122 Chapter 10 pack designed by AESC uses the metal enclosures of the module and the pack to act as a heat sink to spread the heat out. But in hot climates or in frequent rapid discharges, there is no means to increase the rate of cooling in order to more rapidly respond to the increasing temperatures. While this provided a low cost and fast to market solution, as we have seen it also caused some other problems on which they are still working hard to resolve. Finally, we should talk about the high-voltage electronics and balancing systems when we talk about thermal management.
In many systems, the high-voltage electronics can be a major portion of the heat generation of the pack, especially in smaller packs. Additionally, cell balancing by its very act is the transference of electrical energy into heat energy. In essence, as you balance the pack you also heat it up. In the cases where level 3 charging is used, most battery systems are designed to turn the thermal management system on during these charg- ing events due to the rapid heat generation that will otherwise ensue.
Without the cooling system being engaged during a fast-charge event, the battery may generate enough heat to reduce the amount of energy it will be able to hold and could generate enough heat to actually cause the battery system to shut down until it cools. Think of this as trying to use a fire-hose- size nozzle to fill your gas tank; the tank will simply not be able to take that volume of fuel at once. In the battery system, it is the not the speed but in fact the heat that is being generated that causes the problems and stresses the lithium-ion cells.
In the case of the electronics within the battery system and their heat generation, it is gener- ally easy enough to run cooled air across the electronics to help cool them down. However, the designer in these instances needs to ensure that the air is flowing to the lithium-ion cells either before or in parallel with the flow to the electronics. Most electronics have a much wider operating temperature range than the batteries do, so it is more efficient to cool the cells first and the electronics second. In liquid-cooled battery packs, it is somewhat more difficult to ensure the cooling of the electronics unless cooling plates are designed into the pack.
But in both situations the location and placement of the electronics require special attention by the energy storage system designer. All of these need either some amount of thermal management or at least to have a system design that does not negatively impact the performance of the batteries. Why Heating? On the other end of the spectrum is heating the battery. As a general rule, battery system designers do not want to heat a battery except for at very low ambient temperatures and even then it should not be a “rapid” heating.
Most liquid electrolytes used in modern lithium-ion batteries will begin to experience reduced power at about −10 °C and will begin to freeze at between −20 and −30 °C, which makes them unable to provide power at very low temperatures.