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The present work gives the electronic structures of La 3-x Mg x Ni 9 (x = 0.0–2.0) alloys by first-principles calculations using the generalized gradient approximation of Perdew-Wang 91 (GGA-PW91) method within Cambridge Serial Total Energy Package (CASTEP), aiming at gaining insight into the hydrogen storage mechanism of La 3-x Mg x Ni 9 alloys modified by Mg. The results show that the La 3-x Mg x Ni 9 alloys consist predominantly of interactions between La-Ni, Ni-Ni or/and Mg-Ni. Among them, La-Ni interaction is the major factor controlling the structural stability of the alloys. Mg substitution increases the La-Ni bonding interactions to achieve stable Mg-containing metal matrices for reversible hydrogen absorption-desorption. This is particularly obvious at high Mg composition, as the La-Ni interactions gradually increase with Mg content. The increase of La-Ni interactions coupled with the decrease of Mg-Ni and Ni-Ni interactions will relieve the hydrogen-induced amorphization and disproportionation, and subsequently enhance the cyclic stability of La 3-x Mg x Ni 9 alloys at high Mg content. However, Mg substitution for La leads to a subsequent contraction in cell volume, dramatically reducing the reversible H capacity at high Mg composition such as LaMg 2 Ni 9. Suitable Mg content in La-Mg-Ni systems, such as an approximately range x = 1.0–1.4 in La 3-x Mg x Ni 9 alloys, is required in trade-off between hydrogen storage capacity and cycle life. • La 3-x Mg x Ni 9 (x = 0–2) alloys with defined La and Mg atoms are introduced for calculation. • Mg substitution leads to a gradual contraction in cell volume for less H-capacity. • La-Ni interaction is dominant in the structural stability of La 3-x Mg x Ni 9 alloys. • Increased La-Ni and decreased Mg/Ni-Ni interactions favor for cycle stability. [ABSTRACT FROM AUTHOR]

The present work is focused on the studies of the phase-structural transformations in the La 3-x Mg x Ni 9 (x ​= ​1.0, 1.1 and 1.2) alloys as active materials of negative electrodes in the Nickel-Metal Hydride (Ni/MH) batteries. The phase equilibria and phase-structural transformations in the alloys were probed by in situ neutron powder diffraction (NPD) at the temperatures ranging from 300 ​K to 1273 ​K using the measurements of the equilibrated alloys at 8 setpoint temperatures of 300, 973, 1073, 1123, 1173, 1223, 1248 and 1273 ​K. Prepared by induction melting initial alloys were found to be multi-phase structured, containing up to 6 individual intermetallic compounds with different stoichiometric compositions. With the increase of the temperature and holding time, various transformations took place in the studied alloys. These included the formations and transformations of super-stacking intermetallics with variable ratios (La ​+ ​Mg)/Ni, 1:3, 2:7 and 5:19. With increasing temperatures, several systematic changes took place. (a) Abundances of (La,Mg) 2 Ni 4 AB 2 and (La,Mg)Ni 3 AB 3 type intermetallics gradually decreased before they melted/decomposed above 1073 ​K; (b) The (La,Mg) 2 Ni 7 A 2 B 7 type intermetallics began to decrease in abundances above 1123 ​K; (c) The transformation in the (La,Mg) 5 Ni 19 intermetallics from 3R to 2H proceeded above 1223 ​K. The increase of Mg content had no obvious influence on (La,Mg) 2 Ni 4 and (La,Mg) 2 Ni 7 phases, and corresponding reactions R1 and R3 took place at the same temperatures as in the La–Ni system. However, with increasing Mg content the melting point of (La,Mg) 5 Ni 19 phase increased while the melting point of the (La,Mg)Ni 3 phase it decreased, leading to the variation of the reaction temperatures of the corresponding processes. The present study will assist in optimizing phase-structural composition of the alloys in the La–Mg–Ni system which contain Mg-modified layered structures by tailoring the high temperature annealing conditions. [Display omitted] • Transformations in the La 3-x Mg x Ni 9 (x ​= ​1.0, 1.1 and 1.2) alloys were studied by in situ NPD at 300–1273 ​K. • Initial alloy is multi-phase structured containing up to six different intermetallics with five stoichiometric compositions. • Various transformations take place on heating, leading to the disappearance of LaNi5 and LaMgNi 4. • The increase of Mg content has different influences on the intermetallics and affects on the five peritectic reactions. • The results guide optimization of phase-structural composition of La–Mg–Ni alloys by tailoring high temperature annealing conditions. [ABSTRACT FROM AUTHOR]

