Batteries, Overview

Batteries are an important means of generating and storing electrical energy. They are sold at a rate of several billions of dollars per year worldwide. They can be found in nearly all motor vehicles (e.g., automobiles, ships, aircraft), all types of portable electronic equipment (e.g., cellular phones, computers, portable radios), buildings (as backup power supplies), cordless tools, flashlights, smoke alarms, heart pacemakers, biomedical instruments, wristwatches, hearing aids, and the like. Batteries are so useful and ubiquitous, it is difficult to imagine how life would be without them. Batteries, strictly speaking, are composed of more than one electrochemical cell. The electrochemical cell is the basic unit from which batteries are built. A cell contains a negative electrode, a positive electrode, an electrolyte held between the electrodes, and a container or housing. Cells may be electrically connected to one another to form the assembly called a battery. In contrast to the alternating current available in our homes from the electric utility company, batteries deliver a direct current that always flows in one direction. There are a few different types of batteries: Primary batteries can be discharged only once and then are discarded; they cannot be recharged. Secondary batteries are rechargeable. Forcing current through the cells in the reverse direction can reverse the electrochemical reactions that occur during discharge. Both primary and secondary batteries can be categorized based on the type of electrolyte they use: aqueous, organic solvent, polymer, ceramic, molten salt, and so on.