A2B7-type Electrode Alloys Research Articles

Effects of stoichiometric ratio La/Mg on structures and electrochemical performances of as-cast and annealed La–Mg–Ni-based A2B7-type electrode alloys

In order to investigate the influences of the stoichiometric ratio of La/Mg (increasing La and decreasing Mg on the same mole ratio) on the structure and electrochemical performances of the La–Mg–Ni-based A2B7-type electrode alloy, the as-cast and the annealed ternary La0.8+xMg0.2−xNi3.5 (x=0−0.05) electrode alloys were prepared. The characterization of electrode alloys by X-ray diffraction (XRD) and scanning electron microscopy (SEM) shows that all the as-cast and the annealed alloys hold two major phases of (La,Mg)2Ni7 and LaNi5 as well as a residual phase of LaNi3. Moreover, the increase of La/Mg ratio brings on a decline of (La,Mg)2Ni7 phase and a rise of LaNi5 and LaNi3 phases. The variation of La/Mg ratio gives rise to an evident change of the electrochemical performances of the alloys. The discharge capacities of the as-cast and the annealed alloys evidently decrease with growing the La/Mg ratio, while the cycle stabilities of the alloys visibly augment under the same condition. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS), the Tafel polarization curves, and the potential step measurements all indicate that the electrochemical kinetic properties of the alloy electrodes increase with the La/Mg ratio rising.

Effects of Annealing Temperature on the Electrochemical Hydrogen Storage Behaviors of La-Mg-Ni-Based A2B7-Type Electrode Alloys

In an attempt to improve the cyclic stability of La-Mg-Ni-based A2B7-type electrode alloys, La0.8Mg0.2Ni3.3Co0.2Six (x = 0−0.2) electrode alloys were fabricated by casting and annealing, and the effects of annealing temperature on the structures and electrochemical hydrogen storage performances of the alloys were systematically investigated. The results indicate that the as-cast and annealed alloys exhibit multiple structures that contain two major phases, (La,Mg)2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure; and one residual phase, LaNi3. Both the lattice constants and cell volumes of the two major phases increase with the increasing annealing temperature. Instead of altering the phase composition, the annealing treatment causes the abundances of these two major phases to vary. Based on electrochemical measurements, the cycle stabilities of the alloys are found to be considerably improved by annealing, and the alloy’s discharge capacity yields a maximum value with the increasing annealing temperature due to the variation in phase abundance and the homogenization of the composition, respectively. The influence of the annealing treatment on the electrochemical kinetics of the alloys is associated with the alloy’s composition; the electrochemical kinetics of the Si-free alloy become slower with the increasing annealing temperature, whereas those of the Si-added alloys first mount up and then go down under the same conditions.

Electrochemical hydrogen storage performances of the Si added La-Mg-Ni-based A2B7-type electrode alloys for Ni/MH battery application

The casting and annealing technologies were applied to fabricate the La0.8Mg0.2Ni3.3Co0.2Six (x = 0–0.2) electrode alloys. The effects of Si content and annealing temperature on the structure and electrochemical performances of the alloys were investigated systematically. The analyses of XRD and SEM show that all the alloys possess a multiphase structure, involving two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi3. The addition of Si brings on an evident increase in the LaNi5 phase and a decrease in the (La, Mg)2Ni7 phase, without altering the main phase component of the alloy, which also makes the lattice constants and cell volumes of the alloy enlarged. Likewise, the annealing treatment engenders the same action on the lattice constants and cell volumes as adding Si. Simultaneously, it gives rise to the variation of the phase abundance and the coarsening of the alloy grains. The electrochemical measurements indicate that the addition of Si ameliorates the cycle stability of the as-cast and annealed alloys significantly, but impairs their discharge capacities clearly. Similarly, the annealing treatment makes a positive contribution to the cycle stability of the alloy evidently, and the discharge capacity of the alloy shows a maximum value with annealing temperature rising. Furthermore, the high rate discharge ability (HRD) first augments and then declines with the rising of Si content and annealing temperature.

