The Battery

Overview of the battery

The essential principle underlying the functioning of the electric battery is the conversion of chemically stored energy into electrical energy. To that end, despite the diverse range of batteries now available, all possess within their casings an electrolytic solution (a medium permitting the movement of negatively or positive charged particles or ions) in which two electrodes are immersed.

The positive electrode (anode) attracts negatively charged particles (anions) through the electrolyte, while the negative electrode (cathode) attracts positively charged particles (cations) through the solution. Every battery also possesses external terminals to allow the current stored within it to be accessed by a wired connection. The battery’s stored electrical energy can then be used to power any suitable electrical device that is connected to it.

There are two broad categories of battery: disposable (primary) batteries and rechargeable (secondary) batteries. Perhaps the most widely used example of the primary type is the alkaline battery, which is simply disposed of when it degrades and the power is exhausted. Secondary batteries are rechargeable by reversing the current between the electrodes in a battery charger; an example is the lithium ion “18650” or the 12V battery used in transport applications, such as cars, boats, disability scooters and golf buggies. Rechargeable lithium batteries tend to be used in high-performance LED hand torches as well as a plethora of portable electronic devices.

Today, batteries run the gamut in physical size, from tiny cells for powering watches and hearing aids to vast banks that require whole rooms to house them. The latter are used typically to provide emergency power for applications, such as in computer data centres and telephone exchanges.

 

History

Benjamin Franklin was the first person to coin the phrase “battery” for electrical current generators in 1748 because he found the visual appearance of an array of large Leyden Jars (a device invented in the mid-eighteenth century capable of storing static electricity) reminiscent of a battery of artillery cannon.

Fifty-two years later in 1800, its inventor, the Italian physicist Alessandro Volta, dubbed the first electrochemical current generator the “voltaic pile”. Volta’s device bore little resemblance to what most people today would recognise as a battery, consisting of a “pile” of zinc and copper plates interspersed with sheets of paper soaked in brine. The device generated a steady current, although Volta was unaware of how it actually did so. He believed that he had discovered a limitless source of power and regarded the corrosion occurring on the metal electrodes as merely a nuisance, rather than being the necessary result of the transfer of ions from one to another. It was Michael Faraday who identified this intrinsic process in 1834.

The early batteries generated a good deal more interest amongst scientists and engineers than they did power, being incapable of delivering a steady source of electrical energy for more than a very short time; however, by 1836, the problem was largely solved with the invention of the Daniell cell. This consisted of a large copper jar containing a solution of copper sulphate and an unglazed earthenware vessel within which a zinc electrode was immersed in sulphuric acid.

The Daniell cell became widely used as a source of power for networks of electric telegraphs but there were inherent difficulties with such “wet cells”, which relied on liquid electrolytes. They were fragile and easily damaged, and they often leaked. The liquid was eventually replaced with an electrically conductive paste toward the close of the nineteenth century and the portable “dry cell” battery was born.

 

Technical aspects

All batteries are rated for voltage and will deliver a specific quantity of electrical charge (the capacity) when the demand arises. Generally speaking, capacity increases with the quantity of electrode material included.

Capacity, which is measured most commonly in Amp-hours, is calculated by multiplying the quantity of amperes a battery can reliably deliver at room temperature (20ºC) by a time interval, usually 20-hours. This means, for instance, that a battery with a rated capacity of 100 Amp-hours will consistently yield 5 amps per hour. The capacity will fall shortly after the stated time limit due to the progressive deterioration and weakening of the electrochemical reactions inside the battery. Most batteries will perform at a cumulatively lower capacity as the ambient temperature falls below the ideal room temperature.

Capacity diminishes over time in all batteries even if they are stored correctly without being used; this “internal self-discharge” is the inevitable effect of the on-going electrochemical side reactions occurring within the battery, which deplete the charge carriers (ions) upon which the battery’s output depends.

Generally speaking, even rechargeable batteries have a finite life expectancy; each time a recharge takes place, further electrochemical side reactions occur, progressively depleting the battery’s capacity by small amounts each time.

Batteries come with a “C rate”, which is essentially a capacity rating referring to the maximum safe discharge a battery can continuously deliver for one hour. For example, a battery with a capacity of 1.6 amp hours rated at 1C would be fully discharged within an hour if it delivered a discharge current of 1.6 amps continuously over this interval.

 

Product application

Although dry cells have supplanted wet cell batteries in most common domestic devices, wet cell batteries are still widely used by the automotive industry as mentioned earlier. They are also used as sources of stand-by power in some industries.

 

How the battery differs from other energy sources

Unlike other power sources, such as mechanical electricity generators, and flywheel energy storage devices that convert mechanical energy directly into electrical power, batteries function by storing input electrical energy via an electrochemical reaction involving the transfer of charge carriers (ions) in an electrolyte solution between positive and negative electrodes.

 

Current product advantages and limitations

Dry cell batteries are far more robust and portable than their wet cell predecessors, although they can leak and corrode even so. This can create a potential health hazard if the toxic and corrosive chemicals exuded are ingested; however, they are an invaluable, relatively cost-effective and easily transportable source of power.