Electrochemical hydrogen storage characteristics of La0.75-xMxMg0.25Ni3.2Co0.2Al0.1 (M =Zr, Pr; x =0, 0.1) alloys prepared by melt spinning

In order to ameliorate the electrochemical hydrogen storage performances of La-Mg Ni system A2B7-type electrode alloys,the partial substitution ofM (M =Zr,Pr) for La was performed.The melt spinning technology was used to fabricate the La0.75-xMxMg0.25Ni3.2Co0.2Al0.1 (M =Zr,Pr; x =0,0.1) electrode alloys.The influences of the melt spinning and substituting La with M (M =Zr,Pr) on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated.The analysis of XRD,SEM,and TEM reveals that the as-cast and spun alloys have a multiphase structure composed of two main phases (La,Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2.The as-spun (M =Pr) alloy displays an entire nanocrystalline structure,while an amorphous-like structure is detected in the as-spun (M =Zr) alloy,implying that the substitution of Zr for La facilitates the amorphous formation.The electrochemical measurements exhibit that the substitution of Pr for La clearly increases the discharge capacity of the alloys; however,the Zr substitution brings on an adverse impact.Meanwhile,the M (M =Zr,Pr) substitution significantly enhances its cycle stability.The melt spinning exerts an evident effect on the electrochemical performances of the alloys,whose discharge capacity and high rate discharge ability (HRD) first mount up and then fall with the growing spinning rate,whereas their cycle stabilities monotonously augment as the spinning rate increases.     

Improved Cycle Stability of La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1 (x=0-0.4) Electrode Alloys by Melt Spinning

为了改善 La-Mg-Ni 系 A2B7型电极合金的电化学循环稳定性,用 Pr 部分替代合金中的 La,并用熔体快淬工艺制备了La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1(x = 0, 0.1, 0.2, 0.3, 0.4)电极合金。用 XRD、SEM、TEM 分析了铸态及快淬态合金的微观结构。结果表明,铸态及快淬态合金均具有多相结构,包括 2 个主相(La,Mg)Ni3及 LaNi5和 1 个残余相 LaNi2。熔体快淬导致 LaNi5相增加而(La,Mg)Ni3相减少。电化学测试结果表明,熔体快淬显著地提高合金的电化学循环稳定性。当淬速从 0 m/s (铸态被定义为淬速 0 m/s)增加到 20 m/s 时,x=0 合金 100 次充放循环后的容量保持率从 65.32%增加到 73.97%,x=0.4 合金的容量保持率从 79.36%增加到 93.08%。     

Hydrogen storage behaviours of nanocrystalline and amorphous Mg_(20)Ni_(10-x)Co_x(x=0-4) alloys prepared by melt spinning

The Mg2Ni-type alloys with nominal compositions of Mg20Ni10-xCox(x=0,1,2,3,4,%,mass fraction) were prepared by melt-spinning technology.The structures of the alloys were studied by XRD,SEM and HRTEM.The hydrogen absorption/desorption kinetics and the electrochemical performances of the alloys were measured.The results show that no amorphous phase forms in the as-spun Co-free alloy,but the as-spun alloys containing Co show a certain amount of amorphous phase.The hydrogen absorption capacities of the as-cast ...     

Effects of rapid quenching on structure and electrochemical characteristics of La0.5Ce0.2Mg0.3Co0.4Ni2.6-xMnx （x=0-0.4） electrode alloys

The La-Mg-Ni system PuNi3-type La0.5Ce0.2Mg0.3Co0.4Ni2.6-xMnx (x=0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the rapid quenching on the structure and electrochemical characteristics of the alloys were studied. The results obtained by XRD, SEM and TEM indicate that the as-cast and quenched alloys mainly consist of two major phases, (La,Mg)Ni3 and LaNi5, as well as a residual phase LaNi. The rapid quenching does not exert an obvious influence on the phase composition of the alloys, but it leads to an increase of the LaNi5 phase and a decrease of the (La, Mg)Ni3 phase. The as-quenched alloys have a nano-crystalline structure, and the grain sizes of the alloys are in the range of 20-30 nm. The results by the electrochemical measurements indicate that both the discharge capacity and the high rate discharge(HRD) ability of the alloy first increase and then decrease with the variety of quenching rate and obtain the maximum values at the special quenching rate which is changeable with the variety of Mn content. The rapid quenching significantly improves the cycle stabilities of the alloys, but it slightly impairs the activation capabilities of the alloys.     

