Study on kinetics and electrochemical properties of low-Co AB5-type alloys for high-power Ni/MH battery

The structure and electrochemical kinetics properties of La0.90−xCexPr0.05Nd0.05Ni3.90Co0.40Mn0.40Al0.30 (x = 0.10, 0.20, 0.30, 0.40, 0.50) hydrogen storage alloys have been investigated. XRD shows that the alloys consist of LaNi5 phase with hexagonal CaCu5 structure. With increase in Ce content, the parameter a and cell volume decrease remarkably, but the parameter c increases slightly. The limiting current density IL and the hydrogen diffusion coefficient D increase, and the exchange current density I0 increases firstly from 201.4 mA/g (x = 0.10) to 277.9 mA/g (x = 0.30) and then decreases to 208.5 mA/g (x = 0.50). Meanwhile, high rate dischargeability (HRD) at 1440 mA/g increases from 44.1% (x = 0.10) to 59.9% (x = 0.30), and then decreases to 44.2% (x = 0.50). As the amount of Ce increases, the plateau pressure of P–C isotherms increases gradually, the capacity retention of the alloys increases firstly and then decreases, the alloy with x = 0.30 has the higher capacity retention and cycling stability, but the maximum discharge capacity of alloys decreases. Ce is a vital element in favor of kinetics properties of rare earth-based AB5-type alloys, and the substitution of La with Ce in suitable amount could improve the HRD by increasing kinetics.