Introduction

Chemical cells were the original source of DC, and have always been an important form of power supply for electronic equipment. Historically, cells and batteries have been in use for over two hundred years, and the problems that are encountered with one of the simplest and oldest types of cell are a good introduction to the reasons why so many diverse battery types exist nowadays, and to the technology that is used. Strictly speaking, a battery is an assembly of single cells, so the action of a cell is the subject of this Chapter.

Any type of chemical cell depends on chemical action which is usually between a solid (the cathode plate) and a liquid, the electrolyte. The use of liquids makes cells less portable, and the trend for many years has been to using jellified liquids or moist solids, and also to materials that are not strong acids or alkalis. The voltage that is obtained from any cell depends on the amount of energy liberated in the chemical reaction, but only a limited number of chemical reactions can be used in this way, and for most of them, the energy that is liberated corresponds to a voltage of between 0.8 V and 2.3 V per cell with one notable exception, the 3+ V lithium cell. This range of voltage represents a fundamental chemical action that cannot be altered by refining the mechanical or electrical design of the cell.

The current that can be obtained...