Investigation on the structures and electrochemical performances of La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.2) electrode alloys prepared by melt spinning

In order to improve the electrochemical cycle stability of the La–Mg–Ni system A₂B₇-type electrode alloys, La in the alloy was partially substituted by Zr and the melt-spinning technology was used for preparing La_0.75−xZr_xMg_0.25Ni_3.2Co_0.2Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM showed that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Zr for La leads to an obvious increase of the LaNi₅ phase in the alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. The results of the electrochemical measurement indicated that the substitution of Zr for La obviously decreased the discharge capacity of the as-cast and quenched alloys, but it significantly improved their cycle stability. The discharge capacity of the alloys (x ≤ 0.1) first increased and then decreased with the variety of the quenching rate. The cycle stability of the alloys monotonously rose with increasing quenching rate.     

Electrochemical Hydrogen Storage Characteristics of the as-Cast and Annealed La0.8-xPrxMg0.2Ni3.35Al0.1Si0.05 (x=0~0.4) Electrode Alloys

采用铸造及退火工艺制备了La0.8-xPrxMg0.2Ni3.35Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4)电极合金。系统研究了Pr的替代对合金的结构与电化学储氢性质的影响,结果表明除少量残余LaNi3相外,铸造及退火合金是由六方Ce2Ni7型(La, Mg)2Ni7相与六方CaCu5型LaNi5相构成的。Pr对La的置换对合金的电化学储氢性质产生明显影响,铸造及退火合金的放电容量和高倍率放电能力随Pr含量的增加先升后降。当Pr含量由0增加至0.4时,铸造及退火合金的100次充放电循环后容积保持率S100从64.96%和72.82%分别增加至77.94%和91.81%     

Microstructure and electrochemical properties of La_(0.8-x)MM_xMg_(0.2)Ni_(3.1)Co_(0.3)Al_(0.1)(x=0,0.1,0.2,0.3)alloys

The present study aims to improve electrochemical properties of the La-Mg-Ni-based hydrogen storage alloys through partial substitution for La by mischmetal(MM).The La_(0.8-x)MM_xMg_(0.2)Ni_(3.1)Co_(0.3)Al_(0.1)(x=0,0.1,0.2,0.3)alloys were prepared by inductive melting,and their phase structures and electrochemical properties were studied by X-ray diffraction(XRD),scanning electron microscope(SEM),energy-dispersive X-ray spectrometry(EDX)and electrochemical tests.Results show that the alloys mainly consist of La_2Ni_7-type phase,La_5Ni_(19)-type phase,LaNi_5-type phase and LaNi_3-type phase.The addition of MM does not change the phase compositions,while it leads to more uniform phase distribution and obviously promotes the formation of La_2Ni_7-type phase which possesses favorable electrochemical properties.Electrochemical studies indicate that the substitution for La by MM could effectively improve the high rate dischargeability(HRD)of the alloy electrode,and the optimal value of HRD_(1500)(HRD at 1500 mA·g~(-1))increases from 40.63%(x=0)to 60.55%(x=0.3).Although the activation properties of the alloy electrodes keep almost unchanged,both the maximum discharge capacity(C_(max))and the cycling stability are significantly improved by MM addition.     

退火方式对La_(0.75)Mg_(0.25)Ni_(3.44)Co_(0.2)Al_(0.03)Ti_(0.03)合金的电化学性能影响

为了研究不同退火方式对La0.75Mg0.25Ni3.44Co0.2Al0.03Ti0.03铸态合金的电化学性能影响,设计最终退火温度为1223K,并采用不同保温程序对合金进行退火处理。X射线衍射(XRD)与扫描电镜(SEM)分析一段、两段保温法退火后合金的结构与性能结果表明,铸态及退火后合金由LaNi5,(La,Mg)2(Ni,Co,Al)7相以及少量LaNi2、TiNi3相组成,且退火后合金中(La,Mg)(Ni,Co,Al)3相出现。前者微观组织较后者均匀,并且前者的放电容量、放电效率好于后者。一段保温法更有利于改善合金的循环稳定性。     

La0.8-xCexMg0.2Ni3.5(x=0~0.20)贮氢合金电极的低温放电性能

用冷坩埚磁悬浮熔炼炉制各La0.8-xCexMg0.2Ni3.5(x=0.0.05,0.10,0.15,0.20)贮氢电极合金,采用X射线衍射、三电极体系系统研究合金的微观结构和电化学性能.研究表明:合金为多相结构,主相均为Ce2Ni7型六方相,还包括Cacu5型六方相、PuNi3型菱方相;P-C-T曲线显示,随着Ce含最的增加,合金放氢平台区域变窄,平台压力升高.合金中各组成相单胞体积的减小是其主要原因.随着Ce含量的增加,合金常温最大放电容量逐渐减小并且循环稳定性有一定改善;低温最大放电容量则先增大后减小,合金的低温高倍率放电性能以及交换电流密度均随Ce含量的增加而增加,但氢扩散系数随着Ce含量的增加而减小.     

