Seiko launches mercury/Pb-free silver oxide battery

SII Micro Parts Ltd (SMP), one of the subsidiaries of Seiko Instruments Inc. (SII), announced that it has developed a mercury/Pb-free silver oxide battery.

According to the press release, applying the micro machining technology SMP has been using for a long period of time allowed the company to develop an ideal crimping technology specifically used in button-type silver oxide batteries. This achieved a 40 percent reduction in internal resistance compared to that of the company's conventional batteries. It has also significantly enhanced product reliability, added SMP.

In general, freeing mercury from silver oxide batteries will not only accelerate corrosion of zinc powder, but also deteriorate discharge characteristics. And it will be more apparently noticeable when a drop in temperatures happens. To suppress deterioration, SMP has developed a high-performance and alkaline-based electrolyte. Adopting this high-performance electrolyte enabled the company to widen the operating temperature range from -10°C to 60°C to -20°C to 60°C (patent pending).

Market for silver oxide battery

Silver oxide battery is a button-type cell mainly used in wristwatches and other small-sized devices. It uses silver oxide as the positive electrode, Zinc as the negative electrode and an alkaline electrolyte. Zinc, the active material in the negative electrode, will corrode in alkaline solution, and thereby local cell reaction will happen between Zinc and its contacting collector electrode, and it will be consumed. This may also cause the expansion of the cell or leakage of the inner electrolyte due to generation of hydrogen gas. In the past, minute amounts of mercury or lead were just added to the battery to suppress the above problems.

To solve this, SMP employed its micro machining technology that is conducive to developing mercury-free silver oxide battery. Adopting the high-accuracy negative collector electrode surface process has also successfully resulted in the accomplishment of equal or better performance to or than the company's conventional silver oxide batteries without using mercury or lead as an anti-corrosion material. In particular, SMP has succeeded in improving discharge characteristics at low temperatures and leakage resistance characteristics as well.

Ten million mercury/Pb-free silver oxide batteries are projected to be manufactured in fiscal 2005, while 20 million units are scheduled for the next fiscal year.