Low-temperature Dischargeability Research Articles

Development of high-performance hydrogen storage alloys for applications in nickel-metal hydride batteries at ultra-low temperature

The main challenge for the applications of nickel-metal hydride (Ni-MH) batteries in low-temperature regions derives from the sluggish kinetics of its negative electrode materials—hydrogen storage alloys (HSAs). Here we design and fabricate a series of Co-free HSAs, exhibiting superior electrochemical reaction kinetics and low-temperature dischargeability performance. One novel candidate, La0.95Y0.05Ni4.5Mn0.4Al0.35, shows the highest discharge specific capacity of 283.5 mAh g−1 among reported data of AB5-type HSAs at a high discharge current density of 3000 mA g−1, which is 4.3 times that of the alloy synthesized with the same composition as a commercial alloy (MmNi3.55Co0.75Mn0.4Al0.3) electrode (65.9 mAh g−1). Moreover, this Co-free La0.95Y0.05Ni4.5Mn0.4Al0.35 alloy electrode can remain a discharge specific capacity of 255.8 mAh g−1 at a low temperature of 233 K while the synthesized MmNi3.55Co0.75Mn0.4Al0.3 alloy electrode shows a specific capacity of only 9.5 mAh g−1. The discharge specific capacity of the above Co-free alloy electrode can reach 30.0 mAh g−1 228 K, making it a promising candidate as a negative electrode material for applications in Ni-MH batteries at ultra-low temperature.

Effect of Conductive Material Morphology on Spherical Lithium Iron Phosphate

As an integral part of a lithium-ion battery, carbonaceous conductive agents have an important impact on the performance of the battery. Carbon sources (e.g., granular Super-P and KS-15, linear carbon nanotube, layered graphene) with different morphologies were added into the battery as conductive agents, and the effects of their morphologies on the electrochemical performance and processability of spherical lithium iron phosphate were investigated. The results show that the linear carbon nanotube and layered graphene enable conductive agents to efficiently connect to the cathode materials, which contribute to improving the stability of the electrode-slurry and reducing the internal resistance of cells. The batteries using nanotubes and graphene as conductive agents showed weaker battery internal resistance, excellent electrochemical performance and low-temperature dischargeability. The battery using carbon nanotube as the conductive agent had the best overall performance with an internal resistance of 30 mΩ. The battery using a carbon nanotube as the conductive agent exhibited better low-temperature performance, whose discharge capacity at −20 °C can reach 343 mAh, corresponding to 65.0% of that at 25 °C.

Long-life Ni-MH batteries with high-power delivery at lower temperatures: Coordination of low-temperature and high-power delivery with cycling life of low-Al AB5-type hydrogen storage alloys

Although a low-Al or an Al-free design is an efficient way to develop low-temperature and high-rate metal hydride alloys, the cycling life of these alloys is poor. Our strategy is to employ B-side anti-corrosion elements (e.g., Fe, Si, Sn, Cu) to coordinate the low-temperature and high-power delivery with cycling life. We confirmed that excellent electrochemical kinetics (i.e., surface catalytic and bulk H-diffusion ability) is the primary condition for low-temperature and high-rate delivery, while it reverses with anti-corrosion ability. As a result, the low-temperature dischargeability (LTD), high-rate dischargeability (HRD) and peak power (Ppeak) progressively decrease with Ni, Si, Cu, Fe, Sn and Al substitution, but the cycling stability successively increases with Ni, Si, Fe, Sn, Cu and Al substitution. Based on the thermodynamics and the coordination of the LTD, the HRD and Ppeak with the cycling life, the (LaCe)1.0(NiCoMn)4.85Al0.05Cu0.1 alloy presents the best overall electrochemical properties. Notably, when using an as-designed Cu-doped anode, the assembled commercial 100 Ah prismatic Ni-MH batteries present excellent power delivery at −40 °C.

