In order to correctly look after the batteries that you use for your various applications, it is necessary to have a basic understanding of some chemical terms – particularly if you use lithium batteries. In this article, we explain what is meant by passivation in lithium batteries to help you understand this key process that can potentially affect your application.
What is passivation in lithium batteries?
Specific to batteries, the term “passivation” refers to a phenomenon that occurs within the cells of lithium thionyl chloride primary cells. On the surface of the lithium anode, a highly resistant film of lithium chloride is formed as a result of a chemical reaction between the fixed lithium anode and the interaction of the battery electrolyte. This process is known as passivation in lithium batteries.
Why is passivation important?
As a result of the highly resistant film of lithium chloride that forms, the self-discharge rate of lithium cells is low. If the passivation layer did not exist and could not be stored, the lithium within the cells would degrade extremely quickly, rendering the lithium batteries practically unusable. Due to passivation, the standard rated shelf life of a lithium thionyl chloride battery exceeds ten years, and this is fundamentally due to the passivation layer, as it protects the cell from high self-discharge rates.
What’s the downside of passivation?
The primary disadvantage to passivation is voltage delay. When an electrical load is placed on a passivated cell, the measured output voltage drops in relation to the requested current. This is directly caused by a drop in internal voltage over the resistive passivation layer. As a result, the electrical current that flows through the passivation layer is able to break down the protective film. In cases where the load is increased, the output voltage is likely to periodically dip until recovering to a steady state of charge.
Solving passivation issues in lithium batteries
When you start an application or system and a voltage delay cannot be tolerated, you can employ several techniques to reduce the severity of the passivation effect. Primarily, you can prevent the passivation layer from growing too thick by applying a continuously low current to the application or by offering a periodic high current discharge when the battery is in storage. However, this process will shorten the life span of the cell. Another option is to place the battery under a high load immediately before usage. This isn’t foolproof either, as it will waste capacity during the depassivation procedure.
For more information about passivation in lithium batteries
If you’re concerned about passivation in your lithium batteries or would like to speak to an expert about getting the most out of lithium cells for your application, get in touch with the AceOn team today – we’d be delighted to help you.
