TechnologyDifficulty 2-4

Batteries

A battery stores energy chemically and releases it as electricity: in each cell, a chemical reaction pushes electrons out of the negative electrode (anode), through the circuit, and into the positive electrode (cathode). Single-use (primary) cells cannot be recharged; rechargeable (secondary) cells use reversible reactions. Lithium-ion cells, honoured by the 2019 Nobel Prize in Chemistry, power phones and laptops; because their lithium ions move in and out of the electrodes without consuming them, they can be recharged hundreds of times.

Lithium-ion chemistry

Yoshino's practical cell paired Goodenough's lithium cobalt oxide cathode with a carbon anode that intercalates lithium ions. In use, electrons and lithium ions flow towards the cobalt oxide cathode, which has the higher potential; charging drives them back. Lithium cells are popular because they deliver large currents, are light for their capacity, give a nearly constant voltage as they discharge and lose charge only slowly in storage.

\mathrm{LiCoO_2 + x\,C_6 \rightleftharpoons Li_{1-x}CoO_2 + x\,LiC_6}

Lithium-ion cell reaction as given in OpenStax Chemistry 2e (cell voltage about 3.7 V; x usually no more than 0.5).

Whittingham's early lithium battery gave more than 2 V; Goodenough's cobalt-oxide cathode (1980) reached about 4 V.
Yoshino replaced reactive lithium metal with a carbon anode that intercalates lithium ions (1985), making the battery workable in practice.
Nominal voltage is partly convention: 3.6 V is the classic rating for cobalt-based cells, while some makers mark 3.7 V, which boosts watt-hours on paper.

Common misconception: A higher marked voltage (3.7 V vs 3.6 V) does not by itself mean more energy in the device; Battery University notes that the higher figure is often set arbitrarily and does not change how portable devices or chargers operate.

Full explanation — the complete reference version every reading depth is based on

What a battery is

A battery is an electrochemical (galvanic) cell, or several joined together, built to be a convenient source of electrical power. Each cell has a negative electrode (anode), a positive electrode (cathode) and an electrolyte between them. When a circuit is connected, oxidation at the anode releases electrons, which flow through the external wire to the cathode, where reduction uses them; ions move through the electrolyte inside the cell.

Single-use and rechargeable

Primary cells (for example most alkaline cells) are made for single use and cannot be recharged; trying to recharge one can make it rupture and leak.
Secondary cells use reversible reactions, so an external power source can drive the reaction backwards to recharge them.
Typical nominal voltages per cell: lead acid about 2 V, NiCd/NiMH about 1.2 V, cobalt-based lithium-ion about 3.6 V.

How lithium-ion cells work

In a lithium-ion cell, lithium ions are held (intercalated) in the layered materials of both electrodes. During use they travel through the electrolyte to the cathode while electrons travel through the device; charging pushes them back. Because the ions move in and out without the electrodes being consumed, the cell can be recharged hundreds of times. Whittingham, Goodenough and Yoshino shared the 2019 Nobel Prize in Chemistry for developing this battery, and the first ones went on sale in 1991.

Capacity, voltage and energy

E\,[\text{Wh}] = Q\,[\text{Ah}] \times V\,[\text{V}]

Stored energy in watt-hours is charge capacity in ampere-hours multiplied by voltage.

Worked example (our calculation): a 3.6 V lithium-ion cell rated at 3.0 Ah stores about 3.0 × 3.6 = 10.8 Wh. Three such cells in series give 3 × 3.6 = 10.8 V; if each is 3.0 Ah, the pack still has 3.0 Ah but stores 3.0 × 10.8 ≈ 32.4 Wh.

How we know

The chemistry of cells is set out in the open textbook Chemistry 2e; the lithium-ion story is from the Nobel committee's own account; voltage conventions come from Battery University, an engineering reference sponsored by the battery company Cadex; and the safety advice comes from the UK Office for Product Safety and Standards.

Assumptions and limits

A cell's voltage is not one fixed number. A cobalt-based lithium-ion cell reads about 4.2 V when fully charged and is cut off at about 3.0 V; its nominal 3.6 V is the midpoint measured under a set load. Watt-hour figures worked out from nominal values are therefore approximate.

Warning: Safety: most lithium-ion batteries are safe when used correctly, but damaged, poor-quality or misused ones can cause serious fires. Only use a charger that is right for the battery, and never try to recharge a battery that is not rechargeable. If a battery ever catches fire, do not try to put it out — get away from it straight away, tell an adult and call 999 (UK).