Hydrogen storage and low-temperature electrochemical performances of A2B7 type La-Mg-Ni-Co-Al-Mo alloys

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 1123K for 8h. The major phases in the annealed alloys are consisted of (La, Mg)2Ni7, (La, Mg)5Ni19 and LaNi5 phases. Mo-addition facilitates phase transformation of LaNi5 into (La, Mg)2Ni7 and (La, Mg)5Ni19 phases. Hydrogen absorption/desorption PCI curves indicates that the hydrogen storage capacity of the alloy increases remarkably with the addition of Mo. Furthermore, the La0.75Mg0.25Ni3.05Co0.2Al0.05Mo0.2 alloy shows excellent hydriding/dehydriding kinetics with a higher capacity, requiring only 100s to reach its saturated hydrogen capacity of 1.58wt% at low temperature of 303K, and releasing 1.57wt% hydrogen within 400s at 338K. 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 La0.75Mg0.25Ni3.05Co0.2Al0.05Mo0.2 alloy exhibits the excellent low-temperature discharge performance, and the maximum discharge capacity is improved from 231.0 to 334.6mAh/g at 253K. The HRD property of the alloy electrode is enhanced, suggesting that Mo enhances the kinetic ability at low-temperature.

Improvement in low-temperature and instantaneous high-rate output performance of Al-free AB5-type hydrogen storage alloy for negative electrode in Ni/MH battery: Effect of thermodynamic and kinetic regulation via partial Mn substituting

Abstract A series of Al-free Mn-modified AB 5 -type hydrogen storage alloys have been designed and the effects of thermodynamic stability and electrochemical kinetics on electrochemical performance via Mn substituting have been investigated. Compared with high-Al alloys, the Al-free alloys in this study have better low-temperature performance and instantaneous high-rate output because of the higher surface catalytic ability. After partial substitution of Ni by Mn, both the hydrogen desorption capacity and plateau pressure decrease, and correspondingly results in an improved thermodynamic stability which is adverse to low-temperature delivery. Additionally, with the improvement of charge acceptance ability and anti-corrosion property via Mn substitution, the room-temperature discharge capacity and cycling stability increase slightly. However, Mn adversely affects the electrochemical kinetics and deteriorates both the surface catalytic ability and the bulk hydrogen diffusion ability, leading to the drop of low-temperature dischargeability, high-rate dischargeability and peak power ( P peak ). Based on the thermodynamic and kinetic regulation and overall electrochemical properties, the optimal composition is obtained when x = 0.2, the discharge capacity is 243.6 mAh g −1 at −40 °C with 60 mA g −1 , and the P peak attains to 969.6 W kg −1 at −40 °C.

Low-temperature and instantaneous high-rate output performance of AB5-type hydrogen storage alloy with duplex surface hot-alkali treatment

The excellent low-temperature and instantaneous high-rate output performance of MmNi3.7Co0.7Mn0.3Al0.3 alloy are obtained via hot-alkali treatment (K alloy) and duplex hot-alkali treatments with reducing agents, including N2H4 (KN alloy), NaH2PO2 (KP alloy) and NaBH4 (KB alloy). The charge transfer process on the alloy surface is the primary control step that influences the electrochemical properties at −40 °C. Scanning electron microscopy and energy dispersive X-ray analyses demonstrate that a high electrocatalytic Ni-and Co-rich layer is formed via the preferential dissolution of Al and Mn and that the alloy surface oxide is effectively removed via the duplex surface hot-alkali treatments. Thus, the charge-transfer resistance decreases and the exchange current density increases obviously in the treated alloys, making the K, KN, KP and KB alloys exhibit better activation property, high-rate dischargeability and instantaneous high-rate output performance at 20 °C, as well as higher discharge capacity, low-temperature dischargeability and high-power delivery at −40 °C. Based on the overall electrochemical properties of the alloys at various temperatures, a duplex surface modification of the hot-alkali treatment with NaH2PO2 is determined to be the best.

