Zinc Air Batteries By: Ana Brar

General Information Oxygen from air Activated when oxygen is absorbed into the electrolyte through a membrane Usually reaches full operating voltage within 5 seconds of being exposed to air Oxygen diffused directly into battery Electrolyte that catalytically promotes the reaction of oxygen, but is not depleted or transformed at discharge Zinc and alkaline electrolyte Button cell

Advantages Weight - not necessary to carry a second reactant High energy density Competitive with Lithium-ion Inexpensive materials Flat discharge voltage Safety - don't require volatile materials, so zinc-air batteries are not prone to catching fire like lithium- ion batteries Excellent shelf life, with a self-discharge rate of only 2% per year Available in a range of button and coin cell sizes Rechargeable high power fuel cells in the process of development Environmental benefits Have high volumetric energy density compared to most primary batteries

Disadvantages Sensitive to extreme temperature and humid conditions Carbon dioxide from the air forms carbonate which reduces conductivity High self discharge (after seal is broken) After activation, chemicals tend to dry out and the batteries have to be used quickly Although recharging is possible for fuel cells, it’s also inconvenient and is only suitable for high power types Zinc air batteries must be larger to satisfy high current needs High power batteries use mechanical charging in which discharged zinc cartridges are replaced by fresh zinc cartridges—therefore the used cartridges must be recycled Have flooding potential Limited output When zinc turns it into zinc oxide it expands, space

Common uses Hearing Aids Watches Mobile phones Digital Cameras Pagers Power sources for electric fences Recharging Li-Ion batteries Transportation: Cars - EVs Buses

Rechargeability Zn/Air Batteries – not rechargeable Zn/Air Fuel Cells – rechargeable ReVolt has developed rechargeable Zinc/Air batteries In future: EVs using Zn/Air? Zinc-air batteries can be made for high rate applications, which have a short life but high output Or low rate, with low power but last a longer amount of time

Transportation Would use Zn/Air Fuel Cells Currently used in Las Vegas Electrical Vehicle Division Contain a central static replaceable anode cassette To refuel: discharged zinc-air module removed from the vehicle and is "refueled" by exchanging spent "cassettes" with fresh cassettes Regeneration

Revolt Swiss Company Opened U.S. center of operations - Portland Disadvantages: They can't deliver sufficient power They lose a lot of power very quickly The cell dry out, becoming useless after only a few months There is no satisfactory way to recharge them The solution: ReVolt's new technology has a theoretical potential of up to 4x the energy density of Li-Ion batteries at a comparable or lower production cost Extended battery life due to stable reaction zone, low rates of dry-out and flooding, and no pressure build-up problems Rechargeability Compact size Can manage the humidity within the cell

More on revolt ReVolt technology claims to have overcome the main problem with zinc-air rechargeable batteries--that they typically stop working after relatively few charges (air electrode can become deactivated) For electric vehicles: plan to use two flat electrodes – one containing zinc “slurry” Air electrodes in the form of tubes Zinc slurry is pumped through the tubes where it's oxidized, forming zinc oxide and releasing electrons

Revolt’s ev battery Plan to increase energy density by increasing the amount of zinc slurry relative to the amount of material in the air electrode Much like a fuel cell system or conventional engine – zinc slurry ~ fuel, pumping through the air electrode like gas in a combustion engine Longer life span - from 2,000 to 10,000 cycles As with fuel cells, may need to be paired with another type of battery for bursts of acceleration or regenerative braking

Zn/air vs. al/air Al/Air: produces electricity from the reaction of oxygen in the air with aluminum Has one of the highest energy densities of all batteries Not widely used - cost, shelf-life, start-up time and byproduct removal, which have restricted their use to mainly military applications An electric vehicle with aluminum batteries could have potentially ten to fifteen times the range of lead-acid batteries with a far smaller total weight

Mg/air Li/Air High energy density Safe Inexpensive Not been widely used - self-discharge in neutral solution Reaction mechanism of magnesium alloy anode Effects of different additives on performance of Mg alloy in solution Approach energy density of fuel cells PolyPlus Single use and rechargeable lithium metal-air – could power Evs Theoretically: max energy density 5,000+ watt-hours per kilogram Lower self discharge rate and longer shelf life

conclusion Many promising metal-air batteries: Zinc/Air Aluminum/Air Magnesium/Air Lithium/Air Still mostly in developmental stages Hope for use in electric vehicles in the future

References http://news.cnet.com/8301-11128_3-10388553-54.html http://www.technologyreview.com/energy/22926/ http://www.treehugger.com/files/2009/10/zinc-air- battery-revolt-3-times-more-energy-lithium-ion-battery- electric-cars.php http://www.mpoweruk.com/zinc_air.htm http://www.duracell.com/oem/primary/Zinc/zinc_air_tec h.asp http://www.revolttechnology.com/technology/revolt- introduction.php http://www.technologyreview.com/business/23812/page2 /