Page 26 - Lindens Handbook of Batteries

CHAPTER 1
BASIC CONCEPTS

David Linden and Thomas B. Reddy

1.1 COMPONENTS OF CELLS AND BATTERIES

A battery is a device that converts the chemical energy contained in its active materials directly into
electric energy by means of an electrochemical oxidation-reduction (redox) reaction. In the case of
a rechargeable system, the battery is recharged by a reversal of the process. This type of reaction
involves the transfer of electrons from one material to another through an electric circuit. In a non-
electrochemical redox reaction, such as rusting or burning, the transfer of electrons occurs directly
and only heat is involved. As the battery electrochemically converts chemical energy into electric
energy, it is not subject, as are combustion or heat engines, to the limitations of the Carnot cycle
dictated by the second law of thermodynamics. Batteries, therefore, are capable of having higher
energy conversion efficiencies.
While the term “battery” is often used, the basic electrochemical unit being referred to is the
“cell.” A battery consists of one or more of these cells, connected in series or parallel, or both,
depending on the desired output voltage and capacity.*
The cell consists of three major components:
1. The anode or negative electrode—the reducing or fuel electrode—which gives up electrons to the
external circuit and is oxidized during the electrochemical reaction.
2. The cathode or positive electrode—the oxidizing electrode—which accepts electrons from the
external circuit and is reduced during the electrochemical reaction.
3. The electrolyte—the ionic conductor—which provides the medium for transfer of charge, as
ions, inside the cell between the anode and cathode. The electrolyte is typically a liquid, such as
water or other solvents, with dissolved salts, acids, or alkalis to impart ionic conductivity. Some
batteries use solid electrolytes or gel-type polymer electrolytes, which are ionic conductors at the
operating temperature of the cell.

*Cell versus battery: A cell is the basic electrochemical unit providing a source of electrical energy by direct conversion
of chemical energy. The cell consists of an assembly of electrodes, separators, electrolyte, container, and terminals. A battery
consists of one or more electrochemical cells, electrically connected in an appropriate series/parallel arrangement to provide the
required operating voltage and current levels, including, if any, monitors, controls, and other ancillary components (e.g., fuses,
diodes), case, terminals, and markings. (In some publications, the term “battery” is considered to contain two or more cells.)
Popular usage considers the “battery” and not the “cell” to be the product that is sold or provided to the “user.” In this 4th
edition, the term “cell” will normally be used when describing the cell component of the battery and its chemistry. The term “bat-
tery” will be used when presenting performance characteristics, etc., of the product. Most often, the electrical data is presented
on the basis of a single-cell battery. The performance of a multicell battery will usually be different than the performance of the
individual cells or a single-cell battery (see Section 3.2.13).

1.3