Effects of size of nickel powder additive on the low-temperature electrochemical performances and kinetics parameters of AB5-type hydrogen storage alloy for negative electrode in Ni/MH battery

The purpose of this study is to systematically investigate the effects of size of nickel powder additive on the low-temperature electrochemical performances and kinetics of MmNi0.38Co0.7Mn0.3Al0.2 hydrogen storage alloy under various assigned low temperatures, including 273 K, 253 K and 233 K. The results demonstrate that replacement of nano-nickel powder with average particle size of 40 nm (N40) for T255 nickel powder enhances the low-temperature electrochemical performances more dramatically than those of nano-nickel powder with average particle size of 100 nm (N100). The discharge capacity of N40 electrode at 233 K and 0.2 C rate is 216.8 mA h g−1 and low-temperature dischargeability (LTD) even reaches 67.6%, both of which are more higher than those of T255 electrode (150.4 mA h g−1, 51.3%, respectively). The kinetics parameters measured by linear polarization, electrochemical impedance spectrum (EIS) and potentiostatic discharge technology expound that, both the electrochemical charge-transfer process at the alloy–electrolyte interface and the hydrogen diffusion process in the bulk of alloy particles become increasingly limited with the decrease of the temperatures from 293 K down to 233 K, which correspondingly results in poor electrochemical performances of the electrodes at low temperatures. Further, the substitution of N40 for T255 nickel powder reduces the charge-transfer resistances and increases both the exchange current densities and the hydrogen diffusion coefficients of the electrodes more significantly than those of N100 at low temperatures, which were attributed to the excellent electro–catalytic activity of N40, explaining the evident differences on the low-temperature electrochemical performances of T255, N100 and N40 electrodes.

TiO2-based ionogel electrolytes for lithium metal batteries

In this work, TiO2-based ionogel electrolytes (TIEs), TiO2/ionic liquid/LiTFSI, are prepared by a one-pot sol–gel processing. The electrochemical performance and potential application in lithium metal batteries (LMBs) of TIEs are evaluated for the first time. It is found that the as-prepared TIE system reveals liquid-like high ionic conductivity, good electrochemical stability and ability to promote uniform lithium electrodeposition. Specifically, LMBs containing the TIE show high discharge capacity and good capacity retention at 25 °C under the 0.1C rate. Also, acceptable rate performance and low-temperature discharge ability can be obtained.

Effect of the partial substitution of samarium for lanthanum on the structure and electrochemical properties of La15Fe77B8-type hydrogen storage alloys

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

Electrochemical hydrogen storage characteristics of Ti0.10Zr0.15V0.35Cr0.10Ni0.30–10% LaNi3 composite and its synergetic effect

Hydrogen storage composite alloy Ti0.10Zr0.15V0.35Cr0.10Ni0.30–10% LaNi3 was prepared by two-step arc-melting to improve the electro-catalytic activity and the kinetic performance of Ti–V-based solid solution alloy. The electrochemical properties and synergetic effect of the composite alloy electrode were systematically investigated by using X-ray diffractometry, field emission scanning electron microscopy, energy-dispersive spectrometry, electrochemical impedance spectroscopy and galvanostatic charge/discharge test. It is found that the main phase of the composite alloy is composed of V-based solid solution phase with a BCC structure and C14 Laves phase with hexagonal structure, while the secondary phase is formed in the composite alloy. The comprehensive electrochemical properties of the composite alloy electrode are significantly improved. The activation cycle number, the maximum discharge capacity and the low temperature dischargeability of the composite alloy are 5 cycles, 362.5 mA·h/g and 65.84% at 233 K, respectively. It is suggested that distinct synergetic effect occurs in the activation process, composite process, cyclic process and discharge process at a low or high temperature under different current densities, in the charge–transfer resistance and exchange current density.

