Improvement of the low temperature performances of MmNi3.55Co0.75Mn0.4Al0.3 hydrogen storage alloy

Without treatment, commercial MmNi(3.55)Co(0.75)Mn(0.4)Al(0.3) hydrogen storage alloy shows very poor discharge performance below 253 K, especially under higher current densities and cannot meet the low temperature requirements of Ni/metal hydride (MH) batteries. The poor low temperature performance of MH material mainly stems from the lower electrochemical activity of hydrogen storage alloys. The influence of boron additives on the low temperature performance of MmNi(3.55)Co(0.75)Mn(0.4)Al(0.3) has been studied. The results show that the addition of boron remarkably improves the low temperature discharge capacity and rate capability. With an increase of boron content, such good influences become even more appreciable. Electrochemical kinetic studies show that the addition of boron significantly enhances the electrochemical activity of hydrogen storage alloys. These hydrogen storage alloys with a proper amount of boron are suitable for use in a Ni/MH battery with a lower limit temperature of 238 K under lower current densities (less than or equal to120 mA/g). (C) 2001 The Electrochemical Society.