enhanced the maximum and effective hydrogen storage capacity,improved the hydrogen absorption/desorption kinetics,but also increased the discharge capacity.The cyclic stability had been improved markedly by annealing,e.g.,when the discharge capacity reduced to 60% of maximum discharge capacity,the charge/discharge cycles increased from 66(as-cast) to 89(annealed at 800℃) and 127 times(annealed at 900℃).La 1.6 Ti 0.4 MgNi 9 alloy annealed at 900℃ exhibited better electrochemical properties compared to the other two alloy electrodes.     

快淬对La0.67Mg0.33(NiCo)3贮氢合金电化学性能的影响

测试了AB3型贮氢合金La0.67Mg0.33(NiCo)3铸态与快淬态的电化学性能,用XRD和SEM测试了合金的微观结构,研究了快淬对AB3型贮氢合金电化学性能的影响.结果表明,快淬使合金的放电容量降低,对合金的活化性能没有明显影响;快淬降低了合金的容量衰减率,提高了合金的循环寿命,其主要原因是快淬使合金的晶粒显著细化.铸态和快淬态合金均具有多相结构,包括斜六面体的(La,Mg)Ni3相,六方的LaNi5相及少量的LaNi2相.快淬使合金中的LaNi2相含量增加,这是快淬使合金放电容量下降的一个主要原因.     

Relations between Quenching Rate and Electrochemical Characteristics of Mm (NiCoMnA1) 5Bx (x=0～0.2) Electrode Alloys

Low-Co AB5-type Mm(NiCoMnA1)5Bx (x = 0, 0.1, 0.2 ) electrode alloys were prepared by casting and rapid quenching.The effects of the rapid quenching on the lattice constants, microstructures and electrochemical characteristics of the alloys were investigated in detail.The obtained results show that the rapid quenching made lattice constants and cell volume increased.In a range of the quenching rate, rapid quenching can increase the discharge capacities of the alloys.However, the discharge capacity of the as-quenched alloy is lower than that of the as-cast alloy when quenching rate is more than a critical value.The cycle lives of the alloys increase monotonously with the increase of the quenching rate.     

Phase Structure and Electrochemical Properties of RE-Mg Based Composite Hydrogen Storage Alloys

Rareearth basedAB5 typealloy ,akindofhy drogenstoragealloyusedasnegativeelectrodemateri alsofthenickel/metalhydride (Ni/MH )secondarybattery ,haseasyinitialactivation ,longcyclelifeandlowcost ,butstillasmalldischargecapacity ,poorhigh ratedischargeability(HRD)andpoorpropertiesatlowtemperature[1,2 ] .Therefore ,howtoincreaseitsdischargecapacityandtoimproveotherelectrochemi calpropertiesismeaningfulbothintheoryandinpracticalapplication .Mg basedhydrogenstorageal loysareremarkablebecauseofitsr…     

快淬纳米晶/非晶Mg2-xLaxNi (x=0～0.6)合金的贮氢动力学

为了改善Mg2Ni型合金气态及电化学贮氢动力学性能,用La部分替代合金中的Mg,用快淬技术制备了Mg2-xLaxNi(x=0,0.2,0.4,0.6)合金,用XRD,SEM,HRTEM分析了铸态及快淬态合金的微观结构;用自动控制的Sieverts设备测试了合金的气态贮氢动力学性能,用程控电池测试仪测试了合金的电化学贮氢动力学.结果发现,快淬无La合金具有典型的纳米晶结构,而快淬含La合金显示了以非晶相为主的结构,表明La替代Mg提高Mg2Ni型合金的非晶形成能力.La替代Mg明显地改变Mg2Ni型合金的相组成.当La替代量x=0.4时,合金的主相改变为(La,Mg) Ni3+ LaMg3.合金的气态及电化学吸放氢动力学对La含量及快淬工艺敏感,La替代使合金的吸氢动力学降低,但适量的La替代可以明显改善合金的放氢动力学及高倍率放电能力.适当的快淬处理可以提高合金的气态及电化学贮氢动力学,但获得最佳贮氢动力学的快淬工艺与合金的成分密切相关.     