Effects of substituting La with M (M=Sm, Nd, Pr) on electrochemical hydrogen storage characteristics of A2B7-type electrode alloys

The partial substitution of M (M=Sm, Nd, Pr) for La was performed in order to ameliorate the electrochemical hydrogen storage performance of RE–Mg–Ni-based A2B7-type electrode alloys. The La0.8–xMxMg0.2Ni3.35Al0.1Si0.05 (M=Sm, Nd, Pr; x=0–0.4) electrode alloys were fabricated by casting and annealing and their microstructures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The major phases (La, Mg)2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCu5-type structure make up the basic microstructure of the experimental alloys. The discharge capacities of the as-cast and annealed alloys all gain their maximum values with the M (M=Sm, Nd, Pr) content varying. The electrochemical cycle stability of the as-cast and annealed alloys clearly rises with the M (M=Sm, Nd, Pr) content growing. Furthermore, the electrochemical kinetics of the alloys, including the high rate discharge ability, charge transfer rate, limiting current density and hydrogen diffusion coefficient, all present a increase trend at first and then decrease with the rising of M (M=Sm, Nd, Pr) content.

Structures and electrochemical hydrogen storage performance of Si added A2B7-type alloy electrodes

In order to ameliorate the electrochemical hydrogen storage performance of La–Mg–Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six (x=0–0.2) electrode alloys were prepared by casting and annealing. The effects of adding Si on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated systematically. The results indicate that the as-cast and annealed alloys hold multiple structures, involving two major phases of (La, Mg)2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure as well as one residual phase LaNi3. The addition of Si results in a decrease in (La, Mg)2Ni7 phase and an increase in LaNi5 phase without changing the phase structure of the alloys. What is more, it brings on an obvious effect on electrochemical hydrogen storage characteristics of the alloys. The discharge capacities of the as-cast and annealed alloys decline with the increase of Si content, but their cycle stabilities clearly grow under the same condition. Furthermore, the measurements of the high rate discharge ability, the limiting current density, hydrogen diffusion coefficient as well as electrochemical impedance spectra all indicate that the electrochemical kinetic properties of the electrode alloys first increase and then decrease with the rising of Si content.

Influence of Melt Spinning on the Electrochemical Hydrogen Storage Kinetics of RE-Mg-Ni-Based A2B7-Type Alloys

Abstract In order to improve the electrochemical characteristics of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of M (M=Pr, Zr) for La has been performed. The melt spinning technology was used to prepare the La0.65M0.1Mg0.25Ni3.2Co0.2Al0.1 (M=Pr, Zr) electrode alloys. The influences of the melt spinning and substithting La with M (M=Pr, Zr) on the structures and the electrochemical hydrogen storage kinetics of the alloys were investigated. The results obtained by XRD and TEM reveal that the as-cast and spun alloys hold a multiphase structure, containing 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 measurement indicates that the high rate discharge ability (HRD) of the alloys first mounts up and then falls with rising of spinning rate. Furthermore, the electrochemical impedance spectrum (EIS), the Tafel polarization curves and the potential-step measurements all indicate that the electrochemical kinetics first increase and then decreases with growing of spinning rate.

The electrochemical hydrogen storage performances of Si-added La–Mg–Ni–Co-based A2B7-type electrode alloys

In order to improve the electrochemical cycle stability of the RE–Mg–Ni-based A2B7-type electrode alloys, a small amount of Si has been added into the alloys. The casting and annealing technologies were adopted to fabricate the La0.8Mg0.2Ni3.3Co0.2Six (x = 0–0.2) electrode alloys. The impacts of the addition of Si and annealing treatment on the structures and electrochemical performances of the alloys were investigated systematically. The results obtained by XRD and SEM show that all the as-cast and annealed alloys are of a multiphase structure, involving two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi3. Both adding Si and the annealing treatment lead to an evident change in the phase abundance and cell parameters of (La, Mg)2Ni7 and LaNi5 major phases of the alloy without altering its main phase component. Moreover, the annealing treatment has the composition of the alloy distributed more homogeneously overall and simultaneously causes the grain of the alloy to be coarsened obviously. The electrochemical measurements indicate that adding Si and the annealing treatment give a significant rise to the influence on the electrochemical performances of the alloys. In brief, the cycle stability of the as-cast and annealed alloys evidently increases with the rising of Si content, while their discharge capacities obviously decrease under the same circumstances. Furthermore, the electrochemical kinetic properties of the electrode alloys, including the high rate discharge ability, the limiting current density (IL), hydrogen diffusion coefficient (D), and the charge-transfer resistance, first augment and then decline with the rising of Si content. Similarly, it is found that the above-mentioned electrochemical properties first mount up and then go down with the rising annealing temperature.

