Single-wall carbon nanotubes embedded in active masses for high-performance lead-acid batteries

This work reports on successful attempts to improve the performance of lead-acid batteries by the use of carbon nanotubes asadditives to the active mass of both positive and negative electrodes. Both single-wall carbon nanotubes (SWCNT) and multi-wallcarbon nanotubes (MWCNT) from commercial sources were tested. The use of SWCNT seems to be very advantageous based onthis work. Lead-acid prototype cells which electrodes contained SWCNT showed superior performance in terms of high specificcapacity, improved cycle-life, low resistivity, better kinetics and higher rate capability. Post mortem analysis by electron microscopyand Raman spectroscopy indicated their stability in both electrodes during prolonged cycling. Morphological, structural and surfacearea analyses seemed to prove that the presence of SWCNT mitigates pronouncedly the detrimental sulfation phenomena, namely,formation of large, inaccessible PbSO₄ particles upon discharge. We suggest that their presence in both positive and negativeelectrodes of these batteries increases the effective electronic conductivity and improves the contact among the particles, thus leadingto homogeneous current distribution throughout the electrodes.We achieved specific electrodes capacities around 120 mAh g^-1andcould demonstrate 950 cycles with cells operating at 25% depth-of-discharge by adding SWCNT, while CNT-free cells could exhibitonly 90 mAh g^-1and reach only 200 cycles at the same experimental conditions.