Effects of Co3O4 as additive on the performance of metal hydride electrode and Ni–MH battery

In this paper, the performance of metal hydride electrodes prepared with different amounts of tricobalt tetraoxide (Co3O4) and AA size cylindrical Ni–MH battery with the capacity of 1500 mAh prepared with Co3O4 as negative additive has been investigated. The investigation reveals that the charge and discharge efficiency at 1400 mA g−1 at room temperature, and the discharge efficiency at 140 mA g−1 at −20 °C of metal hydride electrode are increased from 82.2% to 92.4%, from 55.1% to 84.7%, and from 30.2% to 68.8%, respectively, by adding proper amounts of Co3O4. Furthermore, it is also found that the high-rate and low-temperature discharge ability, overcharge endurance ability, cycle life, inner pressure of battery are greatly improved by adding Co3O4. These results can be attributed to the high electrocatalytic activity and extended hydride storage capability of Co3O4, the improvement of gas consumption ability and the restraining of oxidation of electrode alloys by adding Co3O4.

Structure and electrochemical characteristics of LaNi 5-Ti 0.10Zr 0.16V 0.34Cr 0.10Ni 0.30 composite alloy electrode

Composite LaNi 5+ x wt.% Ti 0.10Zr 0.16V 0.34Cr 0.10Ni 0.30 ( x=0, 1, 5, 10) alloys were prepared by two-step re-melting. X-ray diffractometer (XRD), scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS), inductively coupled plasma (ICP) and electrochemical impedance spectroscopy (EIS) analyses showed that the matrix phase of LaNi 5 alloy with CaCu 5 structure remained unchanged after additive alloy was added, the amount of the second phase increased with increasing x. The synergetic effect within constituent alloys appeared during the composite process. The electrochemical characteristics of the composite alloy electrodes were greatly improved, and the optimum composition was x=5, at which the low temperature dischargeability at 233 K was 87.37 %, and the maximum discharge capacity and the high rate dischargeability at discharge current density of 1800 mA/g were 326.1 mAh/g and 71.98 % at 303 K, respectively. The HRD was controlled by both the charge-transfer reaction of hydrogen on the electrode/electrolyte interface and hydrogen diffusion coefficient in the bulk of the alloys at discharge current density of 1800 mA/g.

New La–Fe–B ternary system hydrogen storage alloys

The new La 8Fe 28B 24-, La 15Fe 77B 8- and La 17Fe 76B 7-type alloys have multiphase structures including LaNi 5, La 3Ni 13B 2 and (Fe, Ni) phases. The amount of La 3Ni 13B 2 phase increased and that of (Fe, Ni) phase decreased with an increasing La/(Fe + B) atomic ratio. The measurement of P–C–I curves revealed that the maximum hydrogen capacity exceeded 1.12 wt% at 313 K in the pressure range of 10 −3 MPa–2.0 MPa. The alloys exhibited good absorption/desorption kinetics at room temperature, and electrochemical experiments showed that all of the alloy electrodes exhibited good activation characteristics, high-rate dischargeability (HRD) and low-temperature (233 K) dischargeability (LTD).

Effect of AB5 alloy on Ti0.10Zr0.15V0.35Cr0.10Ni0.30 hydrogen storage alloy

The structure and electrochemical characteristics of melted composite Ti0.10Zr0.15V0.35Cr0.10Ni0.30 + x% LaNi4Al0.4Mn0.3Co0.3 (x = 0, 1, 5) hydrogen storage alloys have been investigated systematically. XRD shows that though the main phase of the matrix alloy remains unchanged after LaNi4Al0.4Mn0.3Co0.3 alloy is added, a new specimen is formed. The amount of the new specimen increases with increasing x. SEM-EDS analysis indicates that the V-based solid solution phase is mainly composed of V, Cr and Ni; C14 Laves phase is mainly composed of Ni, Zr and V; the new specimen containing La is mainly composed of Zr, V and Ni. The electrochemical measurements suggest that the activation performance, the low temperature discharge ability, the high rate discharge ability and the cyclic stability of composite alloy electrodes increase greatly with the growth of x. The HRD is controlled by the charge-transfer reaction of hydrogen and the hydrogen diffusion in the bulk of the alloy under the present experimental conditions.