Structure and electrochemical hydrogen storage characteristics of La0.8−x Pr x Mg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0–0.4) electrode alloys

For the purpose of improving the electrochemical cycle stability of the La-Mg-Ni based A2B7-type electrode alloys, both reducing Mg content and substituting La with Pr were adopted. The La0.8−xPrxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys were fabricated by casting and annealing. The investigation on the structures and electrochemical performances of the alloys was performed. The obtained results reveal that the as-cast and annealed alloys comprise two major phases, (La, Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure, as well as a little residual LaNi3 phase. It is also found that the addition of Pr element observably affects the electrochemical hydrogen storage characteristics of the alloys, just as the discharge capacity and high rate discharge ability (HRD) first rise then fall with the growing of Pr content, and among all the alloys, the as-cast and annealed (x=0.3) alloys generate the largest discharge capacities of 360.8 and 386.5 mA·h/g, respectively. Additionally, the electrochemical cycle stability of all the alloys markedly grows with the increase of Pr content. The capacity retaining rate (S100) at the 100th charging and discharging cycle is enhanced from 64.98% to 77.55% for the as-cast alloy, and from 76.60% to 95.72% for the as-annealed alloy by rising Pr content from 0 to 0.4. Furthermore, the substitution of Pr for La results in first increase and then decrease in the hydrogen diffusion coefficient (D), the limiting current density (IL) as well as the electrochemical impedance.

Electrochemical hydrogen storage characteristics of La0.75−x M x Mg0.25Ni3.2Co0.2Al0.1 (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 of M (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.

Electrochemical performances of the as-melt La0.75−xMxMg0.25Ni3.2Co0.2Al0.1 (M = Pr, Zr; x = 0, 0.2) alloys applied to Ni/metal hydride (MH) battery

The partial replacement of La by M (M = Pr, Zr) has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni-based A2B7-type electrode alloys. For this purpose, we adopt melt spinning technology to prepare the La0.75−xMxMg0.25Ni3.2Co0.2Al0.1 (M = Pr, Zr; x = 0, 0.2) electrode alloys. Then systemically investigate the effects that the preparation methods and M (M = Pr, Zr) substitution have on the structures and electrochemical hydrogen storage characteristics of the alloys. The analysis of XRD and TEM reveals that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)2Ni7 and LaNi5 as well as a trace of residual phase LaNi2. Besides, the as-spun (M = Pr) alloy displays an entire crystalline structure, while an amorphous-like structure is detected in the as-spun (M = Zr) alloy, implying the replacement of La by Zr facilitates forming amorphous phase. Based upon electrochemical measurements, an impact engendered by melt spinning on the electrochemical performances of the alloys appears to be evident. The cycle stabilities monotonously augment with the growing of the spinning rate. The discharge capacity and high rate discharge ability (HRD), however, exhibit difference. For the (M = Pr) alloy, they first mount up and then fall with the rising of the spinning rate, whereas for the (M = Zr) alloy, they always decline as the spinning rate elevates. Furthermore, the replacement of La by M (M = Pr, Zr) considerably enhances the cycle stability of the alloys and the replacement of La by Pr clearly increases the discharge capacity, but the Zr replacement results in an adverse impact.

Influence of Substituting La with Zr on Electrochemical Characteristics of As-Spun RE–Mg–Ni-Based A<sub>2</sub>B<sub>7</sub>-Type Alloys

In order to ameriolate the electrochemical hydrogen storage performances of La–Mg–Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys were prepared by melt spinning. The influences of substithting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated. The structure characterized by XRD and TEM displays that the as-spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun Zr-free alloy displays an entire nanocrystalline structure, while an like amorphous structure is detected in the as-spun alloy substituted by Zr, implying that the substitution of Zr for La facilitates the amorphous formation. The substitution of Zr for La markedly enhances the electrochemical cycle stability of the alloys, whereas the impact generated by such substitution on the high rate discharge ability (HRD) of the alloys is different with the variation of the spinning rate. The HRD of the as-spun (5 m/s) alloys yields the largest value with the change of Zr content, but that of the as-spun (20 m/s) alloys always declines with the growing amount of Zr substitution.

