Power Budget per Reading across Competing Sensing Principles
Sensing power budgets depend on physical excitation energy, analog settling delays, and converter sampling overhead across operating duty cycles.
Lithium Thionyl Chloride Passivation
Surface Barrier
Primary battery chemistries involving high energy density metals often form a protective layer to prevent self discharge during storage. Lithium thionyl chloride passivation occurs as a thin film of lithium chloride crystals grows on the surface of the anode. This layer acts as an insulator that stops the chemical reaction until a load is applied to the cell.
Voltage Delay
When the circuit closes, the internal resistance appears high because the ions cannot easily penetrate the crystalline film. Lithium thionyl chloride passivation causes a momentary dip in output voltage known as a startup delay. As the current flows, the crystals break apart and the battery voltage recovers to its nominal operating level.
Storage Environment
Higher temperatures accelerate the growth of the insulating layer and increase its physical toughness. A cell kept at 40 degrees Celsius for a year will exhibit much more lithium thionyl chloride passivation than one stored in a refrigerator. Engineers often program periodic depassivation pulses into low power devices to keep the anode surface active.
This ensures the device can respond to an emergency signal without a catastrophic voltage drop.
Discharge Rate
Low current draws do not provide enough mechanical stress to strip the film. Frequent lithium thionyl chloride passivation is therefore a major concern in remote sensors that sleep for long periods.