The initial series of experiments was carried out in two different
cells and employing two slightly different electrolytes but check
experiments indicated that, in general, the conclusions were the
sameunder both conditions. Table 1 reports thecompounds studied
together with their effect on the deposit quality and, in some cases,
the current efficiency during a first charge/discharge cycle. The photographs
of the deposits in Fig. 2(A)–(D) are intended to illustratethe quality of the lead deposits obtained. In the absence of an additive,
see Fig. 2(C), the deposit is composed of intergrowing lead
crystallites; the layer is not completely uniform and some protrusions
towards the positive electrode are clearly visible. Many of the
compounds studied had little or no influence on the deposit quality.
A fewof the possible additives had the effect of making the deposit
quality worse and certainly unacceptable in a secondary battery;
this is illustrated in Fig. 2(D) where structured growths and/or dentrites
are clearly visible and the cross-sectional view shows that
the deposit is thicker and much less compact. Another group of the
compounds improved the deposit quality and typical deposits are
shown in Figs. 2(A) and (B). These included long chain tetraalkylammonium
cations, TritonTM X 100, BrijTM56, TyloxapolTM and
sodium ligninsulfonate. In the case of the best deposits, Fig. 2(A),
the crystallite size is smaller and more uniform and the deposit
appears uniform and free of protrusions over the entire surface.
The cross-sectional image shows that the deposit is thin and compact.
Interestingly, the current efficiency is acceptable for the first
charge/discharge cycle of the small battery with electrolytes containing
almost all the additives; not surprisingly, the exception is
the solution where bromine can be formed via oxidation of bromide
ions during charge.