Self-Discharge Characteristic of La_0.60Nd_0.15Mg_0.25Ni_3.50 Alloy with Single-Phase Ce₂Ni₇-Type Super-Stacking Structure

Abstract

Self-discharge performance is one of the key indexes of nickel-metal hydride batteries. In this work, single-phase Ce 2 Ni 7 -type La-Nd-Mg-Ni-based alloy with great application potential in long-term storage Ni/MH batteries are prepared by step-wise annealing. The as-cast alloy contains CaCu 5 -, Gd 2 Co 7 -and Ce 5 Co 19 -type phases. After annealed at 1248 K, CaCu 5 -and Ce 5 Co 19 -type phases disappear and a single-phase Gd 2 Co 7 -type structure is obtained. With the temperature increase, Gd 2 Co 7 -type structure begins to transform into Ce 2 Ni 7 -type structure. As annealed at 1323 K, the alloy shows a Ce 2 Ni 7 -type single-phase structure. The C 60 (discharge capacity at 60 mA g −1 ) of Ce 2 Ni 7 -type electrode reaches 405 mAh g −1 , and the C 1900 is even high to 210 mAh g −1 .The Ce 2 Ni 7 -type electrode also shows superior self-discharge properties and the charge retention rate for 1 d (CRT 1d ) is 96.5%. Moreover after 150 cycles, the CRT 1d is even high to 97.7% and CRT 7d is 81.5%. While those of the as-cast electrodes are only 79% and 36%, respectively. Electrochemical pressure-composition isotherms show that Ce 2 Ni 7 -type electrode has relatively lower hydrogen desorption plateau pressure, indicating more stable hydride and less reversible self-discharge. After 150 cycles, the plateau pressure gets even lower. Moreover Ce 2 Ni 7 -type electrode possesses smaller corrosion current density, indicating minor oxidation/corrosion degree.