A device that converts chemical energy into electrical energy. The first battery, made by Alessandro Volta in c.1800, was the basis of the voltaic cell - two chemicals immersed in an electrolyte, enabling electrons to travel from one to the other along a circuit. Primary cells only discharge electricity, whereas secondary cells (or accumulators) can also be recharged. The batteries commonly encountered in torches, toys, cameras, etc are dry primary cells, in which the electrolyte has been treated so that it will not spill out of the battery. Wet primary cells are used in telephone and railway signalling systems. Secondary cells are used in motor vehicles.
Batteries consist of electrochemical devices such as one or more galvanic cells, fuel cells or flow cells.Battery concepts
A battery is a device in which chemical energy is directly converted to electrical energy. In the figure to the right, the battery consists of one or more voltaic cells in series. Non-faradaic reactions are one reason that voltaic cells (particularly the lead-acid cell of ordinary car batteries) "run down" when sitting unused.
Voltaic cells, and batteries of voltaic cells, are rated in volts, the SI unit of electromotive force. The voltage across the terminals of a battery is known as its terminal voltage. The terminal voltage of a battery that is neither charging nor discharging (the open-circuit voltage) equals its emf. The terminal voltage of a battery that is discharging is less than the emf, and that of a battery that is charging is greater than the emf.
The simplest characterization of a battery would give its emf (voltage), its internal resistance, and its capacity. In principle, the energy stored by a battery equals the product of its emf and its capacity.
Battery capacity
Since the voltage of a battery is relatively constant, the capacity of a battery to store energy is often expressed in terms of the total amount of charge able to pass through the device. If a battery can pump charges for one hour at a rate of one coulomb/sec or one ampere (1 A), it has a capacity of 1 A·h. Because of the chemical reactions within the cells, the capacity of a battery depends on the discharge conditions such as the magnitude of the current, the duration of the current, the allowable terminal voltage of the battery, temperature, and other factors.
Battery manufacturers use a standard method to determine how to rate their batteries. The battery is discharged at a constant rate of current over a fixed period of time, such as 10 hours or 20 hours, down to a set terminal voltage per cell. So a 100 ampere-hour battery is rated to provide 5 A for 20 hours at room temperature. The efficiency of a battery is different at different discharge rates. When discharging at low rate, the battery's energy is delivered more efficiently than at higher discharge rates. See also Battery (electricity)#Common battery capacities
Battery lifetime
Even if never taken out of the original package, disposable (or "primary") batteries can lose two to twenty-five percent of their original charge every year. Batteries should be stored at cool or low temperatures to reduce the rate of the side reactions. For instance, some people make a practice of storing unused batteries in their refrigerators to extend battery lifetime, although care should be taken to ensure the batteries do not freeze.
Rechargeable batteries self-discharge more rapidly than disposable alkaline batteries;
Most NiMH and NiCd batteries can be charged several hundred times. Automotive lead-acid rechargeable batteries have a much harder life. Because of vibration, shock, heat, cold, and sulfation of their lead plates, few automotive batteries last beyond six years of regular use. Automotive starting batteries have many thin plates to provide as many amps as possible in a reasonably small package, and are only drained a small amount before being immediately recharged. Care should be taken to avoid deep discharging a starter battery, as the recharging process melts a small amount of the lead from the plates. Leaving a lead-acid battery in a deeply discharged state for any length of time allows the sulfate to become more deeply adhered to the plate, making sulfate removal during the charging process difficult. This can result in less available plate surface and the resulting lower voltage, shortening the batterys life. "Deep-Cycle" lead-acid batteries such as those used in electric golf carts have much thicker plates to aid their longevity. Lead-acid batteries should never be discharged to below 20% of their full capacity as internal resistance will cause heat and damage when attempting to recharge them. Deep-cycle lead-acid systems often use a low-charge warning light or a low-charge power cut-off switch to prevent the type of damage that will shorten the batterys life.
Special "reserve" batteries intended for long storage in emergency equipment or munitions keep the electrolyte of the battery separate from the plates until the battery is activated, allowing the cells to be filled with the electrolyte.
Battery explosion
A battery explosion is caused by the misuse or malfunction of a battery, such as attempting to recharge a primary battery, or short circuiting a battery. With car batteries, explosions are most likely to occur when a short circuit generates very large currents. In addition, car batteries liberate hydrogen when they are overcharged (because of electrolysis of the water in the electrolyte). However, when "jumping" a car battery, the high current can cause the rapid release of large volumes of hydrogen, which can be ignited by a nearby spark (for example, when removing the jumper cables).
When a battery is recharged at an excessive rate, an explosive gas mixture of hydrogen and oxygen may be produced faster than it can escape from within the walls of the battery, leading to pressure build-up and the possibility of the battery case bursting. In extreme cases, the battery acid may spray violently from the casing of the battery and cause injury. Some people claim that it is possible to recharge primary cells using special technique and that the dangers of explosion are overstated by the battery industry.
Additionally, disposing of a battery in fire may cause an explosion as steam builds up within the sealed case of the battery.
Overcharging -- that is, attempting to charge a battery beyond its electrical capacity -- can also lead to a battery explosion, leakage, or irreversible damage to the battery. It may also cause damage to the charger or device in which the overcharged battery is later used.
Rechargeable and disposable batteries
From a user's viewpoint, at least, batteries can be generally divided into two main types—rechargeable and non-rechargeable (disposable).
Disposable batteries, also called primary cells, are intended to be used once and discarded. Battery manufacturers recommend against attempting to recharge primary cells.
By contrast, rechargeable batteries or secondary cells can be re-charged after they have been drained.
