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Abstract 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 (P peak) 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 P peak with the cycling life, the (LaCe) 1.0 (NiCoMn) 4.85 Al 0.05 Cu 0.1 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. Graphical abstract Image 1 Highlights • Low-Al design is an efficient way for developing low-temperature and high-rate MH. • Various B-side elements coordinate the electrode kinetics and anti-corrosion property. • Anti-corrosion property presents a contradictory rule with electrode kinetics. • Electrode kinetics progressively drops via Ni, Si, Cu, Fe, Sn and Al substituting. • The designed Cu/Si-doped low-Al alloy offers a promising solution for low-temperature and high-power applications. [ABSTRACT FROM AUTHOR]

Abstract The current main application of nickel-metal hydride (Ni-MH) batteries is offering high power assist for electric transportation, putting a high demand on the high-rate capability of the electrode materials. In this work, Co-free α-Ni(OH) 2 micron-bulks comprising ultrafine primary particles with average size of ∼40 nm are presented as the high-rate cathode material for Ni-MH batteries. The micron-sized secondary particles are not only industry-compatible but also beneficial for tapping density, while the nano-sized primary particles ensure fast electrochemical kinetics. As a result, this material exhibits good overall performance, especially an excellent high-rate capability. When being discharged or charged at an ultrahigh current density up to 6000 mA g−1, it can deliver a capacity of 245.1 mAh g−1 (∼82% of the rated capacity) or accept a capacity of 272.6 mAh g−1 (∼91% of the rated capacity) only within 3 min. When further operating in a more practical 'charge sustaining' mode, it also displays superior potential depolarization under high-current pulses. This impressive high-rate capability highlights the advantages of our sample, providing a promising candidate for the high-power Ni-MH batteries. Graphical abstract Image 1 Highlights • Micron-sized Co-free α-Ni(OH) 2 with excellent high-rate ability is demonstrated. • The micron-sized secondary particles comprise ultrafine primary nanoparticles. • This material delivers ∼82% of the rated capacity at a current up to 6000 mA g−1. • This material recharges ∼91% of the rated capacity only within 3 min. • This material displays superior potential depolarization under high-current pulses. [ABSTRACT FROM AUTHOR]

Various properties of La 0.78 Ce 0.22 Ni 3.73 Co 0.30 Mn 0.30 Al 0.17 Fe 0.5−x Si x (x = 0, 0.05, 0.075 and 0.1) hydrogen storage alloys at 20–80 °C have been investigated systematically. With the increase of Si content, the hydrogen storage capacity increases and the equilibrium pressure decreases, thus the improved thermodynamic stability of the metal hydrides makes the Si-containing alloys more suitable for working at higher temperatures. Appropriate addition of Si (x = 0–0.075) improves the anti-corrosion capability of the alloy, as a result, the temperature insensitivity, high-temperature dischargeability and high-temperature recoverability increase accordingly, particularly the cycling stability ( S 150 ) increases from 43.7% to 71.8%. In addition, the charge-transfer process is suppressed gradually by Si substituting (x = 0–0.075) at 20 °C, but gets promoted due to the improved surface catalytic ability when that at 60 °C, consequently the high-rate dischargeability and high-power delivery deteriorate at room temperature, but increase gradually at higher temperature. Therefore, an optimum alloy electrode is got when x = 0.075, the deterioration of x = 0.1 alloy on high-temperature performance is attributed to the appearance of the second A 2 B 7 phase. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel pyrolysis carbonization treatment is proposed to modify MH anode. • The stable porous N-doped carbon layers were in-situ coated on MH anode. • Electrochemical kinetics and anti-corrosion ability of MH anode are optimized by NC. • The carbonization treated MH anode exhibits an ultra-high capacity of 247.21 mAh g−1 at 15C. The conflicting relationship between anti-corrosion ability and electrochemical kinetics significantly hinders the comprehensive performance of hydrogen storage alloys in nickel-metal hydride batteries. In this study, we successfully coated a nano carbon layer on the AB 5 -type hydrogen storage alloy to achieve exceptional peak power, high-rate discharge capability, low-temperature performance, and cycling stability simultaneously as the MH electrodes. The surface carbon layer could not only enhance the surface conductivity, but also result in a reduced state of the alloy to mitigate the oxidation of alloy owing to the electronic transfer from the carbon layer to metal. The carbon-coated alloy electrode thus exhibits superior electrochemical properties compared to the pure alloy electrodes. The discharge capacity of the carbon-coated electrode at a discharge current density of 4.5 A g−1 is 247.21 mAh/g, which is 2.37 times that of the master electrode (104.12 mAh/g). Additionally, the discharge capacity of the carbon-coated electrode at −40 °C reaches an impressive 250.85 mAh/g. More importantly, these carbon-coated alloy electrodes exhibit outstanding cycle performance. This technology offers a promising solution for high-power, low-temperature, and long-cycling Ni-MH batteries. [ABSTRACT FROM AUTHOR]