Phase Structure and Electrochemical Properties of Rare Earth Based Hydrogen Storage Alloys

The rare earth based hydrogen storage alloys MmxM1 1 - x ( Ni3.55 Co0.75 Mn0.4 A10.3 ) ( x = 0 ～ 0.5 ) were investigated in this work.Adjusted Ml: Mm ratio to change the content of La,Ce,Pr and Nd in the alloys and then to change the phase structure, the influences of phase structure on the electrochemical properties were analyzed.The results indicate that the main phase of all alloys is LaNi5 with CaCu5 type structure and the crystal lattices constants of LaNi5 are changed with increasing x value, i.e, decreased a-axis, increased c-axis and axis ratio and nonlinear decreased crystal volume.The crystal volume of the alloy with x = 0.3 is larger than others.There is second phase A1LaNi4 in alloys when x≥0.3, which decrease the discharge capacity, but increase the cycling stability and high rate discharge ability.Compared comprehensively, the alloy with x = 0.3 shows the higher discharge capacity and the better cycling stability.     

Electrochemical hydrogen storage performances of the nanocrystalline and amorphous（Mg24 Ni10 Cu2）100-x Ndx（x=0–20） alloys applied to Ni-MH battery

Melt spinning technology was used to prepare the Mg2 Ni-type（Mg24 Ni10 Cu2）100–x Ndx（x=0,5,10,15,20） alloys in order to obtain a nanocrystalline and amorphous structure.The effects of Nd content and spinning rate on the structures and electrochemical hydrogen storage performances of the alloys were investigated.The structure characterizations of X-ray diffraction（XRD）,transmission electron microscopy（TEM） and scanning electron microscopy（SEM） linked with energy dispersive spectroscopy（EDS） revealed that the as-spun Nd-free alloy displayed an entire nanocrystalline structure,whereas the as-spun Nd-added alloys held a nanocrystalline and amorphous structure and the degree of amorphization visibly increased with the rising of Nd content and spinning rate,suggesting that the addition of Nd facilitated the glass forming of the Mg2 Ni-type alloy.The electrochemical measurements indicated that the addition of Nd and melt spinning improved the electrochemical hydrogen storage performances of the alloys significantly.The discharge capacities of the as-cast and spun alloys exhibited maximum values when Nd content was x=10,which were 86.4,200.5,266.3,402.5 and 452.8 mAh/g corresponding to the spinning rate of 0（As-cast was defined as the spinning rate of 0 m/s）,10,20,30 and 40 m/s,respectively.The cycle stability（S20,the capacity maintain rate at 20thcycle） of the as-cast alloy always rose with the increasing of Nd content,and those of the as-spun alloys exhibited the maximum values for Nd content x=10,which were 77.9%,83.4% 89.2% and 89.7%,corresponding to the spinning rate of 10,20,30 and 40 m/s,respectively.     

Effects of annealing on microstructures and electrochemical properties of La0.8Mg0.2Ni2.4Mn0.10Co0.55Al0.10 alloy

The La0.8Mg0.2Ni2.4Mn0.10Co0.55Al0.10 alloy was prepared by induction melting. The structural and morphological characterizations were performed by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical measurements were performed using LAND and CHI 660b electrochemical workstation. The main phases of the alloy were LaNi5 and (La,Mg)Ni3. After annealing, the maximum discharge capacity, cycle stability and high rate dischargeability (HRD) were improved obviously. The maximum discharge capacity reached 373.80 mAh/g (T=1173 K), the C100/Cmax(%) was 72.63% (T=1173 K), and the value of HRD reached 51.8% at a discharge current density of 1150 mA/g (T=1173 K). The cyclic voltammetry (CV) and potentiodynamic polarization were also studied.