Power Electronics
Power Designers May Soon Think Zinc

Power Designers May Soon Think Zinc

Zinc Matrix Power has recently been awarded the “Technology Innovation Accelerated” (TIA) Award at the Intel Developers Forum (IDF) for its Silver-Zinc rechargeable battery technology. The technology, which has not yet been branded, is a battery chemistry based on zinc, silver and water, and was developed to improve battery safety and performance in portable applications (see figure below).

This technology is fundamentally different from Li-ion, and comparisons between the two battery chemistries underscore the implications of an alternative power source for portable electronics, especially laptop computers. Given the recent recalls of Li-ion laptop batteries manufactured by Sony, which began with Dell and Apple and now include IBM and Toshiba, the most important point of comparison between Li-ion and Silver-Zinc is battery safety.

According to Ross Dueber, CEO of Zinc Matrix Power, the failure mechanism of the silver-zinc chemistry is relatively benign. While it is possible for the growth of the zinc electrode to cause internal shorting, it would not result in a fire or explosion. This is because the electrolyte for the reaction is water, and a safety vent of the type used in many other battery technologies would prevent the buildup of dangerous pressure in the event of self heating. In contrast, the reactants of a Li-ion cell are flammable and possibly explosive under the heating or venting conditions caused by an internal short.

Dueber said silver-zinc batteries are currently rated to operate up to 50°C and even 60°C. They may be capable of operation at even higher temperatures without the inherent risks that would be present in Li-ion batteries.

In addition to improved safety, Silver-Zinc batteries also provide improved performance. Dueber stated the volumetric energy density of silver-zinc batteries from Zinc Matrix Power represents as much as a 50% increase over comparable Li-ion cells, and the power density of the two technologies is essentially the same.

Dueber stated that Li-ion cells have a typical endurance of about 300 to 500 charge cycles, and at present, silver-zinc batteries are also rated for several hundred charge cycles. This will be increased as the technology matures. Furthermore, the increased energy density of silver-zinc further contributes to the cell’s endurance by extending the time between battery recharges. As with other battery technologies, endurance can also be increased by electrical techniques that protect the battery from excessive current spikes during operation.

The basic charging method for silver-zinc is based on carefully managed constant-current techniques. This is different from the multi-stage charge techniques of Li-ion batteries, and is one of the major reasons why silver-zinc technology is unsuitable for the Li-ion aftermarket in the wake of laptop battery recalls.

Dueber also stated that Silver-Zinc batteries provide flexibility in the design of the cells and can be configured to accommodate various load spikes for a variety of applications. While the initial focus is on portable applications such as laptops and cell phones, other potential markets could include power tools and hybrid-electric vehicles. As load demands increase and air-breathing power sources such as fuel cells emerge as options for the power designer, Zinc Matrix Power could even explore the possibility of adapting Silver-Zinc technology to develop its own version of the rechargeable zinc-air battery.

For the present, Zinc Matrix Power plans to partner with Tyco Electronics to manufacture its Silver-Zinc battery. Multiple laptop OEMs are planning to test samples, which will be available in Q1 of 2007. This battery is poised to significantly increase the runtime of portable devices, as well as the range of energy-storage options available to designers for powering them.

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