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Safer, Higher-Capacity Batteries

Silver-zinc battery chemistry could replace lithium ion in laptops and other electronics–if such batteries can be made cheaply enough.
October 11, 2006

An alternative to lithium-ion batteries–silver-zinc batteries–could add several hours to the time that laptops can run between charges, while at the same time avoiding the safety issues that have resulted in the recent massive recalls of laptop batteries made by Sony, according to Zinc Matrix Power in Camarillo, CA.

Zinc Matrix Power of Camarillo, CA, is working on a laptop battery pack that it says could double capacity–and also not catch fire. (Credit: Zinc Matrix Power)

The company, which received an innovation award from Intel last month for its new battery, has now demonstrated the silver-zinc technology in a laptop. Zinc Matrix plans to begin distributing test batteries to manufacturers early next year, focusing on applications in laptops and cell phones.

In part, the gains in laptop runtimes would come because the silver-zinc batteries can store about 25 percent more energy in the same space, a result of both the chemistry and a more space-efficient flat shape, compared with cylindrical lithium-ion cells inside laptop battery packs, says Ross Dueber, president and CEO of Zinc Matrix Power. What’s more, because silver-zinc batteries use a safer chemistry than most lithium-ion batteries, manufacturers could use larger batteries packs in laptops.

Silver-zinc rechargeable batteries are not new–for example, they’ve been used by the Navy in submarines for years. But they’ve been plagued by high costs due to the use of silver, and by a short lifespan because they can be charged and discharged for only a relatively few cycles, and so have to be replaced more frequently than other types of batteries.

Dueber says the company plans to keep down the costs with a recycling program that will allow it to reuse the silver and zinc. And it has extended the charging cycle-life to hundreds of cycles–similar to many lithium-ion batteries. One of the reasons for the previously low cycle-life is that, as the batteries charge and recharge, zinc in the cell undergoes physical changes that lead to decreasing cell capacities. The company addressed this problem by embedding zinc granules within a conductive polymer.

The safety of the batteries in part results from the use of a nonflammable electrolyte. “It is an inherently safe technology in comparison to lithium ion,” Dueber says. “The fundamental difference is we do not use a highly flammable electrolyte, like lithium ion does. If you have an internal short circuit, which has recently plagued lithium ion, it does not have the possibility of bursting into flames and exploding.”

Zinc Matrix Power is one of several companies working on a safer alternative to conventional lithium-ion batteries. Although current lithium-ion electrolytes are flammable, 3M is developing nonflammable electrolytes for use with lithium-ion batteries. Other companies, such as Valence Technology (Austin, TX) and A123 Systems (Watertown, MA), are marketing batteries that use a phosphate material in one electrode, which is safer than the oxides typically used in lithium-ion batteries.

Donald Sadoway, professor of chemistry at MIT, is skeptical that a recycling program will be sufficient to keep down the costs of silver-zinc batteries. “The capital costs of this thing is going to kill you,” he says. Even the Navy, which has used the expensive silver-zinc technology, is funding his group to study advances in lithium-ion batteries, Sadoway says. If anyone has indeed found a way to make affordable, high-performance silver-zinc batteries, though, it could be “really good,” he says, adding that “remarkable claims require remarkable proof. And this sounds remarkable.”

But the reaction of Yet-Ming Chiang, a MIT materials scientist and a founder of battery-maker A123 Systems, to the recent Zinc Matrix announcement reflects the fast development of new battery technologies. “A competitor every day,” he says. “We’ll have to get used to it.”

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