Nickel metal hydride battery/cell

Hydrogen-storage alloys (18,19) are commercially available from several companies in the United States, Japan, and Europe. A commercial use has been developed in rechargeable nickel—metal hydride batteries which are superior to nickel—cadmium batteries by virtue of improved capacity and elimination of the toxic metal cadmium (see BATTERIES, SECONDARYCELLS-ALKALINe). Other uses are expected to develop in nonpolluting internal combustion engines and fuel cells (qv), heat pumps and refrigerators, and electric utility peak-load shaving. 

The aimual production value of small, sealed nickel—cadmium cells is over 1.2 biUion. However, environmental considerations relating to cadmium are necessitating changes in the fabrication techniques, as well as recovery of failed cells. Battery system designers are switching to nickel —metal hydride (MH) cells for some appHcations, typically in "AA"-si2e cells, to increase capacity in the same volume and avoid the use of cadmium. 

Lithium-Ion Cells. Lithium-ion cells and the newer alternative, lithium-ion-polymer, can usually run much longer on a charge than comparable-size Nicad and nickel-metal hydride batteries. Usually is the keyword here since it depends on the battery s application. If the product using the battery requires low levels of sustained current, the lithium battery will perform very well however, for high-power technology, lithium cells do not perform as well as Nicad or nickel-metal hydride batteries. 

The Peugeot Quark ATV uses an air-cooled fuel cell with a 40 cell nickel metal hydride battery. The 9 liter hydrogen tank can be pressurized to 10,150 psi for a range of up to 80 miles. The tank is designed to be exchanged for a full one when empty. Each 17 inch wheel has its own electric motor that can produce 74 pound-feet of torque. The motors also supply regenerative braking. 

Those rare-earth AB -type hydrides were quickly utilized in rechargeable nickel metal hydride batteries where electrochemical hydrogen charging and discharging take place at ambient temperature. Such electrochemical hydrogen storage is reversible, when the negative hydride electrode (anode) is combined with the positive Ni electrode (cathode) in the battery cell.. 

In 1990, Sanyo and Matsushita initiated large-scale commercialization of small sealed nickel-metal hydride batteries. They are now joined by Dur-acell, Toshiba and Varta in a consortium which is known as the 3C alliance (camcorders, cellular telephones and computers). Several plants have been commissioned which are each producing 100-200 million cells per annum. It is forecast that nickel-metal hydride may overtake nickel-cadmium before the end of the century. In addition to the 3Cs nickel-metal hydride cells are used for a wide variety of cordless consumer products, communications equipment and other high rate long cycle life applications. 

Union Carbide showed the possibility of developing D-size hydrogen-nickel batteries with satisfactory performance. However, safety and cost considerations have restricted the applications of such units and the discovery of hydrogen storage alloys led to the development of the nickel-metal hydride secondary cell which was described in Chapter 6. 

Nanostructured Li and Ni containing nickel-metal hydride batteries are widely used in cell phones, video camcorders, quartz watches, and pacemakers to name a few uses. Electrically conducting nanostructured mesoporous materials are envisaged as new materials for fuel cell applications, batteries, and ultracapacitors. 

The major issues to be solved for nickel-metal hydride batteries are the temperature control during charge (damage occurs if the cell operates at T > 65°C), the high self-discharge (15 % in two days at 38 °C), and cell cost. Nevertheless, efforts to develop nickel-metal hydride batteries for use in electric vehicles have even led several automotive companies to offer models powered by this type of battery [14]. 

Nickel-metal-hydride batteries of both prismatic and cylindrical cell designs are now available for automotive use. In 2003, the fleet of hybrid vehicles with Ni-MH batteries is more than 100,000 world-wide, most of these are in Japan. This can be considered as a significant and reliable fleet test that demonstrates the maturity of this battery system for automotive use [70]. 

Nickel is used extensively in alloys, notably in stainless steel, other corrosion-resistant alloys such as Monel metal, and coinage metals. Electroplated Ni provides a protective coat for other metals. Nickel has widespread use in batteries recently, this has included the production of environmentally friendly nickel-metal hydride batteries (see Box 9.5) which out-perform NiCd cells (equation 21.5) as rechargeable sources of power in portable appliances. 

In contrast to primary batteries, a secondary, or rechargeable, battery is recharged when it runs down by supplying electrical energy to reverse the cell reaction and re-form reactant. In other words, in this type of battery, the voltaic cells are periodically converted to electrolytic cells to restore nonequilibrium concentrations of the cell components. By far the most widely used secondary battery is the common car battery. Two newer types are the nickel-metal hydride battery and the lithium-ion battery. 

Toyota uses a technology that combines fuel cells with a nickel-metal hydride battery to gain increased efficiency and driving range. 

However, concerns about the toxicity of cadmium have accelerated the replacement of these batteries by nickel-metal hydride batteries, described in Section 9.3.5. In nickel-cadmium (nicad) batteries, the anode is cadmium and the cathode is an unstable nickel oxyhydroxide, formed in the unusual conditions found in the cell, and written variously as Ni(OH)3 or NiO(OH). It is generally formed together with stable nickel hydroxide, Ni(OH)2. The electrolyte is NaOH or KOH. The anode and cathode are assembled in a roll separated by a cellulose separator containing the electrolyte. The cathode/separator/anode roll is contained in a nickel-plated stainless steel can (Figure 9.10). The cell voltage is 1.3 V but the working voltage is usually nearer to 1.2 V. The schematic cell reactions are as follows. 

SECTION 20.7 A battery is a self-contained electrochemical power source that contains one or more voltaic cells. Batteries are based on a variety of different redox reactions. Several common batteries were discussed. The lead-acid battery, the nickel-cadmium battery, the nickel-metal-hydride battery, and the lithium-ion battery are examples of rechargeable batteries. The common alkaline dry cell is not rechargeable. Fuel cells are voltaic cells that utilize redox reactions in which reactants such as H2 have to be continuously supplied to the cell to generate voltage. 

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