The structure and 233K electrochemical properties of La0.8−xNdxMg0.2Ni3.1Co0.25Al0.15 (x=0.0–0.4) hydrogen storage alloys

The effect of neodymium content on the structure and low-temperature (233 K) electrochemical properties of the La0.8−xNdxMg0.2Ni3.1Co0.25Al0.15 (x = 0.0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys was investigated systematically. The result of the Rietveld analyses suggested that all these alloys mainly consist of two phases: the (La, Mg)2Ni7 phase and the LaNi5 phase. The electrochemical studies revealed that, at temperature 233 K, the maximum discharge capacity first increased from 188.5 mAh/g (x = 0.0) to 201.7 mAh/g (x = 0.1) and then decreased to 153.9 mAh/g (x = 0.4). The low-temperature dischargeability (LTD) first increased and then decreased with increasing x, also reaching an extreme when x was 0.10. The LTD was in agreement with the I0, but was irrespective of the diffusion of hydrogen. From our work, the optimum composition of the La0.8−xNdxMg0.2Ni3.1Co0.25Al0.15 (x = 0.0–0.4) alloy electrodes was found to be x = 0.10.

Effect of rare earth elements on electrochemical properties of La–Mg–Ni-based hydrogen storage alloys

La 0.60R 0.20Mg 0.20(NiCoMnAl) 3.5 (R = La, Ce, Pr, Nd) alloys were prepared by inductive melting. Variations in phase structure and electrochemical properties due to partial replacement of La by Ce, Pr and Nd, were investigated. The alloys consist mainly of LaNi 5 phase, La 2Ni 7 phase and LaNi 3 phase as explored by XRD and SEM. The maximum discharge capacity decreases with Ce, Pr and Nd substitution for La. However, the cycling stability is improved by substituting Pr and Nd at La sites, capacity retention rate at the 100th cycle increases by 13.4% for the Nd-substituted alloy. The electrochemical kinetics measurements show that Ce and Pr substitution improves kinetics and thus ameliorates the high rate dischargeability (HRD) and low temperature dischargeability. The HRD at 1200 mA g −1 increases from 22.1% to 61.3% and the capacity at 233 K mounts up from 90 mAh g −1 to 220 mAh g −1 for the Ce-substituted alloy.

Study on microstructure and electrochemical performance of La 0.7Mg 0.3(Ni 0.9Co 0.1) x hydrogen storage alloys

Hydrogen storage alloys La 0.7Mg 0.3(Ni 0.9Co 0.1) x ( x = 3.0, 3.1, 3.3, 3.4, 3.5, 3.7 and 3.8) were prepared by inductive melting followed by annealing treatment at 1173 K for 6 h. The effects of the stoichiometry ( x) on the structural and electrochemical characteristics of the alloys were investigated systematically. X-ray diffraction (XRD), optical morphology and energy dispersive spectrometry (EDS) analyses showed that these alloys have a multiphase structure which consists of a (La, Mg)Ni 3 phase with the PuNi 3-type rhombohedral structure, a LaNi 5 phase with the CaCu 5-type hexagonal structure and a (La, Mg) 2Ni 7 phase with the Ce 2Ni 7-type hexagonal structure. The main phase of the alloys with x = 3.0 and 3.1 is (La, Mg)Ni 3 phase (PuNi 3-type structure), the main phase of the alloys with x = 3.3, 3.4 and 3.5 is (La, Mg) 2Ni 7 phase (Ce 2Ni 7-type structure), and the main phase of the alloys with x = 3.7 and 3.8 is LaNi 5 phase (CaCu 5-type structure). Moreover, the lattice parameters of the (La, Mg)Ni 3 phase, (La, Mg) 2Ni 7 phase and LaNi 5 phase decrease monotonously with the increase of the value x. The electrochemical analysis shows that the maximum discharge capacity increases from 356.6 mA h g −1 ( x = 3.0) to 392.1 mA h g −1 ( x = 3.5) and then decreases to 344.1 mA h g −1 ( x = 3.8), and the alloys exhibit good cycling stability. As the discharge current density is 3000 mA g −1, the high-rate dischargeability (HRD) increases from 30.1% ( x = 3.0) to 56.1% ( x = 3.8). The low temperature dischargeability (LTD) increases from 24.3% ( x = 3.0) to 58.96% ( x = 3.7) and then decreases to 48.1% ( x = 3.8).

