How a lithium-ion cell works
Ions in the electrolyte, electrons in the wire — the whole story in one diagram.
- Explain how a lithium-ion cell works at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real pack
Overview
Every EV battery is built from one repeated trick: lithium ions shuttle between two host materials while electrons take the long way round through your motor.
In depth
Ion movement simulator
Charge and discharge a cell and watch where the lithium goes.
The four ingredients
A cell needs a cathode (the lithium source, usually a layered oxide or a phosphate), an anode (usually graphite), a separator that blocks electrons but passes ions, and an electrolyte that carries the ions.
Cell energy is simply how much charge it can move multiplied by the voltage it moves it at.
Battery Capacity Calculator
Convert pack voltage and amp-hours into usable energy.
E (kWh) = V × Ah ÷ 1000 ; usable = E × usableFractionCell capacity is measured in amp-hours. Multiplying by nominal pack voltage gives watt-hours. Manufacturers reserve a buffer at both ends of the pack, so usable energy is always less than gross energy.
Example: 400 V × 200 Ah ÷ 1000 = 80 kWh gross. With a 94% usable window that is 75.2 kWh.
- Nominal voltage ≈ cell nominal voltage × cells in series (3.65 V for LFP, 3.7 V for NMC).
- LFP packs are often released to 100% because the buffer strategy differs.
- Gross capacity is what marketing quotes; usable is what you drive on.
Key takeaways
- Ions move through the electrolyte, electrons through the circuit.
- Charging pushes lithium into the anode; discharging returns it to the cathode.
- Cell energy is capacity times nominal voltage.
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