LaNi5-based Alloys Research Articles

Thermodynamic assessment of the Ce[sbnd]H and CeNi5[sbnd]H system

Interstitial metal hydrides (MHs) have attracted considerable attention in the field of hydrogen technology, particularly in the context of storage and compression applications. Because of their minor hysteresis effects, good cyclability, activation simplicity, and high volumetric storage density, LaNi5-based alloys are recognized as prominent candidates for hydrogen storage application. Additionally, the system’s thermodynamic and electrochemical properties can be modified to suit the requirements of a particular application by alloying specific substituents. To ascertain the thermodynamic effects of Ce addition within LaNi5, in this work the CeH and CeNi5H systems have been modeled with the CALPHAD method. For this reason, in this work, two different thermodynamic models have been developed and assessed using the same pressure-composition isotherms (PCIs) datasets obtained from literature and theoretical formation energies newly calculated employing periodic density functional theory (DFT). Direct comparison of the models against each other in terms of accuracy and physical plausibility revealed that extrapolation of thermodynamic properties to data-scarce regions is more reasonable with fewer model parameters and in agreement with other similar systems within the rare-earth (RE) metal-hydride class. In addition, the CeNi5H system was investigated by assessing the (Ce)(Ni)5(V a,H)7 phase model, which could accurately predict hydrogen storage properties while being compatible with previously developed LaNi5H models. Ultimately, the models developed in this study may be employed and extended to describe multi-component REH systems and allow for thermodynamic computations that are highly desirable for accurate predictions of hydrogen absorption/desorption properties and degradation characteristics within the (La,Ce)Ni5H metal hydride family.

The Role of Surface in Hydride Formation Processes

Several LaNi5-based hydrogen storage alloys were studied using secondary ion mass spectrometry (SIMS) technique. Ar+ ions with the energy of 10 - 18 keV were used as primary ions. The study of the initial stages of the processes of LaNi5-based alloys interaction with hydrogen under the experimental conditions showed that on the areas of clean surface, hydrogen formed chemical compounds with the both of the main components of the alloy: nickel and lanthanum. As hydrogen accumulates on the surface and in the near-surface region, a hydrogen-containing structure is formed, which is characterized by a certain stoichiometric ratio of components. Nickel in this structure has strong chemical bonds with two hydrogen atoms, and lanthanum – with two or more hydrogen atoms. Along with such compounds, some structures with lower hydrogen content are also formed. The formed hydrogen-containing structure includes both main alloy components, La and Ni for all the studied samples, even though only lanthanum is generally accepted to be the hydride-forming element in such alloys. The SIMS studies of the chemical composition of the surface monolayers of the intermetallic alloy LaNi5, in the process of its interaction with oxygen, showed the following. As a result of the oxygen interaction with the alloy, a complex chemical structure including oxygen, lanthanum and nickel is formed on the surface and in the near-surface region of LaNi5. Oxygen in such a structure, similarly to hydrogen, forms strong chemical bonds with both components of the alloy. This is indicated by the presence in the mass spectra of a large set of oxygen-containing emissions of positive and negative secondary ions with lanthanum and nickel, as well as oxygen-containing lanthanum-nickel cluster secondary ions. The formed oxide compounds have a three-dimensional structure and occupy tens of monolayers. Oxygen poisoning of the surface of the hydride-forming alloy LaNi5 can occur regardless of whether the surface of the alloy was clean from the very beginning or it was covered with a layer of hydrogen-containing chemical compounds.

Hydrogen Absorption Reactions of Hydrogen Storage Alloy LaNi5 under High Pressure.

