Phase structure and electrochemical properties of La-Y-Ni-based A5B19-type annealed alloys

The effect of annealing temperature (1173-1373 K) on the phase structure and electrochemical performance of new A5B19 type hydrogen storage alloy La0.4Y0.6Ni3.52Mn0.18Al0.1 was systematically investigated. The results show that the content of the main phase A5B19 (3R-Ce5Co19+2H-Pr5Co19)-phase increases with the increase of annealing temperature, of which the 3R-Ce5Co19 phase abundance is the highest (57%, mass fraction) at 1273 K, and further increasing the annealing temperature will help the alloy form 2H-Pr5Co19 type phase. The unit cell parameters a, c and unit cell volume V of the 3R-Ce5Co19 and 2H-Pr5Co19 type phases all gradually increase with the increase of annealing temperature, but the unit cell parameters and volume decrease after annealing at 1373 K. With the increase of annealing temperature, the desorption plateau of the electrochemical P-C isotherms increases. The electrochemical analysis show that increasing the abundance of Ce5Co19 type phase is beneficial to improve the discharge capacity, rate performance and cycle stability of the alloy electrodes. When the annealing temperature is 1273 K, the electrochemical properties of the alloy electrode are the best, the maximum discharge capacity reaches 386.6 mA∙h/g (60 mA/g), the high-rate discharge ability at current density of 900 mA/g (HRD900) is 76.7%, and the capacity retention after 100 cycles (S100) is 90.1% (300 mA/g). The diffusion of hydrogen atoms in the alloy body is control step that affects the high-rate discharge performance and dynamic reaction of the alloy electrodes. © 2022, China Science Publishing & Media Ltd. All right reserved.