Thin-film zinc/manganese dioxide electrodes

Thin-film electrodes allow the manufacturing of flat batteries of variable design. Their electric performance is better than that of customary cells because of a larger contact area between anode and cathode and better utilization of the electrochemically active materials. Bipolar thin-film electrodes for the rechargeable alkaline zinc/manganese dioxide system were assembled using graphite-filled plastics (high-density polyethylene and polyisobutylene). In a different approach, extremely thin electrodes were obtained using 25 μm thick foils made of non-conductive micro-porous polypropylene. The electroactive materials were electrolytically deposited into the pores of the previously metallized foil, providing the required conductive connection through the plastic matrix by themselves. Cycle behavior, cumulated capacities, and energies of batteries with up to two bipolar units were measured. At this early stage of development, batteries based on graphite-filled polymer foils showed better results with regard to storage capacity per unit area and to cycle life. Prototypes based on micro-porous polypropylene suffered from the relatively small fraction of pore volume available for the deposition of active material (about 38%) and from current collector corrosion.