Hydrogen can be stored in the interstitial sites of the lattices of intermetallic compounds. To date, intermetallic compound LaNi5 or related LaNi5-based alloys are known to be practical hydrogen storage materials owing to their higher volumetric hydrogen densities, making them a compact hydrogen storage method and allowing stable reversible hydrogen absorption and desorption reactions to take place at room temperature below 1.0 MPa. By contrast, gravimetric hydrogen density is required for key improvements (e.g., gravimetric hydrogen density of LaNi5: 1.38 mass%). Although hydrogen storage materials have typically been evaluated for their hydrogen storage properties below 10 MPa, reactions between hydrogen and materials can be facilitated above 1 GPa because the chemical potential of hydrogen dramatically increases at a higher pressure. This indicates that high-pressure experiments above 1 GPa could clarify the latent hydrogen absorption reactions below 10 MPa and potentially explore new hydride phases. In this study, we investigated the hydrogen absorption reaction of LaNi5 above 1 GPa at room temperature to understand their potential hydrogen storage capacities. The high-pressure experiments on LaNi5 with and without an internal hydrogen source (BH3NH3) were performed using a multi-anvil-type high-pressure apparatus, and the reactions were observed using in situ synchrotron radiation X-ray diffraction with an energy dispersive method. The results showed that 2.07 mass% hydrogen was absorbed by LaNi5 at 6 GPa. Considering the unit cell volume expansion, the estimated hydrogen storage capacity could be 1.5 times higher than that obtained from hydrogen absorption reaction below 1.0 MPa at 303 K. Thus, 33% of the available interstitial sites in LaNi5 remained unoccupied by hydrogen atoms under conventional conditions. Although the hydrogen-absorbed LaNi5Hx (x < 9) was maintained below 573 K at 10 GPa, LaNi5Hx began decomposing into NiH, and the formation of a new phase was observed at 873 K and 10 GPa. The new phase was indexed to a hexagonal or trigonal unit cell with a ≈ 4.44 Å and c ≈ 8.44 Å. Further, the newly-formed phase was speculated to be a new hydride phase because the Bragg peak positions and unit cell parameters were inconsistent with those reported for the La-Ni intermetallic compounds and La-Ni hydride phases.

Flame Sprayed LaNi5-Based Mischmetal Alloy: Building-up Negative Electrodes for Potential Application in Ni-Based Batteries

Flame Sprayed LaNi5-Based Mischmetal Alloy: Building-up Negative Electrodes for Potential Application in Ni-Based Batteries

Temperature rise of LaNi5-based alloys by hydrogen adsorption.

The temperature rise of AB5-type alloys by hydrogen adsorption was limited by their critical temperatures (Tc). We found the relation between the H2 desorption temperatures of metal hydrides at atmospheric pressure (Ts) and their Tc followed the Guldberg rule (Tc = 3/2 Ts), revealing a simple method to estimate Tc.

Study of Sulfur-Based Electrodes By Operando Acoustic Emission

The acoustic emission (AE) technique has been widely used since the 70’s for detecting anomalies such as leakages and cracks on large structure (e.g. bridges, pressure containers, and pipe lines). The analysis of the AE signals (transient elastic waves) can also be used to characterize the degradation mechanisms (crack growth, friction, delamination, matrix cracking, corrosion, etc) of various materials subjected to a stress by mechanical, pressure or thermal means. Recently, AE technique has also been used to evaluate the degradation of metal hydride electrodes for Ni-MH [1] and Si-based electrodes for Li-ion batteries [2,3]. Cracking of the active material and gas evolution are the main sources of AE signals identified in these studies. In the present study, the AE technique is used for studying upon cycling the mechanical degradation of S-based electrodes for Li/S batteries. The AE signals were recorded by a piezoelectric transducer fixed on the back of the working electrode. S-based electrodes made with two different binders (PVdF vs. CMC) and two different current collectors (standard Al foil vs. porous 3D carbon paper) were studied. In all cases, AE signals were mainly detected during the first plateau of the first discharge, suggesting that the electrode degradation mostly occurs during the initial dissolution of the S8 particles. AE signals were also detected during a few subsequent cycles when CMC binder is used. This is attributed to a better propagation of the AE signals through the electrode thanks to an improved adhesion of the electrode to the current collector in comparison to PVdF binder. This is confirmed by further mechanical resistance testing (peel and scratch tests). The use of a carbon paper as a current collector combined to CMC binder greatly improves the electrochemical performance of the S electrode by preventing the collapse of the electrode upon cycling. This electrode also presents an increased amount of AE signals, suggesting that the carbon fibres of the C paper act as an AE waveguide. This study demonstrated that AE could be used as an efficient tool to monitor the morphological degradation of S-based electrodes upon their cycling and offers relevant information for optimizing their formulation and architecture. A. Etiemble, H. Idrissi, P. Bernard, L. Roué. New insights into the pulverization of LaNi5-based alloys with different Co contents from electrochemical acoustic emission measurements. Electrochim. Acta 186 (2015) 112-116 A. Tranchot, A. Etiemble, P-X. Thivel, H. Idrissi., L. Roué. In-situ acoustic emission study of Si-based electrodes for Li-ion batteries, J. Power Sources 279 (2015) 259-266. A. Tranchot, P-X. Thivel, H. Idrissi, L. Roué. Influence of the Si particle size on the mechanical stability of Si-based electrodes evaluated by in-operando dilatometry and acoustic emission. J. Power Sources 330 (2016) 253-260. Figure 1

