ABSTRACT
At the end of this chapter you should be able to:
• list practical applications of batteries • understand electrolysis and its applications, including electroplating • appreciate the purpose and construction of a simple cell • explain polarization and local action • explain corrosion and its effects • define the terms e.m.f., E , and internal resistance, r , of a cell
• perform calculations using V =E− Ir • determine the total e.m.f. and total internal resistance for cells connected in series and in parallel • distinguish between primary and secondary cells • explain the construction and practical applications of the Leclanché, mercury, lead-acid and alkaline cells • list the advantages and disadvantages of alkaline cells over lead-acid cells • understand the term ‘cell capacity’ and state its unit • understand the importance of safe battery disposal • appreciate advantages of fuel cells and their likely future applications • understand the implications of alternative energy sources and state five examples
A battery is a device that converts chemical energy to electricity. If an appliance is placed between its terminals the current generated will power the device. Batteries are an indispensable item for many electronic devices and are essential for devices that require power when nomains power is available. For example,without the battery, there would be no mobile phones or laptop computers. The battery is now over 200 years old and batteries are found almost everywhere in consumer and industrial products. Some practical examples where batteries are used include:
in laptops, in cameras, in mobile phones, in cars, in watches and clocks, for security equipment, in electronic meters, for smoke alarms, for meters used to read gas, water and electricity consumption at home, to power a camera for an endoscope looking internally at the body, and for transponders used for toll collection on highways throughout the world
Batteries tend to be split into two categories – primary, which are not designed to be electrically re-charged, i.e. are disposable (see Section 4.6), and secondary batteries, which are designed to be re-charged, such as those used in mobile phones (see Section 4.7). In more recent years it has been necessary to design batteries with reduced size, but with increased lifespan and capacity. If an application requires small size and high power then the 1.5V battery is used. If longer lifetime is required then the 3 to 3.6V battery is used. In the 1970s the 1.5V manganese battery was gradually replaced by
the alkaline battery. Silver oxide batteries were gradually introduced in the 1960s and are still the preferred technology for watch batteries today. Lithium-ion batteries were introduced in the 1970s because of the need for longer lifetime applications. Indeed, some such batteries have been known to lastwell over ten years before replacement, a characteristic that means that these batteries are still very much in demand today for digital cameras, and sometimes for watches and computer clocks. Lithium batteries are capable of delivering high currents but tend to be expensive. More types of batteries and their uses are listed in Table 4.2 on page 38.
