Development of an aluminium/sea water battery for sub-sea applications

There are two modes of operation for an aluminium/water battery: use of hydrogen-evolving or oxygen-reduction cathodes. In the first case, the current density is ≈10 mA cm−2 at 0.5 V. This leads to significant increase of pH and deposition of Ca/Mg(OH)2 at the cathode, leading to sharp decrease in battery performance. On the other hand, in the oxygen-reduction mode, the current density is ≈0.1 mA cm−2 at 1.4 V, because of the low concentration of O2 in sea-water. Long-term tests of an Al/water battery using Teflon-bonded CO3O4/C oxygen reduction cathodes in Brightlingsea Harbour, Essex, over a test period of 70 days have shown that the performance of this battery is stable and that it is possible to increase its performance by means of multi-cathodes on either side of the anode. A conceptual design shows that such a battery has an energy density of 1008 Wh kg−1 over an operating period of one year, significantly higher than all the conventional primary batteries considered for use in sub-sea environments.