Page 28 - Lindens Handbook of Batteries

BASIC CONCEPTS 1.5

Positioning System devices, and a myriad of other applications. The general advantages of primary
batteries are good shelf life, high energy density at low to moderate discharge rates, little, if any, mainte-
nance, and ease of use. Although large high-capacity primary batteries are used in military applications,
signaling, and standby power, the vast majority of primary batteries are the familiar single-cell cylindri-
cal and flat button batteries or multicell batteries using these component cells.

1.2.2 Secondary or Rechargeable Cells or Batteries
These batteries can be recharged electrically, after discharge, to their original condition by passing
current through them in the opposite direction to that of the discharge current. They are storage
devices for electric energy and are known also as “storage batteries” or “accumulators.”
The applications of secondary batteries fall into two main categories:
1. Those applications in which the secondary battery is used as an energy-storage device, gener-
ally being electrically connected to and charged by a prime energy source and delivering its
energy to the load on demand. Examples are automotive and aircraft systems, emergency no-fail
and standby (UPS) power sources, hybrid electric vehicles, and battery energy storage systems
(BESSs) for electric utility load leveling.
2. Those applications in which the secondary battery is used or discharged essentially as a primary
battery, but recharged after use rather than being discarded. Secondary batteries are used in this
manner as, for example, in portable consumer electronics, such as cell phones, laptop computers,
power tools etc., for cost savings (as they can be recharged rather than replaced) and in applica-
tions requiring power drains beyond the capability of primary batteries. Electric vehicles (EVs)
and plug-in hybrid PHEVs also fall into this category.

Secondary batteries are characterized (in addition to their ability to be recharged) by high power
density, high discharge rate, flat discharge curves, and, in most cases, good low-temperature per-
formance. Their energy densities are generally lower than those of primary batteries. Their charge
retention also is poorer than that of most primary batteries, although the capacity of the secondary
battery that is lost on standing can be restored by recharging.
Some batteries, known as “mechanically rechargeable types,” are “recharged” by replacement of
the discharged or depleted electrode, usually the metal anode, with a fresh one. Some of the metal/
air batteries (Chap. 33) are representative of this type of battery.

1.2.3 Reserve Batteries
In these primary types, a key component is separated from the rest of the battery prior to activation.
In this condition, chemical deterioration or self-discharge is essentially eliminated, and the battery is
capable of long-term storage. Usually the electrolyte is the component that is isolated. In other sys-
tems, such as the thermal battery, the battery is inactive until it is heated, melting a solid electrolyte
which then becomes conductive.
The reserve battery design is used to meet extremely long or environmentally severe storage
requirements that cannot be met with an “active” battery designed for the same performance charac-
teristics. These batteries are used, for example, to deliver high power for relatively short periods of
time, in missiles, torpedoes, and other weapon systems. (See Chapters 34, 35, and 36.)

1.2.4 Fuel Cells

Fuel cells, like batteries, are electrochemical galvanic cells that convert chemical energy directly
into electrical energy and are not subject to the Carnot cycle limitations of heat engines. Fuel cells
are similar to batteries except that the active materials are not an integral part of the device (as in a
battery) but are fed into the fuel cell from an external source when power is desired. The fuel cell