Effects of the amount of Mg impurity on the electrochemical properties of Ml(NiCoMnTi)(5) hydrogen storage alloy

For the purpose of scientific control of the content of magnesium impurity in hydrogen storage electrode alloys during industrial production, the effe cts of magnesium content on electrochemical performances of a mischmetal ba sed alloy Ml(NiCoMnTi)(5) has been investigated by doping the alloy with va rious amounts of magnesium intentionally. The electrochemical measurement s hows that the discharge capacity increases slightly from 302 to 315 mAh/g a s the magnesium content in the alloy increases from 0.003 to 0263%. However , when the magnesium content increases further, the capacity starts to decr ease gradually. As the magnesium content increases, the activation behavior and high-rate-dischargeability are enhanced to some degree, but the self-d ischarge (24 h) of the electrode rises greatly. It is found that the cyclin g stability deteriorates rapidly as the magnesium content increases beyond 0.100%. Therefore, it is appropriate to control the content of magnesium im purity in the MI(NiCoMnTi)(5) alloy under 0.100%. (C) 1999 Published by Els evier Science S.A. All rights reserved.