 For liquid cathode systems such as lithium-thionyl chloride, another phenomenon is affecting battery performance. Passivation. Passivation is the main observable effect of a surface reaction that occurs spontaneously onto lithium metal surfaces in all primary lithium batteries based on liquid cathode. This reaction corresponds to the corrosion of lithium metal by liquid-thionyl chloride into lithium ions. It leads to the formation of a solid protecting layer preventing further corrosion and more importantly avoiding any internal short circuit of the battery. This surface layer is called a passivation layer. It acts in a similar way to paint protecting against metal corrosion. It protects the cells from discharging on their own and enables their long shelf life. The passivation layer is electronically insulating, which may have some detrimental consequences for battery operation. Therefore, its structure, morphology and buildup over time must be properly managed. Indeed, internal resistance of the cell is enhanced due to the presence of the passivation layer and this causes low voltage readings at initial times upon the IoT device's data transmission. After this rapid transient minimum voltage stage, diffusion of lithium ions through the passivation layer enables cell voltage to recover to nominal values. This second stage is called depassivation and is very important for efficient operation of the battery. The passivation phenomenon occurs at each data transmission of your IoT device. Several factors are known to have an impact on the passivation effect, affecting the length and depth of voltage delay. Number one, the lithium cell electrochemistry, construction and manufacturer. Some chemistries based on liquid cathodes are far more prone to passivation than others. Nevertheless, within a given type of technology, some battery brands may display different levels of passivation. This is essential know-how in the toolkit of every lithium primary battery maker. Number two, the storage duration. The longer the storage time before use, the more the passivation layer will grow, like rust on iron. Number three, the temperature during storage and operation. The higher the temperature, the faster the passivation layer will grow and the bigger crystals will build up. While at cold temperatures, the passivation will grow more slowly, but the layer will be more compact. This is due to the fact that both electrical, chemical and diffusion reactions are slowed down at low temperatures and electrolyte viscosity is higher. Thus, the effects of passivation could be more likely visible, especially under high current draw. Saft, we energize the world, on land, at sea, in the air and in space.