Study of Sulfur-Based Electrodes By Operando Acoustic Emission

The acoustic emission (AE) technique has been widely used since the 70’s for detecting anomalies such as leakages and cracks on large structure (e.g. bridges, pressure containers, and pipe lines). The analysis of the AE signals (transient elastic waves) can also be used to characterize the degradation mechanisms (crack growth, friction, delamination, matrix cracking, corrosion, etc) of various materials subjected to a stress by mechanical, pressure or thermal means. Recently, AE technique has also been used to evaluate the degradation of metal hydride electrodes for Ni-MH [1] and Si-based electrodes for Li-ion batteries [2,3]. Cracking of the active material and gas evolution are the main sources of AE signals identified in these studies. In the present study, the AE technique is used for studying upon cycling the mechanical degradation of S-based electrodes for Li/S batteries. The AE signals were recorded by a piezoelectric transducer fixed on the back of the working electrode. S-based electrodes made with two different binders (PVdF vs. CMC) and two different current collectors (standard Al foil vs. porous 3D carbon paper) were studied. In all cases, AE signals were mainly detected during the first plateau of the first discharge, suggesting that the electrode degradation mostly occurs during the initial dissolution of the S8 particles. AE signals were also detected during a few subsequent cycles when CMC binder is used. This is attributed to a better propagation of the AE signals through the electrode thanks to an improved adhesion of the electrode to the current collector in comparison to PVdF binder. This is confirmed by further mechanical resistance testing (peel and scratch tests). The use of a carbon paper as a current collector combined to CMC binder greatly improves the electrochemical performance of the S electrode by preventing the collapse of the electrode upon cycling. This electrode also presents an increased amount of AE signals, suggesting that the carbon fibres of the C paper act as an AE waveguide. This study demonstrated that AE could be used as an efficient tool to monitor the morphological degradation of S-based electrodes upon their cycling and offers relevant information for optimizing their formulation and architecture. A. Etiemble, H. Idrissi, P. Bernard, L. Roué. New insights into the pulverization of LaNi5-based alloys with different Co contents from electrochemical acoustic emission measurements. Electrochim. Acta 186 (2015) 112-116 A. Tranchot, A. Etiemble, P-X. Thivel, H. Idrissi., L. Roué. In-situ acoustic emission study of Si-based electrodes for Li-ion batteries, J. Power Sources 279 (2015) 259-266. A. Tranchot, P-X. Thivel, H. Idrissi, L. Roué. Influence of the Si particle size on the mechanical stability of Si-based electrodes evaluated by in-operando dilatometry and acoustic emission. J. Power Sources 330 (2016) 253-260. Figure 1

Crystal structure and hydrogen storage properties of (La,Ce)Ni5−xMx (M = Al, Fe, or Co) alloys

The effects of partial substitution of La by Ce and Ni by Al, Fe, or Co in LaNi5-based alloys on hydrogen storage performance were systematically studied. All samples were prepared using vacuum arc melting in an argon atmosphere. The results showed that for La-Ni5−xMx (M = Al, Fe, or Co) alloys, the lattice constants and unit cell volumes increased with an increasing amount of Al and Fe. On the other hand, these parameters decreased upon partial substitution of La by Ce. In addition, the lattice constant remained almost constant in the La0.6Ce0.4Ni5–xCox alloys regardless of the value of x (x = 0.3, 0.6, or 0.9), as Ce might enhance the homogeneity of the CaCu5-type phase in Co-containing alloys. The hydrogen storage properties of the alloys were investigated using pressure, composition, and temperature isotherms. The experimental results showed that the plateau pressure decreased with an increasing content of Al, Fe, or Co, but it increased with Ce addition. Furthermore, the plateau pressures of all Co-containing alloys were almost identical upon substitution with Ce. Finally, the enthalpy (ΔH) and entropy (ΔS) values for all alloys were calculated using van’t Hoff plots. The relationship between the lattice parameters and enthalpy changes for hydrogenation will be discussed.

