Alternative Fuel Update: Zinc Air Batteries

T.Edison's Electric Car (via the Smithsonian Institution)

A few years ago, E.O. Lawrence Berkeley National Laboratory described zinc air batteries as “Electrochemical cell that shows promise of exceeding performance targets set by the Department of Energy for battery power and energy density in electric vehicles.”

This year, Energizer began marketing their “prism” battery, a zinc air battery that, though not rechargeable, is meant to have as much as three times the life of a lithium battery. Other manufacturers are considering rechargeable zinc air batteries, and zinc air button cells are already used for hearing aid and watch batteries. Some of the attraction for this technology stems from the fact that it produces very dense energy (although at a low level), manufacturing may be cheaper than other types of batteries and – when properly sealed – zinc air cells have a much longer shelf life than lithium. But there are drawbacks.

Electropaedia lists several shortcomings for zinc air:

• Sensitive to extreme temperature and humid conditions.
• Carbon dioxide from the air forms carbonate which reduces conductivity.
• High self discharge.
• After activation, chemicals tend to dry out and the batteries have to be used quickly.
• Although recharging is possible it is also inconvenient and is only suitable for high power types.
• High internal resistance which means zinc air batteries must be huge to satisfy high electrical current needs
• Huge, inconvenient-to-recharge batteries that don’t work well in the rain.

Doesn’t sound like the promising technology described by the Berkeley National Laboratory, does it?

Zinc air has been looked at as a fuel alternative for more than a decade. In 1995, the Science & Technology Review printed a paper on the development of the air cell by Lawrence Livermore Laboratory in California and its use in a shuttle bus borrowed from the Santa Barbara transit district. The paper, written by John Cooper, PhD. of the Laboratory, indicated that commercial production of the zinc air battery could begin as early as 2000 if significant progress could be made:

• Determining how many times the zinc reaction products could be recycled
• Determining the longevity of the battery in actual or simulated road conditions

From 2000 to 2003, the electric vehicle division of the Electric Fuel Corporation partnered with the U.S. Department of Transportation for a four-phase electric transit system using buses powered by zinc air technology, with an emphasis on commercialization. For reasons not stated, the program shutdown in 2004, though the information on it is still available, including a downloadable PDF. There is also a video on one of the buses as it was used in Las Vegas.

Metal air cell batteries could give a big boost to electric car sales if the technology can be improved so that the batteries don’t use up almost all of the car space and if recharging them wasn’t such a pain. Unfortunately not much research seems to have been done in the last five years, so we’re not likely to hear any more until 2020, when Toyota hopes to unveil a next-generation zinc or vanadium battery created by their new battery lab.

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