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Anleitung Zusammenfassung
The trend towards smaller, lighter more portable battery-powered devices is expected to continue well into the future, with the so-called “3C” applications — cellular phones, portable computers and consumer electronics — expanding rapidly beyond the traditional business user and into the consumer marketplace. As with other battery-powered consumer devices, battery performance and convenience will influence the rate of consumer acceptance for 3C devices. Yet conventional rechargeable batteries often fail to meet the needs of consumers, as well as equipment designers, in terms of their size and weight, operating time, ease- of-use, availability and environmental acceptability. New battery systems are needed to meet their growing list of demands. The sealed nickel-metal hydride (Ni-MH) battery is one rechargeable battery system that is responding to these demands by offering significant improvements over conventional rechargeable batteries in terms of performance and environmental friendliness. First introduced to the commercial market in 1988, nickel-metal hydride battery technology is at a very early stage of maturity and manufacturers such as Duracell have identified many opportunities to improve battery performance. These improvements will make DURACELL nickel-metal hydride batteries an attractive power source for 3C devices for many years to come. 22General Characteristics Many of the operating characteristics of the sealed nickel-metal hydride rechargeable battery are similar to those of the sealed nickel-cadmium rechargeable battery. The nickel-metal hydride battery, however, has the advantage of higher energy density (or capacity) which translates into longer service life. In addition, the nickel-metal hydride battery is environmentally friendlier than nickel-cadmium and other battery systems because it contains no added cadmium, mercury or lead. Features of the sealed nickel-metal hydride battery include: • Higher capacity — Up to 40 percent longer service life than ordinary nickel-cadmium batteries of equivalent size. • High rate discharge — Efficient discharge at rates as high as 2C. • Fast charge — Can be charged in approximately one hour. • Safe — Designed to safely withstand abusive conditions in consumer devices. • Long cycle life — Up to 500 charge/discharge cycles. • Performs at extreme temperatures — Capable of operation on discharge from -20° C to 50° C (-4° Fto 122° F) and charge from 0° C to 45° C (32° F to 113° F). • Environmentally friendlier than nickel-cadmium batteries — Zero percent cadmium. • Similar operating voltage to nickel-cadmium batteries — Allows user to upgrade easily to longer lasting nickel-metal hydride batteries. Ni-MH Rechargeable BatteriesNi-MH Rechargeable Batteries 3 3CompositionandChemistry A rechargeable battery is based on the principle that the charge/discharge process is reversible, that is, the energy delivered by the battery during discharge can be replaced or restored by recharging. 3.1 Active Components: Positive and Negative Electrodes Nickel oxyhydroxide (NiOOH) is the active material in the positive electrode of the nickel-metal hydride battery in the charged state, the same as in the nickel- cadmium battery. The negative active material, in the charged state, is hydrogen in the form of a metal hydride. This metal alloy is capable of undergoing a reversible hydrogen absorbing/desorbing reaction as the battery is charged and discharged, respectively. The unique attribute of the hydrogen storage alloy is its ability to store hundreds of times its own volume of hydrogen gas at a pressure less than atmospheric pressure. Many different intermetallic compounds have been evaluated as electrode materials for nickel-metal hydride batteries. Typically, these fall into two classes: AB5 alloys, of which LaNi5 is an example, and AB2 alloys, of which TiMn2 or ZrMn2 are examples. DURACELL nickel-metal hydride battery technology is based on the use of AB5 instead of AB2 alloys. AB5 alloys offer better corrosion resistance characteristics, resulting in longer cycle life and better recharge- ability following storage. The composition of the metal alloy is formulated for optimal stability over a large number of charge/discharge cycles. Other important properties of the alloy include: • Large hydrogen storage capability for high energy density and battery capacity. • Favorable kinetic properties for high rate capability during charge and discharge. • Low hydrogen pressure alloy and high purity materials to minimize self-discharge. 3.2 Electrolyte An aqueous solution of potassium hydroxide is the major component of the electrolyte of a nickel- metal hydride battery. A minimum amount of electrolyte is used in this sealed cell design, with most of this liquid being absorbed by the separator and the electrodes. This “starved electrolyte” design facilitates the diffusion of oxygen to the negative electrode at the end-of-charge for the “oxygen recombination” reaction. 3.3 Cell Re...