Enhanced hydrogen storage properties of 1.1MgH2-2LiNH2-0.1LiBH4 system with LaNi5-based alloy hydrides addition.

Significant improvements in the hydrogen sorption properties of the Li–Mg–N–H system have been achieved by adding a small amount of LiBH4. Herein, the hydrogen storage properties of the 1.1MgH2–2LiNH2–0.1LiBH4 system are further enhanced by addition of LaNi5-based (LaNi3.8Al0.75Mn0.45, LaNi4.5Mn0.5, LaNi4Co) alloy hydrides. The refinement of the Li–Mg–B–N–H particles and the metathesis reaction are facilitated by adding LaNi5-based alloy hydrides during the ball milling process. The addition of LaNi5-based alloy hydrides can enhance the hydrogen sorption kinetics, reduce the dehydrogenation temperature and promote a more thorough dehydrogenation of the Li–Mg–B–N–H system. The LaNi5-based alloy hydrides are involved in hydrogen de/hydrogenation reaction. Among the three alloys, LaNi4.5Mn0.5 makes the most obvious improvement on the reaction kinetics, and the dehydrogenation peak temperature is reduced by 12 °C, while the activation energy is reduced by 11% with 10 wt% LaNi4.5Mn0.5 addition. The weakening of the N–H bond and the homogeneous distribution of the LaNi5-based alloy hydrides in the Li–Mg–B–N–H composite have important roles in the reduction of the desorption barrier and the kinetics enhancement.

Creating the hydrogen absorption capability of CeNi5 through the addition of Al

The hydrogenation capacities of CeNi5−xAlx (x = 0, 0.75, 1.0, 1.25, 1.5 and 1.75) alloys were assessed. In contrast to LaNi5-based alloys, the addition of Al to CeNi5 enables hydrogen absorption by creating larger interstitial sites as the result of an expanded lattice. Structure analyses indicate that each of these alloys maintained a CeNi5 (CaCu5-type) structure in which Al atoms exclusively occupied Ni 3g sites. Among these specimens, CeNi4Al absorbed the greatest proportion of hydrogen atoms, decreasing its c/a ratio from 0.826 to 0.802 upon the formation of CeNi4AlH4.3. This drastic decrease in the c/a ratio is attributed to an anisotropic lattice expansion along the a-axis, as verified by in situ X-ray diffraction under H2. The enhanced hydrogen absorption of these alloys is thought to be associated with the preferential situation of hydrogen atoms at interstitial sites located at the centers of octagons as well as a charge transition of Ce ions upon hydrogenation. It is verified that CeNi4Al after hydrogenation shows high catalytic activity toward propyne hydrogenation: 100% conversion of propyne even at room temperature.

New insights into the pulverization of LaNi5-based alloys with different Co contents from electrochemical acoustic emission measurements

The pulverization (particle cracking) of LaNi5-based electrodes with different Co contents (ca.5, 8 and 10 wt%) is studied by means of electrochemical acoustic emission measurements. Through an appropriate analysis of the acoustic signals detected during electrode cycling, the acoustic events related to particle cracking can be identified and quantified. It is shown that the particle cracking occurs mostly during the first charge. For the 5 and 8 wt% Co alloys, the particle cracking is mainly detected in the early stage of the hydriding reaction, i.e.when the α-to-β phase transition is initiated. In contrast, for the 10 wt% Co alloy, the particle cracking is more progressive during the first charge with the presence of two successive increases of the acoustic activity, which is attributed to the formation of an intermediate γ-phase hydride. On the basis of the number of acoustic events detected during the first charge, the influence of the Co content on the alloy pulverization is quantified with mean values of 13700, 5600 and 1300 events for a Co content in the alloy of 5, 8 and 10 wt%, respectively.