Zr替代La对快淬态A2B7型电极合金结构及电化学性能的影响

用铸造及快淬工艺制备了A2B7型电极合金,合金的名义成分为La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2)。深入研究了Zr替代La对合金微观结构及电化学性能的影响。用XRD、SEM、TEM分析了合金的结构。结果表明,铸态及快淬态合金均具有多相结构,含有两个主相(La,Mg)Ni3和LaNi5以及一个残余相LaNi2。Zr替代La使合金中LaNi5相明显增加,并促进快淬态合金中形成非晶相。电化学测试的结果表明,Zr替代La明显降低合金的放电容量,但显著改善合金的电化学循环稳定性。当Zr含量小于0.1时,合金的放电容量随淬速的增加而先增加后减小,合金的循环稳定性随淬速的增加而单调增加。     

添加Si对A_2B_7型电极合金结构及电化学贮氢性能的影响(英文)

为改善La–Mg–Ni系A2B7型合金的电化学贮氢性能,在合金中添加一定量的Si元素,通过真空熔炼及退火处理的方法制备La0.8Mg0.2Ni3.3Co0.2Six(x=0-0.2)电极合金。研究Si元素的添加对合金结构及电化学贮氢性能的影响。结果表明,铸态及退火态合金均为多相结构,分别为Ce2Ni7型的(La,Mg)2Ni7相和CaCu5型的LaNi5相以及少量的残余相LaNi3。Si元素的添加没有改变合金的主相,但使得合金中的(La,Mg)2Ni7相减少而LaNi5相增加。添加Si显著地影响了合金的电化学性能。随着Si含量的增加,铸态及退火态合金的放电容量逐步降低,但循环稳定性却随着Si含量的增加而增强。此外,合金电极的高倍率放电性能、极限电流密度、氢扩散系数以及电化学交流阻抗谱的测试均表明合金的电化学动力学性能随着Si含量的增加先增加而后减小。     

Effects of rapid quenching on microstructures and electrochemical properties of La_(0.7)Mg_(0.3)Ni_(2.55)Co_(0.45)B_x(x=0-0.2) hydrogen storage alloy

1 Introduction Ni-MH batteries have been used widely by virtue of several of their advantages, such as high capacity, capable of performing a high rate charge/discharge, high resistance to overcharging and over-discharging, a long cycle life, environment…     

铸态及快淬态La2Mg（Ni0.85Co0.15）9Crx（x=0～0.2）电极合金的微观结构及电化学性能

为了提高La-Mg-Ni系（PuNi3）型贮氢合金的电化学循环稳定性,在La2Mg（Ni0.85Co0.15）9合金中加入微量Cr,用铸造及快淬工艺制备了La2Mg（Ni0.85Co0.15）9Crx（x=0,0.1,0.2）贮氢合金.分析测试了铸态及快淬态合金的电化学性能及微观结构,研究了Cr对铸态及快淬态合金微观结构及电化学性能的影响.结果表明,铸态及快淬态合金具有多相结构,包括（La,Mg）Ni3相（PuNi3结构））,LaNi5相和一定量的LaNi2相.快淬对合金的相组成没有影响,但使合金的相丰度产生变化.Cr的加入提高了铸态及快淬态合金的循环稳定性,但使合金的容量下降.合金的循环寿命随淬速的增加而增加,铸态及快淬态合金均有优良的活化性能.     

Effects of rapid quenching on microstructures and electrochemical properties of La0.7Mg0.3Ni2.55Co0.45Bx（x=O-0.2） hydrogen storage alloy

In order to improve the electrochemical performances of La-Mg-Ni based electrode alloys with PuNi3-type structure, a trace of boron was added in La0.7Mg0.3Ni2.55Co0.45 alloy. The La0.7Mg0.3Ni2.55Co0.45Bx（a=0, 0.05, 0.1, 0.15 and 0.2） alloys were prepared by casting and rapid quenching. The electrochemical performances and microstructures of the as-cast and quenched alloys were investigated. The effects of rapid quenching on the microstructures and electrochemical performances of the above alloys were investigated. The results show that the as-cast and quenched alloys are composed of （La, Mg）Ni3 phase, LaNi5 phase and LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloys containing boron, and the Ni2B phase in the B-contained alloys nearly disappears after rapid quenching. Rapid quenching increases the amount of the LaNi2 phase in the B-free alloy, but it decreases the amount of the LaNi2 phase in the boron-containing alloys. The effects of rapid quenching on the capacities of the boron-containing and boron-free alloys are different. The capacity of the B-free alloy monotonously decreases with increasing quenching rate, whereas the capacities of the B-contained alloys have a maximum value with the change of the quenching rate. The rapid quenching can improve the stability of La-Mg-Ni based electrode alloy but lowers the discharge plateau voltage and decreases the plateau length. The effect of rapid quenching on the activation capabilities of the alloys was complicated.     

