Page 263 - Handbook of Battery Materials

References 233

convection, carbon substrates [196]), the possibility to ignore self-discharge by
chemical attack of the acid on the deposited zinc because the stack runs dry in the
standby mode, and use of relatively cheap construction materials (polymers) and
reactants.
The most unpleasant drawbacks are:the requirement for tanks, tubes, and pumps
for the electrolyte storage and transport system, increasing the volume of the battery
and consuming energy (in the case of the zinc/chlorine battery an extra cooling
device had to be provided); highly corrosive electrolytes; public distrust of storing
halogens in any form (though it is frequently stated that organic polybromide
complexes are quite harmless); and a certain imbalance of the electrochemistry
involved (zinc ions form halide complexes of the type [ZnX 4 ] 2− which behave – due
to their charge – as anions in the electric field).
Despite the fact that the zinc/ferricyanide system employs an alkaline electrolyte,
the electrode reactions are quite similar to those in zinc/halogen batteries, and
battery constructions are usually bipolar too.
Zinc is electrodeposited from the sodium zincate electrolyte during charge. As
in the zinc/bromine battery two separate electrolyte loops (‘posilyte’ and ‘negalyte’)
are required. The only difference is the quality of the separator: the zinc/bromine
system works with a microporous foil made from sintered polymer powder, but
the zinc/ferricyanide battery needs a cationic exchange membrane in order to
obtain acceptable coulombic efficiencies. The occasional transfer of solid sodium
ferrocyanide from the negative to the positive tank, to correct for the slow transport
of complex cyanide through the membrane, is proposed [197].
All in all, this system is more complicated than the other flow batteries, and this
handicap is hindering wider application.

8.3.7.6 Zinc Electrodes for Printed Thin-Layer Batteries
Since the turn of the millennium, some companies in Israel (Power Paper, 2000),
Finland (Enfucell, 2002), and the USA (Thin Battery Technology, 2002, meanwhile
Blue Spark Technologies) are marketing thin and flexible zinc/manganese dioxide
batteries produced by industrial printing, drying, and laminating techniques. They
are preferably integrated in ‘smart’ cards for different applications or in active or
semi-active tags. The user in general cannot even see the battery and may not have
any idea about the nature of the power source operating his/her device.
The key technologies, for example, the production of proprietary printing inks,
particular binder/solvent systems containing the active components in the form of
very fine powders (e.g., zinc for anodes with an average particle diameter of 30 µm)
are patented. Power Paper, as an example, is holding by more than 60 patents
covering the applied materials and details of the production process.
Nevertheless, from time to time additional zinc electrode formulations for either
zinc/nickel batteries [198] or for the zinc/manganese system [199] are presented.
Up to 2003, a joint project of Power Paper and the Institute for Chemical
Technology of Inorganic Materials, Graz University of Technology, explored a
rechargeable version of printed thin and flexible zinc/manganese dioxide batteries
based on experience with RAM cells (see Section 8.3.7.4) [200].