Description of the capacity degradation mechanism in LaNi5-based alloy electrodes

The mechanism of the capacity degradation of LaNi5-based alloy electrodes was investigated with a special focus on the influence of the alloy and surface composition, as well as the unique structure obtained by gas atomisation. The electrochemical properties, especially the cycle life curve (i.e. the capacity as a function of the cycle number of LaNi4.5Al0.5, LaNi2.5Co2.4Al0.1, (La+Mm)Ni3.5Co0.7Al0.35Mn0.4Zr0.05, and MmNi4.3Al0.2Mn0.5 alloy electrodes), was analysed and modelled. The capacity degradation upon cycling is determined by the chemical state of the alloy elements and the solubility of their oxides. The cycle life curves for the alloy electrodes without Co exhibited a rapid activation (3–4 cycles to reach maximum capacity), as well as rapid degradation (130–180 cycles for 50% maximum discharge capacity). LaNi2.5Co2.4Al0.1 and (La+Mm)Ni3.5Co0.7Al0.35Mn0.4Zr0.05 alloy electrodes activated after 7–10 cycles and showed very stable discharge behaviour (more than 400 cycles). The Co-containing alloy electrodes primarily lose the cycle stability because of mechanical decrepitation, whereas the alloys without Co suffer from selective dissolution of the unstable elements in the potential window, which was shown by our model of alloy degradation and confirmed by means of SEM, WDX, and ICP-OES data.

Effect of composition and particle morphology on the electrochemical properties of LaNi5-based alloy electrodes

Al and Co substituted LaNi5-based intermetallic compounds were investigated as negative electrode materials in alkaline KOH-electrolyte. The structure, morphology and electrochemical properties of gas-atomised and cast LaNi4.5Al0.5 and LaNi2.5Co2.4Al0.1 alloys were investigated and the effect of the substitutions and the production method on the surface and bulk composition is compared to cast LaNi5 as a reference.While the rapid solidification of the gas-atomised alloys affects the site energy distribution for hydrogen on the interstitial sites, the activation and degradation mechanism of the electrodes cycle life is dominated by the elemental composition of the alloy and especially the surface. Therefore, the alloys with the larger Al content activate within a few cycles and also degrade faster as compared to the alloys with a high Co content. Furthermore, the dissolution of Al leads to a highly active surface with a lower reaction resistance, which leads to an order of magnitude increased high rate dischargeability.

In situ investigation of the volume change and pulverization of hydride materials for Ni-MH batteries by concomitant generated force and acoustic emission measurements

A new experimental set-up constituted of an electrochemical cell connected to a compression load cell and acoustic emission (AE) equipment was used for monitoring the force and the cracking of metal hydride electrodes generated by their volume expansion/contraction during their cycling. Two materials were studied: a commercial LaNi5-based alloy and an amorphous MgNi alloy prepared by ball milling. During the charge of the LaNi5-based electrode, a concordance was observed between the increase of the force generated by its volume expansion and the increase of the AE activity associated with the particle cracking. This correlation was not observed during the charge of the MgNi electrode, which tends to confirm that the main origin of the cracking of the MgNi particles is not their volume expansion but is rather due to the mechanical action of the H2 bubbles produced at the end of the charge step. In addition, on the basis of the generated/relaxed force rates, the volume expansion/contraction of the electrode appeared more progressive with the MgNi alloy than with the LaNi5-based alloy. This could result from the lack of abrupt α–β phase transition region in the MgNi alloy due to its amorphous structure.

Lattice defects introduced into LaNi 5-based alloys during hydrogen absorption/desorption cycling

LaNi 5-based intermetallic compounds before and after hydrogen absorption/desorption cycling were observed by transmission electron microscopy. Both a-type and c-type dislocations, which had respective Burgers vectors of 1 / 3 < 1 1 2 ¯ 0 > and <0 0 0 1> in the { 0 1 1 ¯ 0 } slip plane, were introduced into LaNi 5, LaNi 4.5Cu 0.5 and LaNi 4.5Fe 0.5 after the first absorption/desorption cycle. These alloys exhibited large difference in the equilibrium pressure between the first absorption and first desorption. Dislocations were introduced during hydrogenation in order to accommodate lattice mismatch between the metal-hydrogen solid solution and the metal hydride; furthermore, the interface between the solid solution and hydride was suggested to be the { 0 1 1 ¯ 0 } plane. In contrast, neither dislocations nor stacking faults were observed in LaNi 4.5Si 0.5, LaNi 4.5Al 0.5 and LaNi 4.75Sn 0.75, which showed little or no hysteresis in the hydrogen pressure–composition isotherms. Excess pressure was needed in the absorption process for the formation of misfit dislocations.

