Effects of Alkaline Pre-Etching to Metal Hydride Alloys

Ouchi²,

Nei³

et al. 2017

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Abstract:The effects of seven constituent phases-CeNi 3 , NdNi 3 , Nd 2 Ni 7 , Pr 2 Ni 7 , Sm 5 Ni 19 , Nd 5 Co 19 , and CaCu 5 -on the gaseous phase and electrochemical characteristics of a superlattice metal hydride alloy made by induction melting with a composition of Sm 14 La 5.7 Mg 4.0 Ni 73 Al 3.3 were studied through a series of annealing experiments. With an increase in annealing temperature, the abundance of non-superlattice CaCu 5 phase first decreases and then increases, which is opposite to the phase abundance evolution of Nd 2 Ni 7 -the phase with the best electrochemical performance. The optimal annealing condition for the composition in this study is 920 • C for 5 h. Extensive correlation studies reveal that the A 2 B 7 phase demonstrates higher gaseous phase hydrogen storage and electrochemical discharge capacities and better battery performance in high-rate dischargeability, charge retention, and cycle life. Moreover, the hexagonal stacking structure is found to be more favorable than the rhombohedral structure.

Section: Performance Correlation With Individual Phasementioning

confidence: 92%

Comparison among Constituent Phases in Superlattice Metal Hydride Alloys for Battery Applications

Ouchi²,

Nei³

et al. 2017

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“…Alloy B with a composition of La 11.3 Pr 1.7 Nd 5.1 Mg 4.5 Ni 63.6 Co 13.6 Zr 0.2 , which shows the lowest charge-transfer resistance in a comparative study [28], was the superlattice alloy under the current study. In this composition, Pr and Nd were added to reduce the corrosion nature of the alloy, Ce and Mn were not included in the consideration of cycle stability and self-discharge [2,21], Co was added for low-temperature performance enhancement [19], and a very small amount of Zr was added for scavenging residual oxygen in the chamber.…”

Section: Alloy Properties Comparisonmentioning

confidence: 81%

“…The B/A stoichiometry of 3.42 was chosen through an optimization study judging the electrochemical performance. While annealed alloy A has only one CaCu 5 phase, as seen from its XRD pattern (Figure 10a in [28]), alloy B shows a multi-phase structure in both pristine and annealed conditions ( Figure 1). Phase abundances calculated from the XRD data are listed in Table 1.…”

Section: Alloy Properties Comparisonmentioning

confidence: 99%

“…Another reason for the lower R ct values in cell B is the higher surface catalytic ability of the superlattice alloy [28]. Out of many factors contributing to Rint, ohmic resistance (R0) and surface charge-transfer resistance (Rct) can be deduced from the Cole-Cole plot obtained by the alternating current (AC) impedance measurement [35].…”

Section: Internal Resistancementioning

confidence: 99%

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Performance Comparison between AB5 and Superlattice Metal Hydride Alloys in Sealed Cells

Koch¹,

Nei³

et al. 2017

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High-power cylindrical nickel metal/hydride batteries using a misch metal-based Al-free superlattice alloy with a composition of La 11.3 Pr 1.7 Nd 5.1 Mg 4.5 Ni 63.6 Co 13.6 Zr 0.2 were fabricated and evaluated against those using a standard AB 5 metal hydride alloy. At room temperature, cells made with the superlattice alloy showed a 40% lower internal resistance and a 59% lower surface charge-transfer resistance compared to cells made with the AB 5 alloy. At a low temperature (−10 • C), cells made with the superlattice alloy demonstrated an 18% lower internal resistance and a 60% lower surface charge-transfer resistance compared to cells made with the AB 5 alloy. Cells made with the superlattice alloy exhibited a better charge retention at −10 • C. A cycle life comparison in a regular cell configuration indicated that the Al-free superlattice alloy contributes to a shorter cycle life as a result of the pulverization from the lattice expansion of the main phase.

“…This paper elaborates on the continuing efforts to validate the third item-high-capacity positive electrode material in the pouch design tested with various regimens. [8]; it was supplied by Eutectix (Troy, MI, USA). Positive electrode active materials (AP50 and WM12) were fabricated by a continuous stirred-tank reactor process [7,9,10] in BASF-Ovonic (Rochester Hills, MI, USA).…”

Section: Introductionmentioning

confidence: 99%

A Ni/MH Pouch Cell with High-Capacity Ni(OH)2

Yan¹,

Meng²,

et al. 2017

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Electrochemical performances of a high-capacity and long life β-α core-shell structured Ni 0.84 Co 0.12 Al 0.04 (OH) 2 as the positive electrode active material were tested in a pouch design and compared to those of a standard β-Ni 0.91 Co 0.045 Zn 0.045 (OH) 2 . The core-shell materials were fabricated with a continuous co-precipitation process, which created an Al-poor core and an Al-rich shell during the nucleation and particle growth stages, respectively. The Al-rich shell became α-Ni(OH) 2 after electrical activation and remained intact through the cycling. Pouch cells with the high-capacity β-α core-shell positive electrode material show higher charge acceptances and discharge capacities at 0.1C, 0.2C, 0.5C, and 1C, improved self-discharge performances, and reduced internal and surface charge-transfer resistances, at both room temperature and −10 • C when compared to those with the standard positive electrode material. While the high capacity of the core-shell material can be attributed to the α phase with a multi-electron transfer capability, the improvement in high-rate capability (lower resistance) is caused by the unique surface morphology and abundant interface sites at the β-α grain boundaries. Gravimetric energy densities of pouch cells made with the high-capacity and standard positive materials are 127 and 110 Wh·kg −1 , respectively. A further improvement in capacity is expected via the continued optimization of pouch design and the use of high-capacity metal hydride alloy.