Zn-air battery

EAR Energy Resources, which develops Zn-air batteries for portable computers, claims about 250 Wh for a computer unit. The price (in 1994) was 600, including the charger. For the first discharge, ten operating hours are claimed. However, it must be realized that the subsequent cycle behavior is not well established. Sony s Li... 

The overpotentials for oxygen reduction and evolution on carbon-based bifunctional air electrodes for rechargeable Zn/air batteries are reduced by utilizing metal oxide electrocatalysts. Besides enhancing the electrochemical kinetics of the oxygen reactions, the electrocatalysts serve to reduce the overpotential to minimize... 

Figure 5. Galvanostatic charge/discharge curves of the coin cell mockups of Zn-Air battery...

Zinc is commonly used as an anode in metal-air batteries. Zinc-air batteries are commercially available and used as power supply for navigation buoys, communication systems, hearing aids, and etc. [2], Mechanically rechargeable Zn-air batteries are developed recently for traction [3],... 

Zn-Air Batteries The reactions occurring in these batteries may be represented by the following equations ... 

Modeling of rechargeable alkaline Zn-air batteries was also described [333], useful for optimizing zinc cell designs for specific applications. 

As well-known, Mn02 finds wide-spread applications in the classical Leclanche cell in which, put simply, Zn is oxidized to ZnO by Mn02. Zn is a cheap anode material which is also employed in the Zn-air battery.7 This intriguing battery concept represents a primary battery but exhibits similarities with a fuel cell.63 64 69 Table 6 gives an overview on zinc-based primary elements. 

Another approach to the rechargeability of the Zn-air battery is to make the recharging mechanical. When the cell has discharged to (say) 80% of the maximal theoretical amount, the zinc electrodes (now largely ZnO) are removed and fresh ones inserted (e.g., in an automotive application).32 The advantage is that the Oz electrode now functions only as a cathode and does not have to be bifunctional. This... 

Fig. 13.45. Schematic view of the Zn-air battery consisting of a single cell with a central Zn anode facing two bifunctional air electrodes. (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.

They could serve as reserve batteries to be used with an electrolyte of sea water. Despic (1981) utilized the properties of A1 alloys with tin to shift the potential of A1 in the negative direction and increase the potential of the cell formed with Oz. The CF ion in sea water breaks down protective layers that would reduce the rate of anodic dissolution in an Al-02 battery. In fact, in sea water, such batteries can function at the extraordinarily high rate of 1 A cm4. The watt hours per kilogram at low rates of discharge are 500, which is well above the practical range for other batteries. In view of the commercialization of mechanically rechargeable Zn-air batteries for automotive applications, the commercialization of A1 batteries in the United States is conspicuous for its slowness.38... 

This indicates that potentiostatic plating is better than galvanostatic plating for fabricating fern-shaped deposits, which are, for example, ideal electrodes for Zn-air batteries due to the relatively large specific area. 

An interesting example of the application of perovskites as electrodes was published by Muller et al. (1994). Lao.6Cao4Co03 has excellent catalytic properties for O2 reduction and evolution as shown by Shimizu et al. (1990). In order to obtain a more durable electrode material, Muller et al. (1994) used graphitized carbon (70 m2/g) as support of the perovskite catalysts. They described in detail the technique used to prepare the electrode which was assayed using an experimental setup adequate for the intended application of this electrode, namely Zn/air batteries. Their main advance over previous formulations was to achieve longer durability of the electrode with some reduction in current density when compared to the previous work of Shimizu et al. (1990). The authors also suggest routes to improve the overall performance of this attractive system. 

The prepared PVA/KOH/H2O SPE was employed for both Ni/MH and Zn/air batteries. Fig. 4 shows typical charge and discharge curves of all solid-state Ni/MH battery. The results exhibited the advantage of flat plateau discharge curve and the battery had average 82% current efficiency after ten cycles [33]. In addition, the PVA/KOH SPE was successfully assembled into Zn/air battery with a high zinc utilization of 83%. 

The PEO-PVA-H2O alkaline SPE was further developed and applied in the Zn/air and Ni/MH batteries [35], It was found that the new alkaline SPE with the composition of PEO PVA = 2 8 had the higher ionie eonductivity of 0.0608 S cm. For the Ni/MH battery, after 40 cycles of charge/discharge tests, the Ni(OH)2 aetive material still had an average capacity density of 250 mAh g. However, the PVA-PEO blend could form a porous and brittle structure membrane. This is not favorable for Zn/air battery application, because the zinc dendrite would penetrate through the air cathode and cause short-circuit dming the discharge. 

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