Electric battery

An electric battery is a source of electric power made of one or more electrochemical cells, with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode, and its negative terminal is the anode. The negative terminal is the source of electrons. When a battery is connected to an external electric load, those negatively charged electrons flow through the circuit and reach the positive terminal. There they cause a redox reaction by attracting positively charged ions, or cations. Higher energy reactants are turned into lower energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Historically, the word "battery" referred specifically to a device made of several cells, but its use has grown to include devices made of a single cell.

Primary batteries are single-use, or "disposable," batteries. They are discarded after use because the electrode materials change in a way that cannot be reversed during discharge. A common example is the alkaline battery, which is used in flashlights and many portable electronic devices. Secondary (rechargeable) batteries can be discharged and recharged many times with an applied electric current, and reverse current can restore the original composition of the electrodes. Examples include the lead–acid automotive battery, used in vehicles with internal combustion engines, and lithium-ion batteries, used in portable electronics and electric cars.

Batteries come in many shapes and sizes. They range from miniature cells that power hearing aids and wristwatches to huge battery banks the size of rooms. These large banks provide standby or emergency power for telephone exchanges and computer data centers.

Batteries have much lower specific energy, meaning energy per unit mass, than common fuels such as gasoline. In automobiles, this difference is partly made up for by the higher efficiency of electric motors, which convert electrical energy into mechanical work better than combustion engines do.

History

Main article: History of the battery

Benjamin Franklin first used the word "battery" in 1749 while experimenting with electricity. He linked several Leyden jar capacitors together and called the group a "battery," borrowing a military word for weapons that work together. In 1800, Italian physicist Alessandro Volta built the first electrochemical battery, the voltaic pile. It was a stack of copper and zinc plates separated by brine-soaked paper disks, and it could produce a steady current for a long time. Volta did not understand that the power came from chemical reactions. Michael Faraday showed in 1834 that the corrosion at the electrodes was an unavoidable result of how the cells worked. Early batteries were valuable for experiments, but their voltages fluctuated and they could not supply a large current for long. The Daniell cell, invented in 1836 by British chemist John Frederic Daniell, became the first practical source of electricity and an industry standard. It was widely used to power electrical telegraph networks. Wet cells used liquid electrolytes that could leak or spill, and many were held in fragile glass jars, so they were unsuitable for portable devices. Near the end of the nineteenth century, dry cell batteries, which used a paste instead of a liquid, made portable electrical devices practical.

Battery demand grew by 30% each year between 2010 and 2018, reaching 180 GWh in 2018. Growth is expected to continue at an estimated 25%, reaching 2600 GWh in 2030, and falling costs could push demand as high as 3562 GWh. Major reasons for this growth include the electrification of transport and large-scale use in electricity grids, supported by decarbonization efforts. Batteries in battery electric vehicles (vehicle-to-grid) and in home energy storage with smart metering can connect to smart grids for demand response and help power supply. Used vehicle electric batteries with less than 80% of their capacity, usually after 5–8 years of service, can be reused for backup power or renewable energy storage. Grid-scale energy storage uses large batteries to collect and store energy from the grid or a power plant, then release it later when electricity or other grid services are needed. Computational modeling has changed how battery materials are designed, helping scientists find new electrolytes and electrodes faster than trial and error.

Chemistry and principles

Main articles: Electrochemical cell and Voltaic cell

Batteries change chemical energy directly into electrical energy. The electrical energy often comes from the difference in the bond energies of the metals, oxides, or molecules that react. Zinc and lithium store a lot of energy, unlike transition metals. A battery is built so that its useful redox reaction can happen only when electrons travel through the outside of the circuit. A battery is made of one or more voltaic cells. Each cell has two half-cells joined by an electrolyte that carries metal ions. One half-cell has the negative electrode, where anions (negatively charged ions) move, and the other has the positive electrode, where cations (positively charged ions) move. Some cells use different electrolytes in each half-cell, so a separator keeps them from mixing while still letting ions pass to complete the circuit. Each half-cell has an electromotive force (emf, measured in volts) compared to a standard, and the cell's net emf is the difference between the reduction potentials of its half-reactions.

The voltage across the terminals of a cell is called the terminal voltage and is measured in volts. When a cell is neither charging nor discharging, this is its open-circuit voltage, which equals its emf. An ideal cell producing 1.5 volts and one coulomb of charge would do 1.5 joules of work. Alkaline and zinc–carbon cells have different chemistries but both have an emf of about 1.5 volts, while NiCd and NiMH cells have about 1.2 volts. Lithium cells have an emf of 3 volts or more. Almost any liquid or moist object with enough ions can act as an electrolyte, so a lemon or potato can produce a small amount of electricity when two different metal electrodes are placed in it. A simple stack can be made from a nickel and a penny with a paper towel soaked in salt water. Many of these stacked in series can briefly replace normal batteries.

Types

See also: Battery nomenclature and List of battery types

Batteries are sorted into two groups. Primary cells are used until their energy runs out and are then thrown away, because their chemical reactions are hard to reverse, so they cannot be recharged safely. Common examples are zinc–carbon batteries and alkaline batteries. Rechargeable batteries can be recharged by sending electric current through them, which reverses the chemical reactions so they can be used many times. The oldest rechargeable type is the lead–acid battery, which is widely used in automotive and boating applications, such as the car battery.

