Excellent high-rate capability of micron-sized Co-free α-Ni(OH)2 for high-power Ni-MH battery

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. 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.