Carbon nanotube buckypaper/MmNi₅ composite film as anode for Ni/MH batteries

An efficient and cost-effective method has been developed to produce high quality buckypapers from multi-walled carbon nanotubes. The buckypapers were then used as a substrate for AB₅ hydrogen storage alloy electrodes, and electrochemical performances of these composite films in Ni/MH batteries have been investigated. AB₅ alloy was coated on the buckypaper using magnetron sputtering. The buckypapers prepared by our approach were thin, highly flexible and provided sufficient strength as substrates for the hydrogen storage alloy film. A good contact between the buckypaper and the MmNi ₅ alloy was established. The electrochemical results show that the buckypapers can be a versatile replacement for conventional metal substrates for the anode in Ni/MH batteries. They provide exceptional electrical conductivity and significant reduction in weight and cost. The obtained maximum discharge capacity of 276 mAh/g for BM-1 electrode is higher than what was previously obtained on electrode with metal substrate of 220 mAh/g. Amongst the two different thickness of AB₅ film studied, it was found that the reduction of MmNi₅ layer thickness enhanced the discharge capacity of the electrode, but the high rate discharge capability was irrelevant to the film thickness. However, the thicker film exhibits better chargeability and cycle stability. Thus all these are beneficial for the miniaturisation of the Ni/MH batteries.