The La–Mg–Ni–Co-based AB 2 -type alloys, namely La 0.7 Sm 0.3 MgNi 3·6 Co 0.4 x wt.%Ni (x = 0,5,10, 15, 20), were synthesized through ball milling. The study focused on investigating the impact of Ni content on the structures and electrochemical properties. The structures of the samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Transmission electron microscope (TEM). It has been demonstrated that the experimental samples consist of a primary phase, LaMgNi 4 , and a secondary phase, LaNi 5. The abundance of phases undergoes significant changes with variations in Ni content, while the phase composition remains constant. The results indicate that a rise in Ni concentration results in an elevation of the LaNi 5 phase and a reduction of the LaMgNi 4 phase. Additionally, ball milling and the addition of nickel contribute to the refinement of the alloy grains. As the nickel concentration reached 20 wt%, the cycle retention rate(S 30) of the composite alloy electrode achieved its maximum value of 73.42 %. In addition, the electrochemical kinetic test findings demonstrated that the maximum D value of the hydrogen diffusion system was 1.807 × 10−10 cm2/s and that the maximum current density of the composite hydrogen storage alloy electrode was 723 mA/g when x = 0 wt%. The La–Mg–Ni–Co-based AB 2 -type alloys, namely La 0.7 Sm 0.3 MgNi 3·6 Co 0.4 x wt.%Ni (x = 0,5,10, 15, 20), were synthesized through ball milling. The study focused on investigating the impact of Ni content on the structures and electrochemical properties. The structures of the samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Transmission electron microscope (TEM). It has been demonstrated that the experimental samples consist of a primary phase, LaMgNi 4 , and a secondary phase, LaNi 5. The abundance of phases undergoes significant changes with variations in Ni content, while the phase composition remains constant. The results indicate that a rise in Ni concentration results in an elevation of the LaNi 5 phase and a reduction of the LaMgNi 4 phase. Additionally, ball milling and the addition of nickel contribute to the refinement of the alloy grains. As the nickel concentration reached 20 wt%, the cycle retention rate(S 30) of the composite alloy electrode achieved its maximum value of 73.42 %. In addition, the electrochemical kinetic test findings demonstrated that the maximum D value of the hydrogen diffusion system was 1.807 × 10−10 cm2/s and that the maximum current density of the composite hydrogen storage alloy electrode was 723 mA/g when x = 0 wt%. [Display omitted] • The mechanism of the effect of microstructure on electrochemical performance was explored. • The capacity fading mechanism of ball milling on RE-Mg-Ni-based alloys was explored. • The comprehensive electrochemical properties of RE-Mg-Ni-based alloys are improved. [ABSTRACT FROM AUTHOR]

The effect of Mo-addition on hydrogen storage and low-temperature electrochemical performances of La-Mg-Ni-Co-Al alloys is investigated. The alloys were synthetized via vacuum induction melting followed by annealing treatment at 1123 K for 8 h. The major phases in the annealed alloys are consisted of (La, Mg) 2 Ni 7 , (La, Mg) 5 Ni 19 and LaNi 5 phases. Mo-addition facilitates phase transformation of LaNi 5 into (La, Mg) 2 Ni 7 and (La, Mg) 5 Ni 19 phases. Hydrogen absorption/desorption PCI curves indicates that the hydrogen storage capacity of the alloy increases remarkably with the addition of Mo. Furthermore, the La 0.75 Mg 0.25 Ni 3.05 Co 0.2 Al 0.05 Mo 0.2 alloy shows excellent hydriding/dehydriding kinetics with a higher capacity, requiring only 100 s to reach its saturated hydrogen capacity of 1.58 wt% at low temperature of 303 K, and releasing 1.57 wt% hydrogen within 400 s at 338 K. Electrochemical experiments manifest that the Mo-added alloy electrode has perfect activation properties and the maximum discharge capacity. The low-temperature dischargeability shows that the La 0.75 Mg 0.25 Ni 3.05 Co 0.2 Al 0.05 Mo 0.2 alloy exhibits the excellent low-temperature discharge performance, and the maximum discharge capacity is improved from 231.0 to 334.6 mAh/g at 253 K. The HRD property of the alloy electrode is enhanced, suggesting that Mo enhances the kinetic ability at low-temperature. [ABSTRACT FROM AUTHOR]