Electrochemical Cycle Stability and Kinetics of the As-Cast and Spun La<sub>0.75−x</sub>Zr<sub>x</sub>Mg<sub>0.25</sub>Ni<sub>3.2</sub>Co<sub>0.2</sub>Al<sub>0.1</sub> (x = 0-0.2) Alloys

The poor electrochemical cycle stability of Re-Mg-Ni system A2B7-type electrode alloys has limited their practical application as the negative electrode materials of Ni-MH battery. In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.2) electrode alloys were fabricated by casting and melt-spinning. The microstructures and the electrochemical cycle stability and kinetics of the alloys were investigated. The structure characterized by XRD, SEM and HRTEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun Zr-free alloy displays an entire nanocrystalline structure, but a like amorphous structure is detected in the as-spun alloy substituted by Zr, suggesting that the substitution of Zr for La facilitates the formation of an amorphous structure. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning remarkably ameliorate electrochemical cycle stability of the alloys. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) and the potential-step measurements all indicate that both of the melt spinning and the Zr substitution bring on a notable decline of the electrochemical kinetics of the alloys.

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) electrode 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 increased and then decreased for the as-cast and annealed alloys, whereas the capacity retaining rate (S100) after 100 cycles increased continuously.

Improved Electrochemical Cycle Stability of La–Mg–Ni-Based A<sub>2</sub>B<sub>7</sub>-Type Alloys by Melt Spinning and Substituting La with Pr

The poor electrochemical cycle stability of RE–Mg–Ni system A2B7-type electrode alloys have limited their practical application as the negative electrode materials of Ni–MH battery. In order to improve the electrochemical cycle stability of the La–Mg–Ni system A2B7-type electrode alloys, the partial substitution of Pr for La has been performed. The La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.4) electrode alloys were fabricated by casting and melt-spinning. The microstructures and electrochemical cycle stability of the as-cast and spun alloys were investigated by XRD, SEM and HRTEM. The results show that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La brings on a notable grain refinement of the as-cast alloys instead of altering the phase structure of the alloys. The electrochemical measurement indicates that the cycle stability of the alloy remarkably grows with increasing both Pr content and spinning rate. The substitution of Pr for La and the melt spinning significantly ameliorate electrochemical cycle stability of the alloys. The capacity retaining rate (S100) of the as-spun (15 m/s) alloys at 100th charging/discharging cycle is enhanced from 72.38% to 90.33% by increasing Pr content from 0 to 0.4. And that of the Pr0.3 alloy is increased from 78.11% to 92.32% by growing spinning rate from 0 (as-cast was defined as the spinning rate of 0 m/s) to 20 m/s.

Investigation on the Electrochemical Cycle Stability of La–Mg–Ni-based A<sub>2</sub>B<sub>7</sub>-type Alloys Prepared by Melt Spinning

In order to improve the electrochemical cycle stability of the La–Mg–Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys were fabricated by casting and melt-spinning. The influences of both the substitution of Zr for La and the melt spinning on the structures and the electrochemical cycle stability of the alloys were investigated. The structure characterization of XRD, SEM and HRTEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2 Ni7 and LaNi5 as well as a residual phase LaNi2. The substitution of Zr for La results in an evident refinement of the grains of the alloys instead of changing the structures of two major phases. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning remarkably ameliorate electrochemical cycle stability of the alloys. The capacity retaining rate (R100) of the as-spun (5 m/s) alloys at 100th charging/discharging cycle is enhanced from 67.43% to 79.22% by increasing Zr content from 0 to 0.2. And that of the Zr0.1 alloy is increased from 73.21% to 82.07% by growing spinning rate from 0 (as-cast was defined as the spinning rate of 0 m/s) to 20 m/s.

