Batteries

In electronics, a battery is a combination of two or more electrochemical cells which store chemical energy and make it available as electrical energy. Since its invention in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial applications, becoming a multibillion-dollar industry.
The name "battery" was coined by Benjamin Franklin for an arrangement of multiple Leyden jars (an early type of capacitor) after a battery of cannons. Common usage has evolved to include a single electrical cell in the definition. Cables4computer also includes many types of batteries.

History

Although an early form of electrochemical battery called the Baghdad Battery may have been used in antiquity, the modern development of batteries started with the Voltaic pile, invented by the Italian physicist Alessandro Volta in 1800.

How batteries work

A voltaic cell for demonstration purposes. In this example the two half-cells are linked by a salt bridge separator that permits the transfer of ions, but not water molecules.
A battery is a device that converts chemical energy directly to electrical energy. It consists of one or more voltaic cells. Each voltaic cell consists of two half cells connected in series by a conductive electrolyte. One half-cell is the positive electrode (the cathode) and the other is the negative electrode (the anode). In the redox reaction that powers the battery, reduction occurs in the cathode, while oxidation occurs in the anode. The electrodes do not touch each other but are electrically connected by the electrolyte, which can be either solid or liquid. In many cells, the materials are enclosed in a container, and a separator, which is porous to the electrolyte, which prevents the electrodes from coming into contact.
Each half cell has an electromotive force (or emf), determined by its ability to drive electric current from the interior to the exterior of the cell. The net emf of the battery is the difference between the emfs of its half-cells, as first recognized by Volta. Thus, if the electrodes have emfs and , then the net emf is ; in other words, the net emf is difference between the reduction potentials of the half-reactions
The electrical potential difference, or across the terminals of a battery is known as terminal voltage and is measured in volts. The terminal voltage of a battery that is neither charging nor discharging is called the open-circuit voltage and equals the emf of the battery. Because of internal resistance, the terminal voltage of a battery that is discharging is smaller in magnitude than the open-circuit voltage and the terminal voltage of a battery that is charging exceeds the open-circuit voltage. An ideal battery has negligible internal resistance, so it would maintain a constant terminal voltage of until exhausted, then dropping to zero. If such a battery maintained 1.5 volts and stored a charge of one Coulomb than it would perform 1.5 Joule of work. In practical batteries, the internal resistance will increase as it is discharged, and the open circuit voltage will also decrease as the cell is discharged. If the voltage and resistance are plotted against time the resulting graphs will typically not be a straight line, and the shape of the curve will vary with the chemistry and internal arrangement employed.
The voltage developed across a cell's terminals depends on the chemicals used in it and their respective concentrations. For example, alkaline and carbon-zinc cells both measure approximately 1.5 volts, due to the energy release of the associated chemical reactions. Because of the high electrochemical potential changes in the reactions of lithium compounds, lithium cells can provide as much as 3 volts or more.

Types of batteries

There are two main types of batteries

Primary batteries irreversibly (within limits of practicality) transform chemical energy to electrical energy. When the initial supply of reactants is exhausted, energy cannot be readily restored to the battery by electrical means.

Secondary batteries can be recharged; that is, they can have their chemical reactions reversed by supplying electrical energy to the cell, restoring their original composition.

Applications

Unlike nonrechargeable batteries (primary cells), secondary cells must be charged before use. Attempting to recharge nonrechargeable batteries has a small chance of causing a battery explosion.

Rechargeable batteries are susceptible to damage due to reverse charging if they are fully discharged. Fully integrated battery chargers that optimize the charging current are available.

Rechargeable batteries currently are used for applications such as automobile starters, portable consumer devices, tools, and uninterruptible power supplies. Emerging applications in Hybrid electric vehicles and electric vehicles are driving the technology to improve cost, reduce weight, and increase lifetime. Rechargeable batteries have been known since the lead acid battery was invented in 1859.

Grid energy storage applications use rechargeable batteries for load leveling, where they store electric energy for use during peak load periods, and for renewable energy uses, such as storing power generated from photovoltaic arrays during the day to be used at night. By charging batteries during periods of low demand and returning energy to the grid during periods of high electrical demand, load-leveling helps eliminate the need for expensive peaking power plants and helps amortize the cost of generators over more hours of operation.

The National Electrical Manufacturers Association has estimated that U.S. demand for rechargeables is growing twice as fast as demand for nonrechargeables.