La 0.75 Mg 0.25 Ni 3.2−x Co 0.2 Al 0.1 Mo x (x = 0, 0.10, 0.15, 0.20) hydrogen storage alloys were synthesized via vacuum induction melting combined with a heat-treatment at 1173 K for 8 h. All alloys have multiphase constitutions including (La, Mg) 2 Ni 7 , (La, Mg) 5 Ni 19 , LaNi 5 phase and there is residual Mo phase in the Mo-added alloys. Increasing Mo content, the abundance of (La, Mg) 2 Ni 7 and (La, Mg) 5 Ni 19 phase with super-lattice stacking structure initially increases and then decreases while that of LaNi 5 phase shares a reverse trend. In all Mo-added alloys, Ni is partially substituted by Mo leading to an overall expansion in unit cell volumes. The electrochemical analyses show that the cyclic stability of the alloy electrodes are significantly improved after Mo is added especially when x = 0.15 the cyclic retention is 80.9%, which is 16.4% higher than that of the original one. The maximum discharge capacity are almost unchanged between the alloy electrodes for x = 0 and x = 0.15 while the high-rate discharge ability at the discharge current density of 1500 mA/g is enhanced from 55.2% to 60.1%. The comprehensive electrochemical properties reach a compromise for La 0.75 Mg 0.25 Ni 3.05 Co 0.20 Al 0.10 Mo 0.15 alloy electrode which possesses remarkably improved cyclic stability, enhanced kinetic property and maintains almost unimpaired discharge capacity in the meanwhile. [ABSTRACT FROM AUTHOR]

The effect of annealing temperature on microstructures and electrochemical performances of La 0.75 Mg 0.25 Ni 3.05 Co 0.2 Al 0.1 Mo 0.15 hydrogen storage alloy is investigated. The alloys was prepared via vacuum induction melting followed by annealing treatment for 8 h at the temperatures of 1073, 1123, 1173, and 1223 K, respectively. The major phases in the as-cast and annealed alloys are consisted of (La, Mg) 2 Ni 7 , (La, Mg) 5 Ni 19 and LaNi 5 phase while the residual phase MoNi 4 existing in the as-cast alloy decomposes into Mo phase after heat treatment. Annealing treatment facilitates LaNi 5 phase transforms into (La, Mg) 2 Ni 7 and (La, Mg) 5 Ni 19 phase, but the tendency is suppressed as annealing temperature increases. Furthermore, the annealed alloys have more homogeneous phase distribution and better crystallization. Electrochemical experiments manifest that annealing treatment is beneficial for the increase of the maximum discharge capacity while impairs the activation ability of the alloy electrodes. The cycle life is prolonged in consequence of the homogeneous phase distribution created by annealing treatment at 1073–1173 K. Nonetheless, annealing treatment distinctly deteriorates the kinetic property of the alloys electrodes which is mainly ascribed to the disappearance of MoNi 4 phase with high-efficiency electrocatalytic activity. The comprehensive electrochemical properties of the annealed alloy at 1173 K presents a good balance between superior discharge capacity, kinetic property and remarkably improved cyclic stability. [ABSTRACT FROM AUTHOR]

Abstract: Present paper focuses on studies of the Co-free La2MgNi9 alloys as active materials of negative electrodes in nickel-metal hydride (NiMH) batteries. The effect of annealing treatment on the phase composition, microstructure, hydrogen absorption–desorption and electrochemical properties was investigated. The phase-structural composition, microstructures and morphologies of the phases were analyzed by X-ray diffraction and by scanning electron microscopy. Increase of the annealing temperature to 950°C leads to a higher abundance of the La2MgNi9 and La3MgNi14 phases and an elimination of the present at lower temperatures LaNi5−x and LaMgNi4 intermetallics. The hydrogen absorption–desorption behaviors, the electrochemical performance and electrochemical cycling stability significantly improve after the annealing. For pasted electrodes, the annealed alloys had a discharge capacity of 350–360mAhg−1 compared to 325mAhg−1 for the as-cast sample. The discharge capacity of the annealed samples remained high, almost 50% after 300 cycles with 100% depth of discharge (DOD) in half-cell tests. Pellet electrodes prepared from the annealed alloy and carbonyl nickel powder showed a discharge capacity of 396mAhg−1. In present work we also report the performance of a small prototype NiMH cell where the annealed alloy was used as the active material in the negative MH electrode and a sintered Ni electrode acted as the positive electrode. After 300 cycles at charge/discharge rates of 0.2C the cell showed a very good cycling stability with its capacity remaining on the level of 87%. [Copyright &y& Elsevier]

