Cell baking is a deceptively simple process: heat the cell under vacuum to remove moisture. The difficulty is in the uniformity, the vacuum integrity and the handling of thousands of cells without damaging terminals or mixing batches.
Key takeaways
- Temperature uniformity and vacuum quality matter more than heating power.
- The tray and the chamber must be designed for airflow around each cell.
- Moisture measurement, not time alone, should determine the endpoint.
- Cell handling must protect the terminals and maintain batch traceability.
Process parameters
Typical baking temperatures are 60–85 °C, depending on the cell chemistry and the moisture target. The vacuum level is usually in the range of 10–100 Pa, applied in stages to avoid rapid boiling and cell damage. The process may include nitrogen purge or dry air backfill.
The endpoint is defined by the residual moisture in the cell, not by a fixed time. A moisture analyzer or a dew-point sensor in the exhaust can be used to determine when the cell is dry. A fixed time that is too short leaves moisture; too long wastes capacity and may degrade the cell.
Chamber design
The chamber should have uniform temperature across the tray stack and uniform vacuum. A chamber with a single heating jacket and a large door will have cold spots near the door and at the bottom. Use a chamber with circulating air or a heated plenum, and measure uniformity with a loaded chamber.
The door seal is critical. A vacuum chamber with a leaking door will not reach the target vacuum, and the process will take longer or fail. Use a double seal and a door that is supported when open.
| Parameter | Typical range | Why it matters |
|---|---|---|
| Temperature | 60–85 °C | Moisture removal rate, cell safety |
| Vacuum | 10–100 Pa | Boiling point, vapour removal |
| Ramp rate | 1–3 °C/min | Thermal stress, uniformity |
| Dwell | 4–12 h | Moisture target |
| Cooling | Controlled | Cell handling, condensation |
Trays and handling
Cells are usually loaded in trays or magazines. The tray should locate each cell and protect the terminals. The material should be compatible with the temperature and should not outgas under vacuum.
The handling system should move the tray into the chamber without tilting or shaking. A conveyor with a smooth transfer and a locating pin is better than a manual cart. The tray ID should be read at the chamber entry and exit so the batch record is complete.
Moisture measurement
Residual moisture can be measured by taking a sample cell and using a moisture analyzer, or by monitoring the dew point of the exhaust gas. The dew-point method is continuous and non-destructive; the sample method is more accurate but destructive.
Use both: the dew point for the process endpoint, and periodic sample checks to validate the correlation. Record the data with the batch ID.
Safety
Battery cells can release flammable gas if overheated or damaged. The chamber should have a pressure relief, a gas detection system and a fire suppression plan. The exhaust should be routed to a safe location, and the area should be classified for the gas hazard.
Do not open a chamber while it is hot and under vacuum. Follow a defined cooling and venting procedure, and train operators on the interlocks.
Frequently asked questions
How long does cell baking take?
It depends on the cell and the moisture target, but 4–12 hours is typical. The endpoint should be based on moisture measurement, not time alone.
Can I use a standard industrial oven?
Only if it is rated for vacuum and the process atmosphere. A standard oven is not designed for vacuum or solvent removal and may be a safety risk.
What is the biggest cause of non-uniform baking?
Poor airflow or radiant heat from the chamber walls. A loaded chamber test will show the cold spots.
Send your cell format, moisture target and throughput to our engineers through the contact page; we will specify the chamber and the handling system.