The oldest form of rechargeable battery still in modern usage is the "wet cell" lead-acid battery. This battery is notable in that it contains a liquid in an unsealed container, requiring that the battery be kept upright and the area be well-ventilated to ensure safe dispersal of the hydrogen gas which is vented by these batteries during overcharging. The lead-acid battery is also very heavy for the amount of electrical energy it can supply.
A common form of lead-acid battery is the modern wet-cell car battery. An improved type of lead-acid battery called a gel battery (or "gel cell") has become popular in automotive industry as a replacement for the lead-acid wet cell. The gel battery contains a semi-solid electrolyte to prevent spillage, electrolyte evaporation, and out-gassing, as well as greatly improving its resistance to damage from vibration and heat. Another type of battery, the Absorbed Glass Mat (AGM) suspends the electrolyte in a special fibreglass matting to achieve similar results. More portable rechargeable batteries include several "dry cell" types, which are sealed units and are therefore useful in appliances like mobile phones and laptops.
Zinc-carbon battery - mid cost - used in light drain applications Zinc-chloride battery - similar to zinc carbon but slightly longer life Alkaline battery - alkaline/manganese "long life" batteries widely used in both light drain and heavy drain applications Silver-oxide battery - commonly used in hearing aids Lithium battery - commonly used in digital cameras. Very long life (up to ten years in wristwatches) and capable of delivering high currents but expensive Mercury battery - commonly used in digital watches Zinc-air battery - commonly used in hearing aids Thermal battery - high temperature reserve. Water-activated battery - used for radiosondes and emergency applicationsRechargeable
Also known as secondary batteries or accumulators.
Lead-acid battery - commonly used in vehicles, alarm systems and uninterruptible power supplies. Used to be used as an "A" or "wet" battery in valve/vacuum tube radio sets. The major advantage of this chemistry is its low cost - a large battery (e.g. However, this battery chemistry has lower energy density than other battery chemistries available today (see below) Absorbed glass mat Gel battery Lithium ion battery - a relatively modern battery chemistry that offers a very high charge density (i.e. a light battery will store a lot of energy) and which does not suffer from any "memory" effect whatsoever. Lithium ion polymer battery - similar characteristics to lithium-ion, but with slightly less charge density. This battery chemistry can be used for any battery to suit the manufacturer's needs, such as ultra-thin (1 mm thick) cells for the latest PDAs NaS battery Nickel-iron battery Nickel metal hydride battery Nickel-cadmium battery - used in many domestic applications but being superseded by Li-Ion and Ni-MH types. Ni-Cd cells using older technology suffer from memory effect, but this has been reduced drastically in modern batteries. Sodium-metal chloride battery Nickel-zinc battery Molten salt batteryHomemade cells
Almost any liquid or moist object that has enough ions to be electrically conductive can serve as the electrolyte for a cell. they consist of a pair of cells, each consisting of a potato (lemon, etc.) with two electrodes inserted into it, wired in series to form a battery with enough voltage to power a digital clock. Each of these can make up to 0.3 volts and when many of them are used, they can replace normal batteries for a short amount of time
Lead acid cells can easily be manufactured at home, but a tedious charge/discharge cycle is needed to 'form' the plates.
Traction batteries
Traction batteries (secondary batteries or accumulators) are designed to provide power to move a vehicle, such as an electric car or tow motor. While conventional lead acid batteries with liquid electrolyte have been used, the electrolyte in traction batteries is often gelled to prevent spilling.
Battery types used in electric vehicles
Conventional lead-acid batteries with liquid electrolyte. AGM-type (Absorbed Glass Mat) Zebra Na/NiCl2 battery operating at 270 °C requiring cooling in case of temperature excursions NiZn battery (higher cell voltage 1.6 V and thus 25% increased specific energy, very short lifespan)Lithium-ion batteries are now pushing out NiMh-technology in the sector while for low investment costs the lead-acid technology remains in the leading role.
See also: Battery pack
Flow batteries
Flow batteries are a special class of battery where additional quantities of electrolyte are stored outside the main power cell of the battery, and circulated through it by pumps or by movement. Flow batteries can have extremely large capacities and are used in marine applications and are gaining popularity in grid energy storage applications.
Zinc-bromine and vanadium redox batteries are typical examples of commercially-available flow batteries.
Environmental considerations
Since their development over 250 years ago, batteries have remained among the most expensive energy sources, and their manufacture consumes many valuable resources and often involves hazardous chemicals. For this reason many areas now have battery recycling services available to recover some of the more toxic (and sometimes valuable) materials from used batteries. battery
Strictly, an electrical "battery" is an interconnected array of similar voltaic cells ("cells").
Electrical component
The cells in a battery can be connected in parallel, series, or in both. Most practical electrochemical batteries, such as 9 volt flashlight (torch) batteries and 12 V automobile (car) batteries, have several cells connected in series inside the casing. In both series and parallel types, the energy stored in the battery is equal to the sum of the energies stored in all the cells.
A battery can be simply modelled as a perfect voltage source (i.e. The voltage source depends mainly on the chemistry of the battery, not on whether it is empty or full. When a battery runs down, its internal resistance increases. a light bulb), which has its own resistance, the resulting voltage across the load depends on the ratio of the battery's internal resistance to the resistance of the load. When the battery is fresh, its internal resistance is low, so the voltage across the load is almost equal to that of the battery's internal voltage source. As the battery runs down and its internal resistance increases, the voltage drop across its internal resistance increases, so the voltage at its terminals decreases, and the battery's ability to deliver power to the load decreases.
User Comments Add a comment…