Many kinds of electrochemical cells have been made. A wet cell has a liquid electrolyte, while a dry cell uses a paste, so it can be used in any position without spilling. This makes dry cells good for portable devices. Other rechargeable types include nickel–cadmium, nickel–metal hydride, and lithium-ion cells. Batteries also come in many sizes, from tiny button cells used in watches to very large batteries that can power a submarine or help an electrical grid. As of 2017, the world's largest battery was built in South Australia by Tesla.

Main article: List of battery sizes

Main article: Comparison of commercial battery types

See also: State of charge, Depth of discharge, and Trickle charging

A battery's performance can change over time and with use, depending on its inside chemistry, how much current it supplies, and its temperature. In cold weather, a battery cannot deliver as much power. A battery's capacity is the amount of electric charge it can deliver. Bigger batteries with the same chemistry have more capacity. Capacity is usually measured in ampere-hours (A·h). The rated capacity is based on a battery supplying current for 20 hours at room temperature. The higher the rate of discharge, the lower the capacity. Peukert's law gives a rough estimate of this relationship for lead acid batteries, using the current drawn from the battery (A). Batteries slowly lose charge even when they are not used. Each time a battery is recharged, its capacity drops a little more, until it stops producing power. Higher efficiency is found when a battery discharges slowly. High-drain devices, such as digital cameras, can reduce how much energy a battery can supply.

The C-rate measures how fast a battery is charged or discharged. Batteries usually have the most capacity at a low C-rate, and using a higher C-rate reduces their useful life. Some batteries made for special uses, such as in a computer uninterruptible power supply, are rated for very short discharge times but may not last as many cycles. In 2009, experimental lithium iron phosphate (LiFePO₄) battery technology provided the fastest charging and energy delivery. In 2024, a prototype battery for electric cars was shown to charge from 10% to 80% in five minutes. A Chinese company claimed its car batteries charged from 10% to 80% in 10.5 minutes, compared with Tesla's 15 minutes to half-charge.

Lifespan and endurance

See also: State of health

Battery life can mean different things. For rechargeable batteries, it can mean how long a device runs on a full charge, which is called "endurance." It can also mean how many charge and discharge cycles a battery can go through before it stops working well, which is called "lifespan." For batteries that cannot be recharged, battery life only means how long they run a device. "Shelf life" describes how long a battery keeps its performance between being made and being used. All batteries hold less power when it gets colder. The Zamboni pile, invented in 1812, can last a very long time without being recharged, but it can supply only a tiny amount of current. The Oxford Electric Bell has been ringing almost nonstop since 1840 on its first pair of batteries, which are thought to be Zamboni piles.

Batteries slowly lose their charge even when they are not used. Disposable batteries usually lose 8–20% of their charge per year at room temperature. Old rechargeable batteries lose charge faster, especially nickel-based ones. Newer low self-discharge nickel–metal hydride (NiMH) batteries and modern lithium batteries lose charge more slowly. Each charge and discharge wears a battery down a little. Some nickel cadmium batteries can lose capacity from the memory effect, but simple habits can prevent it. Car batteries, which are automotive lead–acid batteries, must handle vibration, shock, and changing temperatures, and few last beyond six years because of these stresses and sulfation of their lead plates. Storing batteries in a refrigerator or freezer slows the reactions that drain them, and can extend alkaline battery life by about 5%. However, batteries must return to room temperature before they reach their full voltage, and Duracell does not recommend refrigerating alkaline batteries.

Hazards

See also: Lithium-ion battery § Safety, and Battery leakage

Batteries can explode when they are misused or malfunction, such as when someone tries to recharge a non-rechargeable battery or a short circuit occurs. If a battery is recharged too quickly, explosive hydrogen and oxygen gas can build up faster than it can escape, causing the case to burst. Overcharging can also cause explosions, leakage, or permanent damage. Burning a battery can cause an explosion too, because steam builds up inside the sealed case. Many battery chemicals are corrosive or poisonous, so leakage can be dangerous and can damage the devices the batteries power. For this reason, many manufacturers recommend removing batteries from devices that will not be used for a long time.

Many batteries contain toxic materials such as lead, mercury, and cadmium, so used batteries must be disposed of properly to prevent environmental damage. Batteries are a form of electronic waste, and e-waste recycling services can recover these substances for use in new batteries. Batteries can be harmful if swallowed, especially small button cells, which young children may swallow. Further information: Lithium battery § Health issues on ingestion, and Button cell § Accidental ingestion

Legislation and regulation

See also: Battery regulations in the United Kingdom

Laws about electric batteries cover safe disposal and recycling. After reported accidents and failures, sometimes with fires or explosions, devices that use lithium-ion batteries have been recalled more often in recent years. In the United States, the Mercury-Containing and Rechargeable Battery Management Act of 1996 banned the sale of batteries containing mercury. It also required rechargeable batteries to be labeled in a standard way and to be easy to remove. California and New York City do not allow rechargeable batteries to be thrown away with ordinary trash. The rechargeable battery industry runs recycling programs across the United States and Canada, with drop-off points at local stores.

See also: Battery passport

The Battery Directive of the European Union has similar rules. It also requires more batteries to be recycled and supports research into better battery recycling methods. Batteries sold in the EU must be marked with a crossed-out wheeled bin symbol, and all packaging must be marked the same way. On 9 December 2022, the European Parliament agreed that from 2026, manufacturers must design electrical products sold in the EU so that people can easily remove and replace the batteries themselves.