Electric battery

An electric battery is a source of electric power made of one or more electrochemical cells. It has outside connections that let it power electrical devices. When a battery is giving power, its positive terminal is the cathode, and its negative terminal is the anode. The negative terminal gives off electrons. When a battery is connected to an outside electric load, those negatively charged electrons travel through the circuit to the positive terminal. There they cause a redox reaction by pulling in positively charged ions, called cations. A reaction that starts with higher energy materials ends with lower energy materials. The leftover energy is sent to the outside circuit as electricity. In the past, the word "battery" meant a device made of several cells. Today it also includes devices made of just one 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 undone. A common example is the alkaline battery, which is used in flashlights and many portable electronic devices. Secondary (rechargeable) batteries can be used and recharged many times with an electric current. Running current backward can restore the original materials in the electrodes. Examples include the lead–acid automotive battery, used in vehicles with engines, and lithium-ion batteries, used in portable electronics and electric cars.

Batteries come in many shapes and sizes. Some are tiny cells that power hearing aids and wristwatches. Others are huge battery banks as big as a room. These large banks provide backup power for telephone exchanges and computer data centers.

Batteries store much less energy for their weight than common fuels such as gasoline. This is called specific energy. In cars, electric motors make up for some of this difference because they turn electrical energy into movement better than engines do.

History

Main article: History of the battery

Benjamin Franklin first used the word "battery" in 1749 while he experimented with electricity. He joined several Leyden jar capacitors together and called the group a "battery." He borrowed the word from the military, where it means weapons that work together. In 1800, Italian physicist Alessandro Volta built the first electrochemical battery, called the voltaic pile. It was a stack of copper and zinc plates with paper disks soaked in salty water between them. It could produce a steady flow of electricity for a long time. Volta did not know that the power came from chemical reactions. In 1834, Michael Faraday showed that the wearing away at the electrodes was a normal result of how the cells worked. Early batteries were useful for experiments, but their power levels went up and down, and they could not give a strong flow of electricity for long. The Daniell cell was invented in 1836 by British chemist John Frederic Daniell. It became the first practical source of electricity and a standard for the industry. It was widely used to power electrical telegraph networks. Wet cells used liquid that could leak or spill, and many were kept in fragile glass jars, so they were not good for portable devices. Near the end of the nineteenth century, dry cell batteries were invented. They used a paste instead of a liquid, which 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. Falling costs could push demand even higher, to 3562 GWh. Major reasons for this growth include the use of batteries in transport and in large electricity systems. Decarbonization efforts also support this growth. Batteries in battery electric vehicles can work with vehicle-to-grid systems. Batteries in home energy storage with smart metering can connect to smart grids for demand response. They can also help supply power. Used vehicle electric batteries that have less than 80% of their capacity, usually after 5 to 8 years of use, can be reused. They can provide backup power or store renewable energy. Grid-scale energy storage uses large batteries to collect and store energy from the grid or a power plant. Later, they release it when electricity or other grid services are needed. Computer modeling has changed how battery materials are designed. It helps 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. This electrical energy often comes from differences in the energy held by 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 only happen 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. The other has the positive electrode, where cations (positively charged ions) move. Some cells use different electrolytes in each half-cell. A separator keeps them from mixing but still lets ions pass through to complete the circuit. Each half-cell has an electromotive force (emf, measured in volts) compared to a standard. The cell's total 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 not charging or 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. 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. This means a lemon or potato can make a small amount of electricity when two different metal electrodes are placed in it. A simple stack can be made from a nickel, a penny, 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 then they are thrown away. 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. This 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. A dry cell uses a paste instead, 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. They range 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. It depends 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 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. 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. They 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. This is called "endurance." It can also mean how many times a battery can be charged and used before it stops working well. This is called "lifespan." For batteries that cannot be recharged, battery life only means how long they run a device. "Shelf life" is how long a battery keeps its power 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. However, 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 a small part of their charge each 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 bumps, shaking, and changing temperatures. 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. This can extend alkaline battery life by about 5%. However, batteries must return to room temperature before they reach their full voltage. Duracell does not recommend refrigerating alkaline batteries.

Hazards

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

Batteries can explode if they are misused or do not work properly. This can happen when someone tries to recharge a battery that is not meant to be recharged, or when a short circuit happens. If a battery is charged too quickly, hydrogen and oxygen gas can build up inside it faster than it can escape. This can make the case burst. Charging for too long can also cause explosions, leakage, or permanent damage. Burning a battery can cause it to explode, because steam builds up inside its sealed case. Many battery chemicals are corrosive or poisonous. Because of this, leakage can be dangerous and can damage the devices that the batteries power. For this reason, many manufacturers suggest taking batteries out of devices that will not be used for a long time.

Many batteries contain harmful materials such as lead, mercury, and cadmium. Used batteries must be thrown away carefully to protect the environment. Batteries are a type of electronic waste. E-waste recycling services can recover these materials so they can be used in new batteries. Batteries can be harmful if swallowed. Small button cells are especially risky, because young children may swallow them. 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 how they are thrown away and recycled. Some batteries caught fire or exploded, so 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 batteries containing mercury from being sold. It also said rechargeable batteries must have a standard label and must be easy to remove. California and New York City do not allow rechargeable batteries to go in ordinary trash. The rechargeable battery industry runs recycling programs in 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 asks for more batteries to be recycled and supports research into better battery recycling methods. Batteries sold in the EU must have a crossed-out wheeled bin symbol, and so must all packaging. 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.