THE LAST STEPS

Finish a cell

After the electrodes are wound or stacked and sealed in, the cell still can't work: it needs electrolyte, a first charge and a long rest.

A cell is not finished until it has been formed and tested.

FILLING

Every pore must get wet

💉

Where A dry room, often with a dew point of about −40 °C or drier

How Vacuum pulls air out, then electrolyte is dosed in

Wetting Hours of rest, sometimes with pressure or warmth, so the liquid soaks every pore

A dry patch is a dead patch.

FORMATION

The first, careful charge

🐢

Cells get a slow first charge, often around 0.1C, sometimes warm and under pressure. This builds an even SEI on the anode. Gas from the SEI reactions is let out, and pouch cells have their gas bag cut off and resealed.

Formation is slow because a rushed SEI makes a short-lived cell.

AGING AND GRADING

Wait, then measure

📅

⏳

Rest

Cells sit for days to weeks

📉

Self-discharge check

A cell that loses voltage while resting may have a tiny internal short

🏷️

Grade

Capacity and resistance are measured and similar cells are grouped

Grading is how factories catch the rare bad cell.

THE COST

Why formation matters to price

Formation and aging tie up huge racks of chargers and floor space for days. They are among the most expensive steps in a factory, so faster formation recipes are a big target for cutting the cost of each kWh.

Time on the rack is money.

UNIT 13 STUDY COMPLETE

🏭

Ready for the Fab Challenge?

You've finished a cell: filled, formed, degassed, aged and graded.