Common misconception: Misconception: 'a battery stores electricity (or electrons)'. A battery stores chemical energy. It does not run out of electrons; it runs down when the chemical reaction that pushes electrons around the circuit is used up.

Info: Connections: batteries are a way of storing Energy; they run on Chemical reactions and on how readily Atoms such as lithium give up electrons; their current drives the circuits described under Electricity; and they made portable Computers and phones possible.

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Sources and methodology

A battery is a galvanic cell specially designed and constructed to suit its intended use as a source of electrical power for specific applications. (awaiting scientific review)
- Chemistry 2e (OpenStax), §17.5 Batteries and Fuel Cells — LibreTexts copy, CC BY 4.0 — Textbook
Primary cells are designed for single use and cannot be recharged, whereas secondary cells are based on conveniently reversible cell reactions that allow recharging by an external power source. (awaiting scientific review)
- Chemistry 2e (OpenStax), §17.5 Batteries and Fuel Cells — LibreTexts copy, CC BY 4.0 — Textbook
Most alkaline batteries are not rechargeable, and attempting to recharge one that is not designed for it often leads to rupture of the battery and leakage of its potassium hydroxide electrolyte. (awaiting scientific review)
- Chemistry 2e (OpenStax), §17.5 Batteries and Fuel Cells — LibreTexts copy, CC BY 4.0 — Textbook
In a battery, electrons flow through the external circuit from the negative electrode (the anode) to the positive electrode (the cathode), so the anode should contain a material that readily gives up electrons. (awaiting scientific review)
- The Nobel Prize in Chemistry 2019 — Popular information: They developed the world's most powerful battery — Science media
In a lithium-ion battery the lithium ions are intercalated in the electrodes and flow between them without reacting with their surroundings, which is why the battery can be charged hundreds of times before its performance deteriorates. (awaiting scientific review)
- The Nobel Prize in Chemistry 2019 — Popular information: They developed the world's most powerful battery — Science media
John B. Goodenough, M. Stanley Whittingham and Akira Yoshino shared the 2019 Nobel Prize in Chemistry for the development of lithium-ion batteries. (awaiting scientific review)
- The Nobel Prize in Chemistry 2019 — Summary — Science media
The rechargeable lithium-ion battery laid the foundation for wireless electronics such as mobile phones and laptops, and the first lithium-ion batteries went on sale in 1991. (awaiting scientific review)
- The Nobel Prize in Chemistry 2019 — Popular information: They developed the world's most powerful battery — Science media
Nominal cell voltages depend on chemistry: about 2 V per cell for lead acid, 1.2 V for consumer nickel-cadmium and nickel-metal-hydride cells, and 3.6 V for cobalt-based lithium-ion (some makers mark 3.7 V). (awaiting scientific review)
- BU-303: Confusion with Voltages — Other (unclassified)
A battery's energy in watt-hours equals its capacity in ampere-hours multiplied by its voltage (Wh = Ah × V), and three 3.6 V lithium-ion cells connected in series give 10.8 V. (awaiting scientific review)
- BU-303: Confusion with Voltages — Other (unclassified)
The nominal voltage of a cobalt-based lithium-ion cell is the mid-way point between a full charge of about 4.2 V and a cut-off of about 3.0 V, measured under a set load, which gives about 3.6 V. (awaiting scientific review)
- BU-303: Confusion with Voltages — Other (unclassified)
Most e-bikes, e-scooters and their lithium-ion batteries are safe when used correctly, but lithium-ion batteries can cause serious fires, particularly if they are of poor quality, damaged or improperly used. (awaiting scientific review)
- Buy Safe, Be Safe: avoid e-bike and e-scooter fires — Government or standards body
UK product-safety guidance says people should never try to put out a lithium-ion battery fire themselves, but should leave the area or building as quickly as possible and call 999. (awaiting scientific review)
- Buy Safe, Be Safe: avoid e-bike and e-scooter fires — Government or standards body
Heat-related failures of lithium-ion batteries are rare when they are used correctly, but an internal short circuit can start a thermal runaway that external protection circuits cannot stop once it is in progress. (awaiting scientific review)
- BU-304a: Safety Concerns with Li-ion — Other (unclassified)

Claims marked “awaiting scientific review” cite the sources listed but have not yet been signed off by a scientific reviewer.

Content status: published 1 October 2026.

Scientific review: this version has not yet been signed off by a scientific reviewer.
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