Effects of substituting Ni with M (M=Cu, Al and Mn) on microstructures and electrochemical characteristics of La-Mg-Ni system (PuNi3-type) electrode alloys

In order to improve the electrochemical cycle stability of La-Mg-Ni system (PuNi3-type) hydrogen storage alloy, Ni in the alloys was partially substituted by M (M=Cu, Al, Mn). A new La-Mg-Ni system electrode alloys La0.7Mg0.3Ni2.55-xCo0.45Mx (M=Cu, Al, Mn;x =0,0.1) were prepared by casting and rapid quenching. The effects of element substitution and rapid quenching on the microstructures and electrochemical performances of the alloys were investigated. The results by XRD, SEM and TEM show that the alloys havea multiphase structure, including the (La, Mg)Ni3 phase, the LaNi5 phase and the LaNi2 phase. The rapid quenching and element substitution have an imperceptible influence on the phase compositions of the alloys, but both change the phase abundance of the alloys. The rapid quenching significantly improves the composition homogeneity of the alloys and markedly decreases the grain size of the alloys. The Cu substitution promotes the formation of an amorphous phase in the as-quenched alloy, and a reversal result by the Al substitution. The electrochemical measurement indicates that the element substitution decreases the discharge capacity of the alloys, whereas it obviously improves the cycle stability of the alloys. The positive influence of element substitution on the cycle life of the alloys is in sequence Al＞Cu＞Mn, and negative influence on the discharge capacity is in sequence Al＞Mn＞Cu. The rapid quenching significantly enhances the cycle stability of the alloys, but it leads to a different extent decrease of thedischarge capacity of the alloys.     

High-temperature electrochemical performance and phase composition of Ti_(0.7) Zr_(0.5) V_(0.2) Mn_(1.8-x)Ni_x hydrogen storage electrode alloys

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Cycle stability of La0.7Mg0.3Ni2.55-xCo0.45Cux （x=0-0.4） electrode alloys

La0.7Mg0.3Ni2.55-xCo0.45Cux（x=0, 0.1, 0.2, 0.3, 0.4） electrode alloys were prepared by casting and rapid quenching. Ni in the alloy was partially substituted by Cu in order to improve the cycle stability of La-Mg-Ni system （PuNi3-type） hydrogen storage alloy. The effects of substituting Ni with Cu on the microstructures and cycle stability of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the substitution of Cu for Ni is favourable for the formation of an amorphous in the as-quenched alloy, and this leads to an obvious refinement of the as-quenched alloy grains and a growth of the lattice constants and cell volumes of the as-cast and quenched alloys. The results obtained by the electrochemical measurement indicate that the cycle stability of the alloys significantly rises with the incremental variety of Cu content. When Cu content changes from 0 to 0.4, the cycle lives of the as-cast and quenched （30 m/s） alloys are enhanced from 72 to 88 cycles and from 100 to 121 cycles, respectively.     

Enhanced Electrochemical Hydrogen Storage Characteristics of Nanocrystalline and Amorphous Mg20Ni10-xCox (x=0-4) Alloys by Melt Spinning

In order to improve the electrochemical hydrogen storage performances of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by element Co. The nanocrystalline and amorphous Mg20Ni10-xCox (x=0, 1, 2, 3, 4) alloys were prepared by melt-spinning technology. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The electrochemical hydrogen storage characteristics of the alloys were measured. The results show that the substitution of Co for Ni leads to the formation of secondary phase MgCo2 without altering the major phase of Mg2Ni. No amorphous phase is detected in the as-spun alloy (x=0), whereas the as-spun alloy (x=4) holds a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni significantly increases the glass forming ability of the Mg2Ni-type alloy. The substitution of Co for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, including the discharge capacity and the cycle stability, for which the increased glass forming ability by Co substitution is mainly responsible     

Structure and electrochemical performances of Mg_(20-x)Y_xNi_(10)(x=0-4) alloys prepared by mechanical milling

Mg_2Ni-type Mg_(20-x)Y_xNi_(10)(x=0,1,2,3 and4) electrode alloys were fabricated by vacuum induction melting.Subsequently,the as-cast alloys were mechanically milled on a planetary-type ball mill.The effects of milling time and Y content on the microstructures and electrochemical performances of the alloys were investigated in detail.The results show that nanocrystalline and amorphous structure can be successfully obtained through mechanical milling.The substitution of Y for Mg facilitates the glass forming of the Mg_2Ni-type alloy and significantly enhances the electrochemical characteristics of the alloy electrodes.Moreover,the discharge capacity of Y-free alloy monotonously grows with the milling time prolonging,while that of the Y-substituted alloys has the maximum values in the same case.The milling time of obtaining the greatest discharge capacity markedly decreases with Y content increasing.The electrochemical kinetics of the alloys,including high rate discharge ability(HRD),diffusion coefficient(D),limiting current density(I_L) and charge transfer rate,monotonously increase with milling time extending.     

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.