Battery Technology Tutorial & Overview

- information, tutorial about the basics of battery technology giving an overview of the different types of battery with links to additional pages for specific battery technologies.

Batteries are an essential element of today's electronics scene. Batteries are used in virtually all portable electronics devices from mobile phones to laptop computers and MP3 players to torches. Without battery technology many electronics devices would not be viable. As a result, battery technology and battery developments are essential to today's electronics..

In recent years there has been a dramatic growth in the number of battery powered items and this has resulted in many new developments in battery technology. The sheer volume of demand has meant that manufacturers are trying to improve their products to increase their share of the market. If they can achieve this, enormous returns can be made on their investment.

With the huge demand for batteries, there is a wide variety of different battery and cell technologies available. These range from the established non-rechargeable technologies such as zinc-carbon and alkaline batteries to rechargeable batteries that have moved from NiCd through NiMH cells to the newer lithium ion rechargeable batteries. With a huge need for batteries, there is a large amount of battery technology development underway and new types of cells and batteries will no doubt become available offering even higher levels of performance.

Another area of battery technology that is becoming more important is the green or environmental aspects. Some of the old battery technologies contain chemicals which can be considered as toxic. Now new designs are seeking to use more environmentally friendly chemicals. Nickel cadmium cells are now considered as being environmentally unfriendly and are not as widely used as they were previously. Other batteries also contain harmful chemicals and this is likely to have a significant impact on the direction of future developments.


Basic battery and cell concepts

Looking at the very basics of battery technology, a battery is a combination of two or more electrochemical cells. These electrochemical cells store energy in the form of chemical energy, and this is converted into electrical energy when connected to an electrical circuit in which an electrical current can flow.

A cell consists of two electrodes with an electrolyte placed between them. The negative electrode is known as the cathode, while the positive electrode is known as the anode. The electrolyte between them can either be a liquid or a solid. Today many cells are enclosed in a special container, and there is an element known as a separator placed between the anode and cathode. This is porous to the electrolyte and prevents the tow electrodes from coming into contact with each other.

The potential difference across the terminals of the battery is known as the terminal voltage. If the battery is not passing any current, e.g. when it is not connected to any circuit, then the terminal voltage seen is the open circuit voltage and this equals the EMF or electro-motive force of the battery.

It is found that all batteries have a certain level of internal resistance. As a result the terminal voltage falls when it is connected to an external load. As the battery becomes exhausted it is found that the internal resistance rises and the voltage under load falls.


Primary and secondary cells

Although there are many different types of battery, there are two main categories of cell or battery that can be used to provide electrical power. Each type has its own advantages and disadvantages and therefore each type of battery is used in different applications, although they can often be interchanged:

  1. Primary batteries:   Primary batteries are essentially batteries that cannot be recharged. They irreversibly transform chemical energy to electrical energy. When the chemicals within the battery have all reacted to produce electrical energy and they are exhausted, the battery or cell cannot be readily restored by electrical means.

  2. Secondary batteries:   Secondary batteries or secondary cells are different to primary ones in that they can be recharged. The chemical reactions within the cell or battery can be reversed by supplying electrical energy to the cell, restoring their original composition.

Standard cell and battery sizes

It is essential that batteries, and in particular primary batteries can be changed when their useful life is over. As a result batteries normally come in standard battery sizes so that batteries from different manufacturers can be used. As a result there are a number of standard battery sizes that are used.

A summary of the more common standard battery sizes is given below:


Cell type Diameter
mm
Height
mm
AAA 10.5 44.5
AA 14.5 50.5
C 26.2 50.0
D 34.2 61.5


Cell types

There are many different types of cell or battery technology that are available. Each different type of battery technology has its own advantages and disadvantages. Accordingly different types of cell or battery technology may be used in different applications. The table below gives a summary of some of the different types that are in more common use today.


Cell type Nominal voltage
V
Characteristics
Primary cells and batteries    
Alkaline manganese dioxide 1.5 Widely available, providing high capacity. Shelf life normally up to about five years. Capable of providing moderate current.
Lithium thionyl chloride 3.6 Good for low to medium currents. High energy density and long shelf life.
Lithium manganese dioxide 3.0 Long shelf life combined with high energy density and moderate current capability.
Mercury oxide 1.35 Used for button cells but are virtually phased out now because of the mercury they contain.
Silve oxide 1.5 Good energy density. Mainly used for button cells.
Zinc carbon 1.5 Widely used for consumer applications. Low cost, moderate capacity. Operate best under intermittent use conditions.
Zinc air 1.4 Mostly used for button cells. Have a limited life once opened and low current capability but a high energy density.
Secondary cells and batteries    
Nickel cadmium
NiCd
1.2 Were in very common use, but now giving way to NiMH cells and batteries in view of environmental impacts. Low internal resistance and can supply large currents. Long life if used with care. Read more about the NiCd battery
Nickel metal hydride
NiMH
1.2 Higher capacity but more expensive than NiCads. Charging must be carefully controlled. Being used in many applications where NiCads were previously used. Read more about the NiMH battery
Lithium ion
Lion
  Highest capacity and they are now widely used in many laptops, mobile phones, cameras . . etc. Charging must be carefully controlled and often have a limited life ~ typically 300 charge discharge cycles. Read more about the Lithium ion battery
Lead acid 2.0 Widely used for automotive applications. Relatively cheap, but life expectancy often short. Read more about the Lead acid battery


Battery technology has come a long way in recent years. Levels of energy density have risen considerably with the introduction of new battery technologies. While primary technologies such as alkaline batteries being far more widely used than they were even a few years ago, secondary batteries are turning to lithium ion or Li-ion technology. These new battery technologies are now powering the many devices from torches, games and toys through to mobile phones, PDAs and laptop computers. With the demand for portable electronics equipment growing, the investment in new battery technology will remain high and new technologies will continue to emerge.

By Ian Poole


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