Thin-film zinc manganese dioxide electrodes based on microporous polymer foils

Thin-film electrodes allow manufacturing of flat batteries of variable desi gn which can be used for the development of smaller electric appliances. Su bstituting the metal carrier by conductive plastics leads to a considerable reduction of battery weight. Usually the electroactive materials are depos ited onto the surface of the carrier. A significant improvement of the orig inally poor adherence between polymer foil and electroactive layers can be achieved by mechanical (surface roughening) or chemical (etching) pretreatm ent. Another way to form extremely thin electrodes having a thickness in th e range of some ten micrometers is reported here. First, a metallic layer i s deposited onto one surface of a 25 mu m thin porous polypropylene foil. S ubsequently, the electroactive materials are electrolytically deposited int o the pores of the metallized foil providing the required conductive connec tion through the plastic matrix by themselves. In this case the flexibility of the polymer has a positive influence on the problem of volume change of manganese dioxide during charging and discharging, respectively, because t he plastic provides flexible 'mechanical struts' which act as a 'binder' an d therefore prevent increasing internal resistance due to contact problems. Assembling a zinc filled polymer and a manganese dioxide filled one in suc h a way that both metallic back-layers are in contact, a thin bipolar zinc/ manganese dioxide electrode can be obtained. (C) 1999 Elsevier Science S.A. All rights reserved.