Impacts of Melt Spinning and Element Substitution on Electrochemical Characteristics of the La–Mg–Ni-based A<sub>2</sub>B<sub>7</sub>-Type Alloys

The partial substitution of Zr for La has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni based A2B7-type electrode alloys. The melt spinning technology was used to prepare the La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x=0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The impacts of the melt spinning and the substituting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were systemically investigated. The analysis of XRD and TEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning ameliorate the electrochemical cycle stability of the alloys dramatically. Furthermore, the high rate discharge ability (HRD) of the as-spun (10 m/s) alloys notably declines with growing the amount of Zr substitution, while it first augments and then falls for the (x=0.1) alloy with rising the spinning rate.

Enhanced Electrochemical Cycle Stability of RE-Mg-Ni System A<sub>2</sub>B<sub>7</sub>-Type Alloys by Melt Spinning and Substituting La with Pr

It has come to light that the poor electrochemical cycle stability of RE-Mg-Ni based AB3and A2B7-types electrode alloys limited their practical application as the negative electrode materials of Ni-MH battery. In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys, La in the alloy is partially substituted by Pr and the melt-spinning technology was used for preparing La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1(x = 0-0.4) electrode alloys. The microstructures and electrochemical cycle stability of the as-cast and spun alloys were investigated. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)2Ni7and LaNi5as well as a residual phase LaNi2. The substitution of Pr for La gives rise to a visible grain refinement of the as-cast alloys instead of changing the phase structure of the alloys. The electrochemical measurement indicates that the cycle stability of the alloy remarkably grows with increasing both Pr content and spinning rate.

An Investigation on the Electrochemical Cycle Stability of La<sub>0.75−x</sub>Zr<sub>x</sub>Mg<sub>0.25</sub>Ni<sub>3.2</sub>Co<sub>0.2</sub>Al<sub>0.1</sub> (x = 0-0.2) 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. The melt-spinning technology was used for preparing La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1(x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The influences of both the substitution of Zr for La and the melt spinning on the structures and the electrochemical cycle stability of the alloys were investigated in detail. The structure analysis of XRD, SEM and TEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7and LaNi5as well as a residual phase LaNi2. The substitution of Zr for La facilitates to form a like amorphous structure in the as-spun alloy without altering the structures of two major phases. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning remarkably improves cycle stability of the alloys. The capacity retaining rate (S100) of the Zr0.2alloy at 100th charging/discharging cycle is enhanced from 76.69 to 85.18% by growing spinning rate from 0 (as-cast was defined as the spinning rate of 0 m/s) to 30 m/s. And that of the as-spun (10 m/s) alloys is increased from 69.25 to 83.09% by rising Zr content from 0 to 0.2.

Improved Cycle Stability of La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1 (x=0-0.4) Electrode Alloys 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 Pr. The melt-spinning technology was used for preparing La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures of the as-cast and spun alloys were investigated by XRD, SEM and TEM. The results show that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The melt spinning leads to an obvious increase of the LaNi5 phase and a decrease of the (La, Mg)Ni3 phase in the alloys. The melt spinning significantly improves the cycle stability of the alloys. The capacity retaining rate at 100th charging and discharging cycle (S100) is enhanced from 65.32% to 73.97% for the x = 0 alloy and from 79.36% to 93.08% for the x = 0.4 alloy with increasing of spinning rate from 0 m/s (as-cast was defined as spinning rate of 0 m/s) to 20 m/s.

Influences of Substitution of Zr for La on Structures and Electrochemical Performances of A2B7-Type Electrode Alloys by Melt-Spinning

Abstract A 2 B 7 -type electrode alloys with a nominal composition of La 0.75- x Zr x Mg 0.25 Ni 3.2 Co 0.2 Al 0.1 ( x = 0, 0.05, 0.1, 0.15, 0.2) were prepared by casting and melt-spinning. The influences of the substitution of Zr for La on the structures as well as the electrochemical performances of the alloys were investigated. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La, Mg)Ni 3 and LaNi 5 as well as a residual phase LaNi 2 . The substitution of Zr for La leads to an obvious increase of the LaNi 5 phase in the alloys, and it also helps the formation of a like amorphous structure in the as-spun alloy. The results of the electrochemical measurements indicate that the substitution of Zr for La obviously decreases the discharge capacity of the as-cast and spun alloys, but significantly improves their cycle stability. With increasing the spinning rate, the discharge capacity of the alloys ( x =0.1) first increases and then decreases, while the cycle stability monotonously rises.