Abstract
High-power cylindrical nickel metal/hydride batteries using a misch metal-based Al-free superlattice alloy with a composition of La11.3Pr1.7Nd5.1Mg4.5Ni63.6Co13.6Zr0.2 were fabricated and evaluated against those using a standard AB5 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 AB5 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 AB5 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.
Highlights
Nickel/metal hydride (Ni/MH) batteries have been serving consumer portable electronics, hybrid electric vehicles, and stationary applications for more than 30 years [1,2,3,4,5,6]
The misch metal (Mm)-based superlattice MH alloy began to take over the market share because of its higher capacities; better high-rate dischargeability; and superior low-temperature, high-temperature, and charge retention performances compared to the conventional
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
Summary
Nickel/metal hydride (Ni/MH) batteries have been serving consumer portable electronics, hybrid electric vehicles, and stationary applications for more than 30 years [1,2,3,4,5,6]. The misch metal (Mm)-based AB5 metal hydride (MH) alloy was the mainstream negative electrode active material [7]. The Mm-based superlattice MH alloy began to take over the market share because of its higher capacities; better high-rate dischargeability; and superior low-temperature, high-temperature, and charge retention performances compared to the conventional. The A-site of the superlattice MH alloy contains both rare-earth (RE) and alkaline earth (usually Mg) elements. While almost all academic research has focused on the single RE element (La or Nd)-based superlattice MH alloys (for reviews, see [9,10,11]), commercial applications have adopted the Mm composition for a higher cycle stability [2,12]. A few papers about the substitution works performed in the Mm-based superlattice alloy family with Al [13], Mn [14,15], Fe [16,17], Co [18,19,20], and Ce [21] were published, but a systematic performance comparison between a Mm-based superlattice MH alloy and a standard
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