Structure and electrochemical characteristics of melted composite Ti 0 .10 Zr 0 .15 V 0 .35 Cr 0.10Ni 0.30–LaNi 5 hydrogen storage alloys

The structure and electrochemical characteristics of melted composite Ti 0.10Zr 0.15V 0.35Cr 0.10Ni 0.30 + x% LaNi 5 ( x = 0, 1, 5 and 10) hydrogen storage alloys have been investigated systematically. XRD shows that the matrix phase structure of V-based solid solution phase with a BCC structure and C14 Laves phase with hexagonal structure is not changed after adding LaNi 5 alloy. However, the amount of the secondary phase increases with increasing LaNi 5 content. Field emission scanning electron microscopy–energy dispersive spectroscopy (FESEM–EDS) shows that the C14 Laves phase contains more Zr and the white lard phase has a composition close to (Zr, Ti)(V, Cr, Ni, La) 2. The electrochemical measurements show that the hysteresis effect decreases dramatically with increasing x. The activation performance, the low temperature dischargeability, high rate dischargeability and cyclic stability of composite alloy electrodes increase greatly with increasing x. The maximum discharge capacity first increases as x increases from 0 to 5 and then decreases when x increases further from 5 to 10. The improvement of the electrochemical characteristics caused by adding LaNi 5 seems to be related to formation of the secondary phase.

Study on kinetics and electrochemical properties of Ml 0.70Mg 0.30(Ni 3.95Co 0.75Mn 0.15Al 0.15) x ( x = 0.60, 0.64, 0.68, 0.70, 0.76) alloys

In our endeavor to obtain hydrogen storage alloys with high discharge capacity and good cycling stability, the Ml 0.70Mg 0.30(Ni 3.95Co 0.75Mn 0.15Al 0.15) x ( x = 0.60, 0.64, 0.68, 0.70, 0.76) (where Ml denotes La-rich misch metal) alloys with Ml substitution for La and B-side multi-alloying have been prepared by inductive melting, and the effect of stoichiometry x on the electrochemical properties has been investigated systematically. XRD analysis shows that the alloys are mainly composed of LaNi 5 phase and LaNi 3 phase. The electrochemical test shows that the maximum discharge capacity, kinetics, high rate dischargeability (HRD) and low temperature dischargeability (LTD) all increase and then decrease with increasing x. The alloy with x = 0.64 has larger maximum discharge capacity, 372 mAh g −1. As the case of x = 0.70, the alloy exhibits better kinetics, HRD and LTD. The testing alloys exhibit good cycling stability, and the capacity retention of the alloys at the 100th cycles increases from 78.0% ( x = 0.60) to 90.3% ( x = 0.76).

The effect of Nd content on the electrochemical properties of low-Co La–Mg–Ni-based hydrogen storage alloys

The low-Co content La 0.80− x Nd x Mg 0.20Ni 3.20Co 0.20Al 0.20 ( x = 0.20, 0.30, 0.40, 0.50, 0.60) alloys were prepared by inductive melting and the effect of Nd content on the electrochemical properties was investigated. XRD shows that the alloys consist mainly of LaNi 5 phase, La 2Ni 7 phase and minor LaNi 3 phase. The electrochemical P–C–T test shows hydrogen storage capacity increases first and then decreases with increasing x, which is also testified by the electrochemical measurement that the maximum discharge capacity increases from 290 mAh/g ( x = 0.20) to 374 mAh/g ( x = 0.30), and then decreases to 338 mAh/g ( x = 0.60). The electrochemical kinetics test shows exchange current density I 0 increases with x increasing from 0.20 to 0.50 followed by a decrease for x = 0.60, and hydrogen diffusion coefficient D increases with increasing x. Accordingly high rate dischargeability increases with a slight decrease at x = 0.60 and the low temperature dischargeability increases with increase in Nd content. When x is 0.50, the alloy exhibits a better cycling stability.