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World’s First Mercury-Free Silver Oxide Battery


New Environmentally-Conscious Battery Sparks a Revolution in the Watch Market

Sony announced today the launch of the world’s first (as of September 29th, 2004) mercury-free Silver Oxide battery. Considered one of the most difficult challenges within the industry, the introduction of the battery heralds a revolution for millions of watch owners around the world and a major advance for the environment. As a leader in the watch battery market, Sony has utilized its expertise to develop the new product, overcoming major technical obstacles. The new range of ten mercury-free batteries will be launched from January 2005.

"By developing the world’s first ever mercury-free watch battery, Sony has demonstrated its concern for the environment, as well as its ability to innovate" Says Eric Prieur, Senior Product Manager of Sony Recording Media Europe. "The new battery is a serious step forward in our quest to produce environmentally-conscious products that minimize any impact on nature."

Sony produces a wide range of Silver Oxide batteries for wrist watches, small thermometers and mobile game products and is worldwide brand leader. The company began its Silver Oxide battery business in 1977 and as of September 2004 has manufactured cumulatively around 5 billion cells.

The Role of Mercury in Silver Oxide Batteries

A 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.

Zinc is the activator in the negative electrode and corrodes in alkaline solution. When this happens, it becomes difficult to maintain the capacity of the unused battery. The zinc corrosion causes electrolysis in the electrolyte resulting in the production of Hydrogen gas, a rise of inner pressure and expansion of the cell (Figure 2). Mercury has been used in the past to suppress the corrosion, despite its harmful effects on the environment.

Innovation for a Cleaner, Healthier World

In order to develop a mercury-free Silver Oxide battery, Sony has introduced three technical innovations to prevent zinc corrosion and the generation of hydrogen gas.

- High quality Zinc alloy powder with improved corrosion resistance

This new Zinc-alloy powder includes an extremely small amount of another metal and by optimizing the mixed ration of fine metal used, corrosion rates have been dramatically reduced, i.e. ten times less compared to conventional material.

- Anti-corrosion agents in anode materials

This additive prevents the generation of Hydrogen gas by blocking gas-generation spots. This leads to reducing the corrosion rate by a half, thus reducing the Hydrogen gas generation dramatically.

- Anti-corrosion technology in collector materials

Suppressing the corrosion of the collector electrode can suppress the corrosion of Zinc, but if not processed properly, causes leakage of the inner electrolyte. Sony’s unique anti-corrosion technology adopted from electronic device manufacturing improves processing accuracy and precents liquid leakage. Furthermore, a Sony-unique active cathode material delivers a high hydrogen absorption capacity, eradicating the problem of cell expansion.

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.

Protecting the Environment

With approximately 400 million Silver Oxide batteries sold every year 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, introducing mercury-free products will reduce the annual usage of mercury by 320 kg and will clearly have a dramatic impact. By developing an innovative range of cells that are free of mercury, lead, cadmium and a variety of other harmful materials, Sony has demonstrated a long-standing commitment to protect the environment. The latest Silver Oxide batteries break new ground, heralding a technical revolution for millions of watch-users across the globe while exceeding the requirements of the European Parliament and European Environmental Council. Currently, revisions in the battery directives are being made in the European Parliament and European Environmental Council, however it is expected that eliminating mercury from Silver Oxide batteries will be an exception due to the difficulty in realizing it. However, Sony succeeded in reaching the 0% mercury level in Silver Oxide batteries and will continue to pursue the advancement of environmentally-conscious policies through innovative technology, aiming to eliminate mercury from all Silver Oxide battery cells in the near future.

Sylvia Shin | Sony Europe
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