Avoiding Passivation

Saft, a global leader in batteries, has written an excellent article and made a video outlining some things you can do to help mitigate issues with passivation.

Lithium Thionyl Chloride batteries offer a high operating voltage, voltage stability, high pulse capability, and the highest energy density among primary lithium chemistries. They can operate over a wide temperature range, have proven to be a reliable long-life solution, and is also one of the cheapest options.

Those features make it a favourite choice for building smart devices. They are, however, not without their pitfalls.

What is passivation?

"Passivation" is a surface protecting reaction which occurs on the lithium metal surface of Lithium Thionyl Chloride batteries. A film of lithium chloride forms on the lithium metal anode, and this solid protecting film is called the "passivation layer". This film prevents direct contact between the anode and the cathode, and plays a major role in many of the benefits of Lithium Thionyl Chloride batteries. Basically, this film prevents the battery from internally short circuiting and therefore from discharging of its own accord. That is why these batteries have a long shelf life. However, if not well managed, passivation can adversely affect the operation of the application.

The passivation layer acts as an insulator, which may have some consequences for battery operation. The internal resistance of the cell is increased by the passivation layer, which can cause low voltage readings at startup. The passivation layer is broken down after initial startup and cell voltage then recovers to its nominal value. The passivation process then restarts each time current draw ceases. 

Passivation is influenced by several factors that will affect the length and depth of the voltage delay such as its chemistry, ambient temperature, or the length of time in storage. 

 

Click here to read the article - https://www.saft.com/energizing-iot/seven-passivation-pitfalls-and-how-avoid-them