Effect of Sm on performance of Pr/Nd/Mg-free and low-cobalt AB4.6 alloys in nickel-metal hydride battery electrode

Abstract

In this study, Sm-doped Pr/Nd/Mg-free low-cobalt La3.0xCexSm0.98-4xZr0.02Ni3.91Co0.14Mn0.25Al0.30 (x = 0.08; 0.12; 0.16; 0.20; 0.245) metal hydride electrodes were synthesized for the first time in the literature, and their structural characteristics and electrochemical performance were investigated. The CaCu5-type main phase and Ce2Ni7-type minor phase were found to coexist in the electrodes via XRD analysis. A large volume of the unit cell with increasing values of x led to a lower desorption plateau pressure, and high thermodynamic stability of the hydride and a maximum discharge capacity of 331.2 mA h g−1 were obtained at x = 0.245. The HRD3000 of the electrode alloy exhibited 81.40% at x = 0.245, and this contributed to excellent catalytic performance of the CaCu5-type phase and provided phase boundary layers in the Ce2Ni7-type phase. The retention capacity was maintained at 78.30% at x = 0.12 after 100 cycles owing to the combined effect of Ce and Sm. The mechanisms of the related electrochemical thermodynamics and kinetics were also systematically investigated.