Batteries are becoming more widely used. As the use of portable and mobile equipment increases, so does the use of battery technology.
The increasing demands being placed on batteries has meant that the technology has developed considerably in the past few years, and more development can be expected in the future.
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:
- 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.
- 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:
|Standard Cell & Battery Sizes|
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.
|Battery Types & Their Proeprties|
|Cell type||Nominal voltage|
|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|
|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.|
|Nickel metal hydride|
|1.2||Higher capacity but more expensive than NiCads. Charging must be carefully controlled. Being used in many applications where NiCads were previously used.|
|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.|
|Lead acid||2.0||Widely used for automotive applications. Relatively cheap, but life expectancy often short.|
The performance of battery technology has improved considerably in recent years. As the demands being required of batteries has increased with greater capacity being required in smaller spaces and greater levels of reliability, so considerable amounts of research have been invested in trying to meet the new requirements.
The research has resulted in much longer times between charge, higher capacity levels and greater degrees of reliability. For the future, the demands being placed on batteries will only increase, and no doubt the technology will improve beyond all measure.