Deterioration and Activation of Lithium Thionyl Chloride Batteries after Long-Term Storage
March 6, 2025
Deterioration and Activation of Lithium Thionyl Chloride Batteries after Long-Term Storage
Introduction
Lithium thionyl chloride (Li/SOCl₂) batteries are known for their high energy density and long storage life, making them widely used in low-power devices. However, these batteries may experience passivation after being stored for over a year, leading to reduced discharge performance or even failure to discharge properly.
Causes of Passivation
1. **Formation of Passivation Film**
The positive electrode material, thionyl chloride (SOCl₂), reacts with the negative electrode material, metallic lithium (Li), to form a dense passivation film (mainly composed of LiCl) on the lithium surface. While this film prevents further reactions between Li and SOCl₂, it also hinders the normal discharge process of the battery.
2. **Impact of Storage Conditions**
The longer the storage time and the higher the temperature, the thicker the passivation film becomes, leading to increased internal resistance and more pronounced voltage lag during discharge.
3. **Voltage Lag Phenomenon**
The passivation film restricts the migration rate of lithium ions, causing the battery voltage to drop sharply during high-current discharge, sometimes falling below the device's cut-off voltage.
Solutions
1. **Activation Methods**
- **Low-Current Activation**: Before use, discharge the battery with a low current (e.g., 1 mA) or connect it to an external resistor (e.g., 15 Ω) for 10-20 minutes. This can effectively remove the passivation film and restore battery performance.
- **Pulsed Current Activation**: Using pulsed current activation, such as alternating between 1 mA high-current pulses and 5 mA low-current pulses, can accelerate the breakdown of the passivation film.
- **Shaking the Battery**: For mildly passivated batteries, simply shaking the battery can help restore some performance.
2. **Optimizing Storage Conditions**
- **Low-Temperature Storage**: Store the batteries in a low-temperature environment (e.g., -20°C to 25°C) to slow down the formation of the passivation film.
- **Regular Discharge**: Periodically discharge the battery with a low current to prevent excessive passivation film buildup.
3. **Technical Improvements**
- **Additives**: Introducing chemical additives into the battery can slow down the formation of the passivation film while maintaining the battery's pulse discharge capability.
- **Smart Management Systems**: Implementing a microcontroller-based pulsed discharge management system that automatically adjusts activation methods based on battery voltage and ambient temperature.
Case Example
A user reported that their lithium thionyl chloride batteries, stored for over a year, showed significant voltage lag and short discharge times. After applying the low-current activation method (1 mA for 15 minutes), the batteries' performance was restored, and they were able to discharge normally.
Conclusion
Passivation is an inherent characteristic of lithium thionyl chloride batteries and cannot be completely avoided. However, its impact can be minimized through the methods mentioned above. If your lithium thionyl chloride batteries experience discharge issues after long-term storage, it is recommended to first try low-current or pulsed current activation. If the problem persists, consult professional technicians or the battery manufacturer for further support.