World's First Environmentally Friendly Mercury Free Solver Oxide
Battery Commercialised by Sony
Sony Corporation today announced the accomplishment of the world's
first Mercury-free silver oxide battery, which was considered
difficult within the industry. Starting January 2005, 10 models of
mercury-free batteries will be commercialised on a world-wide basis.
Sony is producing Silver Oxide batteries of all sizes and currently
Sony has the top market share. Silver Oxide battery is mainly used
for wrist watches, small-size thermometers and mobile game products.
Sony started its Silver Oxide battery business in 1977 and, as of
September this year (2004), Sony has realized in producing 5 billion
cells of Silver Oxide battery cumulatively.
The mercury-freeing technology development announced this time will
very much influence the increasing interest of the effect that
mercury incorporate in batteries has on environmental issues.
Currently, revisions in the battery directives are being made in the
European Parliament and European Environmental Council, however it
is expected that freeing mercury from silver oxide batteries will be
an exception, due to the difficulty in realizing it. However, the
new Sony's 0% mercury silver oxide battery made this possible.
Annually, Sony sells approx. 400 Million Silver Oxide batteries
worldwide, and considering the fact that the mercury level of Sony's
silver oxide batteries is 0.2% of the total content of a battery,
making them mercury-free will lead to reducing the annual usage of
mercury by 320 kg, which dramatically contribute to protecting the
Also, in the European battery directives, the determinations on the
regulation of the level of lead is also under discussion (i.e. to be
less than 40ppm), and it should be emphasized that in Sony Mercury-
free silver oxide batteries usage of lead has also been eliminated.
The function of Mercury in Silver Oxide Battery
Silver Oxide battery is a small-sized primary battery using Zinc as
the negative electrode (anode), Silver Oxide as the positive
electrode (cathode) plus an alkaline electrolyte (figure 1).
Figure 1. Schematic diagram of silver oxide battery cell.
Zinc which is the activator in the negative electrode will corrode
in alkaline solution and it is consumed. When this happens, it
becomes difficult to maintain the capacity of the unused battery.
This corrosion of Zinc also causes electrolysis in the electrolyte
and brings about the production of Hydrogen gas, which will result
in ascent of inner pressure and expansion of the cell. (Fig. 2). And
for this reason, mercury which suppressed the corrosion of Zinc was
added in the battery, however it was desired for mercury to be
reduced, for its considerable harm to the environment.
Figure 2. The role of mercury in conventional silver oxide battery
Counter measures to realizing a Mercury-free Silver Oxide Battery
With the below explained three technical countermeasures, Sony has
succeeded in preventing the Zinc corrosion (i.e. Hydrogen gas
generation), which is indispensable for the achievement of Mercury-
free Silver Oxide battery.
Adoption of high quality Zinc alloy powder with improved corrosion
By optimising the mixed ratio of fine metal used (i.e. Zinc-alloy
powder), it has been managed to dramatically reduce the corrosion
rate, 10 times less, compared to conventional material.
Addition of anti-corrosion material into anode materials
This additive can prevent the generation of Hydrogen gas by blocking
the gas-generation spots. This leads to reducing the corrosion rate
by a half, thus reducing the Hydrogen gas generation dramatically.
Adoption of anti-corrosion technology to the collector materials
Suppressing the corrosion of the collector electrode has an effect
of suppressing the corrosion of Zinc as well, however on the other
hand, if not processed properly, it caused leakage of the inner
electrolyte. Using Sony's unique technology used in electronic
device manufacturing, which is to do with surface process
technology, Sony has managed in enhancing the accuracy of
processing, succeeding to achieve anti-corrosion and to prevent
liquid leakage at the same time.
Additionally, a Sony-unique active cathode material, which Sony has
adopted from its current cells, has high hydrogen absorption
capacity, resulting in the maintenance of a safe cell. (i.e. problem
of cell expansion caused by hydrogen gas is solved). In addition, as
a typical evaluation parameter of batteries, it has been achieved to
improve the battery conservation capabilities as well.
As for the patents related to the development of mercury-free silver
oxide batteries, applications of 5 patents have already been made in
Japan, USA and Europe.
Sony will target to eliminate mercury from all Silver Oxide battery
cells and will continue to pursue the advancement of environment-
Posted September 29th, 2004