Figure 1. Galvanostatic data for Bi-birnessite cathodes with and without Cu additive.

(a) First five C/3 cycles of a 45 wt% (∼21 mAh cm⁻²) EMD, Bi₂O₃ and carbon containing cathode fades completely in five cycles. During the first discharge, potentials characteristic of γ-MnO₂ were seen. In the second cycle, potentials characteristic of a δ-MnO₂ layered phase were seen. (b) A comparable electrode with Cu shows negligible capacity fade in five C/3 cycles. (c) Capacity versus cycle number for ∼19 and 60 wt% EMD, Bi₂O₃, Cu and carbon containing cathode at 20C and C/3, respectively. Areal capacities of the ∼19 and 60 wt% EMD cells were ∼12 and 29 mAh cm⁻², respectively, which are indicative of high active loading electrodes. All cycling was against NiOOH counter electrodes. The 60 wt% cell is still cycling at the time of this writing.