Abstract: Herein, we prepared a new type of magnesium and transition metal-based alloys with the formula of LaMg8.40Ni2.34−x Al x (x =0 and 0.20). Their phase structures, morphologies and hydrogen storage properties were studied by different methods. The XRD patterns show that LaMg8.40Ni2.34−x Al x alloys are made of La2Mg17, LaMg2Ni and Mg2Ni phases. The SEM images indicate that the phase distributions in LaMg8.40Ni2.14Al0.20 alloy are more uniform compared with LaMg8.40Ni2.34 alloy. In addition, the reversible hydrogen storage capacity of LaMg8.40Ni2.14Al0.20 alloy is 3.22wt.% at 558K, which is higher than that of LaMg8.40Ni2.34 alloy. The partial substitution of Al for Ni effectively improves the hydrogen storage capacity, as well as the hydriding/dehydriding kinetics of the alloys, with the evidence that 89% hydrogen in the saturated state in LaMg8.40Ni2.14Al0.20 alloy was released in 1500s at 573K, while only 74% hydrogen in the saturated state in LaMg8.40Ni2.34 alloy was released at the same conditions. Consequently, we believe that the alloying of aluminum in the magnesium-rare earth-transition metal-based alloys can effectively improve their hydrogen storage performance. [Copyright &y& Elsevier]

Abstract: La1.9Ti0.1MgNi9 alloys were prepared by magnetic levitation melting followed by annealing treatments. The results of XRD, PCT and electrochemical measurements show that all samples possess a multiphase structure, and LaNi5 phase is the main phase. LaMg2Ni9 phase disappears and Ti2Ni phase appears at 1173 K. Annealed alloys exhibit higher compositional homogeneity and lower absorption/desorption plateau pressures compared to as-cast alloy. The effective hydrogen storage capacity of the alloy annealed at 1073 K is the highest, and it reaches 1.25% (mass fraction) at 303 K. Annealing not only enhances the discharge capacity, but also improves the cyclic stability and the high rate dischargeability markedly. La1.9Ti0.1MgNi9 alloy annealed at 1173 K presents good electrochemical performance with the maximum discharge capacity of 377 mAh/g, the HRD 1100 of 0.839 and the retention of discharge capacity of 60% after 112 charge/discharge cycles. [ABSTRACT FROM AUTHOR]

Hydrogen storage alloys of La 2- x Y x Mg 16 Ni (x = 0, 0.1, 0.2, 0.3, 0.4) were smelted by vacuum induction melting furnace. The microstructure of the cast alloys were observed by scanning electron microscope, and the alloys structure were analyzed by X-ray Diffractometer (XRD) before and after hydrogen absorption. The electrochemical capacity, cyclic stability, high-rate discharge, potentiodynamic polarization curves, and constant potential crossing curves were tested. Besides, the limited current density and diffusion coefficient were calculated. The results show that the main phase of the as-cast alloy is La 2 Mg 17 , and a little amount of the second phase Mg 2 Ni exist. In addition, LaH 3 and MgH 2 and a small amount of Mg 2 NiH 4 phases were formed in the alloy after saturated hydrogen absorption. With the increasing of La element substituted by Y element in La 2 Mg 16 Ni alloy, the discharge specific capacity of alloy shows a decreasing tendency, it's unconspicuous, though. The cyclic stability and high rate discharge of hydrogen storage alloys increase first and then decrease with the increasing of La element substituted by Y element in La 2 Mg 16 Ni alloy. When S 50 is 34.01%, the cyclic stability of La 1.8 Y 0.2 Mg 16 Ni alloy is best. Both the limited discharge current density and hydrogen diffusion coefficient of the alloy increase first and then decrease with the increasing of the La element of La 2 Mg 16 Ni alloy replaced by Y element. The maximum current density of La 1.8 Y 0.2 Mg 16 Ni alloy is I L = 325.11 mA/g, and the maximum diffusion coefficient is D = 1.849 × 10−8 cm2/s. • The main phase of the as-cast alloy is La 2 Mg 17 , and the second phase Mg 2 Ni exist. • With the increasing of La, the discharge specific capacity shows a decreasing tendency. • La 1.8 Y 0.2 Mg 16 Ni alloy has the best cycle stability (S 50 = 34.01%). • The maximum current density and diffusion coefficient are 325.11 mA/g and 1.849 × 10−8 cm2/s. [ABSTRACT FROM AUTHOR]