The electronic and electrochemical properties of the LaNi5-based alloys

Nanocrystalline La(Ni,M)5-type alloys were prepared by mechanical alloying (MA) and subsequent annealing. The alloying elements of 3d transition metals, Mn, Al and Co were substituted for Ni in LaNi5, and the structural, electrochemical as well as electronic properties were studied. It was found that the partial substitution of Ni by Al or Mn in nanocrystalline La(Ni,M)5 alloy leads to an increase in the discharge capacity. On the other hand, cobalt substituting nickel in LaNi4–xMn0.75Al0.25Cox alloy greatly improved the discharge capacity and cycle life of LaNi5 material. The electronic structure has been studied by the tight binding version of the linear muffin-tin orbital method (TB LMTO) for La(Ni0.8–xCoxAl0.1Mn0.1)5 systems, where x = 0, 0.1, 0.2, and 0.3.

Defects Formation in LaNi5-based Alloys Investigated by In-situ X-ray Diffraction

ABSTRACTDefects formation in LaNi5-based alloys was investigated by X-ray diffraction (XRD). In-situ XRD data measured along the first hydriding-dehydriding P-C isotherms were analyzed by the Rietveld method. Lattice strain and crystallite size were evaluated from the peak profile. In LaNi5hydride phase formed accompanying with 2 % of anisotropic lattice strain in &lt;hk0&gt; direction caused by dense dislocations. Coexisting solid solution phase was not affected by the strain in the hydride phase. Lattice parameterabecame smaller after cycles than before hydriding, which is related with vacancies formation.Only 5 % of Al substitution for Ni dramatically changed the defects formation behavior. Hydride phase did not show lattice strain in the first hydriding but showed small strain during dehydriding. Formation of both dislocations and vacancies are strongly affected by substitution of other elements for a part of Ni.

Microstructure-hydrogen sorption property relationships in LaNi5-based alloys

ABSTRACTThe relationship between microstructures and hydrogen absorption-desorption properties described in terms of pressure-composition (P-C) isotherms has been investigated for binary and Co- and Al-added LaNi5-based alloys as a function of the number of hydrogen sorption cycles. From microstructure observations, factors determining absorption pressures are deduced and variations of P-C isotherms with cycle number for these three LaNi5-based alloys are discussed.

Structure and related properties of (La,Ce,Nd,Pr)Ni 5 alloys

The effects of substitution of La by Ce, Nd and Pr in the LaNi 5-based alloys were systematically studied, with the use of factorial analysis. The changes of equilibrium pressure, hydrogen capacity and hysteresis were analyzed in relation to the structure changes of the hexagonal unit cell of (La,Ce,Nd,Pr)Ni 5. Both individual effects of each alloy component, and their interaction in the alloy were studied. It has been shown that variations in the basal plane parameter ( a) can be used as an indication for the plateau pressure changes resulting from substitution, giving better fits than variations in the unit cell volume. Structural anisotropy is discussed as a possible tool for the prediction of the decrepitation resistance of the alloy. Methods for optimization of the electrode alloys (including reduction of the cobalt content) are proposed.

X-ray diffraction peak broadening and degradation in LaNi 5-based alloys

Peak broadening in X-ray powder diffraction (XRD) profiles of LaNi 5-based alloys after hydriding and dehydriding processes, was investigated in order to clarify the relation between the formation of lattice strain and degradation by the hydriding–dehydriding cycling. The degree of peak broadening in XRD profiles was calculated by the Rietveld method and hydrogen capacity was evaluated from P-C isotherms for LaNi 5 and LaNi 5− α M α (M: Mn, Fe, Cu, Al; α=0.25, 0.5) after activation and after 1000 hydriding-dehydriding cycles. It was found that an anisotropic peak broadening parameter expressing lattice strain after activation has a linear relation with the decrease in hydrogen capacity. The above parameter is a suitable indicator of the ease of degradation in LaNi 5-based alloys.