Influence of Sm doping on thermodynamics and electrochemical performance of AB5+z alloys in low-temperature and high-power Ni-metal hydride batteries

Abstract

AB5-type negative electrode materials have been extensively used for Ni-metal hydride batteries. However, their rate capabilities have hindered them from being more extensively applied, especially in hybrid electric vehicles at low temperatures. Here, a hyper-stoichiometric AB5.09 alloy is designed and Sm is doped to achieve high-power performance. The influence of the microstructural characteristics, thermodynamic stabilities and comprehensive electrochemical performance resulting from the substitution of Sm for La and Ce is investigated. This work demonstrates that the addition of Sm results in a decrease in the maximum capacity and hydride stability. Furthermore, with the stress concentration relieving effect from the increase of anisotropy of the c/a ratio, the cycling stability increases significantly. Due to the formation of the Ni2MnAl catalytic phase, all alloys possess a high density of phase boundaries and exhibit good high-rate discharge performance. The high-rate dischargeability and specific power are further improved after Sm doping, with the high-rate discharge capacity retention rate reaching 81.4% at 3000 mA g−1. Although Sm adversely affects the surface catalytic properties of the electrodes, the high Sm content alloy exhibits higher specific power and discharge capacity at −40 °C due to the decrease in hydride stability.