Zinc-air battery

Zinc-air batteries is a non-rechargeable electro-chemcial battery powered by the oxidation of zinc with oxygen from the air. These batteries have very high energy densities and are realatively inexpensive to produce. These batteries are use in hearing aids and in experimental electric vehicles.

Particles of zinc are mixed with a electrolyte; oxygen and water from the air react at the cathode and form hydroxyls which migrate into the zinc pasted and form zincate (Zn(OH)_{4), the zincate decays into zinc oxide, at which point electrons are released from the decay process, which travels to the cathode. The reactions are:}

Cathode: O_{2 + 2H2O + 4e^{- -> 4HO-}}

Anode: Zn + 4HO^{- -> Zn(OH)_{4 -> ZnO + H2O + 2HO- +4e-}}

The water and hydroxyls from the anode are recycled at the cathode, thus the water only serves as a catalyses. Produced voltage levels of 1.35-1.4 volts.

• Zinc-air batteries have very high energy density (110-200 Wh/kg)
• Zinc-air batteries put out continuous energy as they disipate there energy, and the voltage does not drop before the battery is completely depleted.
• Zinc-air batteries have very long shelf lives; as long as they are sealed (no oxygen is let in)
• Zinc-air batteries have a very high self-discharge rates when exposed to air, as the zinc will spontaneously decay with oxygen and the water catalyses in the battery will tend to dry out.
  • To prevent self-discharging the battery has to be resealed when not in use, moisture in the battery can be maintained with use of a humidified environment.
  • Zinc-air batteries must not be over saturated with water though, avoid immersing in water!
• Zinc-air batteries use cheap materials and can be produced in mass quantities inexpensively.
• Zinc-air batteries are not rechargeable, but the zinc can be recycled or “mechanically recharged” in which the zinc oxide from the used batteries can be melted down into zinc metal (and thus deoxidized ) and remixed with recycled electrolyte.

Zinc-air batteries have properties of fuel cells as well as a batteries: the zinc is the fuel, the rate of the reaction can be controlled by controlling the air flow, and used zinc/electrolyte paste can be removed from the cell and replaced with fresh paste. Research is being conducted in powering electric vehicles with zinc-air batteries.

References:

brief overview of Zinc-air battieries

Zinc-air powered buses