Zinc-oxygen cell

Zinc oxide beds Zinc oxide eugenol Zinc oxides Zinc-oxygen cell... 

Zinc—Oxygen Cells. On the basis of reactants the zinc—oxygen or air system is the highest energy density system of all the alkaline rechargeable systems with the exception of the 2 Th reactants are cheap and abundant and therefore a number of attempts have been made to develop a practical rechargeable system. The reactions of this system are as follows ... 

Zinc oxide-eugenol surgical pastes, 8 286 Zinc oxide treatments, 26 613-614 Zinc-oxygen cells, 3 512-515 Zinc perchlorate, 18 278 Zinc peroxide, 18 397 Zinc phenolsulfonate... 

Fig. 13.46. Zinc-oxygen cell voltages and available capacity for different rates of discharge measured for two 25-cm2 cells with pasted zinc electrodes containing 10 wt.% cellulose fibers with a fiber length of 1 mm. Discharge currents are x, 0.064 A o, 0.3 A a, 0.6 A a, 0.9 A , 1.2 A. (Reprinted from K. Muller, R. Holze, and O. Haas, Progress Towards a 20 Ah/12V Electrically Rechargeable Zinc/Air Battery in Batteries for Portable Applications and Electric Vehicles, C. F. Holmes and A. R. Landgrebe, eds., Electrochemical Society Proc. PV 97-18, pp. 859-868, Fig. 3,1997. Reproduced by permission of The Electrochemical Society, Inc.)...

Other alkaline primary cells couple zinc with oxides of mercury or silver and some even use atmospheric oxygen (zinc—air cell). Frequendy, zinc powder is used in the fabrication of batteries because of its high surface area. Secondary (rechargeable) cells with zinc anodes under development are the alkaline zinc—nickel oxide and zinc—chlorine (see Batteries). 

Earlier, such catalyst was used for the preparation of a 100 W rechargeable bipolar zinc-oxygen battery [328]. Also, nanostructured Mn02 combined with mesocarbon microbeads was prepared and used [329] in such batteries as a catalyst for oxygen reduction, which has a very good electrocatalytic activity with respect to oxygen, and in comparison with electrolytic Mn02. Prepared with this material, the all solid-state zinc-air cell... 

The electrolyte for zinc-based cells is always caustic alkali. Calcium hydroxide is sometimes added to remove zinc ions as insoluble CaZn2O3.5H20. A caustic alkali electrolyte is effectively buffered against OHion production by the oxygen cathode, so that OH concentration... 

Zinc has found application in several other types of battery, including industrially important zinc-air cells in which the oxygen of the air is used as the cathodic reactant in a cell such as... 

Zinc/air cells were commercialized in 1932. They use oxygen from the environment to produce electrical energy. Oxygen diffuses into the cell and is used as cathode, powdered zinc is used as anode, and an aqueous solution of potassium hydroxide is used as electrolyte. Excess of water vapor can degrade the performance of the cell to minimize this situation a hydrophobic membrane is used as separator. The cell reactions are... 

Gulf General Atomic Company was one of the first parties to develop a zinc/air and zinc/oxygen system for an electric vehicle. A 20 kW zinc/oxygen battery was tested in a mini-moke jeep. The system employed electrolyte circulation and continuous removal of Zn(OH)2 reaction product. Zinc electrodes were regenerated from spent alkaline zincate solution in external recharging cells [16]. 

However, the positive electrode material for zinc-air cells is atmospheric oxygen, O2. A thin electrode, or cathode, similar to a fuel cell electrode that provides a site for O2 to be reduced during cell discharge is all that is necessary. As a result, there is more space within the cell that can be loaded with more of the zinc (Zn) negative electrode material. 

Edison invented the first zinc-air cells in the early 1900s. The Edison Carbonaire (Zn-air) system was used to power raihoad signaling devices in rural areas that were without electricity and as navigation aids. These were large box cells with a zinc plate anode and a porous carbon electrode with Mn02 catalyst for the oxygen electrode. The present Zn-air miniature cell is an offshoot... 

The zinc air cell design is unique in that the cathode active material is supplied by oxygen in the air and, other than a thin reactive electrode sites for absorption and reduction of oxygen, the cells internal volume is primarily occupied by zinc anode. However, void volume must be reserved to account for the volumetric expansion of zinc to zinc oxide upon discharge. 

Figures 10 and 11 provide a comparison of the volumetric energy densities in the various commercial coin cell chemistries. While zinc air cells by far exceed the other systems, on a watt-hour per cc basis, its application has been mostly limited to hearing aid applications. This application limitation is in part because the path way for oxygen into the cell also allows moisture in and out of the cell, as well as carbon dioxide which may cause wasteful carbonation of the anode components. As a result, the zinc air chemistry has been limited to applications with duration of a month or less.

The zinc-based cells combine atmospheric oxygen with zinc pellets to produce electricity. When all the zinc is consumed, the only by-product is zinc oxide, which is completely recyclable. The cells can be refueled in less than 10 minutes, thereby allowing the cells to be used almost constantly. This type of cell would never require shutdown for refueling purposes. Note that zinc cells offer several advantages over Li-ion batteries. First, zinc is widely available. Second, zinc is cheaper than lithium. Third, the worldwide zinc supply is enough to manufacture more than 1 billion 10 kWh zinc-air cells. By contrast, it would take roughly 180 years of hthium production to make an equivalent amount of Li-ion batteries. Fourth, most supphes of lithium are located outside of the United States, which means that Li-ion batteries would be manufactured outside of the country on the basis of cost-effective criterion. 

Filiform Corrosion. Filiform corrosion is a special form of crevice or oxygen cell corrosion occurring beneath organic or metallic coatings on steel, zinc, aluminum, or magnesium. Filiform corrosion normally starts at small, sometimes microscopic, defects in the coating. Lacquers and "quick-dry" paints are most susceptible to the problem. 

In the zinc/oxygen couple, which also uses an alkaline electrolyte, it is necessary to increase only the amount of zinc present to increase cell capacity. The oxygen is supplied from the outside air which diffuses into the cell as it is needed. The air cathode acts only as a reaction site and is not consumed. Theoretically, the air cathode has infinite useful life and its physical size and electrochemical properties remain unchanged during the discharge. The reactions of the air cathode are complex but can be simplified to show the cell reactions as follows ... 

Zinc/air cells can handle pulse currents much higher than the limiting current (4), the current level depending on the nature of the pulse. This capability results from a reservoir of oxygen that builds up within the cell when the load is below the limiting current. 

During storage the air access holes of a zinc/air battery can be sealed to prevent gas transfer decay. A typical material for sealing a battery is a polyester tape. Note that, unlike conventional batteries, one of the zinc/air cell s reactants, oxygen, is sealed outside the cell during storage. This characteristic gives zinc/air batteries excellent shelf-life performance. 

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