How Batteries Work: Galvanic Cells and Lithium-Ion Chemistry
Understand how batteries turn chemical energy into electricity: galvanic cells, the Daniell cell, electron flow, and how lithium-ion batteries shuttle ions to power the modern world.
Quick answer
A battery is a device that stores chemical energy and releases it as electrical energy through a spontaneous redox reaction. In a galvanic cell, oxidation at the anode releases electrons that travel through an external circuit to the cathode, where reduction occurs — that flow of electrons is the electric current.
Example: In a lithium-ion battery, lithium ions shuttle back and forth between a graphite anode and a metal-oxide cathode through the electrolyte, while the electrons they 'leave behind' flow through your phone's circuitry to power it.
What you will learn
- Explain how a galvanic cell converts chemical energy to electrical energy
- Identify the anode and cathode and the direction of electron flow
- Describe the Daniell cell as a concrete example
- Explain lithium-ion operation as shuttling of Li+ ions
- Distinguish rechargeable (secondary) from single-use (primary) cells
A battery is a galvanic cell
Every battery is a galvanic cell: a device in which a spontaneous redox reaction is split into two half-reactions kept in separate compartments. Oxidation — loss of electrons — happens at one electrode, and reduction — gain of electrons — happens at the other. Because the electrons cannot jump directly between the compartments, they are forced to travel through an external wire, and that detour is the useful electric current.
The materials of the electrodes decide which reaction occurs, how much voltage the cell produces, and how much charge it can store. Battery chemistry is, at its core, materials chemistry: choosing the right substances for the anode, cathode, and electrolyte.
Anode, cathode, and electron flow
The two electrodes have fixed roles, defined by chemistry rather than by plus and minus signs:
- The anode is where oxidation occurs. It releases electrons, so in a discharging battery it is the negative terminal.
- The cathode is where reduction occurs. It consumes electrons arriving through the wire, so it is the positive terminal.
Electrons flow through the external circuit from anode to cathode. Inside the cell, ions migrate through the electrolyte in the opposite sense to balance the charge — positive ions drift toward the cathode, negative ions toward the anode. Both flows are needed: stop the ion movement and the current stops too.
Anode = oxidation, cathode = reduction. This holds in every electrochemical cell, galvanic or electrolytic — only the signs of the terminals change.
The Daniell cell: a classic example
The classic classroom galvanic cell is the Daniell cell: a zinc strip in zinc sulfate solution connected to a copper strip in copper sulfate solution. Zinc is the more reactive metal, so it oxidizes:
The released electrons travel through the wire to the copper electrode, where copper ions in solution are reduced:
Zinc is the anode (negative), copper is the cathode (positive), and the cell produces about 1.1 volts. Over time the zinc strip visibly shrinks as it dissolves, while fresh copper plates onto the copper strip — the chemistry made visible.
Lithium-ion batteries: ions on the move
A lithium-ion cell works on the same galvanic principle but with a clever twist: instead of the electrodes being consumed, lithium ions simply shuttle between them. During discharge:
- At the graphite anode, lithium atoms held between the carbon layers release their electrons and enter the electrolyte as Li+ ions.
- The Li+ ions migrate through the electrolyte to the metal-oxide cathode (typically a lithium cobalt oxide or similar material).
- The electrons flow through the external circuit — powering your device — and reunite with the ions at the cathode.
Charging reverses the process: an external voltage drives the lithium ions back to the anode, restoring the cell to its charged state. Because the electrodes act as hosts that lithium enters and leaves, rather than being dissolved and replated, the cell survives hundreds of charge cycles.
Lithium is the lightest metal and gives up its electron very readily, which means lithium-ion cells pack more energy per kilogram than any earlier rechargeable chemistry — the reason they dominate phones, laptops, and electric cars.
Rechargeable versus single-use
Batteries come in two kinds:
- Primary (single-use) cells, like ordinary alkaline AA batteries, run their redox reaction in one direction only. Once the reactants are consumed, the battery is finished.
- Secondary (rechargeable) cells, like lithium-ion, lead-acid car batteries, and nickel-metal hydride cells, use reactions that can be driven backward. Connecting a charger forces current the 'wrong' way, reversing the chemistry and restoring the reactants.
Rechargeable cells cost more and store somewhat less energy per use, but paying once for hundreds of cycles wins for anything used daily.
Why battery materials matter
The electrode and electrolyte materials are what battery engineers obsess over, because they set the three numbers that matter:
- Voltage, set by how strongly the anode wants to give up electrons and the cathode wants to accept them.
- Capacity, set by how many ions the electrodes can host and release.
- Cycle life, set by how well the materials survive repeated shuttling without cracking or degrading.
That is why lithium-ion research focuses on new cathode materials and better electrolytes: each improvement in the materials is an improvement in every device the battery powers.
Common mistakes
Electrons cannot travel through the electrolyte — they flow through the external wire, which is why the battery can power a device. Inside the cell, ions migrate through the electrolyte to complete the circuit and balance charge.
In a galvanic cell (a discharging battery), the anode is negative because oxidation releases electrons there. In an electrolytic cell (a battery being charged), the terminals' signs flip. Anode means 'where oxidation happens,' not 'positive.'
Charging pushes electrical energy into the cell to reverse the chemical reaction, storing that energy as chemical potential. The energy comes from the charger — the wall outlet — not from nowhere.
Real-world applications
Smartphones, laptops, and tablets
Electric vehicles
Storing solar and wind energy for the grid
Medical devices such as pacemakers and hearing aids
Emergency backup power systems
Frequently asked questions
Why do rechargeable batteries eventually wear out?
Each recharge slightly degrades the electrode materials — the crystal structures that host lithium ions crack and change over many cycles, some lithium gets trapped in side reactions, and the electrolyte slowly breaks down. After hundreds of cycles the battery simply cannot store as much charge as when new.
What makes a lithium-ion battery rechargeable but not an alkaline one?
In a lithium-ion cell the electrode reactions are reversible. Applying an external voltage forces lithium ions to shuttle back from the cathode to the anode, restoring the original chemical state. A single-use alkaline cell's reactions cannot be cleanly reversed, so attempting to recharge it is ineffective and unsafe.
Do batteries actually run out of chemicals?
Yes — a battery converts stored chemical energy into electrical energy through redox reactions that consume the reactants. When the reactants are used up (in a single-use cell) or can no longer shuttle effectively (in a worn rechargeable), the battery is dead.
What is the difference between a battery and a cell?
A cell is a single unit with one anode and one cathode. A battery is two or more cells connected together to give more voltage or capacity — a car battery, for example, contains six lead-acid cells. In everyday speech the word 'battery' is used for single cells too, like a AA battery.